MEPS 218:17-31 (2001)  -  doi:10.3354/meps218017

ABSTRACT: Exposed to over 30 yr of continuous eutrophication, the Darß-Zingst bodden chain, a shallow tideless estuary accumulated large amounts of particulate organic matter (POM). We sampled along the eutrophication gradient throughout the vegetation period 1996, in order to assess POM properties. Besides parameters describing the chemical composition, such as C/N ratio, protein content and protein:carbohydrate ratio, particles were microscopically analysed. From the volumes of non-transparent, nucleic acid-containing (fluorescently labelled by propidium iodide) and organic particles (stained with DTAF), the percentages of detrital and transparent mucoid material were derived. Ten to 63% of particulate organic carbon (POC) in the bodden system consisted of carbon from bacteria, phytoplankton and protozoans. Of the total organic particle volume, up to 46% were microorganisms. Although detritus volume averaged 14%, maximum values of 68% could be determined. Most of the organic particle volume consisted to 64% of transparent mucoid matter, which is an important carbon compartment in material cycling (e.g. settling substrate). At higher POC concentrations the chemically unidentified material as well as the mucoid matter were quantitatively more important compared to the mesotrophic Baltic Sea station, where the portion of detritus (62% on average) was much higher. The microscopically derived quantification of detrital and mucoid matter provides additional information on the suitability of seston as settling substrate, its age, origin and physical properties. Since the riverine water input into the bodden system is small and its POC concentration lower compared to the bodden itself, most of the estuarine POM was obviously produced locally. Detritus from submersed macrophytes did not occur before the end of the vegetation period in October and thus cannot contribute significantly to the POM analysed in this study. The high amounts of POM in the bodden system probably originate mainly from pelagic primary production. The sedimentation of POM, its processing in and frequent resuspension from the several mm-thick flocculent sediment layers, seems to be the main source for the high amount of mucoid particles.

KEY WORDS: Detritus · Transparent mucoid material · Microscopical analyses · Chemical composition of POM · Eutrophication gradient · Shallow estuary