For state and local governments in the Bay watershed, 2025 may get here sooner than anyone thought.

Growth in the Bay watershed's population is projected to increase needed nutrient reductions, and the added burden is not expected to be evenly distributed. (Dave Harp)

In what may be a significant change for some areas, the state-federal Bay Program is looking to use projections of 2025 growth in human population, farm animal numbers and land use changes when it updates nutrient and sediment reduction goals next year.

Since the end of 2010, when the U.S. Environmental Protection Agency established the Bay pollution diet — or total maximum daily load (TMDL) — states have worked to control the amount of nutrients and sediment that wash off the landscape and ultimately into the Chesapeake, where they contribute to murky water, algae blooms and oxygen-starved dead zones.

But by the time those goals are to be met at the end of 2025, the watershed population will have grown 11.5 percent since 2010, reaching about 19.4 million. Those additional people will generate more sewage that gets piped to wastewater treatment plants or pumped into new septic systems.

The extra people will require more houses, stores and places to work, which will result in more roads and roofs — and more stormwater runoff — likely coupled with the loss of forests, farmlands and meadows.

At the same time, the number of some farm animals, particularly chickens, is increasing, and the amount of cropland in cultivation has edged upward.

All of those factors can result in more nitrogen and phosphorus running off the land and into the Bay, at least partially offsetting the region’s multi-billion-dollar nutrient reduction efforts.

The TMDL had called for states to identify new pollution control measures “that are at least sufficient to offset the growth and development” anticipated by 2025. But efforts to monitor and compensate for growth have been uneven across the watershed. Several times, updated data — such as revised farm animal tallies or cropland estimates in a state — have erased some of the estimated impact of new runoff control efforts.

“Every couple of years, there was another surprise,” said Matt Johnston, a data analyst with the University of Maryland who works with the Bay Program and helps states to estimate growth.

Now, Bay Program participants have tentatively agreed on techniques to forecast county-level trends in population, land use and agriculture into the future. Those projections can be used to predict what the landscape will look like in 2025 — and the amount of nutrient reductions that will be needed to meet Bay cleanup goals under those conditions.

Any reductions needed to offset that growth can be assigned to each state next year when they develop new watershed implementation plans — or WIPs — which will guide cleanup efforts through the 2025 deadline. Those growth projections would then be updated every two years.

“There will still be some surprises out there,” Johnston said, but he added that those surprises will be easier to adapt to if states are already planning for an alternative future.

It’s not yet clear exactly how much that will alter the estimates of nutrient reductions that are needed to meet cleanup goals. “We’re not talking about huge increases,” said Peter Claggett, a research geographer with the U.S. Geological Survey who has been working to develop the land use projections. “Probably a couple percent.”

But the uptick would not be spread evenly across the landscape, as growth patterns vary widely, he noted. Poultry production has been growing recently on the Eastern Shore and in parts of Southcentral Pennsylvania. Rapidly growing human populations along parts of the Interstate 95 and I-81 corridors are likely to result in new development popping up in places where forests now stand.

One advantage of the new growth tracking technique, Claggett said, is the predictions can inform future decision-making. The greatest increases in nutrient runoff, for instance, tend to happen when low-polluting forest lands are cleared to make way for development, with the accompanying pavement and rooftops.

If future development does not look like past growth patterns, Claggett noted that some of the predicted increases in runoff might not occur. States and local governments could therefore help meet cleanup goals through better land use planning. “We can help jurisdictions hold the line and not increase their impact,” he said.

Some see potential drawbacks to the new approach, though. Beth McGee, senior water quality scientist with the Chesapeake Bay Foundation, agreed the projections would be useful if they help deter growth. But she worried that states and local governments are more likely to accept the predicted growth as their fate.

“Our issue with building the WIPs on the forecasts is you are sort of baking development growth into the process,” she said. “It is just a given that this new development is going to occur.”

Instead of placing the burden of offsetting new pollution loads on developers, she said, it shifts the responsibility of planning for the impact of growth to state and local governments.

“We believe it runs the risk of shifting the burden to offset those loads from additional development from the private sector — where they belong — to the public sector,” McGee said.

Others, though, say the change could increase the protection of ecologically valuable undeveloped lands. Forests, they note, not only generate little nutrient pollution, but also provide habitat, protect stream health and even reduce air pollution.

If state and local governments protect woodlands that are projected to be developed, it would help them meet their 2025 goals — essentially by preventing some of the pollution increases stemming from growth from ever happening.

Finding a way to use the Bay cleanup effort to incentivize the protection of low-polluting landscapes has long been a goal of some land conservation groups.

“We know the watershed will continue to change over time. If we acknowledge that and hopefully create incentives, then we are planning for the future,” said Mark Bryer, Chesapeake Bay Program director for The Nature Conservancy. “We are acknowledging that the forests of the watershed today are providing benefits, and we don’t want to lose those benefits.”

Indeed, factoring future growth into nutrient reduction goals was one of the main recommendations to come out of a 2013 report, Crediting Conservation, from the Chesapeake Bay Commission, an advisory panel that represents lawmakers from the Bay states.

“If this is going to incentivize local governments to consider putting more land in natural conserved categories to promote water quality,” said Ann Swanson, the commission’s executive director, “then that’s a fantastic opportunity to educate citizens, it’s a fantastic opportunity to promote clean water and healthy fisheries. And, it’s a better destiny.”

A panel of senior state and federal officials will decide in December whether to use the future land use projections when setting revised goals next year.

The issue is being considered as part of the Bay Program’s “midpoint assessment” of progress toward meeting the 2025 cleanup goals under the TMDL. The assessment is also looking at how climate change, the filling of the reservoir at the Conowingo Dam on the Susquehanna River, and other factors will affect efforts to attain Bay water requirements and will revise nutrient reduction goals accordingly.