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Rainfall is a variable that drives community structure in aquatic ecosystems and is even more important in dry regions. Most studies have evaluated how the seasonal variation of rainfall influences aquatic communities. However, studies that evaluate the influence of spatial gradients of rainfall on aquatic organisms are scarce, especially regarding biological diversity and thermodynamic information. This study evaluated the response from diversity metrics and thermodynamic indices (eco-exergy and specific eco-exergy) in phytoplankton and benthic macroinvertebrate communities in 13 reservoirs distributed along a spatial gradient of rainfall in the Brazilian semiarid region. We hypothesized that the phytoplankton and benthic macroinvertebrate communities are congruent in response to the spatial gradient of rainfall in terms of diversity and thermodynamic indices in semiarid reservoirs. We expect to find higher values of biomass and the eco-exergy index under lower rainfall. To test our hypothesis, generalized linear models (GLMs) were used to relate the effects of rainfall changes on community structure. The eco-exergy and specific eco-exergy indices of the phytoplankton community were positively related to rainfall and reflected a greater investment in biomass production and genetic information (e.g., Chlorophyceae). As for the macroinvertebrate community, the reduction in rainfall promoted a greater investment in energy storage by generalist organisms (e.g., Melanoides tuberculata and some genera of Chironomidae). Thus, for a holistic evaluation of ecosystem health, the joint analysis of thermodynamic indices associated with an assessment of taxonomic composition, diversity and taxonomic richness is important, providing a more complete and multifaceted response. Additionally, thermodynamic indices better reflected the changes in both aquatic communities in response to rainfall, and were more sensitive than the diversity and richness indices. Consequently, the thermodynamic indices represent an efficient tool in the assessment of aquatic community responses to climate change, even when these communities respond in an opposite manner.

Evaluating the conservation of aquatic ecosystems, especially those which serve to supply, has been carried out using a variety of tools. However, the perception of water quality by the local community which lives in direct contact with water resources has not been considered with enough importance. This study analysed the relationship between the conservation status of reservoirs as perceived by the local community and their conservation status according to physical, chemical, and biological indicators. To do so, we calculated the Trophic State Index (TSI) of the reservoirs, the diversity and richness of benthic macroinvertebrate and we analysed the human influence in the riparian zone. Thus, we created the Community Conservation Perception Index (CCPI) to quantitatively associate the perception of the local community with environmental quality indicators (TSI, diversity, richness and anthropogenic influences in the riparian zone). We found that interviewee perception of reservoir conservation (using the CCPI) was related to trophic state, richness and diversity of benthic macroinvertebrate, and the presence of residences and agriculture in the riparian zone. It is necessary to consider the environmental perception of the local community as a relevant factor in management programmes and the conservation of ecosystems, even if artificial, as is the case with reservoirs. These communities can significantly contribute to maintaining the environmental quality through their performance in participatory management in projects such as: participating in the investigation of pollution in reservoirs, collecting parameters related to water quality, and community action in designing conservation strategies.

Evaluating the conservation of aquatic ecosystems, especially those which serve to supply, has been carried out using a variety of tools. However, the perception of water quality by the local community which lives in direct contact with water resources has not been considered with enough importance. This study analysed the relationship between the conservation status of reservoirs as perceived by the local community and their conservation status according to physical, chemical, and biological indicators. To do so, we calculated the Trophic State Index (TSI) of the reservoirs, the diversity and richness of benthic macroinvertebrate and we analysed the human influence in the riparian zone. Thus, we created the Community Conservation Perception Index (CCPI) to quantitatively associate the perception of the local community with environmental quality indicators (TSI, diversity, richness and anthropogenic influences in the riparian zone). We found that interviewee perception of reservoir conservation (using the CCPI) was related to trophic state, richness and diversity of benthic macroinvertebrate, and the presence of residences and agriculture in the riparian zone. It is necessary to consider the environmental perception of the local community as a relevant factor in management programmes and the conservation of ecosystems, even if artificial, as is the case with reservoirs. These communities can significantly contribute to maintaining the environmental quality through their performance in participatory management in projects such as: participating in the investigation of pollution in reservoirs, collecting parameters related to water quality, and community action in designing conservation strategies.