Date Approved

4-12-2023

Graduate Degree Type

Thesis

Degree Name

Biology (M.S.)

Degree Program

Annis Water Resources Institute

First Advisor

Alan Steinman

Second Advisor

Bopi Biddanda

Third Advisor

Carla Koretsky

Academic Year

2022/2023

Abstract

Road salt runoff from de-icing applications has notably increased chloride concentrations in lakes throughout north temperate regions of the planet, with negative impacts on freshwater ecosystems. For the past 20 months, I have monitored the water quality of a chloride-impaired lake and associated tributary in Grand Rapids, Michigan. Chloride levels in the deepest part of the lake have reached up to 331 mg/L, above EPA chronic toxicity thresholds. The salt-induced density gradient has prevented the lake from completely mixing during my study period and created persistent hypoxia in the hypolimnion. Total phosphorus (TP) concentrations in the hypolimnion can exceed 7500 µg/L, in contrast to epilimnion TP concentrations of ≤40 µg/L, suggesting internal phosphorus loading may be significant in this lake. I conducted an experiment to examine the impacts of excess chloride on sediment phosphorus release. Sediment cores collected from the lake bottom were brought back to the lab and measured for phosphorus release under different oxygen (present/absent) and chloride (high/low) treatments over the course of 25 days in a controlled environment. Mean maximum TP release was greatest in cores exposed to the high chloride/anoxic treatment (1.71 – 2.23 mg m−2 d−1) compared to low chloride/anoxic treatment (0.83 -1.42 mg m−2 d−1), suggesting that elevated road salt concentrations may exacerbate internal phosphorus loading. However, the release of soluble reactive phosphorus was influenced by the sediment source, suggesting that phosphorus release from salinization is dependent on sediment composition. The results from my study have management implications. Excess phosphorus concentrations in the hypolimnion need to be reduced prior to addressing the elevated chloride, to avoid lake turnover and introduction of high phosphorus concentrations into the upper layers of water, where in combination with higher light levels, algal blooms would form. Once phosphorus concentrations are reduced, perhaps via chemical inactivation, the excess salt issue can be addressed. However, elevated hypolimnetic phosphorus concentrations are a symptom of the larger issue of road salt runoff into the lake. Without a reduction in saline deicer application and associated runoff into the ecosystem, lakes will continue to experience negative impacts from elevated chloride concentrations.

Comments

Church Lake homeowners association

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