7. CONCLUSIONS
1) For the overall DIC isotopic composition in the Genggahai Basin, we
found that δ13CDIC-I was the most
negative, with an average value of –11.1 ‰, followed by
δ13CDIC-R, with an average value of
–10.8 ‰; δ13CDIC-L was the most
positive, with an average value of –6.91 ‰. This was caused by isotope
fractionation resulting from the photosynthesis of aquatic plants after
spring water inflow into the lake.
2) Owing to variations in the photosynthetic activity intensity of
different aquatic plants, there were also significant variations in the
δ13CDIC-L values in areas with
different aquatic plants. We found that areas with M. spicatumand P. pectinatus communities had similar
δ13CDIC-L values, with an average of
–6.8 ‰, whereas the δ13CDIC-L value
of the Chara spp. community was more positive, at –4.0 ‰. This
likely occurred because Chara spp. plants have a higher
photosynthetic rate and are more capable of using CO2for photosynthetic activity, converting them into plant organism.
3) Based on hydrochemical observations, we found that the
δ13CDIC of the lake water was
primarily affected by the δ13CDIC-Iand aquatic plant photosynthesis. The change in
δ13CDIC-I to a more positive value
resulted from carbon isotope equilibration between 13C
from carbonate weathering in the watershed and12CO2 from soil respiration.
4) The changes in the δ13CDIC-Lcomposition of the Genggahai Lake indicated that the DIC from lake
inflow and the photosynthesis of aquatic plants were the key components
in the carbon cycle of the lake.