In situ quantum yield of phyto plankton in a subalpine lake
Journal of Plankton Research 6(4): 531-542
ISSN/ISBN: 0142-7873 Accession: 005644940
The percent of light absorbed by algae, estimated from a regression of attenuation of downwelling photosynthetic photon flux density on chlorophyll a concentration, was used conjunction with measurements of phytoplankton photosynthesis to estimate quantum yields (.PHI.) of Castle Lake phytoplankton populations during the 1980 ice-free season. The maximum .PHI. values occurred during mid-summer in the deep hypolimnion (< 1% of surface photo flux) and were .apprx. 78% of the theoretical maximum. Later in the season (Sept.) the deep-water .PHI. values decreased significantly to .apprx. 27% of the theoretical maximum in conjunction with a decrease in quantum flux density of these waters. The .PHI. values for epilimnetic phytoplankton populations were never > 15% of the theoretical maximum. The presence of relatively high concentrations of peridinin and chlorophyll c in the deep-water algae enabled these organisms to absorb the predominantly green light in this region of the lake which allowed the use of a single extinction value per unit of chlorophyll (kc) at all depths when calculating .PHI. and increased the .PHI. of the deep-water algae, relative to those in the near-surface waters. The deep-water algae in Castle Lake were able to utilize their ambient light field, particularly in the early summer, and the deep-chlorophyll layer in this lake is maintained primarily by in situ algal growth rather than sinking and accumulation of organisms from near surface waters.