A RETROSPECTIVE VIEW OF THE IMPACTS OF URBANIZATION ON UTAH LAKE, UTAH FROM PRE-EUROPEAN SETTLEMENT TO THE PRESENT

At 380 km², Utah Lake is the third-largest lake in the USA west of the Mississippi River. Adjacent to an urban corridor, it is an important water and recreational resource for surrounding communities as wells as being impacted by them. Recently, large harmful algal blooms have drawn attention to the ecosystem health of this large water body, and a rapidly-growing population, infrastructure development and a recent lengthy drought continue to stress the lake’s health. Although the lake has always had high nutrient levels, urbanization has stressed the lake much further.

Three freeze cores were obtained in 2019 to investigate ecosystem changes and human impacts since European settlement began in ~1850. Sediment consists of marl throughout (calcite>quartz>dolomite). After establishing core chronologies using ²¹⁰Pb, ¹³⁷Cs as well as by correlation, proxies investigated included pollen, C- and N-isotopes, nutrients (C, N and P), RockEval pyrolysis and heavy metals. At ~1850 there was a drop in Utah Juniper and sedge pollen likely due to land clearing for cultivation, followed by an increase in AMARANTHACEAE (sugar beets and other food crops?) and POACEAE (cereals?). C:N ratios indicate that the organic matter budget has been dominated by the burial of algae rather than vascular plant debris, but with increasing algal input up to the present.

Discernable increases in sediment-bound nutrients began in the mid-20^th century, whereas increases in Pb began as early as ~1900. Nutrient increases were related to agricultural runoff and variably-treated wastewater effluent, whereas heavy metal loading was due to heavy industry, coal combustion, and urban runoff. Particularly impactful were the Ironton pig iron and Geneva steel mills, the latter of which was decommissioned in 2002. Over the last several decades nutrient and metal loadings have stabilized, indicating a steady state has been reached: Gains in nutrient removal from effluent have been approximately offset by growing populations. Decreases in heavy industry and coal combustion have been countered by urbanization.

In sum, Utah Lake sediment comprises an important archive of the increased stresses placed on an already nutrient-rich lake as it passed from pre-European settlement into being surrounded by a highly urbanized corridor and a changing development patterns.