The future is being charted for Virginia’s Chesapeake tributaries — and it may offer a glimpse of what’s in store for the rest of the Bay’s rivers.

Unlike rivers from the Potomac north, which have had firm nutrient reduction targets since 1992, Virginia’s “lower tributaries” — the James, York, Rappahannock and Eastern Shore — have never had official goals.

The reason: Back in 1992, computer models indicated those rivers had little impact on the Chesapeake.

At the same time, it was recognized that the large, tidal rivers each contain substantial amounts of habitat for fish, crabs and other resources. Those areas might benefit from nutrient action, but no one knew what those reductions should be.

So, establishing nutrient reduction goals was put off until the Bay Program developed sophisticated, new computer models that could better determine whether things like grass beds would make a comeback if the amounts of nitrogen, phosphorus and sediments were curbed.

That day has finally arrived.

For months, Bay Program models have been calculating what would happen in each tributary with various levels of nutrient and sediment reductions.

And the answer is — it depends on the river.

“Each of these river systems responds significantly different to different levels of nutrient and sediment reductions,” said Rich Batiuk, associate director for science with the EPA’s Bay Program Office.

Indeed, the models predict dramatically varied outcomes for each river south of the Potomac:

  • Nutrient reductions appear to accomplish no significant living resource or water quality changes in the lower tidal James. Reductions in its upper tidal areas — near Richmond — may produce relatively small water quality and habitat benefits.
  • Reductions in the Rappahannock River will significantly improve water quality and habitat in the river. But even more improvement would take place if further nutrient reductions were made in tributaries to the north.
  • Like the Rappahannock, the York River responds to nutrient reductions within its basin, but would also realize benefits from further reductions made in other tributaries.
  • Habitat along the Eastern Shore improves incrementally as local nutrient and sediment inputs are reduced, but some places, like the Tangier area, would benefit from further, up the Bay reductions as well.

Virginia and Bay Program officials have, for the last few months, been presenting the model results to teams of “stakeholders” — farmers, wastewater treatment plant operators, environmentalists, elected officials and others — in each basin.

The teams will try to make recommendations about what reductions they think are “right” for their basins. But the final decision for reduction goals — and implementation timeframes — is up to Virginia Secretary of Natural Resources John Paul Woodley Jr.

But this is more than just a Virginia story.

What’s happening there will ultimately take place in other tributaries as well. The Chesapeake Executive Council in 1997 directed the Bay Program to review other tributaries, from the Potomac north to the Susquehanna, to see if previously agreed-upon nutrient reduction goals will “assure water quality that will support the living resources of the Bay and its tributaries.”

If not, new, river-specific goals are to be set by the Council’s 2000 meeting, with detailed implementation plans to be adopted by the Council in 2001. The Council is the top, policy-making body for the Bay restoration effort, including the governors of Virginia, Maryland and Pennsylvania; the mayor of the District of Columbia; the EPA administrator; and the chairman of the Chesapeake Bay Commission, which represents state legislatures.

The more detailed analysis from the new computer models — looking at rivers individually instead of Baywide — may well challenge future policy.
For example, if nutrient controls accomplish less in one basin than another, should cost-share money for farmers or wastewater treatment plant grants be directed to other watersheds?

Or, should further reductions be made in one river because they will improve water quality in another?

For example, the new modeling shows that additional “up-Bay” nutrient reductions would improve aquatic habitats in some “down-Bay” areas. “We’re starting to make the case that there are needs for further reductions in those other tributaries north of the Rappahannock for water quality and habitat benefits in the lower Bay tributaries,” Batiuk said.

These estimates come from two Bay Program computer models. First, its Watershed Model takes rainfall, land use, nutrient management practice data and wastewater discharge information to estimate the amount of nitrogen, phosphorus and sediment flowing down the rivers and into tidal waters.

Those estimates feed into a three-dimensional water quality model, which simulates the movement of the water, both vertically and horizontally.

That model estimates how nutrient and sediment reductions will be translated into responses by underwater grasses and bottom-dwelling organisms — important food for many fish.

Excess nutrients cause a variety of problems in the Bay and its tidal rivers. They spur the growth of algae, which block sunlight from reaching important underwater grasses that provide food and habitat for blue crabs, waterfowl, juvenile fish and others. When the algae die, they sink to the bottom and decompose in a process that depletes the water of oxygen.

Either the loss of grasses or the loss of oxygen can ultimately lead to a loss of aquatic habitat, which, in turn, may mean fewer fish, crabs and ducks in the Bay.

But nutrients aren’t the only factor that comes into play. The fine soils characteristic for much of the Virginia basins can also block light to the plants when washed into the water, so the models are also factoring in the benefits of sediment reductions.

For each river, the models show some common characteristics. For example, nutrient and sediment control within the watershed of each river clearly affects the upper tidal area of that waterway, which is mostly fresh water.

But in the lower tidal areas of both the Rappahannock and the York, tidal exchanges with the Chesapeake become a factor. Water quality in those areas is affected not only by the river, but also the water quality of the Bay.

As a result of these river-by-river differences, the computer results become murky — at least in the sense that they don’t always lend themselves to obvious policy objectives.

For example, nutrient reductions appear to have no effect on the high-salinity, lower tidal James. There is no low-oxygen problem to begin with, and no currently feasible level of nutrient and sediment reductions seem to result in the significant growth of underwater grasses.

“This is something different,” said Lewis Linker, modeling coordinator for the Bay Program. “For the first time, we’ve looked at a regional part of the Bay and not seen a significant impact.”

The models indicate there could be a slight improvement in the upper tidal area of the river, roughly in the vicinity between the Chickahominy River and Richmond. But a key question people must grapple with is whether the modest reduction in algae production and the sparse recovery in grass beds projected for the upper tidal area of the James is worth the cost. The model projects that new grass beds would be thin, which means they could be hard to maintain.

“That’s one of the points that we have to debate,” said Mark Bennett, of the Virginia Department of Conservation and Natural Resources, who is coordinating tributary strategy development for the James. “To some people, any improvement is enough to pursue.”

On the other hand, the model projections are considered to be conservative: It estimates water clarity — a key factor for grass survival — at a depth of 1 meter. Shallower areas would get more sunlight, and could have denser grass beds than predicted by the model.

“We do know that fisheries in tidal fresh regions do benefit from SAV [submerged aquatic vegetation] recovery,” Bennett said. “But there’s always going to be the open question of how much 20 acres of SAV is worth.”

The James River stakeholders may ultimately decide that those benefits are worth pursuing for the upper tidal areas, and seek further nutrient and sediment reductions, Bennett said.

In the lower tidal James, where the model projects no improvements from further nutrient and sediment reductions, a nutrient “cap” at the present levels may be adopted. “We probably don’t want to continue to increase loadings, because bad things might start to happen,” Bennett said.

The story is altogether different for the Rappahannock, and to a lesser degree, the York. Water quality, grasses beds and oxygen conditions would all get better if nutrient and sediment reductions are made within the river’s drainage basin. But its water quality would improve even further if more nutrient reductions are made in upstream areas of the Bay than are planned.

That’s because tidal exchanges flush nutrient-laden water from the Bay into the Rappahannock, spurring algae blooms that sink to the bottom and deplete the water of oxygen. A bottom ridge near the mouth of the river traps that oxygen-starved water in the Rappahannock.

Nonetheless, the model predicts that a sharp nutrient reduction in the basin could eliminate oxygen-depleted conditions in some years. That would mean a reduction on the order of 48 percent of the “controllable” amount of nutrients. (Nitrogen and phosphorus occur naturally, and background levels are considered “uncontrollable.)

By contrast, the upper Bay tributaries are currently working to achieve a 40 percent reduction of controllable nutrients.

For the Rappahannock, such a reduction borders on the limit of what is presently possible. Yet stakeholders in the basin seem to think that is a goal worth shooting for — given enough time, perhaps a decade.

“That is our vision for the river, but we want to make sure that the program is voluntary, and local determination is still maintained,” said Colin Powers, who is coordinating the Rappahannock tributary strategy development for the Department of Environmental Quality.

If further nutrient reductions were made in other Bay tributaries, the model predicts that low-oxygen conditions would be reduced still further for most years in the Rappahannock, and grass beds would expand farther and become more dense.

That will raise questions for other Bay Program states. The Rappahannock, Batiuk noted, is an important area for juvenile blue crabs. And, juvenile blue crabs are found in far greater abundances in grass beds, which offer them protection from predators, than anyplace else.

“This area makes or breaks what we’re going to have for future crab habitat in the Chesapeake Bay,” Batiuk said.

Will others want to do further nutrient reductions for the Rappahannock in the hope that resources, like crabs, will trickle up the estuary? It’s an issue to be examined when the models begin turning to other rivers, and new goals are considered.

“Through the goal evaluation process, we hope they [people in upper tributaries] recognize that additional reductions will not only benefit their rivers and the Chesapeake Bay, but also enhance and support our efforts to improve the Rappahannock,” Powers said. “If their efforts help improve the Rappahannock’s living resources, that should help them too.”