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- All Subjects: Soil Sciences
- Creators: Childers, Daniel L.
Permafrost degradation is leading to rapid wetland formation in northern peatland ecosystems, altering the role of these ecosystems in the global carbon cycle. I reviewed the literature on the history of the MPP theory, including tracing its origins to The Second Law of Thermodynamics. To empirically test the MPP, I collected soils along a gradient of ecosystem development and: 1) quantified the rate of adenosine triphosphate (ATP) production--literally cellular energy--to test the MPP; 2) quantified greenhouse gas production (CO2, CH4, and N2O) and microbial genes that produce enzymes catalyzing greenhouse gas production, and; 3) sequenced the 16s rRNA gene from soil microbes to investigate microbial community composition across the chronosequence of wetland development. My results suggested that the MPP and other related theoretical constructs have strong potential to further inform our understanding of ecosystem development. Soil system power (ATP) decreased temporarily as the ecosystem reorganized after disturbance to rates of power production that approached pre-disturbance levels. Rates of CH4 and N2O production were higher at the newly formed bog and microbial genes involved with greenhouse gas production were strongly related to the amount of greenhouse gas produced. DNA sequencing results showed that across the chronosequence of development, the two relatively mature ecosystems--the peatland forest ecosystem prior to permafrost degradation and the oldest bog--were more similar to one another than to the intermediate, less mature bog. Collectively, my results suggest that ecosystem age, rather than ecosystem state, was a more important driver for ecosystem structure and function.
Constructed treatment wetlands (CTW) have been a cost-efficient technological solution to treat different types of wastewater but may also be sources of emitters of methane (CH4) and nitrous oxide (N2O). Thus, my objective for this dissertation was to investigate CH4 and N2O fluxes via multiple pathways from the Tres Rios CTW located in Phoenix, AZ, USA. I measured gas fluxes from the CTW along a whole-system gradient (from inflow to outflow) and a within-marsh gradient (shoreline, middle, and open water sites). I found higher diffusive CH4 release in the summer compared to spring and winter seasons. Along the whole-system gradient, I found greater CH4 and N2O emission fluxes near the inflow compared to near the outflow. Within the vegetated marsh, I found greater CH4 emission fluxes at the vegetated marsh subsites compared to the open water. In contrast, N2O emissions were greater at the marsh-open water locations compared to interior marsh. To study the plant-mediated pathway, I constructed small gas chambers fitted to Typha spp. leaves. I found plant-mediated CH4 fluxes were greater near the outflow than near the inflow and that CH4 fluxes were higher from lower sections of plants compared to higher sections. Overall, Typha spp. emitted a mean annual daily flux rate of 358.23 mg CH4 m-2 d-1. Third, using a 30-day mesocosm experiment I studied the effects of three different drydown treatments (2, 7, 14 days) on the fluxes of CH4 and N2O from flooded CTW soils. I found that CH4 fluxes were not significantly affected by soil drydown events. Soils that were dry for 7 days shifted from being N2O sources to sinks upon inundation. As a result, the 7-day drydown soils were sinks while the 14-day drydown soils showed significant N2O release. My results emphasize the importance of studying ecological processes in CTWs to improve their design and management strategies so we can better mitigate their greenhouse gas emissions.