Linking metrics of hydrological function and transit times to landscape controls in a heterogeneous mesoscale catchment

Long-term river flow data and one year of isotopic tracer data in a nested 749 km(2) catchment were analysed conjunctively to evaluate the relationships between hydrometric statistics, transit times, and catchment characteristics. The catchment comprised two distinct geomorphic provinces; upland headwaters draining glaciated landscapes underlain by crystalline geology and lowland headwaters draining a major regional sandstone aquifer. In the uplands, flow regimes were flashy with high runoff coefficients for storm hydrographs, steep recession curves and strong nonlinearity in event responses. In the lowlands, runoff coefficients were low, recessions less steep, and event responses more linear. Flow data from the catchment outfall showing damping of these extremes, but was most strongly influenced by the upland headwaters where precipitation was highest. The damping of variability in stable water isotopes between precipitation inputs and streamflow outputs reflected this; with upland tributaries least damped and lowland tributaries most damped. Attempts to quantify the mean transit times of the sampling points met with mixed success; partly reflecting the short run (1 year) of data, but mainly as a result of the marked damping in lowland sites. As a consequence, MTT estimates can only be said to be in the order of a few years in upland sites, but are probably decadal or greater in lowland tributaries. Again, the catchment outfall averages these extremes, but is more similar to the upland headwaters. Despite the difficulties in quantifying MTTs, it is clear that they, like the hydrological response, primarily reflect the dominant control of catchment soil cover, which in turn is determined by geology and glacial history. Copyright (C) 2011 John Wiley & Sons, Ltd.