In:
Freshwater Biology, Wiley, Vol. 62, No. 6 ( 2017-06), p. 1105-1115
Abstract:
Sedimentary geochemical proxies and carbon stable isotopes of subfossil chironomid head capsules (δ 13 C) were combined to reconstruct long‐term changes in organic matter sources contributing to chironomid biomass in two soft‐water lakes (Vosges Mountains, France). Here, we test how basal carbon sources fueling the benthic food web responded to two millennia of environmental changes. Sedimentary organic matter characteristics were strongly variable over time, and were mainly influenced by human activities within the watershed basin. During the pre‐eutrophication phase, subfossil chironomid δ 13 C (δ 13 C HC ) values were lower than those of sedimentary organic matter. These results suggested that chironomid larvae preferentially fed on the autochthonous part of the total sedimentary organic matter. During the modern period, higher accumulation rates of organic matter and a decrease in C/N ratio suggested a steep rise in aquatic productivity for both lakes. As suggested by the synchronous increase in organic matter δ 13 C values, this higher productivity and the subsequent increase in dissolved CO 2 uptake may have induced either a marked increase in atmospheric CO 2 uptake by phytoplankton or a reduction in the phytoplankton trophic fractionation. These changes led to overlaps in terrestrial and aquatic carbon stable‐isotopic baselines, hampering the reliable reconstruction of the chironomid palaeo‐diet. These results seem to indicate the minor role of allochthony to sustain aquatic food webs of large and soft‐water lakes, and underscore the necessity to apply an independent compound‐specific stable‐isotope analysis to better estimate the temporal changes in isotopic baseline and, thus, strengthen the reliability of the chironomid palaeo‐diet reconstructions.
Type of Medium:
Online Resource
ISSN:
0046-5070
,
1365-2427
DOI:
10.1111/fwb.2017.62.issue-6
Language:
English
Publisher:
Wiley
Publication Date:
2017
detail.hit.zdb_id:
2020306-8
detail.hit.zdb_id:
121180-8
SSG:
12
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