Dialogue Earth has roots in a broad, stakeholder-based national report on the condition and use of U.S. ecosystems published by the Heinz Center in Washington, D.C. (the report is available in hard-copy from Island Press). Curiosity about the ongoing relevance of these indicators has led me to dive in and see what, if anything, can be said about trends since the release of the report in 2008.
The first indicator in the spotlight is one that describes the movement of nitrogen (N) into major waterways, through run-off as well as point discharges such as sewage treatment facilities (here’s a link to download a pdf of the indicator). Why is this an important indicator of the state of U.S. ecosystems? Our explanation in the report does a good job of answering this question:
Nitrogen is an important plant nutrient and is essential to all life. Nitrogen is an abundant component of the earth’s atmosphere, but it is unavailable to most life in gaseous form. In order to be used by plants and other organisms, nitrogen gas must be “fixed,” or converted to a “reactive” form, that plants can use, such as nitrate. Nitrogen is fixed and accumulates in ecosystems through natural processes, such as the growth of nitrogen-fixing plants like clover and soybeans. However, human activity has greatly increased the amount of reactive nitrogen added to ecosystems. The largest human-caused input of nitrogen to ecosystems comes from the conversion of atmospheric nitrogen gas into fertilizers. Additional reactive nitrogen gas is produced by the combustion of fossil fuels. Reactive nitrogen from all these sources can ultimately enter streams and rivers. Excess nitrogen transported to coastal waters by rivers can lead to low oxygen conditions, threaten fish and animal life, and degrade coastal water quality. (more…)