Prolonged drought brings changes to Chesapeake Bay
Parke Rublee, a Smithsonian research associate at the Maryland Chesapeake Bay Center, was intrigued. There had been an unusual spring surge of carp looking for fresh water in which to spawn. He had never seen them come up so far in this small tributary of the Rhode River near Annapolis.
Moreover, instead of returning to the saltwater of the bay they inexplicably lingered after spawning. When the winter freeze came the fish were stranded in the icy shallows.
This spring, Rublee says, a boat trip up the stream confirmed an unprecedented fish kill. It was an unexpected effect of the prolonged East Coast drought.
Scientists note that the effects of drought concatenate downstream in rivers. Mild winters and dry summers eventually show up in a shortfall of runoff and, finally, as reduced fresh water flow into coastal bays.
In some rivers along the East Coast, the freshwater flows that normally force back and dilute the twice daily tidal intrusions of sea water are at their lowest rates in 50 years. The 36-month rainfall deficit has so reduced flows from Virginia's James and York Rivers that saltwater from the Chesapeake Bay has pushed to points 30 miles upstream, moving 20 of those miles within the last year.
Rublee, observing the increased tidal push, realized it was the high salinity levels upstream which fooled the carp. They remained in the shallow water instead of returning, as they normally would, to the saltier water of the bay.
Sea water at the mouths of these bays contains approximately 19,000 milligrams per liter (mg/l) of chlorides, a measure of its salinity. Concentrations of salinity in excess of 250 mg/l are undesirable in drinking water. Concentrations of greater than only 50 mg/l are unsatisfactory for some industrial uses.
The 16-inch rainfall deficit recorded over the last two years by the Delaware River Basin Commission has resulted in a salinity in the Delaware Bay which is, at some points, double that of years with normal precipitation. This is despite a system of water releases from upstream reservoirs designed to supplement the low stream flow.
The system was put into effect after the drought years 1961 to 1965 had so reduced river flow that the City of Philadelphia was considering moving its water system intake upstream to protect it from saltwater contamination.
The 1965 drought was characterized by the US Geological Survey as ''the most severe drought on record in the Delaware River Basin, exceeding the drought of 1929-32.'' However, in the Chesapeake Basin where there is no reservoir system to maintain stream flows, the March 1981 spring runoff recorded in Virginia's Rivers was 30 percent lower than in the drought year 1931.
As evidenced by the the carp, relatively little change in salinity brings significant changes in the natural life of an estuary.
Migrating Atlantic croaker, which move up the James River, are a valuable commercial fish. Last year, they lingered too long and became contaminated with kepone.
Herbert Austin, a research scientist at the Virginia Institute of Marine Science, has cataloged effects of the present drought upon the life of the bay.
He finds some species make the most of the situation. The blue crab, whose spawning grounds are usually limited to the highly saline mouth of the bay, has moved upstream for what may be the largest spawn of the last 10 years.
The salinity also seems to induce a greater productivity in the bay oyster. Austin points out, however, that too great an increase could threaten the adult oysters with shellfish disease and attack by the snaillike oyster drill which thrives in highly saline water.
On the other hand, ''The shad, the river herring, and the striped bass all look for fresh water. If the fish are forced to spawn in a very small area there will be a great deal of competition for food which could cause a high juvenile mortality rate,'' Austin said. Also, the food chain of the bay may be affected by the lack of the microscopic plants and nutrients.
Austin said that a group which went to study the spring bloom of a plankton species at the mouth of the Susquehanna River found little there to study. It was theorized that a lack of flow from what is the Chesapeake's main source of fresh water caused a lack of proper conditions for the plankton: ''No freshwater flow, no pulse of nutrients, no phytoplankton.''
From that, Austin suggests, one might suspect the shrimp population suffered, as well as the menhaden and anchovy which feed on the plankton. That might also explain the failure of sea trout to migrate in any great numbers into either the Chesapeake or Delaware Bays last spring. The species feeds on the menhaden in the bay.
Fishermen, Austin says, may have to be patient with the fish even more than usual. Species such as weakfish, perch, and striped bass may not be found in their usual haunts. In fact, a spokesman for the Delaware Department of Natural Resources said there is a great deal of pressure from fishermen to explain the lack of both weakfish and flounder in the bay.
''If we find an unexpected result,'' Rublee says, ''the first thing we consider is the drought because it's affected both the flow and salinity. And in the last year things just haven't been the same.
In fact, increase in salinity can alter the very chemistry of the water. Metals present tend to precipitate out farther upstream than usual. This creates a potential for what is known as ''the greening of oysters,'' or the contamination of the shellfish with dissolved copper.
The lack of freshwater flow also prevents the flushing of pollutants from estuaries. Loss of this cleansing action can also reduce the amount of dissolved oxygen in the water. During the 1965 drought there were several fish kills on the Delaware estuary in which fish literally suffocated from the lack of oxygen.
Meanwhile, geologists are concerned with possible intrusion of saltwater into potable water supplies. The prospect of saltwater has greatly increased with development along shorelines. Its occurrence in several northern New Jersey coastal communities a decade ago encouraged other coastal communities to monitor well fields carefully.
A spokesman for the Maryland Geological Survey said that, although there has been no evidence so far of saltwater intrusion into freshwater aquifers along the Chesapeake, the increased development ''is setting up a situation which makes you very concerned.''
The most immediate water problems, he said, will arise in shallow wells close to the bay and on farms which pump water directly from streams for irrigation.
From the arrival of Hurricane Agnes in June, 1972 until 1979, the East Coast recorded the wettest years on record. Chesapeake Bay was nearly flushed clear of saltwater. Oyster beds, clam beds, and crab spawning grounds failed. The present drought, then, presents biologists with some interesting contrasts.
Rublee says: ''We can watch the ecological balance shift and the organisms attempt to adjust. Some will die off, some will thrive, but the environment is handling all of this just fine.''