Larson, G. L. USGS Forest and Rangeland Ecosystem Science Center, larsong@ccmail.orst.edu
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LIMNOLOGICAL CHARACTERISTICS OF AN EXTREMELY DEEP AND CLEAR CALDERA LAKE
 
CRATER LAKE (OREGON) COVERS THE FLOOR OF A CALDERA FORMED ABOUT 6,850 YEARS AGO. THE LAKE OCCUPIES 78% OF THE CATCHMENT BASIN. AT THE BENCHMEARK SURFACE ELEVATION OF 1,882 M THE LAKE HAS A SURFACE AREA OF 53.2 KM2 AND A MAXIMUM DEPTH OF 589 M. THERE IS NO SURFACE OUTLET OR MAJOR INLET STREAM. DURING THIS CENTURY, THE SURFACE ELEVATION OF THE LAKE HAS EXHIBITED LONG-TERM FLUCTUATIONS OF UP TO 4 M. THE LAKE MIXES TO A DEPTH OF ABOUT 200 M BY WIND ENERGY AND CONVECTION IN WINTER. THE DEEP LAKE MIXES IN WINTER AND SPRING BY SINKING MASSES OF COLD WATER.THE LAKE RARELY FREEZES IN WINTER, BUT IT IS THERMALLY STRATIFIED IN SUMMER AND FALL. THE LAKE IS EXTREMELY CLEAR (MAXIMUM SECCHI DISK READINGS EXCEED 40 M) AND LOW IN NUTRIENTS, PRIMARY PRODUCTION, PHYTOPLANKTON BIOMASS AND ZOOPLANKTON BIOMASS. PRIMARY PRODUCTION IN THE UPPER 200 M OF THE WATER COLUMN IS INFLUENCED BY NUTRIENT UPWELLING FROM THE DEEP LAKE IN WINTER AND SPRING. IN SUMMER AND FALL, MAXIMUM PRIMARY PRODUCTION IN SUMMER TYPICALLY OCCURS BETWEEN 40 AND 80 M, A CHLOROPHYLL MAXIMUM OCCURS BETWEEN 100 AND 120 M, AND PHYTOPLANKTON AND ZOOPLANKTON TAXA PARTITION THE WATER COLUMN TO A DEPTH OF 200 M. SOME COMPONENTS OF THE LAKE SYSTEM EXHIBIT CONSIDERABLE LONG-TERM
 
Day: Tuesday, Feb. 2
Time: 04:15 - 04:30pm
Location: Sweeney Center
 
Code: SS27TU0415S