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

During tidal inundation, exchange of particulate organic matter POM between salt marshes and tidal water may occur. This may result in changes in the seston-POM characteristics of the water. We investigated wheter such changes were found after inundation of Saeftinge, a salt marsh in the Westerschelde estuary (SW Netherlands). Seston was collected from a tidal creek of the marsh during 22 flood-ebb tide cycles. The characteristics of the flood and ebb seston samples were assessed by microbial bioassays, pyrolysis-mass spectrometry, and the determination of chlorophyll (a+b). There was a very strong agreement between the seasonal pattern in biodegradability and the seasonal pattern in chemical signature of the seston-POM. During autumn and winter, the degradability of seston-POM in the Westerschelde was relatively low. Neither the degradability nor the chemical characteristics of the POM showed much variation in this period. The enrichment of the POM-pool with phytoplankton appeared to be the major factor increasing the biodegradability 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 POM characteristics between flood and ebb: compared to the POM in the flood water, the POM leaving the marsh during the ebb was more refractory. In other periods, salt marsh inundation hardly affected biodegradability and chemical composition of seston-POM. This is considered an indication that the large estuarine salt marsh of Saeftinge is an irrelevant factor in determining the nature of POM in the estuary. The lack of differences between flood and ebb tide seston-POM also suggests that export of vascular plant detritus from this marsh, at least during moderate weather conditions, is insignificant.