Algal communities of the Hadera River (Israel) under dramatic niche changes

The Hadera River is the most polluted among the Mediterranean coastal rivers of Israel due to abundant E. coli, high concentrations of heavy metals and nutrients, and high temperatures. In 2003-2008 we found 191 species of algae and cyanobacteria belonging to seven taxonomic divisions. The upper reaches were dominated by cyanobacteria and exhibited levels of toxic pollution. Downstream, the ecological niches of algal communities dramatically changed: upper stream diversity first increased and then decreased due to the influx of rainwater in the tidal zone during winter. On one hand, seasonal dynamics show that in winter, inorganic contamination was reduced because of dilution by the influx of rainwater, but, on the other hand, organic pollution increased from agriculture. Down the river, diversity increases and the community composition undergoes considerable change. In summer, algal blooms indicate a reduction of stress and aid in the river's self-purification. The WESI indices and RPI show steady year-round stressful conditions for algal photosynthesis with increasing instability in the river. Perpetuation of the current situation would disturb the self-purification capacity of the river ecosystem through destruction of biotic components. Statistical analysis (CCA) reveals the impact of wastewater as the most important stress factor for the Hadera River ecosystem, which is an exceptionally strong example of self-purification.