Seasonal variations in the physical and chemical characteristics of ponds:: implications for biodiversity conservation

1. The natural evolution of ponds leads to the filling up of these small ecosystems, and human intervention may sometimes be necessary to ensure their continued nature conservation interest. 2. In the and karstic region of the 'Causses du Quercy' (France), there are numerous ponds bored into parts of the calcareous rock where water cannot percolate. Without human management they are destined to disappear, although they constitute the only available surface water resource on this limestone plateau. 3. Little information is available about the physical and chemical changes occurring as ponds go through different successional stages. A comparative study of three ponds at various stages of succession allowed an analysis to be made of the seasonal changes in a number of abiotic variables. 4. There was evidence that the temporal and spatial variability of abiotic factors (such as temperature, water level and dissolved oxygen concentrations) increased as ponds progressed through successional stages. 5. This study indicated that ponds varied in terms of plant and animal species richness and rarity, temperature, and oxygen concentration at different successional stages. Each pond supported a distinctive fauna. The results suggest that biotic diversity is, in part, driven by local-scale physical and chemical heterogeneity. Management plans should be drawn at a scale that maintains the heterogeneity of such pond networks. Copyright (C) 2004 John Wiley Sons, Ltd.