Mapping and Modeling Chlorophyll-a Concentration in Utah Lake Using Landsat 7 ETM+ Imagery

Chlorophyll-a concentrations in the turbid surface waters of Utah Lake were determined using Landsat 7 ETM+ satellite imagery and field measured concentrations of chlorophyll-a. A log transformation of red/near-infrared reflectance (i.e. ln[Band3/Band4]) was used to estimate chlorophyll-a and had a high correlation with the field measured chlorophyll-a concentrations (R2 = 0.9337). With this relationship, a model and 19 contour maps showing the spatial distribution of chlorophyll-a concentrations over Utah Lake was developed for the spring, summer, and fall seasons of 2003 to 2010. High concentrations of Chlorophyll-a (355μg/L and over) were observed mostly at the Provo Bay and Goshen Bay areas of the Lake. Occasionally, elevated levels of chlorophyll-a were observed at the northeastern, middle, and western sections of the lake. Utah Lake's average chlorophyll-a concentration is declining over time. Field measured concentrations of phosphorus and model estimates for chlorophyll-a concentrations were highly correlated (R2 = 0.9046). This suggests that the elevated levels of chlorophyll-a might be a result of the point and non-point discharge of phosphorus-laden wastewater from treatment plants, municipal storm drains, and agricultural activities.