How do exergy-based indicators respond to physical habitat changes?

Abstract

Eco-exergy and specific eco-exergy are thermodynamic indicators widely used in recent decades to monitor the ecological status of aquatic ecosystems. However, there is still a gap in the knowledge of how these indicators respond to variations in stream physical habitat resulting from natural variation or anthropogenic disturbances. Our objective was to determine what instream physical habitat metrics are related to the variation of eco-exergy and specific eco-exergy from benthic macroinvertebrates and fish assemblages in southeastern Brazil. For benthic macroinvertebrate assemblages, eco-exergy positively correlated with Catchment Disturbance Index scores, whereas specific eco-exergy was positively correlated with Mean Depth. For fish assemblages, eco-exergy was positively correlated with Mean Dead Wood Fish Cover. In contrast, specific eco-exergy was positively correlated with Local Disturbance Index scores and was negatively associated with Mean Depth, Mean Percentage of Riffle, and Mean Undergrowth Proportion. Our results show that exergy-based indicators respond well to natural and human changes in various aspects of instream physical habitat. Whereas their capacity to respond directly to anthropogenic disturbances differ by the assemblage used to calculate eco-exergy and specific eco-exergy, both indices may be useful tools for environmental managers and decision-makers to respond to multiple aspects of lotic ecosystem physical habitat conditions.