The nation's ecosystems

Humans can't help but impact the surrounding landscape. We build roads and dams; clear lands to grow food and raise livestock; and dig mines and wells to access precious metals and fossil fuels.

On Wednesday, the Heinz Center for Science, Economics and the Environment — a nonprofit environmental think tank — released its second assessment of how these activities affect the nation's ecosystems.

The 300-page report attempts to provide an integrated picture of ecosystem condition. The authors used 108 environmental indicators to track changes in water quality, erosion, chemical contaminants, invasive species, biodiversity and much more.

Although the Heinz Center doesn't interpret the data, the overall picture is sobering. For example, chemical contaminants were detected in nearly all streams and three-quarters of groundwater wells. And four out of five freshwater fish tested positive for at least one contaminant. Often that contaminant was DDT, a pesticide that was banned in the United States more than 30 years ago.

With respect to biodiversity, about one-third of native plant and animal species are at risk of extinction, including the whooping crane, the California condor and the Florida manatee.

But the report isn't all bleak. Wind erosion is threatening fewer croplands than it did 25 years ago.

To find out more about the state of our nation's ecosystems, please visit http://www.heinzcenter.org/ecosystems.

Cassandra Willyard

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