FLUXES OF WATER AND SOLUTE IN A COASTAL WETLAND SEDIMENT .1. THE CONTRIBUTION OF REGIONAL GROUNDWATER DISCHARGE

Upward discharge of fresh groundwater into a mid-Atlantic intertidal w etland contributed 62% of the water needed to replace evapotranspirati on losses from the sediment during an 11 day period in September. Infi ltration during flooding by tides provided most of the balance; thus t here was a net advection of salt into the sediment. The amount of grou ndwater discharge was estimated from changes in water storage in the s ediment, as inferred from measurements of hydraulic head made every 10 min. We argue that this approach is inherently more accurate than cal culating the flux as the product of hydraulic conductivity and head gr adient. Evapotranspiration was estimated from direct measurements of n et radiation. On an annual time-scale, our results suggest that ground water discharge at this site may exceed the evapotranspiration flux du ring months of reduced evapotranspiration. Should this occur, groundwa ter-driven advection would supplement diffusion, during flooding, in r emoving salt from the sediment.