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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]

• 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]

The purpose of the presented paper is to recognize the impact of the Baltic Sea drainage basin, located on Polish territory, on nitrogen and phosphorus riverrine exports to sea. Yearly figures from 1990 to 2011 in Statistical Yearbooks were used. Figures comprising data before were not presented. Load of substance transferred was significantly correlated with water inflow to sea. No trend to increase the load of total and nitrate and total nitrogen was observed, though significant trends to decrease the loads of ammonia nitrogen and phosphate phosphorus were ascertained. Nitrogen and phosphorus loads in wastewater discharged after its purification were significant. The greatest future risk to the Baltic Sea environment is the huge amount of phosphorus application in agriculture in the drainage basin. [ABSTRACT FROM AUTHOR]

This study proposed an integrated biogeochemical modelling of nitrogen loads from anthropogenic and natural sources in Japan. Firstly, the nitrogen load (NL) from different sources such as crop, livestock, industrial plant, urban and rural resident was calculated by using datasets of fertilizer utilization, population distribution, land use map, and social census. Then, the nitrate leaching from soil layers in farmland, grassland and natural conditions was calculated by using a terrestrial nitrogen cycle model (TNCM). The Total Runoff Integrating Pathways (TRIP) was used to transport nitrogen from natural and anthropogenic sources through river channels, as well as collect and route nitrogen to the river mouths. The forcing meteorological and hydrological data is a 30-year (1976–2005) dataset for Japan which were obtained by the land surface model, Minimal Advanced Treatments of Surface Interaction and Runoff (MATSIRO). For the model validation, we collected total nitrogen (TN) concentration data from 59 rivers in Japan. As a comparison result, calculated TN concentration values were in good agreement with the observed ones, which shows the reliability of the proposed model. Finally, the TN loads from point and nonpoint sources were summarized and evaluated for 59 river basins in Japan. The proposed modelling framework can be used as a tool for quantitative evaluation of nitrogen load in terrestrial ecosystems at a national scale. The connection to land use and climate data provides a possibility to use this model for analysis of climate change and land use change impacts on hydrology and water quality. [Copyright &y& Elsevier]

Nitrate concentration of groundwater was surveyed in 741 wells in 10 districts in central Miyakonojo Basin, southern Kyushu, Japan, to determine the nitrate status in the region and to examine its association with livestock farming. Nitrate-N concentration averaged 5.4 mg L−1, with 13% of the wells exceeding the maximum contaminant level (MCL) for drinking water (10 mg L−1). Wells possessed by farmers had a higher maximum (48.6 versus 27.6 mg L−1), mean (7.4 vs 3.6 mg L−1) and percentage above the MCL (23 versus 5%) than those possessed by nonfarmers. Occurrence of nitrate in groundwater varied not only with the ownership of wells but also among the districts (mean nitrate-N concentration = 3.0–8.6 mg L−1, percentage above the MCL = 0–32%). The mean nitrate-N concentration of individual districts was positively correlated with both excretal nitrogen output from livestock ( r = 0.725, P = 0.018) and excretal nitrogen load to farmland ( r = 0.864, P = 0.001). The results show that groundwater quality in central Miyakonojo Basin was considerably deteriorated mainly in farmers’ wells, with livestock farming as a responsible source of nitrate contamination. [ABSTRACT FROM AUTHOR]

Abstract: The characterisation of pollution sources impact on water quality and the implementation of river basin management plans require an analysis of the basin status including the dynamic of nutrient transfer and the relative significance of the different sources of pollution. Models can contribute in understanding the sources and the processes responsible for pollution, and identifying the areas of concern. A variety of methods have been used to model the nitrogen pressure in river basins. In this study we describe a comparison between two methodologies: a statistical model and the physically-based SWAT model. The two models were calibrated on the Wash catchment (UK), 8900km2. The nitrogen losses from land to surface waters and the source apportionment of riverine nitrogen load were estimated by the two approaches, and the results were compared. Moreover their potentiality for evaluating management strategies was analysed. [Copyright &y& Elsevier]

Changes in environmental conditions within a river basin in South Central Sweden (1400 km2) and impacts on riverine nitrogen (N) transport were evaluated. A historical database was compiled and the process-based HBV-N model used to estimate flow normalised N loads in 1885, 1905, 1927, 1956, 1976, and 1994, using a standard climatological record (1985–1994). The study shows the value of process-based modelling in environmental impact assessment, by making it possible to assess and integrate the effect of a number of factors, both with regard to human impact and natural climatic variability. Factors taken into account include: the effects of land use, agricultural practices, atmospheric deposition, human dietary intake, use of flush toilets, lowering of lakes, building of dams, and climatic variability. For all years studied, agriculture was the overriding source of N, and changes in riverine N over time mainly reflected changes in land use and agricultural practices. In spite of decreasing N-leaching from agriculture, the net load remained fairly constant between 1885 and 1927, due to reduced N retention. Drainage of agricultural land had a dominating impact on reducing N retention, which increased the N loads, while the effects of the lowering of lake levels and dam building were less pronounced. Household N emission per capita was higher in 1994 than in 1927, as the increased consumption of meat and dairy products alone resulted in a higher increase of the emission than was compensated for with wastewater treatment improvement. In addition, introduction of flush toilets increased the emission from households. In total, the net load in 1976 was twofold higher than that in 1885, 1905 and 1927, due to increased leaching from agriculture, wastewater emission, and atmospheric deposition on lake surfaces. Finally, the impact of climatological variability was assessed, using a 110-yr climatological record. The choice of 10-yr period of climatological data was the factor that had the largest impact on calculated N load. [ABSTRACT FROM AUTHOR]