Quantitative response of riverine benthic invertebrates to sediment grain size and shear stress
The most widespread pressure impacting river ecological status is the degradation of key hydromorphologic elements, such as sediment type and flow rate. However, almost nothing is known about the quantitative relationship between benthic invertebrate abundance and these elements. This synthesis compiles quantitative data on physical requirements and thresholds for invertebrates relative to two hydromorphologic factors: substrate size and hydraulic energy (measured as shear stress). Both factors are commonly a focus of river rehabilitation. However, we found only limited literature data that we could use to identify invertebrate preferences (189 taxa). Preferred substrate sizes of all stream epifauna we examined varied between 0.05 and 400 mm and they prefer shear stresses from 0.13 to 3.67 N m−2. There was no difference in variation of preferred conditions between the examined taxonomic levels. We suspect that taxa preferring hydraulic environments with shear stresses < 0.64 N m−2 are affected more by environmental factors than solely being constrained by substrate or hydraulic energy preferences. Such taxa might be useful as sensitive indicator species for evaluating stream integrity. Hence, to optimize restoration success for riverine biota, hydromorphological forces should be mitigated by manipulating habitat complexity in a way that it enhances intact ecological processes.