Understanding The Temporal Dynamics Of Regional Lakes PDF Download

In recent years, freshwater ecology has moved away from a focus on the temporal dynamics and stability of single water bodies towards a greater understanding of multiple regional systems. Part of the reason for this shift is the recognition that many lake problems and processes are regional, or even global, such as climate change or eutrophication. Understanding the behaviors of lakes in a landscape could enable the prediction of patterns and trends of lake ecosystems in a broad geographical context, which is also fundamental to the concept of ecosystem management. A useful concept for understanding the dynamics of ecosystem change in a regional context is ‘temporal coherence’, or the degree to which change in limnological variables is temporally synchronous across multiple lakes. Strong temporal coherence in ecological conditions can indicate the importance of regional drivers such as climate conditions, while weak temporal coherence implies that within-lake processes are more important than regional controls. In this study, I examined the temporal coherence of a number of physical and biological features of seven New Zealand lakes that differed in trophic status, morphological features, catchment land uses and spatial distance. The results suggest that coherence of lake plankton communities was weak, indicating the importance of lake-specific processes such as lake-specific nutrient dynamics or species interactions. The degree of coherence differs between plankton communities: the temporal coherence was low for phytoplankton community composition, but even weaker for rotifer community composition. The weak coherence in phytoplankton community composition was significantly related to the lake-specific temporal variations of water quality conditions. However, temporal changes in rotifer community composition were more likely to be influenced by a combination of abiotic and biotic factors, including interspecific competition, nutrient dynamics and predation, all of which vary in importance across lakes. Physical variables such as water temperature exhibited stronger temporal coherence than plankton communities, indicating the importance of regional climate controls on lake conditions. Regional climate controls more strongly influenced the temporal coherence of epilimnetic temperature in the study lakes, whereas coherence in bottom temperature was more related to individual lake morphological features. Finally, the temporal coherence of cyanobacteria abundance across the regional study lakes was assessed. Based on the results from temporal coherence analysis, two regression-based models were developed to predict the temporal dynamics of cyanobacteria across the region. The predictions of regional models that relate various water quality factors and the abundance of cyanobacteria reached accuracy rates of c. 90-100% in most study lakes. The results of this modelling exercise indicate the feasibility of regional-scale models as a baseline for monitoring the temporal dynamics of cyanobacteria. My overall results suggest that, in general, the coherence of lake plankton was weak, indicating the importance of lake-specific processes such as lake-specific nutrient dynamics or species interactions. Physical variables such as water temperatures exhibited stronger temporal coherence than plankton communities, indicating the importance of regional climate controls on lake physical conditions.