https://hdl.handle.net/10388/14566

Taylor, M. (2023). Biogenic greenhouse gas dynamics for wetland ponds in the Prairie Pothole Region of Canada. University of Saskatchewan https://hdl.handle.net/10388/14566

Inland waters are important processors in global biogeochemical cycles, and their many roles include the transformation of organic matter into greenhouse gases (GHGs) which can then be released to the atmosphere. While aquatic release of biogenic GHGs methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) can be perceived as less desirable under climate change, this behaviour represents a poorly quantified flux, and one that is important in the context of carbon (C) storage in sediments and wetland soils. My research aimed to characterize the behaviour of GHG in shallow wetland ponds across the Canadian Prairie Pothole Region using two approaches. I investigated dissolved GHG concentrations in surface waters spanning chemical gradients and seasons using a regional survey (Chapter 2), and examined multiple pathways of GHG exchange with the atmosphere at four wetlands (Chapter 3). Through the first approach, CH4 was found to be consistently supersaturated in ponds and was strongly related to SO42– concentrations. Sulphate appears to act as a strong thresholding agent, limiting diffusive CH4 release at concentrations above ~175 mg L−1. While the ponds exhibited both sink and source behaviour for CO2 and N2O, CO2 was strongly linked to pH, and seasonal patterns highlight the potential for greater GHG exchange with the atmosphere during warmer months. In the focused study of four ponds of different hydrochemical character, it was clear that the diffusive pathway, which has been most commonly measured for most waterbodies globally, often has lower rates of exchange with the atmosphere compared to other pathways for CH4 (ebullition), CO2 and N2O (exposed sediments). While some of these releases can be transient, measuring fluxes from multiple pathways provides valuable context for the range of GHG fluxes possible for these systems. This is also important in the context of the hydrological behaviour of these systems, where ponded surface water can be greatly reduced seasonally, and during periods of extended drought. This research fills an important knowledge gap about the GHG dynamics of Prairie pothole ponds, identifying important links between GHG behaviour and water chemistry, and beginning to disentangle the roles of different flux pathways. Ultimately this work will contribute to enhanced regional estimates of the role of these landscapes as a climate feedback.

This thesis is under an embargo. Access to the abstract and all associated documents will not be permitted until 2024-04-13.