EFFECT OF SALT-MARSH INUNDATION ON ESTUARINE PARTICULATE ORGANIC-MATTER CHARACTERISTICS

During tidal inundation, exchange of particulate organic matter POM be tween salt marshes and tidal water may occur. This may result in chang es in the seston-POM characteristics of the water. We investigated whe ter such changes were found after inundation of Saeftinge, a salt mars h in the Westerschelde estuary (SW Netherlands). Seston was collected from a tidal creek of the marsh during 22 flood-ebb tide cycles. The c haracteristics of the flood and ebb seston samples were assessed by mi crobial bioassays, pyrolysis-mass spectrometry, and the determination of chlorophyll (a+b). There was a very strong agreement between the se asonal pattern in biodegradability and the seasonal pattern in chemica l signature of the seston-POM. During autumn and winter, the degradabi lity of seston-POM in the Westerschelde was relatively low. Neither th e degradability nor the chemical characteristics of the POM showed muc h variation in this period. The enrichment of the POM-pool with phytop lankton appeared to be the major factor increasing the biodegradabilit y and causing the changes in chemical characteristics of seston-POM in the Westerschelde in spring and summer. Only during a 2 mo period in summer did salt marsh inundation result in consistent differences in P OM characteristics between flood and ebb: compared to the POM in the f lood water, the POM leaving the marsh during the ebb was more refracto ry. In other periods, salt marsh inundation hardly affected biodegrada bility and chemical composition of seston-POM. This is considered an i ndication that the large estuarine salt marsh of Saeftinge is an irrel evant factor in determining the nature of POM in the estuary. The lack of differences between flood and ebb tide seston-POM also suggests th at export of vascular plant detritus from this marsh, at least during moderate weather conditions, is insignificant.