Roger Pieters

Limnology of Pavilion Lake, B. C., Canada - characterization of a microbialite forming environment.

The objectives of this study are two-fold: (1) to describe and quantify the seasonal physical and chemical limnological properties of Pavilion Lake, a microbialite-rich lake in British Columbia, Canada, and (2) to gain a broader limnological context of Pavilion Lake by examining the limnology and hydrology of the lakes and groundwater systems in the area (∼30 km radius). Pavilion Lake is a dimictic lake with annual ice-cover. It is a hard water (mean CaCO 3 = 181.8 mg L -1), ultra-oligotrophic (mean Total Phosphorus [TP] = 3.3 μg L -1) lake, that is groundwater fed most likely through diffuse, low velocity local and regional sources. Principal Components Analysis (PCA) separated Pavilion Lake from the other groundwater, stream and lake samples along a conductivity and pH gradient on Axis 1 (λ 1 =0.392), and a nutrient (Total Nitrogen [TN], TP) and K +, Mg 2+, Si gradient on the second axis (λ 2 = 0.160). Pavilion Lake has the lowest Ca 2+ and TP concentrations, and the highest Na + concentrations and optical transmissivity amongst all sampled sites. Furthermore, the lake is characterized by low sedimentation rates. These characteristics are potentially important factors in supporting the past and on-going development of microbialites within the lake. Our study provides a limnochemical reference to consider in the conceptualization of ideal environments supporting large-scale microbialites.

Symmetric Holmboe instabilities in a laboratory exchange flow

Laboratory experiments have been conducted that test the predictions of Holmboe ( Geofys. Publ ., vol. 24, 1962, pp. 67–112). Symmetric Holmboe instabilities are observed during steady, maximal two-layer exchange flow in a long laboratory channel of rectangular cross-section. Internal hydraulic controls at each end of the channel isolate the subcritical region within the channel from disturbances in the reservoirs. Inside the channel, the instabilities form cusp-like waves that propagate in both directions. The phase speed of the instabilities is consistent with Holmboes theory and increases along the length of the channel as a result of the gradual acceleration of each layer. This acceleration causes the wavelength of any given instability to increase in the flow direction until it is approximately twice the most amplified wavelength. At this point new waves develop with the result that the average wavelength is almost constant along the length of the channel.

Frictional two-layer exchange flow

A numerical model is developed to study the effects of friction on the steady exchange flow that evolves when a barrier is removed from a constriction separating two reservoirs of slightly different densities. The model has excellent agreement with an analytical solution and laboratory measurements of exchange flows through channels of constant width and depth. The model reveals three viscous flow regimes for a convergent-divergent contraction of constant depth, and three additional viscous flow regimes when an offset sill is introduced. Each regime is characterized by a different set of internal hydraulic control locations. Examination of the predicted interface profiles reveals that it is not possible to distinguish between different flow regimes on the basis of these profiles alone.