Glacial watersheds may contribute to oceanic food web

Terra Daily: A study recently completed in the gulf coast of Alaska by federal and university researchers has found that as glacial ice disappears, the production and export of high- quality food from glacial watersheds to marine ecosystems may disappear too. This trend could have serious consequences for marine food webs. The study, "Glaciers as a source of ancient and labile organic matter to the marine environment," was recently published in the December 24, 2009, issue of the journal Nature.

The research, which was conducted on 11 coastal watersheds in the Gulf of Alaska, has documented an interesting paradox with important implications for coastal ecosystems. "Glacial watersheds comprise 30 percent of the Tongass National Forest and supply about 35 to 40 percent of the stream discharge," says Rick Edwards, a coauthor on the study.

"These watersheds export dissolved organic matter that is remarkably biologically active in contrast to that found in other rivers. Generally, scientists expect that organic matter decreases in its quality as a food source as it ages, becoming less and less active over time."

But the dissolved organic material discharged from the glacial watersheds in this study was almost 4,000 years old; yet surprisingly, more than 66 percent of it was rapidly metabolized by marine microbes into living biomass to support marine food webs, adds Edwards.

…Rivers fringing the gulf coast of Alaska discharge as much water as the Mississippi River into a marine system that harbors the most productive salmon fishery in the world. As these rivers flow through the temperate rain forests on the coastal margin, they are influenced by vegetation, soils and wetlands, which control the amount and timing of carbon and nutrients delivered to the productive coastal ecosystems receiving that drainage….

Dry bay at Alaska's Pacific coast, where it meets the Alsek River, shot by Sam Beebe, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 License