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Philben Research Group

Overview

Peatlands are hotspots for natural carbon sequestration and contain about twice as much carbon as there is CO₂ in the atmosphere. However, many are located in the boreal and Arctic regions, which are warming much more rapidly than the global average. This rapid warming could disrupt the carbon balance of peatlands, turning them from carbon sinks to carbon sources. It could also increase emissions of other powerful greenhouse gasses such as methane and nitrous oxide.

The Philben Group is investigating these hypothesized impacts using a climate transect of Michigan peatlands. In a project funded by a prestigious NSF CAREER award, we have established a network of seven bog field sites, spanning from Portage in the south, to Newberry (in the Upper Peninsula) in the north. The sites vary by 5掳C in mean annual temperature, approximately equivalent to warming expected over the next century in Michigan. Thus, the natural climate variability observed along the transect can be used as a 亚洲色吧渟pace-for-time亚洲色吧� experiment to evaluate how future warming will impact a range of biogeochemical processes in these critical ecosystems.

In addition, southern Michigan lies at the southern edge of the climate window for Sphagnum-rich bogs, and has already experienced about 1掳C of warming since 1850. This could make them particularly vulnerable to ecosystem state change. These bogs are therefore useful sentinels for the larger peatland complexes further north, which contain globally significant carbon stocks and will begin to experience similar climate conditions within the next 100 years.

We are using the Michigan peatland climate transect to investigate how several processes in peatlands are responding to warming:

Impact of warming on peatland methane emissions

Methane is a potent greenhouse gas, with warming potential approximately 30 times greater than carbon dioxide over a 100 year timeframe. Wetlands are the largest natural source of methane because it is produced by methanogenic archaea in waterlogged, anoxic soils during anaerobic respiration. The impact of climate change on peatland methane emissions is uncertain because it will depend on the temperature sensitivity of both methanogenesis and methanotrophy (consumption of methane). In addition, changes in water balance could alter the waterlogged portion of the peat profile. We are using the climate variability of the transect to evaluate the relationship between temperature, water table position and methane emissions using a combination of field observations and lab experiments.

Warming effects on peatland nitrogen availability

Nitrogen is an essential nutrient for both plants and microorganisms, and it limits growth in many ecosystems. It is relatively abundant in peatlands, but is mostly found in organic compounds that are not readily assimilated into cells. These compounds must be degraded (mineralized) before they are available to support plant or microbial growth. Both the production and decomposition of organic matter are therefore dependent on the turnover of these organic nitrogen compounds, so understanding their dynamics is essential for predicting future carbon cycling in these ecosystems. We are using measurements of in situ nitrogen mineralization across the transect to infer the effect of climate change on nitrogen availability under natural field conditions.

Changes in the net ecosystem carbon balance

The net carbon balance of a peatland is the difference between carbon inputs to the soil (through plant growth) and carbon losses from the soil (through microbial decomposition of organic matter). Both are expected to increase with warming, making the change in the net balance difficult to predict. We are assessing the changes in the carbon balance of our peatland sites using a combination of direct and indirect techniques. Direct approaches involve measuring gas fluxes into and out of the soil at a variety of scales, while indirect techniques utilize radiometric dating of peat cores to infer the net carbon balance over the history of the peatlands.

Join the Philben Group

We are always looking for new lab members! The group is interdisciplinary and there are many roles to fill, so there are opportunities available for students with interests ranging from analytical chemistry to geology to ecology. Email Professor Philben to discuss current opportunities.