Sediment stabilization by benthic diatoms in intertidal sandy shoals: qualitative and quantitative observations
Vos, P.C.; de Boer, P.L.; Misdorp, R. (1988). Sediment stabilization by benthic diatoms in intertidal sandy shoals: qualitative and quantitative observations, in: de Boer, P.L. et al. (Ed.) Tide-influenced sedimentary environments and facies. Extended versions of papers presented at the Symposium on Classic Tidal Deposits, held August 1985 in Utrecht, Netherlands. pp. 511-526
In: de Boer, P.L. et al. (Ed.) (1988). Tide-influenced sedimentary environments and facies. Extended versions of papers presented at the Symposium on Classic Tidal Deposits, held August 1985 in Utrecht, Netherlands. D. Reidel Publishing: Dordrecht. ISBN 90-277-2622-1. ix, 530 pp., more
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| Authors | | Top |
- Vos, P.C.
- de Boer, P.L.
- Misdorp, R.
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| Abstract |
Field and laboratory experiments show that benthic diatoms play an important role in stabilizing intertidal sediments. The magnitude of the sediment stabilizing activity depends upon the density and the mucilage secretion of the various species. Two groups of benthic diatoms are distinguished: epipsammic diatoms (immotile diatoms, living semi-permanently attached to sand grains) and epipelic diatoms (motile diatoms, moving freely through the sediment). In relation to the life-form of the benthic diatoms, two effects of sediment stabilization are observed: 1) Cohesive effect. The mucus, secreted by epipsammic diatoms, epipelic diatoms and bacteria, on sand grains improves the cohesion of the particles. The effect of the organic coating on the sand grains was studied in the laboratory in a small circular flume (012 cm), using samples from the field. An organic coating on the grains was found to cause a 5-17% increase in critical erosion velocity, relative to sterile sediment cleaned with H202. 2) Network effect. When large numbers of epipelic diatoms migrate to the sediment surface, they can form an extensive network of mutual attachment and mucus threads. In laboratory conditions the formation of an epipelic diatom mat leads, in 24 hours, to an increase in the threshold of sediment motion by 25% to 100%. In the field the network formation by epipelic diatoms and the physical processes are interdependent. The network protects the sediment surface against erosion by tidal currents and wave action, and conversely, the diatom population depends on these factors. In settings with relatively strong tidal currents and waves in the Oosterschelde estuary, the benthic diatom population was found to be poor, with a predominance of epipsammic species. In moderate energy conditions epipsammic diatoms prevail and strongly dominate the epipelic forms, except for incidental, local blooms on the margins of sandy shoals in early Spring. Epipelic diatoms prevail throughout, the year in places where currents are weak and intensive wave action is absent. The formation of an epipelic diatom mat has two implications for the sediment surface: 1) decrease of the grain size because of the entrapment of fine sediment, and 2) reduction of the bottom roughness. |
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