SEDIMENT-WATER EXCHANGE IN SHALLOW-WATER ESTUARINE SEDIMENTS

Pore water profiles in shallow estuarine sediments of Puget Sound [USA] show the characteristics of enhanced interstitial-water transport by animal activity. Using an in situ 3H experiment and dissolved silicate profiles the transport parameter due to animal activity was evaluated in the surface 20 cm of sediments to be 1-5 .times. 10-7 s-1 which is in the range of similar parameters determined in other nearshore environments in the USA. The fluxes of alkalinity, ammonia and silicate across the sediment-water inferface due to biological processes are greater than that by 1-dimensional molecular diffusion. For the metals Fe, Mn, Cu, Ni and Cd the dominant transport mechanism depends upon the depth at which the metal is released to the pore waters. The most important effect of biological activity on metal remobilization may be the removal of sulfide from the pore waters, via ventilation of sediments with oxic overlying water, allowing the enrichment of dissolved metals which might otherwise be very low in concentration due to insoluble sulfide formation. The result is a greatly enhanced flux of metals to the bottom waters.