Environmental biologists have now made it possible to directly compare, for instance, the Chesapeake Bay to the Gulf of Gdansk in Poland. The uniform methodology they have developed to measure the carbon, nitrogen and phosphorus levels -- indicating runoff from industry and agriculture -- in the world's waters will be discussed today (Feb. 13) at the American Geophysical Union Ocean Sciences meeting, at the Hawaii Convention Center in Honolulu.
"There have been many studies around the globe of the world's estuaries and coastal water systems. But to date there has not been a uniform approach to measure the effects of loads of nitrogen and phosphorus in those waters," says Dennis Swaney, an environmental biologist at the Boyce Thompson Institute (BTI) for Plant Research Inc., located on the campus of Cornell University in Ithaca, N.Y. Swaney works with the environmental biology group, primarily in watershed modeling, at the institute. He and his colleagues, Stephen Smith and Vilma Dupra, both of the University of Hawaii, will discuss this system -- the Land Ocean Interactions in Coastal Zones, or LOICZ -- in a talk, "Patterns Emerging from the LOICZ Biogeochemical Budget and Typology Datasets." (Fredrik Wulff of Stockholm University, Sweden, also collaborated on the project.)
The researchers' approach is based on the conservation of mass. While water volume and salt content in the estuaries and coastal water areas remain approximately constant over time, nutrients such as nitrogen and phosphorus are taken up, or released, by biological processes in estuaries. As water flows through the system and mixes with adjacent systems, such as oceans or seas, the flows of water are described by scientists in terms of "water budgets" and the nutrients carried by these flows are described by "nutrient budgets." By examining discrepancies in nutrient budgets, scientists make inferences about biological productivity and other processes in estuaries around the globe. This data, obtained through the collaboration of hundreds of scientists, has been used to establish at least crude nutrient and water budgets for many sites around the globe. From that, the scientists can determine the relative health of these bodies of water.
The estuary project, which started in 1993 and is funded by the United Nations, is located at the Netherlands Institute for Sea Research. Part of the goal of the project is to gather and disseminate information, and as of January, data from 195 coastal systems globally had been compiled. The biogeochemical budget web site http://data.ecology.su.se/mnode , which contains detailed information about coastal ecosystems, is maintained at Stockholm University. Project scientists are comparing data from the budgets with global data sets of other variables collected in a companion project at the University of Kansas.
The data show that the state of the Chesapeake Bay may not be a reason to rejoice, but compared to some estuaries, it is in better shape. The bay, about 11,000 square kilometers (4,247 square miles) in area, with an average depth of nine meters (30 feet), and a watershed basin of 164,000 square kilometers (63,320 square miles) has a nitrogen load of about 1.6 millimoles, per meter squared, per day. The importance of that number is its use to scientists in making comparisons. For example, Tokyo Bay in Japan has an area of 1,000 square kilometers (386 square miles), with an average depth of 16 meters (53 feet). The nitrogen load in Tokyo Bay is about 16 millimoles per meter squared per day or 10 times the level of Chesapeake Bay. "In smaller water systems, you're going to have higher impacts, and this is an enormous load," says Swaney.
Comparing the Chesapeake Bay to the Gulf of Gdansk could offer clues to how Europe is handling phosphorus and nitrogen run-off. The Gulf of Gdansk, which is surrounded by a heavily populated region and agricultural land, has an area of 3,800 square kilometers (1,467 square miles) and is 53 meters (174 feet) deep. The drainage basin, or watershed area, for the gulf is 194,000 square kilometers (74,904 square miles). The nitrogen load for the Gulf of Gdansk is 5 millimoles per meter squared per day, says Swaney. That is more than twice the nitrogen in the Chesapeake Bay and is a cause of concern for European environmentalists.
Swaney says the next challenge posed for the group will be to extrapolate these site-specific results into more--detailed, environmental information. "We can't simply come up with a global average. We are trying to find patterns of estuarine productivity -- how it varies with system area, region, and human and environmental factors," he says.