| CO2in the atmosphere was absorbed as the form of dissolved inorganic carbon (DIC) in the karst groundwater throughing karst effect and was transformed to the organism of aguatic plant, this process was fast and going on with the water transfer and water chemistry change in the epikarst zone. The karst effect was affected by the hydro-geological conditions, meteorological conditions and human activities,it all respond as the change of water chemistry and shows an obveirous sensitivity to the change of the environment. The rate of karst effect can be illustrated by the CO2flux of the water basion.Shuifang spring is a typical subalpine epikarst spring which located in a relatively primitive environment and only affect by tourism activities.The water chemistry of the spring have annual variation, seasonal variation and changed during the rain and also affect by the human activities and aguatic plant.It’s a typical study area for research the sensitivity of karst effect and carbon sink effect, field work and experiment was convenient because of the small area and scarce human activities.Water sample collection, monitoring,soil CO2concentration determine and limestone table dissolution experiment were held during research time. karst effect sensitivity and area carbon sink were studied in many aspect. Research time was start from May2010to June2011.Field work include groundwater temperature(T), conductivity(Ec),pH,dissolved oxygen(DO) detect and Ca2+,HCO3-concentration determine.Anions,cations,carbon stable isotope and soil physical and chemical properties were analyzed in the laboratory. CDTP300data include water temperature (T), conductivity (Ec),pH,water level and meteorological data were collected once ever month.Real-time monitoring was also conducted during the rain and all day long when the alga is growing. Soil CO2concentration determine, limestone table dissolution experiment and analysis of soil physical and chemical properties were held in different landuse (forest land, grass land, shrub) in the area. By studying and research we got conclutions:Shuifang spring is a typical subalpine epikarst spring, Anion concentration and cation concentration all shows higher in autumn and winter and lowest in summer which affected by the human activities and dilution effect. There is a time delay between the highest Ca2+,HCO3-concentration and soil CO2content.The water chemistry was changed rapidly and exist a conspicuous CO2effect during the rain which lead to a higher PCO2and Ca2+HCO3-increase, also increase the dissolved inorganic carbon sink.By using the water chemistry data, water level and monitoring data from May2010to June2011. we calculate the limestone table dissolution rate of the watershed is146.4mg.m-2.d-1,the discharge and CO2consumption of the spring outlet as55778.61m3and2945.11kg. Using the limestone table dissolution experiment we calculate the CO2consumption of the watershed is29.64t/a, CO2flux22.8t/a/km2,carbon flux6.21tC/a/km2.The result of limestone table dissolution experiment is forest land>grass land>shrub, while the dissolution amount shows summer>autumen>spring>winter it is related with soil CO2content. The content of soil CO2differ from different landuse, which shows forest land>shrub>grass land and seasonal change is summer>autumen>spring>winter. Spring water δ13CDIC vary between-9.7‰～-14.65‰shows more negative in summer and positive in autumn and winter which may influenced by the soil microbial activity and content of CO2soil. Value of δ13CSOC and δ13C from plants (-27.31‰～-24.77%o) are well fitted with the C3plant type-soil system, The soil δ13CSOC also became more positive when the soil organic matter decreased and sampling level gets deeper. |
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