Total Nitrogen Transport Research Articles

Short-Term Contribution of Conservation Practice Implementation to Water Quality Impairments in Small Streams

Voluntary conservation practice adoption is a key strategy to reduce the transport of non-point source pollutants from agricultural lands to downstream ecosystems. This study assessed the short-term (1 year) efficacy of conservation practices to reduce non-point source sediment, nutrient, and fecal indicator bacteria (FIB) transport from working agricultural lands on the Mississippi State University campus, Mississippi State, MS, USA. Water quality was monitored at three treatment sites downstream of the critical resource areas, two of which had paired reference locations. All five sites were monitored for one year pre- and post-conservation practice implementation. Downstream treatment sites generally had higher nutrient and sediment concentrations than upstream reference sites. The results confirmed that the total nitrogen (TN) concentration was reduced post implementation at only the treatment site with the smallest catchment area (p < 0.01). Water quality impairments from FIB were observed across all sites, while treatment locations with livestock presence were found to have significantly elevated staphylococci and E. coli levels following the conservation practice implementation during the winter period. The results of this study showed minimal improvements to TN transport, and in some cases declines in water quality evidenced by increases in FIB, one year after conservation practice implementation. The implementation of conservation practices did not improve the overall water quality to reference levels in the short-term, despite anticipated long-term benefits.

Forest harvesting affects soil organic carbon and total nitrogen transports by facilitating landslides

Landslides considerably affect soil organic carbon (SOC) and total nitrogen (TN) transports. However, the quantitative assessment of these effects remain limited. Furthermore, it is unresolved how forestry practices, especially clearcutting and subsequent planting, affect the SOC and TN transports by facilitating landslides. Therefore, we quantified the SOC and TN transports attributable to landslides from 1948 to 2012 in a steep mountainous area in Japan and examined the impacts of forest clearcutting on SOC and TN transports through landslides. We used 12 aerial photographs and two LiDAR DEMs to identify the landslide areas and to estimate their scar depths. In addition, we sampled soil at 17 points to examine the relationship between SOC and TN and soil depth. Subsequently, we estimated the temporal changes in SOC and TN transports due to landslides and examined the relationships between forest age and rates of SOC or TN transport due to landslides. During the 64 years, the average annual rate of landslide was 3.7 × 10−2 ha km−2 yr−1. Large temporal variability existed in rates of landslide, and the maximum rate of landslide was around 11.0 × 10−2 ha km−2 yr−1, while almost no landslide occurred in some periods. The average annual SOC and TN transport rates were 5.8–9.3 MgC km−2 yr−1 and 0.5–0.9 MgN km−2 yr−1, respectively. Many landslides occurred at places where trees were 15 years old or less in plated forests. The amount of SOC and TN transports in landslide areas with < 20 forest age accounted for 87% of the total amounts moved owing to landslides. That is, our results clearly showed that forest harvesting increased landslide frequency and SOC and TN transport rates. We expect our results to be useful for predicting carbon stock in forest ecosystems and optimizing forestry practices in steep mountainous regions.

Nitrogen and phosphorus losses in Nordic and Baltic agricultural monitoring catchments – Spatial and temporal variations in relation to natural conditions and mitigation programmes

Nitrogen (N) and phosphorus (P) losses via agricultural drainage water have negative impacts on receiving water bodies and large-scale programmes to reduce nutrient losses have been established in the Nordic and Baltic countries, together with agricultural catchment monitoring programmes. This study evaluated time series (9–40 years) of data from 34 selected Nordic-Baltic catchments for spatial and temporal variations in area-specific water discharge (mm) and in concentrations and transport of total nitrogen (TN) and total phosphorus (TP).Water discharge from the catchments varied from 125 mm (Denmark) to > 1000 mm (Norway). Catchments with low TN concentrations (≤3 mg L-1) were dominated by clay or grass leys or were undrained with reduction of nitrate (NO3) in shallow groundwater. Catchments with high TN concentrations (≥10 mg L-1) had loams and cereal crops. TP concentrations were highest (≥0.45 mg L-1) in catchments with erosive soils, relatively high water discharge and cereal crops, and lowest (≤0.07 mg L-1) in catchments with permeable soils.Generalised additive mixed model (GAMM) analysis of time series of transport and flow-weighted concentrations of TN and TP for temporal patterns revealed decreases in TN concentrations in seven catchments and increases in eight, while four had periods with opposing trends. TN concentrations decreased in Denmark and Sweden in 1990–2010, following introduction of mitigation programmes. TP concentrations decreased in eight catchments and increased in six, while one showed opposing trends. Decreases in TP coincided with improved P balance in catchments with sand and loam. To further reduce N and P losses, a tailored set of mitigation measures is needed for each combination of soil, climate, geohydrology and agricultural production. Intensive monitoring of small catchments can reveal how N and P losses relate to natural conditions and to changes in agricultural production.

Simulation Study on Nitrogen Pollution in Shallow Groundwater in Small Agricultural Watersheds in the Huixian Wetland

In this study, we investigated the influence of different simulations on the transport of shallow groundwater nitrogen in the Mudong River watershed of the Huixian Wetland, a karst wetland. Based on GMS (Groundwater Modeling System) software, the equivalent porous media model was used to simulate the transport of total nitrogen under different conditions in the study area. Two years of field monitoring data in the study area provided the input for the modeling. The SWAT (soil and water assessment tool) model was used to divide the study area into sub-basins. The initial concentration flux index W is first introduced in the equivalent porous medium model to calculate the initial concentration. The simulation results showed the difference between the simulated and monitored values of total nitrogen concentration was between 20% and 40% in 22.2% of the cases, and less than 20% in 66.7% of the cases, indicating that the solute transport model has good applicability in the Huixian Wetland. Parameter sensitivity analysis showed that fertilizer application was the main factor influencing total nitrogen. A 25% reduction in fertilizer application reduced total nitrogen emissions by 31.5% in sub-basin S3 and 22.5% in sub-basin S4. These reductions were greater than the abatement effect of changing land cover and managing river pollution. The pollution plume of total nitrogen was reduced by 38.5% in the southern part of sub-basin S3 (Mudong Lake) and by 40.2% in the western part of sub-basin S4 (Blacksmithing Village). The average concentration was reduced by 2.04 mg/L and 1.22 mg/L, respectively. This study shows that reasonable control of double-season rice nitrogen fertilizer application and appropriate land cover modification can help reduce total nitrogen emissions from wetlands in the Li River watershed and ensure the sustainable development of the local economy and groundwater.

The effects of mulching with organic materials on the soil nutrient and carbon transport by runoff under simulated rainfall conditions

The aim of this study is to reveal the effects of different organic mulch materials and application at different rates on the transport of nitrate nitrogen (NO3−), ammonium nitrogen (NH4+), total nitrogen (TN), phosphate phosphorus (PO4−3) and total organic carbon (TOC) by runoff under the laboratory conditions and determine whether they affect the pH and electrical conductivity (EC) values in runoff after the application. Three different organic mulch materials (dry weed, wheat straw, and peanut hay) were applied on experimental plots prepared using Cambisol soils developed on sedimentary bedrock under laboratory conditions at four different rates (0 t/ha, 2 t/ha, 4 t/ha, and 6 t/ha). The experimental plots were placed on a smooth surface with a 9% slope, and simulated rainfall was applied at an intensity of 97 mm/h for 1 h. Runoff was collected, and NO3−, NH4+, TN, PO4−3, TOC, pH, and EC were analysed. According to the results, peanut hay and straw mulch applications reduced NH4+concentrations in runoff. The most effective mulch type in reducing NO3− concentration was straw mulch at a rate of 4 t/ha. All three mulch types increased the concentration of TN, TOC, and PO4−3 in runoff. The lowest TN transport in water was found in the plots with straw mulch at 4 t/ha. The lowest TOC transport was found in plots with mulch application at a rate of 2 t/ha. The minimum PO4−3 loss was found in dry weed mulch treatments at a rate of 2 t/ha. Mulch applications generally increased the pH and EC values of runoff. In general, straw mulch reducing nutrient and TOC transport by runoff, followed by dry weed mulch applications. The type and application rate of mulches should be chosen carefully in terms of protecting water resources.

Risk assessment of non-point source pollution of land use system of mountainous watershed and spatially referenced regressions on watershed attributes simulation under geological environment assessment

In order to evaluate and analyze the non-point source pollution risk of mountainous watershed, the multi-criteria analysis method is used for assessment, and the Spatially Referenced Regressions on Watershed Attributes (SPARROW) model is adopted for simulation analysis. The non-point source pollution risk is evaluated based on the geological environment assessment and the relevant theories of the land use system combined with the multi-criteria analysis method. According to the evaluation results, subarea governance is implemented in the mountainous watershed. Besides, the SPARROW model is applied to simulate and analyze the total nitrogen transport in the watershed. The evaluation results reveal that the NPA value, the non-point source pollution risk assessment index, of some areas of the mountainous watershed has reached 0.9 or higher, which belong to heavily polluted areas. The pollution sources mainly come from agricultural production, and deep application of fertilizer can reduce total nitrogen emission. The simulation results show that the pH of the soil is instrumental in the total nitrogen reduction, with the total nitrogen loading coefficient being about 2.74. The research provides important reference for the control and governance of non-point source pollution in mountainous watershed.

Estimate of nutrient sources and transport into Bohai Bay in China from a lower plain urban watershed using a SPARROW model.

In the development of a land-sea coordination management strategy, it is necessary to analyze pollution sources and loads of pollutants entering the sea. This study estimated the sources and transport of total nitrogen (TN) and total phosphorus (TP) entering Bohai Bay in Tianjin, a lower plain urban watershed, using a SPAtially Referenced Regression On Watershed attributes (SPARROW) model. We calibrated the model using TN and TP data from 26 and 27 sites, respectively. The results demonstrated that the R2 values of TN and TP were both above 0.99. In 2013, the TN load delivered to Bohai Bay was 21,320 ton, which could be traced to various sources: upstream (39%), industrial discharge (10%), sewage discharge (34%), fertilizer application (3%), livestock breeding (7%), aquaculture (5%), and rural communities (2%). The TP load delivered to Bohai Bay was 1504 ton, which originated from upstream (33%), industrial discharge (5%), sewage discharge (21%), fertilizer application (5%), livestock breeding (12%), aquaculture (10%), and rural communities (14%). Rational management of the water resources in streams, enhancement of water circulation between rivers and wetlands, and making full use of the effect of both land and water on pollutant retention are the suitable strategies in watershed management, reducing marine pollution.

The nutrient and carbon losses of soils from different land cover systems under simulated rainfall conditions

Nutrient losses constitute an important issue for the protection of both soil and water resources. Organic carbon transport is also important for the global carbon cycle. In this study, it was aimed to determine the amount of nutrients and the total organic carbon which was transported by surface runoff water formed under simulated rainfall conditions from areas with different land cover systems.Accordingly, 3 cultivated areas having various product patterns under similar conditions (potato field (P), bean-cultivated area (B), abandoned farmland covered with Noaea sp. (AB)), 2 plantation areas (cedar (C) and almond (AL)) and 2 rangelands covered with Thymus sp. (T) and Stipa sp. (S) were chosen for performing applications. The applications were performed in two repetitions on 0.28 m2 circular experimental plots established in the above-mentioned areas. The collection of surface runoff was performed during land applications. The pH, electrical conductivity, nitrate (NO3−), ammonium (NH4+), total phosphorus, orthophosphate (PO43−), total organic carbon (TOC), and total nitrogen (TN) parameters of surface runoff water were measured. The land cover change affects total nitrogen, nitrate, ammonium, pH, electrical conductivity, total phosphorus, orthophosphate and TOC parameters. Nitrate transport was found to be B > P > T > AB > C > AL > S from highest to lowest. Ammonium transport was B > T > AL > C > AB > P > S. The total nitrogen transport was B > P > T > AB > C > AL. The total phosphorus transport was found to be P > B = T > AB > AL > C > S. Ortho-phosphate transport was P > B > T > AB > C > AL > S. In terms of the TOC transport, the order was found to be T > B > P > AB > AL > C from highest to lowest.

Modeling nutrient sources, transport and management strategies in a coastal watershed, Southeast China

Integrated watershed management requires an analytical model capable of revealing the full range of impacts that would be caused by the uses and developments in the watershed. The SPAtially Referenced Regressions On Watershed Attributes (SPARROW) model was developed in this study to provide empirical estimates of the sources, transport of total nitrogen (TN) and total phosphorus (TP) and to develop nutrient management strategies in the Jiulong River Watershed, southeast China that has enormous influence on the region's ecological safety. We calibrated the model using data related to daily streamflow, monthly TN and TP concentrations in 2014 at 30 locations. The model produced R2 values for TN with 0.95 and TP with 0.94. It was found that for the entire watershed, TN came from fertilizer application (43%), livestock breeding (39%) and sewage discharge (18%), while TP came from livestock breeding (46%), fertilizer application (46%), and industrial discharge (8%). Fifty-eight percent of the TN and 80% of the TP in upstream reaches are delivered to the outlets of North and West rivers. A scenario analysis with SPARROW was coupled to develop suitable management strategies. Results revealed that controlling nutrient sources was effective in improving water quality. Normally sharp reduction in nutrient sources is not operational feasible. Hence, it is recommended that preventing nutrient on land from entering into the river as a suitable strategy in watershed management.

Effects of flow hydraulics on total nitrogen loss on steep slopes under simulated rainfall conditions

Abstract Flow hydraulics play important roles in soil erosion and loss of soil nutrients. A better understanding of the relationship between flow hydraulics and nutrient losses will improve chemical transport modeling. The laboratory experiment was conducted to determine flow hydraulics' effects on total nitrogen (TN) loss. The impacts of rainfall intensities (0.6, 1.1, 1.61, 2.12, and 2.54 mm·min−1) and slope gradients (10°, 15°, and 20°) on TN loss were also studied. Selected soils were derived from purple sandy shales, which are the main parent materials in Wangjiaqiao watershed, southern China. Results show that negative linear relationships (R2 = 0.71) were observed between the rate of Manning roughness coefficient to average flow depth and the unit area runoff-associated TN transport rate. There was a good linear relationship between the unit area sediment-associated TN transport rate and Reynolds numbers (R2 = 0.90), flow velocity (R2 = 0.87), and stream power (R2 = 0.73), while Froude numbers, Darcy–Weisbach and Manning friction coefficients were not good hydraulic indicators of the sediment-associated TN loss of purple soil. The equation including stream power and flow velocity may have a better correlation coefficient (R2 = 0.94).

A GIS-aided two-phase grey fuzzy optimization model for nonpoint source pollution control in a small watershed

A method for allocating allowable ranges of total nitrogen (TN) load to nonpoint (diffuse pollution) sources in a watershed has been developed by adopting the two-phase grey fuzzy optimization approach. Competing goals of water quality management authorities and TN load dischargers at nonpoint sources such as paddy field, upland crop field, and residential area are described with linear imprecise membership functions including interval numbers. TN load discharged from each cell of the nonpoint sources is assumed to be transported along with surface, subsurface, and river flow under the conventional first-order kinetic removal with respect to distance. The travel length of the load is estimated with a digital elevation model in a geographic information system (GIS). Uncertainty of river discharge and self-purification coefficients appearing in the TN transport model is also expressed with interval numbers. The GIS-aided grey fuzzy optimization model developed here is applied to the Seimei River watershed, Japan. By solving the optimization model, the allowable load represented by an interval number at each cell is procured, which would be a scientific base for effluent control regarding nonpoint sources in the area.

How effective are created or restored freshwater wetlands for nitrogen and phosphorus removal? A systematic review

AbstractBackgroundEutrophication of aquatic environments is a major environmental problem in large parts of the world. In Europe, EU legislation (the Water Framework Directive and the Marine Strategy Framework Directive), international conventions (OSPAR, HELCOM) and national environmental objectives emphasize the need to reduce the input of nutrients to freshwater and marine environments. A widely used method to achieve this is to allow water to pass through a created or restored wetland. However, the large variation in measured nutrient removal rates in such wetlands calls for a systematic review.MethodsSearches for primary studies were performed in electronic databases and on the internet. One author performed the screening of all retrieved articles at the title and abstract level. To check that the screening was consistent and complied with the agreed inclusion/exclusion criteria, subsets of 100 articles were screened by the other authors. When screening at full-text level the articles were evenly distributed among the authors. Kappa tests were used to evaluate screening consistency. Relevant articles remaining after screening were critically appraised and assigned to three quality categories, from two of which data were extracted. Quantitative synthesis consists of meta-analyses and response surface analyses. Regressions were performed using generalized additive models that can handle nonlinear relationships and interaction effects.ResultsSearches generated 5853 unique records. After screening on relevance and critical appraisal, 93 articles including 203 wetlands were used for data extraction. Most of the wetlands were situated in Europe and North America. The removal rate of both total nitrogen (TN) and total phosphorus (TP) is highly dependent on the loading rate. Significant relationships were also found for annual average air temperature (T) and wetland area (A). Median removal rates of TN and TP were 93 and 1.2 g m−2 year−1, respectively. Removal efficiency for TN was significantly correlated with hydrologic loading rate (HLR) and T, and the median was 37 %, with a 95 % confidence interval of 29–44 %. Removal efficiency for TP was significantly correlated with inlet TP concentration, HLR, T, and A. Median TP removal efficiency was 46 % with a 95 % confidence interval of 37–55 %. Although there are small differences in average values between the two quality categories, the variation is considerably smaller among high quality studies compared to studies with lower quality. This suggests that part of the large variation between studies may be explained by less rigorous study designs.ConclusionsOn average, created and restored wetlands significantly reduce the transport of TN and TP in treated wastewater and urban and agricultural runoff, and may thus be effective in efforts to counteract eutrophication. However, restored wetlands on former farmland were significantly less efficient than other wetlands at TP removal. In addition, wetlands with precipitation-driven HLRs and/or hydrologic pulsing show significantly lower TP removal efficiencies compared to wetlands with controlled HLRs. Loading rate (inlet concentrations × hydraulic loading rates) needs to be carefully estimated as part of the wetland design. More research is needed on the effects of hydrologic pulsing on wetlands. There is also a lack of evidence for long-term (&gt;20 years) performance of wetlands.

Finite Element Simulation of Total Nitrogen Transport in Riparian Buffer in an Agricultural Watershed

Riparian buffers can influence water quality in downstream lakes or rivers by buffering non-point source pollution in upstream agricultural fields. With increasing nitrogen (N) pollution in small agricultural watersheds, a major function of riparian buffers is to retain N in the soil. A series of field experiments were conducted to monitor pollutant transport in riparian buffers of small watersheds, while numerical model-based analysis is scarce. In this study, we set up a field experiment to monitor the retention rates of total N in different widths of buffer strips and used a finite element model (HYDRUS 2D/3D) to simulate the total N transport in the riparian buffer of an agricultural non-point source polluted area in the Liaohe River basin. The field experiment retention rates for total N were 19.4%, 26.6%, 29.5%, and 42.9% in 1,3,4, and 6m-wide buffer strips, respectively. Throughout the simulation period, the concentration of total N of the 1mwide buffer strip reached a maximum of 1.27 mg/cm3 at 30 min, decreasing before leveling off. The concentration of total N about the 3mwide buffer strip consistently increased, with a maximum of 1.05 mg/cm3 observed at 60 min. Under rainfall infiltration, the buffer strips of different widths showed a retention effect on total N transport, and the optimum effect was simulated in the 6mwide buffer strip. A comparison between measured and simulated data revealed that finite element simulation could simulate N transport in the soil of riparian buffer strips.

A GIS Framework for Regional Modeling of Riverine Nitrogen Transport: Case Study, San Antonio and Guadalupe Basins

AbstractThis article presents a framework for integrating a regional geographic information system (GIS)‐based nitrogen dataset (Texas Anthropogenic Nitrogen Dataset, TX‐ANB) and a GIS‐based river routing model (Routing Application for Parallel computation of Discharge) to simulate steady‐state riverine total nitrogen (TN) transport in river networks containing thousands of reaches. A two‐year case study was conducted in the San Antonio and Guadalupe basins during dry and wet years (2008 and 2009, respectively). This article investigates TN export in urbanized (San Antonio) vs. rural (Guadalupe) drainage basins and considers the effect of reservoirs on TN transport. Simulated TN export values are within 10 percent of measured export values for selected stations in 2008 and 2009. Results show that in both years the San Antonio basin contributed a larger quantity than the Guadalupe basin of delivered TN to the coastal ocean. The San Antonio basin is affected by urban activities including point sources, associated with the city of San Antonio, in addition to greater agricultural activities. The Guadalupe basin lacks major metropolitan areas and is dominated by rangeland, rather than fertilized agricultural fields. Both basins delivered more TN to coastal waters in 2009 than in 2008. Furthermore, TN removal in the San Antonio and Guadalupe basins is inversely related to stream orders: the higher the order the more TN delivery (or the less TN removal).

SPARROW Modeling of Nitrogen Sources and Transport in Rivers and Streams of California and Adjacent States, U.S.

AbstractThe SPARROW (SPAtially Referenced Regressions On Watershed attributes) model was used to evaluate the spatial distribution of total nitrogen (TN) sources, loads, watershed yields, and factors affecting transport and decay in the stream network of California and portions of adjacent states for the year 2002. The two major TN sources to local catchments on a mass basis were fertilizers and manure (51.7%) and wastewater discharge (15.9%). Other sources contributed &lt; 12%. Fertilizer use is widespread in the Central Valley region of California, and also important in several other regions because of the diversity of California agriculture. Precipitation, sand content of surficial soils, wetlands, and tile drains were important for TN movement to stream reaches. Median streamflow in the study area is about 0.04 m3/s. Aquatic losses of nitrogen were found to be most important in intermittent and small to medium sized streams (0.2‐14 m3/s), while larger streams showed less loss, and therefore are important for TN transport. Nitrogen loss in reservoirs was found to be insignificant, possibly because most of the larger ones are located upstream of nitrogen sources. The model was used to show loadings, sources, and tributary inputs to several major rivers. The information provided by the SPARROW model is useful for determining both the major sources contributing nitrogen to streams and the specific tributaries that transport the load.

Evaluation of a Stepwise, Multiobjective, Multivariable Parameter Optimization Method for the APEX Model

Hydrologic models are essential tools for environmental assessment of agricultural nonpoint-source pollution. The automatic calibration of hydrologic models, though efficient, demands significant computational power, limiting their application. The study objective was to develop and evaluate a stepwise, multiobjective, multivariable automatic calibration method for the Agricultural Environmental Policy eXtender (APEX) model for simulating runoff, sediment, total phosphorus (TP), and total nitrogen (TN). The most sensitive parameters were grouped according to the process they primarily affect (runoff, sediment transport, soil biological activity, TP transport, and TN transport) and were optimized separately and consecutively. Two multiobjective functions comprising combinations of coefficient of determination (), regression slope, and Nash-Sutcliffe coefficient (NSC) and a global objective function, the Generalized Likelihood Uncertainty Estimation, were considered to select the optimal parameter combination. A previously manually calibrated and validated APEX model for three adjacent row-crop field-size watersheds in northeast Missouri was used as the baseline. The greatest improvements in model performance for sediment, TP, and TN, but not for runoff, were found after runoff parameter optimization, indicating that runoff parameter optimization was crucial for good simulation of sediment and nutrients. The values for sediment, TP, and TN improved from 0.59-0.87 to 0.77-0.94. The NSC values for TP also improved after soil biological activity and TP parameter optimizations, but subsequent optimizations did not improve sediment or TN simulations. The objective function based on , slope, and NSC outperformed the other objective functions. Modelers can benefit from this cost-efficient optimization technique (2570 runs for 23 parameters).

Partitioning and First-Flush of Nitrogen in Rainfall-Runoff from an Urban Source Area

AbstractThe urban surface is a largely impervious interface across which nitrogen (N) in runoff is transported and partitions between dissolved and particulate phases. In this study intraevent partitioning and transport are examined across 14 runoff events loading a source area; representative of urban land uses that support motor vehicle activities; specifically parking. N is fractionated as: suspended N for suspended PM (0.45∼25 μm); settleable N for settleable PM; sediment N for sediment PM (greater than 75 μm); and dissolved N as filtered through a 0.45-μm filter. The median total nitrogen (TN) was 4.5 mg/L, much higher than Florida nutrient criteria, and the median of dissolved, suspended, settleable, and sediment N fractions was 2.02, 0.72, 0.29, and 0.78 mg/L. As would be expected for a source area of less complex geometry, transport of TN was generally mass limited (a first flush); however, the suspended and dissolved fractions did exhibit flow-limited transport. Hydrograph unsteadiness also im...

Sprinkler-based rainfall simulation experiments to assess nitrogen and phosphorus losses from a hillslope cropland of purple soil in China

Abstract Currently, water eutrophication has become a serious environmental pollution problem in China due to large amounts of nutrients input into Chinese rivers every year. In order to better understand the mechanisms of nitrogen and phosphorus transport induced by agricultural non-point pollution, we conducted simulated rainfall experiment on a hilly cropland of purple soil under different levels of rainfall intensity and cropland gradient. The dimensions of the experimental plot are: length × width × depth = 4.5 m × 1.5 m × 0.6 m, wherein cropland gradient can be adjusted. The results showed that the discharge process of surface and subsurface runoff was significantly enhanced with the elevated cropland gradient and simulated rainfall intensity. The total phosphorus (TP) transported by runoff was significantly increased with the elevated cropland gradient and simulated rainfall intensity, and accompanied by irregular fluctuation. The discrepancy of TP transport caused by rainfall intensity and cropland gradient was smaller by subsurface runoff than by surface runoff. The transport concentration of total nitrogen (TN) was higher for the subsurface runoff than for surface runoff. Due to different rainfall intensity and cropland gradient, the discrepancy on TN transport was larger by subsurface runoff than by surface runoff. In current study, TN transport by surface runoff was observed between 3.5 and 5.5 mg/L, but the concentration of TP is close to 100 g P/L under rainstorm events, which is the threshold for P eutrophication. The large nutrients losses for local farmers would be an important non-point pollution source to the Three Gorges Reservoir area that receives runoff from the watershed.

Effects of Rainfall Intensity and Amount on the Transport of Total Nitrogen and Phosphorus in a Small Agricultural Watershed

Precipitation-runoff partitioning of small basins plays an important role in the non-point pollution study. This study analyzes the contribution of precipitation and rainfall intensity in a basin scale to pollutants(e.g. nitrogen, phosphorus) migration by monitoring rainfall and runoff responses in Meilin watershed. According to the field data, the concentration of nitrogen keeps an increasing trend with the increase of rainfall amount, while phosphorus seems not so evident. Intense rainfall has a fierce scouring effect on the pollutants which have a large using amount such as total nitrogen in the steep experimental field, thus leading to a sudden decrease of pollutant concentration. After the intensity is weakened, pollutant concentration gradually goes up due to the dissolving effect of runoff.

Estimating the Sources and Transport of Nitrogen Pollution in the Ishikari River Basin, Japan

The hybrid mechanistic-statistical watershed model SPARROW (Spatially Referenced Regression on Watershed Attributes) was applied to estimate the sources and transport of total nitrogen (TN) in surface waters of Ishikari River Basin (14,330 km2), the largest watershed on the Hokkaido Island of Japan. The loads from atmospheric deposition, point sources and erosion are routed through the drainage network (900 streams) with first-order stream decay. Then we calibrated the model using measurements of TN from 31 monitoring sites of mixed spatial data on topography, soils and stream hydrography. The R2 and MSE are 0.82 and 0.62 separately. On this basis, the predication of TN distribution was evaluated, and the mean incremental annual TN yield was 11.61kg/ha/yr.