Seasonal increase of methane in sediment decreases δ13C of larval chironomids in a eutrophic shallow lake

Abstract

Recent studies have shown that larval chironomids assimilate 13 C-depleted carbon derived from biogenic methane by feeding on methane-oxidizing bacteria (MOB). The dietary contribution of MOB is known to be maximized in the autumn overturn period or winter in eutrophic dimictic lakes due to the increase of MOB biomass following the supply of oxygenated water, but in polymictic lakes, such seasonal variability has not been revealed. We investigated the seasonal patterns of larval d 13 C and methane concentrations in the sediment of a eutrophic polymictic lake, Izunuma, Japan. Larval d 13 C decreased in late summer and autumn. Methane concentrations above a 6 cm depth peaked in late summer or autumn, while those in the 10-11-and 20-21-cm layers peaked in October. Negative correlations between methane concentrations in the 5-6/10-11-cm layers and larval d 13 C were found. This suggests that an increase in the supply of methane stimulated the activity of MOB in a polymictic lake, where water above the lake bottom rarely became anoxic because of frequent overturn, thus increasing the dietary contribution of MOB to larval chironomids.

Biogenic methane contributes to the food web of a large, shallow lake

“…However, Yasuno et al . () found that the frequent mixing of the water column, providing oxygen for methanotrophs in the sediment, sustained their activity over a longer period in a seasonal cycle in shallow polymictic Lake Izunuma (Japan), a lake with conditions similar to the main part of Lake Võrtsjärv. Deines et al .…”

“…Even less is known about the food web interactions that enhance methane‐carbon transfer up food chains. The few existing studies, however, indicate that biogenic methane can also form an important carbon supplement for food webs (MOB, invertebrates, higher trophic levels) in shallow lakes (Grey et al ., ; Sanseverino et al ., ; Yasuno et al ., ).…”

Differences in feeding behaviour amongChironomusspecies revealed by measurements of sulphur stable isotopes and cadmium in larvae

“…In lakes where methane-derived C is important, the d 13 C signatures of Chironomus larvae tend to be much more negative (À56 to À46&; Deines et al, 2009;Eller et al, 2005;Kelly et al, 2004). First, we collected Chironomus larvae in the spring when populations of methane-oxidising bacteria are likely to be smaller than those in the late summer to autumn (Jones & Grey, 2011;Yasuno et al, 2012) when methane production is thought to reach a peak (Thebrath et al, 1993;Casper et al, 2000). First, we collected Chironomus larvae in the spring when populations of methane-oxidising bacteria are likely to be smaller than those in the late summer to autumn (Jones & Grey, 2011;Yasuno et al, 2012) when methane production is thought to reach a peak (Thebrath et al, 1993;Casper et al, 2000).…”

The Incredible Lightness of Being Methane-Fuelled: Stable Isotopes Reveal Alternative Energy Pathways in Aquatic Ecosystems and Beyond

“…In the benthos, there is also typically a more consistent supply of 13 C-enriched phytoplankton production from above which will "swamp" the lower δ 13 C values from MOB. Examples of such lakes with permanently oxic sediment surface layers in which MDC has been shown to make only a limited (maximum ∼20%) or negligible contribution to chironomid biomass include Großer Binnensee and Schöhsee in north Germany (Grey et al, 2004b;Deines et al, 2007b), Lough Neagh and Rostherne Mere in the UK (Kelly et al, 2004), Izunuma in Japan (Yasuno et al, 2012), and Võrtsjärv in Estonia Cremona et al, 2014). Interestingly, the latter lake was sampled at various sites and it was only at one particular site dominated by vegetation that low δ 13 C values were recorded in both zooplankton and chironomids.…”