Geographia Polonica (1998) vol. 71

Temperature and nutrient dynamics in eutrophic freshwater ecosystems

Maciej Zalewski, Iwona Wagner

Geographia Polonica (1998) vol. 71, pp. 79-92 | Full text

If properly situated in the landscape mosaic, ecotonal land-water vegeta-tion can reduce effect of catchment degradation on freshwaters. The development of ecotones positively depends on temperature, rain and water level. If long dry period appear due to climate changes, vegetation in ecotone zones may decline so during heavy rains the surface flow may cause high external nutrient load to freshwaters. Internal load may also be intensified because of acceleration of organic matter mineralization due to higher microorganisms and phosphataze activity and also higher rate of organ-isms excretion.At elevated temperatures primary production will be higher. Consequently, accel-eration of phytoplankton succession, and extension of the period of blue-green algae (cyanophyta) blooms is probable. During periods when the temperature is above 18°C winds intensity may regulate blooms appearance. Long periods of epilimnion stability intensify cyanophyta blooming, contrary strong winds may be an inhibitor of blooms appearance. In elevated temperatures toxicity of blue-green algae tends to be higher.Zooplankton communities regulate phytoplankton density, if not reduced by zoo-planktivorous fish. Due to higher energy needs with increasing temperature, pressure of fish on zooplankton will result in zooplankton number reduction. At temperatures above 15° (data for Daphnia sp.) zooplankton body size is reduced because smaller specimen posses energetic and behavioral advantages. Lower number of large filtrators may reduce filtering ability of zooplankton and intensify phytoplankton growth.Freshwaters biota is mostly composed of polikilothermie organisms (zooplankton, fish). The temperature dependent physiological processes have been characterised by right skewed parabolic function. In consequence, water temperature increase may seriously modify (mostly accelerate) rates of energy flow and matter cycling in temper-ature freshwaters.Concerning the above processes, especially shallow, eutrophic reservoirs will re-spond to climate changes by intensification of biological processes. To prevent intensi-fication of eutrophication symptoms it is necessary to consider environmentaly sound management of the catchment and tributaries and control of internal hydrological and biological processes in the reservoir.

Keywords: eutrophic ecosystem, global climate changes impact, nutrient dynamics

Maciej Zalewski, Department of Applie d Ecology, University of Łódź ul. Banacha 12/16, 90-237 Łódź, Poland
Iwona Wagner, Department of Applie d Ecology, University of Łódź ul. Banacha 12/16, 90-237 Łódź, Poland