Shore's ditches drain too well

Man-made systems eliminate filters found naturally

April 08, 1999|By Tom Horton | Tom Horton,SUN STAFF

HEBRON -- To the acknowledged icons of the Eastern Shore and Delmarva Peninsula -- the seafood and the waterfowl, the sandy beaches and tidewater coves -- add another: ditches.

For thousands of miles across Delaware and Maryland, farm drainage ditches -- up to 14 feet deep and 80 feet across -- have extended, replaced and bypassed natural streams and wetlands of Chesapeake rivers from the Chester to the Pocomoke.

The ditches make possible low-lying Delmarva's agricultural bounty. But they are also rapid-delivery systems to the bay for the nutrients that reduce oxygen, kill underwater grasses and possibly trigger toxic Pfiesteria outbreaks.

So as environmental officials focus on reducing the leakage of pollutants from farmland into the bay, conflicts are brewing with the almost 400"public drainage" and "tax ditch" associations of Delaware and Maryland farmers.

U.S. Environmental Protection Agency officials, who have largely ignored ditching, say they will be getting more involved with the issue and plan to challenge a large ditching project proposed in Delaware.

The networks that maintain and expand the ditches are legal subdivisions, with elected officials and powers of taxation. They cover areas ranging from 2 acres to 56,000 acres.

The ditching of the peninsula, explains Owen Bricker of the U.S. Geological Survey, is like "a series of pipes bypassing and short-circuiting the natural processing of nitrogen and phosphorus."

Huge amounts of these nutrients also enter the bay from sewage treatment plants and from airborne auto and power plant emissions, but on Delmarva the dominant sources are poultry manure and other agricultural fertilizers.

Across the peninsula, water once flowed more slowly from land to bay, through sinuous stream channels, boggy soils, forested swamps and marshes, says Bricker, whose agency is studying the movement of sediments and nutrients into the Pocomoke River, where toxic Pfiesteria arose two summers ago.

In that more natural drainage system, nutrients were filtered, buried, taken up by the growth of extensive vegetation or converted into harmless nitrogen gas before they could enter the bay, scientists say.

This still happens to varying degrees even in the ditches, especially where some farmers have experimented with such modifications as water control gates to make them perform more like natural systems.

But mostly, modern drainage systems perform exactly as they were designed -- whisking water, and pollution, efficiently downstream. The "public" or "tax" ditches, joined to smaller, on-farm ditches, are built to remove an inch of rain every 24 hours.

So that the ditches are free of vegetation that would impede drainage, their managers tend to keep at least one side, and usually both, shorn of trees or other natural growth that would help filter out polluted runoff.

And although drainage systems have been in use for centuries, the system on Delmarva in recent decades has been greatly enlarged and extended. This occurred as the amounts of fertilizer, poultry manure, airborne emissions and sludge from metropolitan sewage plants put on farmland have all increased greatly.

A complicating factor in trying to reduce ditches' impact on the environment is that many rural roads and, increasingly, housing developments sprawling into the countryside depend on farm drainage networks to minimize flooding.

"You plug up the ditches, and it's not just farming you'd affect. You'd have trouble inhabiting some of these areas at all," says John McCoy, a stream restoration specialist with Maryland's Department of Natural Resources.

Besides affecting the bay, ditching has had an impact on Delmarva's streams.

"We call these ditches, but they are streams, waters of the state, natural resources," says John Maxted, an ecologist with Delaware's Department of Natural Resources and Environmental Control (DNREC).

A 1994 DNREC survey estimated that about 87 percent of Delaware's stream mileage has habitat and water quality that are "moderately to severely degraded," Maxted said.

He said ditching is the biggest factor in that, with roughly two-thirds of the state's 3,000 stream miles routinely maintained for farm drainage. About 70 percent of Delaware ditches drain toward the bay, DNREC says.

Maryland's experience is similar. In its heavily ditched Pocomoke River watershed, 97 percent of the 271 miles of small streams have habitats in the "very poor to fair" range, according to DNR biologists. In the Choptank River watershed, 95 percent of the small streams rated very poor to fair.

As a whole, the Eastern Shore has about half the state-average stream quality (5 percent "good" vs. the state average of 11 percent).

Once a stream becomes part of a Public Drainage Association (PDA), as farmers' drainage groups are called in Maryland, it gets less regulatory attention, with jurisdiction passing from Maryland's Department of Environment to the state Department of Agriculture.

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