Hyporheic discharge of river water into fall chinook salmon (Oncorhynchus tshawytscha) spawning areas in the Hanford Reach, Columbia River

Fall chinook salmon (Oncorhynchus tshawytscha) spawned predominantly in are as of the Hanford Reach of the Columbia River where hyporheic water dischar ged into the river channel. This upwelling water had a dissolved solids con tent (i.e., specific conductance) indicative of river water and was presume d to have entered highly permeable riverbed substrate at locations upstream of the spawning areas. Hyporheic discharge zones composed of undiluted gro und water or areas with little or no upwelling were not used by spawning sa lmon. Rates of upwelling into spawning areas averaged 1200 L.m(-2).day(-1) (95% CI = 784-1665 L.m(-2).day(-1)) as compared with approximately 500 L.m( -2).day(-1) (95% CI = 303-1159 L.m(-2).day(-1)) in nonspawning areas. Disso lved oxygen content of the hyporheic discharge near salmon spawning areas w as about 9 mg.L-1 (+/- 0.4 mg.L-1) whereas in nonspawning areas, dissolved oxygen values were 7 mg.L-1 (+/- 0.9 mg.L-1) or lower. In both cases, disso lved oxygen of the river water was higher (11.3 +/- 0.3 mg.L-1). Physical a nd chemical gradients between the hyporheic zone and the river may provide cues for adult salmon to locate suitable spawning areas. This information w ill help fisheries managers to describe the suitability of salmon spawning habitat in large rivers.