Revisiting the concept of longitudinal gradients in reservoirs

Abstract

Aim: Reservoirs are an increasingly common type of aquatic ecosystem in countries where hydropower is a dominant energy source. Understanding the functioning of these systems is essential to establish monitoring strategies or priorities for their use. The main goal of this study was to test for the presence of longitudinal gradients in reservoirs. Methods: We gathered data along the main axes of 17 tropical reservoirs to test the relationship between different ecological indicators (e.g., turbidity, nutrient concentrations, and phytoplankton abundance) and distance to the dam. After, we tested whether the strengths of longitudinal gradients were related to a set of explanatory variables (occurrence in a reservoir cascade, presence of tributaries near the dam, land-use, morphology and reservoir age). Results: We did not find significant relationships between our set of ecological indicators and distance to the dam and the strengths of these relationships were not consistently predicted by the explanatory variables. However, different indicators suggested patterns consistent with expectations. Conclusion: The distance to the dam is not a consistent predictor of the spatial variation of different limnological variables in tropical reservoirs, highlighting a high degree of context-dependency.