|M.Sc Student||Sima Usvyatsov|
|Subject||The Relationship between Extreme Climatic Conditions and|
Phytoplankton Temporal and Vertical Distribution
and Species Composition in Lake Kinneret
|Department||Department of Biology||Supervisors||Full Professor Beja Oded|
|Dr. Tamar Zohary|
Continuous sampling of several water quality parameters at the center of Lake Kinneret has become possible in May 2002 with the setting-up and operation of the Remote Underwater Sampling System (RUSS) - an autonomous profiling apparatus equipped with a set of sensors that sends data to the shore by telemetry in near real-time. The data collected is of high resolution in space and time, providing sub-daily to seasonal tracking of Chlorophyll (Chl) distribution in the water column. The RUSS Chl record required post-calibration, which was done against weekly extracted Chl data (laboratory analyses of water samples collected from discrete depths at the same location), collected as part of the Kinneret Limnological Laboratory routine monitoring program. The relationships between unusual climatic events, e.g. storms or periods of high air temperature and low wind (khamsins), and phytoplankton data, collected during these disturbances, were analyzed. The plankton species or assemblages to be studied were chosen according to their relative importance in the annual cycle at Lake Kinneret. The general pattern of blooms consists of Aulacoseira granulata winter bloom, Peridinium gatunense spring bloom and a summer population of mainly nanoplanktonic chlorophytes, diatoms and cyanobacteria. The aims of this study were as following: (1) To compile and calibrate the 2-year raw high-resolution Chl RUSS dataset and examine it at timescales ranging from sub-daily to seasonal. (2) To study the relationships between climatic events and the abundance and vertical distribution of Peridinium, Aulacoseira and the summer phytoplankton assemblage.
The post-calibrated RUSS Chl dataset had high correlation to both laboratory extracted monitoring Chl values and biomass levels. These results support its applicability at Lake Kinneret for qualitative and quantitative high-resolution Chl measurements and phytoplankton biomass approximation. The dataset reveals not only seasonal and annual phytoplankton dynamics (e.g. Peridinium and Aulacoseira blooms, summer low Chl values, photosynthetic bacteria metalimnetic bloom), but also daily to sub-daily phenomena and patterns (such as the transition from Aulacoseira to Peridinium bloom, Peridinium vertical migration, summer daily Chl fluctuation). No correlation was found between depth distributions of Peridinium, Aulacoseira and summer population and wind conditions. Correlations between Chl, biomass and phytoplankton species composition vs. water temperature and wind conditions yielded no results. These results could be explained by either (1) insufficient data or (2) the existence of factors of stronger influence on phytoplankton than the examined parameters, e.g. nutrient concentrations, CO2 availability, light intensity, trace metals, grazing pressure, allelopathy, or fungal and viral parasites.