Details

Autor(en) / Beteiligte

• Trimmer, Mark
• Hildrew, Alan G.
• Jackson, Michelle C.
• Pretty, James L.
• Grey, Jonathan

Titel

Evidence for the Role of Methane-Derived Carbon in a Free-Flowing, Lowland River Food Web

Ist Teil von

• Limnology and oceanography, 2009-09, Vol.54 (5), p.1541-1547

Ort / Verlag

Waco, TX: American Society of Limnology and Oceanography

Erscheinungsjahr

2009

Quelle

Wiley-Blackwell Journals

Beschreibungen/Notizen

• We measured the δ¹³C values of dominant primary consumers and their potential food sources in a groundwater-fed lowland river. The δ¹³C of most consumers, such as Gammarus and Simulium, reflected that of the dominant forms of photosynthetic production, whereas the cased larvae of two caddis flies (Agapetus and Silo) were consistently ¹³C depleted (mean δ¹³C: –41.2‰ and –40.4‰, respectively) throughout the year. The river water was supersaturated (approximately 50 times atmospheric) with methane, reflecting both super saturation in the ground water and local production in fine sediments. We measured appreciable rates of methane oxidation, relative to water only controls, in the biofilms on gravel, on the caddis fly cases, and on the bottom of larger rocks. In addition, there was a marked difference in the ratio of methane-oxidizing potential to chlorophyll across those substrata. This ratio was below detection in the biofilm (i.e., no methane oxidation) on the tops of rocks, greater on the bottom of rocks, and maximal for the gravels and the caddis cases. If the caddis larvae acquire most of their carbon by grazing the tops of such rocks (where they are normally found), then they must acquire their depleted δ¹³C values by occasionally grazing biofilm where the ratio of methane oxidation to chlorophyll was much greater, and the most likely candidate is from their own or conspecifìc cases. Grazing methane-oxidizing bacteria could provide the caddis larvae with up to 30% of their carbon, which could represent a true subsidy from an ancient groundwater source.