Date of Award

Spring 2024

Project Type

Thesis

Program or Major

Earth Sciences

Degree Name

Master of Science

First Advisor

Ruth K Varner

Second Advisor

Anne Lightbody

Third Advisor

Amanda McQuaid

Abstract

Northern freshwater lakes (> 40°N) are an increasingly recognized major contributor of methane (CH4), a potent greenhouse gas, to the atmosphere. Climate warming and eutrophication acceleration threaten to increase CH4 emissions from these lake ecosystems, particularly in littoral (shallow lake edge) zones where ebullition (bubbling) is often a dominant flux pathway. Few studies have investigated the impacts of lake productivity on limnological CH4 cycling for a range of trophic classes and provided a comparison between different latitudes. Here, we analyzed chlorophyll α (chlα; proxy for lake productivity), other water quality parameters, sediment CH4 production rates, and ebullition rates at nine temperate lakes in NH in June with a range in trophic classes and three subarctic lakes in northern Sweden in July. Mean sediment CH4 production rates for all study lakes (n = 12) were positively correlated with mean turbidity and negatively correlated with mean water column temperature. Mean ebullition rates for all study sites (n = 12) were positively correlated with mean sediment carbon content. Mean chlα was negatively correlated with both mean sediment CH4 production and ebullition rates for eutrophic lakes only (n = 3). Temporal variability may have been important for understanding the relationships between chlα, sediment CH4 production rates, and ebullition rates in NH study lakes. Lakes in Sweden showed no significant correlations between sediment CH4 production rates, ebullition rates, water chemistry (chlα, total nitrogen and phosphorus, turbidity, dissolved organic carbon, chloride, pH, conductivity, water temperature, lake bottom dissolved oxygen), and sediment chemistry (carbon, nitrogen, carbon:nitrogen), highlighting the need for further investigation of sediment dynamics and spatial variability. As climate warming accelerates cultural eutrophication, the relationships between lake productivity, sediment CH4 production, and ebullition will be increasingly important for global atmospheric CH4 emissions from lakes.

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