Methane is an important greenhouse gas whose atmospheric concentration is currently rising by about 1 percent every year. Methane also is an important component of the carbon cycle in the earth's water bodies. The goal of this doctoral dissertation research project is to measure the magnitude, rate, and spatial distribution of methane that is lost to the atmosphere as opposed to that lost to oxidation by micoorganisms in a freshwater lake. Quantifying methane processes in natural waters is difficult because of the patchy and transient nature of production, emission, and consumption. One hypothesis to be tested during this project is that bubbling -- a spatially and temporally heterogenous process -- is the major mode of methane release to the atmosphere from the bottom of the lake. The doctoral candidate will use modern sensor technology to obtain continuous measurements of methane bubbling. Custom-made conical chambers will be used to capture the bubbles and will be deployed at various locations in the lake. The chambers will be equipped with pressure sensors and infra-red based sensors to continuously measure the volume of gas that is collected and the average concentration of methane present in the bubbles. Software will be developed to analyze the data to detect and record major ebullition events. In addition, water samples will be collected via a syringe-based sampling device, and the methane present in the samples will be analyzed using gas chromatography. The samples also will be used to test the extent of methane oxidation at various lake depths through incubation experiments. In order to provide a context for the above measurements, ancillary data such as water quality parameters (e.g. water temperature, dissolved oxygen), atmospheric conditions (e.g. air temperature, air pressure) and major ions (e.g. sulfate, nitrate) will also be collected. The primary field site for this project is the methane-rich Upper Mystic Lake in Woburn, Massachusetts.
The release of methane to the atmosphere not only affects the planetary radiation budget; it also represents a loss of carbon, reducing power, and energy from aquatic ecosystems. The amount of methane currently emitted from water bodies, and freshwater lakes in particular, is thought to be greatly underestimated due to the lack of continuity in measurement techniques used in prior methane studies. The results of this research will help bridge existing gaps in the methane-driven component of global warming. Such knowledge is essential in formulating public policies on climate change mitigation that appropriately prioritize management efforts. Because methane in lakes could represent a locally useful alternate source of fuel; an enhanced comprehension of methane processes would help determine the feasibility of harvesting this fuel as a benign source of power for surrounding areas. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.
