Light dependent sediment-water exchange of dissolved reactive phosphorus and silicon in a producing microflora mat

Light dependent sediment-water exchange rates of dissolved reactive silicon (DRSi) and phosphorus (DRP) were studied on field station Archipel (3 m water depth) in Lake Grevelingen (SW Netherlands). Bell jars, either light or darkened, were fixed permanently over a productive microflora mat of mainly Navicula spp.; sediment-water exchange was monitored over an 11 days period. Gross primary production values in the mat amounted to 1000 mg C·m^–2·day^–1.In the dark bell jar, DRSi and DRP release rates from the sediment were ca. 275 and 85 mg·m^–2·day^–1, respectively. Release rates in the light bell jars were on average only 15% of these values. Parallel bell jar experiments under different environmental conditions indicate a direct relationship between the primary production figures and nutrient sediment-water exchange rates.Communication nr. 369 of the Delta Institute for Hydrobiological Research, Yerseke, the Netherlands. This paper was presented at the first International Workshop on phosphorus fractionation, availability and release of the Sediment Phosphorus Group, held in Vienna, 23–26 March, 1986.