Honors Theses and Capstones

Date of Award

Summer 2023

Project Type

Senior Honors Thesis

College or School

COLSA

Department

Natural Resources and the Environment

Program or Major

Environmental Science: Ecosystems

Degree Name

Bachelor of Science

First Advisor

Wilfred Wollheim

Second Advisor

Jacques Finlay

Abstract

Urban aquatic ecosystems are highly threatened by excess concentrations of chloride (Cl-), which can negatively impact the biodiversity and functioning of aquatic ecosystems. High Cl- concentrations in most northern cities come primarily from road salt use for de-icing, in the form of NaCl. Specific pathways of runoff and hydrology of waterbodies will regulate Cl-concentrations in the months after the snowmelt season. This study attempted to understand the hydrologic controls on Cl- concentrations and identify how the hydrology of urban ecosystems may impact exposure to chloride in streams. To accomplish this, stream sites around the Twin Cities Metro Area in Minnesota were sampled for Cl- as well as several biogeochemical tracers to indicate groundwater inputs, including oxygen isotope ratios of water (d18O) and dissolved inorganic carbon (DIC), and landcover information, including road density and percentage developed of the various site watersheds. Trends between Cl- and the landcover showed a positive linear relationship, signifying how winter road salt application can have an ongoing effect on ecosystems in the more productive summer months. There was a surprising lack of correlation between the groundwater tracers and Cl-, possibly explained by the unusual water year Minnesota had faced at the time of sampling, which likely diminished the correlation between water source and Cl- concentration. This study highlights the variety of factors that shape seasonal variations in Cl- and underscores the need to understand these factors to inform future environmental management and monitoring.

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