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

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 clays agree to within 1 mm day^-1 with estimates of mire discharge obtained by two other methods, namely direct measurement using pure 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.