Search

We investigated the occurrence and distribution of multi-annual cycles in abundance of mountain hare populations across a wide area of their range in northern Europe. We analysed 125 time-series of mountain hare abundance indexed from hunting bag records and questionnaire responses from Scotland, Sweden, Finland and Switzerland. We also reanalysed 17 previously published time-series based on hunting bag records and snow track indices from mountain hare populations in Scotland, Norway, Sweden, Finland, Russia and Italy. Autocorrelation analysis showed that 45% of mountain hare populations showed evidence of cycles, characterised by significant negative autocorrelations at half or the whole cycle period. The amplitude and periodicity of cycles varied between and within countries. Time-series in Scotland were characterised by high-amplitude weak cycles with a mean periodicity of nine years but with a range of 4-15 years. Norwegian and Swedish time-series revealed low amplitude weak cycles with a 3-7 year period. Finnish time-series showed low amplitude cycles with a 4-11 year period. Alpine time-series were predominantly non-cyclic, while the limited number of series from Russia showed high amplitude weak cycles with an 8-11 year period. The results reveal that mountain hare populations show a wide range of population dynamics with distinct regional differences in periodicity, amplitude and density dependent structure of cycles. These findings suggest that different factors may limit or regulate mountain hare populations in different regions of Europe thus supporting the results of recent field studies.

In cold climates, temperatures higher than the ambient have been observed near the bottom of water lakes in the vicinity of thermal discharges. Concern has been expressed about the adverse effects of such abnormally warm water on the winter ecology of lake bottoms. It is expected that the existence of a density extremum in water at 4° C and the resulting nonlinear relation between density and temperature gives rise to densimetric flows which are markedly different from those in the linear range. This thesis presents experimental and numerical investigations that give some insight into the phenomenon of the thermal bar and the manner in which it may infIuence nearshore transport processes in the vicinity of a thermal outfalI in a cold climate. The investigations are restricted to an idealized model where the lock exchange mechanism is selected due to the fact that its behaviour is close to that expected in the prototype situation. The experimental investigation provides dramatic proof that the existence of an extremum in the density-temperature relation has a profound influence on the behaviour of densimetric flows in general and lock exchange behaviour in particular. Three zones in the vicinity of a thermal bar are clearly demonstrated viz. (i) the thermal overflow region. (ii) the thermal bar, and (iii) the thermal underflow region. The experiments provide data on the horizontal scale at which sinking takes place. A numerical model has been constructed to develop a means of modelling the behaviour of a thermal bar at the outfall of a steam electric generating station cooling water system. The numerical model employs a finite-difference scheme where the resulting algebraic finite difference equations are soIved using an alternating direction implicit method and a sparse-matrix package. The numericaI modeI has been verified by comparing it to numerical solutions of four different cases of the idealized problem of steady laminar flow in an encl, Doctor of Philosophy (PhD)

Over the years, rapidly varying channel flow and discontinuities in the solution of fluid mechanics problems have provided stimulation and challenge to numerical modelers. Traditional finite difference and finite element methods produce accurate but oscillatory solutions. Attempts to selectively eliminate these parasitic waves have been only partially successful in that the cost of a smoother profile was a lower accuracy solution. It is common to employ either internal and external dissipation parameters or a provision of dispersive interface. In this thesis, the problem of rapidly varying open channel flow is represented by a pair of nonlinear partial differential equations which are solved by a powerful moving finite element technique. The method developed in this research is based on the linking of a novel Lagrangian mode solution with the convenience of the Eularian grid at each time step. This second order scheme was employed in solving a variety of devised and reported open channel flow problems with near discontinuities. Comparisons with solutions obtained using the finite difference and finite element methods with Crank-Nicholson centred weightings demonstrates the quality improvements which have been achieved by this moving element scheme. The basic scheme was further generalized in both spatial and temporal dimensions. Sensitivity analysis of these generalized parameters established the grid size relaxations for a variety of problems. The moving element technique solved near discontinuous and gradually varied flow problems both in supercritical and subcritical regimes. An alternate form of Petrov-Galerkin weighting function was tested and found to give promising results. Further experimentation and testing are required before implementation. The robustness of the solution procedure is indicated by the adaptation of the model from the numerical and laboratory experiment stage to field problems. The model was successfully appli, Doctor of Philosophy (PhD)