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Critical source areas’ identification for non-point source pollution related to nitrogen and phosphorus in an agricultural watershed based on SWAT model

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Abstract

Water eutrophication caused by the extensive expansion of slope farming has caused the high attention of the Chinese government. We choose Lake Tianmu basin as the study area because it can represent vast majority of basins plagued by water eutrophication derived from slope tillage in southern China. The water ecosystem in the reservoir Daxi and Shahe within the basin has been seriously threatened by multiple pollution sources related to many intricate human activities especially agricultural production. For the first time, we identified the critical source areas (CSAs) within the basin based on nutrient load and nutrient load intensity (NLI), and on this basis, we further excavated the main causes of pollution and proposed pertinent remediation measures. The results based on the calibrated Soil and Water Assessment Tool model indicated that the TN load of each reservoir remarkably exceeded their respective water environmental capacity from 2014 to 2018. Accordingly, six main tributaries with great nutrient contributions and their corresponding sub-basins were then identified. Overall, tea and rice plantations appear to be the major nutrient contributors to reservoir Daxi. And the main nutrient sources for reservoir Shahe are tea plantations, orchards, farmland, forestland, and point sources. Regarding the CSAs identified only by nutrient load, agronomic measures such as reducing fertilizer amount, biochar application, straw incorporation, and plastic mulch coverage can be employed to improve soil water retention and curb soil erosion. Regarding the CSAs identified by nutrient load intensity (NLI), the CSAs with narrow areas should be turned directly into forestland. For the CSAs with large areas, engineering measures such as constructing ecological riparian zone, filtration, and sedimentation tank can be employed to prevent pollutants from entering downstream reaches. Overall, the present results can provide the decision-making support for the safe and efficient management of watershed land use in southern China.

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Availability of data and materials

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Funding

The National Natural Science Foundation of China (No. 41671388) and the Natural Science Foundation of Jiangsu Province (No. BK20190711) provided the financial supports for the study.

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Contributions

All authors contributed to the study conception and design. Material preparation and data collection were performed by ZQL, SL, DL, and JZ. The data analysis and first draft of the manuscript were written by DC. All authors read and approved the final manuscript.

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Correspondence to Zhengqing Lai or Shuo Li.

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The authors declare no competing interests.

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Responsible Editor: Thomas Hein

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Highlights

• A typical slope tillage watershed plagued by water eutrophication in southern China was studied.

• TN loads of the reservoirs remarkably exceed their water environmental capacity.

• Critical source areas of TN/TP are identified and assessed using the SWAT model.

• Nutrient contributions to water from different land use are quantitatively assessed.

• Specific restoration strategies tailored to water quality target are proposed.

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Chang, D., Lai, Z., Li, S. et al. Critical source areas’ identification for non-point source pollution related to nitrogen and phosphorus in an agricultural watershed based on SWAT model. Environ Sci Pollut Res 28, 47162–47181 (2021). https://doi.org/10.1007/s11356-021-13973-9

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  • DOI: https://doi.org/10.1007/s11356-021-13973-9

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