Research On Karst/Geological Carbon Sinks Process And Flux In Chaotian Watershed,Guilin, China

Natural disasters such as global climate warming, extreme climate events, is becoming more and more frequenct, which has attracted economy development all over the world. So it is focus on by many people or institutional framework. Some scholars believe that climate change have larger relationship with greenhouse gas (mainly CO2) at present. The atmospheric CO2concentration is increased and human survival environment is changed year by year since the monitored data.According to the global carbon balance, the carbon has a difference which is called missing carbon. The missing carbon is increasing gradually as the atmospheric CO2concentration increases to this day. The missing carbon was studied in land carbon sink and sea carbon sink. Many scholars also studied the relationship of the carbon element and other elements, the carbon element and soil, the carbon element and vegetation, the carbon element and wetlands, rivers and oceans, etc. The aim is to find out the carbon sink.Generally speaking, carbonate rock, the atmosphere CO2and water can rapidly alkaline reaction and produced carbon sinks. So carbonate rock can absort quickly CO2in the atmosphere in a short time, but in a long time scale, the carbonate-weathering-related carbon sink and silicate-weathering-related carbon sink are about the same.According to the global carbon balance, there are about2.8PgC missing carbon now. The carbon sinks were studied in one or several aspects. For a comprehensive basin, few studies focus on the carbon sinks. Chaotian watershed, located on Guilin city, China, as a research site was choosed to study carbon sink.24points which come from different geological background were selected. And some water parameters such as electrical conductivity(EC), temperature, PH, HCO3-, SO42-, K+, Na+, Ca2+, Mg2+, stable isotope such as δD,δ18O,δ13CDIC, heavy metal elements such as Pb, Cr, Cd, Zn, were monitored. At the same time, the element Ca, Mg and some heavy metals which came from soil and rock were detected. All data were analyzed, and found that:1, The type of water mainly depends on the formation of lithologic and the mineral. So the non-karst area water belongs to Mg·Ca-HCO3-SO4and Ca·Mg-HCO3mainly; The karst area water belongs to Ca-HCO3and Mg·Ca-HCO3mainly. However, Mg9Ca-HCO3-SO4water also affected by many factors,for example, mixing, enrichment, and fertilization etc. The water type of Mg·Ca-HCO3-SO4is influenced greatly by human activities.2,8D isotope has an opposite trend to surface water and groundwater. When the process that flow from upstream to downstream,δD become heaverier in surface water and become lighter in groundwater; δD and δ18O also have an trend, from August2011to November2011,δD and δ18O are lighter than December2011to July2012, the reason may be that rainy and temperature. In study area,δD and δ18O are between-45.70%o～29.40%o and-7.50%o～4.89%o, respectively, and the value is hearvier than plateau. It shows that monsoon climate influence the rainfall. It also illustratesmost of the Chaotian watershed water comes from rain that is imported by monsoon climate.3、The δ13CDIC ranges from-18.00‰to-1.86‰proves that carbon from the atmosphere, the carbon source in non-karst area affected obviously by vegetation, and karst area is mainly affected by rock. With the seasonal and precipitation changes,δ13CDIC present cyclical changes in a year, which reaches the heaviest point in February, while to the lightest point from May to September (rainy season). It possible results from vegetation photosynthesis absorbs a large number of carbon leading to lighten the DIC in water, especially inorganic carbon (HCO3-) lighter. Low temperature and little rainfall in the winter, and plant is relatively weak, makes δ13CDIC heavier.4、The HC03-concentration in Karst water is about10times than non-karst area water. Along the river (non-karst area water (allogenic water) come into the karst area), the HCO3-concentration increases gradually. In seasonal changes, the HCO3-concentration in the dry season is slightly higher than the rainy season, mainly due to the dilution effects; Annual change of HCO3-concentration in non-karst area is small. But in the same day, HCO3-concentration diurnal variation is obvious in the rich aquatic plants.5、PCO2in water have obviously differences which in Karst area is Higher than non-karst area; And the groundwater is higher than the surface water in Karst area.6、Most of the ions in the water mainly come from the rocks weathering. And there is a different carbon source between karst and non-karst area. Most of Carbon source come from atomsphere in non-karst area, to the contrary, the carbon source is almost the same in karst area where are57.9%come from bedrock and42.1%.7、There are many factors affecting geological carbon sink. Amount of calcium and magnesium elements in the soil and water are controled by the geological background directly, even though the amount of HCO3-. But the amount of geological carbon sinks are not just influenced by the geological background; heavy rain can increase the amount of geological carbon sinks, but the HCO3-concentration of water in rainstorm is lower than non rainstorm; Assume the flow is a constant, the largest carbon sinks occur at20.2℃in the Chaotian watershed karst area. If the tempreature is lower than20.2℃, the water can continue to dissolve carbonate rocks. To the contary, the tempreature is higher than20.2℃, parts of HCO3-converted into CO2and H2O, and then release the CO2; Also, biological action play an important role in the entire geological carbon sinks, especially the growth of algae and other plants in Water; The ore mining caused the geological carbon sinks to decrease, and the amount of geological carbon sinks reduce to half of the original. The reason is that the sulphur lead-zinc mining was ored, led to the oxidation of sulfide can be reduced, and the SO42-in water decreased. Also the SO42-in water can chang the carbon cycle in karst area, but the SO42-in water in non-karst area stand for the carbon sinks increased. So the sulphur lead-zinc mining can increased carbon sinks more quickly.8、 Not consider the organic carbon and suspended particulate carbon of water, according to the rainfall, runoff depth, runoff area and available:the non-karst area in Chaotian watershed the amount of annual carbon sinks are1586.9tc/a, while in karst area the amount of carbon sinks are4318.3tc/a, allogenic water flow into the karst area can increase carbon sinks about2818.8tc/a. By all account, the amount of annual carbon sinks are about8724.0tc/a in Chaotian watershed. So the average geological carbon sinks per square kilometer in Chaotian watershed are:non-karst geological carbon sinks is5.2tc.a-1.km-2, karst geological carbon sinks is25.0tc.a-1.km-2, the allogenic water can increase the karst geological carbon sinks is16.3tc.a-1.km-2, that is to say extraterritorial source of water can make the karst geological carbon sinks increase to1.7times. Including23%of carbon sinks produced by aquatic photosynthesis and33.8%of carbon sinks generated by undercurrent. Therefore, the calculation of the amount of carbon sinks Chaotian watershed need to consider the the aquatic biological and undercurrents.9, Through the establishment of Ca2+, Mg2+and HCO3-relationship model can obtained:Ca2+and HCO3-established a good model in limestone area, the correlation is well; While in dolomite zone, Ca2+, Mg2+and HCO3-1s relationship is better than the correlation of Ca2+and HCO3-. So Ca2+, Mg2+and HCO3-relationship model can indirectly illustrate the major impact factor of carbon sinks; From Ca2+, Mg2+and HCO3-relationship model, it can come to a conclusion that the stream segments, waterborn organisms photosynthesis is the major impact factors affect carbon sink in flow, but for the underground river or at the outlet of spring water geological processes, CO2partial pressure may be the main factors affecting carbon sinks.10、The SWAT model simulation shows Chaotian watershed flow not only affected by rainfall,also the permeability coefficient, the storage and drainage of the reservoir affect the export flow of the river, thereby affect the amount of the carbon sinks in Chaotian watershed; There is a direct relationship between drainage of the reservoir, permeability coefficient and the Chaotian river’s flow. The results show that the flow fitting curve and actual flow are basically the same in Chaotian watershed. So carbon sinks are basically the same. And the Chaotian watershed carbon sinks can be represented as:F=42.43Q+13.98Q1(g)...