Development and validation of an environmental fragility index (EFI) for the neotropical savannah biome

Diego R Macedo; Robert M Hughes; Philip R Kaufmann; Marcos Callisto

doi:10.1016/j.scitotenv.2018.04.216

Development and validation of an environmental fragility index (EFI) for the neotropical savannah biome

Sci Total Environ. 2018 Sep 1:635:1267-1279. doi: 10.1016/j.scitotenv.2018.04.216. Epub 2018 Apr 24.

Authors

Diego R Macedo¹, Robert M Hughes², Philip R Kaufmann³, Marcos Callisto⁴

Affiliations

¹ Departamento de Geografia, Instituto de Geociências, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, CEP 31270-901, Belo Horizonte, MG, Brazil; Laboratório de Ecologia de Bentos, Departamento de Biologia Geral, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, CP 486, CEP 31270-901, Belo Horizonte, MG, Brazil. Electronic address: diegorm@ufmg.br.
² Amnis Opes Institute and Department of Fisheries and Wildlife, Oregon State University, 200 SW 35th Street, Corvallis, OR 97333, USA.
³ Western Ecology Division, National Health and Environmental Effects Laboratory, Office of Research and Development, United States Environmental Protection Agency, 200 SW 35th Street, Corvallis, OR 97333, USA.
⁴ Laboratório de Ecologia de Bentos, Departamento de Biologia Geral, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, CP 486, CEP 31270-901, Belo Horizonte, MG, Brazil.

Abstract

Augmented production and transport of fine sediments resulting from increased human activities are major threats to freshwater ecosystems, including reservoirs and their ecosystem services. To support large scale assessment of the likelihood of soil erosion and reservoir sedimentation, we developed and validated an environmental fragility index (EFI) for the Brazilian neotropical savannah. The EFI was derived from measured geoclimatic controls on sediment production (rainfall, variation of elevation and slope, geology) and anthropogenic pressures (natural cover, road density, distance from roads and urban centers) in 111 catchments upstream of four large hydroelectric reservoirs. We evaluated the effectiveness of the EFI by regressing it against a relative bed stability index (LRBS) that assesses the degree to which stream sites draining into the reservoirs are affected by excess fine sediments. We developed the EFI on 111 of these sites and validated our model on the remaining 37 independent sites. We also compared the effectiveness of the EFI in predicting LRBS with that of a multiple linear regression model (via best-subset procedure) using 7 independent variables. The EFI was significantly correlated with the LRBS, with regression R² values of 0.32 and 0.40, respectively, in development and validation sites. Although the EFI and multiple regression explained similar amounts of variability (R² = 0.32 vs 0.36), the EFI had a higher F-ratio (51.6 vs 8.5) and better AICc value (333 vs 338). Because the sites were randomly selected and well-distributed across geoclimatic controlling factors, we were able to calculate spatially-explicit EFI values for all hydrologic units within the study area (~38,500 km²). This model-based inference showed that over 65% of those units had high or extreme fragility. This methodology has great potential for application in the management, recovery, and preservation of hydroelectric reservoirs and streams in tropical river basins.

Keywords: Analytic hierarchy process; Brazil; Erosion; Ottobasins; Sedimentation; Spatial analysis.

Grants and funding

EPA999999/Intramural EPA/United States