PRIMARY RESEARCH PAPER Zooplankton contribution to the particulate N and P in Lake Kinneret, Israel, under changing water levels Tamar Rachamim • Noga Stambler • Tamar Zohary • Ilana Berman-Frank • Gideon Gal Received: 24 March 2010 / Revised: 29 July 2010 / Accepted: 10 August 2010 / Published online: 27 August 2010 Ó Springer Science+Business Media B.V. 2010 Abstract The association of water level changes and the relative (%) contributions of crustacean zooplank- ton 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 preda- tion pressure, both are a by-product of the large water influx during extreme wet winters. Keywords Stoichiometry  Copepod  Cladoceran  N-content  P-content  Zooplankton N:P Introduction Zooplankton are an important component of aquatic ecosystems, contributing to the N:P ratios of dis- solved and particulate matter in two ways: providing sources of dissolved nutrients via excretion, and comprising a sink for nutrients via removal and transfer of dissolved nutrients consumed by bacteria and phytoplankton to the particulate fraction by assimilating nitrogen (N hereafter) and phosphorous (P hereafter) into their biomass (Urabe et al., 1995). Zooplankton are homeostatic organisms, requiring relatively fixed N and P in their body tissues (Sterner Handling editor: L. Naselli-Flores This study is in partial fulfillment of the requirements for a Ph.D. thesis from the Bar Ilan University, for T. Rachamim. T. Rachamim (&)  N. Stambler  I. Berman-Frank The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, 52900 Ramat-Gan, Israel e-mail: tamarbsor@gmail.com T. Rachamim  T. Zohary  G. Gal Kinneret Limnological Laboratory, Israel Oceanographic and Limnological Research, PO Box 447, 14950 Migdal, Israel N. Stambler Department of Geography and Environment, Bar-Ilan University, 52900 Ramat-Gan, Israel 123 Hydrobiologia (2010) 655:121–135 DOI 10.1007/s10750-010-0413-6