Spatial linkages between geomorphic and hydraulic conditions and invertebrate drift characteristics in a small mountain stream

Although invertebrate drift plays a fundamental role in river ecosystems, spatial linkages between its characteristics and hydrogeomorphic conditions remain poorly understood. This study, conducted in a small stream in British Columbia, provides insight into such relationships. Most notably, drift concentration was positively correlated with bed scour, and mean body size was negatively correlated with bed fill. Although correlational design precludes inference regarding mechanisms, these results are consistent with protracted effects of flood-related bed disturbances on spatial pattern of drift characteristics under low flow conditions. We detected no robust associations between drift and flow characteristics that could not be explained by bed disturbances. Because of high spatial variability, drift characteristics were statistically distinct only in few habitat types. Compared with middepth, invertebrate drift concentration was higher near water surface, and mean body size was larger near the bed. Mean body size was also statistically smaller in riffle-pool transitions, which experienced largest bed fill. Possible legacy effects of bed disturbances could have broader implications for drift-related energy and nutrient fluxes in river corridors and for quantitative drift models.