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Eutrophication is one of the most widespread environmental problems of inland waters,either because external loading has not been reduced sufficiently or because internal lake mechanisms.High internal loading of nitrogen(N) and phosphorus(P) from lake sediments is frequently reported as an important mechanism delaying lake recovery after a reduction of external loading.In this paper,the seasonal changes of ammonia nitrogen and phosphorus releasing rate from sediment were evaluated using intact sediment core simulation methods in the Beili Lake of the Hangzhou West Lake.Besides,vertical distribution characteristics of ammonia nitrogen and phosphors in the pore water were analyzed.The results showed that the concentration of ammonia nitrogen was expressed as the increasing trend with depth,while an increasing trend followed by decreasing was found for phosphorus.The difference in ammonia nitrogen and phosphorus concentration between pore water and overlying water can cause inner nitrogen and phosphorus nutrients releasing.The seasonal releasing rates from sediments were 0.074 mg · m-2 · d-1,0.340 mg · m-2 · d-1,0.087 mg · m-2 · d-1,0.0004 mg · m-2 · d-1 for ammonia nitrogen,and 0.340 mg · m-2 · d-1,0.518 mg · m-2 · d-1,0.094 mg · m-2 · d-1,-0.037 mg · m-2 · d-1 for phosphorus,respectively.Seasonal and spatial variations of releasing rate were found from this study.The ammonia nitrogen and phosphorus releasing rate was higher in summer than in spring and autumn,but lowest in winter.The release fluxes of nitrogen and phosphorus across the sediment-water interface in different points were estimated using results from intact sediment core simulation methods.This difference is mainly focus on nitrogen and phosphorus releasing from the sediments in different environmental conditions including temperature,pH,dissolved oxygen(DO) and transparency.In summer,the temperature was the highest,the activity of bacterium was stronger than in other seasons.At the same time,the DO value decreased.The transparency was the lowest in summer,indicating the disturbance strength was the highest than other seasons.The results demonstrated the internal loading were 0.0004 t,0.0025 t,0.0008 t,0 t for ammonia nitrogen,and 0.0015 t,0.0038 t,0.0009 t,-0.0005 t for phosphorus,respectively.The conclusions indicated that the internal loading of N and P in the whole lake were estimated about 0.0037 and 0.0057 t/a,respectively.Therefore,nutrients from sediment made a contribution to lake eutrophication.The phosphorus was the limiting factor to the lake entrophication in Beili Lake,and the releasing of phosphorus was related to the forms.The active phosphorus including the dissolved phosphorus,Fe-bound P and Al-bound P,can release from sediment to overlying water easily.The proportion of active P was accounted 5.3% of TP in spring,and then decreased to 3.72% in summer.After that,the active P increased to 6.16% and 6.73% in autumn and winter.The seasonal variation characteristics of active P were consitent with those of the phosphorus releasing.However,the simulation method used in this study didn′t analyze the effect of environmental factors such as waves′ disturbance and turbulence on nitrogen and phosphorus releasing rate,the results from simulation may be lower than the dynamic simulation value.Afterwards,the results from this study are important for the eutrophication control and ecological restoration in Beli Lake.

The new simple mathematical expression for geoethermal distribution in country rock in deep tunnels can reflect the essential relation of the rock temperature to the geothermal parameters, radial distance and ventilation time. The results obtained both by numerical simulations and through in -situ measurements prove that the new mathematical expression for geothermal distribution is close to reality.

It is still a difficult problem to find the analytical solutions for the gas flow equation, the nonlinear partial differential equation of the radial flow field in the coal seam. The approximate analytical solutions, with variable substitution and proper simplification, that is, the distribution expressions of gas pressure in a radial flow field are developed. The analytical formulas for gas drainage in the coal seam are presented. The numerical calculation with computers demonstrates that the new analytical formulas are accurate and easy to use for the design of a gas drainage system.

The effective radius and the rational distances between boreholes for gas drainage in coal seams are two of the fundamental parameters for the rational arrangement of boreholes in a gas drainage system. Mathematical formulae for the rational arrangement of boreholes for gas drainage in coal seams have been deduced based on the theoretical model of coal gas dynamics. It is shown, by using the formulae for calculations for actual areas in the collieries, that these formulae, which have primarily been applied in the design of a gas drainage system for the prevention of coal gas outbursts, are rapid, simple and useful.

Coal gas dynamics is a fundamental theory for controlling gas in coal mines and preventing catastrophe. Starting from Darcy's law and the equation of continuity, a number of fundamental problems of coal gas dynamics are analysed using the theory of dimensional analysis and the current models for gas flow fields in coal seams are corrected. The mathematical solutions for three kinds of models of gas flow fields are studied and developed and the rationality of the new linear dynamic models is proven.

Based on the extended formula of the Power law, partial differential equations for a compressible gas flow in homogeneous and heterogeneous coal seams have been set up. The measured parameters of coal gas dynamics were used to check the accuracy of the new nonlinear dynamic models for gas flow fields in coal seams. The results of the comparison revealed that the new nonlinear theory for coal gas dynamics is closer to the actual situation than the other two existing theories.

Coal-seam gas permeability is one of the fundamental parameters in the study of coal gas dynamics and mine gases. A simple, rapid and accurate method is presented for the calculation and determination of the permeability.

New method of analysis to describe the propagation of induced fluid-driven fractures in rock masses which contain pre-existing discontinuities such as joints, bed interfaces, lens boundaries, etc. The analysis is based on a 2-D model, with coupled solid mechanics, fracture mechanics and fluid mechanics. The solid and fracture mechanics are solved by an implicit finite-element approach. The fluid mechanics capability first was established for steady-state conditions. This initial coupling resulted in the version 1.0 of the FEFFLAP model (Finite Element Fracture and Flow Analysis Program). The developments were then extended to the time-dependent domain by replacing the original fluid flow model with a model based on the FAST fluid dynamics module. These new analysis tools can be used for a wide variety of applications such as obtaining a better understanding of the stimulation of unconventional gas reservoirs, i.e. lenticular sandstones, coal beds and Devonian shales, or making improvements in the design of underground waste disposal by hydrofracturing or enhancing the fracturing of geothermal reservoirs