Farmers Question Bay Models

At the Bay Journal, Farmers question whether Chesapeake Bay model reflects reality, as they should. 

Actually, a pretty good, but long article on the use of models in the Chesapeake Bay diet. They are enormously complex, which raises the specter that modelers have modeled their own prejudices in to the mix.

Efforts to understand the Chesapeake ecosystem through models date to the late 1970s, when the U.S. Army Corps of Engineers began designing and building an 8-acre, three-dimensional model of the Bay.

Carved from concrete and filled with water pouring in from simulated rivers, it helped provide an understanding of complex water movements within an estuary where rivers and ocean water mix.

Since then, modeling has become an indispensable part of the Bay cleanup effort. The 8-acre model has long since been replaced by sophisticated computer simulations that drive decisions about how billions of dollars are spent.

The Bay Program relies on four models:An airshed model, which estimates the amount of nitrogen (a nutrient) deposited directly on the Bay and its watershed from air pollution

• A land use model, which predicts the nutrient impact of development, human population and changes in agricultural land use, such as shifts from pasture to crops
• A watershed model, which estimates the amount of nutrients that reach the Bay from all of the activities in its 64,000-square-mile drainage basin
• An estuarine model, which estimates the impact that changes in nutrient inputs will have on Bay water quality

. . .
When the EPA established its Chesapeake Bay total maximum daily load, or “pollution diet,” in 2010, it relied on models to estimate the amount of nutrients (nitrogen and phosphorus) that must be reduced to clear the water and eliminate dead zones.

The modeled answer: The amount of nitrogen reaching the Bay needs to be slashed from 270.8 million pounds a year, measured from a 2009 baseline, to 199.3 million pounds. Phosphorus needs to be cut from 17.17 million pounds to 12.86 million pounds.

The models were then used to divide the needed nutrient reductions among the states and major rivers.

States used the models to write cleanup plans outlining the number of wastewater treatment plants that needed to be upgraded and the amount of nutrient-reducing best management practices, or BMPs, that were needed to meet the goals. In agriculture, BMPs include things like nutrient-absorbing cover crops, stream buffers and no-till farming.

Each year, states report on their actions, and the models use that data to estimate cleanup progress, which is then publicly reported. It is hard, therefore, to overstate the region’s reliance on models to drive cleanup efforts and evaluate results.

“You absolutely need a model to be able to do those things,” said Zach Easton, a Virginia Tech computer modeler who has participated in several reviews of Bay Program models. “But we have put all our eggs in the watershed model basket, and we don’t at this point have a way around that.”

There's an old saying the "all models are wrong, but some are useful." I suspect the jury is still out on whether this one is useful.