Eutrophication Of Surface Waters Research Articles

Factors Affecting Nitrogen Use Efficiency (NUE): Meta Analysis

Nitrogen (N) is an essential and limiting nutrient for crop production, as it is a structural part of plants and is involved in various processes. Worldwide, agricultural soils lack one or more essential nutrients, and nitrogen is one of them. Adding a sufficient amount of N will increase production. However, the overuse of N and loss of N from the soil-plant system is detrimental to the environment and results in economic losses. Nitrogen has reactive forms like ammonia, ammonium, nitrate, nitrite, nitric oxide, and nitrous oxide. Some reactive forms of N are harmful to humans, animals, plants, and microbial ecology. Nitrate can cause the eutrophication of surface water and contamination of groundwater. Drinking nitrate-contaminated water can cause methemoglobinemia and other health issues. Nitrous oxide emission depletes the ozone layer and contributes to climate change. Ammonia emissions contribute to acid rain and are also responsible for nitrous oxide emissions. This review addresses different factors/pathways/circumstances that contribute to the loss of N from the soil-plant system and reduce nitrogen use efficiency (NUE). Different factors influence NUE like ammonia volatilization, nitrification, denitrification, immobilization, leaching, runoff, temperature, soil pH, soil texture, rainfall and irrigation, soil salinity, tillage, weeds, pests, diseases, N loss from plants, fires, crop rotation, crop nutrition, crop varieties, and nitrogen management (right time, right source, right place, and right rate/amount).

Conventional soil test phosphorus failed to accurately predict dissolved phosphorus release in agricultural hydromorphic soils in Brittany, Western France

Researches have proved that agricultural phosphorus (P) loss contributes significantly to surface water eutrophication. Various soil test P (STP) methods have been developed to assess the P loss risk from agricultural soils. In the intensively-cultivated Brittany region of Western France, hydromorphic soils in wetland domains exhibit high risks of leaching and transferring dissolved P - the most bio-available form of P - to surface waters. It remains unclear whether STP conventionally developed for well-drained soils can accurately predict the risk of dissolved P release from these hydromorphic soils. In this study, we measured the dissolved reactive P (DRP) concentrations in soil solutions sampled in situ from 26 hydromorphic soils in the Brittany region and examined their relationship with several STPs available on the corresponding soils, such as the degree of soil P saturation, the equilibrium soil P concentration, or the soil Olsen P, Dyer P, and water extractable P contents. DRP concentrations ranged from 0.01 to 0.310 mg P l−1 (mean = 0.075 mg P l−1), highlighting the potential of hydromorphic soils as hotspots for DRP release in agricultural landscapes. Correlations between DRP concentrations and STPs were relatively weak (0.09 < r2 < 0.64), indicating that conventional STPs are generally unable to accurately predict the DRP release risks in hydromorphic soils. Tentatively, Olsen P showed promises as a useful risk indicator, with a relatively high r2 value of 0.6 and wide inclusion in the current STP database, especially in the Brittany region. Nevertheless, this hypothesis requires further evaluation with additional data. This study confirms the high risk of dissolved P release from hydromorphic soils in agricultural wetland domains and emphasizes the need for developing specific risk assessment tools to these hydromorphic soils.

Effect of depositional evolution on phosphorus enrichment in aquifer sediments of alluvial-lacustrine plain

Groundwater with high geogenic phosphorus (P) is increasingly concerned as a potential risk to surface water eutrophication. Although hydrogeochemical processes responsible for P mobilization in groundwater systems have been studied, the burial characteristics of P and the effect of depositional evolution on P enrichment in aquifer sediments remain unclear. In this study, aquifer sediments were collected from the Dongting Lake Plain (DTP) within the central Yangtze River Basin, a high P groundwater area, and the effect of depositional evolution on P enrichment was elucidated by comprehensively analyzing the lithology, grain size, geochronology, and geochemistry of the sediments, coupled with groundwater chemistry and sediment incubation experiments. The results showed that the contents of total organic carbon (TOC), iron (Fe), and P (the relative content of bioavailable phosphorus (BAP)) were higher in lacustrine sediments deposited under a warm-wet climate, but lower in fluvial sediments deposited under a cold-dry climate. During depositional evolution, the sedimentary facies mainly controlled the content of organic phosphorus (OP), while the paleo-climate controlled the content of both OP and Fe-bound inorganic P (FeP), which jointly affected total P content in aquifer sediments. Under the interaction of groundwater and sediment, the reductive dissolution of P-rich Fe (oxyhydr)oxides and the mineralization of OP in sediment continuously release P into groundwater. Notably, the rapid accumulation of alluvial sediments after the Last Glacial Maximum in the DTP and rapid evolution of Dongting Lake during the Holocene led to a large amount of organic matter (OM) and P buried in sediments, providing materials for P release in aquifers, which seriously threatens groundwater quality. This exploration can provide a new understanding of the enrichment of geogenic P in groundwater from the perspective of depositional evolution.

Algal organic matter accelerates the photodegradation of tetracycline: Mechanisms, degradation pathways and product toxicity

Algae are ubiquitous in eutrophic surface waters and they play important roles in the sunlight-driven transformation of environmental contaminants. The present study aims to investigate the role of algal organic matter (AOM) separated from Microcystis aeruginosa at different growth stages in tetracycline photodegradation along with the related photosensitive mechanisms. The results showed that AOM, both extracellular organic matter (EOM) and intracellular organic matter (IOM) at different growth phases all promote tetracycline photodegradation, but in different ways and performances. EOM exerts greater photolysis effectiveness than IOM with logarithmic phase (LP) organic matter more effective than that from the algae’s declining growth phase (DP). The promoting efficiencies of tetracycline photodegradation by four AOM types follow the order of LP-EOM > DP-EOM > LP-IOM > DP-IOM, accounting for 1.0420 h−1, 0.8281 h−1, 0.6527 h−1 and 0.4974 h−1, respectively. Such discrepant effectiveness is related to the different chemical constituents and structures of EOM and IOM. Scavenger experiments further demonstrated that triplet-state AOM (3AOM*) contributes the most to tetracycline degradation (30.01%∼48.51%), followed by OH (1.68%∼10.66%) and 1O2 (1.34%∼10.08%). The steady-state concentrations of 3AOM*, OH and 1O2 were measured with probe compounds in the range of 13.950 ∼ 155.234 L/mol, 2.494 × 10−17 ∼ 27.636 × 10−17 M and 1.410 × 10−14 ∼ 26.493 × 10−14 M, respectively. Interestingly, the photolytic intermediates show increasing toxicity to Photobacterium phosphoreum at first which then decreases with the extension of irradiation. These results provide comprehensive insight into the transport and environmental behavior of antibiotics in a eutrophic aqueous environment.

Nitrogen Metabolism and Flora Characteristics of Bacteria Algae Complex System

In order to denitrify the urban tail water deeply and control the eutrophication of surface water, the molecular biology methods were used to study the nitrogen metabolism performance of the denitrification complex flora and the algal-bacteria symbiotic system. The results showed that the nitrogen metabolism complex flora was high ammonification and denitrification performance. The removal effect of ammonia nitrogen of group JZ was very well in urban tailwater, and the degradation rate was as high as 95%. The removal effect of total nitrogen of group JZ was better than that of group J in the experimental water distribution. High-throughput sequencing showed that the main dominant flora and proportion of group J were Firmicutes 44.53%, Proteobacteria 43.41%, Actinobacteria 5.37%, Bacteroidetes 3.04%, and Chloroflexi 1.35%. The main dominant bacterial groups in the group JZ were 33.89% Cyanobacteria, 25.34% Chloroflexi, 19.38% Proteobacteria, 10.02% Firmicutes, and 4.20% Acidobacteria. The dominant species in group J were compared with those in group JZ; the proportions were 82% and 18% in Firmicutes, 69% and 31% in Proteobacteria, 1% and 99% in Cyanobacteria, 5.1% and 95% in Chloroflexi, 73% and 27% in Actinobacteria. It was concluded that the removal effect of ammonia nitrogen of group JZ was high in the urban tailwater. With the addition and growth of Micrococcus in group J, the nitrogen metabolism flora in group JZ changed accordingly, so as to adapt to the environment in which the dominant algae formed. It forms a new nitrogen metabolism system of bacteria and algae with Micrococcus. This research provides a theoretical and data basis for the application of algal-bacterial co-metabolism systems.

Simultaneous Removal of Ammonia and Nitrate from Wastewater Using a Pulse Electrolysis Technique

The Environmental Protection Agency (EPA) considers ammonia and nitrate as large-scale threats to environmental quality and human health, causing impaired air quality, surface water eutrophication, and other serious health problems. This work examines the viability of using a pulse electrolysis technique to accomplish the simultaneous removal of ammonia and nitrate in an undivided flow cell using CuNi/PtIr supported on carbon electrocatalysts (CuNi/PtIr/C). Different series of PtIr/C and CuNi/C compositions were examined, and it was found that among all series of the synthesized catalysts, 60% Pt9Ir/C and 40% Cu9Ni/C had greater activity toward Ammonia Oxidation Reaction (AOR) and Nitrate Reduction Reaction (NRR), respectively. Throughout the pulsing potentials, the nitrogen contaminants were gradually removed with the overall reaction that generated harmless nitrogen and hydrogen gases. The average ammonia and nitrate removal rates were 5.17 ppm-ammonia and 0.074 ppm-nitrate/min, respectively. The selectivity of nitrate to ammonia was 82% with an average nitrate removal rate of 65%. The catalysts exhibited pronounced stability after 10 cycles of pulse electrolysis.

Numerical modeling of aerobic bio-phosphorus removal by phosphorus accumulating organisms using coupled lattice Boltzmann method and cellular automata platform

The removal of phosphorus (P) from wastewater is important to reduce water pollution and potential eutrophication in surface waters. In previous studies, the multilateral interactions of biofilm growth and spatiotemporal concentrations of species were not considered or not affected by flow field and reaction rates. To fill some important parts of these gaps, an integrated platform of lattice Boltzmann method and cellular automata was developed to model the spatiotemporal nutrient transport and biofilm growth of an enhanced bio‑phosphorus removal process in a T-shaped bioreactor. The model was validated against the data available in the literature. The effects of different dissolved oxygen concentrations and fluid velocities were investigated. The results showed that increasing the velocity ratio decreased the biofilm growth, leading to a decrease in the polyphosphate concentrations in the bioreactor. There was a difference of up to 33.9 % between the lowest normalized biofilm concentration and the highest one. Increasing dissolved oxygen concentrations through the primary inlet produced more biofilm in the bioreactor, especially in its bottom zone, than that through the secondary inlet. It is also found that there is a specific biofilm concentration threshold. After the threshold, the biofilm growth and the biochemical reaction rates decreased, leading to a decrease in the phosphorus removal rate and an increase in phosphorus concentration. This study demonstrates the LBM-CA model could improve our understanding of biological P-removal and help to optimize and improve the efficiency of such operations.

Nitrogen species and microbial community coevolution along groundwater flowpath in the southwest of Poyang Lake area, China

Nitrate and ammonia overload in groundwater can lead to eutrophication of surface water in areas where surface water is recharged by groundwater. However, this process remained elusive due to the complicated groundwater N cycling, which is governed by the co-evolution of hydrogeochemical conditions and N-cycling microbial communities. Herein, this process was studied along a generalized groundwater flowpath in Ganjing Delta, Poyang Lake area, China. From groundwater recharge to the discharge area near the lake, oxidation-reduction potential (ORP), NO3–N, and NO2–N decreased progressively, while NH3–N, total organic carbon (TOC), Fe2+, sulfide, and TOC/NO3− ratio accumulated in the lakeside samples. The anthropogenic influences such as sewage and agricultural activities drove the nitrate distribution, as observed by Cl− vs. NO3−/Cl− ratio and isotopic composition of nitrate. The hydrogeochemical evolution was intimately coupled with the changes in microbial communities. Variations in microbial community structures was significantly explained by Fe2+, NH3–N, and sulfide, while TOC/NO3− controlled the distribution of predicted N cycling gene. The absence of NH3–N in groundwater upstream was accompanied by the enrichment in Acinetobacter capable of nitrification and aerobic denitrification. These two processes were also supported by Ca2+ + Mg2+ vs. HCO3− ratio and isotopic composition of NO3−. The DNRA process downstream was revealed by both the presence of DNRA-capable microbes such as Arthrobacter and the isotopic composition of NH4+ in environments with high concentrations of NH3–N, TOC/NO3−, Fe2+, and sulfide. This coupled evolution of N cycling and microbial community sheds new light on the N biogeochemical cycle in areas where surface water is recharged by groundwater.

Existing evidence related to soil retention of phosphorus from on-site wastewater treatment systems in boreal and temperate climate zones: a systematic map

BackgroundIn Sweden there are nearly one million soil-based on-site wastewater treatment systems (OWTSs). OWTSs may contribute to eutrophication of surface waters, due to the discharge of phosphorus (P). Hence, in certain cases, a high P removal rate (up to 90%) of OWTSs is required by Swedish authorities. Since these requirements may have costly consequences to property owners, it is debated whether they are too strict. In this debate, it is often claimed that the soil retention of P occurring in the natural environments may be underestimated by authorities. Soil retention is the inhibition of the transport of P through the ground, due to different chemical, physical and biological processes occurring there. These processes make the P transport slower, which may reduce the unwanted impact on receiving water bodies. However, the efficiency of soil retention of P remains unclear. The objective of this systematic map was to collect, code, organise and elucidate the relevant evidence related to the topic, to be able to guide stakeholders through the evidence base, and to support future research synthesising, commissioning, and funding. The systematic map was carried out in response to needs declared by the Swedish Agency for Marine and Water Management but the conclusions should be valid for a wider range of countries across boreo-temperate regions.MethodsSearches were made for peer-reviewed and grey literature using bibliographic databases, search engines, specialist websites, and stakeholder contacts. The references were screened for relevance according to a predefined set of eligibility criteria. A detailed database of the relevant studies was compiled. Data and metadata that enable evaluation and discussion of the character and quality of the evidence base were extracted and coded. Special focus was placed on assessing if existing evidence could contribute to policy and practice decision making. Descriptive information about the evidence base was presented in tables and figures. An interactive evidence atlas and a choropleth were created, displaying the locations of all studies.Review findings234 articles out of 10,797 screened records fulfilled the eligibility criteria. These articles contain 256 studies, performed in the field or in the laboratory. Six different study types were identified, based on where the measurements were conducted. Most studies, including laboratory studies, lack replicates. Most field studies are observational case studies.ConclusionsIt is not possible to derive valid generic measures of the efficiency of soil retention of P occurring in the natural soil environment from available research. Neither does the evidence base allow for answering the question of the magnitude of the potential impact of OWTSs on the P concentration in recipients on a general basis, or under what conditions OWTSs generally have such an impact. A compilation of groundwater studies may provide examples of how far the P may reach in x years, but the number of groundwater studies is insufficient to draw any general conclusions, given the complexity and variability of the systems. Future research should strive for replicated study designs, more elaborate reporting, and the establishment of a reporting standard.

Controlling Nitrogen Removal Processes in Improved Vertical Flow Constructed Wetland with Hydroponic Materials: Effect of Influent COD/N Ratios

Discharge of nitrogen (N) with wastewater causes eutrophication in surface water. On the other hand, nutrient-rich wastewater can be valuable for agriculture. Tailoring N removal or conservation is important to meet the requirements of different water end uses. Improved vertical flow constructed wetlands with hydroponic materials (CWH) as substrata were developed at lab scale in a greenhouse and studied to optimize N removal in CWH. This study investigated the effect of influent COD/N ratios of 5/1 and 15/1 on the removal or conservation of N in CWHs with Syngonium as vegetation and three substrata, pumice, cocopeat, and mineral wool. CWH with pumice showed the highest TN removal at both COD/N ratios. The Syngonium plant significantly contributed to the additional 50% TN removal in CWH. Nitrification of above 90% was observed at both studied COD/N ratios, indicating sufficient oxygenation due to the vertical pulse flow operated CWH. The denitrification process was enhanced at a higher COD/N ratio of 15/1 compared to 5/1 by around 10–40%. The occurring nitrification and denitrification indicate the coexistence of aerobic and anaerobic conditions in CWH, and balancing these conditions is necessary for future applications to remove N for its specific end use, i.e., irrigation water (high standards) or discharge to surface water (low standards).

Composite iron-carbon constructed wetland combined with photocatalytic film to restore eutrophic water body and the hydraulic performance of constructed wetland

Eutrophication is a globally faced environmental issue against which water resources need to be protected as it impairs water quality, threatens the safety of drinking water, and hinders the sustainable development of the regional economy. Given severe environmental impacts and risks of eutrophication, there is an urgent need for an effective method to restore eutrophic surface water bodies. This study proposed an effective technical program for a composite iron‑carbon constructed wetland combined with a photocatalytic film (WIC&PF) to restore eutrophic water. The removal efficiencies of WIC&PF were estimated at 81.77 ± 6.98 % for ammonia nitrogen (NH4+-N), 79.18 ± 5.58 % for total nitrogen (TN), 80.45 ± 5.55 % total phosphorus (TP), 80.12 ± 5.87 % for chemical oxygen demand (COD) and 93.96 ± 4.68 % for chlorophyll a. According to the experimental results, compared with the pre-treatment water quality, the post-treatment water quality improved significantly. A large number of microalgae growing on WIC&PF exerted a significant reoxygenation effect on the treated water, improving the self-purification capacity of the receiving water body. Boosting the pollutant removal efficiency via enhancing the hydraulic performance of constructed wetlands as well as the activity of photocatalytic films may serve to improve the remediation of eutrophic water bodies.

Use of Meltblown Nonwoven Fabric Filter for Stormwater Runoff Treatment

Anthropogenic activities (e.g., rural urbanization) play major roles in preventing the achievement of sustainable water quality, where eutrophication—the exacerbation of increase in nutrient concentrations combined with warmer temperatures and lower light availability, leading to the dense growth of plant life depleting the amount of available oxygen and killing aquatic life—remains a major challenge for surface water bodies. Filtration mechanisms, with a wide range of applicability, capture common waterborne pathogens as small as 0.1–20.0 μm (bacteria, cysts, spores) and 0.001–0.100 μm (protein, viruses, endotoxins) through the process of microfiltration and ultrafiltration. This study follows the premise of using a designed water flow-through system, with meltblown nonwoven fabrics to measure its performance to capture water contaminant constituents of surface water contamination and eutrophication: total coliforms, nitrate, and orthophosphate. The achieved fabric filtration mechanism showed capture of total coliforms (59%), nitrate (51%), and orthophosphate (46%). The current study provides an alternative solution to more common and traditional water treatment technologies, such as chlorine and ozone disinfection, which (1) introduces disinfection or treatment byproducts and (2) cannot adapt to the permanent changing conditions and newer environmental challenges.

Effect of Incorporating Cowpea (&amp;lt;i&amp;gt;Vigna unguiculata&amp;lt;/i&amp;gt;) Meal into Broiler Diets on Environmental Pollution by Nitrogen from Poultry Excreta: A Review

Poultry feeds are formulated using soybean meal and animal by-products as sources of protein. Animal proteins like fish meal, blood meal, meat and bone meal are being shunned in formulating poultry feeds nowadays because they are associated with zoonotic diseases like salmonellosis and this has left soybean meal as the only source of dietary protein in broiler feeds. Soybean meal is in short supply in Zimbabwe and this country is relying on some soybean meal imports from South Africa and Zambia resulting in prices of poultry feed and broiler meat going upwards. Cheap and locally available alternative sources of protein to soybean meal must be found in order to reduce the cost of making poultry feed. The selected alternative source of protein must have protein which is highly digestible such that the bulk of this protein can be metabolized and utilized by broilers to synthesize meat leaving a little of it to be excreted through faeces and urine. Highly digestible protein is very important in broiler feed making because this reduces the amount of nitrogen lost through poultry excreta into the environment. Cowpea has been chosen to entirely or partially replace soybean meal in this review paper because it is locally grown, drought tolerant, cheap and its true protein digestibility (TPD) of 71% to 76% is generally comparable to 81% to 83% of soybean meal. Nowadays, people are concerned about protecting the environment from being polluted by wastes from industrial and agricultural activities. Poultry farming pollutes the environment with ammonia emitted from poultry excreta. The grain legumes used in formulating broiler feed such as soybean meal contain anti-nutritional factors which reduce protein digestibility and increase nitrogen excretion through poultry faeces. The nitrogen in faeces is volatilized into ammonia, emitted into the atmosphere and cause eutrophication of surface waters. Therefore, the effect of incorporating cowpea meal in broiler diets on environmental pollution by nitrogen excretion from broiler faeces needs to be explored.

Evaluation of flue gas desulfurization gypsum as a low-cost precipitant for phosphorus removal from anaerobic digestion effluent filtrate

Land application of anaerobic digestion (AD) effluent as a fertilizer is desirable for nutrient recycle, but often supplies excess phosphorus (P), which contributes to surface water eutrophication. Reducing the P content in AD effluent using calcium treatment prior to land application is a potential strategy for improving effluent disposability. In order to solve the problems of low phosphorus removal efficiency and high operating cost in wastewaters, this study took flue gas desulphurization (FGD) gypsum, a by-product of coal-fired power plants, as a low-cost calcium source, and combined with traditional phosphorus removal agents to achieve high phosphorus removal efficiency with less chemical inputs. As the results showed, FGD gypsum dosages of 20 mM Ca (3.44 g/L) and 40 mM Ca (6.89 g/L) removed up to 97.1% of soluble P (initially 102.8 mg/L) within 60-90 minutes. Combining FGD gypsum treatment with traditional chemical treatments using Ca(OH)2 or FeCl3 could achieve >99% P removal with reduced chemical costs. This study demonstrated that FGD gypsum is an effective calcium precipitant for phosphorus removal.

Hydrological transport pathways of dissolved organic nitrogen and their seasonal changes in an agricultural watershed

The role of dissolved organic nitrogen (DON) in the eutrophication of surface water and the potential risk to drinking water safety as a precursor of disinfection by-products is gradually emphasized. Therefore, accurate estimates of watershed DON load fluxes and identifying thresholds of streamflow that cause abrupt changes in riverine DON concentration are important. Here, we adopted the load estimator model (LOADEST) and nonparametric change-point analysis (nCPA) to comprehensively investigate the variation of DON load from 2011 to 2016 in different seasons in the Fengyu River watershed, Southwest China. Results indicated that the wet season is the hot moment of DON loss, and the average cumulative load reaches 14.1 t, accounting for 72.5 % of the annual load. Meanwhile, baseflow is the main pathway of DON export, accounting for about 74.4 % of the stream export load. Furthermore, the abrupt threshold of streamflow on DON concentration is 2.03 m3/s to 2.15 m3/s. When the stream flow is below 2.15 m3/s, the concentration of river DON increases rapidly and poses a great threat to human drinking water safety. This study will provide a scientific basis for regulating DON at the watershed scale and water quality protection in drinking water source areas.

Improving performance of pilot-scale ecological bed coupled with microbial electrochemical system for urban tail water treatment

Recycling urban tail water for ecological base flow and landscape use offers a reliable solution for the problem of water resource shortage. But the long-term direct discharge of urban tail water can aggravate the eutrophication of surface water based on the present drainage standard of sewage plant. It is of great significance to develop low-cost and low-energy ecological technologies as transitional region between urban tail water and surface water. In this study, a pilot-scale ecological bed coupled with microbial electrochemical system (EB-MES) was established to treat urban tail water deeply. The system was operated for 96 days from June to September. Average TN removal efficiency in EB-MES under the condition of submerged plant coupled closed-circuit MES could reach 59.0 ± 16.6 %, which was 82.7 % and 38.1 % higher than that of open-circuit EB-MES and MES without plants, respectively. Microbial community structure testing indicated that multiple nitrogen metabolic mechanisms occurred in the system, including nitrification, electrode autotrophic denitrification, anammox, simultaneous nitrification and denitrification, and aerobic denitrification, which results in better denitrification efficiency under tail water. Our research provided a novel ecological technology with advantages of high-efficiency, low-energy and low-carbon and verified the feasibility in pilot scale for application in the advanced treatment of urban tail water.

Modelling of electrochemical phosphate removal from water

Phosphate contamination in surface water is a common problem that still needs a dependable solution because the presence of phosphate is the main motivator of the eutrophication of surface water which leads to many economic and health problems. In terms of the economy, eutrophication ruins the quality of the water inhibits tourism activities and requires expensive treatments and management plans. While in terms of health, eutrophication results in the generation of toxins via algal activities. The present article presents the results of phosphate removal from water using an electrocoagulation unit supplied with aluminium electrodes, and also it presents the results of modelling of phosphate removal by the electrocoagulation method. The experimental work focused on the effects of distance between electrodes (D), current density (CD) and contact time (Time), and the modelling process was developed using Response Surface Methodology (RSM) (a three-factor Box-Behnken design). The results of both experimental and modelling studies were agreed with an R2 of 0.9779, and it was noticed that the 20 mg/L of phosphate was removed after 55 minutes of electrolysing at CD of 5 mA/cm2 and D of 3 mm. The results encourage the use of this method for phosphate removal from domestic wastewater or use the method as a pre-treatment for industrial wastewater because the latter is usually highly loaded with phosphate.

Inversion and Monitoring of the TP Concentration in Taihu Lake Using the Landsat-8 and Sentinel-2 Images

Eutrophication is a significant factor that damages the water ecosystem’s species balance. The total phosphorus (TP) concentration is a vital water quality indicator in assessing surface water eutrophication. This paper predicts the spatial distribution of TP concentration using remote sensing, measured data, and the partial least squares regression (PLSR) method. Based on the correlation analysis, the models were built and tested using the TP concentration and Sentinel-2 Multispectral Instrument (MSI) and Landsat-8 Operational Land Imager (OLI) image spectra. The results demonstrated that the best technique based on band combinations of the Sentinel-2 and Landsat-8 images achieved good precision. The coefficient of determination (R2), root mean square error of prediction (RMSEP), and residual prediction deviation (RPD) were 0.771, 0.023 mg/L, and 2.086 for Sentinel-2 images and 0.630, 0.032 mg/L, and 1.644 for Landsat-8 images, respectively. The TP concentration maps were interpolated using the inverse distance weighting method, and the inversion results obtained from the images were in good agreement. The western and northwestern regions of Taihu Lake, where significant cyanobacterial blooms occurred, had TP concentrations greater than 0.20 mg/L; nevertheless, the central and eastern regions had amounts ranging from 0.05 to 0.20 mg/L. In order to prove the extensibility of the model, the optimal algorithm was applied to the Sentinel-2 and Landsat-8 images in 2017. The optimal algorithm based on Landsat-8 images has a better verification effect (RMSEP = 0.027 mg/L, and R = 0.879 for one Landsat-8 image), and the optimal algorithm based on Sentinel-2 images has moderate verification effect (RMSEP = 0.054 mg/L and 0.045 mg/L, and R = 0.771 and 0.787 for two Sentinel-2 images). The interpolation and inversion maps are in good agreement, indicating that the model is suitable for the Landsat-8 and Sentinel-2 images, which can be complementary for higher temporal resolutions. Monitoring water quality using multiple remote sensing images can provide the scientific basis for water quality dynamic monitoring and prevention in China.

Surface Water under Growing Anthropogenic Loads: From Global Perspectives to Regional Implications

This paper reviews currently available evaluations of the effects of continuously increasing anthropogenic loads on water resources. The increase in the fluxes of elements and compounds into the environment, such as the emission of greenhouse gases and dispersion of nutrients (nitrogen and phosphorus), acidifying gases, and toxic elements and compounds that adversely affect water quality, are considered. The significance of fresh waters as a life support factor for human populations is demonstrated. Examples illustrate how key anthropogenic-induced processes develop in land waters under the effect of anthropogenic loads, as exemplified by the Russian Kola regions. Climate warming and the increasing dispersion of elements are demonstrated to result in the eutrophication of surface waters, even in areas remote from anthropogenically impacted regions. Although the emissions of acidifying gases diminish, the waters are still acidified in acid-vulnerable areas, and the chemical compositions of the waters have been significantly modified over the past decades, indicating that the changes in the chemical composition of the waters are irreversible. A new feature of the waters is distinguished: the toxicity of the habitats for aquatic organisms. The novelty of the work was to highlight the bridge between anthropogenic loads on surface water on a planetary scale and their consequences in certain regions, which reflect changes in water quality. Arguments are presented for establishing a theoretical approach for evaluating critical loads.

Spatial effects of urban green infrastructure on instream water quality assessed by chemical and sensory indicators

Urban green infrastructure has been simulated effectively and economically to reduce volume and pollutants of stormwater runoffs but its spatial effects remain unclear. A snap sampling campaign was carried out for surface water quality in the downtown waterway network of a pilot sponge city (Suzhou) in China, dividing into 7 subwatersheds according to the digital elevation map. In total, 144 sampling points were investigated and measured for chemical quality of surface water while 68 out of the sampling points had a sensory evaluation questionnaire interview for water quality with 321 respondents, in whom the native residents scored a significant spatiality of water quality. The downtown waterway network had phosphorus-limited eutrophic surface water with total nitrogen worse than Class V of the national guidelines. Chemical and sensory evaluation indexes of surface water quality had significant spatial consistency (p < 0.001). All types of green spaces (%) in subwatershed, especially along the urban waterway network (waterfront) and roadside, and in the 100 m riparian buffer zone, significantly influenced nutrient loads in surface water. Findings of the present study suggest that the 100 m riparian buffer zone would be priority areas and the waterfront and roadside should be the highly efficient spots for planning strategy on urban green infrastructure implementation to reduce nutrient loads in surface water and to improve urban landscape aesthetics.