Castello & Macedo: Large-scale degradation of Amazonian freshwater ecosystems

Castello, L., Macedo, N.M. 2015. Large-scale degradation of Amazonian freshwater ecosystems. Global Change Biology. doi: 10.1111/gcb.13173 pdf

From the Washington Post

When it comes to conservation efforts, few regions of the Earth have garnered as much attention as the Amazon. Considering that it’s home to the world’s largest remaining rain forest and some of the highest levels of biodiversity on the planet, halting deforestation in the Amazon basin has been a major priority of environmentalists around the globe. But while preserving the trees is undoubtedly important, there’s another equally significant, but often less talked-about, aspect of the Amazon that scientists believe is in trouble.

Freshwater ecosystems are critical to the overall health of the Amazon basin — but they’re facing a variety of threats, ranging from dam-building to climate change, according to a major paper just published in the journal Global Change Biology. And the authors argue that finding better ways to protect these water systems is crucial, not just for the plants and animals that rely on them, but also for the humans who call the Amazon home.

“Working with fish conservation in the Amazon, I was always frustrated with the largely disproportionate emphasis that has been on the scientific, the media and even the policy developments surrounding conservation issues in the Amazon on terrestrial issues,” said the new paper’s lead author Leandro Castello, an assistant professor of fisheries at Virginia Tech.

In fact, freshwater ecosystems in the Amazon — a vast, interconnected network of rivers, streams and lakes covering a million square kilometers of space — provide countless important services to the plants, animals and people who live in the basin. These systems transport water throughout the rain forest, cycle nutrients in the soil, help regulate microclimates and play host to variety of organisms, including thousands of fish species alone. They also represent a life source for many indigenous peoples in the Amazon, who rely on these systems for both water and food.

But in spite of their critical importance, these freshwater ecosystems are under siege. The new paper highlights a variety of threats contributing to the degradation of these water systems and interrupting their connectivity by changing or obstructing water as it flows from one system to the next.

Such changes in hydrology — that is, the way water moves around — are “probably one of the worst things that can happen to a freshwater ecosystem,” Castello noted. “If you change the amount of water in either a lake or river or stream, you will change a lot of processes.”

Dams, for instance, interrupt natural water flow and cause water to collect in reservoirs, preventing fish and other animals from moving through and preventing the downstream transport of nutrients. Previous studies have already shown that damming can have serious effects on fisheries, which is not only an economic threat to people who rely on fishing for their income, but also a threat to the food security of populations whose diet consists heavily of fish.

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