School of Environmental Studies, China University of Geosciences, Wuhan 430074, China; MOE Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China.
School of Environmental Studies, China University of Geosciences, Wuhan 430074, China; MOE Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China.
Sci Total Environ. 2020 Nov 1;741:140350. doi: 10.1016/j.scitotenv.2020.140350. Epub 2020 Jun 18.
The controlling processes of excessive ammonium in surface water and groundwater in the central Yangtze River Basin remain unclear. In this study, monitoring of water levels and temporal-spatial distributions of major N compounds were implemented at the large Jiangshan plain and at the local site scale in the central Yangtze River Basin. The results indicate that the recharge, movement and transformation of ammonium were controlled by hydrogeological conditions. Manure and sewage from anthropogenic activities were identified as the main source of nitrogen compounds. The nitrogen loading into aquifers were governed by water table and groundwater flow. After entering subsurface soils, nitrification and dissimilatory nitrate reduction to ammonium (DNRA) were proposed as the ammonium consumption and production mechanisms, respectively, by combining the concentrations of ammonium‑nitrogen and nitrate‑nitrogen with the corresponding isotopic compositions. These microbially mediated processes controlling transport and transformation of nitrogen compounds were influenced by the seasonally varying groundwater flow regime that changed the redox conditions in the aquifers. In the subsurface environments, ammonium was converted to nitrate when sufficient oxygen supply was available, and this process was reversed under anoxic conditions along the groundwater flow path. A conceptual model for the reactive transport of nitrogen compounds jointly controlled by the vertical groundwater flows and biogeochemical processes was proposed, which provides new insights into the genesis of high ammonium groundwater.
长江中下游地区地表水和地下水中过量铵的控制过程仍不清楚。本研究在长江中下游大型江山平原和局部地区尺度上对主要氮化合物的水位和时空分布进行了监测。结果表明，铵的补给、运移和转化受水文地质条件控制。人为活动产生的粪肥和污水被确定为氮化合物的主要来源。氮素进入含水层受地下水位和地下水流动控制。进入地下土壤后，硝化和异化硝酸盐还原为铵（DNRA）分别被提出作为铵消耗和产生的机制，这是通过将铵氮和硝酸盐氮的浓度与相应的同位素组成相结合来实现的。这些微生物介导的过程控制着氮化合物的运移和转化，受季节性变化的地下水流动模式影响，这种模式改变了含水层中的氧化还原条件。在地下环境中，当有足够的氧气供应时，铵会转化为硝酸盐，而在沿着地下水流动路径的缺氧条件下，这一过程会发生逆转。提出了一个受垂直地下水流动和生物地球化学过程共同控制的氮化合物反应输运的概念模型，为高铵地下水的成因提供了新的见解。
