Einfluss der wassertemperatur auf die nährstoffkonzentrationen im Oderästuar 1996–1998

Abstract

The impact of extreme weather, in terms of temperature, that is the seventh coldest winter 1995/1996 and the warmest summer 1997 in this century, on some peculiarities in nutrient concentrations in the Świna Strait is discussed on the basis of monthly mean sea surface temperature maps. These maps were derived from synoptic remote sensing data of the Advanced Very High Resolution Radiometer (AVHRR) operating at the NOAA (National Oceanic and Atmospheric Administration) weather satellites. The Swina Strait drains ca. 75 % of the water from the Szczecin Lagoon which is a recipient of the Oder waters. Severe winter 1995/1996 with low water temperature and ice sheet in the Oder estuary were found to be responsible for record low oxygen and high ammonium concentrations (90 μmol dm-3) in the Swina Strait. Moreover, harsh winter conditions resulted in passive transport of ammonium through the estuary in 1996; in contrast, mild winter’97 caused significant reduction of ammonium loads exported to the Pomeranian Bay. Delayed spring’96 caused later than in 1997 freshet water outflow and it suppressed/delayed biological uptake of nutrients (spring contribution of inorganic to total nitrogen discharged was by 19 % higher in 1996 than in 1997). Delayed sedimentation of freshly produced organic matter, together with low water temperature must have reduced PO4 fluxes from the sediments and therefore strengthened and prolonged phosphorus limitation of primary production in the Oder estuary on the turn of spring and summer 1996. Extremely hot summer’97 must have intensified phosphate fluxes at water column/sediments interface as their concentrations before the flood’97 were considerably higher than comparable ones in 1996 and 1998. High temperature and low oxygen content in July/August 1996 and 1997 were responsible for ammonium peaks, reaching ca. 20 μmol dm-3 in the Świna bottom waters in summer 1996 and during the Oder flood 1997. Both, high and low water temperatures play extremely important role in nutrient transformation in the Oder estuary.