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Horizontal and Temporal Variability of Transport Processes in Lakes

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Horizontal and Temporal Variability of Transport Processes in Lakes HORIZONTAL AND TEMPORAL VARIABILITY OF TRANSPORT PROCESSES IN LAKES by Alexander LeBaron Forrest B.Eng. & Soc., McMaster University, 2002 B.Sc., McMaster University, 2002 M.A.Sc., University of British Columbia, 2004 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in The Faculty of Graduate Studies (Civil Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) August 2011 © Alexander LeBaron Forrest, 2011 Abstract This work examines the three dimensional nature of three important physical transport processes in lakes: (1) convection generated from a negative surface buoyancy flux; (2) transport resulting from rotational adjustment; and, (3) underflow fate during episodic wind stirring. Vertical and horizontal temperature gradients were characterized using a combination of traditional (moorings and vertical profilers) and novel techniques (an Autonomous Underwater Vehicle) at two sites; Pavilion Lake, British Columbia, Canada and Lake Thingvallavatn, Iceland. The former site is a relatively small (5 km2), temperate lake, with comparatively low snow cover that allows solar radiation to be the dominant energy flux to the system during late winter months. Analysis of water temperature distribution in surface waters during summer and winter enabled convective patterns resulting from a negative surface buoyancy flux to be inferred. In addition to previously studied physical transport phenomena, this work has revealed the existence of a cyclonic eddy under winter ice cover in Pavilion Lake, consistent with the internal Rossby radius of deformation, extending down to ~ 14 m below the ice surface and rotating with an azimuthal speed of ~ 3 cm s-1 (as predicted by equations of cyclogeostrophic flow). Horizontal temperature transects beneath the eddy revealed temperature fluctuations associated with 1 – 2 m vertical displacements in the region 5 m directly below the eddy and are thought to be an undocumented source of mass transport. The latter field site was an embayment of a larger (88 km2) subarctic lake with a groundwater inflow that propagates through the embayment as a negatively buoyant underflow. Surface wind shear events entrain the underflow into the overlying lake water. This entrainment alters the characteristics and the ultimate fate of the underflow in the lake. Calculated entrainment of the underflow and entrainment calculated from the bulk Richardson number are in close agreement. Measurements made during these studies not only elucidated details of the three dimensional nature of known transport mechanisms but also revealed previously undiscovered modes of mass transport associated with wintertime lake hydrodynamics. ii Preface While all of the research presented herein represents original work on behalf of the author, several collaborators have contributed during the editorial process, which have helped guide the creation of this final product. A long list of people also participated in each of the field deployments that helped to ensure successful operations. Chapter 2 is based on fieldwork conducted in Pavilion Lake, British Columbia, Canada in both the summer of 2006 and the winter of 2007 by Alexander Forrest and Dr. Bernard Laval. During both deployments, I was responsible for all logistics, experimental field design, data collection, and post-processing. Dr. Bernard Laval and Dr. Roger Pieters provided guidance during the drafting of the original manuscript with Dr. Darlene S.S. Lim, the other collaborator on this work, contributing to the final editorial process. A version of this chapter has been published; Forrest, A.L., Laval, B.E., Pieters, R., and Lim, D.S.S. 2008. Convectively driven transport in temperate lakes. Limnol. Oceanogr. 53(5, part 2), 2321–2332. Chapter 3 is a return to Pavilion Lake, BC, in the winter of 2008, by Alexander Forrest and Dr. Bernard Laval. Once again, I was responsible for all aspects of the project with Dr. Bernard Laval and Dr. Roger Pieters providing guidance during the drafting of the original manuscript and Dr. Darlene Lim, the other collaborator on this work, contributing to the final editorial process. Initial results have been published as Forrest, A.L., Laval, B.E. and Pieters, R. 2009. Under-ice convection in a temperate lake. International Association of Hydraulic Engineering and Research (IAHR). Vancouver, BC, Canada. 8 pages. The more detailed analysis presented in Chapter 3 of this thesis is in the process of being submitted. Chapter 4 represents collaboration between Alexander Forrest, Dr. Hrund Andradóttir, and Dr. Bernard Laval during the winter of 2009 at Lake Thingvallavatn, Iceland. For this project, I was responsible for all aspects of the project, except for the measurements taken with an Aquadopp ADV, which were provided by Dr. Hrund Andradóttir. Initial results have been published as Andradóttir H.Ó., Forrest A.L., and Laval B.E. 2009. Fate of groundwater inflow in Lake Thingvallavatn during early spring ice-breakup, Proceedings of the 13th International Workshop iii on Physical Processes in Natural Waters, Sept 1 – 4, Palermo, Italy. This previous work was written equally by myself and Dr. Hrund Andradóttir. I was responsible for drafting of this chapter that has been accepted for publication to the Journal of Aquatic Sciences. In addition to the scientific advances that have been made in this work, I have been responsible for, or coauthored, several manuscripts in an effort to document the engineering lessons learnt during the course of my PhD studies: Forrest, A.L. and B.E. Laval. (2007). Charting lacustrine environments with UBC-GAVIA. AUV Science in Extreme Environments, Scott Polar Research Institute, Cambridge, UK. 7 pages. Forrest, A.L. and B.E. Laval. (2007). Seasonal thermal structure of Pavilion Lake. AUV Science in Extreme Environments, Scott Polar Research Institute, Cambridge, UK. 7 pages. Forrest, A.L., H. Bohm, B.E. Laval., E. Magnusson, E., R. Yeo, and M.J. Doble. (2007). Investigation of under-ice thermal structure: Small AUV deployment in Pavilion Lake, BC, Canada. Oceans 2007 IEEE/MTS. Vancouver BC, Canada. 9 pages. Doble, M.J., P. Wadhams, A.L. Forrest, and B.E. Laval. (2008). AUV deployment through ice: two years of Arctic experience. Cold Regions Science and Technology. 56: 90 – 97. Forrest, A.L., B.E. Laval, M.J. Doble, E.J. Magnusson, and R. Yeo. (2008). AUV measurements of under-ice thermal structure. Oceans 2008 IEEE/MTS. Quebec City, PQ, Canada. 10 pages. Forrest, A.L. and B.E. Laval. (2009). From oceans to lakes - applying new tools in limnology. Journal of Ocean Technology. 4(1): 36 – 45. Crees, T., C. Kaminski, J. Ferguson, J.M. Laframboise, A.L. Forrest, J. Williams, E. MacNeil, D. Hopkins, and R. Pederson. 2010. UNCLOS under ice survey - An historic AUV deployment in the Canadian high arctic. Oceans 2010 IEEE/MTS. Seattle, WA, USA. 8 pages. As part of my involvement with different research groups over the course of my PhD studies, I have also been involved with authoring, or coauthoring, other works: Lim, D.S.S., B.E. Laval, G.F. Slater, D. Antoniades, A.L. Forrest, W. Pike, R. Pieters, M. Saffari, D. Reid, D. Schulze-Makuch, D. Andersen, and C.P. McKay. (2009). Limnology of Pavilion Lake, B. C., Canada - Characterization of a microbialite forming environment. Fundamental and Applied Limnology. 173(4): 329 – 351. iv Forrest, A.L., B.E. Laval, D.S.S. Lim, D.R. Williams, A.C. Trembanis, M.M. Marinova, R. Shepard, A.L. Brady, G.F. Slater, M.L. Gernhardt, and C.P. McKay. (2009). Performance evaluation of underwater platforms in the context of space exploration. Planetary and Space Science. 58(4): 706 – 716. Lim, D.S.S., G.L. Warman, M.L. Gernhardt, C.P. McKay, T. Fong, M.M. Marinova, A.F. Davila, D. Andersen, A.L. Brady, Z. Cardman, B. Cowie, M.D. Delaney, A.G. Fairén, A.L. Forrest, J. Heaton, B.E. Laval, R. Arnold, P. Nuytten, G. Osinski, M. Reay, D. Reid, D. Schulze- Makuch, R. Shepard, G.F. Slater, and D. Williams. (2010). Scientific field training for human planetary exploration. Planetary and Space Science. 58(6): 920 – 930. v Table of Contents Abstract ................................................................................................................................................... ii Preface....................................................................................................................................................iii Table of Contents ................................................................................................................................ vi List of Tables.......................................................................................................................................viii List of Figures ....................................................................................................................................... ix Acknowledgements..............................................................................................................................x Dedication ............................................................................................................................................. xi 1 Introduction.................................................................................................................................... 1 1.1 Review of Relevant Limnology.........................................................................................................3 1.1.1 Convection Driven by a Negative Buoyancy Flux...............................................................................3
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