江汉平原典型地区季节性水文条件影响下氮的动态变化规律

江汉平原东部地区地下水硝态氮和氨氮污染严重，地表水-地下水相互作用强烈，季节性水文条件变化极其显著.选取典型试验场地，对试验场内沉积物(0~25 m)氮形态进行测定，并对地下水氮含量及其他水化学指标进行连续性监测.研究表明:沉积物NO₃--N含量较高(25.8~119.48 mg/kg)，是可交换态氮的主要组成部分，NH₃-N含量与TOC和TN均呈一定的正相关性，表明NH₃-N含量主要受沉积物中埋藏有机质的控制.试验场深度较深(≥2 m)地下水氮的含量和形态对地下水位波动有明显响应:雨季开始，地下水位抬升，含水介质还原性增强，NO₃--N生成受抑制且通过反应消耗，矿化作用加强，导致NH₃-N成为氮的主要赋存形态；雨季结束，地下水水位下降，含水介质的氧化性增强，NO₃--N的生成受到促进，硝化作用增强而反硝化作用减弱，导致NO₃--N的浓度增加.近地表人类活动(外源输入)对试验场浅表地层(＜2 m)地下水氮形态有明显的影响.自然或者人为因素引起的水文条件变化导致地下水流场的变化，从而改变含水介质固有的氧化还原环境，是导致试验场氮季节性变化的主要原因. 

Dynamic Variations of Nitrogen in Groundwater under Influence of Seasonal Hydrological Condition in Typical Area of Jianghan Plain

The pollution of NO₃--N and NH₃-N in groundwater is very serious in the eastern of Jianghan plain, which is characterized by strong interactions between groundwater and surface water and obvious variations of seasonal hydrological condition. Sediment samples along vertical profiles of three boreholes and groundwater samples with different depths in different seasons were sampled to analyze the nitrogen speciation coupled with supporting chemistry in a typical field site. The results show that NO₃--N with concentrations from 25.8 to 119.48 mg/kg is a dominant speciation of the total exchangeable nitrogen in sediments. The NH₃-N concentrations have a good positive correlation with TOC and TN contents in sediments, implying NH₃-N was mainly influenced by organic matter. The concentration and speciation of nitrogen in the groundwater deeper than 2 m show a significant response to the fluctuation of groundwater level. During the monsoon season, groundwater level increased, enhancing the reducing potential of aquifer media. As a result, NO₃--N was not liable to be produced and was more likely to be consumed by denitrification. At the same time, with the mineralization enhanced, NH₃-N was gradually becoming the main speciation of dissolved inorganic nitrogen. After the monsoon season, groundwater level declined, enhancing the oxidizing potential of aquifer media.As a result, nitrification was enhanced and denitrification was limited, and the concentration of NO₃--N increased.Anthropogenic activities near the surface had a significant effect on the concentration and speciation of nitrogen in the groundwater shallower than 2 m. In summary, under the coupled influence of natural and anthropogenic factors, seasonal hydrological change resulted in the variation of redox potential, which was the main trigger for seasonal variation of nitrogen concentration and speciation in the groundwater.