| The total area of karst region is about 3.46 × 10~6 km~2, accounting for about one third of the land area of China, and the reserves of karst groundwater account for a quarter of the total reserves of China. In the karst area of Southwest China, the large underground river system and karst springs are well developed and karst groundwater resources occupy an important position in the southwest water resource system in China. However, due to the multiplicity and complexity of karst aqueous medium, the internal structure and the transport parameters of contaminants of underground conduit are lack of analysis. Based on this background, this paper selected the typical underground river basin region in Maocun Village of Guilin, Guangxi, carried out the wet season and dry season quantitative tracer tests based on online high-resolution monitor, depicted groundwater aqueous medium accurately. By monitoring rainstorm in the basin export, we discriminated the primary factor that affecting the water chemistry in karst conduit. While observing DIC temporal and spatial variation of water from sinkholes to underground river exports in Maocun, we quantitatively explained the formation mechanism of karst conduit using water chemistry method. Based on the experimental research above, we obtained several research results as follows:According to the tracer test results and groundwater runoff and distribution characteristics in Maocun groundwater system, Maocun underground river system is divided into Shegengyan, Bianyan underground river system, Dachongli-Beidiping system and Dayanqian sinkholes- Maocun outlet system, which are distributed in upstream and downstream of the Maocun basin respectively. According to the experimental tracer study, the breakthrough curve(BTC) are steep upward and steep drop pinnacle, which suggested that the conduit is relatively simple, and have no large turnout and karst tam developed. Through the hydrogeological parameters comparison between the wet and dry seasons, we can see each section of underground rivers state is generally turbulence which give priority to with convection; the flow velocity and flux in wet season is large, the average travel time is short, and the tracer recovery rate is higher than the dry season. But the change of BTC peak in dry season is more sensitive than wet season and has good effect for recognizing small groundwater bifurcations. The recovery rate in Modaojiang-Shegengyan, Xiaolongbei-Bianyan, and Dayanqian sinkhole in wet season are 58.8%, 21.3% and 68.3%, respectively and the storage in conduit are 3021m~3 、2710 m~3、52338m~3 respectively. The recovery rate in Modaojiang-Shegengyan, Xiaolongbei-Bianyan, and Dayanqian sinkhole in dry season are 26%、2.6%、33% respectively, and the storage rate in conduit are 1294 m~3、434m~3 、17218 m~3respectively. These data indicated that the storage rate in wet season is higher than that in dry season, and the storage capacity in groundwater aquifer increases along the flow rate.The aqueous medium in the middle region is relatively uniform, and have no conduit developed, and groundwater is mainly occurrence in karst aquifer.By monitoring rainstorm in Maocun underground river outlet, there are two important factors controlling the dynamic changes of water chemistry when rainstorm occurred, By monitoring the dissolved inorganic carbon of Maocun sinkhole to underground river outlet, we analyzed that after the water from sinkhole into the underground river system, the dissolved inorganic carbon content increasing and we calculated the change in the amount of flux in karst by water chemistry method, which is 143kg/d, anddemonstrated the large carbon sink capacity of karst conduit. |
PDF Full Text Request