Total Nitrogen Load Research Articles

An Overview of the Effectiveness of Agricultural Conservation Practices for Water Quality Improvement.

This article introduces a Special Collection of literature reviews documenting the performance and cost-effectiveness of six agricultural conservation practices (ACPs): conservation crop rotation, cover crop, filter strip, nutrient management, denitrifying bioreactor, and constructed wetland. The overall objectives of the Special Collection are to: (1) review published studies on ACP effectiveness in reducing nutrient and sediment losses from agricultural fields; (2) compare, integrate, and synthesize the results from those studies to obtain a systematic understanding of the mitigation efficacy of each ACP in a consistent format across the selected ACPs; and (3) assemble cost analyses and obtain general insights on performance-based costs of the ACPs. The specific objectives of this introductory article are to summarize key information from each of the six review articles and develop a comparative understanding of the performance and cost-effectiveness of the six ACPs. Among the selected ACPs, denitrifying bioreactor, constructed wetland, cover crop, crop rotation, and nutrient management were all effective in reducing nitrate-N loads in subsurface drainage, with performance effectiveness in load reduction ranging from 23% to 40%. A corn-soybean rotation (relative to continuous corn) was the most cost-effective among the selected ACPs and can reduce nitrate-N load at a net benefit of about USD $5 per kg nitrate-N compared to continuous corn. Filter strip was most effective in reducing sediment, total nitrogen (N), and total phosphorus (P) loads from surface runoff and can be effective in reducing nitrate-N and dissolved P. Cover crop was also effective in reducing sediment and total P loads. Studies of the selected ACPs for their performance effectiveness for dissolved P are limited, and results varied among the ACPs included; thus, more research is needed relative to ACP effectiveness in reducing dissolved P loss, particularly in subsurface flow. Finally, although each review article included cost-analysis information, more data and analyses are needed to better understand the cost-effectiveness of ACPs and their ecological benefits.

Mechanism of water savings and pollution reduction in paddy fields of three typical areas in southern China

Field irrigation and drainage regulation and fertilization application could affect water utilization and pollution transportation in a paddy field. In this study, representative rice-producing areas of Zhejiang Province in southern China were selected to study the effects of different field water level control (conventional irrigation and drainage W0, controlled irrigation and drainage W1 and W2) and different fertilization methods (2 times of fertilization F2 and three times of fertilization F3) on water irrigation quantity and consumption of rice, rice growth, water utilization, and pollution reduction. Results showed that field water level control had a great effect on irrigation quota in growing period rather than that in soaking period, and irrigation quota for W0 was 37.0%-71.7% higher than that for W1 and W2 in the whole growth period of rice. Although the upper limit of rain storage was greatly increased by W1 and W2, on the contrary, the yield under W1 and W2 was 0.4%-2.1% higher than that under W0. Water consumption, water leakage, and evapotranspiration were 16.63%-34.4%, 39.97%-60.8%, and 9.40%-31.53% lower under W1 and W2 than those under W0, respectively, while it showed no significant changes under W1 and W2. Rainfall use rate and WUEI (water use efficiency of irrigation) under W1 and W2 had been significantly improved by 8.20%-129.58% and 31.58%-201.61% compared to W0. The contribution of nitrogen and phosphorus loss from surface water accounted for 90% and the total pollution load of total nitrogen (TN), NO3−-N, NH4+-N and chemical oxygen demand (COD) were 20.0%-63.4%, 21.8%-66.3%, 21.5%-63.8%, and 21.4%-46.5% lower for W1 and W2 than that for W0, respectively. Meanwhile, compared to F2, dispersed fertilization (F3) was beneficial to increase the yield and decrease pollutant load. Additionally, the path of IRA→NH4+-N→COD and IRA→WCA→WUEI presented partial remediation effect, and the effect size was 23.6% and 38.1%, respectively, the path of IRA→WUEI→WUEET presented a full remediation effect, and the path of IRA→WCA→WUEET presented suppression effect. Keywords: controlled irrigation and drainage, water consumption, water use efficiency, non-point source pollution, structural equation mode DOI: 10.25165/j.ijabe.20221501.6092 Citation: Xiao M H, Li Y Y, Jia Y, Wang J W. Mechanism of water savings and pollution reduction in paddy fields of three typical areas in southern China. Int J Agric & Biol Eng, 2022; 15(1): 199–207.

Evaluation of nitrogen loading in the last 80 years in an urbanized Asian coastal catchment through the reconstruction of severe contamination period

Most semi-enclosed seas have experienced severe eutrophication owing to high nutrient loading from rivers during rapid population growth periods. In Japan, the coastal areas of some megacities (e.g. Tokyo and Osaka) experienced considerable economic growth during the 1960s–1970s. Therefore, determining the amount of nutrient loading during this period is essential to undertake measures for the conservation of coastal environments. However, determining the nutrient loading that occurred several decades ago is generally difficult owing to lacking water quality records. In this study, the nitrogen loading in the Yamato River catchment, an urbanized coastal catchment in Asia, for 80 years from the 1940s to the 2010s is reconstructed using the Soil and Water Assessment Tool. We considered factors such as population growth, wastewater treatment plant (WWTP) construction, and changes in land and fertilizer usage in different urbanization stages. Results show that the total nitrogen loading in the catchment peaked in the 1970s at 6616 tons yr−1 owing to untreated wastewater discharge and rapid increase in population growth. By reducing 57% of the nitrogen loading in the 2010s from the catchment, WWTPs have been instrumental in improving the water environment. The decrease in and integration of agricultural land has reduced nitrogen loading attributed to nonpoint sources; however, this reduction was not obvious because of the high fertilizer usage before the 2000s. Overall, the findings of this study provide a comprehensive understanding of the impact of rapid urbanization in an Asian coastal catchment on nitrogen loading during the high economic growth period in the past. This study will be useful for the long-term assessment of nutrient loading in other.

Cross-effect of wetland substrates properties on anammox process in three single-substrate anammox constructed wetlands for treating high nitrogen sewage with low C/N

Constructing a stable and efficient anammox-driven constructed wetlands (CWs) system for efficiently treating high-nitrogen wastewater with low C/N remains a challenge, due to slow growth rate and high sensitivity of anammox bacteria to changing environmental conditions. Notably, sensitive anammox bacteria is still affected by the physicochemical properties of wetland substrates and their effects are still unknown. Therefore, three single-substrate (gravel, zeolite, and oyster shell) CWs were constructed with the goal of enhancing total nitrogen (TN) removal by anammox-driven/dominant process and determining the effect of substrate on anammox process. The gravel, zeolite and oyster shell systems achieved desired TN removal rates of 20.50, 14.25 and 22.15 g·(m2·d)−1 when influent TN load was 32.57 g·(m2·d)−1 without carbon source and costly aeration, respectively. Oyster shell system exhibited the highest removal ability and better capacity for resistance to influent nitrogen load, followed by gravel and zeolite systems (p < 0.05). Integrated analyses indicated anammox-driven/dominant process was the foremost reason accounted for the enhanced nitrogen treatment performance in all systems. The abundance of anammox gene was higher than the total abundance of denitrifying genes in the three CWs when influent TN load reached 14.85 g·(m2·d)−1. Path analysis further demonstrated anammox process was the foremost nitrogen removal pathway. [anammox] had a highest positive direct contribution (97.3%) on TN transformation rate in gravel system; [anammox/(napA+narG+nirK+nirS+nosZ)] showed highest positive direct contribution (92.4% and 97.4%) on that in zeolite and oyster shell systems, respectively. Substrate configurations significantly affected nitrogen transformation pathway and microbial communities, particularly those of anammox bacteria. Anammox genera of Candidatus Brocadia (primary anammox genera) and Candidatus Kuenenia exhibited different evolutions among the three CWs. Machine learning of Least absolute shrinkage and selection operator (LASSO) analyses showed pH, Ca, Mg, EC, and K were the key physicochemical properties of wetland substrates affecting anammox gene and anammox genera. In conclusion, Oyster shell was the optimal substrate for anammox bacteria growth.

Sub-Watershed Parameter Transplantation Method for Non-Point Source Pollution Estimation in Complex Underlying Surface Environment

The prevention and control of non-point source pollution is an important link in managing basin water quality and is an important factor governing the environmental protection of watershed water in China over the next few decades. The control of non-point source pollution relies on the recognition of the amount, location, and influencing factors. The watershed nonpoint source pollution mechanism model is an effective method to address the issue. However, due to the complexity and randomness of non-point source pollution, both the development and application of the watershed water environment model have always focused on the accuracy and rationality of model parameters. In this pursuit, the present study envisaged the temporal and spatial heterogeneity of non-point source pollution caused by the complex underlying surface conditions of the watershed, and the insufficient coverage of hydrological and water quality monitoring stations. A refined watershed non-point source pollution simulation method, combining the Monte Carlo analytic hierarchy process (MCAHP) and the sub-watershed parameter transplantation method (SWPT), was established on the basis of the migration and transformation theory of the non-point source pollution, considering the index selection, watershed division, sub-watershed simulation, and parameter migration. Taking the Erhai Lake, a typical plateau lake in China, as the representative research object, the MCAHP method effectively reduced the uncertainty of the weights of the watershed division indexes compared to the traditional AHP method. Furthermore, compared to the traditional all watershed parameter simulation (AWPS) approach, the simulation accuracy was improved by 40% using the SWPT method, which is important for the prevention and control of non-point source pollution in large-scale watersheds with significant differences in climatic and topographic conditions. Based on the simulation results, the key factors affecting the load of the non-point source pollution in the Erhai watershed were identified. The results showed that the agricultural land in Erhai Lake contributed a majority of the load for several reasons, including the application of nitro phosphor complex fertilizer. Among the different soil types, paddy soil was responsible for the largest pollution load of total nitrogen and total phosphorus discharge into the lake. The zones with slopes of 0–18° were found to be the appropriate area for farming. Our study presents technical methods for the assessment, prevention, and control of non-point source pollution load in complex watersheds.

Characterizing the impacts of macrophyte-dominated ponds on nitrogen sources and sinks by coupling multiscale models

Macrophyte-dominated ponds, widely distributed in lowland areas, play an important role in nitrogen (N) retention for nonpoint source pollution. However, their impacts on N sources and sinks are scarcely quantified at a watershed scale. This study aimed to investigate N dynamics (sources, sinks, transport, etc.) of macrophyte-dominated ponds and their driving factors in a typical lowland artificial watershed (the Zhong River Watershed) in East China. For this purpose, an hourly-scale pond model (nitrogen dynamic model for macrophyte-dominated ponds, NDP-Pond) was developed, and coupled with a daily scale watershed model (Nitrogen Dynamic Polder model, NDP) to simulate N dynamics, and estimate N retention in macrophyte-dominated ponds. A comparison with the measured water level and total nitrogen (TN) revealed an acceptable model performance (coefficient of determination (R2) > 0.53) for these two models. Based on the N source/sink simulations, we found that 1) macrophyte-dominated ponds showed a large TN removal capacity with a rate of 55%, and a TN loading removal rate of 67 kg·ha−1·yr−1. 2) Denitrification was the main pathway for N removal with a contribution of 57.7%, followed by the uptake of macrophytes (35.8%) and sedimentation (6.5%). 3) The optimal coverage of macrophytes (Alternanthera philoxeroides) to enhance N removal is 2–4 kg·m−2. 4) During the macrophyte-growth period, the TN removal capacity of the pond was higher with a retention time of 1–10 days. Increasing the pond retention time would decrease the N removal efficiency. This study revealed the high value of coupling multiscale models to gain in-depth insights into N retention in macrophyte-dominated pond ecosystems.

Diffuse nutrient export dynamics from accumulated litterfall in forested watersheds with remote sensing data coupled model

Nutrients exported from forest litterfall significantly contribute to the global cycling of elements and the water quality in watersheds. Simulating the watershed discharge load is challenging because of the combined effects of the decomposing litterfall and topographic heterogeneity. We quantified the contribution of diffuse nutrient export from forest litterfall in a low temperature watershed using artificial rainfall experiments and watershed territorial modeling with remote sensing data, and therefore, the critical spatial factors and corresponding nutrient export dynamics were identified. Rainfall intensity and terrain slope were found to be the key factors for nutrient export under different litterfall decomposition conditions. Based on the moderate resolution imaging spectroradiometer data and field observations, the temporal patterns of litterfall biomass of two types of dominant forests (broad-leaved and mixed) were interpreted. The spatial patterns of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) exports from watershed litterfall were simulated by coupling the observed discharge parameters under artificial rainfall conditions and watershed surface flow modeling with the hydrological characteristics of the forested areas. The average watershed TOC, TN, and TP loads exported from the litterfall were approximately 58.22, 7.89, and 0.37 kg ha−1 a−1, respectively. The exported loads of TOC, TN, and TP varied with the forest types, and the loads from the litterfall of deciduous broad-leaved forest were found to be ∼50–70% of loads from the litterfall of mixed forest. A comparison with similar studies worldwide also indicated that low temperature decreased the litterfall decomposition rate and diffuse nutrient export. This study indicated that litterfall nutrients were a key contributor to watershed water pollution, and their spatial discharge trend varied intensively with the terrestrial conditions. The modified simulation methods were found to accurately assess the cycling of nutrients from the forest litterfall on a watershed scale.

Improving quantification of rainfall runoff pollutant loads with consideration of path curb and field ridge

Quantifying the pollutant loads in rainfall runoff plays a critical role in non-point source pollution control at the watershed level. However, the retention effect of path curb in urban areas and field ridge in farmlands on surface rainfall runoff volume and pollutant loads is still unknown and paid little attention. To make it clear, we measured the height of path curb and field ridge and their effects on rainfall runoff, as well as pollutant loads in a comprehensive demonstration area in Taihu Lake basin. A localized Soil Conservation Service-Curve Number (SCS-CN) hydrological model was applied to calculate the rainfall runoff and provided support for the subsequent pollutant loads calculation, including total phosphorus, total nitrogen, ammonia nitrogen and chemical oxygen demand. The results show that the height of path curb in the study area is distributed between 0 to 1 cm and 2 to 3 cm, and the height of field ridge is clustered between 20 to 25 cm. The path curb and the field ridge reduce the runoff volume generation by 17.5% and 91.1% respectively. The path curb and the field ridge reduced more total phosphorus load than the loads of total nitrogen, chemical oxygen demand and ammonia nitrogen. The result improves our understanding on the retention effect of path curb and the field ridge on pollutant loads in rainfall runoff and provides a new idea for non-point source pollution control. • Path curb and field ridge can reduce rainfall runoff volume and pollutant loads. • Path curb reduces about 17.5% of runoff volume generated on green land. • Field ridge reduces about 91.1% of runoff volume generated on farmland. • Path curb and field ridge can reduce more TP than that of TN, COD and NH 3 -N.

Land cover based simulation of urban stormwater runoff and pollutant loading

Urban stormwater models such as PCSWMM are important tools for evaluating urban stormwater quantity and quality. However, due to the lack of consideration of land covers, traditional catchment delineation methods have defects in model precision, parameter transferability and assessment of contribution from individual land cover types. This paper used PCSWMM model as a foundation, built a new land-cover based (LCB) model and made a systematic comparison with the traditional watershed delineation tool (WDT) model to study the impacts of land cover on the simulation of stormwater runoff and pollutant loading. The models were applied to two urban catchments in Calgary, Canada. The results revealed that the LCB model performed better than the WDT model in hydrological simulation, and land cover consideration can considerably improve model accuracy. The two models showed comparable performances in simulation of total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) loading. The LCB model parameters could be regionalized based on land cover types. The hydrologic-hydraulic parameters can be satisfactorily transferred from neighboring gauged catchments to similar ungauged catchments. The transferring of water quality parameters did not perform as satisfactory. The LCB model could quantitively evaluate the contribution to runoff and pollutant loads of different land covers. Roads and roofs were found to be the major contributors to urban runoff and pollutants in the two urban catchments. Green space became important only during large storms events and its contribution could be ignored during dryer years.

Non-point source pollution loads estimation in Three Gorges Reservoir Area based on improved observation experiment and export coefficient model.

The non-point source (NPS) pollution has become an important limitation to the sustainable development of the Three Gorges Reservoir Area (TGRA) water resources. NPS load estimation research has theoretical and realistic significance for water environment security and water pollution control. Therefore, the TGRA was chosen to be the study area, and the export coefficients of different land-use type were calculated through literature consultation method combined with improved observation experiment. The load of total nitrogen (TN) and total phosphorus (TP) of NPS from different pollution sources including farmland, decentralized livestock and poultry breeding and domestic pollution sources were estimated. The results are shown as follows: the order of TN load of different sources in the TGRA from high to low was land use, livestock and poultry breeding, rural life; the TN from land use was 372% higher than that of rural; the order of TP load of different sources in the TGRA from high to low was livestock and poultry breeding, rural life, land use; the TP from livestock and poultry breeding was 114.5% higher than that of land use. Therefore, control of livestock and poultry sewage discharges was the key practice to limit the TP loss, while the optimization of agricultural management was the key practice to control the loss of TN.

Influence of Anthropogenic Load in River Basins on River Water Status: A Case Study in Lithuania

Twenty-four rivers in different parts of Lithuania were selected for the study. The aim of the research was to evaluate the impact of anthropogenic load on the ecological status of rivers. Anthropogenic loads were assessed according to the pollution sources in individual river catchment basins. The total nitrogen (TN) values did not correspond to the “good” and “very good” ecological status classes in 51% of the tested water bodies; 19% had a “bad” to “moderate” BOD7, 50% had “bad” to “moderate” NH4-N, 37% had “bad” to “moderate” NO3-N, and 4% had “bad” to “moderate” PO4-P. The total phosphorus (TP) values did not correspond to the “good” and “very good” ecological status classes in 4% of the tested water bodies. The largest amounts of pollution in river basins were generated from the following sources: transit pollution, with 87,599 t/year of total nitrogen and 5020 t/year of total phosphorus; agricultural pollution, with 56,031 t/year of total nitrogen and 2474 t/year of total phosphorus. The highest total nitrogen load in river basins per year, on average, was from transit pollution, accounting for 53.89%, and agricultural pollution, accounting for 34.47%. The highest total phosphorus load was also from transit pollution, totaling 58.78%, and agricultural pollution, totaling 28.97%. Multiple regression analysis showed the agricultural activity had the biggest negative influence on the ecological status of rivers according to all studied indicators.

Rapid Assessment Method for Evaluation of the Weighted Contribution of Anthropogenic Pollution: A Case Study of Lake Burullus, Egypt

This paper proposes a pragmatic approach for rapid assessment of the weighted contribution of the main waste streams contributing to pollution of surface water bodies. A case study was conducted on Lake Burullus in Egypt. The lake suffers from pollution due to many human-based activities around the lake, such as domestic, industrial, agriculture, fish farming, and solid wastes. The weighted contribution of these activities was assessed in terms of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP). The results showed that the highest organic load is due to the domestic wastewater pollution component (63.2% of COD load), followed by fish aquaculture (35.4%). The highest TN (43.9%) and TP (58.3%) pollutant loads to Lake Burullus are due to the agricultural pollution component, followed by fish aquaculture with pollutant loads of 28.5% and 25.3%, respectively. The industrial wastewater pollution component has a very small effect on the pollution of Lake Burullus. The assessment of this study will help identify and magnify the key polluters and thus guide the decision-makers to prioritize investment planning for depollution intervention projects. For example, if the target is to reduce COD loads, investments must be directed toward the rehabilitation and expansion of wastewater treatment plants (WWTPs).

Elevated loading rates as a low operational intensity and small land footprint design strategy to achieve partial nitritation

An urgent need exists for cost-effective, low operational intensity and small land footprint ammonia treatment systems to meet stringent wastewater discharge regulations. A moving bed biofilm reactor system operating under a novel design strategy using elevated total ammonia nitrogen (TAN) loading rates ranging from 3 to 6.5 g TAN/m2·d has shown promise to achieve robust partial nitritation (PN) and the oxidation of TAN with limited oxidation of nitrite without the need for intense operational measures. An investigation of the biofilm, the viability of the embedded cells and the microbial ecology is necessary to fully understand this low operational intensity design. The investigation revealed that, at a loading rate of 6.5 g TAN/m2·d, the abundance of nitrite oxidizing bacteria (NOB) was 2 ± 0.46%; however, the NOB activity was negligible with 99 ± 0.2% nitrite accumulation; thus, the mechanism to attain robust PN is shown to be the suppression of NOB activity as opposed to NOB population suppression. This decrease in NOB activity is associated with an increase in thickness and mass of the biofilm, as well as the relative increase in ammonia oxidizing bacteria (AOB) that preferentially uptake oxygen compared to NOB. As such, this design strategy results in the suppression of the NOB activity due to limited access to oxygen via mass transfer limitations through thick biofilm and competition with an augmented AOB population in the biofilm. This research presents a low operational intensity and small footprint PN strategy that can be an effective alternative to more intensive strategies.

Multi-watershed nonpoint source pollution management through coupling Bayesian-based simulation and mechanism-based effluent trading optimization

Multiple rivers flowing into the same bay can be correlated in water quality management and together determine the environmental status of the bay. Nonpoint source pollution management for multi-watershed aiming to alleviate environmental contamination as well as yield considerable economic and environmental benefits can be under additional challenges. In this study, a Bayesian simulation-based multi-watershed effluent trading designing model (BS-METM) is established for multi-watershed nonpoint source pollution management through incorporating techniques of water quality simulation, uncertainty analysis with Bayesian inference, optimal design for effluent trading, as well as mechanism analysis. BS-METM is capable of reflecting parameter uncertainties in nutrient simulation, disclosing the detailed optimal trading schemes under the impact of uncertainties and vital factors, and identifying optimal effluent trading mechanisms through revealing interaction among trading processes of multiple watersheds. BS-METM is applied to a real case of adjacent coastal watersheds (i.e. Daguhe and Moshuihe watersheds), which are identified as major sources of total phosphorus and ammonia nitrogen loadings to Jiaozhou Bay, China. Effluent trading optimization under multiple mechanisms, including intra-watershed trading, cross-watershed trading and non-trading, are conducted. The optimized industry scales and trading processes are obtained. The effects of vital factors on the trading process (i.e. environmental allowance-violation risk level and water availability level) are investigated. The interactions between water availability level and trading mechanism are also analyzed. It is proved that non-trading mechanism would be recommended under low water availability level and cross-watershed trading mechanism would be recommended under medium and high water availability level. The results provide a solid scientific basis for nonpoint source pollution management as well as effective sustainable development for multi-watershed region.Graphical abstract

Development and Assessment of a New Framework for Agricultural Nonpoint Source Pollution Control

The transport of agricultural nonpoint source (NPS) pollutants in water pathways is affected by various factors such as precipitation, terrain, soil erosion, surface and subsurface flows, soil texture, land management, and vegetation coverage. In this study, based on the transmission mechanism of NPS pollutants, we constructed a five-factor model for predicting the path-through rate of NPS pollutants. The five indices of the hydrological processes, namely the precipitation index (α), terrain index (β), runoff index (TI), subsurface runoff index (LI), and buffer strip retention index (RI), are integrated with the pollution source data, including the rural living, livestock and farmland data, obtained from the national pollution source census. The proposed model was applied to the headwater of the Miyun Reservoir watershed for identifying the areas with high path-through rates of agricultural NPS pollutants. The results demonstrated the following. (1) The simulation accuracy of the model is acceptable in mesoscale watersheds. The total nitrogen (TN) and total phosphorus (TP) agriculture loads were determined as 705.11 t and 3.16 t in 2014, with the relative errors of the simulations being 19.62% and 24.45%, respectively. (2) From the spatial distribution of the agricultural NPS, the TN and TP resource loads were mainly distributed among the upstream of Dage and downstream of Taishitun, as well as the towns of Bakshiying and Gaoling. The major source of TN was found to be farmland, accounting for 47.6%, followed by livestock, accounting for 37.4%. However, the path-through rates of TP were different from those of TN; rural living was the main TP source (65%). (3) The path-through rates of agricultural NPS were the highest for the towns of Wudaoying, Dage, Tuchengzi, Anchungoumen, and Huodoushan, where the path-through rate of TN ranged from 0.17 to 0.26. As for TP, it was highest in Wudaoying, Kulongshan, Dage, and Tuchengzi, with values ranging from 0.012 to 0.019. (4) A comprehensive analysis of the distribution of the NPS pollution load and the path-through rate revealed the towns of Dage, Wudaoying, and Tuchengzi as the critical source areas of agricultural NPS pollutants. Therefore, these towns should be seriously considered for effective watershed management. In addition, compared with field monitoring, the export coefficient model, and the physical-based model, the proposed five-factor model, which is based on the path-through rate and the mechanism of agricultural NPS pollutant transfer, cannot only obtain the spatial distribution characteristics of the path-through rate on a field scale but also be applicable to large-scale watersheds for estimating the path-through rates of NPS pollutants.

Output Characteristics of Nitrogen and Phosphorus from Non-Point Source Pollution of Typical Land Use in A Micro-Watershed in Hilly Red Soil Region

Scientific identification of runoff output characteristics of different land use patterns is the premise of controlling non-point source pollution in watersheds. The hydrology and output process of non-point source pollutants of forest, planting, and construction land with different rainfall characteristics were observed using a micro-watershed in a low mountain and hilly region of Southern China. The results showed that land use affected the hydrological characteristics and water quality processes of runoff. The characteristics of runoff generation time and cumulative rainfall under typical rainfall conditions were as follows:construction land(9 min, 2.0 mm), planting land(35 min, 11.4 mm), and forest land(108 min, 24 mm). There were significant differences in the three land use types in the pollution output process characteristics, such as pollutant concentration of total suspended matter(TSS), total nitrogen(TN) and phosphorus(TP), their components, N/P ratio change, and output intensity. Under typical rainfall, different land use types had similar pollution output stages, the mass concentrations of TSS, TN, and TP in the initial runoff were high, and then gradually stabilized. In addition, the first 30 min of the flow generation process contributed to the TSS, TN, and TP loads within the 23%-43% range. At the annual scale, there were significant differences between the contribution rate of each land use type to TN and TP load and ratio per unit area; the highest contribution to total pollution load was planting land(57% and 45%), while the highest in pollution load per unit area was construction land(9.50-12.50). The results also showed that the distribution of key non-point source areas had different spatial and temporal dynamics, which was comprehensively determined by the land use types in catchment units, the characteristics of annual rainfall, among other factors. With the increase in rainfall, the main contribution non-point source pollution in the micro-watershed changed from construction land to planting land. Targeted ecological interception strategies should be implemented based on the distribution characteristics of key source areas and characteristics of underlying surface runoff production process.

Challenges in Treatment of Digestate Liquid Fraction from Biogas Plant. Performance of Nitrogen Removal and Microbial Activity in Activated Sludge Process

Even thoughdigestate, which is continually generated in anaerobic digestion process, can only be used as fertilizer during the growing season, digestate treatment is still a critical, environmental problem. That is why the present work aims to develop a method to manage digestate in agricultural biogas plant in periods when its use as fertilizer is not possible. A lab-scale system for the biological treatment of the digestate liquid fraction using the activated sludge method with a separate denitrification chamber was constructed and tested. The nitrogen load that was added tothe digestate liquid fraction accounted for 78.53% of the total nitrogen load fed into the reactor. External carbon sources, such as acetic acid, as well as flume water and molasses, i.e., wastewater and by-products from a sugar factory, were used to support the denitrification process. The best results were obtained using an acetic acid and COD (Chemical Oxygen Demand)/NO3–N (Nitrate Nitrogen) ratio of 7.5. The removal efficiency of TN (Total Nitrogen), NH4–N (Ammonia Nitrogen) and COD was 83.73%, 99.94%, 86.26%, respectively. It was interesting to see results obtained that were similar to those obtained when using flume water and COD/NO3–N at a ratio of 8.7. This indicates that flume water can be used as an alternative carbon source to intensify biological nitrogen removal from digestate.

Stacked conservation practices reduce nitrogen loss: A paired watershed study

Combinations of best management practices (BMPs) are needed to achieve nutrient reduction goals in the Mississippi/Atchafalaya River Basin (MARB), but field results are crucial to encourage stacked adoption of BMPs. A paired catchment-scale study (2015–18) was done to assess the impact of (i) BMPs, (ii) precipitation patterns, and (iii) seasonality on nitrogen (N) export. Flow-weighted samples were collected and analyzed for total ammonia nitrogen (TAN), nitrate (NO3–N), and total nitrogen (TN). Catchments Low-BMP 11 and High-BMP 12 had 27.6% and 87.6% areal coverage of BMPs, respectively. No significant difference (p > 0.05) in TAN concentrations was found between Low-BMP 11 (0.023 mg L−1) and High-BMP 12 (0.020 mg L−1). However, NO3–N and TN concentrations were significantly higher (p < 0.05) at Low-BMP 11 (NO3–N: 26.0 mg L−1, TN: 28.7 mg L−1) than at High-BMP 12 (NO3–N: 8.8 mg L−1, TN: 9.2 mg L−1). Two precipitation factors that affected N export patterns were observed. First, N flushing could continue for several years after a drought as elevated NO3–N concentrations were observed in 2015 (i.e., two years after the 2011–2013 drought). Second, higher annual N export was observed when more precipitation occurred during the pre-planting or early-growing season versus later periods. For both catchments, the highest 50% of flows were responsible for majority of the NO3–N export. We estimated that 33–37%, 61–62%, and 82–85% of the NO3–N loads occurred in the 90th, 75th, and 50th flow percentiles, respectively. As demonstrated in High-BMP 12, stacked BMP application effectively lowered NO3–N and TN loads by 60.3% and 59.1%, respectively, relative to Low-BMP 11. Although 27.6% BMP coverage area in Low-BMP 11 was considered low for this study, this coverage area is higher than many other parts of the MARB. This research highlights the importance of joint efforts between landowners in a watershed to meet downstream water quality goals.

Anthropogenic nitrogen loading and risk of eutrophication in the coastal zone of Atlantic Canada

Nutrient pollution derived from human land-use activities remains a major cause of the eutrophication of coastal ecosystems around the world. In this study, we conduct a nutrient loading analysis for the coastal watersheds bordering the Bay of Fundy and Scotian Shelf of Atlantic Canada, a cold temperate region of the Northwest Atlantic that exhibits strong gradients in oceanographic conditions and human uses of the coastal zone, and where coastal development is expected to increase in the coming decades. Our objective was to apply the Nitrogen Loading Model (NLM) framework to determine the regional distribution and intensity of nitrogen inputs from land-based sources (wastewater, atmospheric deposition, land use, fertilizer applications, and regional industries) to coastal marine environments, and subsequently identify coastal embayments at risk of developing symptoms of eutrophication. Across all 109 watersheds examined, the estimated mean total nitrogen load varied by three orders of magnitude. The largest loads occurred in the most heavily urbanized and densely populated watersheds, where wastewater inputs contributed the most (>80%) to loading rates. Where the footprint of human activity was small, atmospheric deposition of nitrogen was an important contributor to the total load; however, localized point sources (i.e. seafood processing, fur farming) were significant contributors to the total load in smaller sized watersheds. Coastal embayments with small surface areas and low tidal exchange volumes were most likely to have estuarine loading rates that exceeded previously established thresholds for the loss of submerged aquatic vegetation (e.g., eelgrass). In contrast, none of the embayments were deemed likely to develop anoxia. This analysis enables a novel comparison of nitrogen loading from watersheds across a range of land cover types, watershed characteristics, and human land-use activities, while providing a baseline for the detection of future environmental change in the region. Overall, we emphasize the importance of including human activities that occur on the landscape in future marine coastal planning.

Optimal allocation of best management practices based on receiving water capacity constraints

Best management practices (BMPs) are generally considered the most economical and effective methods to control nonpoint source pollution (NPS). However, the existing research on BMPs does not consider the local receiving water capacity, and, thus, may not yield much practical guidance for controlling local NPS. In order to improve the practical function of BMP schemes, load reduction and BMP implementation cost optimization under receiving water capacity constraints were considered to provide a new optimization methodology for BMPs in this study. The Soil Water and Assessment Tool (SWAT) was used to simulate the temporal and spatial distribution of nutrient load and identify priority management areas (PMAs). A multi-objective, non-dominated sorting genetic algorithm-II (NSGA-II) was used to explore optimal BMPs with tradeoffs between economic cost and water quality responses. This optimization methodology is applied to the Chao River watershed (CRW), north China. The main results are as follows. A total nitrogen (TN) priority management area (PMA) was mainly located in the upstream areas of the CRW, while a total phosphorus (TP) PMA was mainly located in the middle of the CRW. Terrace and contour planting were the most effective BMP measures to reduce TN and TP loads from the CRW, and filter belts played an important role in reducing the TN and TP loads. The allocation scheme of BMPs with TN as the control index could meet the receiving water capacity constraints for the CRW. The optimal allocation method yielded a significantly different BMP allocation from the previous objective of a total control strategy, which fully considered the receiving water capacity of the Miyun Reservoir. The new method has been successfully applied in the Miyun Reservoir watershed, and the BMP configuration schemes with practical guidance values were obtained. The applied methodology can be a good alternative for controlling agricultural NPS in other reservoir water source areas.