Distribution and species composition of macroinvertebrates in the hyporheic zone of bed sediment

The hyporheic zone is a layer of substrate on a river bed where benthic animals normally live, grow, feed, reproduce, and exist for any portion of their life cycle. The hyporheic zone was studied by sampling and experiment in mountain streams. Macroinvertebrates in hyporheic zone were sampled from the Juma, Xizhi, Songhua, Yanghe, and Guishui Rivers from May 2008 to August 2009. An experiment of colonization of macroinvertebrates at different depths of gravel or cobble beds was conducted in the Juma River. Results revealed that thickness of the hyporheic zone with living macroinvertebrates varied within a large range. The hyporheic zone is only several centimeters thick in sand bed, but up to 60 cm in cobble bed. The number of taxa increased with increasing median diameter of bed material. Numerous taxa were found in gravel and cobble beds, but few were observed in silt and fine sand beds. The experiment showed that macroinvertebrates colonized in a new habitat in about 6 weeks; predator species took longer to colonize than did other species. Macroinvertebrate abundance varied with bed depth and sediment size. The highest abundance was found at a bed depth of 0-30 cm. More macroinvertebrates were found in the gravel bed with median diameter of 2 cm than in the cobble bed with median diameter of 5-10 cm. Different taxa exhibited different bed depth preferences. Larvae of Dytiscidae, Haliplidae, and Atyidae lived only in upper layers near the bed surface, and taxa with hard covers or shells, such as larvae of Corydalidae, Naucoridae, and Corbiculidae preferred the lower layers with bed depths larger than 30 cm.