Lake bo-om imagery: a simple, fast and inexpensive ...

3 downloads 0 Views 11MB Size Report
A novel, highly integrated lake-‐bo-om imagery strategy for surveying lake-‐boaom ... Brown et al. (1998) ... WHAT? Imaging lake-‐bo-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    

1  

2  

3  

4  

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)  

Kettle lake

•  •  •  •  • 

Numerous  glacial  valleys   Ice-­‐rich  permafrost   Peat-­‐silt  layers   Glacial  &  thermokarst  lakes   GHG  emissions  from  ponds  

Thermokarst lake

WHERE?  

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)  

Funding:  

‘Zodiac Sherpa’