The Chesapeake region may be further away from meeting its 2025 Bay cleanup goals than previously estimated.

The state-federal Bay Program recently presented a series of data revisions to states which, when incorporated into its computer models, suggests that the region has made significantly less progress in reducing nutrient pollution than earlier numbers indicated. The nutrients nitrogen and phosphorus are the main sources of the Bay’s water quality woes, triggering algae blooms and oxygen-starved “dead zones.”

The Chesapeake Bay TMDL, often called the “pollution diet,” sets the maximum amount of various pollutants that states and major rivers can send to the Bay and still meet water quality standards. Credit: Dave Harp / Bay Journal Media

The finding makes attainment of the region’s 2025 cleanup goals, already behind schedule, even more difficult.

The changes, part of a model update submitted to states for review in February, increase the estimated amount of nitrogen reaching the Bay by 6.2 million pounds a year and phosphorus by 600,000 pounds.

That is more than a fifth of the estimated nutrient reductions the region has made since cleanup goals were set in 2010.

Most of the change stemmed from a recent discovery that a large amount of fertilizer data had been accidentally excluded from information fed into the model, causing it to underestimate the number of nutrients being applied to the land. Most of the other changes resulted from incorporating more recent information about farm animals and crops.

Because the data revisions mostly affect agriculture, the changes largely offset the amount of model-estimated progress made in reducing nutrient runoff from farmland in Maryland, Pennsylvania, Virginia, and Delaware. 

The Bay Program has made data adjustments in the past that also have reduced progress estimates. But the new changes, both because of their magnitude and the closeness to its 2025 cleanup deadline, are especially problematic.

The revisions mean the region would need to reduce nitrogen by almost 10 million pounds a year from 2021–25 to reach the goal, compared to an average rate of approximately 2 million pounds a year during the past decade. That’s nearly a five-fold increase.

Even more problematic, the region is counting on making 80% of the reductions from agricultural lands, the largest single source of nutrients to the Bay. But nutrient reductions from agriculture, along with those from urban stormwater runoff, have been especially difficult to achieve.

Most reductions to date have come from wastewater treatment plant upgrades, but little of that work remains to be done.

The computer models, approved by the Bay Program partnership, use a vast amount of data about land use, farms, discharges from wastewater treatment plants, impacts from air pollution, and other factors to estimate the amount of water-fouling nutrients that reach the Bay.

The models also use state-generated information about pollution control actions taken each year, such as wastewater treatment plant upgrades, stream buffer plantings, and the use of cover crops to calculate reductions to those estimated nutrient “loads.”

The U.S. Environmental Protection Agency uses those annual estimates to evaluate state performance toward meeting the region’s 2025 Bay cleanup goals. The new data were not available in time to affect the most recent official report, released last year, which was based on 2020 data.

Still, whether the models fully represent what is happening on the land is a matter of debate. Water quality monitoring does not always align with modeled nutrient trends. And states have long contended that the complex system used to account for and track agricultural pollution control practices results in undercounts of computer-estimated progress. Changes to that system are being considered.

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