Area separation of streamflow in an upland catchment with partial peat cover

Abstract The problem considered here is: how to measure the discharge from a raised mire in terrain that is only partly mire-covered. The approach involves comparison of the stream discharge from a mixed mire and mineral-soil sub-catchment with that from a neighbouring non-mire sub-catchment. Inconclusive results have previously been obtained using naturally occurring chemical tracers, and the validity of an alternative area-separation method is now examined. Estimates of the mire component of discharge derived in this way and summed over periods of 7–12 days agree to within 1 mm day −1 with estimates of mire discharge obtained by two other methods, namely direct measurement using mire lysimeters, and water-balance calculations using on-site rainfall measurements and evapotranspiration data calculated using the Penman–Monteith formula. The area-separation method may, therefore, be a useful adjunct or alternative to more expensive chemical methods for studying both the water yield of mixed catchments and aspects of peatland hydrology.