Nitrate Loading Research Articles

High Resolution Mapping of Nitrate Loads of a Reservoir Using an Uncrewed Surface Vehicle: Potential Opportunities and Challenges

AbstractReliable nutrient load estimation of a reservoir is challenging due to inconsistent spatial extent and temporal frequency of water quality and quantity measurements. This study aims to collect consistent spatial extent and temporal frequency of water depths and nitrate concentrations of a reservoir in South Korea using uncrewed surface vehicle (USV). In this study, reservoir nitrate loads were estimated using four methods to examine how spatial variation in water depth and nitrate concentrations affected load estimates. Based on dual measurements of water depth and nitrate concentration, reservoir nitrate loads across 30 sampling dates (0.7 million tons of fresh water on average) ranged from one to four tons. Results showed that a point measurement of water depths and nitrate concentrations can cause up to −17% of underestimation of nitrate loads, particularly after intense rainfall events. This study highlights potential opportunities and challenges of the USV‐based dual monitoring systems for water quality and quantity.

Adapting to seasonal temperature variations: A dynamic multi-subunit strategy for sulfur autotrophic denitrification bioreactors

Elemental sulfur autotrophic denitrification (S0AD) processes are temperature-sensitive, presenting a substantial challenge for the practical implementation of S0AD bioreactors. In this study, a comprehensive methodology for designing and operating S0AD bioreactors was developed, effectively managing fluctuations in nitrogen removal efficiency caused by seasonal temperature variations. Initially, the nitrate removal rate was correlated with simulated on-site temperature and nitrate loading, revealing correlation coefficients of k1, k2, k3, and A as 5.42×10−4, −0.41, 0.04, and 0.13, respectively, to establish a mathematical model for predicting S0AD efficiency. Subsequently, by considering influence factors such as dissolved oxygen and dynamic sulfur consumption, the model was employed to accurately design a pilot-scale S0AD bioreactor for a case study. By utilizing an alternative multi-subunit operation, a stable effluent nitrate concentration of less than 8 mg-N/L was maintained throughout the year. Importantly, this approach resulted in a substantial reduction of 76.8% in excessive nitrate removal, sulfur consumption, and sulfate production. This study aims to provide an optimal design and operation strategy for the practical application of S0AD bioreactors, thereby enhancing reliability and cost-effectiveness in the face of seasonal temperature changes.

Balancing upland green infrastructure and stream restoration to recover urban stormwater and nitrate load retention

Urban watersheds have experienced ecosystem degradation due to land cover change from vegetation to impervious areas. This transformation results in increased stormwater runoff, stream channel erosion and sedimentation, and both increased inputs and reduced ecosystem retention of nutrients. Ecosystem restoration practices, including terrestrial and aquatic low impact development (LID), are becoming widely implemented in urban watersheds globally. A major question is how “green” and “grey” infrastructure can be optimally balanced to shift ecohydrological behavior towards pre-urbanization conditions. Traditional stormwater engineering typically controls runoff by temporary storage (detention) and release of stormwater, while LID designs are developed to reduce runoff by a combination of infiltrating precipitation and evapotranspiration, while promoting biogeochemical retention of nutrients. These practices are often combined with stream and riparian restoration that increases nutrient retention and reduces in-stream loads. In this study, we simulated the potential impact of three types of terrestrial LID and green infrastructure (GI) on watershed runoff and nitrate (NO3–) loading to local streams, independent of detention storage effects. The treatments included increased tree canopy, vegetated roadside bioswales, and permeable pavement. We then evaluated the individual and interactive impacts of these practices on the effectiveness of NO3– load reduction provided by stream restoration, which is affected by the altered runoff and nutrient loading caused by the LID and GI. Urban reforestation provided the highest effectiveness in terms of reducing stormflow and nutrient export, while bioswales and permeable pavement unexpectedly increased in-stream NO3– loads. Retrofit of the previously developed watershed by LID/GI alone may not provide sufficient mitigation in stormwater and nutrient loads, and should be balanced with additional grey infrastructure, such as detention ponds, rain cisterns, and sewer system upgrades.

Water quality at the end of the Mississippi River for 120 years: the agricultural imperative

AbstractArchived water quality data collected between 1901 and 2019 were used to reconstruct annual averages of various forms of C, N, P, and silicate concentrations and alkalinity in the lower Mississippi River. During this interval the average annual nitrate concentrations doubled pre-dominantly from fertilizer applications and tiling, silicate concentrations decreased by half as diatom sedimentation increased as dams were built, and alkalinity increased 16%. Variances in silicate concentrations were proportional to river discharge before 1980 and concentrations have been stable since then. Average annual temperatures, discharge and alkalinity increased simultaneously around 1980; this suggests that there was greater weathering thereafter and is supported by the positive relationships between variations in alkalinity and variations in nitrate, phosphate, and silicate concentrations. The conversion of forests and grasslands into farmlands and improved drainage resulted in less evapotranspiration, a higher percent of precipitation going into streams and altered soil water bio-geo-chemistries. Field trials demonstrating soil health improvements resulting from more live roots and soil cover and greater biodiversity demonstrate water quality improvements and no effect on farm profitability. Lowering nitrate loading to the coastal waters will reduce summertime hypoxic waters formation offshore, but alkalinity in the river will increase further with climate warming.

Autotrophic nitrogen polishing of secondary effluents: Alkaline pH and residual nitrate control S0-driven denitratation for downstream anammox treatment

Energy-lean nitrogen removal technologies, such as partial nitritation/anammox, often encounter effluent issues due to elevated nitrate and ammonium levels. This study proposed a novel autotrophic polishing strategy coupling sulfur-driven denitratation with anammox. To explore the denitratation potential in obtaining stable and sufficient nitrite accumulation, the effects of pH, residual nitrate level, and biomass-specific nitrate loading rate (BSNLR) were investigated in an S0-packed bed reactor at low hydraulic retention time (i.e., 0.2 h). Implementing pH and residual nitrate control strategies would be easier in practice than BSNLR control to polish secondary effluent. Alkaline pH values could realize successful nitrite accumulation without residual nitrate, and further intensify the accumulation under increased residual nitrate levels. The nitrate level was positively correlated with the nitrite accumulation efficiency. At pH 8.5 and nitrate concentration of 1.0 ± 0.8 mg N L−1, sulfur-driven denitratation could successfully maintain nitrite accumulation of 6.4 ± 1.0 mg NO2−-N L−1, ideally for the downstream anammox in case of residual ammonium levels of around 5 mg N L−1. Since Thiobacillus members play a key role in managing nitrite accumulation, their abundance should be guaranteed in the practical application.

Molecular insights into nitrogen constraint for niche partitioning and physiological adaptation of coastal Synechococcus assemblages

Coastal nitrogen input has substantially increased due to human activity. However, much remains unknown about the nitrogen-driven patterns and the underlying genetic basis of coastal picoplankton. To investigate the response and mechanisms of picoplankton induced by nitrogen variation, we conducted in-situ investigations using high-throughput sequencing in the Bohai Sea and performed laboratory nitrogen simulation experiments accompanied by physiological, genomic, and transcriptomic analyses, with Synechococcus as a representative. The results of in-situ investigation revealed that Synechococcus clades I, III, WPC1, and VI of subcluster 5.1 (S5.1) are prevalent in strait areas characterized by robust water exchange with the North Yellow Sea, while clades II, VIII, and IX of S5.1, as well as subcluster 5.2 (S5.2) and subcluster 5.3 (S5.3) are more abundant in central and bay areas experiencing elevated nitrate and nitrite loads. The laboratory experiments further confirmed that inorganic nitrogen is a crucial determinant of diversity and niche partitioning of Synechococcus lineages. Besides, the raising inorganic nitrogen concentration within the current in-situ range (0.1–10 μmol L−1) enhances photosynthesis and carbon fixation of Synechococcus, however further escalation of inorganic nitrogen (100 μmol L−1) may hinder these processes instead. The phenomenon could be associated with the differential expression of genes in metabolic pathways regulating nitrogen metabolism, photosynthetic system II, and photosynthesis-antenna proteins in response to nitrogen concentration and type variation. These findings expand our understanding of the impact of macronutrient variation resulting from human activities on marine picoplankton and biogeochemical cycles.

Accounting for the annual variability when assessing non-point source pollution potential in Mediterranean regulated watersheds

The characterization of non-point source pollution at the watershed scale difficult owing to its distributed nature combined with the lack of suitable measurements for validation. This study proposes the classification of land within a Mediterranean watershed according to its potential source of non-point pollution, considering interannual precipitation variability and dam regulation effects. For this purpose, the potential non-point pollution index (PNPI) developed by the Italian Environmental Protection Agency was modified to include annual local precipitation behavior, named local annual PNPI (APNPI). PNPI and APNPI were computed for the Guadalquivir River (Spain), which has a drainage surface of 57,500 km2 and is highly regulated by >60 reservoirs. The results reflect the vulnerability along the Guadalquivir River in terms of the spatially variable non-point pollutant nature of its contributing watersheds. The annual average nitrate concentration values on the southern side exceeded the average value on the northern side by almost five times and showed a statistically significant power fit with the PNPI, with an R2 of 0.65. Long-term available nitrate data (1981/82–2006/07) on a monthly scale at the outlets of some watersheds allowed us to rank priority pollutant source areas within the watershed. The power fits between the annual average nitrate loads and the APNPI (R2 = 0.51–0.99) were statistically significant, which validated the utility of adding the variability of precipitation at an annual scale as a dynamic factor in the index. The APNPI can constitute a simple dynamic classification index for assessing the relative risk of non-point source pollution across a large area, especially in data-scarce situations.

A century of nitrogen dynamics in agricultural watersheds of Denmark

Intensive agriculture has been linked to increased nitrogen loads and adverse effects on downstream aquatic ecosystems. Sustained large net nitrogen surpluses have been shown in several contexts to form legacies in soil or waters, which delay the effects of reduction measures. In this study, detailed land use and agricultural statistics were used to reconstruct the annual nitrogen surpluses in three agriculture-dominated watersheds of Denmark (600–2700 km2) with well-drained loamy soils. These surpluses and long-term hydrological records were used as inputs to the process model ELEMeNT to quantify the nitrogen stores and fluxes for 1920–2020. A multi-objective calibration using timeseries of river nitrate loads, as well as other non-conventional data sources, allowed to explore the potential of these different data to constrain the nitrogen cycling model. We found the flux-weighted nitrate concentrations in the root zone percolate below croplands, a dataset not commonly used in calibrating watershed models, to be critical in reducing parameter uncertainty. Groundwater nitrate legacies built up in all three studied watersheds during 1950–1990 corresponding to ∼2% of the surplus (or ∼1 kg N ha yr−1) before they went down at a similar rate during 1990–2015. Over the same periods active soil nitrogen legacies first accumulated by approximately 10% of the surplus (∼5 kg N ha yr−1), before undergoing a commensurate reduction. Both legacies appear to have been the drivers of hysteresis in the diffuse load at the catchments’ outlet and hindrances to reaching water quality goals. Results indicate that the low cropland surpluses enforced during 2008–2015 had a larger impact on the diffuse river loads than the European Union’s untargeted grass set-aside policy of 1993–2008. Collectively, the measures of 1990–2015 are estimated to have reset the diffuse load regimes of the watersheds back to the situation prevailing in the 1960s.

Looking back to move forward: Restoring vegetated canals to meet missing Water Framework Directive goals in agricultural basins

Nitrate pollution and eutrophication remain pressing issues in Europe regarding the quality of aquatic ecosystems and the safety of drinking water. Achieving water quality goals under the Water Framework Directive (WFD) has proven to be particularly challenging in agricultural catchments, where high nitrate concentrations are the main reason for the failure of many water bodies to meet a good ecological status. Canals and ditches are common man-made features of irrigated and drained landscapes and, when vegetated, have recently been identified as denitrification hotspots.By combining experimental data and GIS-based upscaling estimation, the potential capacity of the canal network to reduce nitrate loads was quantified in several scenarios differing in the level of nitrate pollution and in the extent of the canal network length where conservative management practices are implemented. The analysis was carried out in the irrigated lowlands of the Po River basin, which is the largest hydrographic system in Italy and a global hotspot for nitrogen inputs and eutrophication.Scenario simulations showed that maintaining aquatic vegetation in at least 25 % of the canal network length, selecting sites with high nitrate availability (>2.4 mg N L−1), would promote a greater potential for permanent N removal. The increased denitrification capacity would meet the load reduction target required to achieve a WFD good ecological status in waters draining into the Adriatic Sea during the spring-summer months, when the eutrophication risk is higher. Promoting denitrification in the canal network by postponing the mowing of in-stream vegetation to the end of the growing season could be an effective mitigation strategy to improve water quality in agricultural basins and contribute to achieving the WFD goals.

Enhanced nitrogen removal performance of microorganisms to low C/N ratio black-odorous water by coupling with iron-carbon micro-electrolysis

Black-odorous water was caused by urbanization, industrial sewage and domestic sewage. Black-odorous water with low carbon nitrogen ratio (C/N) may inhibit the activity of microorganisms due to the lack of C source during microbial treatment. In this study, iron-carbon micro-electrolysis (ICME) was used to couple nitrifying and denitrifying bacteria. The external factors affecting microbial activity were optimized through experiments, and the effect of low C/N wastewater was studied. The optimal external factors were temperature of 30 ℃, C/N of 3, DO of 3 mg/L and iron-carbon dosage of 150 g/L. Coupled with ICME, it was found that the removal rate of nitrate nitrogen in water increased by 50.74 %, indicating that ICME could make up for the deficiency of microbial C source and improve the removal rate of nitrate nitrogen in low C/N black-odorous water. The improvement of removal rate had much to do with ICME's role as electron donor to provide electrons for denitrification. In addition, the performance of wastewater treatment by this process is tested. The maximum load of ammonia nitrogen, COD, nitrate and total nitrogen was increased to 0.1928, 1.7732, 0.2691 and 0.5181 kg/(m3·d), respectively. High-throughput sequencing results showed that the species of dominant plant population changed after ICME coupling, but the abundance increased significantly, which further indicated that ICME played a synergic role in microbial nitrogen removal, which was related to the release of trace iron by ICME. This study can provide some guidance for the treatment of black-odorous water with high ammonia nitrogen and low C/N.

Improving nitrate load simulation of the SWAT model in an extensively tile-drained watershed

Subsurface drainage systems are effective management practices employed to remove excess soil water, thereby improving soil aeration and crop productivity. However, these systems can also contribute to water quality issues by enhancing nitrate leaching and loads from agricultural fields. The Soil and Water Assessment Tool (SWAT) is commonly used to assess nitrate loads and long-term water quality impacts from agricultural watersheds. However, the current SWAT model oversimplifies nitrate transport processes by assuming a linear relationship between nitrate concentrations in tile flow and soil nitrate content. It also neglects the time lag between nitrate loading and transport with the flow. This study aimed to enhance the accuracy of nitrate load prediction by revising the subsurface drainage routine in the SWAT model. The revised routine was tested using flow and nitrate load measurements from a typical tile-drained watershed in east-central Illinois, U.S. The results demonstrated that the revised SWAT nitrate routine outperformed the current one in simulating nitrate transport at field and watershed scales. The revised routine improved the nitrate load prediction from an “unacceptable” to a “satisfactory” or “good” rating on the field scale. A sensitivity analysis conducted using the revised nitrate module showed the parameters directly associated with transpiration, groundwater discharge to the reach, the lag time of tile flow, and channel flow hydraulics were the most sensitive in nitrate load simulation. In addition, different tile depth scenarios were modeled to evaluate variation in the amount of surface runoff, tile flow, and nitrate loads by the surface flow and tile flow. The results of tile configuration scenarios agreed with understanding the tile flow process. The test results demonstrated the potential of the revised SWAT nitrate module as a tool to accurately evaluate the effects of tile drainage systems on water quality.

Simultaneous denitrification and electricity generation in a methane-powered bioelectrochemical system.

Bioelectrochemical system is a novel method for controlling down nitrate pollution, yet the feasibility of using methane as the electron donors for denitrification in this system remains unknown. In this study, using the effluent from mother BESs as inocula, a denitrifying anaerobic methane oxidation bioelectrochemical system was successfully started up in 92 days. When operated with 50 mmol/L phosphate buffer solution at pH7 and 30°C, the maximum methane consumption, nitrate, and total nitrogen removal load reached 0.23 ± 0.01 mmol/d, 551.0 ± 22.1mg N/m3 /d, and 64.0 ± 18.8mg N/m3 /d, respectively. Meanwhile, the peak voltage of 93 ± 4mV, the anodic coulombic efficiency of 6.99 ± 0.20%, and the maximum power density of 219.86 mW/m3 were obtained. The metagenomics profiles revealed that the dominant denitrifying bacteria in the cathodic chamber reduced most nitrate to nitrite through denitrification and assimilatory reduction. In the anodic chamber, various archaea including methanotrophs and methanogens converted methane via reverse methanogenesis to form formate (or H2 ), acetate, and methyl compounds, which were than utilized by electroactive bacteria to generate electricity. PRACTITIONER POINTS: A denitrifying anaerobic methane oxidation BES was successfully started up in 92 d. Simultaneous removal of methane and nitrate was achieved in the DAMO-BES. Functional genes related to AMO and denitrification were detected in the DAMO-BES. Methylocystis can mediate AMO in the anode and denitrification in the cathode.

Evaluation of Agricultural BMPs’ Impact on Water Quality and Crop Production Using SWAT+ Model

Subsurface (or tile) drainage improves land productivity by enhancing soil aeration and preventing water-logged conditions. However, the continuous expansion of drained agricultural lands and reliance on synthetic fertilizer in the Midwestern United States have increasingly facilitated nitrate transport from agricultural fields to surface water bodies. Hence, there is a need to implement various agricultural best management practices (BMPs) in order to reduce the adverse water quality impacts resulting from excess nitrate, such as eutrophication and the formation of hypoxic zones. In this study, we used a SWAT+ model to assess the overall impacts on the riverine nitrate load and crop yield in the corn–soybean cropping system based on a combination of different management practices. The corn and soybean yields simulated with the model were found to be in good agreement with the observed yields for both the calibration and validation periods. The long-term simulation over a period of 30 years showed a reduction in the nitrate load of up to 32% without impacting the crop yield. The model results suggest that by reducing the current N application rate by 20% and using a 40:60 split between spring pre-plant and side-dressing N applications combined with cereal rye as a cover crop in corn–soybean rotation, one can potentially reduce nitrate losses without impacting crop yields. This study will help researchers, stakeholders, and farmers to explore and adopt alternative management practices beneficial for offsetting the environmental impacts of agricultural productions on the watershed scale.

Nitrate leaching potential from arable land in Germany: Identifying most relevant factors

Diffuse nitrogen losses from agriculture in Germany continue to cause regionally increased nitrate concentrations in groundwater. Groundwater quality monitoring cannot be a timely indicator of the effects of mitigation measures being applied in agriculture, due to frequently long transport routes and high residence times of the leachate. Instead, nitrate leaching potential is often determined at field and farm scale by monitoring soil mineral nitrogen contents at 0–90 cm depth in autumn (SMNa), i.e. before the start of the annual leachate period. In this study, we developed an understanding of the controls on the soil mineral nitrogen content at the start of winter. In an on-farm approach, extensive data was collected from 48 farms in five nitrate-sensitive regions in Germany from 2017 to 2020. From this data set, 25 management and site factors were evaluated with regard to their significance for SMNa by means of a random forest model. With the random forest regression, we identified the role of the factors on SMNa with an acceptable model accuracy with R2 = 0.56. The results show that the cultivated crop is the most important factor influencing SMNa. Potatoes, oilseed rape and maize produced the highest SMNas, whereas SMNas were lowest after spring barley, sugar beet and winter barley. Among site factors, soil type and texture as well as precipitation in October were most decisive. The effects of N fertilisation parameters such as rate and timing were masked by these site factors. The results show that the reduction of nitrogen-intensive crops in crop sequences can be a promising measure for the reduction of nitrate loads. On the other hand, our analysis makes clear that soil-related factors controlling nitrogen release and risk of leaching, as well as weather, can significantly mask the effect of cultivation.

Assessment of nutrients and conductivity in the Wachusett Reservoir watershed: An investigation of land use contributions and trends

The quality of drinking water for the Boston Metropolitan Area, supplied by the Quabbin-Wachusett system, is impacted by environmental trends. The objectives of this study are to increase understanding of the role that small streams may play in degradation of reservoir quality by characterizing seasonal constituent patterns from 1998 to 2020 in the Wachusett Reservoir watershed and by developing enhanced modeling frameworks. Previous monitoring (1998–2012) exhibited increased loads due to increasing flows despite declining solute concentration. This present study analyzed seasonal nitrate (NO3) and total phosphorus (TP) concentration and load trends from 2012 to 2020 across 11 tributaries. Specific conductivity (SC) was also assessed to evaluate the impacts of road salt application. From 2012 to 2020, statistical results for mean nutrient concentrations suggest static or declining temporal trends, while SC in all tributaries exhibited increasing trends. Land use data suggest association with altered drainage landscapes as potential sources of increased constituent transport. Subbasins with the highest concentrations of TP, NO3, and SC have the largest percentage of impervious and cultivated areas, two to three times greater than other subbasins. Daily flows were modeled using the airGR hydrological model, subsequently used to calculate loads. Overall, flow magnitude was a more important load driver than long-term nutrient concentrations, thus, showing that stream discharge controlled load variability. On the other hand, persistently high SC levels controlled the increasing SC load trends. Finally, many nutrient reduction management strategies demonstrated an important impact from 1998 to 2020. Despite watershed programs aimed at reducing salt applications, concentrations in streams are increasing, indicating a long-term legacy of salt accumulation. Although smaller tributaries represent a modest portion of the system, addressing these sources has the potential to further reduce the long-term ecological impacts of reservoir constituent loading.

Effects of climate change on streamflow and nitrate pollution in an agricultural Mediterranean watershed in Northern Spain

Predicting water quality and quantity response to climate change in a watershed is very difficult due to the complexity and uncertainties in estimating and understanding future hydrological conditions. However, hydrological models could simplify the processes and predict future impacts of agricultural activities. This study aimed to evaluate the applicability of the Soil Water Assessment Tool (SWAT) model for climate change prediction of streamflow and nitrate load in an agricultural Mediterranean watershed in northern Spain. The model was first evaluated for simulating streamflow and nitrate load under rainfed agricultural conditions in the Cidacos River watershed in Navarre, Spain. Then, climate change impact analysis on streamflow and nitrate load was conducted in the short-term (2011–2040), medium-term (2041–2070), and long-term (2071–2100) future projections relative to the historical baseline period (1971–2000) under the RCP4.5 and RCP8.5 CO2 emission scenarios. The model evaluation showed a good model performance result during calibration (2000–2010) and validation (2011–2020) for streamflow (NSE = 0.82/0.83) and nitrate load (NSE = 0.71/0.68), indicating its suitability for adoption in the watershed. The climate change projection results showed a steady decline in streamflow and nitrate load for RCP4.5 and RCP8.5 in all projections, with the long-term projection scenario of RCP8.5 greatly affected. Autumn and winter saw a considerable drop in comparison to spring and summer. The decline in streamflow was attributed to the projected decrease in precipitation and increase in temperatures, while the nitrate load decline was consistent with the projected streamflow decline. Based on these projections, the long-term projection scenarios of RCP8.5 indicate dire situations requiring urgent policy changes and management interventions to minimize and mitigate the resulting climate change effects. Therefore, adapted agricultural management practices are needed to ensure sustainable water resource utilization and efficient nitrogen fertilizer application rates in the watershed to reduce pollution.

Field‐scale analysis of miscanthus production indicates climate change may increase the opportunity for water quality improvement in a key Iowa watershed

AbstractThe Raccoon River Basin is the primary source for drinking water in Iowa's largest city and plays a major role in the Mississippi River Basin's high nutrient exports. Future climate change may have major impacts on the biological, physiological, and agronomic processes imposing a threat to ecosystem services. Efforts to reduce nitrogen (N) loads within this basin have included local litigation and the implementation of the Iowa Nutrient Reduction Strategy, which suggest incorporating bioenergy crops (i.e., miscanthus) within the current corn–soybean landscape to reach a 41% reduction in nitrate loads. This study focuses on simulating N export for historical and future land use scenarios by using an agroecosystem model (Agro‐IBIS) and a hydrology model (THMB) at the 500‐m resolution, similar to the scale of agricultural fields. Model simulations are driven by CMIP5 climate data for historical, mid‐century, and late‐century under the RCP 4.5 and 8.5 warming projections. Using recent crop profit analyses for the state of Iowa, profitability maps were generated and nitrogen leaching thresholds were used to determine where miscanthus should replace corn–soybean area to maximize reductions in N pollution. Our results show that miscanthus inclusion on low profit and high N leaching areas can result in a 4% reduction of N loss under current climate conditions and may reduce N loss by 21%–26% under future climate conditions, implying that water quality has the potential continue to improve under future climate conditions when strategically implemented conservation practices are included in future farm management plans.

Study on the performance of anodic desulfurization and cathodic denitrification coupled electricity generation in microbial fuel cell

Sulfide autotrophic denitrification microbial fuel cell was set up and the two reaction processes of desulfurization in anode chamber and denitrification in cathode chamber were separated to study nitrogen and sulfur removal effect and electricity generation capacity. The results showed that simultaneous desulfurization in anode chamber and nitrate removal in cathode chamber was feasible. The removal load of sulfide and nitrate almost increased with the increase of their concentrations under the experiment operation conditions. Higher sulfide concentration in a certain range was beneficial to generate electricity. The change of nitrate concentration in the cathode chamber had less effect on sulfide removal efficiency and electricity production performance of microbial fuel cell, which was mainly depended on the influent sulfide concentration in the anode chamber. The maximum sulfide and nitrate removal loads were 0.36 kg∙m−3∙d−1 and 0.07 kg∙m−3∙d−1 respectively, with a maximum power density of 144.03 mW∙m−3. The external resistance affected the quantities and varieties of reaction products in the anode chamber and the cathode chamber. Lower external resistance was beneficial to improve the efficiency of nitrate removal in the cathode chamber. The microbial community structure of the anode chamber in sulfide autotrophic denitrification MFC was similar to that of sulfide autotrophic denitrification SBR, whose main functional bacterial genera were Clostridium, Thiobacillus and Rhodobacteraceae. However, the functional bacteria in the cathode chamber were completely different, whose dominant bacteria included Thiobacillus, Bacillus, Flavobacteriaceae, Acinetobacter, Sphingomonas and Paracoccus. The research results provided a new idea and method for the sulfur- and nitrogen-containing wastewater treatment.

River Basin Simulations Reveal Wide-Ranging Wetland-Mediated Nitrate Reductions.

River basin-scale wetland restoration and creation is a primary management option for mitigating nitrogen-based water quality challenges. However, the magnitude of nitrogen reduction that will result from adding wetlands across large river basins is uncertain, partly because the areal extent, location, and physical and functional characteristics of the wetlands are unknown. We simulated over 3600 wetland restoration scenarios across the ∼450,000 km2 Upper Mississippi River Basin (UMRB) depicting varied assumptions for wetland areal extent, physical and functional characteristics, and placement strategy. These simulations indicated that restoring wetlands will reduce local nitrate yields and nitrate loads at the UMRB outlet. However, the projected magnitude of nitrate reduction varied widely across disparate scenario assumptions─e.g., restoring 4500 km2 of wetlands (i.e., 1% of UMRB area) decreased mean annual nitrate loads at the UMRB outlet between 3 and 42%. Higher magnitude nitrate reductions correlated with best-case assumptions, particularly for characteristics controlling nitrate loading rates to the wetlands. These results show that simplified claims about basin-scale wetland-mediated water quality improvements discount the breadth of possible wetland impacts across disparate wetland physical and functional conditions and highlight a need for greater clarity regarding the likelihood of these conditions at river basin scales.

Studies with spiral wound Donnan dialysis contactor for nitrate removal from contaminated water

In the present study, we investigated nitrate removal using Donnan dialysis aiming to scale up a process capable of treating 1 m3/day or more. Four different anionic membranes, FAD, FAS, and FAB by Fumatech GmbH and PCA 100 from PC-Cell, were screened in batch Donnan dialysis experiments with nitrate and/or sulfate using chloride as the driving ion. FAD, FAS and FAB showed similar nitrate flux while PCA 100 produced significantly lesser nitrate flux under experimental conditions. Based on the higher selectivity for nitrate over sulfate, FAS was preferred over FAD membrane. A spiral wound module contactor was fabricated each with the FAS and FAD membranes. The steady-state performance of the system revealed excellent nitrate removal at the selected operating conditions, successfully eliminating an average nitrate loading rate of 5.0 kg NO3−/m3/d and producing 30 ± 5 mg/L nitrate. Nitrate transport modeling using MATLAB was performed to predict exit nitrate concentration at any point along the path length of membrane at the given set of conditions. The output of the simulated model came out to be in reasonable agreement with the exit nitrate concentration measured experimentally, reflecting its robustness.