A novel, highly integrated lake-âbo-om imagery strategy for surveying lake-âboaom ... Brown et al. (1998) ... WHAT? Imaging lake-âbo-om under a thick ice cover ...
Lake bo(om imagery: a simple, fast and inexpensive method for surveying shallow freshwater ecosystems of permafrost regions F. Bouchard 1,2,3, D. For+er 1,3, M. Paque2e 1,3, P. N. Bégin 3,4, W. F. Vincent 3,4, and I. Laurion 2,3
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A novel, highly integrated lake-‐bo(om imagery strategy for surveying lake-‐bo2om water and sediments prior to sampling.
WHY?
Ra+onale
WHERE?
Study sites
HOW?
Integrated method
(SO) WHAT?
Examples, benefits and limita+ons
Permafrost freshwater ecosystems: widespread, diverse
Importance of (paleo)limnological studies
WHY?
Lakes are very abundant in permafrost regions
Grosse et al. (2013)
Walter et al. (2007)
WHY?
When sampling, paleolimnologists have faith “I believe.”
Several assump+ons: • Sediment coring site is representaCve • Core was collected at deepest locaCon • Lake-‐bo2om sediments were not disturbed • Core was collected (perfectly) verCcally
Really? Could we just make sure?
WHERE?
Lakes in the Canadian ArcCc: Bylot Island (NU) Brown et al. (1998)
Lakes in the Canadian ArcCc: Ward Hunt (NU) Brown et al. (1998)
• Ward Hunt Lake (WHL) • Perennial ice (up to 4 m) • Recent substan+al reduc+on in extent and thickness • Limnological changes?
Vincent et al. (2011)
WHL
HOW?
Combining GPS-‐assisted sonar technology…
antenna
HOW?
… with waterproof HD photo-‐video camera
1-m depth
10 cm
WHAT?
Finding the best locaCon for sediment coring
Bathymetric map
Sediment core
• Deep trench (> 10-m depth) • Not at the center
• Top: organic mud • Bottom: sand-gravel
WHAT?
Imaging lake-‐bo(om under a thick ice cover
WHAT?
Other applicaCons: greenhouse gas sampling
WHAT?
Other applicaCons: lake-‐ice surveying
Kettle lake
Thermokarst lake
Benefits:
LimitaCons:
• The whole lake survey ‘tool-‐kit’ can be transported and deployed in the field by a single person; • Allows new insights into limnological aspects of remote shallow aqua+c ecosystems; • Efficient for rapidly localizing the best sediment coring sites for paleolimnological reconstruc+ons; • Affordable, easy to deploy, and provides real-‐Cme data in the field that can then be used to guide sampling; • Non-‐destrucCve; • Can be applied to other disciplines.
• User must be careful when manipula+ng instruments (especially cables); • GPS-‐sonar spaCal resoluCon not adequate for very small (few meters) and shallow (< 1m) ponds; • Sonar and camera ba(eries have a limited opera+on +me (2-‐3 hours); • Imagery depth limit is set by the underwater casing (ohen < 20 m).
Both limnological and paleo-‐ limnological inves+ga+ons can greatly benefit from this approach.
Thank You Fieldwork, logisHcs: A. Culley D. Sarrazin V. Preskienis Parks Canada – Sirmilik (Bylot) Parks Canada – Quknirpaaq (Ward Hunt) Team of Prof. G. Gauthier (U. Laval)