A Bayesian analysis of physical habitat changes at tributary confluences in cobble‐bed upland streams of the Acheron River basin, Australia

Wallis, Elizabeth; Nally, Ralph Charles Mac; Lake, Philip Spencer

doi:10.1029/2008wr006831

Cited by 11 publications

(25 citation statements)

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“…Milesi and Melo, 2014;Clay et al, 2015). Ultimately, this reflects the complex nature of tributary-mainstem interactions and the lack of simple systematic relations between tributary properties and their impact (Rhoads, 1987;Wallis et al, 2008). In low order streams, bedrock controls on channel geometry, disruption of sediment connectivity by wood loading and direct coupling of the channel to hillslope sediment sources may mask tributary effects (Krumbein, 1942;Miller, 1958;Benda and Cundy 1990;Rice and Church, 1996;McEwen and Miller, 1998;Rengers and Wohl, 2007;Al Farraj and Harvey, 2010;Kuo and Brierley, 2014;Menting et al, 2015).…”

Section: Tributary-driven Aggradation In River Networkmentioning

confidence: 99%

Tributary connectivity, confluence aggradation and network biodiversity

Rice

2017

Geomorphology

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In fluvial networks, some confluences are associated with tributary-driven aggradation where coarse sediment is stored, downstream sediment connectivity is interrupted and substantial hydraulic and morphological heterogeneity is generated. To the extent that biological diversity is supported by physical diversity, it has been proposed that the distribution and frequency of tributary-driven aggradation is important for the magnitude and spatial structure of river biodiversity. Relevant ideas are formulated within the Link Discontinuity Concept and the Network Dynamics Hypothesis, but many of the issues raised by these conceptual models have not been systematically evaluated. This paper first tests an automated method for predicting the likelihood of tributary-driven aggradation in three large drainage networks in the Rocky Mountain foothills, Canada. The method correctly identified approximately 75% of significant tributary confluences and 97% of insignificant confluences. The method is then used to evaluate two hypotheses of the Network Dynamics Hypothesis: that linear-shaped basins are more likely to show a longitudinal, downstream decline in tributary-driven aggradation; and that larger and more compact basins contain more confluences with a high probability of impact. The use of a predictive model that included a measure of tributary basin sediment delivery, rather than symmetry ratio alone, mediated the outcomes somewhat, but as anticipated, the number of significant confluences increased with basin size and basin shape was a strong control of the number and distribution of significant confluences. Doubling basin area led to a 1.9-fold increase in the number of significant confluences and compact basins contained approximately twice as many significant confluences per unit channel length as linear basins. In compact basins, significant confluences were more widely distributed, whereas in linear basins they were concentrated in proximal reaches. Interesting outstanding issues include the possibility of using spatially-distributed sediment routing models to predict tributary-driven confluence aggradation and the need to gather ecological data sufficient to properly test for increases in local and network-scale biodiversity associated with significant confluences and their network-scale controls.

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Section: Tributary-driven Aggradation In River Networkmentioning

confidence: 99%

Tributary connectivity, confluence aggradation and network biodiversity

Rice

2017

Geomorphology

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“…It is possible that a tributary effect on macroinvertebrate biodiversity may operate further downstream than this. However, many physical tributary effects occur immediately downstream of the confluence, such as confluence scour and change in mean bed particle size (Best 1988;Rice et al 2001;Wallis et al 2008), so it is likely that changes to the assemblages of benthic macroinvertebrates, were they to occur, should have been detectable close to confluences. It is possible that active upstream movements of macroinvertebrates from below the confluence also might contribute to homogenization, reducing effects of the incoming tributary.…”

Section: Discussionmentioning

confidence: 99%

“…Two estimators were used so that we could assess whether our inferences were affected by choice of estimator. We used model (1) (Wallis et al 2008) to analyse patterns of variation in macroinvertebrate taxonomic richness and of density in the vicinity of stream junctions. Angle of junction and discharge ratio of tributary to mainstem are known to affect movement of sediment through confluences and so, plausibly may influence macroinvertebrates (Best 1988); these are regarded as covariates.…”

Section: Statistical Analysesmentioning

confidence: 99%

“…Tributary confluences are important areas in which materials, including biota, are transferred between adjacent river segments (Rice et al 2001;Benda et al 2004;Wallis et al 2008). Boundary zones or transitional habitats often are more heterogeneous and support greater biodiversity than the habitats upon which they border .…”

Section: Introductionmentioning

confidence: 99%

“…We used a systematic design to assess patterns of diversity at eight confluences (in both high and low flows) in cobble-bed streams in the Acheron River basin in Victoria, Australia (Wallis et al 2008). The design was based on five survey zones, which were located upstream of the confluence in the mainstem (two locations), upstream of the confluence in the tributary, at the confluence, and downstream of the confluence (Fig.…”

Section: Introductionmentioning

confidence: 99%

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Geometry of biodiversity patterning: assemblages of benthic macroinvertebrates at tributary confluences

2010

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We assessed whether tributaries in upland catchments (=watersheds) affected assemblages of benthic macroinvertebrates in mainstems, as has been reported in northern hemisphere systems. Eight confluences of small to medium streams (stream orders 1-4, 2.2-10.8 m wide) were studied in the Acheron River basin in Victoria, Australia. For each confluence, two transects were sampled at each of five zones relative to the confluence: two zones upstream in the mainstem, one zone upstream in the tributary, one zone at the confluence and one zone downstream in the mainstem. Surveys were conducted in both high-flow and lowflow conditions. In mainstems, there was no change in macroinvertebrate density, taxonomic richness or functional feeding group composition downstream relative to upstream of the confluences. While tributaries statistically had distinctive benthic macroinvertebrate assemblages compared to mainstems, these distinctions were small. In low flows, densities in tributaries were substantially lower than in mainstems, but densities during high flows were more similar (albeit only about one-third as high as in low flow) in tributaries and mainstems. An inverse pattern was evident for taxonomic richness, where richness in tributaries and mainstems was similar in low flows but was greater in mainstems than in tributaries in high flows. We found little evidence of tributary effects in macroinvertebrate assemblages in this basin, which is at odds with some previous results from other continents. To explain this divergence, we suggest a conceptual model outlining factors that control variation in effects of tributaries on assemblages of benthic macroinvertebrates in mainstems.

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Discontinuities concentrate mobile predators: quantifying organism–environment interactions at a seascape scale

et al. 2016

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Understanding environmental drivers of spatial patterns is an enduring ecological problem that is critical for effective biological conservation. Discontinuities (ecologically meaningful habitat breaks), both naturally occurring (e.g., river confluence, forest edge, drop‐off) and anthropogenic (e.g., dams, roads), can influence the distribution of highly mobile organisms that have land‐ or seascape scale ranges. A geomorphic discontinuity framework, expanded to include ecological patterns, provides a way to incorporate important but irregularly distributed physical features into organism–environment relationships. Here, we test if migratory striped bass (Morone saxatilis) are consistently concentrated by spatial discontinuities and why. We quantified the distribution of 50 acoustically tagged striped bass at 40 sites within Plum Island Estuary, Massachusetts during four‐monthly surveys relative to four physical discontinuities (sandbar, confluence, channel network, drop‐off), one continuous physical feature (depth variation), and a geographic location variable (region). Despite moving throughout the estuary, striped bass were consistently clustered in the middle geographic region at sites with high sandbar area, close to channel networks, adjacent to complex confluences, with intermediate levels of bottom unevenness, and medium sized drop‐offs. In addition, the highest striped bass concentrations occurred at sites with the greatest additive physical heterogeneity (i.e., where multiple discontinuities co‐occurred). The need to incorporate irregularly distributed features in organism–environment relationships will increase as high‐quality telemetry and GIS data accumulate for mobile organisms. The spatially explicit approach we used to address this challenge can aid both researchers who seek to understand the impact of predators on ecosystems and resource managers who require new approaches for biological conservation.

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A Bayesian analysis of physical habitat changes at tributary confluences in cobble‐bed upland streams of the Acheron River basin, Australia

Cited by 11 publications

References 60 publications

Tributary connectivity, confluence aggradation and network biodiversity

Tributary connectivity, confluence aggradation and network biodiversity

Geometry of biodiversity patterning: assemblages of benthic macroinvertebrates at tributary confluences

Discontinuities concentrate mobile predators: quantifying organism–environment interactions at a seascape scale

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