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| Titel |
The geochemical characteristics of soil water and epikarst springs and their response to vegetation-soil degradation in a karst area |
| VerfasserIn |
D. A. Xiao, H. Xu |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250071538
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| Zusammenfassung |
| Samples of soil waters and epi-karst springs in four vegetation types were collected at
Maolan nature reserve in Libo county, which including protogenetic arbors, secondary
arbor-shrub, shrubs and shrub-grass, to analyze their hydro-geochemical properties and the
variations of nutrient elements, and further to illustrate the intrinsic correlations of vegetation,
soil, environment changes and their geochemical information. The conclusions have been
concluded as follows:
(1) The pH of soil waters in the study area varies between 5.32 and 7.93, with a mean
value of 6.78, and the conductivity changes between 31.82 and 353.65 μS/cm, with a mean
value of 126.19 μS/cm. Both descend as the vegetation degrades. The hydro-chemistry of soil
waters are Ca- HCO3-, and their ions mainly consist of Ca2+, Mg2+, HCO3-, SO42-.
Ca2+, Mg2+, HCO3-are very sensitive to vegetations degradation. Ion contents are high in
rain seasons and low in dry ones.
(2) The pH of surface karst springs in the study area vary between 6.7 and 8.42, with a
mean value of 7.65, and the conductivity between 125.6 and 452 μS/cm, with a mean value
of 288.09 μS/cm. The hydro-chemistry of surface karst springs are Ca- HCO3-.
HCO3-and SO42-are the main anions while Ca2+and Mg2+as main cations. The
chemical properties and geochemical process of surface springs are mainly controlled
by the solubility equilibrium of carbonate rocks, thus not sensitive to vegetation
degradations.
(3) All the calcite saturation indices of soil waters in four vegetation types are
below 0, while most indices of surface karst springs are above 0, demonstrating
greater denudation of soil waters than surface karst springs. As soil waters flow
to surface springs, the partial pressure of CO2decreases, the denudation of water
lessens, and saturation index, Ca2+, HCO3-, consequently, pH and conductivity
increase.
(4) Inorganic nitrogen in soil waters exist mainly as N-NO3- and N-NH4+, accounting ~
95% of the 3 Ns. As vegetation degrades, nitrate nitrogen, organic nitrogen and total nitrogen
change in follow way, protogenetic arbors > secondary arbor-shrub, shrubs > shrub-grass,
but the differences among all vegetation types are not prominent. Ammonia nitrogen,
however, changes otherwise as follows: shrubs, shrub-grass > protogenetic arbors, secondary
arbor-shrub.
In surface springs, few inorganic nitrogen exists as NO2--N ( 2 μg/L on average ), and
most exists as NO3-N ( 215 μg/L on average ), and NH4+-N is 185μg/L on average. In
general, NH4+-N, NO3--N and TN formations in the four vegetation types are: protogenetic
arbors > secondary arbor-shrub > shrubs > shrub-grass.
(5) DOC content in soil waters vary between 1.88 and 10.37 mg/L, with an average
4.8 mg/L. DOC content in surface karst springs changes between 0.39 and 9.98
mg/L, with an average 2.25 mg/L. DOCs in soil waters are greater than those in
surface karst springs in all four vegetation types, and have sharp differences ( P-¤0.01
). DOCs in soil waters and surface karst springs share a great relationship and a
similar change tendency, which well illustrates a main source of surface springs
from soil waters. In both of them, DOCs are larger in original vegetations than
in degraded vegetations. This is because the soil-vegetation system is stable in
an original ecology environment which free from outside disturbs. By contrast, a
degraded system is unstable, weak at beating disturbs, and conserves less but loses
more.
Key words: soil waters, epi-karst springs, hydro-geochemical, vegetation, karst area,
Maolan in Guizhou |
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