Filtration and resuspension of particulate matter and phytoplankton onan intertidal mussel bed in the Oosterschelde estuary (SW Netherlands)

Abstract

In situ measurements were carried out on an intertidal mussel bed in theOosterschelde estuary, SW Netherlands. Exchange of suspended particulatematter and phytoplankton between the water column and the mossel bed wasmeasured with a Benthic Ecosystem Tunnel. In situ clearance rates of themussel bed were compared to clearance rates of individual mussels measured ina field station under ambient conditions. Concentrations of suspendedparticulate matter (SPM) and particulate organic carbon (POC) in the watercolumn above the tidal flat were affected by wind-induced resuspension.Chlorophyll a concentrations were higher during flood tides than during ebbtides, and were not affected by wind-induced resuspension. Clearance rates ofthe mussel bed ranged from 1.3 to 7.1 m3 m-2 h-1. In situ increasedclearance rates generally were comparable to rates observed in measurementswith individual mussels in a field station. Uptake of SPM and POC by themussel bed was highly variable. Under calm weather conditions, uptake rateswere correlated with inflow concentrations. Net uptake of phytoplankton wasrelatively higher than the uptake of POC, indicating that a major part of thePOC was resuspended and exported from the mussel bed after filtration. Inaddition, wind stress induced considerable resuspension and export of SPM andPOC from the mussel bed. Chlorophyll a uptake was less influenced by wind,and high rates of uptake, caused by mussel filtration, were observed. Theresult of filtration and resuspension processes was a net uptake by themussel bed of particulate matter containing a relatively high proportion ofphytoplankton: the mussel bed acted as a selective filter for phytoplankton.