Spatial and temporal changes in habitat conditions in the Na'aman stream ecosystem, Israel

Nahal Na'aman is a small, shallow coastal stream in northern Israel. A three year study was conducted to examine the effect of habitat conditions on the biological structure and function of the stream ecosystem. Here we describe temporal and spatial changes in the water regime and water quality as measures of the stream's habitat conditions. Habitat condition is strongly influenced by the hydrological regime and the water quality. In dry years the water level drops and the upper section of the stream may dry up completely. Inflow of polluted water from various sources increasingly reduces water quality downstream. In general, the Na'aman may be categorized as oligo- to mesohaline stream, highly enriched with organic matter and nutrients. Sporadic pollution events markedly affect the water quality resulting in hypertrophic conditions, particularly at times of low stream levels. Low water quality was detected also in association with the drying and refilling of the stream's sections in late summer and in fall, respectively, and following runoff in winter. The oligohaline nature of the stream a priori reduces species diversity relative to other freshwater, lowland streams. Based on water quality conditions, highest species diversity may be expected in the spring area and the upper section of the stream. However, habitat conditions in this section are cost unstable due to changes of the hydrological regime. This, in turn, is expected to further reduce species richness and diversity. The extreme conditions are expected to determine the limit for the development of plant and animal life in the stream. This study illustrates the inherent problems of the coastal streams of Israel, namely, diminishing natural flow which is often replaced by discharge of effluent or sewage. Rehabilitation of the Na'aman and other coastal streams demands a radical solution for these problems.