Abstract
Using a sediment core covering the last 3,500 years, we analysed photosynthetic pigments’ concentrations in lake sediments and carbon stable isotopic composition of chironomid (Diptera, Chironomidae) remains (δ13CHC). We aimed to reconstruct temporal changes in aquatic primary productivity and carbon resources sustaining chironomid larvae in a high mountain lake (Lake Pyramid Inferior; 5,067 m a.s.l.) located in the Nepalese Himalayas. Both pigments and δ13CHC trends followed a similar fluctuating pattern over time, and we found significant positive relationships between these proxies, suggesting the strong reliance of benthic consumers on the aquatic primary production. Temporal trends matched well with main known climatic phases in the Eastern part of the Himalayan Mountains. Past glacier dynamics and associated in-lake solute concentrations appeared to be the main driver of autochthonous primary productivity, suggesting then the indirect impact of climate change on carbon processing in the benthic food web. During warm periods, the glacier retreat induced a rise in in-lake solute concentrations leading to an increasing primary productivity. Complementary investigations are still needed to strengthen our understanding about the response of past aquatic carbon cycling in CO2-limiting environments.
Highlights
Mountain areas play a key role in the regulation of climatic, hydrological and biogeographical processes at a global scale
Using combined analysis of sedimentary pigments and carbon stable isotopic composition of chironomid remains, we aimed to reconstruct the temporal changes in aquatic primary productivity and carbon resources sustaining chironomid larvae in a high mountain lake (Lake Pyramid Inferior; Nepalese Himalayas)
The succession of zones along the sediment core seemed to correspond to a regular temporal pattern (Fig. 2A). ‘‘Black’’ zones (1, 3 and 5) referred to the periods with the high Organic matter content values (OM) contents, and Total carotenoids (TC) and chlorophyll derivatives (CD) values (Fig. 2A)
Summary
Mountain areas play a key role in the regulation of climatic, hydrological and biogeographical processes at a global scale. Mechanisms by which climate affects lake ecosystems can be summarized by the conceptual energy–mass framework published by Leavitt et al (2009; Appendix 1). They proposed to distinguish the energy (E effects; atmospheric heat, irradiance, etc.) and mass fluxes (m effects; precipitation patterns, nutrient run-off, etc.) affecting the different compartments of lake functioning. Climate-induced glacier dynamics (E effects) appear to play a major role in solute concentrations in lakes (indirect m effects; Salerno et al, 2016) leading to the control of aquatic primary production (Lami et al, 2010), and likely the associated pelagic food web (Nevalainen et al, 2014), but nothing is known about the whole ecosystem response
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