Abstract
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.
Highlights
Thornton et al (1981) proposed a conceptual model to describe the spatial patterns of different limnological variables along the main axis of a reservoir
We gathered data along the main axes of 17 tropical reservoirs to test the relationship between different ecological indicators and distance to the dam
We found that the strength of the longitudinal gradient of total phosphorus was negatively related with shoreline development and positively related to land use and the presence of tributaries
Summary
Thornton et al (1981) proposed a conceptual model to describe the spatial patterns of different limnological variables along the main axis of a reservoir. According to this model, water velocity decreases from upstream to downstream reaches (near the dam), with consequent increases in sedimentation rates and water transparency. The patterned variation in different limnological variables (e.g., water transparency, nutrient concentrations and phytoplankton biomass) may be related to the formation of other biological gradients (Rodrigues & Bicudo, 2001; Okada et al, 2005; Draštík et al, 2008; Pamplin et al, 2006; Rychtecký & Znachor, 2011). Studies on different scales and in a variety of geographical contexts are necessary to assess the general applicability of the model
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