Normally, the Bay is very
responsive to impacts that
happen within the year.
Effects of Freshwater Influx
Although this year’s higher-than-normal
influx of freshwater has thrown off the
Bay’s ecosystem, it could also benefit the
Bay in several ways.
In late July, it seemed the rain wouldn’t
stop. Because of the increased volume
of water from the storms, the flood
gates were opened at Conowingo Dam.
Pollution—along with tons of debris—
washed from farm fields and towns in
Pennsylvania and flowed unmitigated
through the dam. Much of the visible
pollution, like trash and tree limbs,
ended up on Maryland’s shorelines.
The July rain was followed by a
second major influx of freshwater in
September—the rainiest in Maryland
since Tropical Storm Lee hit in 2011.
Scientists monitoring the Bay have
warned that the freshwater could reduce
salinity levels enough to potentially
harm oyster populations. Peter Tango,
the Chesapeake Bay Monitoring
Coordinator for the United States
Geological Survey, is continuing to
compile data to better inform scientists
about the effects of the freshwater.
According to Tango, the primary
concerns at this point are the volume of
nutrients and sediment that entered the
Bay and whether pollution-reduction
efforts—such as urban stormwater
infrastructure and streamside forest
buffers—will be able to mitigate the
inflow. “Conditions may not be as bad as
they could be if we are not doing those
sorts of mitigation activities.”
As monitoring continues, there are other
signs that important Bay indicators may
not have been significantly affected.
Brooke Landry, who studies Bay grasses
for Maryland’s Department of Natural
Resources, reported in August that
the large underwater grass field in the
Susquehanna Flats appeared to have
weathered the heavy July rains. Her
photos of the grass bed showed clear
water in the beds.
The freshwater’s effect on the Bay’s
oyster population is not clear. One
positive outcome could be lower disease
rates. Tango notes in his monitoring data
released in October that after Tropical
Storm Lee hit, oyster populations
experienced high mortality in upper
parts of the Bay, but had “excellent Bay-wide survival.” Lower salinity waters
reduce the prevalence of diseases,
according to the National Oceanic and
Atmospheric Administration (NOAA).
In late October, NOAA reported that
excess freshwater may also affect
crab populations. Because male crabs
prefer fresher water and female crabs
are attracted to higher salinity, this
year’s weather may have shifted crab
distribution in the Bay—perhaps sending
male crabs farther north.
What remains unclear about the surge
of freshwater in the Bay is its potential
long-term effects. CBF’s Maryland Senior
Scientist Doug Myers says the biggest
unknown is whether the pollution that
likely flowed into the Bay over the
summer and fall could increase the
Bay’s dead zone next year. And, these
pollutants fuel algal blooms, which
can prevent sunlight from reaching
Tango said effects on the Bay don’t
typically carry over from year to year.
Normally, he said, the Bay is very
responsive to impacts that happen
within the year.
U To learn more about Maryland and
what CBF is doing, visit cbf.org/Maryland.
Spring rains caused severe flooding along the Susquehanna, which in turn sent major
amounts of sediment and pollution down to the Bay.
SAVE THE BAY 23