Glacier dynamics influenced carbon flows through lake food webs: evidence from a chironomid δ13C-based reconstruction in the Nepalese Himalayas
Glacier dynamics influenced carbon flows through lake food webs: evidence from a chironomid d13C-based reconstruction in the Nepalese Himalayas
Simon Belle . Simona Musazzi . Andrea Lami 0 1
0 S. Musazzi A. Lami Istituto per lo Studio degli Ecosistemi, CNR , Verbania Pallanza , Italy
1 S. Belle (&) Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences , Uppsala , Sweden
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 (d13CHC). 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 d13CHC 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 Handling editor: Jasmine Saros 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.
Food webs; Carbon stable isotope; Subfossil chironomid; Sedimentary pigments; Paleolimnology
Introduction
Mountain areas play a key role in the regulation of
climatic, hydrological and biogeographical processes
at a global scale. The Himalayan Mountains are often
considered as the ‘‘Third Pole’’
(Qiu, 2008)
, mainly
because they exhibit the largest glacial area outside of
the Polar Regions and they are located in the most
remote region of the world
(Yao et al., 2012a)
. Glacier
dynamics in the Himalayan Mountains induces
numerous feedbacks on regional climate, water supply
and associated biogeochemical cycles
(Yao et al.,
2012b)
. However, numerous studies revealed dramatic
decreases in glacial area over the last decades due to
climate warming
(Salerno et al., 2008; Chudley et al.,
2017)
. Since glacier retreat in the Himalayan
Mountains is expected to dramatically increase in a near
future due to global warming
(Soncini et al., 2016)
; it
has then become necessary to assess climate change
impacts on ecosystems in this area.
Lakes are sentinels of climate change, and they are
considered as relevant indicators of environmental
quality in high mountain landscapes
(Adrian et al.,
2009; Williamson et al., 2009)
. 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. The
broader catchment area and the lake itself play then
a role of environmental filters to mediate climate
change effects (Blenckner, 2005; Appendix 1). In the
Nepalese Himalayas, lakes seem to be affected by
both E (i.e. water temperature) and m (i.e. nutrients
and solute dynamics) fluxes. However,
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.
The understanding of food web functioning,
including all steps of exchange of energy and matter
among aquatic consumers
(Lindeman, 1942)
, is an
essential knowledge to elucidate the impact of climate
change on lakes at ecosystem level. Among the
complexity of trophic interactions in lakes, the benthic
food web represents an integrative proxy for the
understanding of whole lake trophic functioning
(Vadeboncoeur et al., 2002)
. Indeed, lake sediments
play a central role in recycling processes of organic
matter coming from aquatic ecosystems (i.e.
autochthonous primary production) and the associated
catchment
(i.e. terrestrial organic matter; Meyers &
Ishiwatari, 1993)
. Moreover, the functioning of the
benthic food web involves numerous couplings with
the surrounding terrestrial environment
(Northington
et al., 2010)
and among in-lake compartments
(benthic–pelagic coupling, Wagner et al. 2012;
pelagic–benthic coupling, Jo´nasson (...truncated)