An Examination of Dissolved Oxygen Levels and the Effects of Macroalgae in Chincoteague Bay, Marylan

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An Examination of Dissolved Oxygen Levels and the
Effects of Macroalgae in Chincoteague Bay,
MarylandRenee Harrington, Southampton College,
Honors Thesis, May 2004
Results
Objectives To explore the influence of
macroalgae on the concentration of dissolved
oxygen (DO) in the coastal bays of Maryland.
To identify areas in Chincoteague Bay that
experience or are vulnerable to hypoxic
conditions.
Box plot of results for Mann-Whitney Rank Sum
Test for sample sites. For sites 6, 7, and 10,
DO values recorded for location A
(present/abundant macroalgae) are calculated to
be statistically significantly different from DO
values measured at location B (absent/sparse
macroalgae), with Plt0.001. However, DO values
measured at location A for site 3 are not
statistically significantly different (P0.402)
from DO values measured at location B. This
statistical test was used to determine if a
statistically significant difference exists in
the median values between the two locations at
each site, that is greater than would be expected
by chance. For sites 6, 7, and 10 the value
calculated (Plt0.001) supports the claim that the
presence of macroalgae has a significant impact
on the DO concentrations recorded during this
study. The value calculated for site 3 (P0.402)
was not great enough to exclude the possibility
that the difference is due to random sampling
variability.
Dissolved oxygen distributions for sampling sites
in Chincoteague Bay. Bar lines for each site
denotes range and dots represent average DO level
for each site. Plotting the high, low, and
average DO values for each site, it is easy to
ascertain how the concentration of DO varies in
the selected areas of the bay. The average DO
level for both locations at site 3 were below 5
mg/L and sites 7A, 10A, and 10B were slightly
above that level. Both locations for control
site 6 display moderately high DO average levels.
Conclusions Daily fluctuation in DO levels
were documented at all sites in this study.
The high frequency data collected recorded signs
of stress at these locations that the historical
data may not fully suggest. The study
documented the important periods during which DO
levels fell below the 5 mg/L standard and more
accurately portrayed these potentially
problematic areas. It is clear that the
presence of macroalgae affects the range of DO
values by producing an overall greater range.
Map of Chincoteague, Newport, and Sinepuxent Bays
in the coastal bay system of Maryland, USA,
showing the location of DO and macroalgae
sampling sites (circled are sampling sites 3, 6,
7, and 10). Samples were collected at two
proximal locations Location A (significant
growth of macroalgae) and Location B (sparse or
no macroalgae). YSI water quality sondes
collected water quality data every half hour for
a seven day period for each location of each
site. At the conclusion of the sampling period
for each site a macroalgae dredge sample was
taken from around the equipment to get
representative data of algal species composition
and abundance in the area.
Graphs of daily changes in DO concentration over
the sampling period for site 7 (macroalgae
present and absent locations) and site 10
(abundant and sparse macroalgae) in Chincoteague
Bay. Site 7 represents the pattern also observed
at sites 3 and 6. Locations with macroalgae
present experienced a greater range of DO values,
specifically higher peaks and lower depressions.
Exemplified by data gathered for site 10 is the
daily occurrence of hypoxic episodes observed at
sites 3, 7, and 10. Control site 6 did not
experience any hypoxic events.