Premium
Contrasting effects of Daphnia on ratios of nitrogen to phosphorus in a eutrophic, hard‐water lake
Author(s) -
Sarnelle Orlando
Publication year - 1992
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.1992.37.7.1527
Subject(s) - daphnia , eutrophication , seston , zooplankton , sedimentation , phosphorus , biology , zoology , precipitation , environmental chemistry , grazing , cladocera , ecology , environmental science , phytoplankton , nutrient , sediment , chemistry , organic chemistry , paleontology , physics , meteorology
Daphnia manipulation in large enclosures, and whole‐lake observations before and after a fishkill, showed that intense Daphnia grazing produces large elevations in particulate N : P ratios (PN : PP) during clear‐water periods in a eutrophic lake. The direction of this effect was consistent with expected taxonomic variation among zooplankton in the N : P of excretion. N and P sedimentation (mg m −2 d −1 ) was reduced during Daphnia‐induced, clear‐water periods, despite increases in particle sinking velocities. In addition, there was an unexpected difference between seston N : P and the N : P of settled particles during clear water, resulting in a differential increase in average sinking velocity calculated for PP relative to PN. Daphnia effects on N : P later in the season appeared to be opposite to those during clear water. My data suggest that Daphnia grazing can reduce carbonate precipitation (whitings) by controlling algal biomass. Whitings were accompanied by large increases in sedimentary loss rates for total P (TP) and elevated TN : TP in the euphotic zone. Thus, Daphnia grazing may maintain relatively low TN : TP during summer in eutrophic, hard‐water lakes.