CHARACTERIZING IN-STREAM FLOW REFUGIA

Flow in nine streams was examined in relation to refugia for invertebr ates. Areas of bed maintaining low hydraulic stress throughout the dis charge hydrograph could provide flow refugia for animals during spates . In one stream, near-bed shear stress and velocity were repeatedly me asured in discrete patches. Three types were identified: ''fast'' patc hes maintained high hydraulic stress, ''variable'' patches showed the greatest change in stress, and ''slow'' patches maintained low stress and thus were potential refugia. Average stress increased with dischar ge, but potential refugia were prominent throughout and could be impor tant for invertebrates. Abundances of refugia in eight comparison stre ams were characterized by changes in the frequency distribution of flo w forces with discharge. Three stream types were identified that did n ot simply reflect channel size or morphology. Such stream-specific flo w patterns could affect the structure of comunities through the differ ing provision of refugia. Longitudinal transport processes in these st reams were investigated by solute dilution experiments and by the appl ication of a model to measure an aggregated ''dead zone''. Transport ( and dead zone volume) varied among streams and further reflected their refuge potential. Clearly, flow habitat features could intervene in p opulation and community dynamics by providing refuge from spates.