Carbon isotopic composition of living land snails from the Chinese Loess Plateau

1
Carbon isotopic composition of living land snails
from the Chinese Loess Plateau
Liu Zongxiu Gu Zhaoyan Wu Naiqin Institute of
Geology and Geophysics, CAS, Beijing 100029, P.
R. China
The carbon isotopic composition of
land-snail shells as environmental indicator has
been studied for over two decades. But in natural
settings whether the carbon isotopic composition
of the land-snail shells indicated that of the
dietary plants of the snails need to be studied
further. Here, we selected 27 samples from twelve
localities in the Chinese Loess Plateau (Fig.1).
Each sample consists of ten entire adult snail
shells of a particular species with almost same
size. All of them came from the same region. We
analyzed them homogeneously in order to reduce
the possible biases among individuals, species
etc.
Fig.1 Locations of sample snail sites in the
Loess Plateau
Fig.2 Showing that both of carbon and
oxygen isotope compositions of snail shells in
the China Loess Plateau have wide within-specie
variation and great extra-specie variation at one
site. The analysis shows that full
homogenization of the shells and sufficiently
large sample sizes (better over 10 shells) can
ensure correct data.
Our results indicate that the relationship
between the carbon isotopic of snail shells and
the associated organisms for each snail sample is
a linear (Fig.3), but with somewhat scatter. This
linear equation isd13Cshell 1.023d13Corg14.42,r
0.962. The linear relationship with a slope about
1 shows that the carbon isotopic composition of
snail shells can indicate the carbon isotopic
composition of dietary plants of snails in the
particular location of the Chinese Loess Plateau.
But there is an offset of 14.42. So we think
that the kinetic isotope effects associated with
diffusive loss of metabolic CO2 from snails may
effect on it. Changes in proportion of the total
oxidized carbon that is expelled by snails as
bicarbonate dissolved in body fluid and
13C-dietary limestone should explain for this
scatter. Thus, the carbon isotopic
composition of shells from the Chinese Loess
Plateau can indicate the carbon isotopic
composition of dietary plants of snails.
Fig.3 Carbon isotope relationship between
aragonite shells and the associated organisms
from the Chinese Loess Plateau