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

Abstract

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.

Structure and functional composition of macroinvertebrate communities in coastal plain streams across a precipitation gradient

“…For instance, Mediterranean intermittent streams with dry channels were defined by organisms with life history adaptations such as short life cycles and resistant forms, but intermittent streams with pool availability were similar to perennial sites (García‐Roger, 2017). The positive correlation coefficient between abundance in the drift and increasing annual rainfall rate was probably a function of the greater hydrological stability in sub‐humid streams providing a fitness advantage for taxa that are actively drifting in order to avoid predation and actively seek out new resource patches (Cienciala & Hassan, 2018; Naman et al, 2016; Poff et al, 2006).…”

A simple method for sampling invertebrate drift in large rivers and boulder‐bed streams

“…Although our very small sample size necessitates caution in interpreting this pattern, it is consistent with either (a) higher drift concentrations closer to the stream bed (i.e., in the shallower near‐shore samples; e.g., Sagar & Glova, ), or (b) accumulation of drift in marginal lower velocity (depositional) habitats, analogous to higher vehicle densities as traffic slows in congested traffic (Anderson, Harrison, Nisbet, & Kolpas, ). However, evaluating these competing mechanisms would require vertical profiles of drift concentration (e.g., Cienciala & Hassan, ; Stark, Shearer, & Hayes, ) or measuring drift settling rates in different habitats.…”

“…The split rod could also be fitted with a simple rope and pulley system to manually raise and lower the net for depth integrated sampling. Aperture size of drift nets vary depending on study objectives; larger nets ensure a more spatially representative sample collected in a short time period (Baxter et al, ), whereas smaller nets allow assessment of finer‐scale spatial variation in drift concentration (Cienciala & Hassan, ). Because our intent was to sample high‐velocity habitats with the potential to quickly clog the mesh of the net (Baxter et al, ; Muehlbauer, Kennedy, Copp, & Sabol, ), we used a large 30‐cm diameter collar ring with a 1.8‐m long bag that widened at the downstream end to increase the net surface area and reduce backpressure at the mouth of the net.…”

Vegetation and Geomorphic Connectivity in Mountain Fluvial Systems

“…These effects can persist for decades after the initial disturbance, especially when large quantities of coarse material are supplied [247,248] (Figure 8D). Such changes, in turn, alter disturbance regimes in riverine ecosystems [234,[249][250][251][252], which are tightly linked to sediment dynamics [253][254][255]. Therefore, a better understanding of these cascading effects is critical also from the point of view of ecosystem conservation and restoration [256,257].…”