Risk Of Eutrophication Research Articles

Transformation of sedimentary and colloidal phosphorus across the land‒sea margin received effluents from agricultural and municipal activities

The transformation, transport, and release of phosphorus (P) are highly subject to anthropogenic activities and complex biochemical interactions. Its bioavailability and recalcitrance are generally regulated by P forms, arousing imposition for the accurate identification of chemical speciation. Here, P K-edge X-ray absorption near edge structure spectroscopy was exploited to determine the molecular P species on colloids, canal sludge, and coastal sediments collected in the area receiving mixed effluents from agricultural and municipal activities. Although Fe(III)-bonded P [Fe(III)–P] dominated the P inventory for colloids and sludge collected near the agricultural area, its proportion on colloids was approximately half of that on the sludge, suggesting the emerging contribution of other P species such as Al–P, Fe(II)–P, and organic-P (org-P) to carry colloidal P. Proportions of Fe(III)–P on colloids and sludge both declined seaward, yet the maximum P loss from colloids was derived from the org-P. The organic matter degradation plausibly drove the reduction of SO4 and Fe(III), leading to the prominent increase in FeS and the conversion of org-P to authigenic P. While Al–P accounted for a comparable proportion of colloidal P inventory to that of Fe(III)–P in adjacent coastal wetlands, the proportion of Fe(II)–P showed the greatest increase on colloids in the transition from fresh-to saltwater. Collective results attest to the significance of Fe(II) and Al in partitioning colloidal and sedimentary P, which should be taken into account to improve the assessment of the P dynamics and eutrophication risk.

The Use of Raw Poultry Waste as Soil Amendment Under Field Conditions Caused a Loss of Bacterial Genetic Diversity Together with an Increment of Eutrophic Risk and Phytotoxic Effects.

Poultry waste has been used as fertilizer to avoid soil degradation caused by the long-term application of chemical fertilizer. However, few studies have evaluated field conditions where livestock wastes have been used for extended periods of time. In this study, physicochemical parameters, metabarcoding of the 16S rRNA gene, and ecotoxicity indexes were used for the characterization of chicken manure and poultry litter to examine the effect of their application to agricultural soils for 10years. Poultry wastes showed high concentrations of nutrients and increased electrical conductivity leading to phytotoxic effects on seeds. The bacterial communities were dominated by typical members of the gastrointestinal tract, noting the presence of pathogenic bacteria. Soils subjected to poultry manure applications showed statistically higher values of total and extractable phosphorous, increasing the risk of eutrophication. Moreover, while the soil bacterial community remained dominated by the ones related to the biogeochemical cycles of nutrients and plant growth promotion, losses of alpha diversity were observed on treated soils. Altogether, our work would contribute to understand the effects of common local agricultural practices and support the adoption of the waste treatment process in compliance with environmental sustainability guidelines.

The potential role of sediments in nutrients (N, P) cycle in Marchica lagoon (Mediterranean Sea, Morocco)

The aim of this study is to present the distribution of nutrients in water and sediment of Marchica lagoon, a post-restorated lagoon located in Mediterranean Sea (NE Morocco), to estimate the impact of bottom sediments on the water quality of this lagoon, and to identify the areas more affected by eutrophication risk. Nutrient concentrations in the water column and sediments were determined in thirteen samples taken from different station of the lagoon in October 2019. Nutrient concentrations in sediment were found higher than those in surface water; very high levels of nitrogenous elements showed in all sediments samples and mainly nitrogenous components (averages of 43.58 mg of N-NH4; 0.827 mg of N-NO3; 0.054 mg of N-NO2 and 773 mg of TN per kg of dry sediment) and high levels of phosphorus with average of 620 mg P/kg of dry sediment. A strong positive correlation showed between sediment and water parameters in 0.01 and 0.05 levels. High concentrations were recorded near the nutrient-rich wastewater treatment plant effluent discharges, watershed and groundwater input. The lowest concentrations are near the new pass, this is due to the low continental inputs and the renewal of the lagoon waters by the Mediterranean Sea. Generally, the distribution of nutrient levels is influenced by continental inputs, hydrodynamics, and organic matter content in the sediment. These sediments are considered as a reservoir of nutrient pollutants, which will influence water quality by releasing sedimentary materials in the water.

Probabilistic eutrophication risk mapping in response to reservoir remediation

Reservoir eutrophication is a critical natural hazard in countries with rapid agricultural and industrial development. To simulate the eutrophication of the Fengshan Reservoir, the algal bloom occurrence patterns in the reservoir were modeled using the Environmental Fluid Dynamics Code (EFDC) for understanding the algal dynamics. The calibration and validation of the EFDC were performed by comparing the model results with field data. The model was calibrated against the hydrodynamic data, including the water level and water temperature, and water quality data from four monitoring stations in the study area. Uncertainty analysis was conducted using a perturbance moment method (PMM) with the EFDC model. Parameter uncertainty was considered in this study. The order of importance of model parameters in terms of their uncertainty contribution to the overall uncertainty of water quality simulations was obtained. The calibrated and validated model was then used to investigate three contaminant remediation scenarios: (a) increasing the water level, (b) dilution, and (c) reaeration. Operational uncertainty was also considered, as there exists variability in the remediation effort and project execution for a complex engineering system like reservoirs. Finally, probabilistic eutrophication risk mapping was established for each remediation effort to facilitate decision-making in eutrophication risk assessment.

Physical-chemical characterisation of the urban wastewater – case study of the Boumerdes region, North – Algeria

The objective of this study is to assess the physical-chemical quality of urban wastewater from the city of Boumerdès, in northern Algeria with regard to the threshold values for irrigation or their discharge in aquatic ecosystems. Five sampling points were carried out of the study area in April 2017. The results obtained of physical- chemical parameters indicating pollution show that the water course is exposed to pollution mainly of organic origin. It’s expressed by a high maximum value according to Algerian and World Health Organisation standards: chemical oxygen demand ( COD 886 mg O 2∙dm –3), biochemical oxygen demand ( BOD 5 490 mg O2∙dm –3), nitrate (NO 3 – 73.09 mg∙dm –3), nitrite (NO 2 –6 mg∙dm –3), ammonium (NH 4 + 23 mg∙dm –3) and phosphates (PO 4 3– 7.3 mg∙dm –3). The COD to BOD 5 rate of 1.8, show that the effluents must be treated before being discharged into the receiving environment. However, it is lower than 2, which makes them easily biodegradable and can be treated by a biological system such as a natural lagoon. It shows also a diversified origin of the pollution. It is predominantly domestic origin, it could have an adverse effect on public health, presenting a risk of environmental eutrophication, contamination of soil and water resources. The physical-chemical characterisation of the urban wastewater shows that they are quite loaded and present a pollution in nitrogenous compounds, a treatment is requested before the direct discharge to the receiving environment or their reuse in the irrigation.

Effects of environmental and agronomic factors on pond water quality within an intensive agricultural landscape in subtropical southern China

Water quality deterioration, such as eutrophication, can contribute to the degradation of farm pond ecosystems, threatening numerous ecological services and socioeconomic benefits. However, the variability of water quality and the complexity of influencing variables pose large uncertainties for pond management practices and watershed planning. This study integrated a self-organizing map (SOM) and partial least squares structural equation modeling (PLS-SEM) to evaluate the nitrogen (N) and phosphorus (P) variations in 39 typical farm ponds in the Dongting Lake basin, and related the variations to pond internal factors, external environment, and agronomic management. The results indicated that 39 monitored farm ponds faced a high risk of eutrophication owing to high N and P levels, and that total N (TN), total P (TP), and particulate P (PP) generally exceeded the threshold of level V surface water quality standards in China (2.0 mg N L−1 and 0.2 mg P L−1). Simultaneously, pond water quality showed high spatiotemporal variability, and pollution hotspots occurred mostly during the overlapping periods of fallow-dry-winter and planting-rainy-spring. Based on the constructed SEM model, external environmental factors (meteorology, catchment landscape composition, configuration, topography, and soil chemical properties), pond internal characteristics, and agronomic management combined explained 60.2 ± 2.9 % and 54.2 ± 3.1 % of the N and P variations, respectively. There were intricate interactions among the above latent variables, including such meteorology positively moderated the paths of soil chemical properties→pond P and landscape composition→pond N and P; landscape composition, soil, and pond internal characteristics mediated the effects of other variables on variations of N and P. The total effects (indirect effects + direct effects) of landscape composition on the variations of pond N and P were higher than those of other variables. Among all the indicators composing latent variables, agricultural and residential land area percentage, rainfall, water depth, and fish farming were relatively important in pond water quality variations. The constructed model and analytical results offer essential information for the accurate management and restoration of pond water quality.

A Modified Location-Weighted Landscape Index to Evaluate Nutrient Retention in Agricultural Wetlands: A Case Study of the Honghe Hani Rice Terraces World Heritage Site

Understanding the influence of landscape patterns on the water quality of agricultural wetlands is critically important for their management and related decision-making. However, the question of how to quantify this objectively remains a challenge in the relevant scientific fields. In this study, the location-weighted landscape index (LWLI), a process-oriented indicator that integrates ecological processes with landscape patterns based on the source and sink theory, was modified into the SLWLI by assigning nutrient-based weights in the Honghe Hani Rice Terraces World Heritage Site (HHRT). The results indicate that the five watersheds are dominated by sink landscapes, representing 64 percent of the total area. Rice terraced fields were a composite “source–sink” landscape, and their areas in the five watersheds ranged from 4.82 to 20.40%. The nutrient retention function of the sink landscapes of total nitrogen (TN) ranged from 0.64 to 0.86, whereas the total phosphorus (TP) ranged from 0.72 to 0.82, showing good retention function in regard to both nutrients. The contribution rates of forest land and rice terraces to TN and TP retention were greater than 47.07 and 17.07%, respectively, which indicates their key regulation of the nutrient retention function, reducing the risk of water eutrophication and leading to optimized conservation. The vertical pattern of the HHRT plays an important role in nutrient retention function. The SLWLI is an effective index that can be used to assess nutrient retention function and to identify sink landscapes for regulating water pollution in agricultural wetlands.

Understanding farmers’ conservation behavior over time: A longitudinal application of the transtheoretical model of behavior change

Global waterbodies are experiencing increased risk of eutrophication and harmful algal blooms due to excess nutrients including phosphorus and nitrogen discharged from human activity on the landscape and as a result of climate change. Despite modeling that suggests the efficacy of best management practices in agricultural systems to be sufficient to address the problem, adoption by farmers remains far below the levels needed to achieve significant water quality improvements and new approaches to encourage and sustain adoption are urgently needed. In this work, we apply a modified transtheoretical model (TTM) of behavior change to a longitudinal dataset (N = 584) of farmers’ adoption decisions and stated intentions to use cover crops, collected in the Maumee Basin of Lake Erie, USA in 2016 and 2018. The TTM posits that behavior changes over time and is influenced by different social-psychological processes at each stage of change. Our findings confirm past research into the importance of many of the factors investigated, while providing new insight into their role in specific stages of the change process with potential implications for the design of interventions for farmers in different stages. Several factors investigated (mean environmental concern, education, information from conservation groups and off-farm income) were uniquely important to a particular stage. Other factors (response efficacy at the field level, total farm size and risks of spring planting interference) were important at both an earlier and later stage, but less important in predicting middle stages of change. A third set of factors (self-efficacy, proportion rented, no-till adoption and uncertain long-term paybacks) were statistically important across each stage of the TTM model. In applying the TTM longitudinally, we found evidence that farmers in a more advanced stage of cover crop adoption, in the first wave of data collection (2016) were more likely to have adopted cover crops in the second wave (2018), a result not predicted by individual factors alone. We report findings for cover crops but see the potential for the transtheoretical model of behavior change to be applied to other best management practice adoption decisions and to diverse populations of farmers to generate similarly novel insight and utility for intervention design and targeting.

Increased risk of water quality deterioration under climate change in Ganga River

The industrialized stretch of Kanpur is considered to be one of the most polluted stretches of the Ganga River, with untreated sewage, industrial discharge, and agricultural runoff. Risk assessment studies on water quality for future scenarios are limited for this stretch of the river. In this study, we assess the effect of climate change on water quality, the risk of eutrophication, and fish kill for the mid and end of the twenty-first century for this river stretch. The water quality parameters considered are dissolved oxygen (DO), biochemical oxygen demand (BOD), ammonia, nitrate, total nitrogen (TN), organic-, inorganic- and total phosphorous (TP), and fecal coliform (FC). The risk of eutrophication and fish kill are quantified using simulated concentrations of nutrients and DO, respectively. Downscaled climate change projections for two climate change scenarios (RCP4.5 and RCP8.5) are used to drive a hydrological model coupled to a water quality simulation model. Our simulations indicate a potential deterioration of water quality in this stretch in the mid-twenty-first century, with a potential increase in pollutant concentration by more than 50% due to climate change alone. However, a slight improvement is simulated by the end of the century relative to the mid-twenty-first century which can be attributed to increased streamflow during low-flow periods due to increased summer mean precipitation. The risk of reduced dissolved oxygen and increased organic and nutrient pollution, and the risk of eutrophication and fish kill increase with warming due to the rise in the frequency of low-flow events and a reduction in streamflow during low-flow events. However, the risk of nitrate and microbial pollution is reduced because of an increased denitrification rate and pathogen decay rate with warming. The risk of eutrophication and fish kill is found to increase by 43.5 and 15% due to climate change alone by mid-twenty-first century. Our findings could be helpful to planners in water resource management to take necessary actions to improve the water quality of the Ganga River in this century.

Spatial, temporal, and vertical variability of nutrients in the Southeastern Black Sea.

In this study, the nutrient concentrations along the coastal region of the Southeastern Black Sea were evaluated based on temporal, spatial, and vertical distributions. The water samples were collected seasonally in 2013 from 432 depths covering 55 stations. The nutrient concentrations showed significant spatial and temporal variations that declined abruptly from shore to offshore. The stations near the river discharge had the highest silicate, nitrate, and total dissolved inorganic nitrogen (DIN). The highest nitrate concentrations were determined within the oxycline layer and nitrite within the suboxic layer, while phosphate, ammonium, silicate, and DIN were within the anoxic layer. The findings of this study evinced that the Southeastern Black Sea possessed lower contents of nitrate (mean±s.d., 0.58±1.17μM), phosphate (0.12±1.00μM), than the literature values reported for the western Black Sea, but consistent to the eastern Black Sea. However, the silicate concentrations of the study area were consistent with the western Black Sea while higher than the eastern Black Sea. The Trophic Index showed that two stations located on the coast of the Samsun and Giresun were at increased risk of eutrophication due to intensive urban and industrial inputs. This study provides detailed insights on the nutrient status of the coastal Southeastern Black Sea, which should facilitate the development of long-term monitoring programs concerning environmental aspects of marine and coastal planning.

Phosphorus sorption capacity in soils from freshwater restored coastal wetlands increased with restoration age

• P sorption capacity in soils increased with wetland restoration age. • Elevated P sorption related to the improvement of soil properties in restored wetland. • The P loss potential was less affected by the wetland restoration age. • The restored wetland was identified as the P storage hotspot at the landscape scale. Coastal wetlands, located at the intersection of land and sea, are considered to be a phosphorus (P) sink, source, and reactor in the global P cycle. However, the variation in P sorption capacity with wetland age and the related sorption mechanisms are not well understood. In this study, we collected the surface soil samples (0–20 cm) from 10 coastal freshwater wetlands that had been restored for 0–44 years surrounding China’s Bohai Rim. Through a series of batch experiments, we studied the factors controlling P sorption and release in these soils. The results showed that the maximum P sorption capacity (Q max ) in these wetlands was 294–2447 mg kg −1 , with an average of 1472 mg kg −1 . The Q max generally increased with increasing wetland restoration age. The degree of P saturation (DPS) and the P eutrophication risk index (ERI) for coastal wetlands were 0.5–9.5% and 0.9–21.1%, respectively. The DPS and ERI values did not vary significantly with wetland age. These data suggest that freshwater restoration significantly increases P sorption capacity, while not greatly affecting the P release potential in the coastal wetlands surrounding Bohai Rim. These observations may be related to the soil desalination and organic matter and amorphous Fe and/or Al accumulation that occur during the freshwater restoration of degraded wetlands. Coastal wetlands (especially restored wetlands) were suggested as P storage hotspots among upland, wetland, and offshore along the coastal watersheds of Bohai. These findings indicate that the freshwater restoration significantly improved the soil properties in the degraded coastal wetlands, and therefore increased P sorption capacity in the restored wetlands.

Assessing critical loads and exceedances for acidification and eutrophication in the forests of East and Southeast Asia: A comparison with EANET monitoring data

Spatial variations in sulfur (S) and nitrogen (N) deposition have changed in East and Southeast Asia in recent decades. Nevertheless, in this region, including the tropics, regional-scale assessments of the long-term risk of acidification and eutrophication (N saturation) for terrestrial ecosystems using a critical load approach have not been updated since 2001. To evaluate future risks, maps of critical loads and exceedances were updated using recently acquired spatial datasets of soil properties, soil minerals, climate, tree plantations, and the annual S and N depositions estimated using the Community Multiscale Air Quality (CMAQ) model. The resulting maps were verified using data on long-term trends in soil pH and nitrate concentration in surface water acquired by the Acid Deposition Monitoring Network in East Asia (EANET). It was found that N deposition exceeded the critical load for eutrophication not only in East Asia but also in some parts of the tropical monsoon and humid regions in Southeast Asia, whereas S deposition partly exceeded the critical load for soil acidification in China and small parts of the tropical monsoon region. The high-risk areas for eutrophication coincided well with the EANET sites, where the increase in nitrate concentration in the surface water was significant over the last 20 years. Hence, the estimated map of the critical load exceedance for eutrophication is more plausible for assessing the risk in East and Southeast Asia than that for acidification, although the critical load exceedance for acidification would be sufficiently significant as an updated risk map based on the latest input values. This update also suggests that increased N deposition around megacities, water discharge, and tree plantations may play an important role in the spatial variability of eutrophication risks in the tropics of Southeast Asia.

Risk of eutrophication in the seawater of the coastal Red River aquaculture zone (Thai Binh province, Vietnam)

Coastal aquaculture represents an important economic activity in many countries. Nutrient (N, P and Si) concentrations and phytoplankton diversity and abundance in the coastal aquaculture zone, Tien Hai district, Thai Binh province (North Vietnam) were investigated during 2019–2020. Nutrient concentrations in five types of wastewater were also determined. The mean Eutrophication Index value of surface seawater at the 9 studied sites varied from 0.27 to 0.52, ranking as oligotrophic to mesotrophic. Five phytoplankton groups were observed (Bacillariophyceae (62% relative abundance), Dinophyceae (16%), Chlorophyceae (11%), Cyanobacteria (7%), and Euglenophyceae (4%)). The temporal and spatial distribution of phytoplankton diversity and abundance was governed by water temperature, pH, TSS, and TP and reflected the strong interactions between seawater and riverine water in the area. The presence of certain potentially toxic algal species combined with increasing inorganic nitrogen concentrations and N:P ratios further underlined the risk for harmful algal blooms. The investigation of different nutrient sources in this area revealed that while nitrate and total phosphorus concentrations are related to diffuse sources, point sources may be important in providing ammonium and dissolved phosphate concentrations to coastal seawater in this aquaculture zone. These results provide a scientific basis upon which better management strategies can be constructed in order to assure the sustainable development of aquaculture in the Red River coastal area, in particular, and in the coast of Vietnam, in general.

Retrieving Inland Reservoir Water Quality Parameters Using Landsat 8-9 OLI and Sentinel-2 MSI Sensors with Empirical Multivariate Regression.

Improving water quality is one of the top priorities in the global agenda endorsed by the United Nations. To ensure the achievement of this goal, governments have developed plans to continuously monitor the status of inland waters. Remote sensing provides a low-cost, high-frequency, and practical complement to monitoring systems that can cover a large area. However, it is crucial to evaluate the suitability of sensors for retrieving water quality parameters (WQPs), owing to differences in spatial and spectral sampling from different satellites. Taking Shanmei Reservoir in Fuzhou City, Fujian Province as a case study, this study collected and sorted the water quality data measured at the site in 2020 to 2022 and Landsat 8-9 OLI and Sentinel-2 MSI images, simulated the chlorophyll-a (Chl-a) concentration, algae density, and turbidity using empirical multivariate regression, and explored the relationship between different WQPs using correlation analysis and principal component analysis (PCA). The results showed that the fitting effect of Landsat OLI data was better than that of the Sentinel-2 MSI data. The coefficient of determination (R2) values of Chl-a, algal density, and turbidity simulated by Landsat OLI data were 0.70, 0.81, and 0.80, respectively. Furthermore, the parameters of its validation equation were also smaller than those of Sentinel MSI data. The spatial distribution of three key WQPs retrieved from Landsat OLI data shows their values were generally low, with the mean values of the Chl-a concentration, algal density, and turbidity being 4.25 μg/L, 4.11 × 106 cells/L, and 1.86 NTU, respectively. However, from the end of February 2022, the values of the Chl-a concentration and algae density in the reservoir gradually increase, and the risk of water eutrophication also increases. Therefore, it is still necessary to pay continuous attention and formulate corresponding water quality management measures. The correlation analysis shows that the three key WQPs in this study have a high correlation with pH, water temperature (WT), and dissolved oxygen (DO). The results of PCA showed that pH, DO, Chl-a concentration, WT, TN, and CODMn were dominant in PC1, explaining 35.57% of the total variation, and conductivity, algal density, and WT were dominant in PC2, explaining 13.34% of the total variation. Therefore, the water quality of the Shanmei Reservoir can be better evaluated by measuring pH, conductivity, and WT at the monitoring station, or by establishing the regression fitting equations between DO, CODMn, and TN. The regression algorithm used in this study can identify the most important water quality features in the Shanmei Reservoir, which can be used to monitor the nutritional status of the reservoir and provide a reference for other similar inland water bodies.

Drivers for primary producers’ dynamics: New insights on annual benthos pelagos monitoring in anthropised freshwater marshes (Charente-Maritime, France)

Wetlands, especially marshes, support many services such as carbon catchment control or water purification led by primary producers such as phytoplankton and microphytobenthos (PB). The impact of the sedimentary compartment, as source and sink of essential nutrients for the water column, is often neglected in the study of their dynamics and water purification capacity of the systems. This work compared monthly (between February 2020 and April 2021) the benthic and pelagic primary producers’ dynamics in two anthropised freshwater marshes (Marans and Genouillé), with the simultaneous follow-up of physico-chemical parameters of the water column and nutrient fluxes at the sediment-water (SWI) interface. It was suggested a strong contribution of phytoplankton (pumping) and the benthic compartment (denitrification) to the water purification of these two nitrates (NO3−)-rich marshes. Total phytoplankton production fluctuated between ∼5 (winter) and 1500 mg C m−3 d−1 (fall) at Marans and between 40 (winter) and ∼750 mg C m−3 d−1 (spring) at Genouillé. At Marans, soluble reactive phosphorus (SRP) benthic effluxes (-2.101 to -6.102 µmol m−2 d−1 in fall and summer, respectively) coincided with phytoplankton bloom periods. These effluxes were inhibited by NO3− penetration in the sediment (0 to 5.104 µmol m−2 d−1), by inhibiting iron respiration. At Genouillé, inhibition of SRP effluxes depended on denitrification rate and on P stocks in the sediment, where slight SRP effluxes (-101 µmol m−2 d−1) could have co-occurred with slight NO3− influxes (5.102 µmol m−2 d−1) in spring. The presence of PB (between 10–60 and 40–120 mg gsed−1 at Marans and Genouillé, respectively), suggested a strong contribution of the benthic compartment to the total primary production (benthic and pelagic through resuspension processes) in these environments. This work encourages to consider the benthos and the pelagos as a unicum to provide better sustainable management of such systems and limit eutrophication risks in coastal areas.

Analytical Investigations to Estimate Phosphorus Re-dissolution Rates in Trace Levels of Selected Topsoils and River Sediments

Anthropogenic phosphorus (P) input from fertilised and unfertilised topsoils into surface water and re-dissolution from sediments can be key drivers of eutrophication. This study aimed to (1) analyse the P input processes into streams/rivers particularly via erosion from fertilised and unfertilised fields and (2) study the effectiveness of the riparian strip in reducing P emissions from diffuse sources. For the investigation, Cambisol-Tschernosem and Luvisol samples from Loess were taken from Thuringian test fields (Germany). Three laboratory simulations were designed to analyse P re-dissolution and leaching behaviour from topsoils and sediments and further extrapolated to a realistic scenario based on the P input path into receiving waters via erosion. Organic bonded phosphorus and orthophosphate were leached out at the beginning. Upscaling to a realistic scenario showed that the main source of P in receiving waters was leaching from sediment interstitial sites (57.5%) via percolation while the P re-dissolution via diffusion (13%), due to two heavy rain events (17%), and leaching from soil interstitial sites (12.5%) only played a minor role. The risk of eutrophication exceeded the threshold total P of 0.10 mg L-1 given as an orientation value by the Federal/State water consortium (LAWA). This was observed in percolates from all sandy soils (0.17–0.85 mg L-1), only slightly in the clayey soils (≤ 0.11 mg L-1) but not in either streambed sediment (≤ 0.08 mg L-1). However, local differences such as steeper slope, different soil compositions such as higher sand and lower clay percentages, and poorer buffering due to lower lime and aluminium content were identified as reasons for a higher risk of eutrophication.

An Experimental Study of Paddy Drainage Treatment by Zeolite and Effective Microorganisms (EM)

Eco-ditch systems have increasingly been designed and applied as a strategy to decrease the risks of water eutrophication and contamination pollution for sustainable agriculture. The main goal of this study was to evaluate the water quality of eco-ditch substrates amended with zeolite and Effective Microorganisms (EM), such as pH, dissolved oxygen concentration (DO), ammonium nitrogen concentration (NH4+-N), and nitrate nitrogen concentration (NO3−-N). Laboratory experiments were conducted with four single substrates (soil, none substrates, natural zeolite, and zeolite loaded with EM bacteria) and two mixed substrates (soil and varying proportions of the additives, 0, 5 and 15%, m/m). Results showed that the concentration of NH4+-N was decreased with the increasing rates of additives, and zeolite loaded with EM bacteria had the highest nitrogen removal rate (97.90%) under static experimental condition. The application rate of 15% zeolite loaded with EM bacteria on the eco-ditch exerted a better effect on NH4+-N and NO3−-N removal without pH reduction, decreased by 87.19% for NH4+-N and 30.33% for NO3−-N, respectively. Path analysis showed that zeolite addition had a rapid effect (path coefficient = −0.972) on free NH4+-N ions adsorption in early 1–3 days, then EM loaded at zeolite further decreased NH4+-N (path coefficient = −0.693) and NO3−-N (path coefficient = −0.334) via bacterial metabolism. Based on the results, the applications of natural zeolite and Effective Microorganisms (EM) at an appropriate rate (15%, m/m) can significantly improve water quality of paddy drainage via exerting effects on nitrogen removal.

Distribution Characteristics, Source Analysis, and Pollution Evaluation of Organic Matter in Surface Sediments of Qingpu District, Yangtze River Delta Integration Demonstration Area

The surface sediments were collected from 25 sampling points in the Qingpu District of the Yangtze River Delta integration demonstration area, and the total organic carbon (TOC), total nitrogen (TN), organic carbon isotope (δ13C), and nitrogen isotope (δ15N) content in the samples were analyzed. The distribution characteristics and potential sources of organic matter in the surface sediments were discussed in detail, and the organic pollution index was also evaluated. The results showed that the ω(TOC) in the surface sediments of 31 sampling points in Qingpu District was 0.21%-3.55%, with an average value of 1.18%; ω(TN) ranged from 0.02% to 0.23%, with an average value of 0.09%. The δ13C ranged from -28.04‰ to -10.80 ‰, with an average of -22.28‰, and the δ15N ranged from 2.28‰ to 11.19‰, with an average of 5.76‰. The TOC content was significantly correlated with the TN content. Source analysis showed that the organic matter in the surface sediments of the study area was mainly affected by soil organic matter, sewage organic matter, and terrestrial plants. The calculation results of the contribution rate based on IsoSource software showed that the relative contribution rate of soil organic matter was relatively high (0.3%-96.8%), and domestic sewage had a certain contribution to the organic matter source of most sampling points. In addition, the selected end-member substances had certain differences in the contribution of organic matter sources in samples of different land use types. The evaluation index of organic pollution in the surface sediments of the study area ranged from 0.006-0.745, with an average value of 0.163, indicating that the organic pollution of the study area was considered lightly polluted. Among them, the pollution of sampling points around the Jinze Reservoir was more serious than that in other areas, indicating that there was a potential risk of eutrophication in this area, which requires certain attention.

Ozonation of phosphonate antiscalant 1-hydroxyethane-1,1-diphosphonic acid in reverse osmosis concentrate: Kinetics, phosphorus transformation, and anti-precipitation property changes

1-hydroxyethane-1,1-diphosphonic acid (HEDP) is an intensively used phosphonate antiscalant in reverse osmosis (RO) process. However, HEDP in RO concentrate can increase the eutrophication risks, chelate with heavy metals and inhibit the precipitation treatment of RO concentrate. Ozonation was found to be effective in removing HEDP and mitigating its risks. The removal efficiencies of HEDP and total organic carbon after 20 min of ozonation were 75.2% and 41.6%, respectively. The rate constant of HEDP with ozone and •OH was 0.58 M−1 s-1and 5.4 × 108 M−1 s−1, respectively. Organic phosphorus products and orthophosphates were formed during the process, accounting for 16.7% and 60% of the total phosphorus, respectively. A kinetic model of phosphorus transformation was established. Simulation results indicated that the apparent rate constants of orthophosphate formation from HEDP and organic phosphorus product were 1.1 × 10−3 s−1 and 1.3 × 10−3 s−1, respectively. pH was an important factor affecting HEDP degradation and phosphorus transformation. As the pH value increased from 3 to 9, the removal efficiency of HEDP increased from 6.8% to 95%, and the ratio of orthophosphate formation to HEDP removal increased by more than 3.4 times. The precipitate morphology analysis and scale inhibition ratio tests showed that ozone effectively reduced the anti-precipitation property of HEDP. The dose–response curves of HEDP samples with different ozonation extents indicated that the ozonation products of HEDP didn’t show anti-precipitation effect. The apparent rate constant of HEDP degradation in RO concentrate was 26% lower than that in UPW. The ratios of ozone consumption to HEDP removal were 7.7–9.4 mg-O3/mg-HEDP during ozonation of HEDP in actual RO concentrate.

Metagenomic insights into comparative study of nitrogen metabolic potential and microbial community between primitive and urban river sediments

As a result of anthropogenic pollution, the nitrogen nutrients load in urban rivers has increased, potentially raising the risk of river eutrophication. Here, we studied how anthropogenic impacts alter nitrogen metabolism in river sediments by comparing the metagenomic function of microbial communities between relatively primitive and human-disturbed sediments. The contents of organic matter (OM), total nitrogen (TN), NO3−−N and NO2−−N were higher in primitive site than in polluted sites, which might be due to vegetation density, sediment type, hydrology, etc. Whereas, NH4+−N content was higher in midstream and downstream, indicating that nitrogen loading increased in the anthropogenic regions and subsequently leading higher NH4+−N. Hierarchical cluster analyses revealed significant changes in the community structure and functional potential between the primitive and human-affected sites. Metagenomic analysis demonstrated that Demequina, Streptomyces, Rubrobacter and Dechloromonas were the predominant denitrifiers. Ardenticatena and Dechloromonas species were the most important contributors to dissimilatory nitrate reduction. Furthermore, anthropogenic pollution significantly increased their abundance, and resulting in a decrease in NO3−, NO2−−N and an increase in NH4+−N contents. Additionally, the SOX metabolism of Dechloromonas and Sulfuritalea may involve in the sulfur-dependent autotrophic denitrification process by coupling the conversion of thiosulfate to sulfate with the reduction of NO3−−N to N2. From pristine to anthropogenic pollution sediments, the major nitrifying bacteria harboring Hao transitioned from Nitrospira to Nitrosomonas. This study sheds light on the consequences of anthropogenic activities on nitrogen metabolism in river sediments, allowing for better management of nitrogen pollution and eutrophication in river.