TRACKING PROGRESSION OF EUTROPHICATION IN TWO LAKES IN WI VIA SATELLITE IMAGERY

Eutrophication is a state where there are too many nutrients in a water body. It may cause algae blooms, which in turn can deplete the dissolved oxygen content in water, leading to mass die offs of creatures and plants. Eutrophication is commonly observed in Wisconsin lakes mainly due to runoffs from farming and dairy production. Observing algae blooms using satellite imagery has been achieved in the past using spectral indices such as the Normalized Difference Vegetation Index (NDVI). This study uses Landsat 8 and 9 scenes to identify algae bloom in two connected lakes in Wisconsin. The goal of this study is to determine if Lake Nepko, located south in the Castle Rock watershed, experiences a higher ratio of algae bloom compared to Lake Wazeecha, located north in the watershed. Three time periods were used to detect the trend of algae bloom in the lakes. Due to the high cloud cover in the area, each period was composed of two years. The time periods are 2017-2018, 2019-2020, and 2021-2022. One cloudless Landsat scene per each month between April and November was retrieved from Earth Explorer. Using the near-infrared and red bands, NDVI values were obtained for each lake per month. Then, the ratio was calculated based on the number of pixels with algae bloom and without algae bloom for each lake monthly. A trendline was then made for each lake during the time period. This resulted in a total of two trendlines, one per lake. These trend lines were compared to determine which lake had a higher ratio of algae bloom.