Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Geography

Collaborative Specialization

Environment and Sustainability

Supervisor

Branfireun, Brian A.

Abstract

Northern peatlands store one third of the world’s soil carbon (C), as they remove more C from the atmosphere via photosynthesis than they release to the atmosphere through ecosystem respiration and methane (CH4) production. Climate change threatens this function by stimulating C release from peatland stores as peat temperatures warm and soil moisture is reduced. Ground heating of +4 °C above ambient peat temperatures was initiated in a Sphagnum moss-dominated, nutrient poor fen and a Carex sedge-dominated, intermediate nutrient fen. Over one growing season, Carex fen heated plots had increases in photosynthesis (+23%), ecosystem respiration (+22%), and CH4 production (+57%). While gas fluxes did not change at the Sphagnum fen, belowground organochemical properties revealed heated plots contained more phenolics, which are associated with belowground sedge root growth. Although Sphagnum fens may take longer to respond to climate change, both fen types are at risk for becoming weaker C sinks in the future.

Summary for Lay Audience

Greenhouse gases, such as carbon dioxide (CO2) and methane (CH4) are molecules in the atmosphere that trap heat, warming the Earth. Peatlands are globally widespread ecosystems that accumulate dead plant matter (“peat”) because the waterlogged conditions and cool temperatures slow down decomposition. Peatland plants remove CO2 from the atmosphere through photosynthesis and store it in the ground, which acts as a cooling mechanism for Earth’s surface temperature. As climate change warms the planet, plants in peatlands may grow more and therefore remove even more CO2 from the atmosphere, but if soil warms up and dries out the carbon stores in peatlands may break down and be released to the atmosphere as CO2 and CH4. In this thesis, ground heating rods were used to warm up the soil of two peatland types, a moss-dominated and a sedge-dominated peatland, to determine if future peatlands might lose their carbon stores. I found that in the sedge peatland, plants grew more under warmer conditions and therefore removed more CO2 from the atmosphere, but soil microbes were more active and also released more CO2 and CH4 to the atmosphere. In the moss peatland, low soil nutrients resulted in no change in the amount of greenhouse gases released to the atmosphere, but sedges began to establish communities at this peatland. Since sedges provide ample nutrients to the soil, in the future there will likely be enough soil nutrients to fuel more CO2 and CH4 release to the atmosphere. Therefore, both peatland types may begin storing less carbon over the next century and instead begin emitting more greenhouse gases, which could increase the amount of greenhouse gases trapping heat in the atmosphere and further the rate of global warming through a positive feedback effect.

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