Big Dam West, located in Kejimkujik Park, Nova Scotia, Canada, is a remote lake with elevated Hg concentrations in fish due in part to low pH and high dissolved organic carbon (DOC) concentrations. These features reflect the poor buffering capacity of peat lands in the flat drainage basin. To address the multiple species of Hg, a model was developed by coupling the “multiplier method” for multi-species chemicals with average concentration ratios to the Quantitative Water Air Sediment Interaction (QWASI) model. Elemental Hg was the “key species” modeled. Total Hg fluxes and concentrations were computed using concentration ratios. Many of the concentrations and Hg flux processes within the Big Dam West catchment had been previously measured with concentration ratios that were either computed or taken from the literature when measured data were not available. Measured values for total Hg concentration in each compartment (air, water, sediment) and Hg fluxes (e.g., precipitation, sediment deposition) enable verification of model concentration and flux estimates for total Hg in each environmental compartment. The model was also run with and without the inclusion of upward Hg fluxes from the underlying sediment to determine the significance of this controversial flux. The Hg QWASI model presented in this paper could be a valuable screening tool, especially for remote lakes, due to its ability to provide reasonable Hg estimates with a limited amount of data (water inflow rate, suspended particulate matter, sediment deposition velocity, and concentration of Hg in atmosphere and inflow water). 相似文献
The Banff Formation (Mississippian) is a sequence of limestone and shale exposed in the southern Canadian Rocky Mountains and underlying the adjacent plains. It was chosen as a vehicle to evaluate Markov-inspired techniques in sedimentary sequences where repetition of rock types is typical but a pattern of cyclicity is not obvious. Distributions of rock-unit thickness in two outcrop sections of the Banff Formation are not all exponential, therefore a one-step Markov model using an equal observational interval is not valid. Memory is indicated by the embedded-chain model. The most likely pattern of recurrence is delineated; shale is the most independent lithologic type and therefore the initial lithology in any ideal pattern. Neither factoring nor powering a probability matrix for the Banff Formation revealed geological cyclicity as defined by W. Schwarzacher. Several problems limit the application of Markov models to sedimentary sequences. Statistical validity requires a minimum number of observations, and in the attainment of a sound statistical basis, geological pertinence may be seriously reduced. Treatment of the probability matrix, by principal components analysis or by powering, yields an exacting criterion for cyclicity. 相似文献
The genesis of the Sullivan orebody is reviewed in terms of current concepts of stratiform ore formation. The source of metals and sulfur, the environment and time of ore formation, and the imprint of subsequent metamorphic events are explained in terms of a model which views the ore as one component of a chemical and clastic sequence formed within a rift basin above a thermal anomaly. Classic primary sedimentary structures are displayed in both the chemical (sulfide) and the clastic (silicate) rocks. Fractures and breccia zones beneath the western section of the mine provided passage-ways for boron and metal-rich sulfur-poor brines. Sulfides formed when the metals combined with reduced marine sulfur. The pattern of metal zoning is a reflection of the location of brine vents. The boron-rich solutions produced the tourmaline alteration zone. The sodium-rich brine produced albite within the ore sequence and in the hanging wall perhaps by the modification of analcite. The manganese variation of sulfide minerals between ore bands and laminations reflect changes in the chemistry of solutions during sedimentation and some degree of partitioning during metamorphism. The metamorphism has modified both the sulfide and silicate assemblages. 相似文献
This paper presents a coupled finite and discrete-element model (FEM and DEM) to simulate internal erosion. The model is based on ICY, an interface between COMSOL, an FEM engine, and YADE, a DEM code. With this model, smaller DEM subdomains are generated to simulate particle displacements at the grain scale. Particles in these small subdomains are subjected to buoyancy, gravity, drag and contact forces for short time steps (0.1 s). The DEM subdomains provide the macroscale (continuum) model with a particle flux distribution. Through a mass conservation equation, the flux distribution allows changes in porosity, hydraulic conductivity and hydraulic gradient to be evaluated for the same time steps at a larger, continuum scale. The updated hydraulic gradients from the continuum model provide the DEM subdomains with updated hydrodynamic forces based on a coarse-grid method. The number of particles in the DEM subdomains is also updated based on the new porosity distribution. The hierarchical multiscale model (HMM) was validated with the simulation of suffusion. Results for the proposed HMM algorithm are consistent with results based on a DEM model incorporating the full sample and simulation duration. The proposed HMM algorithm could enable the modelling of internal erosion for soil volumes that are too large to be modelled with a single DEM subdomain.
The Manitou Mine sulphidic-tailings storage facility No. 2, near Val D’Or, Canada, was reclaimed in 2009 by elevating the water table and applying a monolayer cover made of tailings from nearby Goldex Mine. Previous studies showed that production of acid mine drainage can be controlled by lowering the oxygen flux through Manitou tailings with a water table maintained at the interface between the cover and reactive tailings. Simulations of different scenarios were performed using numerical hydrogeological modeling to evaluate the capacity of the reclamation works to maintain the phreatic surface at this interface. A large-scale numerical model was constructed and calibrated using 3 years of field measurements. This model reproduced the field measurements, including the existence of a western zone on the site where the phreatic level targeted is not always met during the summer. A sensitivity analysis was performed to assess the response of the model to varying saturated hydraulic conductivities, porosities, and grain-size distributions. Higher variations of the hydraulic heads, with respect to the calibrated scenario results, were observed when simulating a looser or coarser cover material. Long-term responses were simulated using: the normal climatic data, data for a normal climate with a 2-month dry spell, and a simplified climate-change case. Environmental quality targets were reached less frequently during summer for the dry spell simulation as well as for the simplified climate-change scenario. This study illustrates how numerical simulations can be used as a key tool to assess the eventual performance of various mine-site reclamation scenarios.
