Potomac River Report Card: Better Clarity, Declining Vegetation


The following is a guest post series by JD Willoughby. JD has worked to protect and restore natural resources for more than 20 years in the Chesapeake Bay. Now located in Anchorage, AK, she continues her work in the natural resources field and enjoys exploring the last frontier.


Woodrow Wilson Bridge, Potomac River | © William F. Yurasko

The development around the Woodrow Wilson Bridge expansion has seen increased wildlife habitat, while the aquatic vegetation has declined | © William F. Yurasko

As I mentioned in a previous post, the Potomac Conservancy has released their annual report card for the Potomac River [PDF], which topped American Rivers’ list of America’s Most Endangered Rivers® of 2012. The Potomac earned a “C” this year, representing an improvement from its “D” grade in 2011. Today I will tell you more about the status of habitat in the Potomac River Basin.

Underwater grasses (also known as submerged aquatic vegetation (SAV)) and forested buffers received grades of “D” and “C,” respectively, on the annual report card. SAV abundance between 2000 and 2012 has fluctuated from 60% down to the current 32% of the threshold goal set by University of Maryland assessment for the Potomac.

Bob Murphy, president and executive director of Ecosystem Solutions, noted that overall SAV abundance has decreased over the last two years, but water quality and clarity have increased. “The SAV data seems to be at odds with water clarity data,” said Murphy. Murphy noted that it is important to look at data specific for each tributary and the main-stem Potomac to understand the discrepancy.

Murphy stated that the plant species found in the freshwater, upper tidal, and lower tidal regions of the Potomac River are all different, but they are often lumped together when measured. “They react differently to different stressors,” Murphy said. There are some sections of the Potomac that have an abundance of SAVs and some that are in decline.

Of particular interest is the impact to river habitats of projects such as the Wilson Bridge expansion on Interstate 495. During construction, only five of the surrounding 39 acres were spared to make way for a barge channel. Generally, SAV abundance is expected to fluctuate from year to year, but populations have not rebounded substantially since the bridge expansion was completed. The area around the Wilson Bridge is heavily developed, but it does support songbirds and even bald eagles in small forested patches.

Impervious surfaces that come with development can be countered to some extent with significant forest buffers. Forested buffers are like sponges for waterways. They help slow runoff, allow contaminants such as excess fertilizer to soak through the soil, and help stabilize the river banks. Their overhanging branches keep water cool, sometimes cool enough to support trout. In addition, the leafy debris makes excellent food and shelter for insect larvae and nymphs that then become food for fish.

The Conservancy noted in the report card that about 40%, or 15,170 acres, of agricultural forest buffers have been planted to reach the Potomac River’s 2025 Watershed Implementation Plan (WIP) goals [PDF]. While the U.S. Department of Agriculture’s Conservation Reserve Program does support and fund these restoration plantings on agricultural land, funding is scarce for reforesting other land.

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