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PHYTOPLANKTON, PHOTOSYNTHESIS, AND PHOSPHORUS IN LAKE MINNETONKA, MINNESOTA 1
Author(s) -
Megard Robert O.
Publication year - 1972
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1972.17.1.0068
Subject(s) - photosynthesis , chlorophyll a , chlorophyll , photic zone , phytoplankton , phosphorus , chlorophyll c , zoology , chemistry , botany , biology , chlorophyll fluorescence , nutrient , ecology , organic chemistry
The temporal and spatial variations of chlorophyll concentrations ( n ) and integral photosynthesis ( Σp ) are described for a large, morphometrically complex lake. The daily rate of photosynthesis at the average depth where illumination is optimal ( p max ) increases, whereas the depth where illumination begins to be saturating ( z i ) decreases, as chlorophyll concentrations increase. These opposing effects influence the geometric proportions (expressed by the ratio Σp : p max ) of photosynthesis depth profiles systematically. The regression of the ratio Σp : p max (= z i ) on chlorophyll is fitted to an exponential equation with which z i can be estimated from the chlorophyll concentration. Values of z i so estimated are similar to those expected from the reciprocal relationship between z i and chlorophyll required by Lambert’s law. Therefore daily integral photosynthesis at any locality can be calculated from measurements of the chlorophyll concentration and the rate of photosynthesis in a single water sample incubated for a half day at the average depth where illumination is optimal. Chlorophyll concentrations increase as concentrations of total phosphorus increase, but generally no relationship exists between phosphorus concentrations and maximum specific rates of photosynthesis ( P max ). The linear relationship between phosphorus and chlorophyll occurs only when Anabaena, a nitrogen‐fixing alga, is an important component of the phytoplankton. The quantity of chlorophyll above the depth z i (= n i ) represents ca. 60–80% of the chlorophyll in the photic zone. The value of n i where chlorophyll concentrations are 60 mg/m 3 (the maximum concentration at most localities in Lake Minnetonka) is about 100 mg Chl/m 2 . The usual limit for integral photosynthesis at 20C is therefore 5 g C m ‒2 day ‒1 .