Abstract Past studies have shown that salt marshes have fluctuating nutrient concentrations in a 24 hour period due to seasonal nutrient cycles. In this experiment, we were interested in how dissolved oxygen (DO) levels changed in a diel cycle for a freshwater marsh and how these changes differed between the surface and the bottom of the water. I hypothesized that DO levels would increase overnight and in the morning when temperatures were cool and decrease during the afternoon when temperatures were warmer with no significant difference between the surface and the bottom. We used a DO meter to measure DO levels throughout the day. Generally, the data agreed with my hypothesis, but some ponds had high DO levels at warmer times of the day. …show more content…
Notably, the pond at the middle marsh had negative P/R ratios at both the surface and bottom. This is because respiration was negative at both levels of the water column as respiration was much higher in the second sunset than in the first. Only pond 9 reported different results, heterotrophic at the surface of the water and autotrophic at the bottom of the water (Table 1). This means that respiration exceed production at the surface and production exceeded respiration at the surface. This may be at least partially due to the types of organisms found in and above the water. While most other ponds reported having both autotrophic and heterotrophic organisms, pond 9 only seemed to have algae when we performed the five gallon pour (Table 3). However, there were some seagulls and rabbits spotted around the pond. It is also possible that there could be more photosynthetic organisms such as algae at the bottom of the pond and no heterotrophic organisms were captured in the pour. A past study also indicated that ponds tend to fluctuate between autotrophy and heterotrophy due to changes in the euphotic zone (Copeland et al., 1961). In the case of pond 9, algae population and productivity may have affected the communal oxygen production. Much of this study also occurred during cloudy or windy conditions, so the turbidity of the water and inconsistent sunlight may have affected the amount of energy available for algal photosynthesis. However, because the t-test did not return any usable results, I cannot make any definite conclusions about how statistically significant the difference between pond 9’s surface and bottom P/R ratios