Water Clarity in the World's Largest Freshwater Ecosystem: Modeling Short-Terms Changes Hannah Joy-Warren Sir Winston Churchill Secondary Floor Location : S 226 V

Canada has access to the world?s largest body of fresh water?the Great Lakes, which supply North America with 84% of its surface fresh water, and 21% of the worlds?. It is crucial to find a way to protect the world?s largest body of fresh water from introduced pollutants and figure out how to undo the damage we have already done. I collected data to study how the natural environment, and in particular the weather, can act as a buffer against pollution using water movement in the Georgian Bay, which is in the Great Lakes. I used water clarity as an indicator of water quality, or how polluted the water is.

I studied how the water temperature affects water clarity, and how the wind affects the water temperature. I hypothesized that the wind speed and direction determine the gradient and temperatures of the thermocline (the temperature gradient through a water column). I then hypothesized that the colder the thermocline (on average), the higher the water clarity due to the decreased light and warmth in the colder water, which will cause the colder water to have less algae growth.

Study sites were chosen based on their varying degrees of exposure to wind and water exchange, and water clarity, water temperature, and phosphorus readings were taken every other day. Weather factors (wind direction, wind speed, air temperature) were measured twice a day.

I found that as the phosphorus levels increased, the clarity levels decreased. Since phosphorus is the growth rate limiting nutrient in freshwater ecosystems, the increased phosphorus probably increased algae growth, thus decreasing the water clarity. Because phosphorus only accounts for about 18% of the variation in water clarity, however, it is not the predominant factor in water clarity changes. The wind direction and speed appeared to drive the change in thermoclines. Once only strong winds (above 6 km/h) were observed, a correlation between wind direction and water clarity could be seen. Certain winds caused either warmer or cooler thermoclines, depending on the direction of the wind. The colder a thermocline was, on average, the higher the clarity in that area. Unlike in Vancouver, in my test areas the rainfall does not appear to decrease water clarity. These findings suggest that near my test sites, in Nares Inlet, there are very few pollutants on the land that can be washed into the lake.

Overall, I found that the most important factors in water clarity were wind direction and wind speed, since they determined the thermocline, which then affected the water clarity. I also found, however, that how the variables interact with each other accounts for some of the change in water clarity as well.