VERTICAL AND SEASONAL DISTRIBUTION OF CHLOROPHYLL IN LAKES OF EXPERIMENTAL-LAKES-AREA, NORTHWESTERN ONTARIO - IMPLICATIONS FOR PRIMARY PRODUCTION ESTIMATES

An in vivo flow-through fluorometer system revealed narrow bands of high chlorophyll concentrations in the meta- or hypolimnia of all clear, stratified ELA [Experimental Lakes Area] lakes. In 2 experimentally fertilized lakes, chlorophyll concentrations in the hypolimnion exceeded 300 .mu.g/l while epilimnetic chlorophyll was only 3 .mu.g/l. The hypolimnetic bloom represented the major response to enhanced nutrient loading. The peak was in or below the thermocline at depths where 1-3% of photosynthetically available surface irradiance penetrated; the algae at the peak were growing flagellated colonial chrysophyceans. The autumn surface bloom was due to entrainment of this previously produced chlorophyll, not to growth caused by mixing in of hypolimnetic nutrients.