Free Response Dissolved Oxygen

Free Response Questions

b.) In the observed data, it is evident that the pond contains a larger concentration of DO at 4 o’clock. Although dissolved oxygen can come from the air above the water, in this case the plants below the water are what may be affecting the fluctuating DO concentrations. Plants below the water’s surface, like seaweed, photosynthesize like plants above water in that they release O2 as a byproduct. This O2 is dissolved into the water, increasing its DO concentration. Plants require sunlight in order to photosynthesize energy. Generally, more sunlight will matriculate greater energy production. In the morning there is not much direct sunlight going in the water (unless it is summer in Alaska where I believe it is always sunny), therefore plants in the lake cannot obtain an abundance of light to photosynthesize, thus the low DO concentration. As the day goes on, the sun not only becomes more directly above the lake, but it also becomes much more intense. Around 4 o’clock, there is nearly direct sunlight, and the sunlight that the plants are getting is intense. These two factors allow for greater respiration and photosynthesis of the plants. As the day turns into night, the reverse effects are seen, and the DO concentration falls as a result of less intense sunlight and less light as a whole.

On an overcast day, it could be predicted that the lake’s DO concentration would stay very low in the morning and at night. From 10-6 o’clock it is likely that the rate of photosynthesis will increase slightly but plateau for several hours. The overcast causes a blockage of sunlight to the plants. When the rate of photosynthesis goes down, so does the DO concentration.

c.) They addition of an abundance of nutrients, especially Nitrates and Phosphates, will cause a massive algal bloom. These large mats of algae will sit on the lake top soaking up all the sunlight and not letting any get down through the water to the underwater plant life. It is...