Abstract
Water quality is the restrictive factor for both ecosystem health and social development in the Chinese Loess Plateau, a unique area with most severe soil erosion, fragile ecology, and water shortage. Understanding the characteristics of the pollutant loads is of vital importance for the sustainability of eco-environment in the Loess Plateau. This study investigated the spatiotemporal changes of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) loads by combining the Soil and Water Assessment Tool (SWAT) and regression model Load Estimator (LOADEST) in a typical loess hilly and gully watershed—the Yan River Basin (YanRB). Results showed that the model simulations of monthly streamflow and pollutant loads were in good agreement with those derived from the in situ observations. The temporal variation analysis suggested that the pollutant loads were generally rising in the study period (2001–2018) at four of the five stations and reached the maximum in 2014, and the multi-year (i.e., 2001–2018 with 2013 being excluded due to extreme rainfall) average loads of COD, TN, and TP at the Tanjiahe station, which is close to the outlet of the basin, were 15,021 kg/day, 3835 kg/day, and 168 kg/day, respectively. The spatial distribution of the TN and TP loads along the river seemed to be quite unique because the TP level were obviously higher at the midstream (e.g., Zhujiagou and Ganguyi) than the downstream (e.g., Tanjiahe), and the TN level decreased when the river flowed from Zhujiagou to Ganguyi. Further, the seasonal analysis indicated that the nutrient loads were the highest in summer, followed by autumn, and the loads in these two seasons contributed the most of the annual pollution loads—about 76% and 84% for TN and TP, respectively, indicating the higher flow, the higher pollution load, a similar point based on the inter-annual analysis. In addition, the contribution analysis of point source and non-point source pollutions demonstrated that NPS led to most of the pollutant loads at the whole watershed—70%, 67%, and 71% of the COD, TN, and TP loads, respectively. Overall, this study provided spatiotemporal distributions of the key pollutant loads in the YanRB and can be valuable for water quality protection and pollution control in this area.
Highlights
Pollutant discharge causes widespread organic pollution and eutrophication, along with severe ecological destruction, and further threats human health and agricultural production (Wang and Yang 2016; Dai et al 2017; Lang et al 2013; Schwarzenbach et al 2010)
There was an underestimation of streamflow during the wet season, the overall performance was satisfactory during both calibration (2001–2004) and validation (2005–2008) periods, with R2 and Nash efficiency coefficient (NSE) ranging from 0.50 to 0.67 and percent bias (PBIAS) being less than 15%
We found that the estimation of total nitrogen (TN) and total phosphorus (TP) loads had a better performance than chemical oxygen demand (COD)
Summary
Pollutant discharge causes widespread organic pollution and eutrophication, along with severe ecological destruction, and further threats human health and agricultural production (Wang and Yang 2016; Dai et al 2017; Lang et al 2013; Schwarzenbach et al 2010). Song et al Geoscience Letters (2022) 9:10 government has realized the importance of controlling water pollution, and published Action Plan for Prevention and Control of Water Pollution to protect the surface water and groundwater in April 2015 (Shi et al 2015). Zou et al (2020) used an inventory analysis to estimate the agricultural non-point source (NPS) pollution loads from 1978 to 2017 in China, and found that the pollution loads of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) increased by 91.0%, 196.2%, and 244.1%, respectively. Identifying the current pollution situation and understanding its relationships with human activities are important for water resources protection and pollution control
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
