Abstract
Abstract Nitrate (NO3-N) load characteristics in consecutive dry years in the Huai River Basin (HRB), China, were examined using streamflow and NO3-N concentration data. The data set spanned 12 years including three consecutive dry years. Baseflow separation, load estimation, and nonparametric linear regression were applied to separate point source (PS), baseflow, and surface runoff NO3-N loads from the total load. The mean annual nonpoint source (NPS) load was 2.84 kg·ha−1·yr−1, accounting for 90.8% of the total load. Baseflow contributed approximately one-fourth of the natural runoff and half of the NPS load. The baseflow nitrate index (i.e., the ratio of baseflow NO3-N load to total NPS NO3-N load) was 25.4% higher in consecutive dry years than in individual dry years. This study demonstrated that baseflow is the preferential hydrological pathway for NO3-N transport in the HRB and that baseflow delivers a higher NO3-N percentage to streams under long-term drought than under short-term drought. This study highlights the alarming evidence that continuous drought caused by climate change may lead to a higher rate of nitrogen loss in agricultural watersheds.
Highlights
The Huai River Basin (HRB), where the annual nitrogen fertilizer application rates amount to approximately 600 kg·N·haÀ1·yrÀ1, is one of the major grain-producing areas in China
The baseflow enrichment ratio (BER) in the Raccoon River Watershed, USA, ranged from 0.23 to 1.61 and averaged 1.23 (Schilling & Zhang 2004); the BER in the Daejeon region, South Korea, ranged from 0.6 to 1.5 (Kim et al 2010). These results suggest that controlling the baseflow NO3-N concentration plays a key role in nonpoint source (NPS) NO3-N management of the upper and middle HRB
The baseflow accounted for approximately one-fourth of the total natural runoff and contributed half of the total NPS NO3-N load, and the mean annual BER was 1.82
Summary
The Huai River Basin (HRB), where the annual nitrogen fertilizer application rates amount to approximately 600 kg·N·haÀ1·yrÀ1, is one of the major grain-producing areas in China. The NO3-N concentration in groundwater below agricultural fields is generally much higher than in surface waters (Almasri & Kaluarachchi 2004). This NO3-N in groundwater may be primarily transferred to surface waters under baseflow conditions (He & Lu 2016; Richards et al 2021). Apart from Chen (2013) and Chen et al (2017), who estimated the NO3-N load in groundwater discharge in a small sub-basin, few researchers have reported the long-term baseflow contributions to the nonpoint source (NPS) NO3-N loads in streamflows in the HRB. It is necessary to quantify the NPS NO3-N loads and baseflow contribution for NPS NO3-N assessment and management of the HRB
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
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
