The seasonal dynamics of benthic (micro) organisms and extracellular carbohydrates in an Intertidal mudflat and their effect on the concentration of suspended sediment
Faculty of Sciences. Biology
Fine sediment dynamics in the marine environment
6th International Conference on Cohesive Sediment Transport (INTERCOH, 2000), SEP 04-08, 2000, DELFT, NETHERLANDS
, p. 429-440
University of Antwerp
The Ems-Dollard estuary, situated in the north of the Netherlands near to the German border, is covered for a large part by intertidal flats, Currents and wind- induced waves exert a shear stress on these flats, resulting in resuspension of the sediment. Fluctuations of the suspended sediment concentration in the Dollard are strongly affected by erosion due to wind-induced waves and by settling during calm weather conditions. However it is believed that benthic processes influence the amount of sediment that can be resuspended from the intertidal flats. Therefore suspended sediment concentration above the Heringsplaat, an intertidal flat in the Ems-Dollard estuary, was measured during two seasons and related to the dominant benthic biological features. The benthos and the abiotic sediment characteristics were monitored from 1995 till 1997, at two stations. At both stations a peak of chlorophyll-a concentration was found in spring, caused by a diatom bloom. Meiobenthos was dominated by nematodes, macrobenthos by the polychaete Marenzelleria viridis and the amphipod Corophium volutator. The seasonal pattern was studied most intensively during 1996. Monthly sampling was done on the Heringsplaat, The flat was covered with ice during March. This period was followed by a clear water phase during spring and an increase of the silt content at the edge of the Heringsplaat. During this period an increase was found of chlorophyll-a concentration and of the carbohydrate concentration. This carbohydrate secretion stabilized the sediment. This finally resulted in a stable diatom mat at the end of the spring and a two-centimeter thick layer of silt. During June a high increase of nematodes and Corophium volutator was found. Nematode density was about 5000 ind per 10 cm 2 during June and July and Corophium density reached almost 100,000 per m(2). The diatom population decreased rapidly during June. It is assumed that this is caused by high grazing pressure of the nematodes and of Corophium. The reduced diatom concentration and the increased bioturbation activity of Corophium resulted in reduced sediment stability. The silt content of the sediment surface at the edge of the Heringsplaat reduced and at the same time the turbidity in the water column increased.