Low rainfall and warm temperatures in November contributed to record low streamflow into the Chesapeake Bay for the month, according to the U.S. Geological Survey.
Freshwater flows into the Bay averaged 9.3 billion gallons per day during the month, which is 75 percent below the long-term average for November, according to the USGS.
In fact, streamflow was below average in every month of the year except January and April. The result is that 2001 will be the third straight year where flows into the Bay were below the long-term average.
But the record low flow during November carries few serious implications for the Bay, largely because fall is a relatively quiet time for the Bay, biologically.
“In general, the impacts would be more muted than in the warmer season when submerged aquatic vegetation would be growing or activities such as spawning would be going on,” said Rob Magnien, a scientist with the Maryland Department of Natural Resources.
“If this continues for a couple of months, we would start getting into the yellow perch spawning season, and then other anadromous species and there could be implications there in terms of restricted habitats for spawning,” he added. “But right now, I think it’s a little bit too early to say. We still have some time before biological activity begins picking up again in the Bay.”
One problem is that the low flows mean high salinity waters in the Bay, which allows oyster diseases to spread over greater areas. Normally, scientists count on cold winter temperatures to help hold diseases in check, but the combination of warm temperatures and high salinities could spell bad news for oysters.
The low groundwater levels caused by the lack of rain could result in lower-than-normal nutrient loads from the Bay during the spring months. Scott Phillips, who oversees USGS Chesapeake Bay activities, said it will take time for groundwater — which maintains the “base flow” of rivers and streams during dry periods — to return to normal levels.
“If we don’t get much recharge over the winter season, the nutrient load that comes in from the base flow will be lower in the springtime,” Phillips said.
The National Weather Service is offering little insight on the future. Its long-range winter forecast for the Mid-Atlantic region gives equal chances of above normal, normal or below normal temperatures and precipitations.
The recent spate of dry years has been a reversal from the mid-1990s, which saw a series of high flow years into the Bay, causing increased nutrient loads and contributing to the loss of grass beds and reduced dissolved oxygen levels in much of the Chesapeake.
By contrast, in the spring and summer, extreme low flow conditions result in smaller amounts of nutrients and sediment being carried into the Bay, resulting in clearer water, which would help the growth of underwater grasses. Reduced nutrients usually means less algae and therefore improved summertime dissolved oxygen conditions.
At the same time, low flows result in higher salinities in the Bay, which can restrict spawning habitats for migratory fish, encourage oyster diseases and increase the abundance of jellyfish in the summer. And low flows can fail to flush some slow-moving creeks, causing worsening local water conditions.
For information about flows into the Chesapeake, or information about the USGS’ Bay activities, visit its web site at http://chesapeake.usgs.gov/