Tidal impact on planktonic primary and bacterial production in the German Wadden Sea

Abstract

Tidal variation of biological parameters was studied at three anchor stations in selected inlet channels of the northern German Wadden Sea in May and July 1994. Concentrations of bacteria, chlorophyll a and suspended matter as well as primary and bacterial production were assessed over a period of 25 h in the surface and in the bottom water. Diurnal variation in primary production was found both under in situ light conditions and under constant illumination. Tidal turbulence caused the introduction of detritus, bacteria and pigments from the sediment into the water column. The impact of sediment resuspension was most evident in the bottom water, leading to tidally oscillating bacterial production rates which were high during high stream velocity and low during the slack times. Estimations of the areal daily phytoplankton production and corresponding bacterial carbon demands were unbalanced. Primary production accounted for only 25-45% of the total bacterial carbon requirement. This discrepancy is due to the shallow euphotic depth in the Wadden Sea, allowing net primary production only in the upper 2-3 m of the water column, while the relatively high levels of bacterial activity do not show a vertical decline. Assuming that the specific biological activities in the water columns over the tidal flats are similar to those found in the inlet channels, it was found that production processes dominate in shallow areas whereas decomposition processes dominate in the deep channels. Moreover, the predominance of heterotrophic processes in the inlet channels means that additional organic carbon sources must contribute to the heterotrophic metabolism in the deep parts of the Wadden Sea, and that the horizontal flux of material is important in this turbid mesotidal ecosystem.

A review on substances and processes relevant for optical remote sensing of extremely turbid marine areas, with a focus on the Wadden Sea

“…For Chl-a, not always a correlation with tide was found (Poremba et al 1999;Hommersom et al 2009). DOM was found to correlate with tides (5% diVerence between ebb and Xood) and salinity, indicating a freshwater source as main contributor (Cadée 1982).…”

“…Poremba et al (1999) concluded that high tide results in a supply of primary production from the autotrophic intertidal Xats to the heterotrophic channels. Benthic red algae occur in the Wadden Sea in the subtidal zone, but their amount decreased largely the last century (Reise et al 1989).…”

“…Via resuspension, tidal currents have large eVects on the SPM concentrations (Poremba et al 1999;Hommersom et al 2009). Resuspension will be discussed in more detail in the following section.…”

“…2) (Stanev et al 2009;Poremba et al 1999). In the Wadden Sea, the time lag between the strongest current and high or low water (slack tide) is 1-2 h (Postma 1982), which is clearly visible in time series where the water level and concentration of SPM is plotted (Fig.…”

Spectra of a shallow sea—unmixing for class identification and monitoring of coastal waters

“…for the area near Den Helder the images cover high water (HW) to low water (LW)). The expectation was to find higher influence of SPM about 2 h before slack tide, due to tidal currents (Hommersom et al 2009;Poremba et al 1999, Postma 1982. Fig.…”