ABSTRACT:

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 (precipitation 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.

ABSTRACT:

Utah Lake, the largest freshwater lake in the United States west of the Mississippi River, has received
heavy loading of various contaminants, such as high concentrations of phosphorus (P) and nitrogen (N) wastes
from raw sewage, effluent from sewage treatment plants, runoff from surrounding agricultural and farming land,
and metals from mining and industrial activities since European settlement. However, the rate of loading of N, P,
and trace metals to Utah Lake varies both in space and time. Therefore, a good understanding of such spatial and
temporal variability is critical for developing integrated approaches to managing lake water quality. In this project,
we took water and floc layer sediment samples from the American Fork River, Provo River, Hobble Creek,
Spanish Fork River, Jordan River and Utah Lake to investigate the temporal and spatial variations in nutrient (P,
N) load and trace metal (mercury/methylmercury, arsenic, lead, cadmium, etc.) concentrations. In addition, water
samples were analyzed for H and O stable isotopes to establish a water budget for Utah Lake, and floc layer
sediment samples were analyzed for C and N stable isotopes to differentiate organic matter sources to Utah
Lake. Upon completion of this project, we were able to quantify spatial and temporal variations in nutrient and
metal loading to Utah Lake and to examine how this variability affected water quality. Furthermore, we were
able to trace the origins of organic matter sources to the lake and establish nutrient, metal, and water budget for
Utah Lake. The knowledge from this project can guide actions that are increasingly required to safeguard the
services provided by Utah Lake ecosystem in a future with increasing pressure on freshwater resources. The water,
nutrient, and trace metal budgets developed in this project provide important information for determining
which inflows are contributing the largest contaminant loads to Utah Lake. Consequently, the data derived from
this project can help state agencies to address significant questions in water quality, hydrologic, environmental,
and biogeochemical sciences and management related to human-environment interactions.