The bad news first: You may have read about the bull shark recently found in the Potomac River. Goverment pundits, I'm sure, made some wisecracks about sharks always being alive near the White House. But seriously, bull sharks (especially 8-foot ones) are not common sights in the Potomac.
Now for the good news: There's been a ten-fold increase in seagrasses (otherwise known as "submerged aquatic vegetation" or SAV) in the Potomac according to measurements taken during 18 years of surveys. That means a good chance that the Potomac's water quality has also improved. That's good news for the Chesapeake Bay as well. The surveys (by the U.S. Geological Survey (USGC) and England's National Oceanography Centre) included a 50-mile reach of the tidal Potomac downstream from Washington.
So SAV restoration efforts and upgrades to wastewater treatment plants are paying off. That's especially good news since these efforts are labor-intensive and costly. The Chesapeake Bay Foundation's annual report card for the Chesapeake have not been especially positive in recent years.
Virginia has invested big bucks in improving out-dated wastewater treatment plants. Maryland is playing catchup, and Pennsylvania still needs to do more with agricultural and poultry farm runoff (yuck). Dairy cows standing in creeks chewing their cud may look pastoral, but think about the other end of those critters. Humans need nutrients, but our watershed does not. They stimulate algae blooms that block sunlight from reaching SAV. Then the SAV dies back and the sealife critters have nowhere to hide. Catfish can then find the baby crabs, and so on.
Key Findings on the Potomac River's SAV:
• Native SAV cover increased tenfold from 288 to 3081 acres.
• The overall area covered by SAV in the Potomac more than doubled since 1990, increasing from 4207 to 8441 acres.
• The diversity of SAV has increased. In 1990 the exotic hydrilla was 10 times more abundant than any other species. In 2007 the abundance of the 7 most frequently occurring species are more evenly matched.
• In 1990, more than 80% of the total SAV was hydrilla; in 2007 hydrilla declined to 20%.
• Results suggest declining fitness of exotic species relative to native species during restoration.