AbstractThe stable flow and temperature regimes of spring-fed streams are distinct from the dynamic regimes of other streams. We investigated differences in habitat and macroinvertebrate assemblages among a spring-fed tributary, an adjacent non-spring-fed tributary, and mainstream reaches. Current velocity was slowest in the spring-fed reach and percent fine sediment deposition was 3.8–13.9 times higher than in non-spring streams. Mean periphyton biomass was greatest in the mainstream reach where canopy openness was greatest, whereas the standing stock of detritus was greatest in the spring-fed reach. These results suggest that the stable flow regime in the spring-fed stream leads to the accumulation of fine sediment and detritus on the streambed. Oligochaeta and chironomids, which are burrower-gatherers, were remarkably abundant in the spring-fed reach and total macroinvertebrate abundance was 3.4–12.2 times greater than in the other reaches. Sprawler-grazer ephemeropterans were abundant in the mainstream reaches, likely due to higher primary productivity. Allomyia sp, which depend on cool spring-fed habitats, were found only in the spring-fed reach. The macroinvertebrate assemblage in the spring-fed reach was characterized by numerous burrowers, collector-gatherers, and crenobiont taxa, highlighting the contribution of these habitats to beta diversity in river networks.
Unique habitat and macroinvertebrate assemblage structures in spring-fed streams: a comparison among lowland tributaries and mainstreams in northern Japan