Thermodynamic oriented ecological indicators: Application of Eco-Exergy and Specific Eco-Exergy in capturing environmental changes between disturbed and non-disturbed tropical reservoirs

Abstract

Effective assessment of ecological quality in aquatic ecosystems has become an important issue for researchers and environmental managers worldwide. The potential of thermodynamic oriented ecological indicators in environmental assessment and management was tested and compared with diversity measures in three tropical reservoirs located in the basin of the Paraopeba River, Minas Gerais State-Brazil. We computed Eco-Exergy based indices (Eco-Exergy and Specific Eco-Exergy) and the Margalef and Shannon–Wiener indices and tested differences in their responses to change in benthic communities across reservoirs characterised by different degrees of anthropogenic disturbance. Indices were estimated based on biotic descriptors (macrofauna biomass, composition, and abundance) and their values analysed against abiotic descriptors (pH, conductivity, transparency, turbidity, nutrients concentration, dissolved oxygen, chlorophyll a, and total dissolved solids). The Margalef index showed significant differences between reference and impacted sites, with the highest values in the former type of sites, (Pseudo F2.719=24,506, p=0.001), while the Shannon–Wiener index values showed no significant differences between reference and impacted sites. Eco-Exergy values were significantly higher at stations located in more disturbed sites (Pseudo F2.719=80.319, p=0.001), but Specific Eco-Exergy did not show really significant differences between disturbed and non-disturbed sites, although values were higher in the non-disturbed sites type. This might be explained by the fact that opportunistic tolerant species present high biomass values in polluted sites, since Eco-Exergy values may vary due to changes in biomass or information. On the other hand, differences in information between disturbed and non-disturbed sites were more subtle (although the number of species was higher in the less disturbed sites, it was not clearly reflected in Specific Eco-Exergy values). Our results suggest that thermodynamic oriented indicators can capture coherent structural changes in biological communities, highlighting its indicator potential for assessing the ecological condition/integrity of highly modified water bodies, such as reservoirs.