INVESTIGATING PHOSPHORUS AND NITROGEN INPUT TO UTAH LAKE FROM ITS TRIBUTARIES AND THE SURROUNDING WASTEWATER TREATMENT PLANTS

Harmful algal blooms (HABs) are a common problem for water bodies that affects aquatic life, community health, and recreation. Excessive phosphorus (P) and nitrogen (N) input to aquatic ecosystems often cause HABs. Utah Lake, one of largest freshwater lakes in the western United States, experiences seasonal HABs. Utah Lake is considered hypereutrophic due to nutrient input from agricultural and stormwater runoff, atmospheric deposition (rain and dust), effluent from wastewater treatment plants (WWTPs), etc. This research focused on the nutrient loads from eighteen sites (both upstream and downstream) of ten Utah Lake tributaries and seven WWTPs. Water samples were tested over a six-week period using a CheMetrics V-2000 Photometer to determine the concentrations (mg/L) of four inorganic compounds: orthophosphate (PO₄³⁺), nitrate (NO₃^-), nitrite (NO₂^-), and ammonia (NH₃). A YSIDSS Pro water quality meter was used to measure other water parameters (pH, chlorophyll a, phycocyanin, etc.). Our data showed temporal and spatial variations in nutrient concentrations. Downstream river sites had higher 6-week average concentrations (NH₃:0.87, NO₃^- :3.28, NO₂^- :0.15, and PO₄³⁺ :1.41) than the upstream sites (NH₃:0.09 , NO₃^- :0.62, NO₂^- :0.04, and PO₄³⁺:0.23) for all tributaries. The WWTPs had much higher average concentrations when compared to the tributaries (NH₃:2.10, NO₃^- :42.11, NO₂^- :0.33, and PO₄³⁺:6.50). A limit for P was set at 1 mg/L for the WWTPs on January 1st, 2020, by the Utah Division of Water Quality. Based on our data five of the seven WWTPs exceeded this limit but were allowed because of individual extensions. Each WWTP has their own limit for NH₃ which they all complied to. However, there is no limit for NO₃^- and NO₂^- at the WWTPs. Our results indicated that the failure to abide by the P limit and a lack of limits on total inorganic nitrogen could have resulted in much higher nutrient input to Utah Lake from the WWTPs than previously thought. To minimize HABs, a stricter nutrient standard should be placed on the effluent from the WWTPs, which could be achieved by investment in wastewater treatment technology. Also, improved farming practices (such as crop rotation and efficient irrigation techniques) could help decrease nutrient runoff from agricultural land into the tributaries and the lake.