A potentially harmful algae bloom popped up in the Potomac River in February, prompting state officials to temporarily close oyster harvests in the lower part of the river and its tributaries.

The reason behind the bloom, scientists say, is the drought that has lingered over the area: Rainfall has been so scarce that the freshwater flows into the Chesapeake last year were the lowest since 1941, according to the U.S. Geological Survey.

The lack of freshwater has sent salinity levels soaring to record-high levels in parts of the Bay and its tributaries. Which is why a bloom of Dinophysis acuminata — a marine algae species — turned up in the Potomac.

³It’s a very rare organism to be seen this far up in the Bay,” said Richard Lacouture, of the Academy of Natural Sciences’ Estuarine Research Center. “I think it’s largely the result of the high salinities we’re seeing.”

Salinities in that part of the Potomac were running at almost 19 parts per thousand — a record. Normally, they are less than 11 in February.

Officials closed shellfish grounds to below the Route 301 bridge to harvesting because people who eat shellfish that had consumed the algae could get diarrhetic shellfish poisoning which, though not fatal, causes gastrointestinal illness and vomiting.

The bloom was only the latest side effect of what has become the region’s longest-running dry period since the 1960s, when rivers in the region ran at below-normal levels for seven out of eight years, including four in a row from 1963 to 1966, according to USGS figures.

River flows in the region have been below normal for the past three years, and 2002 has started out dry as well: The USGS reported that river flows into the Bay were the second lowest on record in January, running 87 percent below average.

That is likely to be true much of this year as well.

Groundwater, which typically provides more than half the water to streams, is also at or near record lows in much of the Chesapeake basin. Groundwater is critical to the region’s rivers and streams because it is what maintains a “base flow” in waterways between periods of rain. As groundwater levels fall, so will the base flow.

And the opportunity for groundwater to recharge is rapidly vanishing: Once trees leaf out and plants start blooming beginning in late March, they will absorb almost all of the rainfall that soaks into the ground.

“I think we have a narrow window where we have to have rainfall in order to avoid a serious problem this summer,” said James Gerhart of the USGS. “And that window would probably be now. If it comes while we’re in the heart of the growing season, and everything has leafed out, it probably won’t have much of an impact.”

Some low-flow impacts in the Bay are predictable. Fish in some habitats, and small waterways, will feel squeezed. Oysters will face greater disease pressure. And, certainly, high salinities mean more jellyfish in more parts of the Bay.

But like the Potomac bloom, much is unpredictable. “If we continue to have no rainfall, it will be interesting to see what happens,” Lacouture said.

Ironically, during the unusually wet years of the mid-1990s, many hoped for drier conditions.

Wet years are normally considered bad for the Bay because heavy rain drives large amounts of nutrients off the land and, ultimately, into the Chesapeake, where they spur algae blooms. When algae die and sink, they decompose in a process that depletes deep areas of oxygen.

High flows magnify the problem because freshwater flowing into the Bay does not easily mix with the heavier saltwater on the bottom. As a result, depleted oxygen in deep areas is not replenished with oxygen from the surface.

With the drier conditions in recent years, Bay oxygen conditions have improved somewhat: Levels have bounced back from 1998, which had the largest expanse of oxygen-depleted water ever seen in the Chesapeake.

But the drought also has its drawbacks for the Bay and its tributaries. The low flows often haven’t made problems go away — they just moved.

“Typically, when you have low-flow periods, there is reduced flushing through the river systems, so there is a tendency to have phytoplankton remain within those rivers,” said Harold Marshall, a phytoplankton expert at Old Dominion University.

Instead of being pushed into the Bay, the slow flows give the algae time to absorb more nutrients and burst into blooms while still in the rivers. That can be good news for the Bay because more nutrients are used before the water pours in. But in some slower moving tidal tributaries, that has actually meant worse water quality.

“We actually saw some of the higher algal bloom levels up in these creeks under drought conditions,” said Robert Magnien, director of the Maryland Department of Natural Resources’ tidewater ecosystems division.

“That often crashes the dissolved oxygen levels, resulting in fish kills in the upper tributaries and creeks.”

Ironically, one of the problems in the creeks is that reduced rainfall temporarily improves water quality in some places by washing less dirt off the land. That allows for clearer water, and more light penetration. That, in turn, can spur the growth of phytoplankton — which, like all plants, need sunlight to survive — in areas too murky to support algae in other years.

Despite reduced runoff, nutrient levels are still so high in many places that there are plenty to fuel blooms. “It’s actually improved the conditions for a phytoplankton bloom,” Magnien said.

That problem is not confined to tidal areas. Dry conditions throughout the Bay’s watershed can result in increased algae and reduced water quality in rivers and streams.

Last summer, the effects were obvious near Harrisburg, PA, where the waters of the nutrient-laden Conodoguinet Creek entered the Susquehanna River, which was running lower, and slower than normal.

“That side of the river was very green, obviously there was a lot of algae growing,” said David Heicher, of the Susquehanna River Basin Commission. “I’m sure there were other places like that in the basin.”

Heicher wrote a report several years ago documenting the impacts of low stream flows in the basin. During a tour of the watershed, he found streams at such low levels that riparian wetlands and forest buffers were actually physically disconnected from the waterways, preventing movement back and forth by aquatic creatures.

Low stream levels can greatly reduce habitat available for fish and other stream dwellers, and that habitat is often of poorer quality: As streams withdraw toward the middle of their beds, species can’t use areas near the banks which are often cool, shaded and offer more diverse habitat.

The result is that predators and prey are pushed closer together, and some fish populations can suffer, taking years to recover, according to Heicher’s report.

The smaller, shallower areas that remain are often warmer, and warmer water contains less dissolved oxygen than cool water. And, of course, the slower, warmer water is also more prone to algae blooms. Also, in some areas, it’s even worse — streams can dry up altogether, especially if there is heavy water use nearby.

If there is an industrial or wastewater plant outfall, water quality can be impacted because there is less dilution.
Effects of the drought on some streams will soon be evident to many anglers: Management agencies are already planning to curtail trout stocking in some streams around the watershed this spring because water levels are too low to support the fish.

Freshwater species on the fringes of the Bay, such as yellow perch, will feel squeezed as well. As the salinity works its way up the tributaries, they will have to retreat upstream.

That can be a problem in small tidal drainages, such as some on Maryland’s Western Shore, where there is little area for the fish to retreat. Even if the fish can escape, their offspring may not. “The adults may be able to seek optimal salinities, however the eggs and the larvae may be washed into areas of higher salinity that may be past the bounds of their requirements,” said Harley Speir, a DNR fisheries biologist.

Among the fish that may be pressed are the young produced by American and hickory shad, whose greatly reduced populations had been on the rise in recent years. The compressed habitat areas could result in increased competition for food, increased predation and even cannibalism within some species, Speir said.

There are trade-offs. Saltwater fish will work their way farther up the Bay, which may be good news for anglers, and crabs would go further up tributaries as well. “People are quite happy with that,” Speir noted.
Few species have suffered more in the drought than oysters. The two diseases that have devastated native oyster populations, MSX and Dermo, thrive in high salinities.

The reduced flows have allowed the diseases to move farther up the Bay and its tributaries, infecting oyster beds in areas usually safe from disease. In Maryland this year, 93 percent of the oyster beds were infected — the highest rate ever seen.

As a result, recent surveys suggest that the Bay’s oyster population has fallen below the previous low of 1994, the baseline for measuring the Chesapeake 2000 agreement’s goal of achieving a tenfold oyster increase by 2010. Put another way, a greater than tenfold increase is now needed to meet the commitment.

This winter has compounded the situation. Not only has there been a lack of water to push diseases back down the Bay, but it has also been usually warm, which also favors the diseases.

“A warm winter is terrible [when it comes to] Dermo, and probably MSX too,” said Steve Jordan, a DNR biologist. “We’re in a worst case scenario right now for disease and mortality. That’s for sure.”
But, Jordan noted the Maryland population had bounced back somewhat since 1994, and could again. “There is a lot of resilience out there. I’m not as gloomy as some people are.”

The story was mixed for submerged aquatic vegetation, one of the Bay’s most important habitats.
Although the final figures for 2001 are not yet available, grass beds in some areas benefited from the low flows as low turbidity from sediment, as well as reduced blooms in some areas, resulted in clearer water. “We got huge increases in SAV in a number of areas in the upper Bay,” said Mike Naylor, of the DNR.

But not all of the news was good. “As you get farther down the Bay, you get into a problem where salinities get too high and you end up with a loss of freshwater species,” Naylor added.

According to the National Weather Service, the unusually dry winter was caused by an unrelenting circulation pattern that prevented moist air from the Gulf from reaching the East Coast.

Normally, rainfall begins increasing in October after the dry summer months.

Instead, precipitation in the entire southern half of the watershed has been below normal for the past year, ranging from 15 inches drier than normal near Charlottesville, VA, to a more than a foot below normal in Lancaster County, PA, and Baltimore County, MD. Maryland’s portion of the Eastern Shore remained comparatively moist, with some places only an inch below normal.

Various levels of drought alerts exist throughout much of the watershed.

“At this time of the year, when the water is supposed to be going up, especially as far as groundwater goes, 11 of our 19 wells that we monitor in the basin are lower than they were in December,” said George Lazorchick, a hydraulic engineer with the SusPuehanna River Basin Commission. “It’s not shaping up to be a water-rich 2002.”

USGS scientists say several months of higher-than-normal rainfall will only begin to reverse the low groundwater levels that have developed over the past three years. “A normal amount of rain or snow in the next month or two is not going to alleviate the drought conditions,” said Scott Phillips, who oversees the USGS’ Bay efforts.

Scientists have observed the beginning of a new El Nino in the Pacific. In this region, recent El Ninos have been associated with wetter conditions in the following winter, but scientists caution that impacts are unpredictable, depending both on the strength of El Nino and other regional weather patterns.

Continued low flows will likely mean more high salinity records in the Bay. For a system as complex as the Chesapeake, this mean the future will be as unpredictable as the emergence of the Potomac bloom.

“It’s a fascinating system,” said the ODU’s Marshall. “It changes. That’s what makes it exciting. It’s never stereotyped.”

One thing is predictable. Speir said said that dry years are notable for the strange fish sightings people report: electric toads, spade fish, sharks, inshore lizard fish and more. “We get dozens of calls every summer about odd species,” he said. “And the saltier the summer, the farther up the Bay we get the calls, and more frequent.”