From Hypersaline to Fresh-Brackish: Documenting the Impacts of Human Intervention on a Natural Water Body from Cores, Farmington Bay, UT, USA

Farmington Bay (FB), UT, has undergone major water quality changes due to human interventions. An arm of the Great Salt Lake (GSL), FB, is an endorheic body, actively accumulating nutrients. Human impacts to FB began in 1847 when European settlers arrived and major ecosystem changes have resulted through local development. Major impacts include anthropogenically impacted discharges (AID), causeway construction, and water-level declines. AID includes raw and treated sewage, septic leachate, irrigation returns, and feedlot or pasture runoff. Causeway construction produced freshening (hypersaline to fresh-brackish) via hydrodynamic isolation, whereas diversions and a drying climate prevent AID from mixing with the rest of the GSL. The timing of human interventions is known, allowing identification of ecosystem response in three sediment cores analyzed for 210 Pb chronology, mineralogy, C and N isotopes, pyrolysis, porewater chemistry, and diatom stratigraphy. From these proxies, three events have profoundly altered FB. A sewage canal (1911) brought raw effluent from Salt Lake City, causing a rise in the d 15 N of organic matter (OM). A corresponding increase in carbonate production occurred as enhanced productivity led to higher pH. Causeway construction (1969) spurred algal growth as FB freshened. Declining water levels (> 1990) resulted in a shrinking volume of bay water, resulting in increased eutrophication. P is elevated in porewater due to OM decay. ~ 0.9 gm −2 year −1 phosphate is released to the water column, compared to an estimated 3.0 gm −2 year −1 surface inflow loading. Although ecosystem improvements may result from AID reductions, improvements in water quality are most easily achieved by restoring surface inflows to FB.