『Abstract
Rock weathering by carbonic acid has played a substantial role
in both the global carbon cycle and related climate change. Carbonic
acid as the major weathering agent has been accepted, whereas
the importance of other acid (sulfuric, nitric or organic acids)
as an agent is gradually recognized. Here, we examine sulfate
dual-isotopic evidence (δ34SSO4, δ18OSO4) and water chemistry from the Jialing River
(Sichuan Basin, Southwest China) to identify dissolved sulfate
sources and the role of sulfuric acid in carbonate weathering.
A survey was carried our at 29 sites where surface water was sampled
during the rainy (July, 2008) and dry (February, 2009) seasons
in the Jialing River. The chemical composition of river water
was characterized by a dominance of Ca2+, Mg2+
and HCO3-, and SO42-,
which accounted for more than 90% of the total ion concentrations.
Water chemistry varied greatly in time and space, particularly
for Na+, Cl-, and SO42-.
This variation was a result of anthropogenic influences, such
as acid deposition and domestic sewage inputs. Co-variation of
the equivalent ratios of [Ca2+ + Mg2+] and
[SO42- + HCO3-]
indicate that it required significant additional SO42-
to achieve ionic balance, which implied that sulfuric acid might
play a relatively important role in carbonate weathering of this
river basin. Water samples from the Jialing River were significantly
rich in SO42-, and increased almost
two times from 274μM in the period of 1958-1990 to 499μM in this
study. The use of co-variations of δ34SSO4 vs.δ18OSO4 and of δ18OSO4 vs. δ18OH2O allowed us to demonstrate
that most of the sulfate in the waters of the Jialing River was
derived from sulfide oxidation and atmospheric inputs by high
sulfur-content coal combustion while the contribution of sulfate
from domestic and industrial wastewater could be important in
the dry season. Thus, the contribution of sulfuric acid, produced
by such sulfide oxidation and the oxidation of atmospheric SO2 emitted from coal combustion, as a weathering
agent is also confirmed.
Keywords: Jialing River; Sulfate isotopic composition; Carbonate
weathering; Sulfide oxidation; Sulfuric acid』
1. Introduction
2. Natural setting
2.1. Topography and geology
2.2. Climate and soil
3. Methodology
3.1. Water samples
3.2. Analytical methods
4. Results and discussion
4.1. General characteristics of Jialing River water
4.2. Carbonate dissolution and abundant sulfate in river water
4.2.1. Carbonate dissolution
4.2.2. Abundant sulfate in river water
4.3. Sulfate sources
4.3.1. Long-term variation of sulfate concentration
4.3.2. Spatial and seasonal changes of SO42-
concentration and dual-isotopic values
4.3.3. Contributions from different sulfate sources
5. Conclusions
Acknowledgments
References