SS3.01 Landscape Control of High Latitude Lake and River Ecosystems
Date: Thursday, June 13, 2002
Time: 11:45:00 AM
Location: Carson A
 
SquiresMM, Simon Fraser University, Burnaby, BC, Canada, msquires@sfu.ca
Lesack, L, , Simon Fraser University, Burnaby, BC, Canada, Lance_Lesack@sfu.ca
 
RELATIVE PRODUCTIVITY OF MICRO- AND MACRO-AUTOTROPHS AMONG LAKES IN THE MACKENZIE DELTA, WESTERN CANADIAN ARCTIC
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Among lakes in the Mackenzie Delta (25,000 lakes), we postulated that phytoplankton, epipelon, and submergent macrophytes/epiphytes would respectively prevail at low, intermediate, and high water transparencies (corresponding with high, intermediate, and low flooding-frequencies). A variety of field and lab investigations over 4 years supported this hypothesis, with some qualifications. Macrophyte biomass (SCUBA diving harvest) was high among relatively clear lakes, but peaked where transparency was lowered by colored-DOM, and where inorganic sedimentation moderated the amount of organic matter in lake sediments (frequently-flood lakes with high transparency). Phytoplankton productivity (14C-uptake) peaked in relatively turbid waters (turbidity and nutrients manipulated), but among infrequently-flooded lakes, P-limitation (enrichment experiments) was as likely as limitation by N, P, N and P, or a micro-nutrient. Across the gradient of increasing macrophyte biomass, the productivity of epipelon peaked near the transparency threshold for macrophytes. At saturating irradiances, epipelon productivity was higher than epiphytic productivity. However, in situ epiphytic productivity was much greater than in the case of epipelon, because macrophytes provided considerable surface area to colonize and shaded the epipelon community in more transparent waters.