River Dan, headwater of the Jordan, an aquatic oasis of the Middle East

Abstract

River Dan is the largest of the headwater rivers of the Jordan. The karstic exsurgence of the Dan has a seasonally stable output, a long stretch of strongly turbulent flow, stable temperature around 15.5 °C and high oxygen saturation. A total of 156 taxa, mainly at the species level, were identified from the river. These species are almost exclusively of Palearctic origin. About half of the species are limited to the northernmost part of Israel. The faunal complex described, does not present any longitudinal zonation for the 5 kilometers of turbulent flow; neither does it present seasonal changes in species composition. River Dan is considered to be a post-Pleistocenic river which has an important function of refugium for a wide area of aquatic waterbodies in the area, including the presently drained Lake Hula. It is suggested that in the Illies scheme of stream classification, River Dan might represent a type of stream belonging to a 'pseudorhithral' along with other stenothermic warm water torrents of the tropical-subtropical climatic belt.

Faunal relationships to abiotic factors along the River Dan in northern Israel

“…Stations 1, 2 and 4 were situated upstream of the water diversion pipe, Stations 5 and 6 were situated downstream (see Map). Detailed descriptions of the habitat of each station, including photographs, are to be found in Por et al (1986).…”

“…More detailed information, including site description and photographs can be found in Por et al (1986) and Allan et al (1988).…”

“…Casual comparison with the results of qualitative sampling on natural substrata (Por et al, 1986) indicated the presence of a similar invertebrate assemblage. The only obvious differences are a lower representation of aquatic Hemiptera and surface-dwelling Coleoptera (e.g.…”

“…In order to simplify the myriad factors that can influence the distribution and density of aquatic populations, some researchers have concentrated on spring brook communities, whose reduced environmental variability has been generally thought to lead to a simplified system characterized by low diversity and richness of species (Teal, 1957;Tilly, 1968;Ward & Dufford, 1979;Reice & Herbst, 1982;Por et al, 1986).…”

“…The construction of a water diversion project (for irrigation purposes) on the river, approx. 2.4 km from the source springs, has given impetus to a great deal of research effort (Por et al, 1986;Allan et al, 1988). Such projects can affect aquatic communities via flow reduction (Brooker, 1981;Scullion, 1983;Canton et al, 1984) or by changing environmental constancy (Ward & Dufford, 1979;Scullion etal., 1982;Ward & Stanford, 1983;McAuliffe, 1984).…”