The influence of microtopography to road inundation caused by extreme flood

Microtopography plays a critical role in road inundation during urban flood events. The microtopography in this paper was defined as terrain-scale features that encompass surface roughness, slope, road network and urban building layout. This paper aims to explore the mechanism of depression storage and road inundation under different microtopography. Simulations under 4 rainfall intensities (144.0- 182.88 mm/h) and 14 slope combinations (four transverse slope and five longitudinal slope) were implemented in an 800 by 70 cm local model. The correlation heat map directly reflected that longitudinal slope had higher influence on drainage than other factors. Then real topographical and hydrological data was applied to predict road inundation with five different extreme rainfall events in Jiangning District (Nanjing City, China). The microtopography characteristics of frequent inundation road were extracted, which further verified the conclusions of the local model. Results show that: the microtopography depressions drainage process could be divided into six main stages: filling stage, interaction stage, unstable drainage stage, stable flow stage, drainage stage and stage of drainage end. Water was stored on depressions of road, and the storage volume and discharge efficiency were affected by the surface relief and slope. The emergence of slope provided an altered path and power for water drainage. Only 0.3 % slope could contribute a 28.4 % to discharge efficiency. Upon comparation, the best combination for drainage was 2.0 % transverse slope with 3.0 % longitudinal slope. These findings provided meaningful insights and perspectives for urban flood hazard mitigation and were a more detailed reference for road design.

Characterization of road-deposited sediment wash-off and accurate splitting of initial runoff pollution in heterogeneous urban spaces

Particulate materials arising from road-deposited sediments (RDS) are an essential target for the control and management of surface runoff pollution. However, the heterogeneity of urban spaces hinders the identification and quantification of particulate pollution, which is challenging when formulating precise control measures. To elucidate the factors that drive particulate pollution in heterogeneous urban spaces, the accumulation of RDS on dry days and the total suspended solids during six natural rainfall events were investigated across three urban-rural spatial units (central urban, central suburban, and remote suburban). The underlying surface type (asphalt or cement roads) and particle size composition jointly determined the spatial heterogeneity in the static accumulation and dynamic output loads of RDS during rainfall. These two factors explained 59.6% and 18.9% of the spatial heterogeneity, respectively, according to principal component analysis. A novel CPSI exponential wash-off equation that incorporates particle size composition and underlying surface type was applied. It precisely described the spatial heterogeneity of RDS wash-off loads, the estimated values exhibiting event mean concentration errors of 10.8-18.2%. When coupled with the M(V) curve, this CPSI exponential wash-off equation more precisely split the initial volume of runoff: a lower total volume (17.6-38.0%) was shown to carry a higher proportion of the load (70.0-93.7%) compared to the traditional coupled exponential wash-off equation (volume: 31.6-49.0%, load: 37-90%). This study provides a new approach to characterizing RDS wash-off processes and splitting initial runoff in heterogeneous spaces.

Contributions of climate change and urbanization to urban flood hazard changes in China's 293 major cities since 1980

The growing incidence of urban flood disasters poses a major challenge to urban sustainability in China. Previous studies have reported that climate change and urbanization exacerbate urban flood risk in some major cities of China. However, few assessments have quantified the contributions of these two factors to urban flood changes in recent decades at the nationwide scale. Here, surface runoff caused by precipitation extremes was used as the urban flood hazard to evaluate the impacts of climate change and urbanization in China's 293 major cities. This study assessed the contributions of these drivers to urban flood hazard changes and identified the hotspot cities with increased trends under both factors during the past four decades (1980-2019). The results showed that approximately 70% of the cities analyzed have seen an increase of urban flood hazard in the latest decade. Urbanization made a positive contribution to increased urban flood hazards in more than 90% of the cities. The contribution direction of climate change showed significant variations across China. Overall, the absolute contribution rate of climate change far outweighed that of urbanization. In half of the cities (mainly distributed in eastern China), both climate change and urbanization led to increased urban flood hazard over the past decade. Among them, 33 cities have suffered a consecutive increase in urban flood hazard driven by both factors.

Aquatic ecological risk assessment of imidacloprid and thiacloprid in an urban river of Qingdao, China

Imidacloprid and thiacloprid, two neonicotinoid insecticides that are extensively used in urban areas, are potentially toxic to non-target aquatic organisms. In this study, the concentrations of imidacloprid and thiacloprid in surface runoff after rainfall were 20.79-43.77 ng/L and 25.13-63.84 ng/L, respectively, whereas the levels for the Licun River were 10.78-41.70 ng/L and 2.66-39.68 ng/L, respectively. The acute and chronic criteria for imidacloprid and thiacloprid are 0.865, 0.006, 0.83, and 0.012 μg/L, respectively. Tiered ecological risk assessments revealed the chronic ecological risks of these micropollutants to local aquatic species. There was a moderate chronic toxicity risk associated with imidacloprid and thiacloprid in the Licun River, and the joint probability curves showed a probability of chronic ecological risk to 5 % of the aquatic organisms at 68 %-97 %. The results provide evidence of urban surface runoff transporting micropollutants from surface into rivers and estuaries, highlighting the ecological risks to aquatic ecosystems.

Experimental surface runoff hydrographs from linear impervious subcatchments for rainfalls of extremely high intensity

This study focuses on lab-scale experimental runoff hydrographs from a linear completely impervious plane subcatchment. An improved method of surface runoff physical modelling was developed, allowing for expanded laboratory hydrograph simulations up to a linear scale of 10. Model rains of different intensities and durations were applied, and digital online data processing techniques were employed to ensure high time resolution and accurate flow rate determination. The experimental hydrographs were analyzed in a dimensionless form to facilitate generalization and comparison with widely used nonlinear reservoir method and unit hydrograph method. Wave-like fluctuations of the flow rate were observed in most experimental hydrographs as they approached the maximum runoff. The dimensionless phase time of the experimental hydrographs showed an increasing trend with higher rainfall intensity, and a power-law equation was derived to approximate this relationship. An averaged dimensionless runoff hydrograph was obtained by processing individual hydrographs, and it was approximated by the DR-Hill-Zerobackground model for the initial stage during the rainfall and by the Weibull model for the later stage, after the rainfall stopped. The findings of this study have significant implications for modelling surface runoff from small urban subcatchments, particularly under critical rainfall events with extremely high intensity.

Field migration of veterinary antibiotics via surface runoff from chicken-raising orchard in responding to natural rainfalls

Knowledge on runoff transport of manure-sourced antibiotics from farmland soil to aquatic environment is limited due to complexity of hydrological regime and pathways. This study monitored natural rainfalls in sloping orchard plots with free-range chickens, with an attempt to investigate the migration characteristics of typical antibiotics via surface runoff as well as the impact of manure presence. Results showed that rainstorms continuously carried away antibiotics in surface runoff and all target antibiotics including those with high affinities to soil were detected at the beginning of runoff production. Concentration of antibiotics was found to respond strongly to the instantaneous rainfall intensity, showing consistent fluctuations during rainfalls. Concentrations of sulfonamides and florfenicol were two orders of magnitude higher than that of tetracyclines and fluoroquinolones. Compared to the control without raising chickens, antibiotics migration was considerably increased with the increased runoff production due to soil surface changes caused by chicken activities. Additionally, dynamics of antibiotic concentration significantly correlated with variations of fluorescent DOM components. Chicken manure-derived DOM mainly contained tryptophan moiety, and laboratory fluorescence quenching test with 2D-COS analysis indicated that all antibiotics interacted more strongly and preferentially with tryptophan than humic-like species. Antibiotics bonded to manure DOM with an affinity corresponding to the significance level of their correlations. In this light, potential use of fluorescence indices based on the established correlations may provide a convenient tool for tracing runoff migration of antibiotics during rainfalls.

Exploration of a comprehensive versus a regulatory-oriented modeling framework for field pesticide transport assessment

Numerous computer models have been developed for simulating pesticide fate and transport. It is usually hard to choose which model is the best for a particular research or regulatory purpose. Currently, the PRZM (Pesticide Root Zone Model) model is widely used for regulatory purposes regarding runoff and erosion. However, it simplifies many hydrological processes and management practices which affect pesticide fate simulations. In this study, the APEX (Agricultural Policy / Environmental eXtender model) model, which is more comprehensive and may provide a more realistic representation of pesticide fate, was compared with the PRZM model regarding methods and capabilities of characterizing hydrology, management, and pesticide transport. Four case studies were used to compare the performances of the two models for simulating surface runoff, sediment yield, pesticide in runoff, and pesticide in sediment. Results showed that the APEX model performed better than the PRZM model for simulating surface runoff and sediment yield, and performed similarly to the PRZM model for simulating pesticide loads in runoff and erosion. Both models have limitations for capturing the runoff events caused by high intensity rainfall. APEX is superior to PRZM in simulating detailed management operations, considering more hydrological processes, and achieving spatially distributed simulation, but it requires a higher number of inputs and user-selected parameters compared to PRZM. With further validations of the capabilities of APEX in pesticide modeling and the development of web-based platforms to facilitate the set up and use of comprehensive models, a more accurate and reliable pesticide assessment scheme is anticipated by using comprehensive models like APEX.

Contribution of water erosion to organic carbon and total nitrogen loads in agricultural discharge from boreal mineral soils

While organic carbon (OC) in agricultural mineral soils is widely studied in terms of soil carbon sequestration and gaseous emissions, discharge-induced OC loss from soil is still poorly understood and estimations of boreal soil OC loads within water erosion are lacking. Loss of organic matter from arable soils is a concern for surface water quality, climate change and soil productivity. The main aim of this study was to quantify the role of water erosion in total OC and nitrogen (N) loads exported in agricultural discharge from boreal mineral soils under various cultivation practices. Surface water and subsurface drainage were collected near-continually over 2 years in two clayey and one sandy soil in Finland. Eroded sediment was mechanically separated by centrifugation from all discharge samples to detect sediment OC% and N% by dry-combustion method. Dissolved OC and N concentrations in selected discharge samples were measured with high-temperature catalytic oxidation of unfiltered supernatant. A multiple linear regression model was used to study the significant factors affecting dissolved, sediment and total OC loads. In the clayey soils, the sediment OC (2-24 kg ha-1 y-1) and N (0.2-1.1 kg ha-1 y-1) export accounted for up to 35 % and 20 % of the annual discharge-induced total loads of OC (19-85 kg ha-1) and N (2-8 kg ha-1), respectively. In the sandy soil, erosion was negligible and dissolved loads of 17-35 kg OC ha-1 y-1and 4-7 kg N ha-1 y-1 were detected. Subsurface drainage exported most of the sediment-associated OC and N loads from clayey soils. For the total OC loads, the distribution varied between the discharge routes, while the total N loads were mostly exported in subsurface drainage in both soil types. Sediment OC and N exports were related to soil plowing and discharge intensity, while dissolved OC loss was promoted by high surface soil OC%. Our results also indicated that a single cultivation practice may affect sediment and dissolved loads in opposite ways. These findings can be used to complement carbon budget estimations for mineral agricultural soils, and to assess soil management effects on terrestrial organic matter loading to boreal surface waters.

Evaluating urban park ecosystem services and modeling improvement scenarios

Three ecosystem services of the 25 public parks in Bangkok, including carbon sequestration, avoided runoff, four air pollutant removals (CO, NO2, PM10, and PM2.5), and the relevant monetary values, were determined using i-Tree Eco software. Two modeling scenarios (MS) including MS1 (no greening improvement) and MS2 (improvement by increasing either green area or tree planting, or both in the parks) with tree annual mortality rates (AMR) of 1 and 3% were developed to forecast the parks' ecosystem services for 50 years after 2020 (2021-2071). The results revealed the synergistic interactions of the different tree planting specifications (MS1 and MS2) and tree mortality rates on the parks' ecosystem services. For MC2 with the assigned 1% AMR, the parks' optimal ecosystem services were obtained and the average annual monetary value (0.55 million USD) of the total ecosystem services of the 25 parks over the 50-year forecast was 150% higher than that (0.22 million USD) in 2020. Based on MS1 and MS2, tree rotations should be conducted in the parks after 2057 and 2065, respectively, for the low tree AMR (≤1%) but not later than 2041 and 2043, respectively, for the higher tree AMR.

Agricultural nonpoint source pollutant loads into water bodies in a typical basin in the middle reach of the Yangtze River

Phosphorus and nitrogen pollution from agricultural nonpoint sources heavily burden the water environment, and a scientific calculating system is needed to calculate the pollutant loads under the water pollution treatment. This study established a system to calculate the coefficients of agricultural nonpoint source pollutants into water bodies in the subregion in Poyang Lake basin in the middle reach of the Yangtze River combining with multiple driving factors. Validation results showed that the errors of the typical unit were 30.58% for total phosphorus (TP), 13.43% for total nitrogen (TN) and 33.93% for ammonia nitrogen (NH3-N), respectively. The errors of the subregion were 26.92% for TP, 31.83% for TN and 29.15% for NH3-N, respectively. Besides, there were higher TP and TN loads in the east area of subregion in both units and county scales, which indicated the heavy phosphorus and nitrogen burden on water environment. In contrast, higher NH3-N loads occurred in the north area of subregion. The establishment of coefficient system for agricultural pollutants into water bodies and the pollutant loads calculation would provide enlightenment for water pollution treatment and agricultural nonpoint source pollution controlling.

Current and future water balance of a mountain subcatchment of Issyk-Kul Lake, Tien Shan range, Kyrgyzstan

Snow and ice dominated basins are particularly vulnerable to climate change but estimating their hydrological balance remains challenging in data-scarce regions like the Tien Shan mountains. With the overall aim of modeling of the large Issyk-Kul Lake basin in Kyrgyzstan, this article focuses on the hydrological balance of the Chon Kyzyl-Suu basin, a representative sub-catchment of the lake basin. The study involved two steps: first, calibration/validation of a distributed hydrological snow model, second, assessment of future trends in runoff, evaporation, snow melt and glacier melt under different climate scenarios. Our results show that the balance of the basin is already upset due to glacier mass loss and that groundwater processes play a significant role in generating discharge. Climate projections for the next 40 years (2020-2060) show no significant trend in precipitation under scenario ssp2-4.5 but an 8.9 % decrease in precipitation under scenario ssp5-8.5. at the same time, air temperature will increase by 0.4 °C under scenario ssp2-4.5, and by 1.8 °C under scenario ssp5-8.5. Under the "business as usual" scenario (ssp2-4.5), the annual river flow of the headwater basins should increase by 13 %, or under the "pessimistic" ssp5-8.5 scenario, by 28 %, mainly due to the increase in glacier runoff. These results make it possible to envisage realistic modeling at the scale of the lake at a daily time step.

Are wastewater treatment plants as the source of microplastics in surface water and soil?

Microplastics (MPs) are widely detected in wastewater treatment plants (WWTPs) and natural environment, while the relationship of MPs pollution in both media is not fully understood. In this study, the occurrence of MPs in WWTPs and in surface water and soil was investigated, and their relationship was critically formulated. Results showed although wastewater treatment could effectively remove MPs (58.2%), the effluent was still the important source of MPs in the river, while sludge was not as important as the effluent of MPs in the soil. Specifically, the dominant size ranges of MPs were 0-200 µm, with main type of PE in all wastewater, sludge, river and soil. The dominant shape of MPs in wastewater and river was film. However, the shapes were different between sludge (52.1% of fibers) and soil (40.6% of fragment). Overall, WWTP input and surface runoff were the main source of MPs pollution in surface water, and the abrasion of agricultural films accounted for the MPs pollution in soil. The findings revealed the distribution and interconnection of MPs in WWTPs and environmental media, which could help to trace the sources of MPs pollution and assess the ecological risks in the environment.

Study on hydrological response of runoff to land use change in the Jing River Basin, China

Land use change greatly affects the runoff characteristics of the basin, which in turn affects the distribution of surface water and groundwater in the region. Quantitative analyses of the hydrological response of watershed runoff to land use change are conducive to the formulation of sustainable water resource strategies. In this paper, the impact of land use change on runoff characteristics in the Jing River Basin was evaluated using the SWAT model, the land use pattern of the Jing River Basin in 2040 was predicted using CA-Markov model, and five land use change scenarios were set up in combination with the trend of land use transfer, and the response relationship between land use change and runoff hydrological characteristics in the basin was studied. The results show that the land use changes reduce runoff and change the hydrological cycle process of the basin. The hydrological response of different land use types varies significantly, but only has a less impact on annual runoff. Farmland has a promoting effect on production flow; woodland and grassland are not conducive to the formation of surface runoff and will increase underground runoff and evapotranspiration in the basin. The increase in vegetation coverage after returning farmland to woodlands and grasslands has reduced surface runoff, increased the recharge of groundwater, and played a positive role in ecological restoration in the river basin. The research results are of great significance for understanding the hydrological consequences of land use change and the rational planning of land use patterns in river basins.

Transport of neonicotinoid insecticides in a wetland ecosystem: Has the cultivation of different crops become the major sources?

Extensive application of neonicotinoid insecticides (NNIs) in agricultural production has resulted in widespread contamination of multiple environmental media. To investigate the occurrence and fate of NNIs in the largest marsh distribution area in Northeast China, an integrated ecosystem covering farmlands, rivers, and marshes, referred to as the farmland-river-marsh continuum in this study, was chosen for soil, water, and sediment sampling. Five NNIs were detected, with imidacloprid (IMI), thiamethoxam (THM), and clothianidin (CLO) being the most frequently detected ones in different samples. Concentrations of target NNIs in soil, surface water, and sediment samples were 2.23-136 ng/g dry weight (dw), 3.20-51.7 ng/L, and 1.53-8.40 ng/g dw, respectively. In soils, NNIs were detected more often and at higher concentrations in upland fields, while the concentration of NNIs in the soybean-growing soils (71.5 ng/g dw) was significantly higher than in the rice-growing soils (18.5 ng/g dw) (p < 0.05). Total concentration of NNIs in surface water was lower in the Qixing River channel than inside the marsh, while that in sediments showed an opposite trend. Total migration mass of IMI from approximately 157,000 ha of farmland soil by surface runoff was estimated to be 2636-3402 kg from the application time to the sampling period. The storage of NNIs in sediments was estimated to range from 45.9 to 252 ng/cm². The estimated environmental risks, calculated as the risk quotients (RQs), revealed low risks to aquatic organisms (RQs <0.1) from the residual concentrations of NNIs in water.

Surface runoff and soil erosion from Nitisols and Ferralsols as influenced by different soil organic carbon levels under simulated rainfall conditions

Soil erosion poses a challenge to the environment and the sustainable use of natural resources, particularly in relation to agricultural production. The study aimed to assess the influence of different soil organic carbon (SOC) levels on runoff and soil erosion under varying levels of rainfall intensity. The study was conducted in pre-selected farmers' fields representing low, moderate and adequate SOC levels in Nitisols and Ferralsols. Two parallel experiments were set up in each type of soil using a split-plot layout arranged in Randomized Complete Block Design. The main plots were the different soil organic carbon levels while the sub-plots were the different simulated rainfall intensities. Rainfall simulation was then conducted to determine runoff and sediment losses on each soil type. The simulation was done using a land type sprinkler nozzle rainfall simulator (460 788 type) in an experimental plot of 1 m2, fenced with corrugated iron sheets with a small opening left for runoff collection. Runoff and sediment losses were determined from the volume collected in the jar. The data was subjected to analysis of variance and significant mean differences were determined using Tukey's Honest Test at a 95% confidence level. Pearson correlation was applied to assess the relationship between runoff volume and sediment loss. The results showed that Ferralsols recorded significantly higher runoff and sediment losses compared to Nitisols, by 60.27% and 53.14% respectively. However, adequate SOC level portrayed a significant effect in reducing erosion in both soil types, where it reduced runoff and sediment loss by 45.30% and 48.38% in Ferralsols and by 65.31% and 48.22% in Nitisols, respectively. In both soil types, runoff yield was positively correlated to rainfall intensity while sediment yield was inversely correlated with SOC levels. Therefore, the study recommends incorporation of organic matter to adequate levels in both soils, for reduced soil erosion.

Effectiveness of side-inlet vegetated filter strips at trapping pesticides from agricultural runoff

Agriculture can be a contributor of pollutants, including pesticides and excess sediment, to aquatic environments. However, side-inlet vegetated filter strips (VFSs), which are planted around the upstream side of culverts draining agricultural fields, may provide reductions in pesticide and sediment losses from agricultural fields, and have the additional benefit of removing less land from production than traditional VFS. In this study, reductions of runoff, the soluble pesticide acetochlor, and total suspended solids were estimated using a paired watershed field study and coupled PRZM/VFSMOD modeling for two treatment watersheds with source to buffer area ratios (SBAR) of 80:1 (SI-A) and 481:1 (SI-B). Based on the paired watershed ANCOVA analysis, runoff and acetochlor load reductions were significant following the implementation of a VFS at SIA but not SI-B, indicating the potential for side-inlet VFS to reduce runoff and acetochlor load from a watershed with an area ratio of 80:1 but not a higher ratio of 481:1. VFSMOD simulations were consistent with the results of the paired watershed monitoring study, where simulated reductions of runoff, acetochlor loads, and TSS loads were substantially lower for SI-B than SI-A. VFSMOD simulations of SI-B with the SBAR ratio observed at SI-A (80:1) also show that VFSMOD can be used to capture variability in effectiveness of VFS based on multiple factors including SBAR. While this study focused on the effectiveness of side-inlet VFSs at the field scale, broader adoption of properly sized side-inlet VFSs could improve surface water quality at the watershed or larger scales. Additionally, modeling at the watershed scale could aid in locating, sizing, and assessing the impacts of side-inlet VFSs at this larger scale.

Impact of climate change on hydrologic components using CORDEX Africa climate model in Gilgel Gibe 1 watershed Ethiopia

This study aimed to assess the impact of climate change on the hydrological components of Gilgel Gibe-1 using the ensemble of Coordinated Regional Climate Downscaling Experiments (CORDEX) Africa Domain namely REMO2009, HIRAM5, CCLM4-8 and RCA4 Regional Climate Models (RCMs) simulations. The performance of these RCM models was evaluated using the observed data from 1985 to 2005 and the ensemble was shown to simulate rainfall and air temperature better than individual RCMs. Then the RCMs ensemble data for historical and future projections from 2026 to 2055 years under RCP4.5 and RCP8.5 were corrected for bias and used to evaluate the impact of climate change. A non-linear bias correction and the monthly mean biases corrections method is used to adjust precipitation and temperature respectively. The future projection shows that; rainfall is expected to increase from August to December with maximum values of 1.97-235.23% under RCP4.5. The maximum temperature is expected to increase with maximum value of 1.62 °C under RCP8.5 in the study area. The calibrated and validated Soil and Water Assessment Tool (SWAT) model was used to investigate the impact of climate change on hydrologic components such as surface runoff, lateral flow, water yield, evapotranspiration and sediment yield. The SWAT model was calibrated and validated using monthly stream flow with the statistical performance of R² value of 0.82 and NSE value of 0.72 for calibration and R² of 0.79 and NSE of 0.67 for validation. Surface runoff and sediment yield are expected to increase from August to December under RCP4.5 and from August to February under RCP8.5. Overall both surface runoff and sediment yield are expected to increase in the future.

Influence of concrete material of runoff collection containers on monitoring of nitrogen and phosphorus pollutants

The accurate monitoring of N and P surface runoff losses from farmland is crucial to control agricultural nonpoint source pollution. A pond constructed with concrete material (CM) is a common collection container used during field experiments in China, but the adsorption characteristics of concrete may cause a considerable underestimation of surface runoff losses from farmland. To characterize any neglected error caused by the collection container material, a laboratory experiment was conducted comparing the N and P contents of runoff samples collected from CM and plastic material (PM) containers. The results indicated that CM containers significantly lowered N and P sample contents compared with PM containers, which was attributed to the adsorption capacity of pollutants by CM containers. This was confirmed by scanning electron microscopy (SEM) images of particles retained in CM containers. In an attempt to alleviate this error, three common water-repellent materials were applied to CM containers that significantly limited the pollutant adsorption of CM containers. Moreover, it was shown that there was no significant difference between the calculated concentration of runoff losses and the total amount of pollutants. To calibrate the observational error from CM containers, stepwise multiple regression models of different forms of N and P pollutants were developed. The results of this study suggest that treating CM containers with water repellent is an effective measure for improving the accuracy of new-built monitor points of agricultural nonpoint source pollutants. In addition, the calibration of observational error from CM containers and delayed sampling is essential to estimate agricultural nonpoint source pollution load via the surface runoff from farmland based on data from monitor points.

Determination of nitrogen sources and losses in surface runoff from different lands at a watershed scale

Nitrogen (N) loss by surface runoff inevitably results in severe N pollution and eutrophication of aquatic ecosystems. In this study, surface runoff from different land uses in the East Tiaoxi River watershed was collected, and the N concentrations, sources and losses were measured using the dual isotope (δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^-), a Bayesian isotopic mixing (SIAR) model and Soil Conservation Service Curve Number (SCS-CN) method. The results showed that the N concentrations in surface runoff from agricultural lands were higher than those from urban areas and forestlands, and nitrate (NO₃^-), particulate nitrogen (PN) and dissolved organic nitrogen (DON) were the major forms of N in surface runoff in the East Tiaoxi River watershed. The total loss rate of total nitrogen (TN) from surface runoff in the East Tiaoxi River watershed was 5.38 kg·ha^-1·a^-1, with NO₃^--N (46%) contributing the most to TN loss. The TN, and NO₃^--N loss rates in surface runoff from tea planting lands (21.08 kg·ha^-1·a^-1, 11.98 kg·ha^-1·a^-1) and croplands (16.93 kg·ha^-1·a^-1, 10.96 kg·ha^-1·a^-1) were high, those from vegetable lands and urban areas were medium, and those from economic and natural forestlands were low in the East Tiaoxi River watershed. The NO₃^--N contributions of chemical fertiliser (CF), soil N (SN), sewage/manure (SM), and atmospheric deposition (AD) in surface runoff in the East Tiaoxi River watershed were 124.32 × 10³, 104.84 × 10³, 82.25 × 10³ and 58.69 × 10³ kg·a^-1, respectively. The N pollutant losses in surface runoff from agricultural lands (croplands with rice growing, vegetable lands and tea planting lands) were responsible for most of the N pollutants being transported into the East Tiaoxi River systems.

Topographic constraints on the distribution of selenium in the supergene environment: A case study at Yutangba, China

The local topography and leaching conditions significantly affect the spatial distribution of selenium (Se) in the local environment. However, the driving factors controlling Se distribution have not been well addressed. In this paper, taking Yutangba, a village known for human selenosis in China, as an example, we demonstrate how topographic factors influence the spatial distribution of Se in soils and plants. In the scenarios of slope ≤25°, the correlations among slope and soil/extractable/plant Se are significantly negative (P < 0.05), whereas they become weak or unclear when the slope is > 25°, suggesting that 25° of slope is a critical transition boundary. Similar observations were further verified by the soil erosion modulus (SEM) and the surface runoff intensity index (SRI), indicating that Se transport via soil erosion is limited and accounts for 11.2-17% of the soil Se, while surface runoff plays a dominant role in the Se distribution, accounting for 83-88.1%. Soil extractable Se is negatively correlated with SRI (Pearson r = -0.87 at slope < 25°), showing that the migration capacity of Se is higher at steep terrain and controlled by topography through soil erosion and surface runoff. The positive relationship between plant Se and soil/extractable Se demonstrates that topography indirectly influences plant Se through soil Se bioavailability. Abnormally local Se enrichment observed at the elevated steep hillside (>25°) in northwestern Yutangba primarily was resulted from the weathering of Se-rich rocks. These observations confirm that the topographic slope gradient influences the transport and spatial distribution of soil Se, implying that topography should be considered when studying the spatial distribution of soil Se at a regional scale, especially for the Se-poor belt in China.

Quantifying groundwater phosphorus flux to rivers in a typical agricultural watershed in eastern China

Increasing evidence indicates that groundwater can contain high dissolved phosphorus (P) concentrations, thereby contributing as a potential pollution source for surface waters. However, limited quantitative knowledge is available concerning groundwater P fluxes to rivers. Based on monthly hydrochemical monitoring data for rivers and groundwater in 2017-2020, this study combined baseflow separation methods and a load apportionment model (LAM) to quantify contributions from point sources, surface runoff, and groundwater/subsurface runoff to riverine P pollution in a typical agricultural watershed of eastern China. In the studied Shuanggang River, most total P (TP) and dissolved P (DP) concentrations exceeded targeted water quality standards (i.e., TP ≤ 0.2 mg P L^-1, DP ≤ 0.05 mg P L^-1), with DP (76 ± 20%) being the major riverine P form. Observed DP concentrations in groundwater were generally higher than those of river waters. There was a strong correlation between river and groundwater P concentrations, implying that groundwater might be a considerable P pollution source to rivers. The nonlinear reservoir algorithm estimated that baseflow/groundwater contributed 66-68% of monthly riverine water discharge on average, which was consistent with results estimated by an isotope-based sine-wave fitting method. The LAM incorporating point sources, surface runoff, and groundwater effectively predicted daily riverine TP [calibration: coefficient of determination (R²) = 0.76-0.82, Nash-Sutcliffe Efficiency (NSE) = 0.61-0.77; validation: R² = 0.88-0.98, NSE = 0.54-0.64] and DP loads (calibration: R² = 0.73-0.84, NSE = 0.67-0.72; validation: R² = 0.88-0.97, NSE = 0.56-0.83). The LAM estimated point source, surface runoff, and groundwater contributions to riverine loads were 15-18%, 14-35%, and 46-70% for TP loads and 7-9%, 10-32%, and 59-82% for DP loads, respectively. Groundwater was the dominant riverine P source due to long-term accumulation of P from excess fertilizer and farmyard manure applications. The developed methodology provides an alternative method for quantifying P pollution loads from point sources, surface runoff, and groundwater to rivers. This study highlights the importance of controlling groundwater P pollution from agricultural lands to address riverine water quality objectives and further implies that decreasing fertilizer P application rates and utilizing legacy soil P for crop uptake are required to reduce groundwater P loads to rivers.

Investigating relationships between landscape patterns and surface runoff from a spatial distribution and intensity perspective

Rapid urbanization changes landscape patterns and results in frequent urban waterlogging issues, which affect citizens' daily lives and cause economic loss. Understanding the spatial patterns and impact factors associated with urban waterlogging under different rainfall intensities has significant implications for mitigating this hazard. In this study, the runoff depth calculated according to the Storm Water Management Model (SWMM) simulation results was used to investigate the spatial characteristics of urban waterlogging. Multiple scenario-based designs, a correlation analysis, and a stepwise regression model were employed to detect the relationship between surface runoff depth and landscape patterns under different rainfall intensities. The results show that when the rainfall intensity reached 12.5 mm/12 h, the conversion rate of rainfall to runoff increased significantly, indicating an increased waterlogging risk. Areas with impervious surface proportions of 25-50% and 75-100% were shown to require more attention due to the strong sensitivity of the surface runoff depth to an increase in the impervious surface. It is most cost-effective to maintain the original high-density vegetation or increase the vegetation density from 0-25% to 25-50% for urban green space. Additionally, the landscape configuration also affects the surface runoff depth. The fragmented, scattered, or regular shape of impervious surface patches can reduce surface runoff effectively; larger and less fragmented green space was also shown to have a surface runoff controlling. The adjusted R² values were greater than 0.6 for all stepwise regression models, indicating that the landscape variables selected in the study can effectively predict the surface runoff depth. These models also showed that the landscape composition had a more profound contribution than the landscape configuration on runoff depth. These findings provide meaningful insights and perspectives for urban waterlogging hazard mitigation, quantitative landscape planning, and risk management. The method proposed by this study provides a referable framework for future studies on urban waterlogging and its response to the landscape in the context of global climate change.

Suppression of arbuscular mycorrhizal fungi increased lead uptake in maize leaves and loss via surface runoff and interflow from polluted farmland

Arbuscular mycorrhizal fungi (AMF) are ubiquitous in farmland. But the knowledge on AMF impact on lead (Pb) migration in farmland is limited. A field experiment was conducted in the rainy season (May-October) for two years in a Pb-polluted farmland. Benomyl was used to specifically suppress the native AMF growth in the farmland. The effect of benomyl-induced AMF suppression on the Pb uptake in maize, and Pb loss via surface runoff and interflows (20 cm and 40 cm depth) from the farmland was investigated. The benomyl significantly inhibited the AMF growth, resulting in decreases in the colonization rate, spore number, and contents of total and easily extractable glomalin-related soil protein (GRSP); and promoted the Pb migration into maize shoots and mainly enriched in leaves. The particulate Pb accounted for 83.2%-90.6% of Pb loss via surface runoff, while the proportion of particulate Pb loss via interflow was decreased and the proportion of dissolved Pb loss increased with the increase of soil depth. The AMF suppression led to a decrease in dissolved Pb concentration and loss, but an increase in particulate Pb concentration and loss, and enhanced the total Pb loss via surface runoff and interflows. Moreover, significant or very significant negative correlations were observed between the AMF colonization rate in roots with the Pb uptake in leaves, and the content of easily extractable GRSP with the particulate Pb loss. These results indicated the native AMF contributed to immobilizing Pb in soil and inhibited its migration to crops and the surrounding environment.

The impacts of LULC and climate change scenarios on the hydrology and sediment yield of Rib watershed, Ethiopia

Watershed-scale hydrology and soil erosion are the main environmental components that are greatly affected by environmental perturbations such as climate and land use and land cover (LULC) changes. The purpose of this study is to assess the impacts of scenario-based LULC change and climate change on hydrology and sediment at the watershed scale in Rib watershed, Ethiopia, using the empirical land-use change model, dynamic conversion of land use and its effects (Dyna-CLUE), and soil and water assessment tool (SWAT). Regional climate model (RCM) with Special Report on Emission Scenarios (SRES) and Representative Concentration Pathway (RCP) outputs were bias-corrected and future climate from 2025 to 2099 was analyzed to assess climate changes. Analysis of the LULC change indicated that there has been a high increase in cultivated land at the expense of mixed forest and shrublands and a low and gradual increase in plantation and urban lands in the historical periods (1984-2016) and in the predictions (2016-2049). In general, the predicted climate change indicated that there will be a decrease in precipitation in all of the SRES and RCP scenarios except in the Bega (dry) season and an increase in temperature in all of the scenarios. The impact analysis indicated that there might be an increase in runoff, evapotranspiration (ET), sediment yield, and a decrease in lateral flow, groundwater flow, and water yield. The changing climate and LULC result in an increase in soil erosion and changes in surface and groundwater flow, which might have an impact on reducing crop yield, the main source of livelihood in the area. Therefore, short- and long-term watershed-scale resource management activities have to be designed and implemented to minimize erosion and increase groundwater recharge.

Horizontal transport of macro- and microplastics on soil surface by rainfall induced surface runoff as affected by vegetations

Surface runoff is considered as an important pathway that transport of plastic waste from terrestrial environment into the aquatic environment but the process is still poorly understood. In this work, runoff plot experiment was carried out to study the horizontal transport of macro- and microplastics between 50 mm and 0.25 mm in size on the soil surface by rain induced runoff. The influences of vegetation cover, characteristics of plastics, and rainfall scenarios were investigated. Results showed that the presence of vegetation significantly enhance the retention of plastics by about 20% under the experimental conditions. Lower density and smaller (<1 mm) plastics were found to have higher mobility. The herb plant (Photinia×fraseri Dress) showed a better interception efficiency on plastics than the shrub plant (Ophiopogon japonicus (Linn. f.) Ker-Gawl.) at the same planting density, while increasing plant density contributed litter to the interception of microplastics. Increase rainfall amount from 20 mm to 60 mm enhanced the transport of plastics while repeating 20 mm rainfall every 3 days did not affect the transport of plastics significantly. The same processes may involve in the transport of plastics and soil particles by rainfall induced surface runoff. Strategies controlling soil erosion could also be used to prevent plastics in soil from entering the aquatic environment. However, effects and risks of plastics retained in the soil are still unclear, which need to be investigated in future.

Pesticide concentrations in agricultural storm drainage inlets of a small Swiss catchment

Agricultural pesticides transported to surface waters pose a major risk for aquatic ecosystems. Modelling studies indicate that the inlets of agricultural storm drainage systems can considerably increase the connectivity of surface runoff and pesticides to surface waters. These model results have however not yet been validated with field measurements. In this study, we measured discharge and concentrations of 51 pesticides in four out of 158 storm drainage inlets of a small Swiss agricultural catchment (2.8 km²) and in the receiving stream. For this, we performed an event-triggered sampling during 19 rain events and collected plot-specific pesticide application data. Our results show that agricultural storm drainage inlets strongly influence surface runoff and pesticide transport in the study catchment. The concentrations of single pesticides in inlets amounted up to 62 µg/L. During some rain events, transport through single inlets caused more than 10% of the stream load of certain pesticides. An extrapolation to the entire catchment suggests that during selected events on average 30 to 70% of the load in the stream was transported through inlets. Pesticide applications on fields with surface runoff or spray drift potential to inlets led to increased concentrations in the corresponding inlets. Overall, this study corroborates the relevance of such inlets for pesticide transport by establishing a connectivity between fields and surface waters, and by their potential to deliver substantial pesticide loads to surface waters.

Particle size distribution and total suspended solid concentrations in urban surface runoff

An in-depth understanding of particle size distribution as well as total suspended solids (TSS) in surface runoff is essential for managing urban diffuse pollution. In this study, field experiments and model simulation were undertaken to explore and confirm the dynamic runoff behaviour of TSS and their influencing factors. Field observation results showed that samples with high TSS concentrations contained coarser particles (>100 μm) during three natural rainfall events. Particle size distribution as well as road-deposited sediments (RDS) amount before and after these rainfall events also confirmed that a higher percentage of washed-off coarser particles resulted in higher TSS concentrations in surface runoff water. The impacts of rainfall characteristics, urban-rural gradients, surface roughness, and climate difference on particle distribution as well as TSS concentration were analyzed using the wash-off formula of particle size. These factors mainly affected the contribution rate of RDS to TSS by altering particle size composition; rates ranged from 4% to 44% under different rainfall characteristics. The critical particle size (<100 μm) was developed according to the mass percentage of particles with different sizes in RDS and TSS. Our results can provide a simple and effective way of assessing RDS contribution to TSS in surface runoff.

Surface runoff response to long-term land use changes: Spatial rearrangement of runoff-generating areas reveals a shift in flash flood drivers

Nowadays, rapid growths of urban areas and associated land use/land cover (LULC) changes notably affect the surface runoff response to rainfall in urbanised catchments. This effect of urbanisation on surface runoff is frequently addressed since it relates to the increasing incidence of pluvial floods worldwide. Studies on this issue commonly assess runoff changes over several most recent decades. However, human-induced factors likely resulted in increased surface runoff and associated flash floods in rural catchments even in the past centuries. Such long-term changes have been rarely studied and thus are not well documented. This paper aims to fill this gap and assess the surface runoff response to LULC changes in a small catchment in southwestern Slovakia over more than two centuries. To meet this goal, we applied the Soil Conservation Service Curve Number (SCS-CN) method. We mapped past (1784) and present (2018) LULC classes based on historical maps and modern remote sensing data. Then, we estimated surface runoff depths for specific design rainstorms for both periods by executing CN method equations in the ArcGIS environment. Results revealed significant changes in surface runoff conditions between evaluated periods. In total, surface runoff magnitudes increased by ~230 and ~ 130% for 40- and 65-mm design rainstorms, respectively, compared to 1784. Moreover, surface runoff values show different spatial patterns on historical and present-day output raster images revealing spatial redistribution of runoff-enhancing and runoff-preventing areas during the evaluated period. Although both infiltration-enhancing and runoff-enhancing effects of LULC changes were identified, the latter effect associated with urbanised lowland areas was recognised as prevailing at present. In contrast, runoff-promoting conditions were associated with hilly vineyard areas in the past. These findings likely have important implications for understanding the past and present LULC-based controls of surface runoff generation and flash floods initiation.

Soil water infiltration evaluation from punctual to hillslope scales

Quantifying infiltration and surface runoff at the hillslope scale is indispensable for soil conservation studies. However, the spatial and temporal variability of infiltration imposes a major constraint on surface runoff estimation. Point infiltration values do not fully express the complexity of the surface runoff in the landscape. Considering the need to improve the estimation of runoff volume from infiltration data, this study aimed to measure the apparent infiltration at hillslope-scale and compare it with two methods of infiltration estimative derived from point information. The study was carried out in six hydrological monitoring units paired. A set of hyetographs and hydrographs allowed the determination of apparent infiltration [Formula: see text] to each monitoring unit as a function of precipitation rate P. The measured [Formula: see text] values were used: (1) to evaluate the efficiency of the different land management in increasing infiltration; and (2) to evaluate the efficiency of two methods of hillslope-scale infiltration estimation based on point data: (a) derived from concentric rings method ([Formula: see text]), and (b) derived from a physically-based modeling ([Formula: see text]). Regarding the differences in land managements, terraces proved to be the most efficient land management practice, followed by phytomass addition. Regarding the methods, for precipitation rates greater than 40 [Formula: see text] the point infiltration-based [Formula: see text] underestimates apparent infiltration [Formula: see text] with PBIAS ranging from [Formula: see text] to [Formula: see text]. Even so, [Formula: see text] proved efficient in representing [Formula: see text] at less intense rainfall events. Nonetheless, the point infiltration-based method [Formula: see text] properly represented [Formula: see text] to all rainfall intensities (Nash-Sutcliffe coefficient [Formula: see text]).

Removal of munition constituents in stormwater runoff: Screening of native and cationized cellulosic sorbents for removal of insensitive munition constituents NTO, DNAN, and NQ, and legacy munition constituents HMX, RDX, TNT, and perchlorate

Technologies are needed to address contamination with energetic compounds at military installations. This research developed and evaluated novel and sustainable materials that can be used to remove munition constituents (MC) from stormwater runoff. Initial work focused on 3-nitro-1,2,4-triazol-5-one (NTO), as it is both highly soluble and ionized at environmentally relevant pH values. Screening cellulosic materials indicated that cationized (CAT) versions of pine shavings (pine, henceforth) and burlap (jute) demonstrated >70% removal of NTO from artificial surface runoff. CAT materials also demonstrated >90% removal of the anionic propellant perchlorate. NTO removal (~80%) by CAT pine was similar across initial pH values from 4 to 8.5 S.U. An inverse relationship was observed between NTO removal and the concentration of the major anions chloride, nitrate, and sulfate due to competition for anion binding sites. Sorption isotherms were performed using a mixture of the three primary legacy explosives (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), hexahydro-1,3,5-trinitro-s-triazine (RDX), 2,4,6-trinitrotoluene (TNT)), the three insensitive MC (nitroguanidine (NQ), NTO, 2,4-dinitroanisole (DNAN)), and perchlorate. Isotherm results indicated that effective removal of both legacy and insensitive MC would best be achieved using a mixture of peat moss plus one or more of the cationized cellulosic materials.

Riparian strips as attenuation zones for the toxicity of pesticides in agricultural surface runoff: Relative influence of herbaceous vegetation and terrain slope on toxicity attenuation of 2,4-D

Pesticides reach aquatic ecosystems via surface runoff becoming one of the main contributors to their deterioration. Among the strategies to mitigate these impacts, the use of riparian strips is recommended, but the knowledge of how much each ecosystemic variable contributes to the process is still incipient. We analyzed the influence of terrain slope and vegetation in the attenuation of 2,4-Dichlorophenoxyacetic acid (2,4-D) toxicity in surface runoff using Lactuca sativa as a diagnostic organism. In addition, the differential effects of this herbicide were examined under laboratory conditions, with standardized water and ambient water as a dilution medium. The study was conducted in plots with different terrain slopes and presence/absence of vegetation. The herbicide was applied to each plot and rain was subsequently simulated. The runoff was collected at regular distances and the toxicity was measured. The runoff toxicity decreased with the distance from the application area in all plots, this reduction being greater in low-slope plots. No differences in attenuation of runoff toxicity were found between plots with and without vegetation. The data were incorporated into models to estimate the minimum widths of safety to reduce the toxicity of 2,4-D by 90% under these conditions, suggesting distances of 5 and 20 m for low-slope and high-slope zones, respectively. In laboratory experiments, lower relative toxicity of 2,4-D was detected when natural water was used as solvent. These results contribute to the design of sustainable agricultural practices.

Resilient planning optimization through spatially explicit, Bi-directional sociohydrological modeling

Stormwater runoff is one critical urban issue that exemplifies the complexity in coupling human and natural systems. Innumerable studies have described and assessed the hydrological responses that result from land-use changes through a 'post land use change' hydrological analysis. Complex systems theory, however, suggests that the urban and ecological systems operate as an intertwined whole. This means that typical one-directional analysis can miss critical components of a bi-directional sociohydrological process. In addition, there is a difference in physical scales between hydrological analysis and policymaking that is often left unresolved. Typical hydrological models are limited to a watershed and are not easily applied to policymaking that is generally demarcated by a political boundary. These types of models also lack the spatial explicitness needed for physical design responses. To address these issues, we develop an integrated, finely scaled, spatially explicit sociohydrological modeling system. The coupled land use/stormwater model projects and assesses bi-directional sociohydrological impacts to changing land uses. We apply and test the system in McHenry County, Illinois, by modeling three scenarios to the year 2045. The results show that residential and commercial developments exhibit different responses to hydrological variables, resulting in varying patterns of land use locational choices. We also find that there is a conflict between developmental preferences that prefer to be located near water (housing) and those that prefer to be located away from runoff-prone water areas (commercial land uses). Our bi-directional modeling system simulates cell-to-cell interactions to produce quantifiable and practically useful outputs. The output for McHenry County, Illinois, includes specific, locational information on how to optimize developmental regulations in response to the contradictory developmental preferences and, more importantly, how to live with runoff in the context of resilience. This research supports the need for cell-based forward-looking modeling to better understand complex urban systems and strategically establish a resilient built environment.

Quantitative microbial human exposure model for faecal indicator bacteria and risk assessment of pathogenic Escherichia coli in surface runoff following application of dairy cattle slurry and co-digestate to grassland

Animal waste contains high numbers of microorganisms and therefore can present a potential biological threat to human health. During episodic rainfall events resulting in runoff, microorganisms in the waste and soil may migrate into surface runoff, contaminating surface water resources. A probabilistic human exposure (HE) model was created to determine exposure to faecal indicator bacteria (FIB): total coliforms (TC), E. coli and enterococci following application of bio-based fertiliser (dairy cattle slurry, digestate) to grassland; using a combination of experimental field results and literature-based data. This step was followed by a quantitative microbial risk assessment (QMRA) model for pathogenic E. coli based on a literature-based dose-response model. The results showed that the maximum daily HE (HE_daily) is associated with E. coli for unprocessed slurry (treatment T1) on day 1, the worst-case scenario where the simulated mean HE_daily was calculated as 2.84 CFU day ^-1. The results indicate that the overall annual probability of risk (P_annual) of illness from E. coli is very low or low based on the WHO safe-limit of P_annual as 10 ^-6. In the worst-case scenario, a moderate risk was estimated with simulated mean P_annual as 1.0 × 10 ^-5. Unpasteurised digestate application showed low risk on day 1 and 2 (1.651 × 10 ^-6, 1.167 × 10 ^-6, respectively). Pasteurised digestate showed very low risk in all scenarios. These results support the restriction imposed on applying bio-based fertiliser if there is any rain forecast within 48 h from the application time. This study proposes a future extension of the probabilistic model to include time, intensity, discharge, and distance-dependant dilution factor. The information generated from this model can help policymakers ensure the safety of surface water sources through the quality monitoring of FIB levels in bio-based fertiliser.

Performance of AnnAGNPS model in predicting runoff and sediment yields in Nan Province, Thailand

Land use changes such as deforestation and urban development influences the river discharge, soil erosion and sediment yield. It is important to evaluate tools which can be used to assess such impacts on water and sediment yield. Therefore, this study evaluated the Annualized Agricultural Non-Point Source Pollutant (AnnAGNPS) model's performance in simulating runoff and sediment loads in Nan Province, Thailand using seven years of continuous monitoring data. The river discharge and sediment yield data from 2011–2013 were used for calibration, and data from 2014–2017 were used for validation. Several input parameters were computed using methods suggested by other researchers and previous studies. In this study, the runoff curve number, soil erodibility factor (K), and RUSLE-C value were used to accurately simulate runoff and sediment loads. The results indicate that the model satisfactorily simulated runoff and sediment loads (R² = 0.65 and NSE = 0.53 for runoff volume, and R² = 0.62 and NSE = 0.60 for sediment yields). Moreover, the model estimated the total sediment yield, which contributed 12,932 hundred tons of material to the Nan River in 2017. The maximum sediment yield was obtained below the catchment (Na Noi sub-district, Na Noi district), which corresponds to areas with high crop densities. Cropland generated the highest soil erosion of all investigated land use (87.52% of total soil erosion). Thus, the AnnAGNPS model has the potential to use for investigating management practices to reduce soil erosion and controlling floods and droughts in Nan Province of Thailand.

Quantifying the release of tyre wear particles to the marine environment via multiple pathways

Desk-based studies have suggested tyre wear particles contribute a substantial portion of microplastic emissions to the environment, yet few empirical studies report finding tyre wear. Samples were collected from three pathways to the marine environment: atmospheric deposition, treated wastewater effluent, and untreated surface runoff. Pyrolysis coupled to gas chromatography-mass spectrometry was used to detect benzothiazole, a molecular marker for tyres. Benzothiazole was detected in each pathway, emitting tyre wear in addition to other sources of microplastics. Release via surface water drainage was the principle pathway in the regions examined. Laboratory tests indicated larger particles likely settle close to their entry points, whereas smaller particles have potential for longer-range transport and dispersal. The previous lack of reports are likely a consequence of inadequate methods of detection, rather than a low environmental presence. Further work is required to establish distribution, transport potential, and potential impacts once within the marine environment.

Multivariate analysis of factors influencing the peak flow and runoff volume in the Cerrado and Atlantic Forest biomes in Brazil

This study evaluates the influence of physiographic characteristics on the peak flow to runoff volume ratio in watersheds belonging to the Cerrado and Atlantic Forest biomes, in the Center-South region of Brazil. Specifically, the peak flow and runoff volume values obtained in the outlet section are related to the physiographic characteristics of the watersheds. Using a geographic information system tool, 13 watersheds are delimited, and 38 variables are selected from each watershed. A recursive digital filter is used to separate the direct (surface) flow from base (groundwater) flow. Data are analyzed using multivariate statistics, which allows interpretation of the structure of a data set from the respective correlation matrices. The results indicate that the peak flow and runoff volume are strongly correlated with the physical characteristics of the watersheds and the types of anthropogenic activity in both biomes. Furthermore, the presence of woods and forests reduces the peak flow and runoff volume.

Unpaved road conservation planning at the catchment scale

In addition to soil losses on hillslopes, unpaved rural roads, especially when poorly designed and maintained, can be a significant contributor to the erosive processes seen at the catchment scale. In areas with deep soils, the solutions primarily focus on channeling excess surface runoff into settling ponds or terraces. However, few studies have addressed runoff control from roads on steep slopes in areas of shallow soil. Modeling hydrological processes at the catchment scale is a useful strategy for choosing the most effective and least costly conservation practices to control surface runoff. This study applies a mathematical model to a monitored catchment in southern Brazil to better understand the effects of conservation practices on unpaved roads and their impact on the hydrological and erosive dynamics of a small rural catchment. We calibrated the LISEM model using data from eight stormwater events and evaluated how three different road conservation scenarios-low (LI), medium (MI), and high intensity (HI)-contributed to sediment yield (SY), surface runoff volume (Qe), and peak flow (Qp) reduction. The LI and MI scenarios involved installation of hydraulic structures to control the road surface runoff (i.e. road ditch graveling, diversion weirs and grass waterways) while the HI scenario added surface runoff control practices (grass strips) to surrounding crop fields, in addition to the practices included in the MI scenario. Based on these scenarios, the results showed a Qe reduction at the catchment outlet from - 3.5% (LI) to - 22.5% (HI). The Qp and SY varied from + 6.0% (LI) to - 292.5% (HI) and from + 20.0% (LI) to - 963.9% (HI), respectively. These results show that the low- and medium-intensity practices were not effective in controlling surface runoff from roads, based on the Qe, Qb, and SY observed at the catchment's outlet. On the other hand, when MI scenarios were complemented with practices to control surface runoff in the cultivated areas, a significant reduction in surface runoff (Qe and Qp) and SY was verified.

Effects of urban residential landscape composition on surface runoff generation

Lawns have long been a primary feature of residential landscapes in the United States. However, as population growth in urban areas continues to rise, water conservation is becoming a key priority for many municipalities. In recent years, some municipalities have begun to offer rebate programs which incentivize removal of turfgrass areas and conversion to alternative 'water-efficient' landscapes, with the goal of reducing outdoor water use. The environmental impacts and changes to ecosystem services associated with such landscape alterations are not well understood. Therefore, a 2-year continuous research project was conducted at the Urban Landscape Runoff Research Facility at Texas A&M University to evaluate rainfall capture and runoff volumes associated with several commonly used residential landscape types (including, St. Augustine grass Lawn, Xeriscaping, Mulch, Artificial Turf, and Sand-capped Lawn) and to characterize the flow dynamics of surface runoff in relation to rainfall intensity for each landscape. The results demonstrate that runoff dynamics differ between landscapes, but also change over time as the newly converted landscapes become established. Following the initial months of establishment, the effects of landscape type on runoff volumes were significant, with Artificial Turf and Xeriscaping generating greater runoff volumes than Mulch and St. Augustine grass Lawns for most runoff events, which is partially due to the low infiltration rate of such landscapes. Overall, Artificial Turf and Xeriscaping showed the greatest cumulative runoff volumes (>400 L m^-2), whereas Water Efficient- Mulch, Sand-capped Lawn and St. Augustine grass Lawn had a significantly lower cumulative runoff volumes, ranging from 180 to 290 L m^-2. Information from this research should be useful to municipalities, water purveyors, and homeowner associations as they weigh the long-term hydrological impacts of lawn removal and landscape conversion programs.

Sources and pollution path identification of PAHs in karst aquifers: an example from Liulin karst water system, northern China

Karst water, with constituting major sources for water supply worldwide, is vulnerable and prone to be polluted. In this study, it is reported that karst water polycylic aromatic hydrocarbons (PAHs) pollution is caused by the infiltration of surface runoff in the bared carbonate areas, which is of universal significance for the protection of groundwater resources in karst region. Hydro-geochemistry, stable isotopes (δD, δ¹⁸O and ⁸⁷Sr/⁸⁶Sr) and characteristic ratio method were conducted together to illustrate the concentration, distribution, sources and pollution path of polycyclic aromatic hydrocarbons in groundwater in the Liulin karst water system of northern China. The results showed that total concentration of polycyclic aromatic hydrocarbons ranged from 39.25 to 16,830 ng/L in groundwater, with Naphthalene being the dominant component, and the median value increased gradually along the flow path. The highest polycyclic aromatic hydrocarbons concentrations in karst water were mainly observed in the coal mining and the discharge areas. Based on the characteristic ratios, the polycyclic aromatic hydrocarbons in the study area mainly come from local incomplete combustion of woods, fossil fuels, coal and liquid fuels. The slight shift of δD and δ¹⁸O and moderate ⁸⁷Sr/⁸⁶Sr ratios suggest that the polycyclic aromatic hydrocarbons in karst water is mainly polluted by surface runoff during rain events in the bared karst region. The leakage of river water may partly contribute to the polycyclic aromatic hydrocarbons in some karst water, which normally located close to the karst water - river water mixing line. This study provides a new technical method for tracing the sources and identifying the pollution paths of organic pollution in a karst water system.

A dynamic land use/land cover input helps in picturing the Sahelian paradox: Assessing variability and attribution of changes in surface runoff in a Sahelian watershed

In Sahelian landscapes, land use/land cover (LULC) dynamics and climate variability are already known to affect the water cycle. In its current practice however, hydrological modelling does not account for LULC changes. This issue pertains to rapidly evolving watersheds and might result in critical inaccuracies in the simulated processes. In this study, the Soil and Water Assessment Tool (SWAT) model was used to simulate surface runoff in the small Sahelian watershed of Tougou, which underwent significant LULC changes between 1952 and 2017. Based on rainfall/runoff data acquired from 2004 to 2018, the SWAT model was calibrated under two scenarios: a static land use scenario (SLU) using a single LULC map (in 1999) and a dynamic land use scenario (DLU) integrating 3 LULC maps (1999, 2009 and 2017). The DLU scenario estimated with higher accuracy surface runoff, deep aquifer infiltration and actual evapotranspiration processes. Based on the calibrated parameters, surface runoff was simulated during the historical period 1952-2003 under four scenarios with static LULC maps (in 1952, 1973, 1986 and 1999) opposed to a fifth scenario integrating these LULC maps dynamically. The DLU scenario was found to be more effective at picturing the so-called Sahelian paradox (i.e. the increase in surface runoff despite the decrease in rainfall), reported in the literature for small watersheds in the Sahel. The analysis of variability revealed that fluctuations in surface runoff were both influenced by rainfall and LULC changes. Furthermore, the isolated contributions of climate variability and LULC changes on surface runoff showed that LULC conditions played a dominant role (η_lulc = +393.1%) in the runoff increase over climate (η_cl = -297%) during the historical period. These results highlight the importance of accounting for LULC dynamics in hydrological modelling and advocate the development of integrated modelling frameworks for hydrologists and water resource managers.

Optimizing the soil conservation service curve number model by accounting for rainfall characteristics: a case study of surface water sources in Beijing

The upper catchment of the Miyun reservoir is an important drinking water source in Beijing. In recent years, researchers have used the soil conservation service curve number (SCS-CN) model to calculate surface runoff for the district. Although the runoff forecasting accuracy was unsatisfactory, the lack of understanding of rainfall processes and their influence on runoff may explain the observed deviations. Our study sought to optimize and assess the SCS-CN model simulation accuracy for the district by proposing an SCS-CN calculation method for each runoff event (CN_t) based on observation data for 253 rainfall and runoff events from 7 plots in the Miyun Shixia watershed. This study elucidated a significant positive correlation between the ratio of CN_t and the average SCS-CN (CN₁), as well as the ratio of the maximum X-minute rainfall amount (P_X) to the total rainfall amount for each rainfall event (P). Furthermore, a calculation method involving power function equations between CN_t/CN₁ and P_X/P was proposed for CN_t. When X = 5 min and the initial abstraction ratio (λ) = 0.01, the simulation performance of the optimized model was the highest, with a Nash-Sutcliffe efficiency coefficient of 0.791, which was significantly higher than that of the non-optimized SCS-CN model. The simulation performance for bare and cultivated land was higher than that of other land uses, with E_f values of 0.831 and 0.828, respectively. Future research should focus on improving the prediction accuracy of runoff events resulting from high-intensity and short-duration rainfall events.

Rice straw cover decreases soil erosion and sediment-bound C, N, and P losses but increases dissolved organic C export from upland maize fields as evidenced by δ13C

Soil surface with crop residue is effective in reducing soil erosion and carbon (C), nitrogen (N), and phosphorus (P) losses from sloping fields. However, there is a high possibility that surface cover increases export of dissolved organic C (DOC) though relevant field studies under natural rainfall are lacking. In this study, the effects of surface cover with rice (Oryza sativa L.) straw on soil and CNP losses in both dissolved and sediment-bound forms from maize (Zea mays L.) fields were investigated under two fertilization levels (standard and double) × two types of runoff experiments (natural rainfall and artificial irrigation). Changes in soil properties including moisture, temperature, nutrients, and C concentration as well as maize yield were also examined. Surface cover decreased soil and total CNP losses by up to 82% across the experimental plots with some exceptions. However, surface cover increased DOC export in both natural (by 68-82% in total across all events) and artificial (by 3-4 fold) runoff, suggesting that crop residue cover may act as a DOC pollution source of water bodies. The contribution of rice straw to DOC, which was calculated using the δ¹³C of DOC from covered plots (-24.1 to -28.0‰) and control plots (-19.6 to -25.1‰), was 52.5-95.8%. The concentrations of K₂SO₄-extractable and microbial biomass C of the soils did not differ between covered and control plots, suggesting that DOC produced from rice straw was not incorporated into the soils, but rather, was washed out with surface runoff in this study. Surface cover increased maize growth and yield, particularly in double fertilization plots, through improved soil moisture, temperature, and nutrient conditions. To take full advantage of surface cover with crop residue, a further study on reducing DOC loss from crop residue needs to be conducted.

Efficacy of orchard terrace measures to minimize water erosion caused by extreme rainfall in the hilly region of China: Long-term continuous in situ observations

Terracing and rainfall characteristics notably influence the water erosion processes. However, an extensive long term in situ quantitative evaluation of the approaches to control the water erosion in different orchard terraces has not yet been performed, especially considering the increasing frequency and severity of extreme rainfall events due to the global climate change. In this study, six types of orchard terraces, including slope land as the control (SLck), level terrace with bare (LTb) and vegetation taluses (LTv), outward (OTv) and inward terrace (ITv) with vegetation taluses and level terrace having front mounds and back ditches with vegetation taluses (MDLTv), were used to analyze the effects of extreme and ordinary rainfall events on the surface runoff and soil erosion. According to the measured data for twelve consecutive years, 356 natural rainfall events were divided into extreme and ordinary rainfall, based on the World Meteorological Organization standard. The results indicated that more severe surface runoff and sediment loss occurred under extreme rainfall: the runoff coefficient and soil loss under extreme rainfall were 2.6 and 11.5 times those under ordinary rainfall, respectively. The sediment yield (contribution rate, 42.9%) exhibited a higher sensitivity to extreme rainfall events compared to that of the surface runoff generation (contribution rate, 16.4%). Moreover, the reduction in the surface runoff and sediment in the extreme rainfall case differed for different orchard terraces. The average surface runoff coefficient and soil loss amount decreased in the following order: SLck>LTb>OTv>LTv>ITv>MDLTv. Nevertheless, the highest and lowest contributions of the extreme rainfall to the sediment yield occurred in the LTb (64.8%) and MDLTv (21.7%) plots, respectively. Therefore, severe talus erosion caused by extreme rainfall should be monitored, and a combination of vegetation taluses and front mounds and back ditches on the platforms is recommended as a sustainable strategy to prevent extreme water erosion when transforming slope land into orchard terraces.

Most relevant sources and emission pathways of pollution for selected pharmaceuticals in a catchment area based on substance flow analysis

The release of micropollutants in surface water depends on different sources and on different pathways. Through substance flow analysis, this study estimates the annual load of two pharmaceuticals (carbamazepine and sulfamethoxazole) in a catchment area, due to different emission pathways: wastewater treatment plant effluent, combined sewer overflows, and runoff from sludge and manure amended soil. It emerged that wastewater treatment plant effluent is the main emission pathway for carbamazepine (98.5% referring to the total released annual load) and land runoff (98%) for sulfamethoxazole. The study also investigates the parameters (including manure disposed on the land, removal efficiency and combined sewer overflow flowrate) which mostly influence the results, and those which are affected by higher uncertainty. The most uncertain parameters are those determining the fate of pharmaceuticals once in soil and surface water. The study concludes with a comparison between the predicted concentrations in different points of the receiving water body of the two key compounds, modeled with substance flow analysis, and those directly measured in a dedicated sampling campaign. The main discrepancies were found for sulfamethoxazole. Future research focusing on monitoring campaigns under different weather conditions and in different environmental compartments (soil and water) will certainly provide new insights in this kind of study.

Using an ensemble Kalman filter method to calibrate parameters of a prediction model for chemical transport from soil to surface runoff

Water pollution from surface runoff is an important non-point pollution source, which has been a great threat to our environment. The model proposed by Gao et al. (2004) is of great significance to solve the non-point source pollution problem, which is a numerical advection-diffusion equation (ADE) model for chemical transport from soil to surface runoff. The ensemble Kalman filter (EnKF), the data assimilation (DA) method, is easy to be implemented and widely used in hydrology field. In this study, we use the EnKF method to update model state variables such as chemical concentrations in surface runoff and calibrate model parameters such as water transfer rate in Gao et al. (2004) under different study cases, while other model parameters are assumed to be known. The observations are generated from the simulation results based on synthetic real parameters. The objective of this study was to extend the application of the EnKF to the ADE-based prediction model of chemical transport from soil to surface runoff. The results of the predicted chemical concentration in the surface runoff with EnKF are greatly improved than those without EnKF in comparison with the observations, and the updated parameters are close to the real parameters. We explored feasibility of the EnKF method from six factors, including the initial parameter estimate, the ensemble size, the influence of multi-parameters, the assimilation time interval, the infiltration boundary conditions, and the relationship between the standard deviations of the observation error and initial parameter. Different study strategies are proposed for different factors. For assimilation time interval, the key observation can reduce the assimilation frequency. With the situation of much larger observation error covariance than the prediction covariance, we analyzed influences of the standard deviation of the observation error and initial parameter on the feasibility of the EnKF method. According to the study results, it is concluded that the EnKF is efficient to update the parameter for the ADE-based prediction model of chemical transport from soil to surface runoff.

Long-term effects of climatic and hydrological variation on natural vegetation production and characteristics in a semiarid watershed: The northern Negev, Israel

Climate models for semiarid and arid regions predict increasing average temperatures and reduced amounts of total annual rainfall. This warming and drying trend could have critical, adverse effects on natural vegetation activity and survival in arid and semiarid zones. We investigated the long-term effects of climate change and surface-runoff variations on the production of natural vegetation in a dry, undisturbed, first-order watershed in the northern Negev, Israel. Vegetation dynamics were estimated by normalized difference vegetation index. Yearly annual vegetation cover varied greatly during the monitoring period (2000-2013), but a significant positive regression was found with annual rainfall and runoff amounts, suggesting a strong relationship between annual vegetation dynamics and rainfall amount in a given year. A significant positive linear regression was found between annual ET₀ values and year of measurement (1994-2013), with no corresponding decrease in vegetation condition. Surface runoff in the watershed affected the vegetation's water source. Large variation in annual runoff amounts was observed for 1994-2011, averaging 22.3 and 9 mm for the first (2000-2006) and second (2007-2013) vegetation-monitoring subperiods, respectively. Perennial vegetation was less sensitive to drought years than annual vegetation, likely due to differences in water-source availability. Perennials also benefited from the arrival of nutrients, organic matter, and fertile soil flowing with the surface runoff and eroded soil into their growing area.

Do rainfall characteristics affect the export of copper, zinc and synthetic pesticides in surface runoff from headwater catchments?

Rainfall and runoff characteristics may influence off-site export of pesticides into downstream aquatic ecosystems. However, the relationship between rainfall characteristics and pesticide export from small headwater catchments remains elusive due to confounding factors including the application dose and timing and the variation of pesticide stocks in soil. Here we examined the impact of rainfall characteristics on the export of copper (Cu), zinc (Zn) and 12 legacy and currently used synthetic pesticides in surface runoff from a headwater vineyard catchment. Cluster analysis of rainfall intensity, depth and duration of 78 events revealed four distinct rainfall categories, i.e., Small, Long, Moderate and Intense (p < 0.001). Event mean concentrations of pesticides did not differ among rainfall categories (p > 0.05). In contrast, event loads of both dissolved and solid-bound Cu and Zn significantly differed among rainfall categories (p < 0.001). Rainfall depth and intensity significantly correlated with both Cu and Zn loads in runoff (ρ_s = 0.33 to 0.92, p < 0.002), and might be the main drivers of Cu and Zn export at the catchment scale. In contrast, rainfall depth, intensity or duration did not influence the loads of synthetic pesticides in runoff, even when weekly variations of pesticide stocks in the soil were accounted for. However, intense rainfall-runoff events, that can fragment soil, may control the export of persistent and hydrophobic legacy pesticides stocks in the soil, such as simazine and tetraconazole. Our results show that rainfall characteristics controlled the off-site export of Cu, Zn and legacy synthetic pesticides in a small headwater catchment, whereas the application timing drove the export of currently used synthetic pesticides in runoff. We anticipate our results to be a preliminary step to forecast the influence of regional rainfall patterns on the export of both metallic and synthetic pesticides by surface runoff from small agricultural headwater catchments.

Experimental Study on the Rainfall-Runoff Responses of Typical Urban Surfaces and Two Green Infrastructures Using Scale-Based Models

In this study, scale models of typical urban surfaces and two green infrastructures (concave grassland and porous pavement) were constructed, and two simulated rainfall intensities (low intensity was 0.3 mm/min with 25.4 mm depth, and high intensity was 0.6 mm/min with 42.0 mm) were utilized to investigate their runoff responses and the impacts of pervious surface positions and initial soil moisture on the runoff processes. Results indicated that impervious concrete surface exhibited a faster generation of runoff and with a runoff coefficient of 89%. Grassland surface represented that time to runoff was about 25 times than that of the impervious surface and recorded the smallest runoff coefficient of 34 and 53%. Compared with the impervious area, concave grassland was able to effectively delay time to runoff, while the porous pavement was able to significantly reduce runoff discharge and peak flow rate. A high rainfall intensity led to a reduction in time to runoff and an acceleration of runoff discharge and peak flow rate. Pervious surface under the lower side generated runoff at a slower rate, and registered a smaller runoff coefficient compared with the pervious surface under the upper side. The initial soil moisture and time to runoff had a significant negative correlation, and a positive correlation was found between the initial soil moisture and runoff coefficient. These findings facilitate a better understanding of runoff processes of urban surfaces and green infrastructures that may be able to help in better hydrology system design for mitigating urban flooding.

The microorganism and biochar-augmented bioreactive top-layer soil for degradation removal of 2,4-dichlorophenol from surface runoff

Surface runoff is one of the major pollution sources impacting the quality of the surrounding waterbody. In this study, a highly-bioreactive top-layer soil incorporated with microorganism (BO) and peanut shell (PS) biochar or dairy manure (DM) biochar was proposed for removal of 2,4-dichlorophenol (2,4-DCP) from contaminated surface runoff. Both batch test and sandbox experiment consistently revealed that PS coupled with BO amendment (PS + BO) was most effective for sorption and degradation of 2,4-DCP, compared to BO and DM alone or in combination. About 77% of 6000 μg∙L^-1 2,4-DCP was absorbed within 36 h in the original low permeability bioreactive PS + BO soil layer (15 cm long×15 cm wide×4.5 cm deep) with the 0.33 L∙day^-1 processing capacity of surface runoff. Increasing the addition of quartz sand into the bioreactor soil layer by threefold the original bioreactor improved the processing capacity to 17.5 L∙day^-1. However, this permeability-optimized bioreactive layer was still not large enough to remove 2,4-DCP completely. The optimized scale by the multi-process coupling model of the convection, dispersion, adsorption, and degradation was 60 cm long × 60 cm wide × 18 cm deep where the processing capacity of 280 L·day^-1reached and 97.3% of 2,4-DCP was removed, correspondingly the 2,4-DCP concentration could meet the standard limit. In addition, the obtained model parameters showed that the biochar or microorganism significantly decreased the dispersion coefficient D of 2,4-DCP in the bioreactive layer. The 2,4-DCP distribution coefficient K_d, and first-order reaction rate λ in the PS+BO system significantly greater than that in the control, BO, and PS systems. Results from this study indicated that the top-layer soil incorporated with microorganisms and biochar is a feasible and effective approach for the surface runoff treatment.

Long-term, process-based, continuous simulations for a cluster of six smaller, nested rangeland watersheds near Tombstone, AZ (USA): Establishing a baseline for event-based runoff and sediment yields

Accurately predicting long-term, process-based runoff and sediment yields measured at the outlet of even small watersheds can be challenging. The assessments following careful parameter determination enable establishing a baseline for local land management to assess policy implementations and rehabilitation especially under climate or land use/cover changes. Process-based, continuous models have demonstrated their advantage of representing event-based hydrological responses at smaller spatial and temporal scales. In this study, the Geospatial interface for the Water Erosion Prediction Project (WEPP) is validated for a series six, neighboring, nested subwatersheds (101 to 106) at Lucky Hills, Walnut Gulch Experimental Watershed (WGEW), Tombstone, Arizona (USA). The primary objective of this study is to assess short-term parameterization and long-term verification and simulation validation of GeoWEPP based on 55 years of runoff and sediment yields for six subwatersheds. The effective hydraulic conductivity (K_eff) parameter is adjusted based on runoff observed in watershed 101 using a research-grade 1 m-Digital Elevation Model (DEM). The performance of runoff simulated generated by an aggregated 5 m-resolution DEM lead to better results in contrast to using the original 1 m- or aggregated 3 m-resolution. Since there are no sediment yield observations for that watershed, the similar sized, neighboring watershed 102 and a publicly available DEM were used to parameterize critical shear. The short-term verification of K_eff as well as the long-term verification of K_eff and critical shear stress indicate that both parameters generated based on one subwatershed can be used to accurately predict the runoff in all other watersheds in the study area. However, the results have a tendency to slightly over-estimate runoff, and become more significant with the distance from the rainfall and runoff gauges for the watershed that was used for the K_eff parameter estimation. For sediment yields, the results indicate that the short-term parameterization of shear stress based on one watershed can potentially lead to significantly different results for neighboring watersheds. The results are the baseline for spatially distributed shear stress and channel erosion parameter validation and impact assessment for future climate and land use changes.