Diatom biofilms on intertidal mudflats reveal a patchy distribution. This is probably the result of the fact thatthese microalgae live in a constant varying environment, with different supply of nutrients and light. Moreover, benthic diatoms are motile and migrate up and down in the sediment. During low tide, epipelic (pennate) diatoms migrate upward. Cells at the surface may experience high light stress and they may be deprived of nutrients and CO2. These conditions make it difficult to predict and quantify primary production. The objective of this project is to investigate patchiness in microphytobenthos biomass and primary production and develop optical methods that can be used in combaination with remote sensing to extrapolate these measurements at the scale of whole mudflats. Approach: In this project patchiness in biomass will be studied by optical means, using multispectral surface reflectance scans. The optical characteristics will also be measured vertically, using fiberoptic microprobes. Ground truthing will take place using contact cores, so that a defined depth (2mm) is sampled and analyzed for photosynthetic pigmetns and sediment characteristics. From the data algorithms will be developed which will allow estimation of microbenthic biomass, sediment typpe and vertical light attenuation coefficients. Vertical changes in biomass that are caused by migration of diatioms will be measured using fiberoptic microprobes, in combaination with surface reflectance. Primary production will be studied by oxygen microelectrodes, in combination with PAM-fluorometry. We will construct a special microfiber PAM in order to measure vertical microprofiles of photosynthesis. These estimates will be comparedd with those obtained from oxygen microelectrodes. The advantage of microfiber PAM measurements is that no information about sediment characteristics (diffusion coefficioents, etc.) is necessary, and that more physiological information is obtained. Planning 2000: Synoptic data of microphytobenthic biomass distribution and primary productivity will be obtained for two transects on local intertidal flats; the Biezelingse Ham (Westerschelde) and the Zandkreek (Oosterschelde). Both sites will be sampled monthly. On large sampling campaign with the other BIOPTIS partners will take place at the Eden estuary (Scotland), or at the local sites. In order to get a better grip on the effect of vertical migration, a microfiber PAM will be developed, which will be used to study vertical migration and photosynthesis with depth.
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