Ref ID : 7157
A.J. Boulton, H.M. Valett, and S.G. Fisher; Spatial distribution and taxonomic composition of the hyporheos of several Sonoran Desert streams. Arch.Hydrobiol. 125(1):37-61, 1992
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A survey of desert streams in Arizona, U.S.A. revealed a rich hyporheos (56 taxa) dominated by crustaceans, especially cyclopoid and harpacticoid copepods, amphipods, bathynellaceans, isopods and ostracods. Interstitial water mites formed a diverse assemblage whereas insects were species-poor relative to surface benthos. There was little faunal overlap between the composition of epigean and hyporheic communities. Most hyporheic taxa appeared to be detritivores. We recognized four biotopes that were physicochemically and biotically distinctive in desert streams: a shallow hyporheic biotope down to approximately 50 cm, a phreatic biotope between 50 cm and bedrock, a parafluvial biotope comprising saturated sediments lateral to the wetted channel, and a dry channel hyporheic biotope that exists temporarily after surface water has disappeared. The shallow hyporheic zone is relatively well-oxygenated, low in nutrients, physically unstable (due to floods and drying), and harbours most taxa. Nutrients are higher whereas oxygen levels are lower in the more stable phreatic zone where larger interstitial spaces and higher hydraulic conductivity allow amphipods, isopods, and bathynellaceans free movement. In the parafluvial zone, nutrient levels vary, the water is hypoxic, and only nematodes and bathynellaceans are common. When surface water dries, a subset of the shallow hyporheic assemblage dominated by the water mites Meramecia and Neomamersa, ostracods, ceratopogonid larvae, and nematodes occurs. These biotopes can be viewed as functional subunits of the desert stream ecosystem. The existence of a rich hyporheic biota indicates the importance of subsurface processes in desert streams, and may provide a valuable tool for biomonitoring groundwater pollution in arid zones.