GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 19-2
Presentation Time: 8:15 AM


GUNNELL, Nathan V., Department of Geology, Brigham Young University, Provo, UT 84602, NELSON, Stephen T., Department of Geological Sciences, Brigham Young University, Provo, UT 84602 and ENGSTROM, Daniel R., St. Croix Watershed Research Station, Science Museum of Minnesota, Marine on St. Croix, MN 55047

Influence of human activity on surrounding environments is an important field of research. With respect to aquatic settings, lacustrine deposits provide excellent proxies of environmental change since the sediment accumulates at a relatively constant rate, recording environmental change. This study employs isotopic, mineral, and chemical records from Farmington Bay freeze cores, in particular δ13C, δ15N, and 210Pb isotopes as well as phosphorus level fluctuation. In particular, δ15N provides a record of changing nutrient sources and 210Pb isotopes permit estimation of the age of sediment with depth.

Initial results from these 210Pb isotopes have allowed ages to be assigned to depths along the core dating back roughly 100 years at 30 cm. At this depth, a dramatic shift in the δ15N isotope is observed. Initial δ15N levels indicated a nutrient source related to agriculture. However, beginning around 100 years ago, the δ15N shows the main nutrient source for the bay became wastewater. This may have been a result of the completion of a sewage canal in 1911 which began routing wastewater directly into the bay. Results have also shown a significant rise in phosphorus levels beginning around 1970 which may be due to the construction of the automobile causeway that isolated Farmington Bay from the rest of the Great Salt Lake.