The influence of tidal straining and wind on suspended matter and phytoplankton distribution in the Rhine outflow region

To study the short-term effects of the physical environment on phytoplankto n dynamics in the Rhine outflow area. changes in salinity, beam attenuation and phytoplankton distribution were observed in a series of high resolutio n measurements. During periods of weak wind and neap tide (low turbulent ki netic energy, TKE), the system was dominated by tidal straining that result ed in semi-diurnal oscillations in stratification. Phytoplankton was kept i n resuspension at about 10-15 m depth. Subsequent strong wind and tidal mix ing (high TKE) broke down stratification, enhanced horizontal gradients and suppressed estuarine transport. It is hypothesised that during low TKE, ti dal straining and frontal circulation determined the phytoplankton distribu tion; and at high TKE, input by wind and tide enhanced conditions for growt h, which resulted in a bloom in the surface layer of the Rhine Plume, where light and nutrients were available. (C) 2001 Elsevier Science Ltd. All rig hts reserved.