T61 Lakes through Space and Time II

Sunday, 4 November 2018
1:30 PM - 5:30 PM
Room 134

PHOSPHORUS MOBILITY IN LEGACY SEDIMENTS OF SHALLOW, EUTROPHIC UTAH LAKE

Paper number: T61-5
Program: Technical Sessions
Time: 2:20 PM – 2:35 PM

Authors

Abstract

An increasing number of lakes worldwide are impacted by eutrophication and harmful algal blooms due to anthropogenic nutrient inputs. In Utah Lake, the largest freshwater lake in Utah, decades of nutrient loading from agricultural runoff and wastewater treatment plants (WWTPs) have resulted in elevated P concentrations in the water column and sediments. In an effort to mitigate further eutrophication, the Utah Division of Water Quality has proposed new limitations on P loading from WWTPs. Limiting external loading, however, may not lead to improvements due to a legacy of nutrients in the shallow lake sediments. To investigate P cycling in Utah Lake, we collected water column, pore water, and sediment samples during 2015-2016. Water samples were analyzed for total dissolved P (TDP) and sediment samples were analyzed for total P (TP) and mineralogy. A subset of sediment samples was subjected to a sequential extraction procedure to evaluate P speciation. TP concentrations in sediment ranged from 306-1710 mg/kg, with the highest concentrations on the east side of the lake near WWTP inputs. Sediment TP was reflected in water samples, with TDP concentrations as high as 1.7 mg/L in the water column and 10.8 mg/L in pore water on the east side of the lake. Sequential extractions indicated that ~25-47% of sediment TP is associated with carbonate minerals and 41-61% is associated with Fe oxide/hydroxide minerals. The carbonate-associated P fraction is likely immobile whereas the Fe oxide-bound P is potentially bioavailable under changing redox conditions. Currently we are using sediment flux chambers to monitor dissolved oxygen concentrations in relation to P release at the sediment-water interface. Ultimately, we plan to quantify internal P fluxes relative to external P loading to the nutrient budget of Utah Lake. Mitigating lake eutrophication is a complex problem that goes beyond decreasing external nutrient loads to the water body and requires a better understanding in-lake P cycling.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-323596

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