Novel soil ecosystems created by natural gas leaks

Background/Question/Methods:

We investigated the impacts of natural gas leaks from an urban distribution pipeline system on soil processes. We conducted this study in Boston, Massachusetts, one of the oldest cities in the United States. Boston has an aging natural gas distribution infrastructure, which provides an ideal environment in which to investigate the effects of pervasive natural gas leaks on urban ecosystems. In this study we addressed four questions: [1] Do soils exposed to elevated methane exhibit unique soil properties, microbial community structure, and/or microbial community composition? [2] What role does the microbial community play in mitigating or enhancing methane flux to the atmosphere? [3] Does vegetation play a role in moving methane into the atmosphere? [4] Are there correlations between gas flux rate or concentration and soil/vegetation impacts? Preliminary results from enzyme assay experiments characterize the enzymatic activity of the microbial community found in gassed soils. Carbon and nitrogen contained within soil microbial biomass is estimated using the chloroform fumigation-extraction method. Finally, gassed pot experiments demonstrate the impact of methane on urban trees. 

Results/Conclusions:

Preliminary data show that gassed soils often exceed 90% methane and depress oxygen gas below 10%. Gassed soils are desiccated and anoxic, creating a virtually unexplored extremophile domain. Soil at leak sites often appears black and viscous, forming a crusty substance at the soil’s surface. Preliminary analyses of this soil reveal elevated levels of potassium and low levels of nitrate (NO3-N). While vegetation at leak sites suffered increased rates of mortality, preliminary investigation of still-living tissues reveals that methane at leak sites is able to invade below- and above-ground tissues. Trees and Ganoderma fungus at leak sites exhibit elevated levels of methane in their tissues and may act as conduits, moving methane from the soil into the atmosphere. Characterization of the effects of natural gas on soils, soil biota, and vegetation will inform carbon budget forecasts in urban centers, assist city planners in ameliorating affected soils and vegetation, and contribute to our understanding of methane’s role in global climate change.