Composition of suspended participate matter in the Elbe estuary: Implications for biological and transportation processes

Abstract

The composition and settling behaviour of suspended particulate matter (SPM) from the freshwater to the polyhaline zone of the Elbe Estuary was studied in April and July 1994. SPM was separated into three fractions of different settling velocities. The major portion of SPM (up to 92 %) was found to settle more slowly than 0.3 mm s-1 with a maximum concentration of 159 mg I-1. Special attention was given to organic content and microalgal pigments bound to suspended matter of different settling velocities. The composition of SPM concerning the total amount of organic material, and different algal pigments which can serve as indicators for various algal classes and degradation processes of the algal material, varied depending on the location within the estuary and on different settling velocities of the particles. Organic material was always highest (up to 90 % of the total) in the slow settling fraction. The distribution of algal pigments showed a different pattern: a substantial amount often was associated to fast settling particles (up to 20–30 %). The ratio of phaeopigments and chlorophyll-a was highest in the fast settling fraction of SPM. Variations in the amount of total organic material and algal pigments of different settling velocities result in a different transport behaviour of these components and their deposition within the estuary. The relevance of the results to various biological processes and to decisions concerning sediment dredging in the estuary is discussed.