Total Nitrogen Input Research Articles

Spatiotemporal variation in nitrogen loads and their impacts on river water quality in the upper Yangtze River basin

Understanding the spatiotemporal distribution of nonpoint-source pollutant river loads from catchments and their influences on the water quality along river networks in a large river basin is important for land management and water quality protection. In this study, a geomorphology-based nonpoint-source pollution (GBNP) model was applied to the upper Yangtze River basin (YRB) to analyze the nitrogen loads into the river network, as well as its influences on river water quality. Based on the simulation, we analyzed the spatial and temporal distribution of nonpoint-source nitrogen loads into river networks and the nitrogen retention along the river network. The results illustrated that the annual total nitrogen (TN) loads from the fields/hillslopes into the rivers ranged from 55 × 104 t to 392 × 104 t on average during 1990–2012 in the upper YRB. The export coefficient (the ratio of river TN load to TN input of the same sub-catchment) over the upper YRB varied from 0.04 to 0.82 and had a mean value of 0.26. The spatial variability in the annual TN load (TN load intensity) significantly influenced the export coefficient magnitudes in different tributaries. The river nitrogen retention ratio varied from 3.84% to 85.50%, and Minjiang (MJ) had the highest value among all tributaries. The nitrogen retention ratio was higher in spring and winter than in summer and autumn in all tributaries. Both temperature and stream flow conditions (discharge and velocity) were the major factors that influenced river nitrogen retention. In general, a higher TN load from the catchment resulted in a higher river TN concentration due to the “lift-up and carry-away” functions of the catchment rainfall-runoff processes. However, when the net anthropogenic nitrogen input (NANI) was low, the TN load was also relatively low, and the high flow could dilute the river nitrogen concentration. When the TN load was adequately high, the river flow dilution could disappear, and the river TN concentration had the same pattern as the river discharge.

The control of point and non-point source nitrogen to prevent eutrophication of the Nakdong River basin, Korea

Eutrophication of surface waters is commonly caused by excessive inputs of nutrients such as nitrogen and phosphorus. Nakdong River basin was chosen as the study area to investigate the effect of point and non-point source pollution of nitrogen on eutrophication in water body. Non-point source inputs of nitrogen accounted for approximately 84% in the total nitrogen input of the upper Nakdong river watershed, which mainly consists of agricultural land and forests. However, point source inputs of nitrogen accounted for 58~85% in the total nitrogen input of the middle and lower watersheds, including urban area. Therefore, for watershed near urban area, control of point source inputs of nitrogen may be an optimal method to control eutrophication. In this respect, the enforcing reduction of nitrogen in the final effluent of wastewater treatment facilities is needed. On the other hand, to enact more stringent nitrogen regulations, the LOT (limit of technology) and environmental impact should be considered. In this study nitrogen data were analyzed to propose new nitrogen regulations.

High yield and mitigation of N-loss from paddy fields obtained by irrigation using optimized application of sewage tail water

Reuse of treated wastewater effluent for crop irrigation can be a promising strategy to substitute/reduce chemical fertilizers and mitigate contamination of water environment. The effect of the effluent irrigation strategies on crop yield and nitrogen (N) loss to the environment have not been yet well explored. In the present study, a soil column monitoring experiment was conducted for over two years (2016–2017) to assess the effect of domestic sewage tail water (DSTW) irrigation on rice growth and N-loss. DSTW irrigation was established substituting N fertilizer at percentages of 15 %, 30 % and 45 % (namely N3S1, N2S2 and N1S3) with a total nitrogen (TN) input of 210 kg·hm−2; controls with conventional fertilizer (N210) and no fertilizer (N0) but tap water irrigation were also set up. A field plot experiment was also conducted using the same treatments in 2017. The results of the soil column experiment showed that the grain yield from treatments with different proportions of DSTW and N fertilizer were no lower than those subjected to conventional fertilizer in both years. The NH3 volatilization from the treatments using reclaimed DSTW accounted for 20.9 %–34.4 % TN in 2016, but this fell to 6.9 %–16.1 % in 2017. Compared with N210, the DSTW irrigation treatment (N1S3) significantly reduced NH3 emissions by 32.8 %–61.3 % over the two years (p < 0.05). The field plot experiment also indicated that DSTW reclamation could not significantly affect the rice growth and yield, and treatments with a higher proportion of N substituting by DSTW tended to have lower NH3 volatilization. With respect to the rice yield and N-loss, the recommended ratio of N fertilizer substitution is 30 %–45 %; however, long-term trials would be required to further evaluate of any adverse environmental impacts.

Source apportionment of soil nitrogen and phosphorus based on robust residual kriging and auxiliary soil-type map in Jintan County, China

Previous studies on the source apportionment of soil total nitrogen (TN) and total phosphorus (TP) mainly focused on specific spatial point sites and the closely related information such as soil-type map was seldom used. Moreover, traditional geostatistical models are usually sensitive to outliers. To address these problems, this study first proposed robust residual kriging (RRK) with soil-type data as auxiliary information to increase the spatial prediction accuracies for TN and TP in topsoil (0–20 cm) in Jintan County, China. Then, the spatial distribution patterns of the background concentrations of soil TN and TP were quantitatively assessed based on profile samples (80–100 cm) and the soil-type map. Last, the spatial distribution patterns of exogenous net inputs of TN and TP in topsoil and the corresponding contribution ratios were further calculated. Model comparisons showed that the relative improvement (RI) accuracies of RRK and residual kriging (RK) over the traditionally-used ordinary kriging (OK) were 23.91% and 15.22% for soil TN and 24.14% and 20.69% for soil TP, respectively. The results of the source apportionment indicated that (i) the exogenous net inputs of TN and TP had similar spatial distribution patterns, with the low inputs mainly in the west and high inputs mainly in the northeast and east of the county; (ii) high contribution ratio of exogenous net input of TN (≥67%) in topsoil was mainly located in the north, southeast, and middle of the study area, and the area with the contribution ratio over 70% is 294.16 km2, covering 30.16% of the area of the county; (iii) high contribution ratio of exogenous net input of TP (≥53%) in topsoil was mainly located in the north, northeast, and southeast of the county, and the area with contribution ratio over 70% is 24.35 km2, covering 2.50% of the area of the county. These results provided more accurate spatial decision support for effectively regulating TN and TP in topsoil.

Synergistic Impacts of Rainfall Variability and Land Use Heterogeneity on Nitrate Retention in River Networks: Exacerbation or Compensation?

AbstractEutrophication of rivers and receiving waters has become a major environmental issue worldwide, which may further intensify due to projected climate changes and expansion of urbanization or agricultural development to meet the needs of increased human population. However, our understanding of climatic and land use change impacts on riverine nutrient retention and export to receiving waters is limited due to lack of empirical measurements and uncertainties about the nature of future climate changes. The aim of this paper is to analyze the response of nitrate transport and transformation in river systems to potential changes in climate and land use management, individually, and in combination. A coupled hydrological and biogeochemical model is implemented in a hypothetical river basin, with realistic inputs and parameters, for the simulation of nitrate dynamics in river networks. Results indicate that for the same annual rainfall, increased within‐year rainfall variability propagates to increased streamflow variability and a significant reduction in nitrate retention. Analysis of the effects of the spatial distribution of nitrate inputs around the river network showed that for the same total nitrate input from land, nitrate retention increased considerably through locating land use types with high nitrate input away from the river outlet. Simulation results also indicated that even without a reduction in total nitrogen input from land, optimized land use distribution around the river network can compensate the enhanced nitrogen input that may arise from increased rainfall variability. These findings offer viable strategies for catchment management to mitigate increased water quality degradation caused by expected future climate changes.

HYDRUS-1D Simulation of Nitrogen Dynamics in Rainfed Sweet Corn Production

Nitrogen loss from agricultural fields results in contamination of ground and surface water resources due to leaching and runoff, respectively. Nitrogen transport dynamics vary significantly among agricultural fields of different climates, especially in the tropical climate. This study intended to evaluate the rainfall impact on nitrogen distribution and losses under tropical rain-fed conditions. The study was carried out in a sweet corn field for two growing seasons at the Malaysian Agricultural Research and Development Institute (MARDI) research field. The HYDRUS-1D numerical model was used to simulate nitrogen transport dynamics in this study. The observed nitrogen concentrations were used for calibration and validation of the model. Total nitrogen input to sweet corn was 120 kg/ha for both seasons. Nitrogen losses through surface runoff and leaching were dominating pathways. Surface runoff accounted for 35.3% and 22.2% of total nitrogen input during the first and second seasons, respectively. The leaching loss at 60 cm depth accounted for 4.0% (first season) and 18.5% (second season). The crop N uptake was 37.5% and 24.9% during the first and second seasons, respectively. Nitrate was the dominant form of N uptake by the crop that accounted for 83.6% (first season) and 78.5% (second season). The HYDRUS-1D simulation results of nitrogen concentrations and fluxes were found in good agreement with observed data. The overall results of simulation justified the HYDRUS-1D for improved fertilizer use in the tropical climate.

Atmospheric Nitrogen Depositions in a Highly Human-Impacted Area

Nutrients that fall on the ground from the atmosphere represent a minor component of the total nitrogen (N) input to soils, especially when compared with agricultural, civil and industrial inputs (i.e. sewage treatment plants or sewage systems, fertilizer and manure applications). However, integrating all nitrogen forms, processes and scales can represent a breakthrough challenge for the understanding and the management of the N cycle. A monitoring experiment was set up to collect wet atmospheric depositions in a human-impacted area with multiple land uses, representing different emission sources. Rainwater collection was executed in the surroundings of Milan, in northern Italy, starting from February 2017 to February 2019. The presence of N compounds and their temporal variations in rainwater are consistent with pollution coming from local anthropogenic emission sources of nitrogen oxides and ammonia, mainly related to the use of the heating systems in the cold seasons and the spreading of fertilizers and manure on agricultural fields. Consequently, the total amount of N wet depositions ranges between 14 and about 30 kg/ha yr in the study area. As leaching of N compounds from soils generally increases at deposition rates higher than about 10 kg(N)/ha yr, this work suggests that the N atmospheric input to soils could not be neglected when evaluating the impacts of N sources to terrestrial and aquatic ecosystems, as well as to groundwater resources. This highlights the need of wisely integrating air, soil and water policies for minimising the risk to deteriorate surficial ecosystems and groundwater.

Estimation of N2O Emissions from Agricultural Soils and Determination of Nitrogen Leakage

Leaching of nitrogen from the soil is a natural but unfavorable effect that generates N2O emissions. Exact quantification of nitrogen leakage is a challenging process. Intensive leakage occurs mainly when the soil is without vegetation and under specific climatic conditions. This paper aims to quantify the amount of nitrogen leakage from arable land and grassland, and to estimate N2O emissions in 2017. Estimating the country-specific fraction of leached nitrogen (FracLEACH) is important for the emission balance from this source. Emissions are underestimated when the fraction is low; on the contrary, a high fraction causes overestimation. The internationally recognized fraction is 30%, according to the 2006 Intergovernmental Panel on Climate Control (IPCC) Guidelines. This factor represents the fraction of nitrogen losses compared to total nitrogen inputs and sources. In this study, we analyzed the effects of climatic conditions on agricultural soils in Slovakia to evaluate the area of nitrogen loss through leaching.

In Search for the Missing Nitrogen: Closing the Budget to Assess the Role of Denitrification in Agricultural Watersheds

Although representing a paramount mechanism against nitrogen excess in agricultural landscapes, soil denitrification is still a largely unknown term in nitrogen balances at the watershed scale. In the present work, a comprehensive investigation of nitrogen sources and sinks in agricultural soils and waters was performed with the aim of gaining insights into the relevance of soil denitrification in a highly farmed sub-basin of the Po River delta (Northern Italy). Agricultural statistics, water quality datasets, and results of laboratory experiments targeting nitrogen fluxes in soils were combined to set up a detailed nitrogen budget along the terrestrial–freshwater continuum. The soil nitrogen budget was not closed, with inputs exceeding outputs by 72 kg N·ha−1·year−1, highlighting a potential high risk of nitrate contamination. However, extensive monitoring showed a general scarcity of mineral nitrogen forms in both shallow aquifers and soils. The present study confirmed the importance of denitrification, representing ~37% of the total nitrogen inputs, as the leading process of nitrate removal in heavily fertilized fine-texture soils prone to waterlogged conditions.

Source Apportionment of Nutrient Loads to a Mediterranean River and Potential Mitigation Measures

The aims of the study were to quantify nutrient loads from point and diffuse pollution sources in the Rio Mannu stream and to simulate mitigation measures for reducing nutrient loads delivered to the Santa Gilla wetland. The Soil and Water Assessment Tool model was used for simulating hydrology, nutrient balance and water quality. At the basin scale, the input from fertilisers was 80.3 kg ha−1 year−1 total nitrogen (TN) (87.6% of the total input) and 27.6 kg ha−1 year−1 of total phosphorus (TP) (99.8% of the total input). Atmospheric deposition and biological N-fixation together accounted for about 12% of the total TN input. The TN and TP from wastewater treatment plants (WWTPs) were about 14.2 t year−1 and 3.1 t year−1, respectively. Nutrient loads delivered to the river system differed among the sub-basins, with TP ranging from 0.2 kg ha−1 year−1 to 2.7 kg ha−1 year−1, and the sum of organic N and NO3-N ranging from 1.8 kg ha−1 year−1 to 22.9 kg ha−1 year−1. Under high flow conditions, NO3-N and TP accounted for 89% and 99% of the total load, respectively. The low flow contribution to the total load was very low, with NO3-N and TP accounting for 2.8% and 0.7%, respectively. However, the natural hydrological regime in the study area is intermittent, and low flow represents a critical condition for the water quality due to the high concentrations of TP and NO3-N from WWTP discharge. To improve the water quality, the reuse of treated wastewater from three WWTPs for irrigation purposes on olive cultivation, coupled with a 20% reduction in fertiliser application, was simulated. The results showed a reduction in nutrient loads at the outlet for all hydrological conditions. However, additional measures are needed for improving water quality.

The co-regulation of nitrate and temperature on denitrification at the sediment-water interface in the algae-dominated ecosystem of Lake Taihu, China

Sediment denitrification is a dominant mechanism for nitrogen removal and can help to minimize lake eutrophication. However, the spatio-temporal variability of denitrification rates and its controlling factors in sediments of large shallow lakes are poorly understood. In this study, we investigated the controlling factors on the temporal and spatial variability of denitrification rates in Meiliang Bay in Taihu Lake, China, to determine the contribution of denitrification on the total lacustrine nitrogen budget. We collected 18 intact monthly sediment cores and an additional 36 seasonal sediment cores from January 2013 to January 2014. Cores were collected from the inner and outer sections of Meiliang Bay for analysis of denitrification rates and sediment properties. We also collected in situ surface water samples for water quality analysis. Denitrification rates at the sediment-water interface (SWI) were measured using acetylene inhibition techniques and intact sediment core incubation. We used a t test to determine the differences in water quality and sediment properties between the two sites and a one-way ANOVA to identify seasonal differences in denitrification rates, water quality, and sediment properties. We also applied Pearson’s correlation, distance-based redundancy analysis (db-RDA) and random forest model to identify the relationships between denitrification rates and environmental factors. Denitrification rates ranged from 0.76 to 40.94 μmol N m−2 h−1 and 0.13 to 52.55 μmol N m−2 h−1, with annual mean values of 19.97 and 17.15 μmol N m−2 h−1 for the Inner and Outer Bay, respectively. Sediment denitrification rates in the Inner and Outer Bay showed similar seasonal variability, with the highest values in spring and summer and the lowest values in autumn. Nitrate addition was shown to significantly increase denitrification rates in summer and autumn (P < 0.05); however, carbon addition showed no significant influence on denitrification rates in the four seasons. Our results imply that denitrification rates were nitrate-limited in summer and autumn. Distance-based redundancy analysis (db-RDA) and random forest model showed that denitrification rates were mainly determined by nitrate, temperature, and chlorophyll a (Chla), and that nitrate in the water column was the most important predictor of denitrification rates. In general, denitrification rates showed significant seasonal variability in Meiliang Bay due to the co-regulation of both water temperature and nitrate concentrations. The dominance of each controlling factor on denitrification rates varied in different seasons. Based on our calculations, nitrogen removal by denitrification accounted for approximately 10.7% of the total nitrogen input to Taihu Lake. Therefore, we suggest the need for effective measures to reduce external nitrogen inputs of to Lake Taihu to prevent on-going eutrophication.

Excessive nutrient balance surpluses in newly built solar greenhouses over five years leads to high nutrient accumulations in soil

Over-application of fertilizers is very common in solar greenhouse vegetable production. Therefore, understanding nutrient balances and changes in soil is important for crop production and the environment. A five-year consecutive monitoring was conducted to investigate the nutrient balances and changes of soil properties, including soil organic matter (SOM), nutrient contents, pH and electrical conductivity (EC), in thirteen newly built solar greenhouses in the Loess Plateau. The average annual nutrient inputs from manure and mineral fertilizers were 1,871 kg N ha−1, 1,616 kg P2O5 ha−1, and 1,780 kg K2O ha−1, with manure accounting for 60.7%, 55.1%, and 53.3% of the total nitrogen (N), phosphorus (P), and potassium (K) input, respectively. The annual nutrient apparent balances were 1354 kg N ha−1, 1492 kg P2O5 ha−1 and 960 kg K2O ha−1, respectively. Consequently, SOM and total N significantly increased in the 0–100 cm soil profile, with average annual rates of 0.84–3.76 g C kg−1 and 0.06–0.22 g N kg−1, respectively. Nitrate N in the 0–100 cm and 0–200 cm soil profiles were significantly increased, with annual average rates of 182 kg N ha−1 and 225 kg N ha−1, respectively. Olsen P and exchangeable K significantly increased, with average annual rates of 2.3–44.1 mg P kg−1 and 10.4–63.2 mg K kg−1 in the 0–80 cm and 0–40 cm soil profiles, respectively. The significantly positive linear relationships were found among apparent accumulated balances of N, P and K and soil total N, Olsen P and exchangeable K, respectively. The pH in 0–20 cm soil significantly reduced. However, the EC in 0–100 cm soil significantly increased. In conclusion, excessive nutrient balance surpluses result in rapid nutrient accumulations in soil of newly built greenhouses, and attention should be paid to its negative effects on the environment in near future.

Nitrogen balance in paddy fields under flowing-irrigation condition

Flowing irrigation which drains a large volume of water is one of agricultural techniques for ensuring rice quality. In this study, the nitrogen input and output were characterised in paddy fields under flowing irrigation based on observation in Central Japan, and the estimated nitrogen loadings were compared to the reported values in traditional paddy fields under stagnant irrigation by using budget analysis. The annual water fluxes in the studied fields were calculated to be more than ten times larger than those in traditional fields. The concentrations of most nitrogen forms in surface drainage and subsurface drainage were detected at highest level during paddling periods, while those of nitrate and nitrite in subsurface drainage increased during non-irrigation periods. The total nitrogen inputs were at upper level (236–332 kg N ha−1) of or larger (490–581 kg N ha−1) than the reported values under both flowing irrigation and stagnant irrigation, and the larger contribution of irrigation pathway was observed. Surface drainage (78.3–163.5 kg N ha−1) and transport to underground system (73.1–210.4 kg N ha−1) were significantly higher than reported values obtained from stagnant-irrigation paddy fields. The differences between input and output were thereby estimated and the large negative balance was attributed to the soil accumulation, which was distinctly detected in the field with presumably higher adsorption capacity. Therefore, assessing the effect of water flow on soil nitrogen accumulation as well as discharge is recommended by evaluating nitrogen balance in paddy field.

Developing a nitrogen load apportionment tool: Theory and application

In this work, a new nitrogen load apportionment tool was developed to quantify the anthropogenic pressures from point sources and diffuse sources (DSs) on the water in a basin, and to identify the areas contributing most of the total nitrogen (TN). The model, which is an alternative approach to complex conceptual models, was tested in the Canale d’Aiedda Basin (SE Italy). It integrates the TN soil system budget (SSB), TN riverine export (NRE) and TN export coefficient modelling. The results of the SSB showed a TN surplus for productive land (∼60 kg ha−1 yr−1). Major TN inputs were derived from fertilisers (∼89 kg ha−1 yr−1, 77% of the total input) and animal manure (∼13 kg ha−1 yr−1, 11% of the total input). Crop uptake was the main output (∼39 kg ha−1 yr−1, 70% of the total output). NRE was estimated through the measurement of streamflow and TN concentrations in two stream sections. The average NRE per unit area of productive land was 5.22 kg ha−1 yr−1. Groundwater was the major receptor of the TN from DSs. The TN runoff export coefficients, estimated on the basis of environmental factors and calibrated with riverine load measurements, were lower than the TN leaching fractions. The results show that setting export coefficients based only on environmental factors, without any calibration, leads to an overestimation of TN load in runoff, and to an underestimation of TN load in leaching.

Nutrient export from Finnish rivers into the Baltic Sea has not decreased despite water protection measures

To tackle the symptoms of eutrophication in the open Baltic Sea and Finnish coastal waters, Finland has agreed to reduce both total nitrogen (TN) and total phosphorus (TP) inputs. Due to large investments in treatment of municipal and industrial wastewaters, TP loads started to decrease already in the mid-1970s and the respective TN loads in the mid-1990s. During the last two decades, much effort has been spent in decreasing the load originating from diffuse sources. Trend analyses in 1995–2016 showed that, despite various mitigation measures, riverine nutrient export has not substantially decreased, and especially the export from rivers draining agricultural lands remains high. In some areas TN concentrations and export were increasing and we found evidence that it was linked to ditching of peatlands. Several factors connected to climate/weather (e.g. temperature and precipitation) have counteracted the mitigation measures, and therefore Finland will not achieve the nutrient reduction targets by 2021.

Ammonia removal during leach-bed acidification leads to optimized organic acid production from chicken manure

This work demonstrates the suitability of nitrogen removal during anaerobic acidification in batch configuration for a more efficient pre-treatment of chicken manure prior to anaerobic digestion. High loading rates corresponding to a total nitrogen input between 6.3 and 9.5 g L−1 allowed successful suppression of methanogenic archaea. To eliminate nitrogen, NH3-stripping and MAP (magnesium ammonium phosphate hexahydrate) precipitation were compared. In spite of decreased cell quantities detected using qPCR, removal of nitrogen caused an increase in volatile fatty acid (VFA) formation from 13 to 19%. The highest nitrogen removal during acidification (up to 29%) was achieved with three consecutives MAP precipitation steps, however, conductivity values were affected too, reaching 53.3 and 53.1 mS cm−1 after the three consecutive MAP precipitations. Additionally, MAP-precipitation reduced the concentration of important trace elements and 16S-rRNA amplicon sequencing revealed an altered taxonomic pattern, in which especially the bacterial families Marinilabiliaceae, Bacteroidales UCG-001, M2PB4-65 termite group and Idiomarinaceae were impaired. However, in spite of these inhibitory effects, nitrogen removal proved able to prevent unwanted methanogenesis and to enhance the yield of VFAs, and this strategy thus holds great potential for the optimized production of biogas in a two-phase system.

Shipborne nutrient dynamics and impact on the eutrophication in the Baltic Sea

The Baltic Sea is a severely eutrophicated sea-area where intense shipping as an additional nutrient source is a potential contributor to changes in the ecosystem. The impact of the two most important shipborne nutrients, nitrogen and phosphorus, on the overall nutrient-phytoplankton-oxygen dynamics in the Baltic Sea was determined by using the coupled physical and biogeochemical model system General Estuarine Transport Model–Ecological Regional Ocean Model (GETM-ERGOM) in a cascade with the Ship Traffic Emission Assessment Model (STEAM) and the Community Multiscale Air Quality (CMAQ) model. We compared two nutrient scenarios in the Baltic Sea: with (SHIP) and without nutrient input from ships (NOSHIP). The model uses the combined nutrient input from shipping-related waste streams and atmospheric depositions originating from the ship emission and calculates the effect of excess nutrients on the overall biogeochemical cycle, primary production, detritus formation and nutrient flows. The shipping contribution is about 0.3% of the total phosphorus and 1.25–3.3% of the total nitrogen input to the Baltic Sea, but their impact to the different biogeochemical variables is up to 10%. Excess nitrogen entering the N-limited system of the Baltic Sea slightly alters certain pathways: cyanobacteria growth is compromised due to extra nitrogen available for other functional groups while the biomass of diatoms and especially flagellates increases due to the excess of the limiting nutrient. In terms of the Baltic Sea ecosystem functioning, continuous input of ship-borne nitrogen is compensated by steady decrease of nitrogen fixation and increase of denitrification, which results in stationary level of total nitrogen content in the water. Ship-borne phosphorus input results in a decrease of phosphate content in the water and increase of phosphorus binding to sediments. Oxygen content in the water decreases, but reaches stationary state eventually.

Spatial and temporal distribution characteristics of different forms of inorganic nitrogen in three types of rivers around Lake Taihu, China

In order to control nitrogen (N) pollution of Lake Taihu, China, we studied the spatial and temporal distribution characteristics of inorganic N in inflowing rivers polluted by industry, agriculture, and domestic sewage during low, moderate, and high flow periods. The results showed that dissolved total nitrogen (DTN) was the main fraction of total nitrogen (TN) input from these rivers. Inflowing rivers had distinct impacts on TN, DTN, ammonium N (NH4+), and nitrate N (NO3-) concentrations of Lake Taihu during the low flow period. Particulate nitrogen (PN) had an impact on Lake Taihu during the three flow periods and all the three types of rivers would increase PN concentration in the lake. Rivers polluted by agriculture had the greatest impact on Lake Taihu's TN, DTN, NO3-, and dissolved inorganic N (DIN) concentrations, while rivers polluted by industry had the greatest impact on NH4+ concentration. Therefore, agriculture and industry should be key targets for nutrient reductions. The in-lake N concentrations were higher than those of inflowing rivers during moderate and high flow periods.

Ocean Circulation Causes Strong Variability in the Mid‐Atlantic Bight Nitrogen Budget

AbstractUnderstanding of nitrogen cycling on continental shelves, a critical component of global nutrient cycling, is hampered by limited observations compared to the strong variability on a wide range of time and space scales. Numerical models have the potential to partially alleviate this issue by filling spatiotemporal data gaps and hence resolving annual area‐integrated nutrient fluxes. In this study, a three‐dimensional biogeochemical‐circulation model was implemented to simulate the Mid‐Atlantic Bight (MAB) nitrogen budget. Model results demonstrate that, on average, MAB net community production (NCP) was positive (+0.27 Tg N/year), indicating net autotrophy. Interannual variability in NCP was strong, with annual values ranging between 0.19 and 0.41 Tg N/year. Along‐shelf and across‐shelf horizontal transport fluxes were the other dominant terms in the nitrogen budget and were primarily responsible for this NCP variability. The along‐shelf current transported nitrogen from the north (0.65 Tg N/year) into the MAB, supplementing the nitrogen entering from terrestrial inputs (0.27 Tg N/year). However, NCP was highest in the year when total water volume transport and inorganic nitrogen input was strongest across the continental slope in the southern MAB, rather than when terrestrial inputs were greatest. Interannual variability of NCP appears to be linked to changes in the positions of the Gulf Stream and Slope Water Gyre. Overall, the strong spatiotemporal variability of the nitrogen fluxes highlights the importance of observations throughout all seasons and multiple years in order to accurately resolve the current status and future changes of the MAB nitrogen budget.

Dry and Wet Deposition of Atmospheric Nitrogen in Small Catchments

Atmospheric nitrogen deposition is one of the important pathways for the transmission of terrestrial pollutants and nutrients to aquatic ecosystems. A considerable amount of nitrogen substances is delivered into the surface water environment via atmospheric deposition in the catchments, which are greatly affected by human activities, and have serious negative effects on the nutrient level and aquatic habitat environment. The Shixia Catchment north of the Miyun Reservoir was selected as study area. Samples of particulate dry and wet deposition were collected and tested. Subsequently, the variation of the atmospheric nitrogen deposition flux and factors impacting it were determined; ultimately, the contribution of atmospheric nitrogen deposition to the nitrogen budget of the catchment was estimated. The major results are as follows:① The total nitrogen deposition flux of particulate dry and wet deposition is characterized by a significant temporary variation. Regarding the total nitrogen, the ammonia nitrogen and wet deposition flux are the highest in summer and dissolved organic nitrogen is the highest in spring. However, the flux of nitrate nitrogen shows no notable seasonal fluctuation. The general trend of the particulate dry deposition flux is supreme in winter, followed by that in autumn and spring. In detail, the total nitrogen and ammonia nitrogen deposition are the largest in winter, while the seasonal variance of nitrate nitrogen appears to be less apparent. The dry deposition flux of dissolved organic nitrogen is the greatest in autumn. ② The total flux of nitrogen deposition is 43.14 kg·hm-2 in the Shixia Catchment; the wet and dry deposition flux account for 39.85% and 60.15%, respectively. ③ Rainfall and wind speed conditions are important factors impacting the atmospheric nitrogen deposition. The rainfall and rainfall intensity are negatively correlated with the wet nitrogen deposition concentration. With respect to the particulate dry deposition, the average wind speed during the monitoring period is important to ammonia nitrogen. ④ The contribution of atmospheric nitrogen deposition to the total nitrogen input in this catchment is approximately 15.09%, second only to livestock and poultry farming and rural life. The results of this study provide information that is useful for the nitrogen management in the catchment.