Phosphorus Water Pollution Remains A Potential Challenge Under Chesapeake Bay TMDL

A June 15 Baltimore Sun B’More Green article reported that while progress is being made in reducing pollution in the Chesapeake Bay watershed and its tributaries, phosphorus levels in many rivers have either remained constant or risen over the past decade.  Phosphorus is one of two key pollutants (the other is nitrogen) that are targeted by the Chesapeake Bay Total Maximum Daily Load (TMDL) and contributes to algae blooms and oxygen “dead zones” in the Bay.  Phosphorus can be generated by agricultural practices, waste water treatment plants, and stormwater runoff.  Septic systems generate nitrogen pollution but not phosphorus pollution.  From the article:

Phosphorus levels in the rivers that feed into the bay are still mostly below where they were three decades ago, when the bay restoration effort formally began, officials say. But in the past decade, phosphorus levels have remained unchanged in nearly two-thirds of the rivers and streams routinely monitored by the U.S. Geological Survey, while pollution worsened in 16 percent. Just 21 percent of those waters monitored recorded declines in phosphorus in recent years.  …

“Phosphorus pollution absolutely has to be on our radar screen,” said Ann P. Swanson, executive director of the Chesapeake Bay Commission, which represents state lawmakers from Maryland, Pennsylvania and Virginia. “The progress that we made in the last 25 years is being eclipsed by increases in the last 10, so we’re losing ground.”  …

The article examined recent State efforts to address agricultural phosphorus runoff and soil buildup due to the spreading of poultry litter and sewage sludge.  The article noted that the challenge is particularly high on the Delmarva peninsula and lower Eastern Shore.

The problem is two-fold, experts say. Farmers generally don’t till their fields in an effort to prevent soil erosion, so the manure is spread on the surface, where it’s more likely to wash off in a rain.

Second, because corn, soybeans and other crops need more nitrogen, the phosphorus from the fertilizer builds up in the ground. After repeated annual applications, phosphorus can become so concentrated that it no longer binds to the soil and dissolves in rainfall runoff or shallow ground water, eventually reaching streams and rivers.

The article also reported that scientific reviews of Montgomery and Fairfax County’s stormwater pollution measures are ongoing but that research is indicating stream erosion may play a larger role in urban phosphorus pollution than previously thought.

“Historically, we thought the lion’s share of phosphorus is washing off the landscape,” said William P. Stack, deputy director of the Center for Watershed Protection. “What we’ve found is a large percentage of the phosphorus — as much as 50 percent — is actually originating from stream-bank sediments.”

Stack said that could mean efforts to control runoff are misdirected.

“If we’re really going to put a dent in phosphorus, we really have to look at stream restoration practices,” he said.

The article noted that despite the challenges posed by phosphorus, the Maryland Department of the Environment believes the State is still on track to meet its 2017 TMDL phosphorus goal.