Non-point Source Total Phosphorus Research Articles

Will agricultural land scale management aggravate non-point source pollution? – Chaohu Lake Basin, China as a case study

In this study, we investigated the relationship between scale management and non-point source (NPS) total phosphorus (TP) load in Chaohu Lake Basin. We used agricultural point of interest (POI) density to characterize scale management and employed the Soil and Water Assessment Tool (SWAT) model for simulations. Our findings in 2018 showed that there was a segmented relationship between agricultural POI density and TP load in townships. Significant negative correlations between POI density and TP load were observed in medium-density (0.076 < POI<0.172) and high-density (POI>0.172) scale management townships, but not in low-density (POI<0.076) townships. The slope coefficient for high-density townships was approximately one-tenth of that for medium-density townships, indicating the prevalence of agricultural land scale management at only a certain density can effectively inhibit NPS TP emissions, and this inhibitory effect has a marginal diminishing effect. These observations also applied to vegetable, fruit, and flower nurseries bases. Notably, low-density scale management of farms still had a significant inhibitory effect on TP load. However, scale management of forest farms and tea plantations did not inhibit TP loads due to the influence of high natural background phosphorus content, low hills with large gradients, and low POI density.

Quantitative simulation of the relationships between cultivated land-use patterns and non-point source pollutant loads at a township scale in Chaohu Lake Basin, China

Non-point source (NPS) pollution caused by unsustainable cultivated land use is becoming more severe. It is therefore critical to understand the complex relationships between cultivated land use forms and NPS pollutant loads from the perspective of integrated cultivated land use. This study used the cultivated land use pattern to integration represent the various forms of cultivated land use, and constructed a model to estimate NPS pollutant outputs at an administrative-region scale. This model was used to quantitatively simulate the NPS total phosphorus (TP) loads of townships with different cultivated land-use patterns in Chaohu Lake Basin, China, since 2000. The relationships between the TP loads and the different cultivated land use patterns were then assessed to clarify the corresponding function mechanisms and provide scientific support for effective NPS pollution controls. The cultivated land-use patterns of the townships in Chaohu Lake Basin were classified as suburban compound operations (SC); grain and economical crop scale operations (GES); grain and economical crop extensive operations (GEE); and grain, oil, and cotton scale operations (GOCS). The TP loads of townships with various cultivated land-use patterns were significantly different. The average TP load of GEE pattern townships was the highest (5.39 kg ha−1a−1), which was 1.85 times the lowest value of the SC pattern townships. The TP loads of GES and GOCS pattern were similar (3.52 kg ha−1a−1 and 3.19 kg ha−1a−1, respectively). The heterogeneous NPS TP loads are due to the face that cultivated land-use forms exhibit different marginal inhibition/promotion effects on NPS pollutant outputs with different patterns. Different correlations and significances were observed between various cultivated land-use form factors and NPS TP loads with different patterns. Therefore, accurate classifications and recognition of cultivated land-use patterns can be utilized to clarify the function mechanism between cultivated land use and NPS pollutant loads.

Source apportionment of nitrogen and phosphorus from non-point source pollution in Nansi Lake Basin, China.

Nitrogen (N) and phosphorus (P) from non-point source (NPS) pollution in Nansi Lake Basin greatly influenced the water quality of Nansi Lake, which is the determinant factor for the success of East Route of South-North Water Transfer Project in China. This research improved Johnes export coefficient model (ECM) by developing a method to determine the export coefficients of different land use types based on the hydrological and water quality data. Taking NPS total nitrogen (TN) and total phosphorus (TP) as the study objects, this study estimated the contributions of different pollution sources and analyzed their spatial distributions based on the improved ECM. The results underlined that the method for obtaining output coefficients of land use types using hydrology and water quality data is feasible and accurate, and is suitable for the study of NPS pollution at large-scale basins. The average output structure of NPS TN from land use, rural breeding and rural life is 33.6, 25.9, and 40.5%, and the NPS TP is 31.6, 43.7, and 24.7%, respectively. Especially, dry land was the main land use source for both NPS TN and TP pollution, with the contributed proportions of 81.3 and 81.8% respectively. The counties of Zaozhuang, Tengzhou, Caoxian, Yuncheng, and Shanxian had higher contribution rates and the counties of Dingtao, Juancheng, and Caoxian had the higher load intensities for both NPS TN and TP pollution. The results of this study allowed for an improvement in the understanding of the pollution source contribution and enabled researchers and planners to focus on the most important sources and regions of NPS pollution.

Estimating nonpoint source pollution load using four modified export coefficient models in a large easily eroded watershed of the loess hilly–gully region, China

The quantitative estimation of nonpoint source (NPS) pollution load in large river basins is one of the important issues in watershed modeling. This study focuses on Beiluohe River watershed and takes Johnes export coefficient model as a starting point to establish three kinds of modified export coefficient model and estimate NPS total nitrogen (TN) and total phosphorus (TP) load of the watershed from 1995 to 2010. Results indicate that: (1) The first proposed export coefficient model considering effects of soil loss has characteristics of high precision, simple algorithm and less parameters; it is more suitable for loess hilly and gully region with a sparse vegetation cover and severe soil erosion. (2) NPS TN load in Beiluohe River watershed was 12,778.17 tons in 1995; in 2010, it fell to 4673.37 tons, a decrease of 63.42 %. NPS TP load in Beiluohe River watershed was 643.52 tons in 1995; by the year of 2010, it fell to 254.93 tons, a decrease of 60.38 %. (3) The highest contribution of NPS TN load is from farmland (42.16 %); the contribution rates of agricultural population, big livestock, pig, forestland and grassland are 18.14, 14.05, 8.03, 8.02 and 6.17 %, respectively; The highest contribution of NPS TP load is also from farmland (31.41 %); grassland, agricultural population and pig also account for large proportions, which are 21.80, 19.58 and 16.72 %, respectively. (4) The top priority for improving water environment quality is to further strengthen the source control of NPS pollution. The following is the migration control and then the end control of waste and wastewater treatment. Results may provide a theoretical basis and data reference for quantitative estimation and source control of NPS pollution at watershed scales.

Long-term agricultural non-point source pollution loading dynamics and correlation with outlet sediment geochemistry

Some agricultural non-point source (NPS) pollutants accumulate in sediments in the outlet sections of watersheds. It is crucial to evaluate the historical interactions between sediment properties and watershed NPS loading. Therefore, a sediment core from the outlet of an agricultural watershed was collected. The core age was dated using the 210Pb method, and sedimentation rates were determined using the constant rate of supply (CRS) model. The total nitrogen (TN), total phosphorus (TP), Cd, Pb, Cu, Ni and Cr accumulations in the sediment generally showed fluctuating increases, with the highest sedimentation fluxes all occurring in approximately 1998. The measurement of specific mass sedimentation rates reflected a record of watershed soil erosion dynamics. Using SWAT (Soil and Water Assessment Tool) to simulate long-term watershed agricultural NPS pollution loadings, the historical interactions between sediment properties and NPS loadings were further evaluated. The N leaching process weakened these interactions, but the historical accumulations of TP and heavy metals in sediments generally correlated well with watershed NPS TP loading. The regression analysis suggested that Pb and Cr were the most suitable indexes for assessing long-term NPS TN and TP pollution, respectively. Assessing the NPS loading dynamics using the vertical characteristics of sediment geochemistry is a new method.

Reconstructing historical changes in phosphorus inputs to rivers from point and nonpoint sources in a rapidly developing watershed in eastern China, 1980–2010

Quantifying point (PS) and nonpoint source (NPS) phosphorus inputs to rivers is critical for developing effective watershed remediation strategies. This study reconstructed PS and NPS total phosphorus (TP) inputs to the Yongan River in eastern China in 1980–2010 using a load apportionment model (LAM) from paired riverine TP concentrations and river discharge records. Based on the fundamental hydrological differences between PS and NPS pollution, the LAM statistically quantified their individual inputs as a power-law function of river discharge. The LAM-estimated monthly/annual riverine TP loads were in good agreement with results derived from a regression model, Load Estimator (LOADEST). The annual TP load increased from 18.4 to 357.0Mgyr−1 between 1980 and 2010. The PS input contributed 7–45% of annual total TP load and increased 23-fold, consistent with a 20-fold increase in flow-adjusted average chloride concentration during the low flow regime (a proxy for wastewater inputs), as well as measured increases in population, poultry, and industrial production. Inferring from observed TP and chloride ratios, as well as total suspended solids (TSS) and river discharge dynamics, temporally retained P load within the river during the low flow regime was estimated to contribute 18–65% of the annual PS input load. NPS inputs consistently dominated the annual riverine TP load (55–93%) and increased 19-fold, consistent with the strong correlation between riverine TP and TSS concentrations, increasing developed land area, improved agricultural drainage systems, and phosphorus accumulation in agricultural soils. Based on our analysis, TP pollution control strategies should be preferentially directed at reductions in NPS loads, especially during summer high-flow periods when the greatest eutrophication risk occurs.