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

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 R values of 0.32 and 0.40, respectively, in development and validation sites. Although the EFI and multiple regression explained similar amounts of variability (R = 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 km). 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.

Land use and local environment affect macroinvertebrate metacommunity organization in Neotropical stream networks

“…replacement of trees by pasture) can affect the dispersal of stream macroinvertebrates. This result was clearer in NP, which has the widest land use gradient among the studied HUs (Macedo et al, 2018). This wide gradient of land uses created a patchy landscape of areas with low and high landscape resistance that could have increased the ecological importance of dispersal corridors (Carlson et al, 2016).…”

“…river basin geology) and human impacts (e.g. siltation and water quality alteration; Kaufmann et al., 1999; Macedo et al., 2018). Thereby, the high importance of environmental filters is not surprising, as both natural and anthropogenic environmental factors are strong drivers of macroinvertebrate communities in the Neotropical savanna (Castro et al., 2019).…”

“…This wide gradient of land uses created a patchy landscape of areas with low and high landscape resistance that could have increased the ecological importance of dispersal corridors (Carlson et al., 2016). On the other extreme, the VG and TM were mostly homogeneous HUs at the landscape level (Macedo et al., 2018), the former due to being dominated by anthropogenic land uses, the latter due to being mostly covered by natural vegetation. In both cases, the land use distance had little importance for the distribution of the dispersal groups.…”

Environmental fragility and vegetation cover dynamics in the Lapa Grande State Park, MG, Brazil

“…thus, this analysis of environmental fragility investigates the susceptibility of an environment to a change in its natural balance. thus, it evaluates the environmental vulnerability to degradation, especially the potential to trigger erosive processes and sedimentation, an important evaluation in projects for environmental planning (Cardoso et al 2015, Macedo et al 2018, Valle et al 2016.…”

Assessing environmental fragility in a mining areafor specific spatial planning purposes

“…Moreover, there is an emergent preoccupation with defining environmental fragility in different territorial systems. For example, a recent study by Macedo et al (2018) defines fragility as an "interaction between vulnerability and anthropogenic influences" (p. 1268) and develops an environmental fragility index applied specifically to the neotropical savannah biome.…”