Effects of Redox Potential on the Environmental Behavior of Nitrogen in Riparian Zones of West Dongting Lake Wetlands, C
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GENERAL WETLAND SCIENCE
Effects of Redox Potential on the Environmental Behavior of Nitrogen in Riparian Zones of West Dongting Lake Wetlands, China Shan Zhao 1 & Baoju Zhang 1 & Nianqing Zhou 2 Received: 2 December 2019 / Accepted: 6 April 2020 # Society of Wetland Scientists 2020
Abstract Nitrogen pollution in wetland ecosystems has become a pressing global issue in recent years. The effects of redox potential on the environmental behavior of nitrogen remain elusive. In the present work, both field experiments and laboratory analyses have been carried out to characterize the spatial-temporal changes of dissolved inorganic nitrogen (NO3−, NO2−, NH4+) and redox potential in the riparian zones of West Dongting Lake Wetland, China. The stability field of groundwater for inorganic nitrogen was represented in an Eh-pH diagram. It is noted that NH4+ is the most abundant species in groundwater when −500 mV < Eh < +300 mV at pH < 9.23; while under oxidizing conditions (Eh > 400 mV), nitrogen is generally in the form of NO3−. The range of both Eh and pH scales was from −381 to 193 mV and from 6.84 to 7.32, respectively, which involved two types of reduction, dissimilatory nitrate reduction to ammonia and denitrification, and the inhibition of the oxidation pathway by nitrification. In groundwater, NH4+ accounted for 50%–90% of the total concentration of dissolved inorganic nitrogen, in accordance with the Eh-pH diagram. This study reveals the severe contamination of groundwater by NH4+ in the riparian zones of Li and Yuan. It provided a theoretical basis to predict nitrogen pollution preliminarily and facilitate management and protection of wetlands. Keywords Redox potential . Nitrogen . Riparian zones . Environmental behavior . Dongting Lake
Introduction Nitrogen is an essential component for wetland ecosystems (Gruber and Galloway 2008). Previous works have been conducted concerning the identification of sources and environmental fate (Bowden 1987; Martin and Reddy 1997; Kjellin et al. 2007; Hong et al. 2019). Significant amounts enter the wetlands in stormwater runoff, deposition, or through biological nitrogen fixation (Zhou et al. 2014; Zhao et al. 2016b). In recent years, the inputs of reactive nitrogen primarily from the combustion of fossil fuels, synthetic fertilizers, or cultivation of nitrogen-fixing legumes have increased (Galloway et al. 1995; Vitousek et al. 1997). Some areas, including aquatic
* Shan Zhao [email protected] 1
College of Ocean Science and Engineering, Shanghai Maritime University, 1550 Haigang Ave, Shanghai 201306, People’s Republic of China
2
Department of Hydraulic Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, People’s Republic of China
ecosystems are experiencing increasing levels of nitrogen, resulting in an excess called as nitrogen saturation (Hanson et al. 1994; Earl et al. 2006). When present in excess, nitrogen causes a range of negative effects for wetlands services (Galloway et al. 2004; Canfield et al. 2010), such as water supply, transport, recreation
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