The aquatic and semi-aquatic plant communities of Utah Lake, Utah County, Utah are discussed. This discussion includes the methods of describing and delimiting the major vascular plant communities, the descriptions of the present existent communities, and the determination of the vegetational changes, particularly since 1925. The vegetation around Utah Lake is divided into plant communities. Each community is discussed using: (a) quantitative data, (b) field observations, (c) general and specific locations of the community, and (d) interrelationships and trends of the community. Historical vegetational changes of Utah Lake plant communities are discussed. In this discussion, the plant communities described by Cottam in 1925 are examined in broad outline and then in detail. In 1968, twenty-nine plant communities had developed from fifty-six per cent of the associations and twenty-nine per cent of the societies that were described by Cottam in 1925.

The sources of phosphorus (P) in Utah Lake can be diverse, including natural and anthropogenic point and non-point sources, such as atmospheric deposition, soil erosion, and industrial and urban wastewater effluents. This study collected interface sediments, column water, porewater, and sediment cores across this vast water body. These samples were then analyzed for their mineralogic, organic, and elemental composition to characterize the geochemical nature of water and sediment at the water-sediment interface within Utah Lake. The average concentrations of P and other elements found in the column water of an individual site do not significantly differ across depth suggesting Utah Lake to be well mixed vertically. Furthermore, most sites share similar water column P concentrations, excluding Provo Bay. Water column and pore water sampled with high spatial resolution reveal the redox potential shifts rapidly from oxidizing (+200mV) in the bottom water column to reducing (-100mV) in the porewater within 10 cm below the sediment surface. The influence of reducing conditions on oxidation state within the sediment is an important finding related to phosphate retention in the sediment of Utah Lake. The abundance of reducing conditions in the sediment, even at the shallow depths, suggests that redox sensitive minerals and metals (particularly Fe) are not a stable sink for phosphorus in the sediments. Averaging across all sites within the lake, excluding PB, the porewater conductivity decreased with increasing depth, with a defined shift at the water column-sediment porewater interface. The porewater pH was consistently less (6.5) than the lake water near the top of the water column (8.5). These findings will improve our fundamental understanding of geochemical cycling in shallow eutrophic lakes and be used to enhance the quality of water models that will be used to manage Utah Lake better.

Provo Bay of Utah Lake, Utah, receives the effluents from farms, industry, and three cities. In order to determine the effects of these effluents, eleven stations were established throughout the Bay. At weekly intervals from June 19 to October 26, 1970, and monthly thereafter until March, 1971, the water at these stations was sampled for dissolved oxygen (DO}, carbon dioxide (CO2), turbidity, pH, phosphates, nitrates, biochemical oxygen demand (BOD) and coliform bacteria. Due to intense algal blooms, the quality of the water changes as it passes through Provo Bay. Average values for the inflow, mid-Bay, and point of discharge respectively during the summer are as follows: DO, 5.4--10.2--6.9 mg/l; CO2, 38--0--6 mg/l; turbidity, 19--80--57 Jackson Turbidity Units; pH, 7. 5--9. 0--7. 2; phosphates, 3. 62--0. 94--0.15 mg/l; nitrates, 0.71--0.08--0.00 mg/l; BOD, 17--27--9 mg/l; and coliforms, 31,000--31--0/100 ml. These results indicate that during the summer Provo Bay is acting as a tertiary treatment pond for the effluents which it receives.

The initiation, bloom, and bust of harmful Cyanobacteria and algae blooms (HAB) in lakes are controlled by top-down and bottom-up ecological controls. Excess phosphorous and nitrogen inputs from anthropogenic sources are primary to blame, but eukaryotic grazers may also promote or curb Cyanobacteria dominance. We tracked shifts in bacterial composition, lake chemistry, and eukaryotic grazing community weekly or bi-weekly through spring and summer and modeled the causes of specific Cyanobacterial species blooms and busts across three lakes in Utah, USA, with differing lake trophic states. Regardless of trophic status, all three lakes experienced blooms of varying composition and duration. Aphanizomenon strain MDT14a was the most dominant species in every bloom on Utah Lake, comprising up to 44.16% of the bacterial community. Utah Lake experienced a total of 18 blooms across all sites ranging in duration from one to six weeks. Phormidiaceae sp. (8.5  6.1%) and Microcystis sp. (9.7  4.7%) were the most abundant species in the Deer Creek bloom. Deer creek experienced one bloom at the beginning of fall. Nodularia sp. (9.7  2.1) dominated Great Salt Lake bloom. The Great Salt Lake experienced four separate blooms during the summer months that lasted one to three weeks. Phosphorous concentrations on Utah Lake varied across site and season. Nitrate concentrations on Deer Creek increased over season with a ten-fold increase in concentration. We characterized Cyanobacteria blooms as either bloom communities (growing populations of Cyanobacteria) or as bust communities (declining populations of Cyanobacteria). Using these designations, we modeled the growth and decline of the Cyanobacteria populations across season with top-down and bottom up-controls. Based on generalized least-squared modeling, eukaryotic grazing does not affect relative Cyanobacteria abundances as much as nutrient limitations. Aphanizomenom strain MDT14a was positively correlated with temperature (P < 0.028) and the concentration of K (P = 0.007) and negatively correlated with increases in conductivity (P = 0.0088). Microcystis was positively correlated with increasing levels of SRP (P < 0.001) and negatively correlated with higher Ca concentrations (P = 0.008) and PP (P = 0.008). Busts of Microcystis were related to decreases in nitrate (P = 0.06) and lower total lake depths (P = 0.03). Phormidiaceae sp. relative abundance was negatively correlated with higher levels of TDN (P = 0.01-0.001) and Mg (P = 0.01) and positively correlated with higher S concentrations (P = 0.007). Our findings suggest that micronutrients and more bioavailable forms of P may potentially allow Cyanobacteria to break dormancy and proliferate HAB communities.