Field experiments for in situ measurement of photosynthetic efficiency and quantum yield

A method for the in situ determination of kc¯ , the average in vitro spectral specific attenuation coefficient of chlorophyll is described. This method takes into account changes in the spectral distribution of underwater light throughout the water column using a commonly available cosine collector. The kc¯ values, together with irradiance and primary productivity data gathered during the first GAP workshop at Lake Constance are used to calculate photosynthetic efficiencies Ez and quantum yields φ at different depths. The depth related changes found in φ and kc¯ are discussed, as is the question of constancy of φ max at low irradiance levels.