A flooded gold mine in Madre de Dios, Peru. The study reviewed multiple human impacts on freshwater ecosystems, including dam-building, mining, land-cover change, and climate change. Individually, each of these can cause harm and alter how the ecosystem functions, but the scientists warn that they will also interact, with 'the potential to trigger cascading effects that can significantly degrade these freshwater ecosystems.' Photo: Claire Salisbury

By Claire Salisbury
1 February 2016

(mongabay.com) – The Amazon’s freshwater ecosystems are at risk because current policy and existing protected areas fail to protect the connectivity of the water cycle, scientists warn. The new study, published in Global Change Biology, examines the factors degrading the Amazon basin’s hydrological connectivity: the movement of water — and with it the life-giving matter, nutrients and organisms it carries — between the vast system’s headwaters and the Atlantic Ocean, between the rivers and the forest, and the earth and the atmosphere.

Such connectivity is fundamental to ecosystem health, as it regulates how ecosystems function, the scientists say. The Amazon’s freshwater ecosystems, which cover an area of 1 million square kilometers (386,102 square miles), play crucial roles in regulating climate, transporting nutrients, maintaining water quality, supporting biodiversity, and providing food and fiber, so-called ecosystem services that benefit local, regional and global communities.

If hydrological connectivity is disrupted then the ecosystem can no longer function in the same way and these services may be diminished. This is the danger facing the Amazon.

Lead author Leandro Castello originally studied oceanography, and now works on the conservation of Amazon fish and fisheries, both of which are suffering from habitat change and degradation. “In oceanography they teach you that everything is connected — via water — to everything else. A forested, tropical river basin is not too different: what happens to the trees affects the streams and rivers, and what happens in the headwaters affects everything downstream,” Castello, of Virginia Polytechnic Institute and State University, told Mongabay.

“Everything downstream” can extend for thousands of miles in Amazonia, and include multiple nations and regions with vastly different levels of land and river protection. This political fragmentation makes it difficult to put in place effective basin-wide strategies against ecosystem degradation. “Protected areas [in the Amazon] have limited capacity to protect freshwater ecosystems because they were implemented based on data for terrestrial organisms largely ignoring hydrological connectivity,” Castello explained.

The study examined the impacts of four major drivers of change to the hydrological cycle in the Amazon: dams, mining, land-cover change, and climate change. The scope of the damage being done by these human-caused drivers turned out to be even larger than Castello anticipated. “The surprise was finding how many very strong impacts to the integrity of freshwater ecosystems are happening at such large geographical scale, and yet our policy tools to curb them are less than small,” he warned. […]

If basin-wide research and action is not taken, “the consequences are so overwhelming that they are hard to explain,” Castello said. In their paper, the authors outline the broad implications, saying that individual impacts have “the potential to trigger cascading effects that can significantly degrade these freshwater ecosystems. If current trends continue, more tributary basins will be degraded, compromising ecosystem services such as biodiversity maintenance, water quality, flow regulation, C [carbon] cycling, and food production.” [more]

Imperiled Amazon freshwater ecosystems urgently need basin-wide study, management

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.

Large-scale degradation of Amazonian freshwater ecosystems



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