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During underground mining, accurate revelation on the deformation and failure mechanisms of a high-steep slope under multi-layer mining conditions facilitates the prevention and control of geological disasters in mines. Numerical simulation based on discrete element theory can be used to explore the characteristics and mechanism of action of deformation and failure of a slope under complex geological and multi-layer mining conditions. By utilising PFC2D (particle flow code) software, the deformation and failure characteristics of a high-steep slope in Faer Coal Mine in Guizhou Province, China were investigated. Additionally, the mechanism of influence of different numbers of mining layers on the deformation and failure of the high and steep slope was elucidated. The result showed that after the goaf passed by the slope toe, multi-layer mining aggravated the subsidence and deformation of the slope toe: the slope toppled forward as it sank. The toppling of the slope changed the slope structures: the strata in the front of the slope were transformed from anti-dip to down-dip features. Extruded by collapsed–toppled rock mass, the slope toe and the rock mass located in the lower part of the slope toe generally exhibited a locking effect on the slope. Multi-layer mining degraded the overall stability of the slope, in that the total displacement of the slope was much greater than the total mining thickness of the coal seams. Based on the aforementioned research, ideas for preventing and controlling geological disasters during mining operations under a high-steep slope were proposed. [ABSTRACT FROM AUTHOR]

δ13C and D14C measurements on dissolved inorganic carbon (DIC), particulate organic carbon (POC) and aquatic plants from a karst spring and two spring-fed ponds in Laqiao, Maolan Township, Libo County, southeastern Guizhou of China in January, July and October of 2013 have been carried out to understand the roles of aquatic photosynthesis through DIC uptake in surface karst waters. The mean D14C and δ13C values of DIC for the spring, midstream pond (MP) and downstream pond (DP) are −26 ± 36‰ and −13 ± 2‰, 6 ± 56‰ and −12 ± 3‰, and 0 ± 64‰ and −9 ± 2‰, respectively. The carbon source for the DIC is mainly from biogenic CO 2 rather than the dissolution of limestone rock as the D14C and δ13C of limestone are about −1000‰ and 2‰, respectively. The enrichment trend of D14C DIC and δ13C DIC from the spring to the DP indicates CO 2 exchange between atmospheric CO 2 and DIC, because D14C and δ13C values of atmospheric CO 2 are ca. 50‰ and −8‰, respectively. The average D14C POC values in the spring, MP and DP were −325‰, −123‰ and −158‰, respectively, which are all lower than these of the DIC in each reservoir. The lower D14C values of the POC may be caused by older soil carbon from surface runoff and dust fall. More aquatic algae were formed through photosynthesis in the stream ponds, especially in summer, shown by strongly increased D14C POC and evidence of growth in EDS/SEM analyses. Furthermore, the D14C values of the submerged aquatic plants range from −153‰ to −26‰, reflecting that the aquatic plants used DIC for photosynthesis. The D14C value of an emergent plant which uses atmospheric CO 2 during photosynthesis is 52.5 ± 0.3‰, equivalent to the atmospheric D14C. Seasonal variations of D14C DIC and δ13C DIC are influenced by soil CO 2 input, primary productivity in the ponds, and CO 2 exchange; hydrochemical condition show lower D14C values but higher δ13C values in cold/dry season, and vice versa in summer rainy season. A simple mass balance calculation indicates ~90% of carbon for the spring DIC is from biogenic CO 2 , with higher contribution in summer due to higher productivity. Although this simple calculation may overestimate the biogenic CO 2 , it indicates that organic decomposition is a major carbon source for DIC in the karst hydrological system. The results of the present study have implications for 14C dating on aquatic plant remains, regional and perhaps global carbon budgets, and the different behaviors of 13C and 14C in karst systems. • The DIC carbon source of the karst spring is mainly from biogenic CO2. • 13C and 14C tracing C source and transformation including photosynthesis CO 2 uptake • Aquatic plants uptake DIC CO 2 may cause an older 14C age. • Biological pump effect in terrestrial water can be an important natural carbon sink. [ABSTRACT FROM AUTHOR]