Total Nitrogen Concentrations in Surface Water of Typical Agro- and Forest Ecosystems in China, 2004-2009

Abstract

We assessed the total nitrogen (N) concentrations of 28 still surface water (lake and pond), and 42 flowing surface water (river), monitoring sites under 29 typical terrestrial ecosystems of the Chinese Ecosystem Research Network (CERN) using monitoring data collected between 2004 and 2009. The results showed that the median total N concentrations of still surface water were significantly higher in the agro- (1.5 mg·L−1) and oasis agro- ecosystems (1.8 mg·L−1) than in the forest ecosystems (1.0 mg·L−1). This was also the case for flowing surface water, with total N concentrations of 2.4 mg·L−1, 1.8 mg·L−1 and 0.5 mg·L−1 for the agro-, oasis agro- and forest ecosystems, respectively. In addition, more than 50% of the samples in agro- and oasis agro- ecosystems were seriously polluted (>1.0 mg·L−1) by N. Spatial analysis showed that the total N concentrations in northern and northwestern regions were higher than those in the southern region for both still and flowing surface waters under agro- and oasis agro- ecosystems, with more than 50% of samples exceeding 1.0 mg·L−1 (the Class III limit of the Chinese National Quality Standards for Surface Waters) in surface water in the northern region. Nitrogen pollution in agro- ecosystems is mainly due to fertilizer applications, while the combination of fertilizer and irrigation exacerbates nitrogen pollution in oasis agro- ecosystems.

River export of nutrients to the coastal waters of China: the MARINA model to assess sources, effects and solutions

“…This not only increased Chinese fresh water use (Piao et al 2010), but also heavily polluted Chinese main rivers (Xu et al 2014) and thus eutrophication is abundant in Chinese coastal waters (Tang et al 2006a). In my PhD research, I therefore focus on understanding the trends in nutrient export by Chinese rivers, causes of river pollution and assess solutions to reduce the consequent eutrophication problems in Chinese coastal areas.…”

“…In general, these studies confirm an increase in fluxes of dissolved nutrients by rivers since the 1970s, except for Powers et al (2016) who showed a declining trend in P export by the Yangtze since 1970. Some experimental studies also report on nutrient pollution problems for inland water systems (Huang 2015;Xu et al 2014) and estuaries (Liu et al 2009b;Tong et al 2015). For example, Xu et al (2014) indicate that many Chinese rivers like Huai, Hai, Yellow and river deltas today have concentrations of nutrients at levels that do not allow for human consumption.…”

“…Some experimental studies also report on nutrient pollution problems for inland water systems (Huang 2015;Xu et al 2014) and estuaries (Liu et al 2009b;Tong et al 2015). For example, Xu et al (2014) indicate that many Chinese rivers like Huai, Hai, Yellow and river deltas today have concentrations of nutrients at levels that do not allow for human consumption. However, these studies lack analyses of trends in nutrient export by Chinese rivers.…”

“…Many Chinese rivers show similar trends. Northern rivers, such as the Yellow (Huanghe), Hai, Liao and Huai, and river deltas are polluted by nutrients to the extent that their water is not suitable for human contact (Class VI) (Xu et al 2014). Leaching of nutrients from fertilized soils is generally considered the major cause Liu et al 2008a;Ongley et al 2010;Tao et al 2010;Xu et al 2014).…”

“…Existing studies Liu et al 2008a;Ongley et al 2010;Tao et al 2010;Xu et al 2014) generally do not account for these point sources and thus may underestimate actual nutrient loads to rivers (see Section 4.3 below). Some links between agricultural transitions and water quality were published in studies (e.g., Bai et al 2014;Ma et al 2010;MEP et al 2010;Schneider 2011;Steinfeld et al 2006) focusing largely at national analyses.…”