Chesapeake Bay water quality this summer fared the way scientists had expected it to: It was poor.
In early August, about 41 percent of the mainstem of the Chesapeake was suffering from low-oxygen conditions, and almost 10 percent had virtually no oxygen at all—creating a true biological “dead zone.”
In July, about a third of the Bay suffered from low oxygen, or “hypoxic,” conditions and a bit more than 3 percent was “anoxic”—having none at all.
“Things did rocket up,” said Dave Jasinski, a University of Maryland Center for Environmental Science analyst.
Earlier this year, scientists—making their first ever “ecological forecast” for summertime water quality conditions—had predicted that this could be the fourth worst year for dissolved oxygen since Baywide monitoring began two decades ago. They also made predictions for harmful algae blooms on the Potomac and for Bay grasses.
Scientists had predicted the anoxic area of the Bay would cover 1.7 cubic kilometers of the deepest water in the Upper and Mid Bay, or about 3.4 percent of the mainstem Bay. But that was an average over the entire summer. Although much more of the Chesapeake was anoxic in early August, Jasinski said he expected the summer-long average would turn out close to the prediction.
That’s because he expected conditions to begin improving in late August and early September. Much of the summer’s poor water quality is driven by nutrients carried into the Bay by high runoff levels in late winter and early spring. Those nutrients fuel algae blooms. When the algae die, they sink to the bottom and are decomposed in a process that removes oxygen from the water.
But that springtime supply of nutrients was not replenished during the drier summer months, Jaskinski said. He noted that 1998 had similar precipitation patterns as this year—and similar oxygen conditions—but that anoxic conditions largely vanished by late August when nutrients were used up.
“Past experience would lead me to believe that we are going to see the same thing,” he said. “This is going to run out of fuel.”
The scientists did not make a prediction for the total amount of hypoxic water in the Bay because it is affected by more factors than anoxic water. But the figures showed that this summer would likely be one of the worst years for hypoxia as well.
Also, the prediction only covered anoxia in the mainstem of the Bay—which does not include tidal rivers. But monitoring by state agencies and others showed that many tidal rivers were suffering from low-oxygen conditions as well.
Chuck Epes, of the Chesapeake Bay Foundation’s Virginia office, said that during late July sampling on the Rappahannock River near the mouth of Urbanna Creek, CBF scientists detected almost zero oxygen in water as shallow as 6 to 8 feet.
“We chatted with a waterman who was pulling up crab pots, and he was finding a couple of dead crabs in each pot that were coming up dead from lack of oxygen,” Epes said.
Sampling on other rivers, including parts of the Elizabeth, James and Piankatank, also found low-oxygen conditions.
Not everything came out as poorly as predicted, though. Scientists had predicted a bloom of Microcystis, a type of harmful algae, to cover more than 10 miles of the Potomac River between Maryland Point and Indian Head. In mid-July, monitoring found Microcystis present over a 10-mile area, but it was far below bloom densities.
In early August, the algae had moved upriver between Tougue Creek and Possom Point, but still had not reached bloom densities, said Peter Tango, chief of Quantitative Ecological Assessment for the Maryland Department of Natural Resources.
Tango said it was unclear why Microcystis had not blossomed into the full-fledged bloom that was predicted. “In some ways,” he added, “I’m perfectly happy if the prediction doesn’t totally come to fruition.”
The amount of underwater grasses in the Bay, a third part of the forecast, remained unclear. The prediction had called for increased grass coverage in the Bay’s low-salinity waters, similar acreage in medium-salinity areas and a small increase in high-salinity waters.
Through July, aerial surveys suggested that high-salinity areas would have about the same amount of grasses as in 2004. Surveys had not been completed in medium and low-salinity areas, but anecdotal reports suggested that grasses were doing very well in low-salinity areas this summer.
The Bay Program launched its first ecological forecast this spring to help educate the public. Officials had hoped the forecast would alert people to the factors that lead to different water quality conditions, and spur interest in tracking developments during the summer.
The Bay forecast is also intended to challenge scientists to better understand Chesapeake conditions to improve future forecasts.
In the future, officials say an expanded system of forecasts might be useful for planning where activities such as underwater grass plantings—which require good water clarity—should take place, and which areas should be avoided.
For information, and to keep track of field observations made by scientists this summer, visit the Bay Program’s Ecological Forecasting web page, http://www.chesapeakebay.net/bayforecast.htm