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Baseflow is one of the major pathways of runoff in hilly areas, and its contributions to surface water resources and pollutant loads cannot be ignored. In this study, based on water quantity and quality data from 1988 to 2019 in hilly and low rainfall watersheds, we focused on the impact of long-term baseflow on nitrogen load using the load allocation based on the baseflow separation method. We also constructed a nitrogen balance model for the Chaohe River Basin of China from 2012 to 2021 to analyze the nitrogen accumulation in the basin. We used the baseflow nitrogen load lag analysis method to study the lag characteristics of the baseflow discharge process and analyzed the response and periodicity of baseflow nitrogen to precipitation and soil accumulation using time delay analysis. The results showed that the contribution rate of baseflow nitrogen reached 69% and showed a slight increasing trend from 1988 to 2019. The effects of changes in precipitation and nitrogen accumulation on the baseflow contribution was observed after 1–2 and 2 yr, respectively. After nitrogen accumulation, it entered the river channel through baseflow, which was already the main and continuous source of nitrogen in rivers in hilly areas. [ABSTRACT FROM AUTHOR]

Ammonia, which is toxic to the brain, is converted into non‐toxic urea, through a pathway of six enzymatically catalyzed steps known as the urea cycle. In this pathway, N‐acetylglutamate synthase (NAGS, EC 2.3.1.1) catalyzes the formation of N‐acetylglutamate (NAG) from glutamate and acetyl coenzyme A. NAGS deficiency (NAGSD) is the rarest of the urea cycle disorders, yet is unique in that ureagenesis can be restored with the drug N‐carbamylglutamate (NCG). We investigated whether the rarity of NAGSD could be due to low sequence variation in the NAGS genomic region, high NAGS tolerance for amino acid replacements, and alternative sources of NAG and NCG in the body. We also evaluated whether the small genomic footprint of the NAGS catalytic domain might play a role. The small number of patients diagnosed with NAGSD could result from the absence of specific disease biomarkers and/or short NAGS catalytic domain. We screened for sequence variants in NAGS regulatory regions in patients suspected of having NAGSD and found a novel NAGS regulatory element in the first intron of the NAGS gene. We applied the same datamining approach to identify regulatory elements in the remaining urea cycle genes. In addition to the known promoters and enhancers of each gene, we identified several novel regulatory elements in their upstream regions and first introns. The identification of cis‐regulatory elements of urea cycle genes and their associated transcription factors holds promise for uncovering shared mechanisms governing urea cycle gene expression and potentially leading to new treatments for urea cycle disorders. [ABSTRACT FROM AUTHOR]

Partial nitritation-anammox (PN/A) is a cost-effective technology in high ammonia–nitrogen wastewater treatment. However, PN/A is prone to instability as the ammonia–nitrogen sharply fluctuates. In this study, a packed bed reactor is employed to construct a single-stage PN/A system to investigate the operational characteristics and explore the denitrification mechanism. The effluent NH4+-N concentration, ammonia nitrogen removal rate (ARE), and total nitrogen removal rate (TNR) could be sustained at about 60 mg/L, 80%, and over 70%, respectively, when the influent nitrogen load rate (NLR) is changed from 0.733 to 0.879 kg-N/m3/day. Both ARE and TNR are decreased when NLR continues increasing to 1.026 kg-N/m3/day. The influent NLR decreases from 0.879 to 0.147 kg-N/m3/day, and ARE and TNR reached 98% and 85.4%, respectively. Therefore, the denitrification effect of the reactor could be recovered, and the excellent nitrogen removal capacity could be obtained within a wide range of influent NLR. Moreover, the high-throughput sequencing and metagenomic testing indicate that the Proteobacteria and Planctomycetes that the PN/A functional strains (i.e., ammonia-oxidizing bacteria (AOB) and anammox bacteria (AnAOB)) account for 38.8% in the sludge. The relative abundance of Nitrospira containing the nitrite-oxidizing bacteria (NOB) has dropped to 0.01%, and the functional gene nxr of the nitrite oxidation process is also inhibited. The relative expression of the functional gene is dominated by the short-range nitritation and anammox oxidation, which demonstrates that the nitrogen removal is mainly dominated by nitritation-anammox. [ABSTRACT FROM AUTHOR]

A clear strategy for adapting agricultural drainage to future climate change is important for environmental and economic reasons. In a study aimed at developing recommendations for the subsurface drainage design in clay soils, we evaluated the impact of replacing an old drainage system (1920) with new systems (2018) on nutrient leaching and crop yield. Our field experiment included 12 individually drained plots divided into four treatments: (A) old system with clay tiles at 10 m spacing, without an envelope; (B) new system with plastic pipes at 10 m spacing, gravel envelope; (C) new system with plastic pipes at 5 m spacing, gravel envelope; and (D) new system with plastic pipes at 10 m spacing, gravel envelope and lime incorporated in trench backfill. We conducted flow measurement and flow-proportional, logger-controlled water sampling of the drainage discharge from each plot at a measuring station. Preliminary results (first two years) show a clear effect of the new drainage systems on phosphorus and nitrogen loads in drainage discharge. The lowest total load of phosphorus and highest total load of nitrogen in all treatments were observed in treatment D (with 10 m drain spacing and lime incorporated in trench backfill). The highest total phosphorus load and lowest total nitrogen load in all treatments were observed for the old tile drainage system with 10 m drain spacing (treatment A). The environmental impact of new drainage systems on clay soils may thus be a trade-off between decreased phosphorus loads and increased nitrogen loads with more intensive drainage. Crop data from two experimental years indicated that investing in new drainage systems can be profitable for farmers, as crop yield was 3%-20% higher with new drainage systems compared with old tile drainage. More experimental years are needed to determine the long-term effects of the different drainage system designs. [ABSTRACT FROM AUTHOR]

Stable and efficient partial nitrification reaction and nitrite accumulation are essential for the operation of partial nitrification-anaerobic ammonia oxidation process. This paper investigated the changes in the performance of a partial nitrification bioreactor during the domestication process. After 40 days of domestication, the partial nitrification reaction remained stable, the nitrite accumulation rate (NAR) increased significantly to 85.7%, and the NO2--N/NH4+-N ratio stabilized at 1.25 ± 0.04. Both diversity indices (Simpson and Shannon) and richness indices (Ace and Chao1) tend to decrease with domestication. Nitrosomonas as a typical ammonia oxidizing bacterium it increased its relative abundance in the reactor from 0.02 ± 0.007% at P1 to 11.6 ± 2.2% at P2, and at P3 stage the denitrifying functional bacteria norank_f_AKYH76, Dokdonella and unclassified_f_Comamonadaceae reached 33.4 ± 12.5%, 18.8 ± 1.8%, and 10.1 ± 1.3%, respectively, and the increase in the relative abundance of these functional species was also consistent with the accumulation of nitrite nitrogen in the reactor. [ABSTRACT FROM AUTHOR]

ABSTRACT Biological nitrogen (N) fixation, an important pathway of N, inputs from the atmosphere to Earth’s ecosystems, is well demonstrated to decline under N input. However, it remains unclear why N fixers sustain N fixation in many forests under high atmospheric N deposition. To address this knowledge gap, we analyzed the response of the diazotroph community to low N loads (short-term and low N addition; 3-year N addition at the rates of 25–50 kg N ha−1 year−1) vs high loads (chronic and high N addition; 9-year N addition at the rate of 150 kg N ha−1 year−1) in forest soils using high-throughput sequencing. Rates of N fixation decreased under low and high N loads (by 13%–27% and 10%–12%, respectively). Richness and alpha diversity (ACE and Chao1) of the soil diazotroph community decreased under low but not high N loads. Approximately 67.1%–74.4% of the nifH gene sequences at the OTU level overlapped between the control and low N loads, but only 52.0%–53.6% of those overlapped between the control and high N loads, indicating a larger shift of diazotroph community composition under high N loads. Low N loads increased soil NH4+ concentrations, which decreased diazotroph community richness, diversity, and N fixation rates, whereas the increased soil NH4+ concentrations under high N loads did not have negative impacts on the structure and function of the diazotroph community. These findings indicate that diazotrophs sustain N fixation under high N deposition via adjustment of their community composition in forest soils.IMPORTANCEThis study examined the changes in soil diazotroph community under different loads of simulated N deposition and analyzed its relationship with N fixation rates in in five forests using high-throughput sequencing. The magnitudes of N fixation rates reduced by low N loads were higher than those by high N loads. Low N loads decreased richness and diversity of diazotroph community, whereas diazotroph community structure remained stable under high N loads. Compared with low N loads, high N loads resulted in a less similarity and overlap of nifH gene sequences among the treatments and a larger adjustment of diazotroph community. Low N loads increased soil NH4+ concentrations, which decreased diazotroph community richness, diversity, and N fixation rates, whereas the increased soil NH4+ under high N loads did not have negative impacts on diazotroph community structure and N fixation. Based on these findings, it is urgently needed to incorporate the loads of N deposition and the composition of diazotroph community into terrestrial N-cycling models for accurate understanding of N inputs in forest ecosystems.

The energy cost and harmful effect of residual chlorine produced as a by-product in the electrochemical processes are the main obstacles in the extensive use of electrochemical recirculating aquaculture systems (ERAS). In this study, a pilot electrochemical system was used in a shrimp cultivation experiment to investigate the effects of current density, geometric feature, timing, and other parameters on the effective control of inorganic nitrogen, pathogens, and residual chlorine in aquaculture water. A 50-L electrochemical batch reactor (BR) equipped with Ti-RuO2/Ti electrodes could effectively remove inorganic nitrogen (the initial concentration was 4.0 mg/L) and inactivate Vibrio in the aquaculture seawater in 5 min, when a current density of 66 mA/cm2 and electrodes with a surface area of 154 cm2 were used. Air stripping was found to be effective in resolving residual chlorine produced from electrochemical process. In the experiment of shrimp cultivation, the ERAS equipped with a 50-L batch reactor and 500-L shrimp tank effectively kept the inorganic nitrogen concentration in the rearing water to a desirable concentration (0.2 mg/L) when a nitrogen load of 4.3 g (transformed from a daily quota of commercial prawn feeds) was used. By precisely controlling the time at which electrooxidation and air stripping alternated, an electrochemical recirculating aquaculture system could effectively remove inorganic nitrogen and residual chlorine, carry out disinfection, and reduce energy cost. [ABSTRACT FROM AUTHOR]

Hayvancılık işletmelerinde en önemli sorun gübredir. Üretim yoğunluğunun artmasıyla birlikte gübre miktarının da artması, sorunu daha ciddi boyutlara getirmektedir. Gübrenin depolanması, yönetimi, işletilmesi süreci doğru şekilde planlanmadığı ve uygulanmadığı takdirde yer altı ve yüzey su kaynaklarında önemli çevresel problemleri tetiklemektedir. Bu sebeple gübre kirlilik yükünün belirlenmesi, etkilerinin iyi analiz edilmesi, bunları önlemeye yönelik doğru stratejilerin uygulanması açısından oldukça önemlidir. Bu çalışmada Bursa ilinin son on yıldaki kanatlı üretiminden kaynaklanan gübrenin oluşturduğu atık miktarının ve kirlilik yükünün belirlenerek değerlendirilmesi amaçlanmaktadır. Yapılan çalışmanın sonuçlarına göre Bursa ilinin kanatlı üretiminden kaynaklanan kirlilik potansiyelinin en fazla olduğu ilçeler Karacabey ve Mustafakemalpaşa, en düşük olduğu ilçe ise Gürsu olmuştur. Yumurta tavukçuluğunun, et tavukçuluğu ve hindi yetiştiriciliği ile kıyaslandığında yayılı kirlilik potansiyelinin daha fazla olduğu belirlenmiştir. Kirlilik potansiyelinin %88’ini azot kirliliği oluştururken, %12’sini ise fosfor kirliliği oluşturmaktadır.

Bogs located near agricultural areas often receive high atmospheric nitrogen (N) depositions, and this may result in an increased soil and water N pool and enhanced N supply for plants and microorganisms. The consequences are changes in plant species composition and diffuse emissions of N species from these bogs. However, research on the resilience of rewetted bogs to high atmospheric N inputs is still sparse. Our aim was to evaluate the influence of N depositions on a bog that was rewetted after peat extraction down to bare ‘black’ (highly decomposed) bog peat. We monitored dry (NH3) and wet (NH4+ and NO3-) deposition, and plant available N as NH4+ and NO3- in soil and water, over the course of one year. The amount of N stored in vegetation was also quantified. We detected a total N deposition of 32 kg ha-1 y-1 which by far exceeded the critical load (5–10 kg ha-1 y-1) for bogs, but there were no signs of deposition induced N increase in soil and bog water. Our findings suggest, rather, that levels of plant available N were crucially affected by mineralisation in areas with lower water table. Depending on the sampling station, the amount of N stored in the vegetation was 23 or 30 kg ha-1. Although it was likely that uptake by vegetation played a decisive role in buffering the high N depositions, it did not completely explain the whereabouts of excess N. Accordingly, other processes like peat growth, N removal by mowing or denitrification must have contributed to buffering N levels in soil and water.

Purpose: To evaluate the effects of enhanced nitrogen (N) load on turnover of phosphorus (P) in Suaeda salsa marsh in the Yellow River estuary, the variation and allocation of P in the plant-soil system were investigated in the growing season. Methods: This study was explored by field N addition experiment which included four load levels: NNL (no N load treatment, 0 gN m−2 yr−1), LNL (low N load treatment, 3.0 gN m−2 yr−1), MNL (medium N load treatment, 6 gN m−2 yr−1), and HNL (high N load treatment, 12 gN m−2 yr−1). Results: In most sampling periods, the TP contents in soils in the LNL, MNL, and HNL treatments showed a decreasing trend compared to the NNL treatment. With increasing N load levels, the contents of non-available decomposed P in soils decreased by 3.08 ~ 5.22%, while those of easily available and moderately available P increased by 0.36 ~ 8.92% and 1.21 ~ 24.24%, respectively. The variations of NaOH-Po, Resin-Pi, and NaHCO3-Po contents primarily rested with the duration of N import, while those of NaOH-Pi, Residual-P, NaHCO3-Pi, and HCl-Pi contents mainly depended on the levels of N load. Dissimilar variations of TP contents in plant tissues in the growing season were observed among N load levels, which were dependent on the structure and function of organs and the nutrient function of P at distinct growth stages. The P absorption coefficients (PAC) of plants in N load treatments increased by 31.82 ~ 36.36%, while the P utilization coefficients (PUC) decreased by 4.96 ~ 13.33%. Conclusion: This paper found that the S. salsa was very likely to adjust its growth rhythm and P absorption/utilization capacity to adapt N load environment. Particularly, as N load reached medium level, the P supply relationships between aboveground and belowground tissues and the P transferences in the plant-soil system were greatly altered, indicating that the S. salsa might have a special response to the medium N enrichment. Thus, the potential impacts of medium N load level on S. salsa marsh should be emphasized in the future. [ABSTRACT FROM AUTHOR]

A selection of sites occupied by the EU-protected marsh fritillary (Euphydryas aurinia) in western Czech Republic were subjected to a vegetation survey 15 years ago and again recently. In the 66 time-replicated 25 m2 plots from 12 sites, representing the diversity of E. aurinia-occupied oligotrophic grasslands in the Slavkovský les Protected Landscape Area (and covering a fifth of the currently-occupied Czech sites), we recorded quantitative representation of vascular plants and mosses. We analysed the data using multivariate ordinations, asking how the vegetation changed between the surveys, how was it affected by the conservation management applied and how it affected occupancy by the butterfly larval nests; the vegetation patterns were interpreted using Ellenberg's plant indicator values. Between the two surveys, the overall representation of the larval host plant, Succisa pratensis, did not change; tree and herbs layers (both grasses and forbs) increased and the moss layer decreased. Across surveys, the main driver of vascular plants' species composition was moisture, followed by soil reaction and nitrogen, whereas in mosses, nitrogen was the main factor. The main change between the surveys was the increase of nitrogen accompanied by decreased light, probably due to increase of competitively strong plants. Butterfly occupancy declined at sites with high soil moisture and increased at sites with higher soil reaction. Mowing of moist nitrogen-rich sites, but not drier nitrogenpoor sites, increased occupancy, illustrating the need for context-dependent interventions. All the evidence thus shows that E. aurinia prefers drier, warmer and less acidic conditions within the generally moist acidic grasslands and that ongoing eutrophication represents a potential problem in the future. [ABSTRACT FROM AUTHOR]

Bogs located near agricultural areas often receive high atmospheric nitrogen (N) depositions, and this may result in an increased soil and water N pool and enhanced N supply for plants and microorganisms. The consequences are changes in plant species composition and diffuse emissions of N species from these bogs. However, research on the resilience of rewetted bogs to high atmospheric N inputs is still sparse. Our aim was to evaluate the influence of N depositions on a bog that was rewetted after peat extraction down to bare 'black' (highly decomposed) bog peat. We monitored dry (NH3) and wet (NH4+ and NO3-) deposition, and plant available N as NH4 + and NO3 - in soil and water, over the course of one year. The amount of N stored in vegetation was also quantified. We detected a total N deposition of 32 kg ha-1 y-1 which by far exceeded the critical load (5-10 kg ha-1 y-1) for bogs, but there were no signs of deposition induced N increase in soil and bog water. Our findings suggest, rather, that levels of plant available N were crucially affected by mineralisation in areas with lower water table. Depending on the sampling station, the amount of N stored in the vegetation was 23 or 30 kg ha-1. Although it was likely that uptake by vegetation played a decisive role in buffering the high N depositions, it did not completely explain the whereabouts of excess N. Accordingly, other processes like peat growth, N removal by mowing or denitrification must have contributed to buffering N levels in soil and water. [ABSTRACT FROM AUTHOR]

Copyright of Uludag University Journal of the Faculty of Engineering (UUJFE) is the property of Uludag Universitesi, Muhendislik Fakultesi and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Human population growth has led to increased energy and food production, fertilizer usage and wastewater flows. Increased nitrogen availability is a worldwide cause of eutrophication of rivers, lakes and estuaries, however, quantitative evaluation the impacts of nitrogen loads has been insufficient in developing countries because of poor data availability. The Nam Ngum River basin, Laos, which supplies quality water for domestic use in the Vientiane Metropolis, was selected as the target area for this study. The Nam Ngum River basin is 415 km long with a 17,000 km² catchment area, and the main land uses in 2000 were paddy (15.6%), forest (32.3%), shrub (40.3%) and urban (0.2%). By UN estimation, population in Laos is expected to increase 2.1 times from 2000 to 2050, and fertilizer use also will increase to produce sufficient food. Therefore, future water quality is a main concern in this river basin. Meteorological and hydrological data from 1995 to 2004, and spatial data such as topography, land use, and soil properties were collected for model simulation. A conceptual nitrogen balance model with three nitrogen pools was developed and combined with a rainfall runoff model. Simulated river discharge and nitrogen loads agreed with the observed data. Then, we investigated future nitrogen load variations in the basin under different population growth and agricultural modernization scenarios. As a result, even when population in the basin increased 2.1 times, nitrogen load did not change significantly (11,676 tons/year in 2000 and 11,822 tons/year in 2050). However, the fertilizer increase scenario, from 25 kg/ha/season to 50 kg/ha/season, showed significant increase in nitrogen loading, from 11,676 ton/year to 17,010 ton/year. Our results provide initial insight into the magnitude and spatial distribution of nitrogen loading in Nam Ngum River Basin, showing that this type of model may be useful for future impact assessments. [ABSTRACT FROM AUTHOR]

Copyright of Environmental Science & Technology (10036504) is the property of Editorial Board of Environmental Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Many urban estuaries worldwide suffer from excess phytoplankton and hypoxia (low oxygen) due to high nutrient loads. A common water quality management strategy is to require wastewater treatment facility upgrades. This case study examines Narragansett Bay, a warming temperate mid-latitude urban estuary with seasonal periodic hypoxia, during June through September from 2005 to 2019. Within this period, numerous facilities were upgraded to nitrogen removal over several years. The response of the bay is more consistent with “textbook” expectations for reduced chlorophyll and hypoxia than what was seen in many other systems—despite its complex coastline geometry, numerous river inputs, and widely-distributed treatment facilities. River flow drives inter-annual variability with increased load, density stratification, chlorophyll, and hypoxia in wet years. Mean 2013-2019 bay-wide total nitrogen load was 34% less than the 2005-2012 mean, a reduction of about 106 kg yr-1, comparable to the range of flow-driven inter-annual variations. Chlorophyll Index and Hypoxia Index event-based metrics applied to high-frequency time series observations at eight sites quantify exceedances of severe and moderate thresholds. Relatively steady 33% and 16% Chlorophyll Index declines, for severe and moderate thresholds, occurred from about 2007 to 2019. The Hypoxia Index declined markedly by 2009 and 2014 for severe and moderate thresholds, respectively, and remained at or near zero from 2014 to 2019. The load reduction explains chlorophyll and hypoxia declines better than physical processes including river flow, stratification, tidal variations, winds, sea level differences, and temperatures. River flow about 55% higher than the 2005-2019 mean would increase non-treatment facility loads by an amount comparable to the managed load decrease, so future wet summers could partially reverse the improvements. Long-term trends include warming of about 0.5°C decade-1, which reduces oxygen saturation by 0.1 mg l-1 decade-1. This rate is likely a lower bound for temperature-driven oxygen decreases, because warming can also accelerate phytoplankton growth and bacterial consumption. Without warming, the managed load decrease would have curtailed hypoxia more effectively. Climate trends should be at least as important to future eutrophication as the managed load decline because, in addition to warming influences, long-term increases in river flow would increase load and stratification.

It is increasingly recognised that urban trees can contribute to reducing stormwater runoff by intercepting and retaining a fraction of rainfall received. What is less studied is the translation of this to reduced pollutant loads being transferred to receiving streams, rivers, and water bodies. In this paper, we assess interception of two tree species (Eucalyptus microcorys and Ulmus procera) in an urban park. These data are used in simple water balance modelling to predict the environmental and economic benefit of reducing nitrogen loads to receiving waterways as a function of reduced runoff volume resulting from rainfall interception by urban trees on public land (21% of the catchment area). We use a highly urbanized catchment in Melbourne, Australia to demonstrate the impact of an urban forest dominated by deciduous trees, evergreen trees or a mixed tree canopy cover. We found that doubling the urban canopy cover in the catchment, while keeping the current mix ratio of deciduous and evergreen trees, could reduce annual runoff volume by 30 mm (92 MLyr−1). Using the prescribed values that developers must pay the local water authority for nitrogen treatment as a condition of new development, we calculate that this would deliver a nitrogen load removal benefit of AUD$ 200/tree. If only deciduous trees are planted, the annual runoff reduction would decrease to 24 mm (73 MLyr−1) and increases to 37 mm (112 MLyr−1) if only evergreen trees are planted. This study highlights both the additional benefits of public street trees and the differences in deciduous and evergreen trees which should be accounted for by policy makers.

Changing atmospheric conditions, including above all the deepening extreme weather phenomena, are increasing from year to year. This, in consequence, causes an increase in the incidence of low outflows. The study compares low water levels for two catchments: Biała Woda and Czarna Woda, and phosphorus and nitrogen load using the Nutrient Delivery Ratio (NDR) model in InVEST software. The objective of the NDR is to map nutrient sources from catchment area and transfer to the river bed. The nutrient loads (nitrogen and phosphorus) spread across the landscape are determined based on a land use (LULC) map and associated loading rates described in literature. The studies have shown that low water levels have been more common recently and pose the greatest threat to the biological life in the aquatic ecosystems. The structure of land use is also of great importance, with a significant impact on the runoff and nitrogen and phosphorus load. Phosphorus and runoff from surface sources to the water of Biała Woda and Czarna Woda catchments area has been reduced in forested areas. Only higher run-offs are observed in the residential buildings zone. The nitrogen load was also greater in the lower (estuary) parts of both catchments, where residential buildings dominate. [ABSTRACT FROM AUTHOR]

Copyright of Environmental Science & Technology (10036504) is the property of Editorial Board of Environmental Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To regulate the water level and minimize the occurrence of water eutrophication in shallow lakes, dams and gates are often constructed in rivers. However, this practice may result in a deterioration of water quality in some estuaries. In the present study, using the correction of Nemerow pollution index (CNPI) and a redundancy analysis (RDA), water samples from different dammed rivers around Taihu Lake were compared to assess the pollution risk and identify the factors responsible for water eutrophication. The average total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC) concentrations, and chemical oxygen demand (CODMn) were 2.45 ± 2.28, 0.08 ± 0.06, 43.01 ± 18.75, and 10.78 ± 4.86 mg L−1, respectively. The CNPI values indicated that approximately 76.47% of the estuarine water was moderately polluted (1 < CNPI < 7.28). A positive correlation was observed between dam construction and nutrient concentrations (e.g., rTN = 0.38, p < 0.05; rTP = 0.89, p < 0.01). Under the effects of dam construction, land use change, estuary shape, and meteorological conditions, there was a clear spatial variation of the TN concentrations. Dams that were closed all year round accelerated the TN accumulation in the water around them. The pollution risk in a trumpet-shaped estuary was higher than that in other regions (t = 2.92, p = 0.02). Endogenous release of pollutants was an important factor that may have a priming effect on algal blooms and should be given more attention. In Wuli Lake, exogenous pollution was the dominant pollutant source. A total of 74.49% of the nitrogen losses with the runoff into the estuarine water in 2018 were derived from urban domestic sewage and constructed land, with the load being 4.40 times higher than in 2000. The RDA results revealed that dam construction was the main factor (43.70%) affecting water quality, while meteorological conditions, land use types, estuary shape, and other factors contributed 56.30%. Scientific regulation and control of dam operation is important to protect the water environment of Taihu Lake. [ABSTRACT FROM AUTHOR]

Excessive levels of NO 3 - can result in multiple eco-environmental issues due to potential toxicity, especially in coastal areas. Accurate source tracing is crucial for effective pollutant control and policy development. Bayesian models have been widely employed to trace NO 3 - sources, while limited studies have utilized optimized Bayesian models for NO 3 - tracing in the coastal rivers. The Bohai Rim is highly susceptible to ecological disturbances, particularly N pollution, and has emerged as a critical area. Therefore, identification the N fate and understanding their sources contribution is urgent for pollution mitigation efforts. In addition, understanding the influenced key driven factors to source dynamic in the past ten years is also implication to environmental management. In this study, water samples were collected from 36 major river estuaries that drain into the Bohai Sea of North China. The main transformation processes were analyzed and quantified the sources of NO 3 - using a Bayesian stable isotope mixing model (MixSIAR) with isotopic approach (δ 15N-NO 3 - and δ 18O-NO 3 -). The overall isotopic composition of δ 15N-NO 3 - and δ 18O-NO 3 - in estuary waters ranged from −0.8–19.3‰ (9.3 ± 4.6‰) and from −7.1–10.5‰ (5.0 ± 4.3‰), respectively. The main sources of nitrate in most river estuaries were manure & sewage, and chemical fertilizer, while weak denitrification and mixed processes were observed in Bohai Rim region. A temporal decrease in the nitrogen load entering the Bohai Sea indicates an improvement in water quality in recent years. By incorporating informative priors and utilizing the calculated coefficients, the accuracy of sourcing results was significantly improved. This study highlighted the optimized MixSIAR model enhanced its accuracy for sourcing analysis and providing valuable insights for policy formulation. Future efforts should focus on improving management strategies to reduce nitrogen into the bay. [Display omitted] • N pollution is high in southern rivers of Bohai Rim due to anthropogenic activities. • Effective management has led to decrease in N pollution levels over past ten years. • Sewage & manure and fertilizer contributed three quarters N sources to the study rivers. • Considering fractionation effect and informative prior can enhance precision of source. [ABSTRACT FROM AUTHOR]

Pollution with excess nutrients deteriorate the water quality of the Baltic Sea. The effect of combined land use and climate scenarios on nitrate leaching and nitrogen (N) loads to surface waters from two Baltic Sea catchments (Norsminde in Denmark and Kocinka in Poland) was explored using different models; the NLES and Daisy models for nitrate leaching, and MIKE SHE or MODFLOW/MT3DMS for N transport. Three Shared Socioeconomic Pathways (SSP1, SSP2 and SSP5) defined change in land use and agricultural activities. The climate change scenarios covered 2041–2060 compared with 1991–2010 under RCP8.5, applying four different climate models. Increases in predicted N-load from climate change vary from 20 to 60% depending on climate model. SSPs moderate these N-load changes with small changes for SSP1 to large increases for SSP5, with greater increases for Norsminde than Kocinka due to land use differences. This stresses needs for new measures and governing schemes to meet sustainability targets. [ABSTRACT FROM AUTHOR]

Excessive load of nitrogen from anthropogenic sources is a threat to sustaining a healthy aquatic ecosystem. The difficulty in identifying the critical source areas (CSAs) of nitrogen load and apportioning the in-stream nitrogen to individual sources spatially and seasonally has made the Soil and Water Assessment Tool (SWAT) useful for analyzing nitrogen load at the catchment scale. However, the uncertainty of the nitrogen load simulated by SWAT has rarely been analyzed. The two simulations with the highest or the lowest PBIAS of total nitrogen (TN) load were proposed in this study to represent the range of the prediction uncertainty and therefore were used to generate the uncertainty of CSAs and nitrogen source apportionment. The model was set up for the Yuan River Catchment, which is under threat of extensive nitrogen load. Results indicated the highest nitrogen load was from downstream paddy fields with a denser population and 85% of the load was from fertilizer and feedlots. The relatively high prediction uncertainty was observed on both CSAs and source apportionment, which emphasizes the limitation of calibration only based on certain processes and the necessity to consider parameter uncertainty in the application of nitrogen load simulation. [ABSTRACT FROM AUTHOR]

Current research on, e.g. agricultural supply-chains, engages in implementing new technologies enabling extraction of protein from other sources than soya such as grass, clover, or alfalfa. Still, it is not obvious where to initiate production of the biorefinery crop without damaging existing ecological systems or maybe even to strengthen local environments. This paper uses a targeted approach to identify the most suitable agricultural areas to convert from cereal to grassland production while gaining multiple environmental benefits. For the Danish region, three individual biomass goals were set: 1) reach 3 × 10 6 t dry matter from organically produced non-fertilized grass-clover mixtures, and 2) reach 5 × 10 6 t dry matter from grass fertilized with 300 kg N/ha, or 3) 450 kg N/ha. Areas for conversion were selected based on coastal nitrogen (N) loads and a surrounding nature index in a stepwise manor until the three biomass goals were reached separately. Our results reveal a spatial distribution of some of the areas selected for conversion close to existing nature areas and vulnerable aquatic environments for all goals. Producing 5 × 106 t dry matter fertilizing grass with 450 kg N/ha requires less agricultural area (23% of total agricultural area) compared to fertilizing with 300 kg N/ha (28%) and even less than producing only 3 × 106 t dry matter without fertilizing (24% of total agricultural land). Despite less land area, goal 3 still has a higher coastal N load compared to goal 2, and consequently goal 2 reaches 50–60% of the national N reduction goal to reduce 13,000 t N compared to 21–28% for goal 3. Furthermore, surrounding nature shows a higher index value for goal 2 compared to goal 3. Hence, in our case goal 3 would be preferable if land scarcity was the heaviest weighing factor. Still, the environmental gain resulting from using goal 1 and 2 would increase potential multifunctionality of converting from cereal to grass production. [ABSTRACT FROM AUTHOR]

Abstract Nitrogen (N) loads from municipal and mine wastewater discharges typically increase N concentrations in recipient water bodies which should get more attention especially in cold-climate regions. This study compared N removal efficiency of six constructed wetlands (CWs) treating mine waters and three CWs polishing municipal wastewater. There were clear impacts of point source N loading to recipient water bodies in all cases studied and >300-fold increase in N was seen in some cases. First-order N removal coefficient was determined for seven of these CWs. All CWs studied were observed to remove N efficiently during the warm growing season but the amount of N released increased significantly during the cold season. Although some year-round purification was achieved by both peat-based and pond-type CWs, removal of nitrate + nitrite-N ((NO 3 − + NO 2 −)-N) was low during winter. The first-order N removal coefficient varied from 4.9 · 10−6 to 1.9 · 10−3 d−1 and showed that peat-based CWs were slightly more efficient in N removal than pond-type CWs. However, purification efficiency was steadier and higher for pond-type CWs, as lower hydraulic load or longer water residence time compensated for purification performance. Pond-type CWs showed mean removal efficiency of 59% and 46% for ammonium-N (NH 4 +-N) and (NO 3 − + NO 2 −)-N, respectively, whereas peatland-type CWs had lower removal efficiency for NH 4 +-N (mean of 26%) and in many cases negative removal for (NO 3 − + NO 2 −)-N. Correlation analysis revealed no clear, systematic relationship between temperature and N removal. However, in some CWs the highest correlation was between temperature and (NO 3 − + NO 2 −)-N, reflecting lower denitrification rate at lower temperature. More than 50% removal was found to require a hydraulic load below 10 mm d−1. In order to achieve 70% of NH 4 +-N removal, N tot load lower than 75 g m−2 year−1 and a residence time longer than 80 d are needed in CWs in cold-climate regions. Graphical abstract Unlabelled Image Highlights • Impact of mine water and municipal wastewater on recipient water systems were investigated. • Peat-based and pond-type CWs decreased N load to recipient waters but still clear impacts of point sources were observed. • First-order nitrogen removal coefficient was determined for 7 CWs treating municipa wastewater or mine water in Nordic condition • More than 50% removal efficiency was found to require a hydraulic load below 10 mm d−1 [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the susceptibility of dissolved organic nitrogen (DON) contained in biologically treated wastewater disposed from municipal wastewater treatment plants (WWTPs) to biodegradability and bioavailability in a water environment. Additionally an evaluation was performed of the participation of this organic nitrogen fraction, including bioavailable DON (bDON), in the nitrogen balance for the Baltic Sea. Based on the samples of secondary effluent taken from two large municipal WWTPs located in Northern Poland DON bioavailability and biodegradability tests were carried out. It was concluded that DON concentration in the tested samples was on average from 1.5 to 2.0 g N m−3. This fraction constituted as much as 50% of organic nitrogen and 15–18% of total nitrogen contained in treated wastewater. The participation of biodegradable DON (brDON) in activated sludge tests was on average 24–35%. In the bioavailability tests Selenastrum capricornutum were able to use from 19 to 26% of DON, however taking into account the results of the control test, these values are reduced to 3–4%. On the other hand, taking into account the combined effect of bacteria and algae it was possible to reduce the DON concentration by nearly 40%. The estimated annual bDON load introduced to Baltic Sea waters from Poland through disposal of treated biological wastewater in 2010 reached up to 1.7 thousand tons of N year−1.

Quantification of nitrogen losses and net greenhouse gas (GHG) emissions from catchments is essential for evaluating the sustainability of ecosystems. However, the hydrologic processes without lateral flows hinder the application of biogeochemical models to this challenging task. To solve this issue, we developed a coupled hydrological and biogeochemical model, Catchment Nutrients Management Model - DeNitrification-DeComposition Model (CNMM-DNDC), to include both vertical and lateral mass flows. By incorporating the core biogeochemical processes (including decomposition, nitrification, denitrification and fermentation) of the DNDC into the spatially distributed hydrologic framework of the CNMM, the simulation of lateral water flows and their influences on nitrogen transportation can be realized. The CNMM-DNDC was then calibrated and validated in a small subtropical catchment belonged to Yanting station with comprehensive field observations. Except for the calibration of water flows (surface runoff and leaching water) in 2005, stream discharges of water and nitrate in 2007, the model validations of soil temperature, soil moisture, crop yield, water flows in 2006 and associated nitrate loss, fluxes of methane, ammonia, nitric oxide and nitrous oxide, and stream discharges of water and nitrate in 2008 were statistically in good agreement with the observations. Meanwhile, our initial simulation of the catchment showed scientific predictions. For instance, it revealed the following: (i) dominant ammonia volatilization among the losses of nitrogenous gases (accounting for 11–21% of the applied annual fertilizer nitrogen in croplands); (ii) hotspots of nitrate leaching near the main stream; and (iii) a net GHG sink function of the catchment. These results implicate the model's promising capability of predicting ecosystem productivity, hydrologic nitrogen loads, losses of gaseous nitrogen and emissions of GHGs, which could be used to provide strategies for establishing sustainable catchments. In addition, the model's capability would be further proved by applying in other catchments with different backgrounds. [ABSTRACT FROM AUTHOR]

• Stormwater nitrogen loads from a cold-region urban catchment were examined. • A build-up and wash-off model coupled with a climate change model was conducted. • Correlations among loads, rainfall, land use, and population were analyzed. • Nitrogen loads were predicted to increase in 2050 under three RCPs. Urban stormwater is a primary source of pollution for receiving water, but there is a shortage of studies on pollutant loads from urban catchments in cold regions. In this study, we coupled a build-up and wash-off model (in Mike Urban) with a climate change model to assess the impacts of climate change and urban densification on stormwater nitrogen loads (TN, TKN, NO x -N, and TAN) in an urban catchment in Canada. We calibrated and validated the Mike Urban model against observed event mean concentrations and nitrogen loads from 2010 to 2016. Results show that the nitrogen loads were mainly governed by rainfall intensity, rainfall duration, and antecedent dry days. Future precipitation data were downscaled using the Global Climate Models (GCMs), and three different Representative Concentration Pathways (RCP 2.5, RCP 4.5, and RCP 8.5) were used. Modeling results show that the TN, TKN, NO x -N, and TAN loads in 2050 will increase by 28.5 - 45.2% from May to September under RCP 2.5 compared to those from 2010 to 2016, by 34.6 - 49.9% under RCP 4.5, and by 39.4 - 53.5% under RCP 8.5. The increase of our projected TN load (from 1.33 to 2.93 kg·N/ha) is similar or slightly higher than the limited studies in other urban catchments. This study provides a reference for predicting stormwater nitrogen loads in urban catchments in cold regions. [ABSTRACT FROM AUTHOR]

Key message: Growth of C. japonica under highly irrigated and N-loaded soil is noticeable because of N-induced increase of needle mass and alleviation of high irrigation-induced reduction in photosynthesis. Abstract: To clarify the combined effects of change in precipitation amount and increasing nitrogen load on Japanese forest trees, 2-year-old seedlings of Cryptomeria japonica were treated with combinations of four irrigation levels (80, 100, 120, or 140% of annual precipitation) and three nitrogen loads (15, 50, or 100 kg ha year). The 100% of annual precipitation corresponded to 1520 mm year which was the average annual precipitation in the habitats of C. japonica in Japan. High irrigation amount significantly enhanced the whole-plant dry mass of the seedlings. The N load significantly enhanced the extent of high irrigation-induced increase in needle dry mass. As a result, the irrigation-induced increase in the whole-plant dry mass was greater in the treatment with the highest N. However, increase in needle dry mass induced by high irrigation enhanced plant water consumption and caused dehydration and oxidative damage in needles, thus resulting in reduced net photosynthetic rate. The high irrigation-induced reduction in net photosynthetic rate was alleviated by N load. This alleviation was not caused by N load-induced changes in antioxidative capacity but by a N load-induced increase in ribulose 1,5-bisphosphate carboxylase/oxygenase activity. These results indicate that an increase in the whole-plant dry mass of C. japonica seedlings grown in highly irrigated and N-loaded soil was attributed to N load-induced enhancement of high irrigation-induced increase in needle dry mass and alleviation of high irrigation-induced reduction in net photosynthetic rate. [ABSTRACT FROM AUTHOR]

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Water quality monitoring stations are crucial for detecting excess pollutants in river sections, but identifying the causes of these exceedances can be challenging, especially in heavily polluted rivers with multiple contamination sources. To address this issue, we used the SWAT model to simulate pollution loads from various sources in the Haihe River Basin, analyzing the spatiotemporal distribution of pollutants from seven nitrogen/phosphorus sources in sub-basins. Our results show that crop production is the primary contributor to nitrogen and phosphorus loads in the Haihe River Basin, with the highest loads occurring in summer, followed by fall, spring, and winter. However, industries, atmospheric deposition, and municipal sewage treatment plants have a greater downstream impact on nitrogen/phosphorus contributions due to land use changes. The study highlights the need for targeted prevention and control policies based on the primary sources of pollution loads in different regions. • Soil and Water Assessment Tool model has strong applicability in complex watersheds. • Sources of N and P pollution are influenced by land use in the Haihe River Basin. • The spatiotemporal patterns of TN and TP loads in the Haihe River Basin are similar. • TN/TP contributions from point sources and atmospheric deposition are evident. • Stakeholder engagement and prevention at source are key to improving water quality. [ABSTRACT FROM AUTHOR]

Global and climate changes influence the basic conditions for agriculture. Therefore there is not only a demand for a strict climate protection but also for an adaptation of agriculture to changing conditions. For a study region of 60x40 km within the moraine landscape of North-East Germany mainly used for agriculture, water balance, nitrogen and Sulphur loads and crop yields were calculated for the present and for a possible future. The comparison between the Scenario 2050 and the Initial Situation in 2000 revealed significant changes of the water balance (decrease in percolation water, increase in actual evapotranspiration) and the concentration of nitrogen and Sulphur in the percolation water. The crop yields decrease only slightly if the CO 2 fertilizing effect is taken into account. Measures adopted in response to the changing climate conditions to achieve an economically and sustainable agriculture are recommended. [ABSTRACT FROM AUTHOR]