Zooplankton contribution to the particulate N and P in Lake Kinneret, Israel, under changing water levels
The association of water level changes and the relative (%) contributions of crustacean zooplankton to particulate N (PNz) and particulate P (PPz) in Lake Kinneret, Israel were studied. The PNz and PPz were assessed for a period of 10 years (1999–2008) in relation to water level (WL) changes which occurred during that period. We estimated PNz and PPz, based on crustacean N and P content measured seasonally over 2 years, and a 10-year record of zooplankton densities. Mean cladoceran N and P contents were 8.7 and 1.2% of dry weight, respectively, while for copepods they were 9.5 and 1.5% of dry weight, respectively. Zooplankton density, and hence PNz and PPz, changed dramatically during the 10 years, concurrent with extreme variations in the lake’s WL. The lowest mean values of PNz and PPz occurred during high WL years and the highest PNz and PPz were during low WL years. PNz and PPz were negatively correlated with the total PN and PP concentrations, respectively, in the lake. The reduction in zooplankton contribution to the particulate N and P during high WL is probably due to higher loading of particulate matter in wet years, causing an increase of PN and PP concentration in the lake, as well as lower densities of zooplankton, caused by higher fish predation pressure, both are a by-product of the large water influx during extreme wet winters.
KeywordsStoichiometry Copepod Cladoceran N-content P-content Zooplankton N:P
This study was supported by the Admiral Yohay Ben-Nun Foundation for Marine and Freshwater Sciences Fellowship, and the Bar Ilan University Marine Sciences Fellowship to TR. We thank the researchers and technical staff at the Kinneret Limnological Laboratory: Dr. Ami Nishri for the chemical data, Dr. Werner Eckert for analyses of CHN, Miki Shlichter for database use, and Mina Bizic, Edit Leibovitz, and Sara Chava for their technical help. The chemical analyses were conducted by the Watershed Unit of Mekorot. Funding for the Kinneret monitoring program from which the long-term data were derived was from the Israel Water Authority. Statistical analysis was performed with help from Dr. Rachel S. Levy-Drummer and Dr. Yuri Kamenir from the Mina and Everard Goodman Faculty of Life Sciences, Bar Ilan University.
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