ABSTRAKT

We recognized 247 species of algae from five divisions in 53 samples of plankton and periphyton collected at 14 stations over the Nahal Yarqon in 2003−2004. Of these, 204 species are indicators of environmental conditions. Species distribution over ecological groups is typical of alkaline freshwater or brackish, temperate, slow-running waters habitable for both planktonic and benthic algae. The indicators of saprobity (Watanabe's scale) show a medium level of organic pollution. The saprobity index S (Sladeček's scale) vary from 1.31 (the upper reaches) to 2.88 near the industrial area of Petakh-Tikva corresponding to II-IV classes of water quality. The self-purification capacity of the Nahal Yarqon ecosystem is rather high corresponding to the olgo- to alphamesosaprobic zones. The environmental pollution index (EPI) varies from 2 to 4 indicating a range of slightly to strongly polluted water of Class II and III. The Water Ecosystem State Index (WESI) testifies to a toxic impact on the algae in the low-water season. The River Pollution Index for saprobity (RPIs = 2.3), conductivity (RPIε = 2.0−2.7), nitric nitrogen (RPI_N= 1−8), and pH (RPI_pH= 7.7−7.8) indicate alkaline moderately mineralized waters with an occasional input of nitrates round the year, corresponding to the Class III water quality and the betamesosaprobic self-purification zone. Our results allow an estimate of self-purification capacity for the Nahal Yarqon on the basis of modern international approaches. We provide indicators for evaluation and monitoring of the river. This study shows the potentials of the algal bioindication method for aquatic ecosystems of Israel.