An Examination of Dissolved Oxygen Levels and the Effects of Macroalgae in Chincoteague Bay, Maryland Renee Harrington, Southampton College, Honors Thesis, May 2004 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. 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. 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. 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. 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 P=< However, DO values measured at location A for site 3 are not statistically significantly different (P=0.402) 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 (P=<0.001) 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 (P=0.402) was not great enough to exclude the possibility that the difference is due to random sampling variability. 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. Results: