Sedimentation in a shallow brackish water lagoon influenced by wind-induced waves - A methodical study

In shallow aquatic ecosystems, wave-induced water motions affect the whole water column down to the sediment. To estimate the influence of these motions on short-term sedimentation rates (SR) in a shallow wind-exposed lagoon, we used plate traps (PTs) which, in contrast to cylindrical traps (CTs), allow trapped matter to become resuspended. In a series of experiments, we varied distance to the sediments, water depth, incubation time, and studied the SRs of total suspended matter and of suspended organic matter at varying conditions of wave exposure. The coefficient of variation of SRs did not change with incubation time. While SRs were similar on both trap types at very low wave exposure, they decreased with increasing wave exposure on the PTs probably due to instantaneous resuspension. In the CTs, SRs increased with increasing wave exposure. This resulted in about 55 times higher SRs in the CTs than on the PTs at high wave exposure. We conclude that CTs are not suitable to estimate natural SRs in wave-affected waters as they overestimate SRs. Our results indicate that SR obtained by PTs, which were here used for the first time in a wind-exposed, non-tidal ecosystem, are a far better estimate for natural short-term SRs.