Nutrient flux in short-term enclosures of intertidal sand communities

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Abstract
The investigation was carried out in a shallow water area in the northern Wadden Sea where the euphotic zone reaches down to the bottom. The nutrient flux was measured monthly during 1980 in three communities (an Arenicola-flat, a seagrass-bed and a Nereis-Corophium-belt) in connection with measurements of community metabolism. The nutrient fluxes of NH4 +, NO3 −, NO2 −, Si(OH)4 were determined in light and dark bell jars in relation to temperature, O2 consumption and concentrations of nutrients in the ambient water. Experimentally increased abundance of macrofauna (Arenicola marina) enhanced the regeneration of NH4 +, NO3 −, NO2 −. The plants took up NH4 + more intensely in the light than in the dark. A community dominated by Zostera noltii showed the highest rate of NH4 + uptake (−355 µmol NH4 + · m−2 · h−1). NO3 − was mainly taken up by the communities (up to −354 µmol NO3 − · m−2 · h−1). Si(OH)4 was released as well as taken up by all the three communities. Highest rates of Si(OH)4 release were measured in the Arenicola-flat (up to + 1493 µmol Si(OH)4· m−2 · h−1). This flux was correlated with the O2 consumption, mainly by macrofauna. The system of the three sand flat communities imports nitrate and nitrite and exports ammonia and silicate on an annual basis.