Enhanced nitrogen deposition over China

Abstract

China is experiencing intense air pollution caused in large part by anthropogenic emissions of reactive nitrogen. These emissions result in the deposition of atmospheric nitrogen (N) in terrestrial and aquatic ecosystems, with implications for human and ecosystem health, greenhouse gas balances and biological diversity. However, information on the magnitude and environmental impact of N deposition in China is limited. Here we use nationwide data sets on bulk N deposition, plant foliar N and crop N uptake (from long-term unfertilized soils) to evaluate N deposition dynamics and their effect on ecosystems across China between 1980 and 2010. We find that the average annual bulk deposition of N increased by approximately 8 kilograms of nitrogen per hectare (P < 0.001) between the 1980s (13.2 kilograms of nitrogen per hectare) and the 2000s (21.1 kilograms of nitrogen per hectare). Nitrogen deposition rates in the industrialized and agriculturally intensified regions of China are as high as the peak levels of deposition in northwestern Europe in the 1980s, before the introduction of mitigation measures. Nitrogen from ammonium (NH4(+)) is the dominant form of N in bulk deposition, but the rate of increase is largest for deposition of N from nitrate (NO3(-)), in agreement with decreased ratios of NH3 to NOx emissions since 1980. We also find that the impact of N deposition on Chinese ecosystems includes significantly increased plant foliar N concentrations in natural and semi-natural (that is, non-agricultural) ecosystems and increased crop N uptake from long-term-unfertilized croplands. China and other economies are facing a continuing challenge to reduce emissions of reactive nitrogen, N deposition and their negative effects on human health and the environment.

Are nitrate production and retention processes in subtropical acidic forest soils responsive to ammonium deposition?

“…The low N treatment was to simulate a future increase in the atmospheric N deposition by 3-fold, corresponding to the annual bulk deposition rates in the subtropical region of China (>22.2e35 kg N ha À1 yr À1 ) (Liu et al, 2013;Jia et al, 2014), and the level of low N addition to subtropical/tropical forest ecosystems (50 kg N ha À1 yr À1 ) (Hall and Matson, 1999;Mo et al, 2008;Baldos et al, 2015). The high N treatment was to stimulate N-enriched conditions, exposing soil microbes to abrupt environmental changes to observe the direction of changes in soil N-cycling (Corre et al, 2010).…”

“…Huygens et al (2008) pointed out that DNRA also depends directly on heterotrophic nitrification for substrate generation. Subtropical/tropical forest ecosystems are projected to receive enhanced N deposition (Galloway et al, 2008;Liu et al, 2013), but changes in the processes, rates and controls of soil N-cycling in these ecosystems under anthropogenic N inputs are less well understood (Silver et al, 2005;Corre et al, 2010;Cusack et al, 2011;Baldos et al, 2015;Gao et al, 2015). For example, Corre et al (2010) reported that during 9 years of N addition to an oldgrowth lowland forest with net primary production not limited by N, microbial biomass decreased with increased soil acidity, but gross N mineralization rates increased.…”

The composition, spatial patterns, and influencing factors of atmospheric wet nitrogen deposition in Chinese terrestrial ecosystems

“…Observations of atmospheric N deposition are essential for evaluating its ecological effects on terrestrial ecosystems (Galloway et al, 2008;Liu et al, 2011Liu et al, , 2013. Some studies have reported the observed results of atmospheric N deposition at a local scale (Chen and Mulder, 2007;Huang et al, 2013), from catchments (Chen et al, 2011;Yu et al, 2011), or from belt transects (Sheng et al, 2013;Zhan et al, 2014) in China.…”

Drained coastal peatlands: A potential nitrogen source to marine ecosystems under prolonged drought and heavy storm events—A microcosm experiment

“…Overloading of nitrogen is a leading cause of impairment of coastal marine ecosystems around the world (Boesch et al, 2001;Compton et al, 2011;Diaz and Rosenberg, 2008;Paerl and Piehler, 2008). Currently, most studies focus on anthropogenic nitrogen sources, like fertilizer applied in farmlands and fossil-fuel derived atmospheric deposition Liu et al, 2013;Paerl, 1997;Paerl, 2009;Robert, 2008). However, chronically accumulated organic nitrogen in natural ecosystems can potentially be quickly released and become a substantial source of nitrogen pollution, exacerbating degradation of aquatic ecosystems when environmental conditions, such as climatic warming and drought, change to favor nitrogen mineralization.…”