When a drop of rain falls on the ground, just how long does it take for it to reach the Chesapeake Bay?

No one really knows. But the answer is critical to the Bay cleanup effort and will be a major focus of a multiyear research project being launched by the U.S. Geological Survey.

While the Bay Program has embarked on a major effort to reduce nutrients entering the Bay 40 percent by the turn of the century something that research suggests should significantly improve Chesapeake water quality - it's not certain how long it will take to see those improvements.

During each of the next five years, the USGS will get $1 million to learn more about the nuts and bolts of how land-based nutrient reduction activities will ultimately affect water quality throughout the Bay watershed as well as the grasses living in the Chesapeake that provide critical habitat.

While the project will involve some new research, much of the effort will be based on analyzing information that has been collected by the USGS and other agencies and institutions around the Chesapeake for more than two decades.

"We are building off already existing projects to answer new questions," said Scott Phillips, the USGS coordinator for the project.

The Bay states have been working for years to encourage farmers and landowners to reduce fertilizer applications and to implement a variety of runoff control practices aimed at preventing rainwater from washing nutrients off the land and into waterways.

The effectiveness of those practices may vary greatly in different types of geological settings.

In addition, much of the water - and nutrients - that enter the Bay comes from the groundwater. It may take years - even decades - for those nutrients to be "flushed" through the system.

In other words, enough practices may be in place to control nutrient pollution by the year 2000, but the Bay may continue to be filled will nutrients still working their way through the groundwater. Understanding how long it will take to see improvements is important because state and federal officials are evaluating whether they are on track to meet the turn-of-the-century goal.

"We're trying to help the Bay Program get an idea of how long it's going to take to actually see a water quality response to the 40 percent nutrient reduction," Phillips said.

Using studies from several small watersheds throughout the Bay region, the USGS hopes to develop estimates of how rapidly - or slowly - groundwater moves through different kinds of terrain. This information will then be used to help explain nutrient trends of streams and rivers within the watershed.

Not only will this information provide managers with information about how rapidly they will see responses, it can help them prioritize their efforts. By presenting geologic and related information about water flows on maps, for example, Phillips said managers can direct nutrient reduction efforts toward areas most likely to produce the greatest or most rapid water quality improvements.

The USGS will also develop statistical tools based upon the improved understanding of how nutrients move through small watersheds to help resource managers better predict how water quality in large watersheds - those greater than 100 square miles - will respond to nutrient and sediment control strategies.

This type of information is important in the development of tributary nutrient reduction strategies, Phillips said, because it helps show people what affect cleanup actions will have on their local waterways.

The USGS also plans a more long-term analysis of the Bay. By using new information, and by analyzing previously collected data, the USGS hopes to sort out the effects of humans on the Bay from the effects of natural events.

For example, will large floods overwhelm cleanup efforts? How big of an impact will an expanding population and changing land use patterns have on the Bay? By examining sediments from the bottom of the Bay, scientists hope to piece together a centuries-long view of how conditions in the Chesapeake have varied.

"The Bay, as a natural system, has undergone changes over time," Phillips said. "There are some things that we can't control. We have to keep that in mind as we try to manage the system."

The Bay region is the third area to have been selected by the USGS for multiyear ecosystem studies. Previously, San Francisco ay and the Everglades were chosen for ecosystem work.