| Popis: |
Efforts are increasing globally to harness the potential of forests to alter catchment water runoff and storage dynamics as a ‘natural flood management’ (NFM) strategy, particularly given a projected rise in the frequency and severity of floods with climate change. Despite decades of research on forest hydrology, knowledge of how forests and land use control catchment runoff is still limited, especially in relation to important, though less investigated, subsurface runoff processes. This PhD research aimed to examine how forest cover interacts with soils and geology to influence runoff pathways at different spatial and temporal scales, focusing on the 67 km2 Eddleston Water NFM pilot site in the Scottish Borders. At the catchment scale, isotopic (2H and 18O)and geochemical tracers (Acid Neutralising Capacity (ANC)), conductivity and pH) were used to investigate whether forest cover is a significant control on water storage and mixing over seasonal and storm event timescales. At the hillslope scale, dense subsurface monitoring (soil moisture, groundwater and time-lapse electrical resistivity tomography (ERT)) compared improved grassland to an across-slope forest strip, similar to those promoted in NFM schemes to control runoff, to reveal water storage potential in soil underneath the forest and the downslope extent of any impacts on subsurface hydrological dynamics. The results revealed complex interactions between land cover and runoff processes at different scales. At the catchment scale, soil type and superficial geology were found to be more dominant controls on catchment storage over seasonal timescales, with land cover playing a secondary role. Dynamic storage estimates for headwater catchments underlain predominantly by glacial till were low, ranging from ~16 mm to 46 mm, and were correlated with low mean transit times, ranging from ~130 to ~210 days. There were no differences in these estimates, within the bounds of error, between catchments with up to 90% forest cover and those with much lower cover ( |
