The vertical and seasonal distribution of chlorophyll in lakes of the Experimental Lakes Area, northwestern Ontario: Implications for primary production estimates

Abstract

An in vivo flow‐through fluorometer system revealed narrow bands of very high chlorophyll concentrations in the meta‐ or hypolimnia of all clear, stratified ELA lakes. In two experimentally fertilized lakes chlorophyll concentrations in the hypolimnion exceeded 300 µ g liter −1 while epilimnetic chlorophyll was only 3 µ g liter −1 . 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 actively 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.