Northern Rivers Institute, School of Geosciences, University of Aberdeen, Aberdeen, AB24 3UF, UK.
Leibniz Institute of Freshwater Ecology and Inland Fisheries, 12587, Berlin, Germany.
Environ Monit Assess. 2019 Jan 30;191(2):116. doi: 10.1007/s10661-019-7237-2.
Riparian wetlands (RW) are important variable source areas for runoff generation. They are usually characterised by a combination of groundwater exfiltration-which maintains saturated conditions in low-lying organic-rich soils-and direct precipitation. Both processes interact to generate overland flow as a dominant runoff process. The small-scale details of groundwater-surface water (GW-SW) interactions are usually not well understood in RW. Here, we report the results of a study from an experimental catchment in the Scottish Highlands where spatio-temporal runoff processes in RW were investigated using isotopes, alkalinity and hydrometric measurements. We focused on perennial micro-catchments within the RW and ephemeral zero-order channels draining peatland hollows and hummocks to better understand the heterogeneity in GW-SW interactions. The 12-month study period was dominated by the wettest winter (December/January) period on record. Runoff generation in the RW was strongly controlled by the local groundwater response to direct rainfall, but also the exfiltration of groundwater from upslope. This groundwater drainage is focused in the hollows in ephemeral and perennial drainage channels, but in wet conditions, as exfiltration rates increase, can affect hummocks as well. The hollows provide the dominant areas for mixing groundwater, soil water and direct rainfall to deliver water to the stream network as hollows "fill and spill" to increase connectivity. They also provide wet areas for evaporation which is evident in enriched isotope signatures in summer. Although there is some degree of heterogeneity in the extent to which groundwater influences specific micro-catchments, particularly under low flows, the overall isotopic response is quite similar, especially when the catchment is wet and this responses can explain the isotope signatures observed in the stream. In the future, more longitudinal studies of micro-catchments are needed to better explain the heterogeneity observed.
河岸带湿地（RW）是径流量产生的重要可变源区。它们通常具有地下水渗出-维持低地势富含有机质土壤饱和条件-和直接降水的组合特征。这两个过程相互作用，产生地表径流作为主要的径流过程。RW 中地下水-地表水（GW-SW）相互作用的小尺度细节通常不太清楚。在这里，我们报告了苏格兰高地一个实验流域的研究结果，该研究使用同位素、碱度和水文测量来研究 RW 中的时空径流动态。我们专注于 RW 内的常年微型集水区和排泄泥炭地洼地和丘岗的零级非永久性渠道，以更好地了解 GW-SW 相互作用的异质性。12 个月的研究期间主要受到有记录以来最潮湿的冬季（12 月/1 月）的控制。RW 中的径流动态主要受直接降雨对当地地下水的响应控制，但也受地下水从上游渗出的控制。这种地下水排水集中在零级和常年排水渠道的洼地中，但在潮湿条件下，随着渗出率的增加，也会影响丘岗。洼地为混合地下水、土壤水和直接降雨提供了主要区域，以增加连通性将水输送到河网。它们还为夏季可见的丰富同位素特征提供了潮湿的蒸发区域。尽管地下水对特定微型集水区的影响程度存在一定程度的异质性，尤其是在低流量下，但总体同位素响应非常相似，尤其是在集水区潮湿时，这种响应可以解释在溪流中观察到的同位素特征。未来，需要对微型集水区进行更多的纵向研究，以更好地解释观察到的异质性。
