Conference Presentations by Felicity Shelley
The role of inland waters in carbon cycling is poorly quantified. Most rivers are supersaturated ... more The role of inland waters in carbon cycling is poorly quantified. Most rivers are supersaturated with methane and carbon dioxide relative to the atmosphere and we have measured methane oxidation in the riverbeds of over 20 rivers. We measured the methane concentration and potential for methane oxidation in the top 15cm of a riverbed over an annual cycle, in order to estimate the amount of organic carbon fixed by methane oxidation relative to that fixed via photosynthesis. We quantified the photosynthetic potential of the gravel bed epilithon and modelled the riverbed light regime.
We found high potential for methane oxidation in the subsurface gravels where darkness completely prevents photosynthetic production. The methane concentration (100nM) and potential for methane oxidation peaked in mid-summer when the shading was greatest. Beneath the uppermost layer of sediment methane oxidation is responsible for all new carbon fixation. Considering the high photosynthetic production at the surface, 8% of organic carbon across the riverbed is fixed by methane oxidation. Our results indicate that a significant portion of river food webs could be supported by chemosynthetic carbon.
Papers by Felicity Shelley
Freshwater Biology, 2019
1) Stream ecosystems are supported by both 'green' (i.e, based on grazing) and 'brown' (i.e. detr... more 1) Stream ecosystems are supported by both 'green' (i.e, based on grazing) and 'brown' (i.e. detritus) food webs, whereas methane-derived carbon is not considered generally to be important; here we add circumstantial evidence for this potential 'third way'. 2) Grazing cased-caddis (Trichoptera) larvae in the family Glossosomatidae can be very abundant in springs and headwaters and frequently have much lower stable carbon isotope ratios (i.e. they are depleted in the heavier 13 C stable isotope) than the biofilm ('epilithon') on the upper surfaces of the stones on which they live, and which is their presumed diet. Evidence for similar isotopic depletion in other lotic invertebrates is currently limited, however; even for glossosomatids it has been observed so far only in some streams draining the southern English cretaceous chalk and in a few headwaters in northern California. If this phenomenon proves to be more widespread, among streams or taxa, it could imply a more general underpinning of stream food webs by 'isotopically light' carbon derived from methane and accessed via consumers feeding on methanotrophic bacteria. 3) Here we sampled 58 stream sites to examine whether caddis larvae are also 13 Cdepleted in streams draining other geologies. We focused mainly on carboniferous limestone and sandstone, as well as on further chalk streams representative of most of the British chalk aquifer: together, these new sites covered an area of almost 90,000 km 2 , around three times greater than that surveyed previously. 4) At all 58 sites methane gas was supersaturated relative to the atmospheric equilibrium, and at 49 of them larvae were conspicuously 13 C-depleted (from -17.5 to -3.6‰) relative to the bulk epilithon (components of which we know can oxidise methane). Although still most pronounced on chalk, this phenomenon was geographically and geologically much more widespread than shown previously and suggests methane-derived carbon could indeed play a prominent role in stream food webs (i.e. the 'third way').
Proceedings of the Royal Society B: Biological Sciences, 2014
Methane is oversaturated relative to the atmosphere in many rivers, yet its cycling and fate is p... more Methane is oversaturated relative to the atmosphere in many rivers, yet its cycling and fate is poorly understood. While photosynthesis is the dominant source of autotrophic carbon to rivers, chemosynthesis and particularly methane oxidation could provide alternative sources of primary production where the riverbed is heavily shaded or at depth beneath the sediment surface. Here, we highlight geographically widespread methanotrophic carbon fixation within the gravel riverbeds of over 30 chalk rivers. In 15 of these, the potential for methane oxidation (methanotrophy) was also compared with photosynthesis. In addition, we performed detailed concurrent measurements of photosynthesis and methanotrophy in one large chalk river over a complete annual cycle, where we found methanotrophy to be active to at least 15 cm into the riverbed and to be strongly substrate limited. The seasonal trend in methanotrophic activity reflected that of the riverine methane concentrations, and thus the high...
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Conference Presentations by Felicity Shelley
We found high potential for methane oxidation in the subsurface gravels where darkness completely prevents photosynthetic production. The methane concentration (100nM) and potential for methane oxidation peaked in mid-summer when the shading was greatest. Beneath the uppermost layer of sediment methane oxidation is responsible for all new carbon fixation. Considering the high photosynthetic production at the surface, 8% of organic carbon across the riverbed is fixed by methane oxidation. Our results indicate that a significant portion of river food webs could be supported by chemosynthetic carbon.
Papers by Felicity Shelley
We found high potential for methane oxidation in the subsurface gravels where darkness completely prevents photosynthetic production. The methane concentration (100nM) and potential for methane oxidation peaked in mid-summer when the shading was greatest. Beneath the uppermost layer of sediment methane oxidation is responsible for all new carbon fixation. Considering the high photosynthetic production at the surface, 8% of organic carbon across the riverbed is fixed by methane oxidation. Our results indicate that a significant portion of river food webs could be supported by chemosynthetic carbon.