Original Articles

PHYSICAL, CHEMICAL AND BIOTIC RESPONSES TO DECREASING WATER DEPTH IN A HIGHVELD PAN FOLLOWING WET AND DRY SUMMERS


Abstract

The classification of highveld pans by Geldenhuys (1982) emphasized the spatial diversity of morphology, vegetation and fauna. However, since the characteristics of individual pans also change seasonally and over longer term wet/dry cycles, he called for more detailed limnological studies to improve predictive and management potential. Marked changes occurred in the physical, chemical and biological characteristics of Rolfes pan in response to winter drawdown following dry (1983) and wet (1986) summers. The constancy of physical and chemical conditions during 1986 contrasted with rapid changes in temperature, turbidity, conductivity and salinity as benthic plants disappeared in 1983. The abundance of emergent vegetation provided breeding sites for certain wetland birds in 1986 but shallow water and submerged plants attracted wading birds in 1983. Changes within and between years highlighted the importance of three distinctive limnological characteristics of pans; large surface area to volume ratio, large littoral zone to open water ratio and an endorheic hydrological regime. Conservation of pans, beginning with inventory and classification, must focus on describing systems on the basis of these three characteristics, recognizing that activities in the catchment act through them to alter ecosystem properties.

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