Sources and migration path of chemical compositions in a karst groundwater system during rainfall events
YANG PingHeng
0
1
YUAN DaoXian
0
1
YE XuChun
1
XIE ShiYou
1
CHEN XueBin
1
LIU ZiQi
1
0
The Karst Dynamics Laboratory
, Ministry of Land and Resources,
Institute of Karst Geology, Chinese Academy of Geological Sciences
, Guilin 541004,
China
1
School of Geographical Sciences, Key Laboratory of Eco-environments in Three Gorges Reservoir
, Ministry of Education,
Southwest University
, Chongqing 400715,
China
Physical and chemical dynamics at Jiangjia Spring (JJS), the outlet of the Qingmuguan karst groundwater system in Chongqing, were monitored in situ during rainfall events to acquire a series of high-resolution data. Principal component analysis (PCA) was employed to identify the sources of chemical compositions in the karst groundwater. The coefficients of variations (CVs) of the physical and chemical data of JJS were utilized to interpret the migration path of the chemical compositions. The results showed that water-rock interactions, agricultural activities, and soil erosion were the main sources of the groundwater chemical compositions. Ions of potassium, sodium, nitrate, chloride and phosphate from agricultural activities together with ions of calcium, magnesium, strontium and bicarbonate derived from carbonate dissolution appear to be stored and regulated by the karst unsaturated zone in features such as fissures, pores and solution cracks. The concentrations of the ions remained relatively stable and they showed low CVs owing to their migration by diffuse flow to recharge the underground river. In contrast, concentrations of ions such as total iron, total manganese and aluminum from soil erosion were unstable and showed high CVs owing to their migration by overland flow to recharge the underground river directly via sinkholes. During heavy rainfall events, the nutrients from agricultural activities and sediment from soil erosion could quickly impair the aquatic ecosystem and pose serious threats to water quality. Therefore, it is necessary to reinforce management of the ecological system for better control of the influx of mass nutrients into the karst aquifer system.
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The karst areas of SW China are typically vulnerable
ecological regions that represent the largest consecutive
distribution and most intense karstification in the world. Despite
the areas being favored with good water and heat conditions
in the subtropical zone, they have extremely heterogeneous
water distributions due to long-term karstification. This has
led to the formation of a karst soil and water resource
environment with several issues including structural water
shortage, infertile soil, and ecological vulnerability [1]. In
recent years, the karst water resources in the area have
begun to dry up and the pollution sources have become
diversified under the obvious and increasing influences of
anthropogenic activities and extreme climates [2]. This has
become a hindrance to the sustainable economic and social
development of the area.
Hydrochemical compositions are the basis for
investigations of groundwater and surface runoff sources and are
crucial to groundwater resource evaluation. Accordingly,
they play a significant role in the utilization and
management of groundwater resources in a watershed as well as the
protection and construction within the related ecological
environments. Geochemical analysis is a commonly used
The Author(s) 2013. This article is published with open access at Springerlink.com
method for investigations of groundwater origin, recharge
source, hydraulic connections, and water-rock interactions
[312].
Karst geochemistry is a branch of geochemistry that
studies the principles and application of chemical action in
karst dynamic systems [10]. Previous studies using
conceptual models of karst dynamics [13] and the historic
perspective of research on karst groundwater geochemistry [1417]
have primarily focused on the physical and chemical
compositions (e.g. Ca2+, conductivity, hardness, etc.) associated
with the water-rock interactions of karst groundwater.
Because of limited research methods, the research parameters
are less diversified and cannot comprehensively reflect the
influences from substances of the surface environment on
karst groundwater. Most studies to investigate the
influences of anthropogenic activities on karst groundwater
geochemistry have compared different chemical parameters of
the karst water in different spaces within the same period, or
at the same research site in different periods (e.g. a year, a
season, etc.). However, such data in the studies are usually
contingent, the prerequisite of comparisons are insufficient,
and the descriptions are superficial and probably cannot
comprehensively reflect the sensitivity of the karst system.
In addition, comparison of hourly data (high-resolution
monitoring) and monthly data results in a significant
discrepancy invalidating the latter as an indicator of rapid
changes in karst groundwater systems [18,19]. Therefore,
investigations of kars (...truncated)