ESTIMATING PHOTOSYNTHETICALLY AVAILABLE RADIATION INTO OPEN AND ICE-COVERED FRESH-WATER LAKES FROM SURFACE CHARACTERISTICS - A HIGH TRANSMITTANCE CASE-STUDY

A simple technique, based on several published studies, is presented to estimate photosynthetically available radiation (PAR: 400-700 nm) at the air/water and ice/water interfaces on freshwater lakes. Grand Traverse Bay of Lake Michigan of the Laurentian Great Lakes before, during, and after ice cover is used as a case study. The technique depends on assigning PAR transmittances to air/water or air/ice surfaces from empirically determined relationships. During ice cover, PAR reaching the water column under the ice exceeded 45% of incoming PAR, on the average, due to the amount of clear ice present on the bay.