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The ecological role of methane dynamics in the Nyack aquifer of the Middle Fork of the Flathead River, Montana Amanda G. DelVecchia, Jack A. Stanford, Brian L. Reid, Jon Graham, Bonnie K. Ellis Canada Nyack WA MT ID Stanford, J. A., M. S. Lorang, and F. R. Hauer. 2005. The shifting habitat mosaic of river ecosystems. Verh. Internat. Verein. Limnol. 29:123–136. Ecology of the Nyack aquifer A well-oxygenated, carbon-limited, and heterogeneous environment n = 552 individuals Flowpath Channel – aquifer exchange Vadose– aquifer interaction 1Valett et al. 2013 Ecosystems, Smith et al. 2011 Geo. Chem. Acta et al. 1993 J.NABS 3Craft et al. 2002 FW Biol., 4Helton et al. 2015 L&O 2Ellis •Generally well oxygenated1 •Low DOC (<2mg/L) •Low microbial productivity2 •Limited by labile organic carbon3 •Labile DOC increases along flowpaths4 Ecology of the Nyack aquifer Diverse and abundant macroinvertebrates use methane-derived carbon Amphibitic stonefly species that mature for 1-3 years in the aquifer: •Isocapnia grandis •Isocapnia crinita •Isocapnia integra •Paraperla frontalis •Kathroperla perdita DelVecchia, Amanda G., Jack A. Stanford, Xiaomei Xu. ‘Ancient methane-derived carbon subsidizes a contemporary food web’. Nature Communications. In review. Ecology of the Nyack aquifer Diverse and abundant macroinvertebrates use methane-derived carbon Methanogens requires anoxia production Dissolved methane requires DO consumption Methane-oxidizing bacteria Direct or indirect consumption DelVecchia, Amanda G., Jack A. Stanford, Xiaomei Xu. ‘Ancient methane-derived carbon subsidizes a contemporary food web’. Nature Communications. In review. How is the trophic and community ecology of hyporheic stoneflies related to aquifer methane dynamics? I. What are the trophic positions of each stonefly species in the context of the aquifer food web? II. How are stonefly species assemblages related to biogeochemical variables? Methods • • • • Sampled 20 3-inch wells Sampled 1 and 4m below the baseflow water table every 6 weeks in 2014-2015 for: • Dissolved oxygen concentration (DO) • Dissolved organic carbon concentration (DOC) • Dissolved methane concentration (methane) • Temperature Used standard diaphragm pumping method to collect stoneflies Stable isotope analyses (δ13C, δ15N) of stonefly biomass, OM pools, meiofauna I. What are the trophic positions of the stonefly species collected? Trophic positions vary by species What are the trophic positions of stonefly species? δ15N (‰) Raw stable isotope values show distinct trophic positions • • • Stoneflies have significantly different trophic positions Arranged on a gradient of methanederived carbon contribution More depleted in 13C than any other OM pools δ13C (‰) What are the trophic positions of stonefly species? δ15N (‰) Raw stable isotope values show distinct trophic positions • MOB preferentially assimilate 14N, causing them to have lower δ15N values • Expect positive relationship between δ13C, associated with methane-derived carbon in biomass, and δ15N • Need to assess relative trophic levels by taking this into account δ13C (‰) What are the trophic positions of stonefly species? Stonefly species show distinct trophic positions after correction for MDC in biomass δ15N (‰) Slopes vary by taxa n = 719, R2 = 0.627, p < 0.0001 • Linear relationship because proportional (e.g. proportion basal resources MOB proportion of N in biomass depleted as a result) • Varying intercepts because proportional relationship should remain constant between species δ13C (‰) What are the trophic positions of stonefly species? Intercepts Intercept differences confirm distinct trophic positions • Relative positioning of species remains consistent • Intercepts are significantly different, confirming distinct trophic positions even with more conservative approach δ13C (‰) What are the trophic positions of the stonefly species collected? Trophic positions vary significantly by species, consistent with differing use of methane derived carbon resources and differing trophic levels. II. How are species assemblages related to measured biogeochemical variables? Methane concentration is a significant predictor of species assemblages How are stonefly species assemblages structured? Non-metric multidimensional scaling to determine relationship between community structure (species assemblages) and biogeochemical variables Log(methane) DO DOC Temperature Dayterm Well NMDS1 0.19 -0.34 -0.09 0.22 -0.15 NMDS2 0.98 -0.94 1.00 0.97 -0.99 R2 0.160 0.169 0.067 0.033 0.055 0.310 Pr(>r) 0.002 0.002 0.074 0.304 0.134 0.060 Log(methane) DO DOC Temperature Dayterm Well NMDS2 0.82 -0.99 0.97 0.81 -0.82 NMDS3 0.58 -0.16 -0.23 -0.58 0.57 R2 0.221 0.139 0.070 0.044 0.077 0.192 Pr(>r) 0.001 0.005 0.060 0.180 0.063 0.762 How are species assemblages related to measured biogeochemical variables? Assemblages are structured in part by methane and DO concentrations, with methane concentrations alone explaining 19% of variation. Conclusions •Stonefly species have unique trophic positions, consistent with differing contributions of methane derived carbon to biomass and differing trophic levels. •Stonefly species assemblages are structured in relation to biogeochemical variables, especially methane and DO concentrations. Implications: •Stonefly species can coexist in the aquifer environment because their ecological niches are unique in terms of aquifer biogeochemistry, underscoring the functional diversity present in the aquifer ecosystem. •Because methane is produced in anoxia but converted into a carbon source that is accessible to the stoneflies in oxic conditions, and because stoneflies have varying use of methane derived carbon resources, biogeochemical heterogeneity is important for maintaining macroinvertebrate species diversity in the aquifer. Acknowledgements Advisor: Dr. Jack Stanford Flathead Lake Biological Station, Polson, MT Dr. Bonnie Ellis Dr. Jon Graham Dr. Gordon Luikart Dr. Ryan Jones All FLBS faculty and staff Dr. Shawn Devlin Adam Baumann and the FLBS Freshwater Research Laboratory Dr. Ashley Helton Dr. Geoffrey Poole Dr. Anne Hershey Dr. Steve Whalen Dr. Tim McDermott The Dalimata Family, West Glacier, MT Field and lab Assistants: Hannah Coe, Amelia Schirmer, Matt Bambach, Chad Reynolds, Neal Jacobi, Clinton Begley, Chris Johnson, Emily Winter, Cailey Philmon, and all others who have helped Funding provided by the Jessie M. Bierman Professorship and a philanthropically funded graduate fellowship from the University of Montana Thank you How might 13C depletion occur in stoneflies? Frequency within microbial community (%) 16S analysis of microbial community composition in gut contents n=3 n=4 Methanogenic/ methanotrophic taxa n=4 n=2 n=1 • Stoneflies consume methanogens and methane oxidizing bacteria • Do they preferentially consume these microbes? I. grandis P. frontalis