DOES METHANE CONTRIBUTE SIGNIFICANT CARBON TO GREAT PLAINS RIVER FOOD WEBS? STABLE ISOTOPE EVIDENCE AND FUTURE DIRECTIONS
Methane concentrations are frequently supersaturating in lotic waters, a fact somewhat surprising considering that running waters are often well oxygenated. Methane-oxidizing bacteria (MOBs) convert this methane into carbon that is consumable to higher trophic levels, such as invertebrates. How much of the food web trophic base is fueled by this methane-derived carbon (MDC), and what factors might determine contributions of MDC, if any? We address these questions in 14 sites in two northern Great Plains rivers (Little Missouri, Niobrara) using stable isotope signatures (del-13C) of basal resources and invertebrate consumers. Because methane typically has a distinctively low del-13C (compared to stream resources) and is further heavily fractionated by MOB use, consumers with high MDC have suspiciously low del-13C. We used simple mixing models to estimate the proportion of MDC to multiple invertebrate consumers at each site, analyzed these data in light of several possible predictors (geomorphology, nutrient and organic matter quantity), and suggest future directions that will be key to determining the prevalence and importance of methane in lotic food webs.
Caleb J. Robbins (Primary Presenter/Author), University of Kansas, Caleb_Robbins@ku.edu;
Jackob A. Lutchen (Co-Presenter/Co-Author), University of Kansas, firstname.lastname@example.org;
James H. Thorp (Co-Presenter/Co-Author), University of Kansas/Kansas Biological Survey, email@example.com;