1. INTRODUCTION
Carbon cycles have become one of the most extensively researched topics
with regard to global climate change (Yang et al., 2021). Lakes,
accounting for 3.7% of the global land area, are an important component
of the inland water system, which regulate the carbon cycle by storing,
transporting, and transforming carbon (Tranvik et al., 2009; Holgerson
and Raymond, 2016; Cole et al., 1994; Holgerson & Raymond, 2016; Ran et
al., 2017; Yan et al., 2018). For example, lake sediments can contain
0.03–0.07 Pg C a–1 (Molot & Dillon, 1996; Dean &
Gorham 1998; Kortelainen et al., 2006), which is roughly equal to or
higher than the carbon buried in marine sediments (Cole et al., 2007).
The annual CO2 emissions from lakes has been estimated
at 0.11–0.57 Pg C a–1 (Sobek et al., 2005; Holgerson
and Raymond, 2016). Additionally, the CO2 and
CH4 released by organic matter mineralization play a
major role in and significantly affect the terrestrial carbon cycle
(Kortelainen et al., 2006; Tranvik et al., 2009; Holgerson & Raymond,
2016; Martinsen et al., 2020). Knowledge of the lake carbon cycle can
therefore contribute to a comprehensive understanding of the terrestrial
carbon cycle (Hanson et al., 2004; Balmer & Downing, 2011).
Dissolved inorganic carbon (DIC) occurs in water in the form of
CO2, CO32–,
HCO3–, and
H2CO3. The primary sources of DIC in
lake water are external inflowing water, atmospheric
CO2, organic matter decomposition, and
CO2 produced during metabolism of aquatic organisms.
Carbon isotopes (δ13C) can record the cycling of
carbon cycling during each of these links, which involve equilibrium and
kinetic fractionation (Zhang et al., 1995; Myrbo & Shapely, 2006).
Thus, δ13C analyses of the DIC
(δ13CDIC) provide a powerful tool for
tracing the lake carbon cycle and elucidating carbon fluxes (Quay et
al., 1986; Herczeg, 1987; Stiller and Nissenbaum, 1999; Lei et al.,
2012; Mu et al., 2016; Han et al., 2018; Shtangeeva et al., 2019). For
instance, Striegl et al. (2001) compared the
δ13CDIC values of 142 lakes during ice
cover, suggesting that lakes with a higher CO2(p CO2) partial pressure had lower
δ13CDIC values owing to the dominance
of respiration of terrestrial organic material.
Lake ecosystems on the
Qinghai-Tibetan Plateau are fragile and sensitive to changes in climate
and environment (Fang et al., 2016). Lakes on the Qinghai-Tibetan
Plateau account for approximately 50 % of the total lake area in China
(Guan et al., 1984). Most studies on the
δ13CDIC in lakes on the Tibetan
Plateau have focused on the climatic and environmental implications of
the carbon isotope compositions of lake sediments.
Variations in the
δ13CDIC of various lake types may have
different responses to carbon cycle processes. For example, Lei et al.
(2012) analyse the characteristics of the
δ13CDIC of 24 lakes (mainly closed
lakes) across the Qiangtang Plateau, finding that the high
δ13CDIC values of closed lakes could
be mainly attributed to significant catchment-scale contributions from
carbonate weathering and the evasion of dissolved CO2induced by enhanced lake water evaporation. Therefore, performing a more
in-depth study on the changes in the
δ13CDIC values of lakes on the
Qinghai-Tibetan Plateau is necessary.
This study explored the relationships among the
δ13CDIC values of the Genggahai Lake,
the lake environment, and the watershed climate based on the observed
water physicochemical parameters in areas with different types of
submerged macrophyte communities, as well as the changes in the
temperature and precipitation during the same period.
Our objective was to provide a
theoretical basis to elucidate the response mechanisms of
δ13CDIC to the lake carbon cycle.