Effects of Sediment Deposition on Riverine Benthic Communities

The deposition of fine sediments (particularly those less than <2mm) has been shown to adversely affect riverine biotic communities. Habitat changes caused by sedimentation include: increases in water velocity (by reducing streambed roughness); infilling of interstitial spaces; and reduction in the thickness of the boundary layer.  The goal of this study was to examine the effect of fine sediment embeddedness on growth rates of the critically endangered Nooksack Dace (Rhinichthys cataractae), and on the community structure of benthic invertebrates that constitute dace prey. Sixteen 20-cm wide experimental raceways, were constructed adjacent to Pepin Creek, British Columbia. Each was assigned one of four treatments: 0% embedded, 100% coarse sand embedded (2-7mm), 100% fine sand embedded (0.1-7mm), and 50% fine sand embedded (0.1-7mm). One dace was stocked in each raceway at 4.5dace/m².  Preliminary results indicate that embeddedness caused shifts in benthic invertebrate community structure, resulting in an overall decrease in invertebrate biomass. Effects of embeddedness on dace growth were unclear because of predation by mink. All surviving dace were located in the unembedded treatments, demonstrating the effects of embeddedness on the availability of interstitial refuges and the vulnerability of dace to predation, in addition to altering the structure of invertebrate prey communities.