Nitrate Accumulation and Leaching in Surface and Ground Water Based on Simulated Rainfall Experiments

RESEARCH ARTICLE Nitrate Accumulation and Leaching in Surface and Ground Water Based on Simulated Rainfall Experiments Hong Wang1,3, Jian-en Gao1,2,4*, Xing-hua Li4, Shao-long Zhang4, Hong-jie Wang4 1 Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Yangling, Shaanxi Province, China, 2 Institute of Soil and Water Conservation, Northwest A&F University, Yangling, Shaanxi Province, China, 3 University of Chinese Academy of Sciences, Beijing, China, 4 College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling, Shaanxi Province, China a11111 * Abstract OPEN ACCESS Citation: Wang H, Gao J-e, Li X-h, Zhang S-l, Wang H-j (2015) Nitrate Accumulation and Leaching in Surface and Ground Water Based on Simulated Rainfall Experiments. PLoS ONE 10(8): e0136274. doi:10.1371/journal.pone.0136274 Editor: Jonathan A Coles, Glasgow University, UNITED KINGDOM Received: September 14, 2014 Accepted: August 1, 2015 Published: August 20, 2015 Copyright: © 2015 Wang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and a Supporting Information file. Funding: This paper was supported by Natural Science Foundation of China (41371276, 51309194), by National Technology Support Project (2011BAD31B05), by Science and Technology Project of Shaanxi Province (2013KTDZ03-03-01), by the Subject of National Science and Technology Major Project (2009ZX07212-002-003-02) and by Knowledge Innovation Project of Institute of Soil and Water Conservation, CAS & MWR (A315021304). To evaluate the process of nitrate accumulation and leaching in surface and ground water, we conducted simulated rainfall experiments. The experiments were performed in areas of 5.3 m2 with bare slopes of 3° that were treated with two nitrogen fertilizer inputs, high (22.5 g/m2 NH4NO3) and control (no fertilizer), and subjected to 2 hours of rainfall, with. From the 1st to the 7th experiments, the same content of fertilizer mixed with soil was uniformly applied to the soil surface at 10 minutes before rainfall, and no fertilizer was applied for the 8th through 12th experiments. Initially, the time-series nitrate concentration in the surface flow quickly increased, and then it rapidly decreased and gradually stabilized at a low level during the fertilizer experiments. The nitrogen loss in the surface flow primarily occurred during the first 18.6 minutes of rainfall. For the continuous fertilizer experiments, the mean nitrate concentrations in the groundwater flow remained at less than 10 mg/L before the 5th experiment, and after the 7th experiment, these nitrate concentrations were greater than 10 mg/L throughout the process. The time-series process of the changing concentration in the groundwater flow exhibited the same parabolic trend for each fertilizer experiment. However, the time at which the nitrate concentration began to change lagged behind the start time of groundwater flow by approximately 0.94 hours on average. The experiments were also performed with no fertilizer. In these experiments, the mean nitrate concentration of groundwater initially increased continuously, and then, the process exhibited the same parabolic trend as the results of the fertilization experiments. The nitrate concentration decreased in the subsequent experiments. Eight days after the 12 rainfall experiments, 50.53% of the total nitrate applied remained in the experimental soil. Nitrate residues mainly existed at the surface and in the bottom soil layers, which represents a potentially more dangerous pollution scenario for surface and ground water. The surface and subsurface flow would enter into and contaminate water bodies, thus threatening the water environment. PLOS ONE | DOI:10.1371/journal.pone.0136274 August 20, 2015 1 / 18 The Nitrate Accumulation and Leaching in Surface and Ground Water Competing Interests: The authors have declared that no competing interests exist. Introduction Nitrate is a common contaminant of surface water and groundwater and it can cause health problems in infants and animals as well as eutrophication of water bodies [1–7]. The World Health Organization and the U.S. Environmental Protection Agency have established a maximum contaminant level for nitrate of 10 mg/L as NO3-–N in drinking water [8–10]. Many studies have shown that agricultural activities are a significant source of surface and ground water pollution due to long-term and excessive fertilizer use [7, 11–16]. Non-point source pollution caused by nitrogen from agro-ecosystems is a serious threat to water environments and has received increasing attention regionally and globally [12, 16–20]. Agricultural activities contributed to approximately 75% of non-point pollution, which accounted for approximately two-thirds of the total pollution, in the US [21]. Agriculture is a primary source of river and groundwater pollution in rural areas of the UK [22, 23]. The total nitrogen provided by agricultural non-point sources reached approximately 60% of the total water pollution in the Netherlands [24]. Approximately 94% of the nitrogen loading in 270 rivers was caused by non-point source pollution in Denmark [25]. Since the 1980s, nitrogen fertilizer consumption in China has substantially increased, and nitrate pollution of drinking water has become a serious problem [26]. Fan and Hao [27] summarized the primary factors for the accumulation and leaching of NO3-–N in a soil profile and its potential contamination in surface and underground water in northern China. A number of studies have shown that nitrate-nitrogen (NO3-–N) loss through subsurface drainage is a major source of pollution for surface and groundwater bodies, thus threatening the water environment [28–31]. Nitrate is both soluble and mobile, it is prone to leaching through soil with infiltrating water, and it can persist in shallow groundwater for years [32]. Moreover, the hydrogeological settings, seasonal trends and anthropogenic activities are major factors that influence the mobility and accumulation of nitrates [33]. Under rainfall or irrigation conditions, high levels of soluble nitrates (NO3-–N) leak through soil and into groundwater and then drain away with the groundwater flow. In the Weihe River Basin, groundwater is a streamflow recharge source in the upper reaches; in the middle reaches, one side of the river flow supplies the groundwater, and on the other side, the groundwater supplies the flow [34]. Therefore, nitrate leakage can cause nitrate pollution of groundwater; subsequently, the contaminated groundwater is likely to drain into rivers, resulting in further environmental damage to surface water [35]. Monitoring and modeling approaches ha (...truncated)