Characterizing Light Limitation to Algal Growth in Utah Lake Using Secchi Disk Readings, PAR Meter Measurements, and an Algae Incubator

Limitations to algal growth in Utah Lake, a highly turbid lake, are poorly understood with some studies showing that the lake is nutrient limited and other work showing that this system is light limited and not nutrient limited. To develop effective management strategies and understand ecological and geochemical process for a turbid freshwater system like Utah Lake, it is first vital to understand the limits that may constrain lake functions. To help characterize light limitation to algal growth, we collected secchi disk and photosynthetic available radiation (PAR) meter measurements throughout the summer of 2022. We analyzed the collected data using the U.S Geological Survey water quality standards procedures to characterize light limitation of Utah Lake. Utah Lake turbidity is high due to the shallow nature of the lake and high wind speeds resulting in significant re-suspended sediment. We measured secchi disk readings as low as 10 centimeters, with most readings less than 20 cm. PAR meter readings showed that PAR levels dropped to less than 1% of surface readings by about 75 cm. We developed and deployed an algae incubator to quantify the depth at which algae can grow in Utah Lake. We deployed the algae incubator in August of 2022, the height of algal growth in Utah Lake. We measured algal concentrations using the Utah State approved method for chlorophyll-a (chl-a) extractions and used these data to characterize growth. During this period, we deployed six 10-m diameter mesocosms, that partially isolate the water column, reducing suspended sediment and decreasing turbidity. Preliminary data suggest that this caused increased algal growth. Secchi depth and PAR measurements indicate that Utah Lake is light limited in respect to algal growth. The incubator data show that algal growth is light limited, with benthic organisms becoming dominant less than a meter below the surface.