What's new with . . .
Extremes in Freshwater Flow Affect Bay
Water quality in 1999 was strongly influenced by the
weather and, as in most years, the weather was not "normal."
The most extreme weather lasted from the beginning of the
year through mid-August as a severe drought persisted across
most of the watershed. As a result, the cumulative freshwater
flow from Bay tributaries was below normal from January
through August and set new record lows in May and June.
The year would not end dry, however. Remnants of hurri-
canes Dennis and Floyd hit the Bay watershed in late August
and mid-September, respectively. In some areas, especially
close to the Bay, up to 15 inches of rain fell. In the wake of
Floyd, some rivers, such as the Choptank, neared record flows.
These rains were very helpful in relieving the drought condi-
tion. Cumulative flows to the Bay for September and October
actually exceeded historical averages during these months
when flows typically reach the annual minimum.
Freshwater Flow to the Bay
Drought Affects Salinity Levels Baywide
The drought caused significant seasonal shifts in the salinity
of the Chesapeake Bay. Lower freshwater flow permitted saltwa-
ter from the ocean to move farther north into the Bay and its
tributaries. During June and July, the low-salinity region at the
north end of the Bay was 49% smaller than average for that time
of year. The mid-salinity region was 27% smaller, and the high-
salinity region near the mouth of the Bay was 38%> larger. In
many rivers, such as the Rappahannock, salinity moved farther
up river than in any year since regular monitoring began in 1985.
Salinity is important because it defines habitat for many
plants and animals. Creatures that survive in low-salinity water,
such as yellow perch and largemouth bass and Bay grasses
such as wild celery and sago pondweed, had less habitat in the
summer of 1999. On the other hand, creatures that need high-
salinity water for survival, such as hard clams and blue crab
larvae and the Bay grass species widgeon grass and eel grass,
had more habitat area. The stinging sea
nettle, which requires high salinity, was
more abundant than usual in the early
summer. Oysters suffered this year
because of a greater incidence of the dis-
eases Dermo and MSX, which are
favored in high salinity years.
Low Oxygen Leads
to Fish Kills
U!» » s-" *t I r f •

/ A VT:R A Gfe
. - v»v ' : V
y	A	M
Probably the most severe and obvious
effect of the drought was the prevalence
of summer fish kills due to low oxygen
conditions in creeks, often in combina-
tion with elevated water temperatures.
The low flow conditions reduced flush-
ing in the upper parts of many Bay tribu-
taries, allowing algae to proliferate in
these shallow, nutrient-enriched environ-
ments. Normal flows would have flushed
nutrients and algae farther downstream
where blooms may not have grown as
large or caused the same degree of oxy-
gen depletion. As these algal blooms

decomposed, or consumed oxygen during the night, oxygen
concentrations dropped to lethal levels in several areas, such as
creeks draining to Baltimore Harbor, the Magothy River and the
Pocomoke River. Higher salinity levels added to the problem by
forcing many of the freshwater species, such as yellow perch,
up into creeks in search of suitable, low-salinity habitats. Unfor-
tunately, these small remaining low-salinity habitats were the
same ones experiencing the loss of oxygen and higher water
Low Flow May Help Bay Grasses
in Some Areas
Preliminary data from the 1999 underwater Bay grasses
survey indicate that Bay grass acreage in some areas expanded
and that these improvements may have been related to the low
freshwater flow this year. Low freshwater flow and precipitation
meant that lesser amounts of sediments and nutrients were
washed into the Bay from land-based and atmospheric sources
in 1999. Both of these pollutants reduce the amount of light
available for Bay grasses to grow. One of the areas that has
shown an improvement is Tangier Sound, which has experi-
enced marked declines in recent years.
Potomac River Improves
The give and take of biological communities living at the
boundary between freshwater and saltwater was evident in
the tidal Potomac River during the 1999 summer drought. As
record low river flows in May, June, July and August allowed
saltier water to move upriver, freshwater organisms were
contained in smaller areas of the river while traditional salt-
water species—such as blue crab, bluefish, speckled trout
and flounder— roamed farther upriver. Drought conditions
benefitted some species and hurt others.
Underwater Bay grass beds in parts of the Potomac
expanded their coverage and increased their diversity in
response to the abundant sunlight, low flows and good water
clarity in parts of the river. These same conditions also spur
the growth of large algal blooms. A brilliant bluegreen
(cyanobacteria) algal bloom formed below the District of
Columbia in July and August, and a red tide (dinoflagellate)
bloom developed in the middle of the river. Watermen have
reported heavy oyster mortality in the lower Potomac. The
prolonged drought could have intensified Dermo disease and
possibly caused an outbreak of MSX disease in this area.
Dermo and MSX are caused by oyster parasites that are not
harmful to humans. Offspring of the recovering American
shad population, which needs low salinity nursery grounds,
did poorly in the Potomac. In contrast, numbers of juvenile
striped bass were above their long-term average, possibly
because striped bass adults are now so abundant.
One of the major questions concerning the Potomac is
how have nutrient reductions in the past three decades
improved habitat in the tidal portion of this river? A group of
scientists and managers believes they have—up to a point.
In a recent report, a team of state, federal and university
analysts evaluated long-term Potomac monitoring data and
found signs of recovery.
•	Summer dissolved oxygen near the District of Columbia
no longer drops below five milligrams per liter, the mini-
mum concentration considered acceptable for aquatic life.
The exception to this is in slow-flowing, heavily enriched
tributaries, such as the Anacostia River.
•	Ammonium, a form of nitrogen abundant in poorly treated
sewage, rarely reaches concentrations stressful to animals.
•	Underwater Bay grasses are returning and continue to thrive
despite less-than-ideal water clarity in the tidal portion.
•	The diversity of plankton and bottom-dwelling species is
increasing in the middle, or low-salinity, portion of the
tidal river.
•	Algal blooms do not have the intensity, or the magnitude,
they once had in the 1970s and 1980s, chiefly because
concentrations of phosphorus have been reduced 24% to
95% along the length of the tidal river since 1965.
•	Recently implemented Biological Nutrient Removal
(BNR) at the Blue Plains Sewage Treatment Plant is
expected to reduce nitrogen, the other overabundant nutri-
ent, and further improve water quality.
These signs of improvement are somewhat offset by the rec-
ognition that further efforts are needed to restore a vigorous
Potomac ecosystem. Those efforts must include reducing sedi-
ments suspended in the water, reducing toxics and restoring and
protecting healthy oyster, fish and wildlife populations. How-
ever, the Potomac is continuing on the path toward recovery.
For more information on water quality, go to f
www.chesapeakebay.net/wquality.htm ...-'i *7*"
on the Bay Program website.