Runoff processes, stream water residence times and controlling landscape characteristics in a mesoscale catchment: An initial evaluation

Tracer studies, using Gran alkalinity and δ18O, in nested sub-basins of the 230 km2 Feshie catchment in the Cairngorm mountains, Scotland, were used to characterise hydrology in terms of groundwater contributions to annual runoff and mean residence times. Relationships between these fundamental hydrological descriptors and catchment characteristics were explored with the use of a GIS. Catchment soil distribution—mapped by the UKʹs Hydrology Of Soil Type (HOST) digital data base—exerted the strongest influence on flow path partitioning and mean residence times. Smallest groundwater contributions (∼30–40%) and shortest residence times (∼2–5 months) were observed in catchments dominated by peat and/or shallow alpine soils and bedrock. Longer residence times (∼12–15 months) and greater groundwater contributions (∼45–55%) were observed in catchments dominated by more freely draining podzolic, sub-alpine and alluvial soils. These different subcatchment responses were integrated to give intermediate residence times (∼6 months) at the catchment outfall. The influence of catchment topography and scale appeared to be largely mediated by their influence on soil cover and distribution. The study illustrates the potential utility of integrating digital landscape analysis with tracer studies to understand the hydrological functioning of mesoscale catchments.