Impacts of land-use on surface waters at the watershed scale in southeastern China: Insight from fluorescence excitation-emission matrix and PARAFAC

Source apportionment based on EEM-PARAFAC combined with microbial tracing model and its implication in complex pollution area, Wujin District, China

Further improving the quality of surface water is becoming more difficult after the control of main point-sources, especially in the complex pollution area with mixed industrial and agricultural productions, whereas the pollution source apportionment might be the key to quantify different pollution sources and developing some effective measures. In this study, a technical framework for source apportionment based on three-dimensional fluorescence and microbial traceability model is developed. Based on screening of the main environmental factors and their spatiotemporal characteristics, potential pollution sources have been tentatively identified. Then, the pollution sources are further tested based on the analysis of fluorescence excitation-emission matrix (EEM) and the similarity of fluorescence components in surface water and potential pollution sources. At the same time, the correlation between microbial species and pollution sources is constructed by analyzing the spatiotemporal characteristics of microbial composition and the response of main species to environmental factors. Therefore, pollution source apportionment is quantified using PCA-APCS-MLR, Fast Expectation-maximization for Microbial Source Tracking (FEAST), and Bayesian community-wide culture-independent microbial source tracking (SourceTracker). PCA-APCS-MLR could not effectively distinguish the contributions of different industrial sources in the complex environment of this study, and the contribution of unknown sources was high (average 39.60%). In contrast, the microbial traceability model can accurately identify the contribution of 7 pollution sources and natural sources, effectively reduce the proportion of unknown sources (average of FEAST is 19.81%, SourceTracker is 16.72%), and show better pollution identification and distribution capabilities. FEAST exhibits a more sensitive potential in source apportionment and shorter calculation time than SourceTracker, thus might be used to guide the precise regional pollution control, especially in the complex pollution environments.

Multi-scale response relationship between water quality of rivers entering lakes from different pollution source areas and land use intensity: a case study of the three lakes in central Yunnan

As the main supply source of lakes, the water quality of the rivers entering the lakes directly determines the water safety and sustainable development of the lakes. Human activities are the direct cause of changes in the water quality of rivers entering lakes, and land use intensity is the direct manifestation of human activities on the land surface. Although significant progress has been made in studying the relationship between land use changes and water quality in lakes, there is still a lack of research on exploring the relationship between land use intensity and water quality at multiple scales, especially in comparative studies of different pollution source areas. To address this problem, this study used Pearson's correlation analysis and land use intensity index method to explore the response relationship between river water quality and land use intensity at different spatial and temporal scales and different pollution source areas using three lakes in central Yunnan as examples. The results showed that land use intensity was generally positively correlated with water quality, but the response relationship between land use intensity and different water quality indicators was significantly different at different scales and for different pollution source areas. Compared to non-urban areas, the impact of land use intensity on water quality is more significant in urban areas. Compared to the rainy season, the correlation between CODNa, TP, and NH3-N values and land use intensity is stronger during the dry season, while the correlation between COD, TN, and land use intensity is weaker during the dry season. When viewed at different scales, different water quality indicators have different scale effects, but overall, the larger the scale, the stronger the correlation. Therefore, in the work of lake water environmental governance, it is necessary to consider comprehensively from multiple scales and perspectives and adopt measures that are more suitable for regional water pollution prevention and control.

Interaction between the hydrochemical environment, dissolved organic matter, and microbial communities in groundwater: A case study of a vegetable cultivation area in Huaibei Plain, China

Intensive vegetable planting has a profound impact on the surrounding aquatic environment. The self-purification ability of groundwater is poor, and it is difficult to return groundwater to its original state once polluted. Therefore, it is necessary to clarify the impact of intensive vegetable planting on groundwater. This study selected the groundwater of a typical intensive vegetable planting base in the Huaibei Plain of China as the research object. This work analyzed the content of major ions, the dissolved organic matter (DOM) composition, and the bacterial community structure in groundwater. Redundancy analysis was used to explore the interactions between the major ions, the DOM composition, and the microbial community. The results showed that under the influence of intensive vegetable planting, the F- and NO3--N contents in groundwater were significantly increased; the excitation-emission matrix combined with parallel factor analysis identified four fluorescent components (C1 and C2 were humus-like components, while C3 and C4 were protein-like components), which mainly consisted of protein-like components. Proteobacteria was the dominant phylum (mean = 69.27 %), followed by Actinobacteriota (mean = 7.25 %) and Firmicutes (mean = 4.02 %), which together explained over 80 % of the total abundance; and TDS, pH, K+, and C3 were the main influencing factors affecting the microbial community structure. This study provides a better understanding of the impact of intensive vegetable cultivation on groundwater.

Water quality assessment for organic matter load in urban rivers considering land cover dynamics

The strategy of considering a model that is comparable to the Soil Conservation Service Curve-Number (SCS-CN) method that employs land use maps to estimate the effects of land use on the water quality has considerable potential for application. This paper presents the LUPC (Land Use Pollutant Contribution) Model to estimate water pollution from the watershed land use obtained by satellite image classification (Sentinel-2). It defines that each land use produces a specific pollutant load per unit area, called Pollutant Standard Index (PSI), which undergoes degradation and/or retention until it reaches the river. This decay estimate is based on a Kernel Function. Organic matter (OM) was the pollutant chosen for the definition of the LUPC model and fractions of labile and refractory organic matter (LOM, ROM). The model was applied to the Barigüi River basin, and five samples were collected at 12 points along the river. Water quality parameters such as dissolved organic carbon (DOC) and UV-Visible absorbance in addition to chemical and biological oxygen demand (COD and BOD), dissolved oxygen (DO), and nitrogen and phosphorus fractions were the reference for modeling purposes. The results indicate that organic loads can be estimated from watershed characteristics, despite influence from seasonal influences captured by the PSI values and the basin shape parameter. Considering its versatile response, the LUPC model can be used for integrated water resources and land use planning and management and be indicator of the potential pollution of rivers by OM.

The spectral resolution of DOM in urban rivers affected by different non-point source intensities using self-organizing maps

UV-Vis, three-dimensional excitation-emission matrix fluorescence spectroscopy (EEMs) and a self-organizing map (SOM) were used to study changes in the composition and constituent concentrations of dissolved organic matter (DOM) in the water column of two urban rivers with different non-point source inputs during spring and summer. The level of humification and the relative molecular mass of DOM were remarkably higher in the summer than in the spring (P < 0.01) in both rivers. The SOM model showed that the fluorescence intensity of the spring component was lower than in summer in water bodies with higher levels of non-point source inputs, while the opposite was true for water bodies with lower levels of non-point source inputs. Principal component analysis (PCA) showed that nutrients like nitrogen and phosphorus promoted autogenous processes in these water bodies. Seasonal variations and differing intensities of non-point source inputs had remarkable effects on urban river waters (R² = 0.775, P < 0.001). Non-point source inputs increased the concentrations of humus-like fractions and promoted autogenesis in the water bodies.

Effects of paddy irrigation-drainage system on water quality and productivity of small rivers in the Himi region of Toyama, Central Japan

The aim of this study was to clarify the impact of differences between historical and recently introduced irrigation and drainage management systems on water quality in the rivers around paddy fields. We investigated the seasonal variation in nutrients concentration and dissolved organic carbon (DOC) components in single- (used for intake only) and dual-purpose (used for both intake and drainage) channels during a 4-year period in the Himi region of Toyama, Central Japan. The system of dual-purpose channel has traditionally been used in the region of this study. A total of 197 three-dimensional excitation-emission matrix (3DEEM) fluorescence spectra of DOM in waters were applied for the parallel factor analysis (PARAFAC) modeling. Based on the 3DEEM and PARAFAC, the abundance of terrestrial humic-like components in the dual-purpose channel was significantly higher than that in the single-purpose channel. The even long-chain n-fatty acids derived associated with rice cropping in sediments of the dual-purpose channels were 22-30-fold higher than that of the single-purpose channel. In addition, the turbidity values of the river waters had significantly positive linear correlations with concentrations of K⁺, DOC, and humic-like components. These observations indicate that the dissolved nutrient concentrations in the river water were higher in the dual-purpose channel compared to those of the single-purpose channel, which may be supplied by leaching from the inflow of soil particles from the paddy fields. During the mid-irrigation period, the quantity of epiphytic chlorophyll a on artificial substrate tiles in the dual-purpose channel were 3.1-4.1-fold higher than that in the single-purpose channel. This study clear that the input of paddy drainage during the irrigation season significantly changes the DOC components in river waters and irrigation management is strongly linked to the primary production in agricultural channels. Therefore, it is important to consider the impact of the introduction of different irrigation and drainage management systems on water quality and productivity in order to maintain the riverine ecosystems around rice paddies, which are based on historical water use systems.

Using EEM-PARAFAC to identify and trace the pollution sources of surface water with receptor models in Taihu Lake Basin, China

The identification and apportionment of the multiple pollution sources are essential and crucial for improving the effectiveness of surface water resources management. In this study, the surface water samples were collected from Taihu Lake Basin, and the optimal water quality parameters for the receptor models were selected firstly with multivariate statistical analyses. In order to identify the potential pollution sources in surface water, dissolved organic matter (DOM) was analyzed with the excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC). Through the Pearson correlation analysis of water quality parameters and DOM components, the pollution sources were further verified, i.e., agricultural activities, domestic sewage, phytoplankton growth/terrestrial input and industrial sources. In addition, principal component analysis (PCA) combined with the absolute principal component score-multiple linear regression (APCS-MLR) and positive matrix factorization (PMF) models were employed to quantify pollution sources. Compared with PCA-APCS-MLR model, PMF model resulted in higher performance on evaluation statistics and lower proportion of unexplained variability, thus showed more realistic and robust representation. The results of PMF showed that agricultural activities (42.08%) and domestic sewage (21.16%) were identified as the dominant pollution sources of surface water in the study area. This study highlights the effectiveness of EEM-PARAFAC in identifying the pollution sources, and the applicability of PMF in apportioning the contributions of each potential pollution source in surface water.

Impacts of terrestrial input on the distribution characteristics of microplastics in the East China Sea characterized by chromophoric dissolved organic matter (CDOM) analysis

Large quantities of microplastics are found in the East China Sea (ECS), however, the impacts of complicated terrestrial input on the distribution characteristics of microplastics have not been studied. Hence, we aimed to characterize the microplastic distribution in the ECS combined with the fluorescence characteristics of chromophoric dissolved organic matter (CDOM), a sensitive technique to trace terrestrial substances in seawater. The average microplastic abundance in the surface seawater of ECS was 34.73 ± 4.05 items/m³ and sites in the north ECS had a higher microplastic abundance (55.90 ± 2.47 items/m³) than those in the southern region (11.22 ± 4.01 items/m³), due to its proximity to the Yangtze River estuary and Hangzhou Bay. Polyethylene (PE, 44.2 %) was the most abundant microplastic type in the northern region, whereas polyethylene terephthalate (PET, 28.4 %) had a higher proportion in the south ECS. Besides, sites in the north ECS had a higher diversity index of microplastics, suggesting various sources of microplastic pollution. Interestingly, a stronger correlation with the diversity index was found for protein-like component C3 (R² = 0.56) in northern regions compared to fulvic-like component C1 (R² = 0.32) and humic-like component C2 (R² = 0.28), suggesting the significant impact of anthropogenic discharge. Moreover, no correlation between fluorescence components and microplastic diversity index was found in the south ECS, indicating that CDOM can reflect the impact range of terrestrial input on the distribution characteristics of microplastics. This research might be useful in assessing and reducing the impact of terrestrial input on the distribution characteristics of microplastics in the ECS.

Impacts of haze on the photobleaching of chromophoric dissolved organic matter in surface water

Sunlight plays an important role in the photochemical processes of chromophoric dissolved organic matter (CDOM), which is closely related to water self-purification and primary productivity of healthy aquatic ecosystem health. The fine particles of haze, a widespread air pollutant, absorb natural ultraviolet (UV) irradiation and have an unknown degree of influence on the photochemical transformation of CDOM. Here, an in-situ experiment investigating how the amount and composition of CDOM changes under hazy conditions was conducted in Ningbo, southeastern China, a city that frequently suffers from seasonal haze pollution. The results indicated that haze attenuated UV light under different weather conditions. The UV intensities were reduced from 1124.90 ± 91.58 to 510.26 ± 40.26 μW cm^-2 and 748.54 ± 101.68 to 316.32 ± 40.48 μW cm^-2 on sunny and cloudy days, respectively; these values approached those on rainy days (186.97 ± 28.58 μW cm^-2). Consequently, the loss of dissolved organic carbon during the irradiation test was reduced on hazy days (e.g., from 5.63% to 2.59% on sunny/hazy days). The impact of haze on CDOM photobleaching was further assessed by an excitation-emission matrix (EEM) combined with parallel factor (PARAFAC) analysis. On hazy days, the EEM-PARAFAC components were saved from photobleaching to different degrees; and humic-like substances showed a stronger protective effect from haze than protein-like substances because of their higher photosensitivity. Consequently, haze could cause more terrestrial CDOM to remain in surface water. UV intensity played a critical role in the composition characteristics of CDOM. This study identifies the linkage between atmospheric pollution and water quality and demonstrates that long-term and large-scale haze may adversely influence aquatic ecology through pollutant/nutrient accumulation.

Fluorescence and molecular signatures of dissolved organic matter to monitor and assess its multiple sources from a polluted river in the farming-pastoral ecotone of northern China

The sources and composition of dissolved organic matter (DOM) in rivers are critical to water quality and aquatic ecosystems. Studies on detailed composition of organic matter in rivers in the farming-pastoral ecotone are relatively limited in the research community. To better understand the characteristics and dynamics of DOM, Yang River in North China was selected as the study area because of its profound influences on the farming-pastoral ecotone nearby. A combination of fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) techniques revealed that the DOM composition of Yang River is driven by land use. DOM in Yang River is predominantly imported from allochthonous inputs, together with agricultural runoff, pastureland, and urban sewage, causing a comprehensive impact on DOM. In detail, DOM associated with cropland inputs was dominated by lignin-like species, with higher nitrogen content. In comparison, DOM related to grassland is more diverse and susceptible to degradation. An increase in urban areas led to an increase in sulfur-containing compounds, while their oxygen, nitrogen, and aromaticity contents were significantly lower than those in cropland. Interestingly, urban-influenced lignin-like compounds may be associated with the effluents from the pulp and paper mill. Additionally, synthetic surfactants from the lower section of the river were also structurally identified by tandem mass spectrometry. Overall, this study could provide valuable insights into the DOM sources and their transformation dynamics at a molecular level, which could be an indicator for riverine water quality management and be applied to other farming-pastoral ecotones straightforward.

Interactions of anthropogenic and terrestrial sources drive the varying trends in molecular chemodiversity profiles of DOM in urban storm runoff, compared to land use patterns

Variations in land use drive the heterogeneous nature of dissolved organic matter (DOM) in storm runoff. However, in the context of the currently complicated multifactor interactions of urban land use, contamination occurrence, and environmental management, it is unclear how the molecular chemodiversity of storm runoff DOM responds to land use patterns or potential anthropogenic sources. Using Fourier-transform ion cyclotron resonance mass spectrometry, this study evaluated the molecular chemodiversity profiles of DOM in urban storm runoff from different land use and underlying surface pavement combinations. The chemodiversity of suburban forest runoff-associated DOM was characterized by high lignin and tannin abundance, predominance of CHO molecules, less heteroatoms, high molecular mass, and highly unsaturated and aromatic compounds. Urban storm runoff-associated DOM was predominantly characterized by abundant lipids, proteins, and carbohydrates, low-mass molecules, abundant S- and P-bearing heteroatoms, and high saturation. The low conformity of unique molecular features co-occurring across urban land-uses suggests a relatively incohesive pool in the urban storm runoff-associated DOM, i.e., high chemodiversity. The reconstructed source-derived patterns significantly drive the directional trends in DOM of urban storm runoff, oppositely shifting toward high saturation vs. high unsaturation and aromatization features. This demonstrates that unveiling the interactions of anthropogenic and terrestrial sources in order to understand the underlying mechanism is critical for our ability to track and predict the current and future turnover in DOM chemodiversity in storm runoff in the context of the global trend of upgrading urban environment management, following recognition of their probable links with urban land-uses. Underlying surface pavement can hardly superimpose a directional effect to alter the discrepancies in the dominant molecules of each urban land use further. These findings reveal the importance of understanding DOM characteristics at a molecular level and potentially enable targeted control of ecological risks in receiving ecosystems induced by urban storm runoff.

Spatiotemporal variations of dissolved organic matter in a typical multi-source watershed in northern China: a fluorescent evidence

The amount of dissolved organic matter (DOM) in a multi-source watershed is important for complete management and assessing the river basin's long-term safety. Based on this, we study the composition, spatiotemporal changes, and primary sources of DOM using the excitation-emission matrix (EEM) and parallel factor analysis (PARAFAC). The relationship between DOM composition and water quality was also discussed. It was found that the DOM in the North Canal River watershed was composed of two similar humic acid-like components (230, 335/400 nm and 260, 360/450 nm) and a tryptophan-like component (280/290-350 nm). The intensity of DOM shows obvious seasonal spatiotemporal variations. In terms of time, the relative concentration of DOM in winter is significantly higher than that in other seasons due to the influence of water volume, temperature, and photochemical degradation factors. As for the aspect of space, under the combined effect of land use and multiple sources of pollution, the relative concentration of tryptophan-like in the mainstream was significantly higher than tributaries, while the relative concentration of humic-like components in the tributaries was higher than that in the mainstream. The chief sources of DOM in the North Canal River watershed include human-derived point sources and agricultural non-point sources in the main channel, as well as terrestrial and microbiological sources in the tributaries. Moreover, the composition of DOM is significantly related to water quality indicators, especially nitrogen and phosphorus, which shows that DOM can have an indicative impact on the trophic status in the North Canal River. The findings of this study could have a predictive effect and provide a scientific foundation for water quality monitoring and pollution control in the North Canal River watershed.

Interactions between periphytic biofilms and dissolved organic matter at soil-water interface and the consequent effects on soil phosphorus fraction changes

Dissolved organic matter (DOM) plays vital roles in carbon and other nutrient transformation at soil-water interfaces (SWI) in paddy fields. It is associated with the growth and withering of periphytic biofilms. However, the interactions between DOM and periphytic biofilms remain largely unknown. In this study, a microcosm experiment with different initial DOM contents elucidated that the biomass, and biomass nitrogen and phosphorus contents were greatly influenced by humic-like substances (C2 and C3), while the growth of periphytic biofilms increased the contents of humic-like (C1 and C2) and tryptophan-like substances (C5) in soil. Moreover, the decomposition of periphytic biofilms significantly increased soil pH, DOM, C2, C3 and C5 contents, but caused decrease in Eh, with consequent reduce in water soluble phosphorus (WSP) and release of algal available phosphorus (AAP). Results from this study revealed how DOM interacts with periphytic biofilms and the consequent effects on changes of bioactive phosphorus fractions, and provide practical information for designing periphytic biofilm based biofertilizer from the perspective of soil DOM.

Compositional and structural characteristics of dissolved organic matter in overlying water of the Chaobai River and its environment significance

The composition and structure of dissolved organic matter (DOM) play vital roles in the material cycle of river ecosystems. Based on ultraviolet-visible absorption spectroscopy, excitation-emission matrix fluorescence spectroscopy, and ultrahigh-resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry technology, this study comprehensively characterized the composition and structure of DOM in the overlying water of the Chaobai River in order to determine the potential environmental impact of DOM on the water quality. The results showed that the DOM content of the overlying water in the Chaobai River was between 10.94 and 28.13 mg/L. The main DOM component of the overlying water was humus (70.94%). The relative abundance of CHOS compounds in the Chaobai River was lower than Maozhou River (urbanized river) and significantly higher than Xiangxi Bay (suburban river). In addition, the DOM composition and structure of the overlying water were closely related to anthropogenic input, microbial activity, and phytoplankton. In particular, chlorophyll a can indirectly reflect fresh autochthonous DOM content and composition in the overlying water. The results of this study further reveal the characteristics of suburban rivers and provide theoretical basis and guidance for the water quality evaluation and pollution control of the Chaobai River and other suburban rivers worldwide.

Evaluating sewer exfiltration in groundwater by pharmaceutical tracers after the 2016 Kumamoto earthquakes, Japan

In April 2016, a series of earthquakes (M 7.3 on the Japan Meteorological Agency scale) occurred in Kumamoto, Japan causing serious damage to underground sewerage networks. In this study, we evaluated sewer exfiltration in groundwater in the Kumamoto area after the earthquakes by using multiple tracers. We used 14 pharmaceuticals, including carbamazepine and crotamiton, and anthropogenic Gd as tracers, and we measured concentrations of these tracers from September 2016 to November 2017 seasonally. The detection frequency of caffeine, carbamazepine, crotamiton, ibuprofen, and anthropogenic Gd ranged from 29% to 45%, and the concentrations of the pharmaceuticals in the groundwater were lower than those in previous studies. The median of all pharmaceutical concentrations did not decrease, whereas the median of the sum of crotamiton and carbamazepine concentrations, which are quantitative sewage markers, decreased with time. The sewer exfiltration rates in September 2016 estimated using carbamazepine, crotamiton, and anthropogenic Gd were 0.59 ± 0.27%, 0.66 ± 0.47%, and 0.11 ± 0.18% of sewage dry weather flow, respectively, indicating that the effect of the earthquakes on sewer exfiltration was small, probably because the damaged sewers were quickly repaired. This study demonstrated that a multiple-tracer approach is useful for evaluating sewer exfiltration after major earthquakes.

Novel insights into impacts of the COVID-19 pandemic on aquatic environment of Beijing-Hangzhou Grand Canal in southern Jiangsu region

In 2020, a sudden COVID-19 pandemic unprecedentedly weakened anthropogenic activities and as results minified the pollution discharge to aquatic environment. In this study, the impacts of the COVID-19 pandemic on aquatic environment of the southern Jiangsu (SJ) segment of Beijing-Hangzhou Grand Canal (SJ-BHGC) were explored. Fluorescent component similarity and high-performance size exclusion chromatography analyses indicated that the textile printing and dyeing wastewater might be one of the main pollution sources in SJ-BHGC. The water quality parameters and intensities of fluorescent components (WT-C1(20) and WT-C2(20)) decreased to low level due to the collective shutdown of all industries in SJ region during the Spring Festival holiday and the outbreak of the domestic COVID-19 pandemic in China (January 24th to late February, 2020). Then, they presented a gradual upward trend after the domestic epidemic was under control. In mid-March, the outbreak of the international COVID-19 pandemic hit the garment export trade of China and consequently inhibited the production activities of textile printing and dyeing industry (TPDI) in SJ region. After peaking on March 26th, the intensities of WT-C1(20) and WT-C2(20) decreased again with changed intensity ratio until April 12th. During the study period (135 days), correlation analysis revealed that WT-C1 and WT-C2 possessed homology and their fluorescence intensities were highly positively correlated with conductivity and COD_Mn. With fluorescence fingerprint (FF) technique, this study not only excavated the characteristics and pollution causes of water body in SJ-BHGC, but also provided novel insights into impacts of the COVID-19 pandemic on production activities of TPDI and aquatic environment of SJ-BHGC. The results of this study indicated that FF technique was an effective tool for precise supervision of water environment.

Optical properties and 14C ages of stream DOM from agricultural and forest watersheds during storms

Forest and agricultural land use affects the concentration and composition of dissolved organic carbon (DOC) in streams and rivers. To elucidate the impacts of forest and agricultural land use on stream DOC during storm events, we investigated DOC concentration ([DOC]), optical properties of dissolved organic matter (DOM), and Δ¹⁴C-DOC in both forest- and agriculture-dominated headwater streams in South Korea in the summer of 2012. One forested and five agricultural streams were investigated. During storms, the peak [DOC] of forest stream increased to 5.8 mg L^-1, approximately two times larger than that of the most agricultural stream (3.2 mg L^-1), demonstrating the weaker storm responses of the [DOC] of agricultural streams to hydrological change. Five PARAFAC components were identified, including three terrestrial humic-like substances (C1, C2, C3), one microbial humic substance (C4), and one microbial protein-like substances (C5). The mean (C4+C5)/(C1+C2+C3) of all storm events at the most agricultural stream was 1.5 times larger than that of the most forested stream, suggesting that more protein-like DOM is exported from agricultural watersheds. Whereas a forest stream was primarily composed of terrestrially derived and ¹⁴C-enriched modern DOC, the ¹⁴C-age of the most agricultural stream was up to ∼1000 years old. The results suggest that agricultural practices could decrease the old organic carbon pools from soils. However, how quickly the aged DOC can be degraded to CO₂ in streams is unknown, warranting future investigation on lability of the aged DOC and their effects on CO₂ evasion from rivers and estuaries downstream.

Spatiotemporal variations in chromophoric dissolved organic matter (CDOM) in a mixed land-use river: Implications for surface water restoration

A challenge for current surface water restoration and management in China is acquiring the source information for complex pollution scenarios in order to develop effective control strategies. As an important part of dissolved organic matter, chromophoric dissolved organic matter (CDOM) contains unique chemical signals related to various pollution sources. Spectral methods such as fluorescence excitation-emission matrices coupled with parallel factor analysis enable rapid and low-cost CDOM characterization for source tracking. In this study, a typical small-sized river flowing through mixed land-use regions in southeastern China, the Lujiang River, was investigated to determine the responses of CDOM to spatiotemporal factors. The effects of land-use patterns were reflected by the fluorescent components of terrestrial and sewage substances. A high and stable proportion of terrestrial-like components (C1 + C2) in each sampling period (i.e., March: 47.6 ± 5.7% and October: 44.3 ± 2.7%) indicated a high input of non-point source (NPS) pollution from both agriculture and urban areas. In addition, the difference in solar radiation intensity induced by climate and air quality changes was also reflected by variability in the photodegradation product component (C3) of terrestrial precursors between October (24.8 ± 2.6%) and March (4.5 ± 2.0%), suggesting that terrestrial components could be a sensitive indicator for NPS pollutant monitoring. Increased sewage impact in downstream regions was reflected by a spike in the tryptophan-like component (C4); temporal variations in C4 (paired t-Test, p < 0.005) also indicated that sewage substances were more prone to removal by microbial activity in warmer seasons. The dynamics of C4 could serve as a good indicator of sewage disposal performance. The results of this study demonstrate that CDOM data have important practical applications for existing water restoration campaigns in southeastern China, as well as substantial potential for routine water quality monitoring.

PARAFAC model as an innovative tool for monitoring natural organic matter removal in water treatment plants

The increase of fluorescent natural organic matter (fNOM) fractions during drinking water treatment might lead to an increased coagulant dose and filter clogging, and can be a precursor for disinfection by-products. Consequently, efficient fNOM removal is essential, for which characterisation of fNOM fractions is crucial. This study aims to develop a robust monitoring tool for assessing fNOM fractions across water treatment processes. To achieve this, water samples were collected from six South African water treatment plants (WTPs) during winter and summer, and two plants in Belgium during spring. The removal of fNOM was monitored by assessing fluorescence excitation-emission matrices datasets using parallel factor analysis. The removal of fNOM during summer for South African WTPs was in the range 69-85%, and decreased to 42-64% in winter. In Belgian WTPs, fNOM removal was in the range 74-78%. Principal component analysis revealed a positive correlation between total fluorescence and total organic carbon (TOC). However, TOC had an insignificant contribution to the factors affecting fNOM removal. Overall, the study demonstrated the appearance of fNOM in the final chlorinated water, indicating that fNOM requires a customised monitoring technique.

Fluorescence characteristics and biodegradability of dissolved organic matter (DOM) leached from non-point sources in southeastern China

Under the increasingly intensive measures for surface water restoration in China, point source discharge has been strictly regulated; however, for non-point sources, which constitute a large part of surface water pollutants, effective control has been difficult to reach. A comprehensive understanding of the characteristics of non-point source pollutants is essential for surface water improvement programs of cities such as Ningbo, on the southeast coast of China. Ningbo has made tremendous efforts in the past few years to control point source pollutants, but available data and management strategies on the non-point source pollutants are still limited. To this end, leachates of representative non-point source samples from the territory of Ningbo, including cropland and wetland soil, urban channel sediment, and poultry manure, were examined and compared focusing on the fluorescence characteristics and biodegradability of the dissolved organic matter (DOM). Results indicated that biodegradable dissolved organic carbon (BDOC) accounting for the total DOC was 46.7 ± 0.7% for cropland, wetland (56.3 ± 6.8%), non-sewage channel (60.1 ± 0.4%), sewage channel (74.5 ± 1.1%), and poultry manure (62.7 ± 4.5%). The leachates of the studied samples showed significant differences in both the amount and composition of DOM. However, a fluorescence component representing tryptophan-like substances identified by the excitation-emission matrix (EEM) combined with parallel factor (PARAFAC) analysis effectively predicted the BDOC variations among the studied samples. Moreover, under the studied nutrient concentrations, which were equivalent to Grade III water quality in China, nutrient limitation of microbial degradation was not observed. Threats to water quality, especially excessive consumption of dissolved oxygen, could be posed by the non-point source leachates due to their high bioavailability, large distribution, and weak nutrient restraint. Further investigations, including a quantitative evaluation of the non-point source pollution contribution, and pollutant blocking techniques are required.

The Role of Streamside Native Forests on Dissolved Organic Matter in Forested and Agricultural Watersheds in Northwestern Patagonia

Streamside native forests are known for their key role in water provision, commonly referred to as buffers that control the input or output of nutrients from terrestrial to aquatic ecosystems (i.e., nitrogen or carbon cycle). In order to assess the functional role of indigenous forests along streamside channels, we measured 10 parameters associated with DOM (Dissolved Organic Matter) at 42 points in 12 small catchments (15–200 ha) dominated by native forests (reference, WNF), forest plantations (WFP) and agricultural lands (WAL) in which the land cover portion was calculated in the entire watershed and along 30 and 60-m wide buffer strips. We found that watersheds WFP and WAL were statistically different than WNF, according to DIC concentrations (Dissolved Inorganic Carbon) and the intensity of the maximum fluorescence of DOM components. Using linear models, we related streamside native forest coverage in buffer strips with DOM parameters. The increase of streamside native forest coverage in 60 m wide buffer strips (0–100%) was related to lower DIC concentrations (0.89 to 0.28 mg C L−1). In watersheds WFP and WAL, the humic and fulvic-like components (0.42 to 1.42 R.U./mg C L−1) that predominated were related to an increase in streamside native forest coverage in the form of a 60 m wide buffer strip (0–75%). This is evidence that streamside native forests influence outputs of detritus and lowered in-stream processing with concomitant downstream transport, and functional integrity and water quality. We propose that DOM quantity and quality may be a potential tool for the identification of priority areas near streams for conservation and ecological restoration in terms of recovery of water quality as an important ecosystem service. The results of this study are useful to inform policy and regulations about the width of streamside native forests as well as their characteristics and restrictions.