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Patterns in planktonic P:R ratios in lakes: Influence of lake trophy and dissolved organic carbon
Author(s) -
del Giorgio Paul A.,
Peters Robert H.
Publication year - 1994
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.1994.39.4.0772
Subject(s) - plankton , phytoplankton , photosynthesis , respiration , dissolved organic carbon , bacterioplankton , environmental chemistry , chlorophyll a , carbon cycle , nutrient , environmental science , ecology , biology , chemistry , zoology , oceanography , botany , ecosystem , geology
A comparative analysis of planktonic metabolism in 20 southern Québec lakes was carried out to test the hypothesis that planktonic P : R ratios reflect gradients of both nutrient enrichment and dissolved organic carbon (DOC). Mean epilimnetic phytoplankton photosynthesis ranged from 8 to 377 mg C m −3 d −1 , and the amount of C respired by the plankton in excess of phytoplankton photosynthesis ranged from 30 to 86 mg C m −3 d −1 . Plankton community respiration was 2–8 times greater than phytoplankton photosynthesis in all oligotrophic and mesotrophic lakes during the growing season, and this imbalance narrowed toward the more productive lakes. P : R ratios were positively related to chlorophyll and total P concentration, and inversely related to water color and DOC concentration. The strong influence of DOC on planktonic P : R ratios was almost exclusively due to its depressing effect on phytoplankton photosynthesis; DOC had no statistical effect on respiration. The calculated DOC loading for these lakes suggests that organic C loss through epilimnetic respiration in excess of phytoplankton photosynthesis is comparable to the estimated DOC loss within the lakes and that summer plankton metabolism could be supported by external DOC inputs in most lakes. The highly significant intercept of the respiration to production relationship, 27 mg C m −3 d −1 , may indicate the baseline metabolism supported by external sources of C that occurs in these temperate lakes. Estimates of respiratory CO 2 production from the pelagial of these lakes range from 11 to 60 mmol CO 2 m −2 d −1 , depending on lake trophy and DOC concentration. These estimates suggest that the planktonic metabolism of allochthonous DOC probably constitutes a major source of CO 2 in lakes.