New technique compares pollution at different estuaries

This is said to be the first time that it has been possible to make a uniform comparison between levels of nitrogen, carbon and phosphorus – indicators of agricultural and industrial pollution – in separate water bodies.

The Land Ocean Interactions in Coastal Zones (LOICZ) system was unveiled by scientists from the universities of Hawaii and Stockholm at the recent American Geophysical Union Ocean Sciences meeting in Honolulu.

“There have been many studies around the globe of the world’s estuaries and coastal water systems,” said Dennis Swaney, an environmental biologist at the Boyce Thompson Institute (BTI) for Plant Research at Cornell, and one of the researchers on the project. “But to date there has not been a uniform approach to measure the effects of loads of nitrogen and phosphorus in those waters.”

The researchers used as the basis for their study the principle of conservation of mass. Water volume and salt content in estuarine and coastal waters remain roughly constant over time, but nutrients such as nitrogen and phosphorus are taken up or released by biological processes. Water from one system that mixes with adjacent bodies of water, such as oceans, was described by the researchers in terms of ‘water budgets’, and the nutrients carried in it were described in terms of ‘nutrient budgets’. Scientists were then able to make inferences about the biological productivity and other processes in estuaries by looking at any discrepancies in the nutrient budgets. Such data, en masse, has been used to gain a picture of the relative health of the water body concerned.

The current project began in 1993 at the Netherlands Institute for Sea Research, funded by the United Nations. By this January, data from 195 coastal systems around the world had been collated. The project’s scientists are now comparing the budget data with other global datasets of variables collated in a sister project at the University of Kansas.

Comparing data between Chesapeake Bay in the US and Tokyo Bay in Japan, for instance, shows that Tokyo Bay’s nitrogen load is about 16 millimoles per metre squared per day, compared to just 1.6 millimoles per metre squared per day for Chesapeake Bay. As Tokyo Bay is relatively small in area – just 1,000 square kilometres compared to Chesapeake Bay’s 11,000 square kilometres – the Bay’s nitrogen load is extremely high. Another estuary, the Gulf of Gdansk, which drains from a heavily-industrialised and intensively farmed area of Poland, has twice Chesapeake Bay’s nitrogen load, data that may provide European environmental workers with a future challenge.

Swaney says the next challenge will be to extrapolate more detailed environmental information from these site-specific results. “We can’t simply come up with a global average,” he said. “We are trying to find patterns of estuarine productivity – how it varies with system area, region, and human and environmental factors.”