感潮河岸潜流带地下水三氮时空差异与驱动因子分析

Spatiotemporal Variations and Driving Factors of Inorganic Nitrogen in Groundwater in Tidal Riparian Hyporheic Zones

摘要:

潜流带是河水与地下水频繁转化的场所，其内部氮循环对维持河流生态健康具有重要意义。以上海地区感潮河流为研究对象，采用现场监测、取样测试及统计分析手段，研究了岸滩潜流带地下水中无机氮浓度分布特征随时间变化的差异性及其关键影响因子。结果表明，在研究区潜流带地下水中，氨氮和硝态氮浓度在潜流净入期显著高于潜流净出期，亚硝态氮浓度值极低；随离岸线距离的增加，无机氮赋存形态从硝态氮为主转变为氨氮为主，氨氮浓度先升后降而硝态氮浓度逐渐下降。潜流带地下水中无机氮浓度变化的关键驱动因子在潜流净入期为潜流交换通量、Eh和pH，在潜流净出期为Eh和潜流交换通量。感潮河岸潜流带的功能在潜流净入期更趋向于氮汇，而在潜流净出期更趋向于氮源。

Abstract:

The hyporheic zone is a place where river water and groundwater frequently interact， whose internal nitrogen cycle is of great significance for maintaining the ecological health of rivers. Taking tidal rivers in the Shanghai as the research object， the seasonal variations in inorganic nitrogen concentrations in groundwater in the riparian hyporheic zone and their key driving factors were investigated using on-site monitoring， sampling tests and statistical analysis. The results show that ammonia nitrogen （NH??—N） and nitrate nitrogen （NO??—N） concentrations were significantly higher during the hyporheic flow （HF） net inflow period than those during the HF net outflow period， while nitrite nitrogen （NO??—N） concentration was extremely low. With increasing distance from the river， the dominant form of inorganic nitrogen shifted from NO??—N to NH??—N， and NH??—N concentration initially increased and then decreased while NO??—N concentration gradually decreased. The key factors influencing the changes in inorganic nitrogen concentrations in groundwater in the hyporheic zone were hyporheic exchange flux， Eh， and pH during the HF net inflow period ， and Eh and hyporheic exchange flux during the HF net outflow period. The function of hyporheic zone in tidal riverbanks tends to be a nitrogen sink during the HF net inflow period and a nitrogen source during the HF net outflow period.