The draft Chesapeake 2000 Agreement notes that “accommodating growth will frequently involve difficult choices.” One difficult thing is determining what land uses are “best” for streams and the Bay, and where they should fit on the landscape.

Heavily developed urban areas produce large amounts of nutrient-laden runoff from atmospheric deposition, fertilizers and even pet wastes — all of which are collected by a network of gutters and storm drains and promptly whisked into the nearest stream.

Likewise, intensive agricultural areas produce large amounts of nutrients from animal wastes and fertilizers, especially when placed on the ground in greater quantities than can be taken up by crops.

At the other extreme, as a rule of thumb, forests yield the fewest nutrients per acre of any major land use, and are usually considered the “best” — and most natural — land use for the Bay.

But what about the vast expanses of suburbia which often rest between built-up areas and agricultural lands?

Although farmland on a per-acre basis appears to yield more nutrients than suburban areas, many planners and others increasingly see agriculture as a preferable land use because of the cumulative water quality impacts related to development.

That assessment, though, can change based on individual circumstances. For instance, farms that allow cows in the stream will severely degrade water quality more than almost any other activity.

“There are certain farms in some places that aren’t doing very well for the Bay,” said Lee Epstein of the Chesapeake Bay Foundation. “But on a broad scale, well-managed farmland is definitely a plus. It provides some habitat, and it is open space. It can always convert back to forest, whereas if it goes the way of sprawl, it’s gone. People aren’t going to tear out the houses and let the trees grow back.”

The permanent landscape changes related to development — roads, roofs and other “impervious surfaces” — inflict some of the most harmful impacts to streams. Those surfaces act like a wrecking crew to local streams, causing conditions that destroy aquatic life and erode streambanks, spewing sediment downstream.

Initially, it may appear that minimizing the impact of impervious surfaces means spreading development out. Tom Schueler, executive director of the Center for Watershed Protection, estimates that mitigating impervious surface impacts means allowing only one home per every 1–2 acres, when roads and driveways are taken into account.

While that may reduce the impact of impervious surfaces, and nutrient runoff, it isn’t the whole picture, he said. When lot sizes get that large, he said, they typically become too dispersed to be hooked up to sewer systems. That means they have to have septic systems which — unless they are using expensive nitrogen control technology — can yield almost as many nutrients as farmland.

In addition, lots spread over more land result in more roads, which collect more nutrient-laden atmospheric deposition and flush it toward waterways, often with little opportunity for nutrient removal. And when development is spread farther apart, people have to drive farther, pushing up vehicle emissions.

“We historically have looked at just at the amount of nutrients coming off the residence,” said Tom Simpson, Chesapeake Bay Coordinator with the Maryland Department of Agriculture. “That is a very narrow perspective. Every time you put a new residence in, there is a whole host of supporting things that are needed.”

Joe Tassone, deputy chief of comprehensive planning with the Maryland Office of Planning, agrees. If people lived on 20-acre lots, maintained forest on the land and stayed at home all the time, impacts would be small, he said. But that would also mean the Bay watershed population would have to spread well beyond the basin’s borders.

In reality, Tassone said, when development spreads, it forces the construction of new employment centers, retail centers and services such as schools — as well as all the roads that tie them together. “That is now the footprint that you have all over the watershed,” he said. “Not just the footprint of a 3-, 4- or 5-acre lot.”

Further, because of the permanent nature of development changes, it is more difficult — and costly — to try to mitigate impacts after the fact, even if new technologies and techniques become available. It’s just too difficult to uproot pavement and buildings to make changes

By contrast, Simpson said, “as long as that land is in agriculture, there is a host of things you can do. First, you can continue to apply better and better management practices. Secondly, if you want, you can return it to trees. Thirdly, you can buffer it easier. As long as it is open space, our options for minimizing pollution are pretty wide open. But we don’t know how to turn development back into either farm or forest.”