A Review of the Recharge-Discharge Function of Wetlands

Abstract

The recharge-discharge function is an important but complicated part of wetland hydrology. Groundwater discharge can maintain a high water table in wetlands, whereas recharge to the underlying aquifers can replenish groundwater supplies. However, the methods previously employed to determine groundwater flow in wetlands by indirect estimation are inadequate. The inherent error involved in mesauring the various factors in a water budget is so high that the volume of groundwater flux cannot be accurately determined indirectly as a residual. 'Average' gradients on the water table often cannot be used to determine the major directions of groundwater flow because of the build-up of transient water-table mounds which temporarily reverse flow directions at wetland margins. Most recent advances in understanding the recharge-discharge functions of wetlands have been obtained by using the hydrogeologic systems approach of groundwater study to wetland environments. The purpose of this paper is to review our current understanding of the recharge-discharge function with respect to this approach, with an emphasis on northern wetlands covered by thick accumulations of peat. A complementary review of the function for wetlands not underlain by thich peat can be found in Chapter 7.