Ammonium release from resuspended sediments in the Laguna Madre estuary

Sediments can play an important role in estuarine ecosystems by buffering e nvironmental nutrient concentrations in overlying waters. This study examin ed the role of surface chemistry in controlling the release of NH4+ from re suspended sediments in the large, shallow, negative estuary Laguna Madre, T X. Two techniques were used: a generally accepted elutriate method in which sediments were added at a 1:5 ratio to overlying water and a more dilute p rocedure (closed) where sediments were added at three ratios ranging from 1 :10,000 to 1:100. In general, the more dilute procedure resulted in greater release of NH4+ from sediments. This is the result of the relative positio ns that the final solution concentrations place the systems on for an exper imentally determined Langmuir-type adsorption isotherm. The closed system t echnique also indicated that approximately equal amounts of the released NH 4+ came from porewater, loosely-bound quick-release, and tightly-bound slow -release fractions. Experimental results were supported by observations dur ing dredging activities. Model calculations indicate that resuspension even ts may cause NH4+ releases comparable to NH4+ fluxes from bottom sediments. Resuspension could potentially contribute to such environmental problems i n this estuary as the 'brown tide'. (C) 1999 Published by Elsevier Science B.V.