Geology Department/Trinity Centre for the Environment, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland; Agricultural Catchments Programme, Teagasc, Environment Research Centre, Johnstown Castle, Wexford, Ireland; Crops, Environment and Land Use Programme, Teagasc Environment Research Centre, Johnstown Castle, Wexford, Ireland.
Geology Department/Trinity Centre for the Environment, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland.
Sci Total Environ. 2017 May 15;586:372-389. doi: 10.1016/j.scitotenv.2016.11.083. Epub 2017 Feb 20.
At the catchment scale, a complex mosaic of environmental, hydrogeological and physicochemical characteristics combine to regulate the distribution of groundwater and stream nitrate (NO). The efficiency of NO removal (via denitrification) versus the ratio of accumulated reaction products, dinitrogen (excess N) & nitrous oxide (NO), remains poorly understood. Groundwater was investigated in two well drained agricultural catchments (10km) in Ireland with contrasting subsurface lithologies (sandstone vs. slate) and landuse. Denitrification capacity was assessed by measuring concentration and distribution patterns of nitrogen (N) species, aquifer hydrogeochemistry, stable isotope signatures and aquifer hydraulic properties. A hierarchy of scale whereby physical factors including agronomy, water table elevation and permeability determined the hydrogeochemical signature of the aquifers was observed. This hydrogeochemical signature acted as the dominant control on denitrification reaction progress. High permeability, aerobic conditions and a lack of bacterial energy sources in the slate catchment resulted in low denitrification reaction progress (0-32%), high NO and comparatively low NO emission factors (EF1). In the sandstone catchment denitrification progress ranged from 4 to 94% and was highly dependent on permeability, water table elevation, dissolved oxygen concentration solid phase bacterial energy sources. Denitrification of NO- to N occurred in anaerobic conditions, while at intermediate dissolved oxygen; NO was the dominant reaction product. EF1 (mean: 0.0018) in the denitrifying sandstone catchment was 32% less than the IPCC default. The denitrification observations across catchments were supported by stable isotope signatures. Stream NO occurrence was 32% lower in the sandstone catchment even though N loading was substantially higher than the slate catchment.
在集水区尺度上，环境、水文地质和物理化学特征的复杂镶嵌组合调节地下水和河流硝酸盐 (NO) 的分布。NO 去除（通过反硝化）的效率与积累反应产物（过量 N 和氧化亚氮 (NO)) 的比例之间的关系仍知之甚少。本研究在爱尔兰两个排水良好的农业集水区（10km）中调查了地下水，这两个集水区的地下岩石（砂岩与板岩）和土地利用情况存在差异。通过测量氮 (N) 物种的浓度和分布模式、含水层水文地球化学、稳定同位素特征和含水层水力特性来评估反硝化能力。观察到一个层次结构，其中物理因素（包括农业、地下水位和渗透率）决定了含水层的水文地球化学特征。这种水文地球化学特征是反硝化反应进展的主要控制因素。板岩集水区的高渗透率、好氧条件和缺乏细菌能源导致反硝化反应进展缓慢（0-32%）、NO 浓度高且 NO 排放因子（EF1）相对较低。在砂岩集水区，反硝化反应进展范围从 4%到 94%，高度依赖于渗透率、地下水位、溶解氧浓度和固相细菌能源。NO-向 N 的反硝化在厌氧条件下发生，而在中间溶解氧条件下，NO 是主要的反应产物。在反硝化的砂岩集水区，EF1（平均值：0.0018）比 IPCC 默认值低 32%。同位素特征支持了整个集水区的反硝化观测。尽管氮负荷远高于板岩集水区，但砂岩集水区的河流 NO 发生量仍低 32%。
