Predicted impacts of proposed hydroelectric facilities on fish migration routes upstream from the Pantanal wetland (Brazil)

Abstract

There are 104 hydroelectric facilities proposed to be installed in the watersheds that feed the Pantanal, a vast floodplain wetland located mostly in Brazil. The Pantanal is host to 23 long‐distance migratory fish species that ascend upland tributaries to spawn. A Geographic Information System was used to predict the impact of hydroelectric dams on potential migration routes for these species. Both anthropogenic (hydroelectric dams) and natural barriers were included in the analysis. Natural barriers were identified by river slope. Critical river slopes of 10 and 25%, above which fish were predicted to be incapable of ascending, were modeled as natural barriers. Based on this model, we show that between 2 and 14% of rivers in the Pantanal watershed are naturally blocked to fish migration. An additional 5 to 9% of rivers are currently blocked due to 35 existing hydroelectric facilities. If all proposed dams are built, the area flooded by new reservoirs will triple and the river kilometers blocked will double, blocking 25 to 32% of the river system to fish migration. The Taquari and Cuiabá River sub‐basins will be the most impacted, each having more than 70% of their rivers blocked. The impact of individual proposed facilities on the loss of migration routes is related to their proximity to existing barriers. Fourteen of the proposed dams are upstream from existing barriers and will therefore not further restrict long‐distance fish migration routes while proposed dams are predicted to close an additional 11,000 to 12,000 km of river channels.

Further Development of Small Hydropower Facilities Will Significantly Reduce Sediment Transport to the Pantanal Wetland of Brazil

“…Based on these results as well as our parallel study on nutrient transport (Oliveira et al, in press) and a recent analysis of migratory fish routes in the region (Campos et al, 2020), development of new SHPs on the remaining undammed tributaries to the Pantanal may present serious risks to downstream river and floodplain ecosystems. Although the numerous dams in the northern part of the watershed have only modestly reduced sediment and nutrient transport because many are on rivers with low rates of transport, our modeling indicates that future construction of dams on rivers with higher sediment loads is likely to substantially reduce sediment transport from the uplands to the Pantanal.…”

“…Decisions about whether and where to construct dams in the Upper Paraguay River basin should consider not only sediment transport but also other environmental and social impacts. Two other kinds of impacts that are particularly important are nutrient transport (Oliveira et al, in press) and river system connectivity for migratory fish (Campos et al, 2020).…”

“…Floodplain lands subject to inundation by sedimentrich river water tend to be more productive (Hamilton, 2002;Junk et al, 2011), and sediment-rich rivers maintain dynamic changes in channel and floodplain geomorphology, which in turn increase floodplain ecosystem diversity (e.g., the Taquari River fan in the Pantanal: Jongman, 2005). In addition to impacts on the transport of sediments and associated nutrients, many species of migratory fishes important to fisheries in the region ascend the upland tributaries to spawn and dams present migration barriers (Campos et al, 2020).…”

Further Development of Small Hydropower Facilities May Alter Nutrient Transport to the Pantanal Wetland of Brazil

“…Effects of new hydropower facilities on downstream nutrient concentrations and transport are one of a number of environmental and social considerations for decisions about whether and where to construct dams in the Upper Paraguay River basin. Effects on sediment transport and fish migrations are two other environmental impacts of paramount importance Campos et al, 2020). Considering concentrations and transport of nutrients together with the parallel study of sediments presented by Fantin-Cruz et al (2020), we argue that new hydropower facilities should not be built on undammed rivers entering the Pantanal that have particularly low nutrient concentrations and transport, as well as on those that have the highest absolute rates of transport to the Pantanal.…”

A Modeling Assessment of Large-Scale Hydrologic Alteration in South American Pantanal Due to Upstream Dam Operation

“…Regarding the expansion of the hydroelectric matrix in Brazil and its potential damages, besides the Amazon basin, another location where a large number of dams are planned is the Upper Paraguay river basin, a region that is notable for the Pantanal, a huge wetland ecosystem that is largely dependent on the flow regime of the Paraguay river and its tributaries. In this region, there is a debate about the potential impacts of new dam construction in the highlands (Planalto) on the ecosystems of the lower lying Pantanal (Bergier, 2013;Coelho da Silva et al, 2019;Medinas de Campos et al, 2020). In this context, it is worthwhile to carefully examine the hydrological changes that followed the construction of the major Manso dam, that started operation in 2000 at the headwaters of one of the major tributaries of the Paraguay river.…”