Date of Award

12-2017

Degree Name

Master of Science

Department

Geosciences

First Advisor

Dr. Carla M. Koretsky

Second Advisor

Dr. Kathryn M. Docherty

Third Advisor

Dr. R.V. Krishnamurthy

Access Setting

Masters Thesis-Open Access

Abstract

Influxes of saline water from roads treated with deicers can alter the density structure of urban lakes. This can delay or halt turnover events, which may lead to persistent hypolimnetic anoxia in nutrient-rich lakes. In this study, the lake columns of two urban lakes (Woods Lake and Asylum Lake) and one rural lake (North Lake), were sampled once a month from March 2016 to June 2017. Lake column water was analyzed for conductivity, temperature, dissolved oxygen, ferrous iron, manganese, sulfide, calcium, magnesium, sodium, chloride and methane concentrations as a function of depth. All three lakes are eutrophic with anoxic hypolimnia during at least part of the year. Woods Lake appears to have transitioned to meromixis and Asylum Lake to monomixis due to influx of dense saline water from roads treated with deicers. The lack of turnover in these two lakes during fall and spring results in persistently anoxic, redox-stratified hypolimnia, with large accumulations of methane. This study demonstrates that road salt deicers impact lake mixing and biogeochemistry, and could also lead to significant increases in greenhouse gas emissions from urban lakes.

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