New Publication - Sand and Fines bedded sediment criteria development

 New Article in the Journal of the North American Benthological Society

Protecting sediment-sensitive aquatic species in mountain streams through the application of biologically based streambed sediment criteria

Authors:  Sandra A. Bryce, Gregg A. Lomnicky, and Philip R. Kaufmann

Abstract. We evaluated several lines of evidence to identify bedded fine sediment levels that should protect and maintain self-sustaining populations of native, sediment-sensitive aquatic species in the western US. To identify these potential criterion values for streambed sediments ƒ0.06 mm (fines) and ƒ2 mm (sand and fines) diameter, we examined: 1) the range of areal % fines and areal % sand and fines values at 169 least-disturbed reference sites in our sample, 2) sediment tolerance values calculated for a selection of sediment-sensitive aquatic vertebrate and macroinvertebrate taxa for both particle size ranges, 3) quantile regression predictions of the declines in vertebrate and macroinvertebrate Indices of Biotic Integrity (IBIs) at progressively higher ambient levels of streambed sediment from synoptic survey data acquired in 557 mountain stream sampling sites in 12 western states, 4) a literature review of the effects of sand and fines on the survival of salmonid eggs to hatching, and 5) a literature review of studies that quantitatively linked macroinvertebrate response to the pertinent size ranges of streambed sediment in mountain streams. Predicted maximum vertebrate Index of Biotic Integrity (IBI) declined 4.4 points (SE = 1.0) and macroinvertebrate IBI declined 4.0 points (SE = 0.60) for each 10% increase in % fines. Similarly, for each 10% increase in % sand and fines, the predicted maximum vertebrate IBI decreased 3.7 points (SE = 0.50) and macroinvertebrate IBI decreased 3.0 points (SE = 0.50). Combining all lines of evidence, we concluded that for sediment-sensitive aquatic vertebrates, minimum-effect sediment levels were 5% and 13% for % fines and % sand and fines, respectively, both expressed as areal percentages of the wetted streambed surface. For aquatic macroinvertebrates, minimum-effect levels for the 2 sediment size classes were 3% and 10%, respectively. We encourage managers to consider these biologically based minimum effect values when developing sediment criteria for mountain streams. Quantifying and comparing both vertebrate and macroinvertebrate assemblage responses to streambed sedimentation informs the criteria setting process and allows managers to set stream restoration priorities.