Chesapeake Bay 2006 Weather Extremes Lead to Typical Conditions

This newsletter describes the summer ecological conditions in Chesapeake Bay, focusing on the forecasts that Chesapeake Bay
Program scientists determined in May 2006. With oscillating periods of low and high flow, the annual freshwater flow to the Bay
averaged out to normal. How did this affect dissolved oxygen in the mainstem, harmful algal blooms in the Potomac River and
aquatic grass in the upper, mid and lower Bay?
OSCILLATING PERIODS OF DRY AND WET CONDITIONS
T3
C
O
500,000
400,000
Flow from Susquehanna River
300,000
200,000
100,000
¦ 2006 water year daily mean flow
Average mean daily flow
(37 year dataset)
June rain
event
¦WWyAVj
Hui
Remnants
from
urricane
Ernesto
Brown marshes in Blackwater NWR reflect
the dry spring conditions.
Although the total annual
freshwater flow to Chesapeake
Bay was near normal in 2006,
a dry spring and wet summer
characterized this past year (Figure
1). While flow is typically high in
the spring and tapers off through
summer, 2006 was characterized
by an unusually dry spring ending
with a late June rain event that led
to a rapid increase in river flow and
nutrient and sediment loads. A
second wet period occurred in late
August as a result of the remnants
from Hurricane Ernesto.
The oscillating summer
conditions led to record low
and high nutrient and sediment
loads to the Bay during different
months. The United States
Geological Survey monitors flow
and nutrient and loads from nine
non-tidal tributaries (Susquehanna,
Patuxent,Potomac, Rappahannock,
Mattaponi, Pamunkey, James,
Appomattox, and Choptank
Rivers), which drain 78% of the
Bay's watershed.
800,000n
0®c V » V V O*
Loads from nine tributaries
NITROGEN
~ 2006 water year mean monthly loads
¦ 1990-2006 mean monthly loads
500,000
400,000
200,000
c
T3
m
O
PHOSPHORUS
50
¥40i
~o
bD
30
• 20
-a
aj
O
10-
0
SEDIMENTS
n-rfl n
JUL
. l~l , r~I ,
o
Figure J: Stream flow from the Susquehanna River and loads from nine tributaries for the 2006 water year (October through
September). Yellow shades represent 2005/2006. Data are from U.S. Geological Survey, provisional and subject to revision.

&
,Z*?s
Sediment rushes into a local waterway
after June rains hit the Bay area.
NITROGEN
• Loads were much lower than normal*
in March, April and May.
• March loads were lowest on record.
• July loads were highest on record.
("-normal conditions are the range between the
25and 75s' percentile.)
PHOSPHORUS
• Loads were lower than normal* in
March, April, May and August.
• Loads in March and May were
lowest on record.
• Phosphorus loads are strongly
dependent upon sediment loads.
SEDIMENT
• Loads were lower than normal* in
March, April and May.
• March loads were lowest on record.
• July loads were the second highest on
record.
Produced by the Chesapeake Bay Program's Monitoring and Analysis Subcommittee
30,000-
20,000-
10,000

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SPRING CONDITIONS LEAD TO BELOW AVERAGE ANOXIA
The volume of anoxic (dissolved oxygen < 0.2 mg L"1), or
oxygen-deprived, water during the 2006 summer was better
than average, but still worse than the long-term goal of zero
anoxia. In June, Chesapeake Bay Program scientists predicted
that the average summer anoxic volume in the mainstem
would be 1.08 km3. This forecast was based on the quantity
of nutrients that entered the Bay during the preceding five
months. The anoxic volume duringjune and early July was
well below average, then increased at the end of July, reaching
the long term average for that time of year (Figure 2). Anoxic
volume then decreased until it reached zero during September.
The observed average anoxic volume for the summer was 0.93
km3 or slightly less than the forecasted volume (Figure 3).
(anoxia)
1 2006 Anoxic volume
1 Average anoxic volume
(1985-2005)
No anoxia in
Septem ber
xv ^
Figure 2:2006 bimonthly average anoxic volumes compared to the total bimonthly
average from 1985-2005. By September, no anoxic water could be detected in the
mainstem.
The small anoxic volume at the beginning of July may have
been due to the record flows the Bay experienced at the end
of June. During this time of year there is a boundary, called
the pycnocline, between fresher surface water and saltier
deep waters. This boundary cuts off the supply of oxygenated
water to the deeper waters of the Bay. The large volume of
freshwater from the late June flow apparently pushed the
pycnocline deeper than normal, thereby reducing the volume
of deep waters that could become anoxic.
Figure 4: Map of average dissolved oxygen in the mainstem for summer 2006.
Although the forecast focuses on mainstem anoxia,
dissolved oxygen (DO) is also measured in the shallow regions
of the Bay and its tributaries. Shallow water DO follows a
similar pattern to the mainstem in that most low DO events
occur in the warm summer months (Figure 5). However,
shallow water DO tends to be more dynamic than in the
mainstem, with anoxic events occurring on a daily rather
than monthly time scale (one cause of shallow water anoxia is
discussed on the following page). The minimum DO threshold
for shallow waters has been set at 3.2 mg L1, an amount
needed by the living resources that inhabit shallow water.
Forecast
Observed
Average
¦75 * 1.5
y 1.0
« 0.5
— Dissolved oxygen criteria for living resources

Year
Figure 3: Average annual anoxic volume with 2005 and 2006 forecasted volumes.
Figure 5: Dissolved oxygen at Piney Point, Maryland, on the Potomac River's
northern shore. Data from Maryland Department of Natural Resources.
Area that
experienced
anoxia in 2006
Dissolved oxygen
(mg/l)
| 0.0 - 0.2
I 0.3 - 1
| 1.01
2.01
3.01 -4
4.01 - 5
5.01 -6
| 6.01 - 7
| 7.01 -8
| 8.01 -9
| 9.01- 12

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SHALLOW WATER HABITAT AFFECTED BY DEEP WATER AHOXIA
A combination of harmful algal blooms and low dissolved
oxygen (DO) led to fish kills in several Chesapeake Bay
tributaries this summer. In the Potomac River, more than
8,000 fish, including spot, shad, striped bass, yellow perch and
cownose rays died due to a combination of low DO and fish
toxins released by a bloom of the harmful algae Karloclinium
veneficum (Figure 6). While elevated nutrient levels are likely
responsible for causing the harmful algal bloom and ultimately
the low dissolved oxygen, a sequence of wind events facilitated
low DO deep water moving into the shallows where the fish
kill occurred. The process leading to deep waters moving
into the shallow is known as a seiche event. A seiche is an
oscillating wave caused by atmospheric or seismic activity. In
this case, the seiche was caused by sustained northeasterly
winds that piled surface water into shallow areas of the
Potomac River, pushing deeper waters to the other side of the
Bay (Figure 6a). The wind abruptly changed direction on June
2 (Figure 6b), releasing the surface water wave and causing low
A similar fish kill occurred
in the Corsica River for the
second year in a row. A
combination of karlotoxins
and a crash in dissolved
oxygen from decomposition of
the algal bloom led to a kill of
2,000fish, mostly white perch.
The 2005 event, in comparison,
killed 30,000-50,000 fish (www.
dnr.state.md.us/Bay/hab).
2005 Corsica River fish kill.
dissolved oxygen deep water to slosh back into the shallow
areas (Figure 6c). The impacts of this weather event can be
seen in the temperature, salinity and DO concentrations at the
Piney Point, Maryland, continuous monitoring station (Figure
6). The combination of low DO, algal toxins and in part,
some fish trapped in a pound net that could not avoid the
conditions, was all believed to contribute to the fish kill.
(a) Distinct shallow and deep water habitats
(b)Sudden
\A/inrl
(c) Anoxic deep waters slosh into shallow region
Northeast wind tilts water
towards western shore
Sudden change in wind direction leads to
surface water tilting towards eastern shore
Shallow
Sha low

s/>*//o
Conditions after deep waters
move into shallows:
J) Low temperature
High salinity
Low dissolved oxygen
Leads to fish kill
Pre-existing shallow conditions:
A Karlodinium bloom
High temperature
Low salinity
(?) Good dissolved oxygen
r
£ Piney Point continuous
monitoring station
Location where dead fish
washed up on Virginia shore
Seiche
(d) Some recovery

Potomac
Wind NE
direction
Jun 1 Jun 1 Jun 3 Jun 4 Jun 5
Figure 6: Summary of conditions that led to junefish kill in the lower Potomac River and continuous monitoring data from Piney Point, Maryland. Data from MD DNR.

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AQUATIC GRASSES SHOW RESILIENCE TO RAIN EVENTS
Preliminary survey results indicate
that the distribution of aquatic
grasses was not severely affected
by this year's extreme weather
conditions. In the northern Bay,
aquatic grass beds have expanded
considerably in recent years
and may have led to improved
resilience to turbidity caused by
rain events.
In spring of this year, aquatic
grasses in the northern Bay,
lower Potomac River and Tangier
Sound regions were forecasted
to increase slightly. Current survey results suggest that
the forecasts were not always accurate. The beds in the
Susquehanna Flats increased more than expected and the beds
in the Potomac River had mixed results (Figure 7). The aquatic
grass in Tangier Sound may have recovered slightly this year
from last year's dieback. Full survey results will be available in
early 2007. Figure 7: Fall 2006 field observations of aquatic grass with 2005 distribution.
LATE START TO HARMFUL ALGAL BLOOM
The aquatic grass beds in the
upper Bay were resilient to
summer storm events.
Harmful algal blooms (HABs), predominantly Microcystis
aeruginosa, have been occurring in the mid-reaches of the
Potomac River for over 20 years. For the past two years, bloom
extent, onset and duration have been forecasted in order to
assist management. This year's bloom was forecasted to start
in early summer, extend for up to 20 miles, and last for 1-2
months (see table). The actual bloom occurred later in the
summer and extended farther down the river. The remnants
from Hurricane Ernesto prematurely ended the bloom in late
August, leading to a duration that was close to the forecast.
M. aeruginosa can produce a toxin that is harmful to the
liver if ingested. A recreational health advisory was issued on
Bloom
2006
2006
condition
Forecast
Observed
Bloom onset
Early summer
Late summer
Bloom duration
Moderate
Moderate

(1 to 2 months)
(1.5 months)
Bloom extent
Small to medium
Medium

(<20 miles)
(26 miles)
Comparison of harmful algal bloom forecast to observed conditions.
Newsletter produced by the Chesapeake Bay Program's Monitoring and
Analysis Subcommittee (MASC):

August 31 for affected waters (Figure 8). HABs also occurred
in other regions of the Bay this summer. For more information,
visit www.dnr.state.md.us/bay/hab and www.eyesonthebay.net.
2006 Potomac River bloom occurrence
Washington,
Forecasted: I
Likelihood of bloom
High
Low
Observed:
An advisory was
issued on August
31st to take caution
when swimming
and boating in this
region of the
Potomac River
Thomas Point
08/09/06
670,965 cells mL'
Piscataway Creek
attawoman
Creek
Douglas Point
08/09/06
275,233 cells mL1
Port
CreekC° Blossom Point
07/26/06
18,010 eel Is mL'1
Figure 8:2006 harmful algal bloom occurrence with forecasted likelihood.
Newsletter prepared by: Contributions from:
JWlVlARYLAND
"17 Jf,H DeWKTMB-fTOF
NATURAL Re
Uttmty of Mayftmd
CarltonHaywood -Chair PeterBergstrom BruceMichaeI
Claire Buchanan Maggie Kerchner Mark Trice
Margaret McBride Peter Tango
DerekOrner John SherwelI
Bob Wood
Bill Dennison
Kate Boicourt
David Jasinski
Ben Longstaff
Caroline Wicks
Michael Williams
msGS
science lor a changing world
Scott Phillips
Joel Blomquist
Juarte Landwehr
Mary Ellen Ley
Caroline Wicks
Ben Longstaff
Bill Dennison
Kate Boicourt
Brian Burch
Lewis Linker
Gary Shenk
Nita Sylvester
DRC
Jamie Bosiljevac
MDE
Joe Beaman
CHESAPEAKE I _ \/
lcoQf\tcl
Dave Jasinski, CBP/UMCES
Mark Trice, MD DNR
Peter Tango, MD DNR
Joel Blomquist, USCS
Jeff Raffensperger, USGS
Doug Moyer, USGS
BobOrth, VIMS
www.eco-check.org
Publishing date: November 2006 Printed on 100% recycled paper
Chesapeake Bay Program
A Watershed Partnership
www. chesa pea kebay. net
William.Marv
I/IMS
Virginia iNsnrvre or MakineScietce
School of Maiinf Sciraci
www.vims.edu/bio/sw
2 USGS
science for a changing world
www.usgs.gov
flf Maryland
- Department of
natural resources
www. eyeso nthebay. net
shoreline
There was larger than predicted
growth in Susquehanna Flats.
While it was predicted that aquatic
grass would increase slightly in
the lower Potomac River, there
were mixed results. The beds along
the northern shoreline increased,
but the beds along the southern
decreased.
Although conclusive results
cannot be made, aquatic grass in
Tangier Sound seem to be making
a comeback after the 2005 dieback
from high water temperatures. The
forecast predicted a slight recovery
from the dieback.

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