Can the watershed non-point phosphorus pollution be interpreted by critical soil properties? A new insight of different soil P states

Assessing spatiotemporal risks of nonpoint source pollution via soil erosion: a coastal case in the Yellow River Delta, China

Nonpoint source pollution (NPSP) has always been the dominant threat to regional waters. Based on empirical models of the revised universal soil loss equation and the phosphorus index, an NPSP risk assessment model denoted as SL-NPSRI was developed. The surface soil pollutant loss was estimated by simulating the rain-runoff topographic process, and the influence of path attenuation was quantified. A case study in the Yellow River Delta and corresponding field surveys of soil pollutants and water quality showed that the established model can be applied to evaluate the spatial heterogeneity of NPSP. NPSP usually occurs during high-intensity rainfall periods and in larger estuaries. Summer rainfall increased pollutant transport into the sea from late July to mid-August and caused estuarine dilution. Higher NPSP risks often correspond to coastal areas with lower vegetation coverage, higher soil erodibility, and higher soil pollutant concentrations. Agricultural NPSP originating from cropland significantly increase the pollutant fluxes. Therefore, area-specific land use management and vegetation coverage improvement, and temporal-specific strategies can be explored for NPSP control during source-transport hydrological processes. This research provides a novel insight for coastal NPSP simulations by comprehensively analyzing the soil erosion process and its associated pollutant loss effects, which can be useful for targeted spatiotemporal solutions.

Effects of ecohydrological interfaces on migrations and transformations of pollutants: A critical review

With the rapid development of society, the soil and water environments in many countries are suffering from severe pollution. Pollutants in different phases will eventually gather into the soil and water environments, and a series of migrations and transformations will take place at ecohydrological interfaces with water flow. However, it is still not clear how ecohydrological interfaces affect the migration and the transformation of pollutants. Therefore, this paper summarizes the physical, ecological, and biogeochemical characteristics of ecohydrological interfaces on the basis of introducing the development history of ecohydrology and the concept of ecohydrological interfaces. The effects of ecohydrological interfaces on the migration and transformation of heavy metals, organic pollutants, and carbon‑nitrogen‑phosphorus (C-N-P) pollutants are emphasized. Lastly, the prospects of applying ecohydrological interfaces for the removal of pollutants from the soil and water environment are put forward, including strengthening the ability to monitor and simulate ecohydrological systems at micro and macro scales, enhancing interdisciplinary research, and identifying main influencing factors that can provide theoretical basis and technical support.

Using soil erosion to locate nonpoint source pollution risks in coastal zones: A case study in the Yellow River Delta, China

Soil erosion contributes greatly to nonpoint source pollution (NSP). We built a coastal NSP risk calculation method (CNSPRI) based on the Revised Universal Soil Loss Equation (RUSLE) and geospatial methods. In studies on the formation and transport of coastal NSP, we analysed the pollution impacts on the sea by dividing subbasins into the sea and monitoring the pollutant flux. In this paper, a case study in the Yellow River Delta showed that the CNSPRI could better predict the total nitrogen (TN) and total phosphorus (TP) NSP risks. The value of the soil erodibility factor (K) was 0.0377 t h·MJ^-1·mm^-1, indicating higher soil erodibility levels, and presented an increased trend from the west to the east coast. The NSP risk also showed an increased trend from west to east, and the worst status was found near the Guangli River of the south-eastern region. The contributions of the seven influencing factors to CNSPRI presented an order of vegetation cover > rainfall erosivity > soil content > soil erodibility > flow > flow path > slope. The different roles of source and sink landscapes influenced the pollutant outputs on a subbasin scale. Arable land and saline-alkali land were the two land-use types with the greatest NSP risks. Therefore, in coastal zones, to reduce NSP output risks, we should pay more attention to the spatial distribution of vegetation cover, increase its interception effect on soil loss, and prioritize the improvement of saline-alkali land to reduce the amount of bare land.

Discussing on "source-sink" landscape theory and phytoremediation for non-point source pollution control in China

Water pollution is exacerbated due to irrational human activities in China. Restoring and rebuilding river basin ecosystems are major ecological strategies at present. Controlling the non-point source pollution (NPSP) by reasonable management of land use in the basin and phytoremediation of contaminated waters is the optimum approach. Thus, it is significant to study on the relationship that between landscape change and the aquatic environment, as well as further to analyze on the combined effect of the landscape and water quality. This paper describes the application and development of the "source-sink" landscape theory in China, and the role of the theory in controlling NPSP. From this perspective, a landscape capable of generating NPSP would be a "source" landscape, such as farmland, while another capable of preventing NPSP would be a "sink" landscape, such as forests and wetland. Applying the source-sink landscape theory, it is possible to exert the ecological benefits of the landscape while playing the esthetic value of the landscape. Also, the purification mechanism of plants in contaminated water is discussed. Besides, it is vital that research on water body restoration should focus not only on single discipline but also on integration and coordination between various ones such as ecology, environmental science, and geography to jointly push up researches related to water body phytoremediation. Hopefully, this paper could help to control water pollution from a new perspective, also to improve water environment and benefit human lives.

Identifying the Influence of Land Cover and Human Population on Chlorophyll a Concentrations Using a Pseudo-Watershed Analytical Framework

Increasing agricultural development and urbanization exacerbates the degradation of water quality in vulnerable freshwater systems around the world. Advances in remote sensing and greater availability of open-access data provides a valuable resource for monitoring water quality but harmonizing between databases remains a challenge. Here, we: (i) developed a pseudo-watershed analytical framework to associate freshwater lakes with adjacent land cover and human population data and (ii) applied the framework to quantify the relative influence of land cover and human population on primary production for 9313 lakes from 72 countries. We found that land cover and human population explained 30.2% of the variation in chlorophyll a concentrations worldwide. Chlorophyll a concentrations were highest in regions with higher agricultural activities and human populations. While anthropogenic land cover categories equated to only 4 of the 18 categories, they accounted for 41.5% of the relative explained variation. Applying our pseudo-watershed analytical framework allowed us to quantify the importance of land cover and human population on chlorophyll concentration for over 9000 lakes. However, this framework has broader applicability for any study or monitoring program that requires quantification of lake watersheds.

The Influence of Different Forest Characteristics on Non-point Source Pollution: A Case Study at Chaohu Basin, China

Forestland is a key land use/land cover (LULC) type that affects nonpoint source (NPS) pollution, and has great impacts on the spatiotemporal features of watershed NPS pollution. In this study, the forestland characteristics of the Chaohu Basin, China, were quantitatively represented using forestland types (FLTs), watershed forest coverage (WFC) and forest distance from the river (DFR). To clarify the impact of forests on NPS pollution, the relationship between forestland characteristics and watershed nutrient outputs (TN and TP) was explored on a monthly scale using SWAT (Soil and Water Assessment Tool) and the period simulation was 2008-2016. The results showed that: (1) the TN and TP showed similar output characteristics and the rainy season was the peak period of nitrogen and phosphorus output. (2) Among the forestland characteristics of forestland types, watershed forest coverage and forest distance from the river, watershed forest coverage and forest distance from the river had greater effects than forestland types on the control of watershed nutrient outputs (TN and TP). (3) In different forestland types, the watershed nutrient outputs intensity remained at the lowest level when the FLTs was mixed forest, with a TN output of 1244.73kg/km² and TP output of 341.39 kg/km². (4) The watershed nutrient outputs and watershed forest coverage were negatively correlated, with the highest watershed forest coverage (over 75%) reducing the TN outputs by 56.69% and the TP outputs by 53.46% compared to the lowest watershed forest coverage (below 25%), it showed that in areas with high forest land coverage, the non-point source pollution load in the watershed is smaller than in other areas. (5) forest distance from the river had an uncertain effect on the TN and TP output of the basin, the forestland itself is a source of pollution, but it also has the function of intercepting pollution movement; the forest distance from the river in the range of 500-1000 m had the lowest NPS pollution. Considering the different forest characteristics and topographical factors, an optimal allocation mode of differentiated forest land was proposed, these suggestions will provide a scheme for surface source pollution prevention and control in the basin. This research gap is the basis of real forestland optimization. We may optimize the forestland layout for NPS pollution prevention and control by clarifying the internal mechanism.

Laboratory investigation of phosphorus loss with snowmelt and rainfall runoff from a Steppe wetland catchment

Phosphorus (P) losses from terrestrial soils contribute to eutrophication of surface waters. As priority non-point source pollution ways, rainfall runoff (RS₁) and snowmelt runoff (RS₂) are the main carrier of P loss from terrestrial ecosystem. The aim of this study was to investigate the similarities and differences between P loss with RS₁ and RS₂ of the same soil type. Six types of soil were used in this experiment. Results have shown that 1), Different types of soil have different P loss with RS₁ and RS₂ under different slope, and the changes ranged from 0.003 to 0.370 mg L^-1. 2), The effects of soil type, slope and runoff type on P loss with surface runoff was not independent, both individual effects of all factors and their interaction with the other two factors effected the P loss with runoff. 3), In our experiment, some soils showed no significant difference between P content in RS₁ and RS₂. In some soils, P loss with RS₁ was higher than that with RS₂ while the opposite conclusion was showed in Bog soil (BS) which with higher soil water content. 4), The P loss with RS₁ and RS₂ of different soils were both mainly affected by soil water content (SW), Olsen-P content (OP) and soil organic matter content (OM). These results can help us understand the P loss with different patterns of surface runoff better and are expected to provide pertinent opinions on the analysis of P loss with runoff and its influencing factors of grassland soils.

Technological Challenges of Phosphorus Removal in High-Phosphorus Ores: Sustainability Implications and Possibilities for Greener Ore Processing

With the present rates of iron ore consumption, currently unusable, high-phosphorus iron ore deposits are likely to be the iron ores of the future as higher-grade iron ore reserves are depleted. Consequently, the design and timely development of environmentally-benign processes for the simultaneous beneficiation of high-phosphorus iron ores and phosphorus recovery, currently a technological challenge, might soon become a sustainability challenge. To stimulate interest in this area, phosphorus adsorption and association in iron oxides/hydroxyoxides, and current efforts at its removal, have been reviewed. The important properties of the most relevant crystalline phosphate phases in iron ores are highlighted, and insights provided on plausible routes for the development of sustainable phosphorus recovery solutions from high-phosphorus iron ores. Leveraging literature information from geochemical investigations into phosphorus distribution, speciation, and mobility in various natural systems, key knowledge gaps that are vital for the development of sustainable phosphorus removal/recovery strategies and important factors (white spaces) not yet adequately taken into consideration in current phosphorus removal/recovery solutions are highlighted, and the need for their integration in the development of future phosphorus removal/recovery solutions, as well as their plausible impacts on phosphorus removal/recovery, are put into perspective.

Response of chemical properties, microbial community structure and functional genes abundance to seasonal variations and human disturbance in Nanfei River sediments

The Nanfei River, located in Hefei City, Anhui Province, subjected to increased nutrient loads from point and/or non-point source. Little is known about the indicators indicating heterogeneity of surface sediments. We aimed to identify the suitable indicators that can reflect the sediment heterogeneity by analyzing the sensitivity of sediment physicochemical properties group, microbial communities and diversity indices group and C, N, S-functional genes group to seasonal and regional changes. River sediments from different areas (urban area, urban-rural fringe and rural area) were collected in the level, dry and wet seasons, respectively. The chemical parameters had most significant regional heterogeneity, but no seasonal differences. Seasons had a greater impact on the overall microbial community structure than the areas. Specifically, the relative abundance of Firmicutes and Bacteroidetes were more sensitive to seasonal changes. Overall, seasonal changes showed the greatest impact on the functional genes group, with the S-functional genes (dsrB and aprA) group providing the clearest seasonal variation. Considering the seasonal distribution of functional genes and their sensitivity to environmental factors, we speculated that the sulfate-reducing gene (dsrB), the methanogenic gene (mcrA) and the anammox gene (hzo) could be identified as sensitive indicators to indicate the seasonal heterogeneity of surface sediments in different river sections of the same river in the short term. We also concluded that environmental variables were more conducive to indicating the regional heterogeneity of sediments. This study provided a valuable reference for assessing the heterogeneity or ecological stress of river sediments.

Nonpoint source pollution

A comprehensive review of the research papers published in 2018 focusing on nonpoint source (NPS) pollution is presented in this review article. The identification of pollution from different sources and estimation of NPS pollution using various models are summarized in this review paper. Various innovative techniques are also examined to abate NPS pollution. PRACTITIONER POINTS: The non-point source pollution in 2018 is systematically reviewed and documented. This review evaluates and summarizes the identification, quantification, reduction, and management of NPS pollution. Future perspectives of NPS pollution research are discussed.

Film based on magnesium impregnated biochar/cellulose acetate for phosphorus adsorption from aqueous solution

New hybrid film formed by biopolymer cellulose acetate and biochar for P adsorption in aqueous solution.

Combining emission inventory and isotope ratio analyses for quantitative source apportionment of heavy metals in agricultural soil

Two quantitative methods (emission inventory and isotope ratio analysis) were combined to apportion source contributions of heavy metals entering agricultural soils in the Lihe River watershed (Taihu region, east China). Source apportionment based on the emission inventory method indicated that for Cd, Cr, Cu, Pb, and Zn, the mean percentage input from atmospheric deposition was highest (62-85%), followed by irrigation (12-27%) and fertilization (1-14%). Thus, the heavy metals were derived mainly from industrial activities and traffic emissions. For Ni the combined percentage input from irrigation and fertilization was approximately 20% higher than that from atmospheric deposition, indicating that Ni was mainly derived from agricultural activities. Based on isotope ratio analysis, atmospheric deposition accounted for 57-93% of Pb entering soil, with the mean value of 69.3%, which indicates that this was the major source of Pb entering soil in the study area. The mean contributions of irrigation and fertilization to Pb pollution of soil ranged from 0% to 10%, indicating that they played only a marginally important role. Overall, the results obtained using the two methods were similar. This study provides a reliable approach for source apportionment of heavy metals entering agricultural soils in the study area, and clearly have potential application for future studies in other regions.

Analysis of Historical Sources of Heavy Metals in Lake Taihu Based on the Positive Matrix Factorization Model

Analysis of sediment grain sizes and heavy metal correlations in the western part of Lake Taihu shows that the grain size of the sediment is stable as a whole. With increasing depth, the grain size tends to decrease. Heavy metals such as Cr, Cd, Pd and Sr are strongly correlated and influence each other. Based on the positive matrix factorization (PMF) model, this study classified the origin of heavy metals in the sediments of western Lake Taihu into three major categories: Agricultural, industrial and geogenic. The contributions of the three heavy metal sources in each sample were analyzed and calculated. Overall, prior to the Chinese economic reform, the study area mainly practiced agriculture. The sources of heavy metals in the sediments were mostly of agricultural and geogenic origin, and remained relatively stable with contribution rates of 44.07 ± 11.84% (n = 30) and 35.67 ± 11.70% (n = 30), respectively. After the reform and opening up of China, as the economy experienced rapid development, industry and agriculture became the main sources of heavy metals in sediments, accounting for 56.99 ± 15.73% (n = 15) and 31.22 ± 14.31% (n = 15), respectively. The PMF model is convenient and efficient, and a good method to determine the origin of heavy metals in sediments.