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1. Organic matter supply and bacterial community composition predict methanogenesis rates in temperate lake sediments

   https://doi.org/10.1002/lol2.10114  

   Bertolet, Brittni L. ; West, William E. ; Armitage, David W. ; Jones, Stuart E. ( August 2019 , Limnology and Oceanography Letters)

   The objective of our study was to identify environmental conditions that structure lake sediment microbial communities and determine whether community composition explained inter‐lake variation in potential methanogenesis rates. We performed a comparative analysis of microbial communities and methanogenesis rates in 14 lake sediments along gradients of pH and primary productivity. Variation in methanogen community composition and non‐methanogen microbial community composition was best explained by pH and sediment organic matter content. However, these regulators of methanogen community structure were not associated with differences in methanogenesis rates. Instead, variation in lake methanogenesis rates was best explained by proxies for organic matter supplied to sediments (lake chlorophyllaconcentration and sediment pore‐water total phosphorus) and the composition of the non‐methanogen microbial community. Our results suggest a role for sediment bacterial community in influencing methanogenesis via the supply of growth substrates.

    

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2. Microbial community composition, and not pH , influences lake sediment function

   https://doi.org/10.1002/ecs2.4091  

   Bertolet, Brittni L. ; Louden, Sydney I. ; Jones, Stuart E. ( May 2022 , Ecosphere)

   Lake sediment microbial communities vary across ecosystems and are often differentiated across pH. Additionally, these pH‐mediated differences in community composition are often correlated with changes in sediment functioning, such as methane and carbon dioxide production. However, few studies have experimentally tested pH effects on community assembly or considered how microbial community composition influences ecosystem function independent of differences in the environment. We used common garden experiments to test hypotheses about how pH influences microbial community assembly and function in lake sediments. Using inoculum from three acidic lakes and three near‐neutral lakes, we found that both pH environment and inoculum source significantly influenced sediment microbial community assembly. However, inoculum source had a larger effect size for both the sediment methanogen and nonmethanogen communities, indicating important roles of dispersal and drift. Additionally, inoculum source, but not pH environment, significantly influenced sediment methane and carbon dioxide production. This research is one of the first to experimentally test the influence of pH on sediment microbial community composition, and in doing so, we show the community composition significantly influences sediment function independent of pH. Understanding how lake sediment microbial communities are influenced by environment is the first step toward mechanistically linking changes in community composition to ecosystem function, and we provide critical evidence for how changes in microbial community assembly with environmental change will likely alter carbon cycling in lake sediments.

    

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3. Responses by benthic invertebrate community composition to dissolved organic matter in lakes decline substantially above a threshold concentration

   https://doi.org/10.1111/fwb.14211  

   Jane, Stephen F. ; Johnson, Richard K. ; Rose, Kevin C. ; Eklöv, Peter ; Weyhenmeyer, Gesa A. ( January 2024 , Freshwater Biology)

   Dissolved organic matter (DOM), often measured as dissolved organic carbon (DOC), plays a fundamental role in influencing the structure and function of lake ecosystems. Due to the myriad ecosystem effects of DOM, widespread observations of long‐term increasing DOM concentrations have received much attention from ecologists. DOM positively influences primary production and consumer production at low concentrations due to the fertilising influence of bound nutrients. However, beyond a unimodal peak in production, a reduced light environment may result in a negative effect on production. This unimodal model has been largely developed and tested in lakes with low to moderate DOM concentrations (i.e., typically ≤10 mg/L DOC).

   To understand ecological responses in lakes across a larger range in DOM concentrations, we examined the response of benthic invertebrate communities in 148 Swedish lakes with DOM concentrations ranging between 0.67 and 32.77 mg/L DOC.

   We found that increasing DOM concentrations had a strong effect on invertebrate community composition belowc.10 mg/L. Across this range, abundances of individual taxa both increased and decreased, probably in response to environmental change induced by DOM. However, in lakes above this concentration, increasing DOM had minimal influence on community composition.

   As DOM concentrations continue to increase, faunal communities in lakes below this 10 mg/L DOC threshold are likely to undergo substantial change whereas those above this threshold are likely to be minimally impacted.

    

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4. Diverse sediment microbiota shape methane emission temperature sensitivity in Arctic lakes

   https://doi.org/10.1038/s41467-021-25983-9  

   Emerson, Joanne B. ; Varner, Ruth K. ; Wik, Martin ; Parks, Donovan H. ; Neumann, Rebecca B. ; Johnson, Joel E. ; Singleton, Caitlin M. ; Woodcroft, Ben J. ; Tollerson, II, Rodney ; Owusu-Dommey, Akosua ; et al ( October 2021 , Nature Communications)

   Northern post-glacial lakes are significant, increasing sources of atmospheric carbon through ebullition (bubbling) of microbially-produced methane (CH₄) from sediments. Ebullitive CH₄flux correlates strongly with temperature, reflecting that solar radiation drives emissions. However, here we show that the slope of the temperature-CH₄flux relationship differs spatially across two post-glacial lakes in Sweden. We compared these CH₄emission patterns with sediment microbial (metagenomic and amplicon), isotopic, and geochemical data. The temperature-associated increase in CH₄emissions was greater in lake middles—where methanogens were more abundant—than edges, and sediment communities were distinct between edges and middles. Microbial abundances, including those of CH₄-cycling microorganisms and syntrophs, were predictive of porewater CH₄concentrations. Results suggest that deeper lake regions, which currently emit less CH₄than shallower edges, could add substantially to CH₄emissions in a warmer Arctic and that CH₄emission predictions may be improved by accounting for spatial variations in sediment microbiota.

    

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5. Methane and Primary Productivity in Lakes: Divergence of Temporal and Spatial Relationships

   https://doi.org/10.1029/2020JG005864  

   Bertolet, B. L. ; Olson, C. R. ; Szydlowski, D. K. ; Solomon, C. T. ; Jones, S. E. ( August 2020 , Journal of Geophysical Research: Biogeosciences)

   In lakes, the production and emission of methane (CH₄) have been linked to lake trophic status. However, few studies have quantified the temporal response of lake CH₄dynamics to primary productivity at the ecosystem scale or considered how the response may vary across lakes. Here, we investigate relationships between lake CH₄dynamics and ecosystem primary productivity across both space and time using data from five lakes in northern Wisconsin, USA. From 2014 to 2019, we estimated hypolimnetic CH₄storage rates for each lake using timeseries of hypolimnetic CH₄concentration through the summer season. Across all lakes and years, hypolimnetic CH₄storage ranged from <0.001 to 7.6 mmol CH₄ m⁻² d⁻¹and was positively related to the mean summer rate of gross primary productivity (GPP). However, within‐lake temporal responses to GPP diverged from the spatial relationship, and GPP was not a significant predictor of interannual variability in CH₄storage at the lake scale. Using these data, we consider how and why temporal responses may differ from spatial patterns and demonstrate how extrapolating cross‐lake relationships for prediction at the lake scale may substantially overestimate the rate of change of CH₄dynamics in response to lake primary productivity. We conclude that future predictions of lake‐mediated climate feedbacks in response to a shifting distribution of trophic status should incorporate both varying lake responses and the temporal scale of change.

    

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