CGRG Bibliography of Canadian Geomorphology
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Author : Butler, R.D.; and Gilbert, R.
Date : 2000.
Title : A recent assessment of the physical limnology and sedimentology of montane Meziadin Lake, Northern British Columbia, Canada.
Publication : 30th International Arctic Workshop, Program and Abstracts, 2000. Institute of Arctic and Alpine Research, University of Colorado at Boulder
Issue :
Page(s) : 33-34.
Abstract
An ongoing examination of Meziadin Lake in the northern Coast Mountains of British Columbia, Canada (56° 5' N; 129° 20' W), provides insight into the physical limnology and sedimentology of a glacially oversteepened fiord lake. Drainage basin characteristics such as the presence of glaciers, proximity of the lake to glaciers, and the lack of sediment sinks en route to the lake basin provide the potential for an annually or sub-annually resolved sedimentary record. The use of a lacustrine record as a proxy for other environmental variables is practical only when processes within the drainage basin and the integrated response of the lake can be assessed. As such, the examination of the physical limnology of Meziadin Lake provides an understanding of the interaction between inflowing water and subsequent patterns of sedimentation and, therefore, the genesis of a sedimentary record. Of particular importance to this study is the influence of weather-related events on inflow and response of the lake system (i.e. significant changes to inflow influenced by weather may dominate a lacustrine system depending on the seasonal evolution of limnic conditions). Field observations were carried out on site for 12 weeks from late May to early August 1999. Monitoring of Strohn Creek, which carries a significant portion of the inflow to the lake, provided a continuous record of discharge from June 1 to August 10. Point samples of suspended sediment taken from Strohn Creek and other inflows allow calculation of the suspended sediment flux to the lake over the same period of time. Repeated measurements of temperature, conductivity, and turbidity (suspended sediment concentration) were taken using a Hydrolab Datasonde 3 from 18 sites throughout the lake. Bottom temperature near the delta was continuously recorded using a submerged datalogger. Eleven sediment trap moorings were established prior to spring melt and recorded deposition from suspension from the water column for the entire lake over the course of the summer. Each mooring consisted of two pairs of funnel-shaped traps. One pair was located 40 m below the surface and the other 1 m above the lake floor, thereby distinguishing suspended sediment flux by depth. The shape and size of Meziadin Lake, in proportion to the volume of inflow creates the potential for distinct proximal and distal depositional environments within the lake basin. Sedimentation in Meziadin Lake is controlled primarily by nival (spring) and glacial (summer) melt. Significant rain events during the 1999 field season were relatively infrequent, with fewer than 5 reaching 5 mm. However, the timing the largest rainfall events (8-16 mm per day) correlated with melt-induced discharge peaks and significantly increased suspended sediment entering the lake. Increased discharge and sediment concentration due to rainfall events, timed with a lack of significant thermal stratification allowed inflow to generate an underflow event (initiated on June 17, persisting in the distal arm until June 21). While the presence of underflow activity may not represent an extreme event as understood in established literature (i.e. an externally forced event in which sedimentary characteristics depart significantly from an established mean (Desloges and Gilbert, 1994), its relation to the lake's poorly established thermal condition allowed inflow to surpass a density threshold and became a significant underflow event. This event was recorded particularly well in proximal sediment traps by a significant change in sediment grain size and rate of deposition, as well as showing a strong signature in CTD profiles. The distal arm of Meziadin showed a greatly reduced impact to the underflow event.
Bibliography of Canadian Geomorphology