Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Geography & Environmental Studies

Faculty/School

Faculty of Science

First Advisor

Dr. Homa Kheyrollah Pour

Advisor Role

Supervisor

Second Advisor

Dr. Michael Palmer

Advisor Role

Co-advisor

Abstract

The subarctic shield near Yellowknife, Northwest Territories (NWT), is populated with thousands of small lakes (<1.5 km2) and several large lakes. Historic mining activities in the region have left a legacy of environmental impacts and widespread arsenic (As) contamination in both aquatic and terrestrial environments. In particular, several small subarctic lakes near Yellowknife have been previously documented to be contaminated with high levels of As. Subarctic lakes are characterized by seasonal ice-cover that can persist for more than half of the year, yet little is known about the under-ice spatial and seasonal dynamics of As cycling. The objective of this study is to contrast seasonal changes in As cycling within and among a series of lakes with different basin morphologies during ice-cover and into the ice-free seasons. In this study, a combination of data including water profile sampling, sediment cores, snow and ice measurements, and bathymetric mapping were collected in four lakes from November 2020 to October 2021. Continuous monitoring of lake physical properties (dissolved oxygen, temperature, and light) was conducted via data loggers installed at 1 m depth intervals in each lakes’ water column. Detailed profiles of water chemistry were collected monthly at the deepest part of each lake, examining numerous key water chemistry elements with a focus on dissolved and particulate As concentrations. Key results from this study indicated: 1) Distinct seasonal variation in As over the ice-on and open-water periods, 2) The important role of lake mixing regimes in the mobility of As, 3) Field evidence of Fe attenuation of As from the water column. This project contributes important information on the winter cycling of As, which will help to inform our understanding of the chemical recovery of subarctic lakes from As pollution.

Convocation Year

2023

Convocation Season

Spring

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