Bay's dead zone causes sea creatures to struggle
BY LAWRENCE LATANE III
TIMES-DISPATCH STAFF WRITER Oct 4, 2005
A suffocating mix of pollution, hot weather and light winds combined this summer to produce the biggest average dead zone in 20 years of monitoring dissolved oxygen in the Chesapeake Bay.
On average, from June through September, 5.1 percent of the water in the bay's deep channel contained oxygen concentrations of .2 parts per million or less, meaning little or no oxygen was present.
A much bigger portion of the main stem also suffered from low oxygen, a report from the Chesapeake Bay Program showed yesterday. Thirty percent of the bay's deep channel contained less than 5 parts per million of oxygen, which is in the lower limit that striped bass, white perch and American shad can endure.
The bad water was generally found 15 to 20 feet below the surface, and it stretched from the Baltimore-Annapolis area to the mouth of the York River, a distance of about 125 miles.
"It had to be a tough year for striped bass," said Dave Jasinski, a water-quality data analyst for the University of Maryland, who works at the Virginia Institute of Marine Science. "They like dissolved oxygen greater than 5 [parts per million] and temperatures less than [77 degrees]. Where are they going to find that in the bay's deeper waters? That leads to a striped bass habitat squeeze."
Heavy rainfall this spring led scientists to predict poor oxygen conditions in the bay's deepest waters this year because runoff flushes oxygen-depleting sewage, fertilizers and animal wastes from the land into streams and rivers that feed the estuary.
"But, we couldn't foresee that we'd have an extremely hot summer and, more importantly, have the lowest mean wind speeds" recorded since the mid-1980s, Jasinski added.
That made conditions worse. Little or no wind exacerbated the natural stratification of bay waters between dense, salty ocean water on the bottom and lighter, fresh water on top, he said. High water temperatures stimulated bacteria that deplete dissolved oxygen in deep water.
"The more you heat it up, they more they consume," Jasinski said.
The dead zone reached its peak in early August when 10 percent of the main stem was found to be anoxic. By late last month, only 3 percent of the deep channel was still categorized as anoxic.
Some bay creatures can survive in waters with less dissolved oxygen. Blue crabs, for example, can endure 3 parts oxygen per million, and marine worms can survive with as little as 1 part per million.
The bay program, which coordinates a regional bay cleanup, monitors oxygen in the bay's main stem as a sort of barometer on the estuary's health.
Virginia, Maryland, Pennsylvania and the federal government have been working for 20 years to improve sewage treatment and promote farming practices that reduce the amount of nutrients reaching the bay. They have billions of dollars worth of work to do before reaching their goal.
The Chesapeake Bay Foundation environmental group said the dead-zone findings "should be a wake-up call" for Virginia, where more than $2 billion worth of improvements have been identified to reduce the nutrient flow. A legislative committee is studying ways to finance the cleanup.
"We know we need to upgrade sewage-treatment plants and farming practices," said Ann Jennings, the bay foundation's Virginia executive director. "The last piece of the puzzle is finding the funds to do that."