A taxon-specific analysis of chironomid δ13C to assess carbon cycling of Blakemere Moss during the early Holocene

Weston, Kyle and Wynn, Peter and Barker, Philip (2022) A taxon-specific analysis of chironomid δ13C to assess carbon cycling of Blakemere Moss during the early Holocene. Masters thesis, Lancaster University.

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Abstract

Chironomid remains of the Chironomus genus and Chironomini tribe were extracted and studied for carbon isotopic content from a lake sediment sequence from Blakemere Moss during the early Holocene (10,743 to 10,482 Cal BP). Evidence derived from bulk geochemical proxies and chironomid assemblage was used to elucidate the factors that influenced the chironomid isotopic content. The spatial heterogeneity of carbon processing was revealed by vastly different carbon isotopic signatures (Δδ13CHC; Δδ13CChironomus – Chironomini = –0.7 to 7.0‰). A climatic amelioration beginning the sequence, indicated by a rapid increase in chironomid-inferred temperatures, was mirrored by a rapid fall in Chironomus δ13CHC and δ13COM with the former exhibiting the greater 13C depletion. This indicates that in our shallow paleolake, an increase in methane-derived carbon to Chironomus is likely linked to a strengthened summer thermal stratification. Due to the hydrologically closed nature of Blakemere Moss, a small shift in precipitation/evaporation balance is thought to have induced an ecosystem state shift from algal to macrophyte dominance and increased faunal diversity, indicated by an increase in C/N and δ15N reduction. Despite a concurrent shift in the dominating functional feeding group from collectors to shredders, Chironomini δ13CHC continued to represent the δ13C of aquatic organic matter, indicating that bulked samples of littoral dwelling Chironomini can be used to faithfully reconstruct the δ13C of aquatic organic matter through time. This supports the use of littoral-dwelling Chironomini for tracing temporal variations of aquatic organic matter, and for quantifying methane-derived carbon uptake via ingestion of methane-oxidising bacteria in isotope mixing models.