Large‐scale degradation of Amazonian freshwater ecosystems

Abstract

Hydrological connectivity regulates the structure and function of Amazonian freshwater ecosystems and the provisioning of services that sustain local populations. This connectivity is increasingly being disrupted by the construction of dams, mining, land-cover changes, and global climate change. This review analyzes these drivers of degradation, evaluates their impacts on hydrological connectivity, and identifies policy deficiencies that hinder freshwater ecosystem protection. There are 154 large hydroelectric dams in operation today, and 21 dams under construction. The current trajectory of dam construction will leave only three free-flowing tributaries in the next few decades if all 277 planned dams are completed. Land-cover changes driven by mining, dam and road construction, agriculture and cattle ranching have already affected ~20% of the Basin and up to ~50% of riparian forests in some regions. Global climate change will likely exacerbate these impacts by creating warmer and dryer conditions, with less predictable rainfall and more extreme events (e.g., droughts and floods). The resulting hydrological alterations are rapidly degrading freshwater ecosystems, both independently and via complex feedbacks and synergistic interactions. The ecosystem impacts include biodiversity loss, warmer stream temperatures, stronger and more frequent floodplain fires, and changes to biogeochemical cycles, transport of organic and inorganic materials, and freshwater community structure and function. The impacts also include reductions in water quality, fish yields, and availability of water for navigation, power generation, and human use. This degradation of Amazonian freshwater ecosystems cannot be curbed presently because existing policies are inconsistent across the Basin, ignore cumulative effects, and overlook the hydrological connectivity of freshwater ecosystems. Maintaining the integrity of these freshwater ecosystems requires a basinwide research and policy framework to understand and manage hydrological connectivity across multiple spatial scales and jurisdictional boundaries.

Rivers shape population genetic structure in Mauritia flexuosa (Arecaceae)

“…Hydrological connectivity in Amazonia is increasingly disrupted by dynamic and multifaceted drivers (Ritter et al., 2017), including mining, and land‐use changes that have modified at least 20% of Amazonia, with over 150 hydroelectric dams currently in operation and hundreds more planned (Castello & Macedo, 2016). The understanding of the processes related to the maintenance the gene flow throughout different environments, such as that in M. flexuosa, could aid conservation and management strategies.…”

Carbon-optimised land management strategies for southern Amazonia

“…The Amazon forest is considered a key control for the global and regional climate system (Trumbore et al 2015;Coe et al 2017) and is a principal driver for the global and regional water cycle (Castello and Macedo 2016;Getirana 2016;Gimeno et al 2012). It is home to a unique share of Earth's genetic resources (Laurance et al 2012;Pimm et al 2014;Myers et al 2000) as well as a rich human cultural heritage which includes indigenous populations yet unexplored (Walker et al 2016;Pringle 2014).…”

Damming the rivers of the Amazon basin

“…Amazonian hydroelectric dams are commonly justified on the basis of providing renewable energy and avoiding carbon emissions, while supplying energy needed for economic development. Recent scientific reviews have considered environmental impacts of damming Amazonian rivers [1][2][3] , but regrettably, the effects of dams have mainly been assessed through studies undertaken only in the vicinity of each dam 4 . Such a local-scale approach generally ignores the far larger, basin-scale, geomorphological, ecological, and political dimensions that will determine the future productive and environmental condition of the river system as a whole.…”