Tidal and seasonal variation in particulate and dissolved organic carbon in the western dutch Wadden Sea and Marsdiep tidal inlet

Abstract

Seasonal variation in POC and DOC was measured in the Marsdiep tidal inlet of the Wadden Sea from March 1978 to June 1981, and compared with tidal variation.A POC peak was coincident with the phytoplankton peak (except for 1981), whereas a DOC peak occurred about one month later indicating autolysis and degradation of phytoplankton rather than excretion as the main source of this DOC. DOC production calculated from the spring increase amounted to 4.2 mg C·1−1 or about 40% of the annual phytoplankton primary production in the area. This means that a large part of the phytoplankton production is not used directly by primary consumers but is converted into DOC.Tidal variation in DOC was correlated with salinity, pointing to a fresh water source for the bulk of it. POC was correlated with suspended matter content and phaeopigment, and slightly less with chlorophyll. Compared with the seasonal variation, tidal variation in chlorophyll and temperature was relatively small, but large in POC, DOC, suspended matter and salinity.Although import of POC and export of DOC through the Marsdiep inlet is large on an annual base, the transport cannot be measured directly because of the variability and precision limits of the measurements and as differences in content between ebb and flood current are only 15 and 5% of the POC and DOC content, respectively.