Mixed stream channel morphologies: implications for fish community diversity

Abstract

ABSTRACT1. Stream classification systems are widely used in stream management and restoration. Whereas the principal morphological types of these classification systems are increasingly recognized for their ecological connections, the roles of intermediate and mixed morphologies are still poorly understood, yet may be biologically significant.2. Twenty-five stream reaches in north-western Vermont were classified by channel morphology to determine whether fish community diversity differed among pool-riffle, mixed (i.e. pool-riffle/cascade, pool-riffle/other) and forced pool-riffle stream morphological groups. Stream reach surveys included cross-sectional surveys, longitudinal profiles, bed substrate characterization, and fish surveys.3. Three fish community diversity measures were calculated: (1) species richness (S); (2) Shannon-Weaver Index (H 0 ); and (3) Simpson's Index (1/D). Multivariate analysis of covariance (MANCOVA) followed by analysis of variance (ANOVA) were used to explore potential differences in fish diversity among stream morphological groups. Fish diversity was significantly different for all three community diversity measures (P40.05), with pool-riffle/cascade morphology consistently exhibiting the greatest fish diversity and forced poolriffle the lowest.4. These results suggest that fish community diversity is significantly associated with distinct channel morphologies. Generally, pool-riffle/cascade and pool-riffle/other stream morphological groups supported habitats that fostered greater species diversity than more homogeneous and uniform pool-riffle reaches. The observed patterns of diversity are likely to be the result of habitat patches created by variations in flow and other physical characteristics in reaches of mixed morphologies.5. These results support fish sampling schemes that incorporate morphological heterogeneity, such as proportional-distance designation. Sampling strategies that focus on homogeneous reaches may underestimate diversity, and misrepresent stream condition when fish community data are used in indices of biological integrity (IBIs). Reaches of mixed stream morphologies should be recognized as areas of biological importance in stream and catchment management and in conservation efforts.

Wildfire severity mediates fluxes of plant material and terrestrial invertebrates to mountain streams

“…We measured a suite of common stream channel geomorphologic measurements at each study site following Cianfrani et al (2009) (see Table 1). We recorded one cross-sectional transect at a representative riffle or run.…”

“…We used a hierarchical reach classification approach to identify comparable and representative stream segment types based on channel bankfull width and depth, floodplain width, reach gradient, substrate type, and valley type (Frissell et al, 1986;Montgomery and Buffington, 1997;Bisson et al, 2006). We designated study sites within the selected stream segments by measuring a 100-m length along the stream, which represented at least 10Â bankfull width (see Harrelson et al, 1994;Cianfrani et al, 2009). All streams were 2nd or 3rd order (Strahler, 1952) located in alluvial valleys and reaches were characterized by step-pool morphology (Montgomery and Buffington, 1997).…”

Linkages between reach-scale physical habitat and invertebrate assemblages in upland streams

“…Physical-habitat variables are also directly relevant to other biota, such as fish, that migrate over larger spatial areas, and have more specific habitat requirements (Thomson et al 2004). Different geomorphic units may therefore support fish assemblages of differing richness (Cianfrani et al 2009) or fulfil different life-history functions. For example, runs may act as a feeding source, backwaters and pools as resting or nursery areas and gravel bars as spawning sites (Thomson et al 2004).…”

The Effect of Gabions on the Quality of a Stream Habitat

“…This type of activity has a negative impact on river biota and results in decreased biodiversity (Cianfrani et al, 2009;Palmer et al, 2010). Modifications resulting from regulations are very noticeable in assessments of the availability of specific habitats that are necessary for a river´s restoration (Mažeika et al, 2006).…”