Graduate Student Seed Grant Projects

Assessing the effects of freshwater plankton food webs on methane emissions


Graduate Students: Steven McBride, Jonathan Doubek, Ryan McClure, Fadoua El Moustaid, Biological Sciences;
Faculty Mentors: Michael Strickland, Cayelan Carey, Leah Johnson, and Dana Hawley, Biological Sciences


Methane (CH4) is an important greenhouse gas because it has 34X greater radiative forcing than CO2.  It is estimated that 103 Tg of CH4 year-1 is released into the atmosphere from freshwater ecosystems. CH4 production primarily occurs in anaerobic environments, such as within lake sediments, and diffuses into the water column. Once in the water column, CH4 either effluxes to the atmosphere or is oxidized into CO2 by methane oxidizing bacteria (MOB). There are several abiotic factors that control MOB abundance5, however, how biotic interactions affect MOB abundances and CH4 emissions remains unclear.

Zooplankton and phytoplankton play critical roles in freshwater ecosystem functioning and may directly influence MOB abundance. MOB abundance and CH4 efflux are linked to the abundance of Daphnia, a large grazing zooplankton7. However, other zooplankton groups like rotifers are smaller and graze more heavily on bacteria. Furthermore, phytoplankton can have both positive and negative taxon specific effects on bacterial populations9. However, the relationships with these other zooplankton groups and phytoplankton with MOB and CH4 have not been investigated. Manipulating plankton trophic structure could provide insight that is vital to our understanding of the biotic processes affecting CH4 emissions.

We propose to combine laboratory experiments and mathematical modeling to address three research questions:

Q1: How does MOB abundance change with different plankton combinations?

Q2: How do CH4 concentrations vary with changes in plankton communities?

Q3: How does zooplankton size class affect MOB abundance and CH4 efflux?

The experiments will run for 14 days each. We will measure temperature and Dissolved oxygen daily. We will use our observed data from the experiment to answer the three questions above by developing a mathematical model describing MOB activity and their interactions with the planktonic community. A sensitivity analysis will be performed to identify the key elements directly affecting CH4 efflux changes. Moreover, we will use statistical tools (R Core Team, 2016) to analyze our model. The goal of this study is to determine model variants that are most effective at influencing CH4 efflux.