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Stream Gradient (stream + gradient)
Selected AbstractsHabitat-mediated size selection in endangered Atlantic salmon fry: selectional restoration assessmentEVOLUTIONARY APPLICATIONS (ELECTRONIC), Issue 4 2010Michael M. Bailey Abstract Preservation of adaptive variation is a top priority of many species restoration programs, but most restoration activities are conducted without direct knowledge of selection that might foster or impair adaptation and restoration goals. In this study, we quantified geographic variation in selection on fry size of endangered Atlantic salmon (Salmo salar) during the 6-week period immediately following stocking in the wild. We also used a model selection approach to assess whether habitat variables influence patterns of such selection. We found evidence for significant size-selection in five out of six selection trials. Interestingly, the strength and pattern of selection varied extensively among sites, and model selection suggested that this variation in phenotypic selection was related to geographic variation in the presence of large woody debris and the slope of the stream gradient. The strong selection differentials we observed should be a concern for endangered salmon restoration, whether they reflect natural processes and an opportunity to maintain adaptation, or an indicator of the potentially deleterious phenotypic consequences of hatchery practices. [source] Factors controlling the chemical evolution of travertine-depositing rivers of the Barkly karst, northern AustraliaHYDROLOGICAL PROCESSES, Issue 15 2002Russell N. Drysdale Abstract Groundwaters feeding travertine-depositing rivers of the northeastern segment of the Barkly karst (NW Queensland, Australia) are of comparable chemical composition, allowing a detailed investigation of how the rate of downstream chemical evolution varies from river to river. The discharge, pH, temperature, conductivity and major-ion concentrations of five rivers were determined by standard field and laboratory techniques. The results show that each river experiences similar patterns of downstream chemical evolution, with CO2 outgassing driving the waters to high levels of calcite supersaturation, which in turn leads to widespread calcium carbonate deposition. However, the rate at which the waters evolve, measured as the loss of CaCO3 per kilometre, varies from river to river, and depends primarily upon discharge at the time of sampling and stream gradient. For example, Louie Creek (Q = 0·11 m3 s,1) and Carl Creek (Q = 0·50 m3 s,1) have identical stream gradients, but the loss of CaCO3 per kilometre for Louie Creek is twice that of Carl Creek. The Gregory River (Q = 3·07 m3 s,1), O'Shanassy River (Q = 0·57 m3 s,1) and Lawn Hill Creek (Q = 0·72 m3 s,1) have very similar gradients, but the rate of hydrochemical evolution of the Gregory River is significantly less than either of the other two systems. The results have major implications for travertine deposition: the stream reach required for waters to evolve to critical levels of calcite supersaturation will, all others things being equal, increase with increasing discharge, and the length of reach over which travertine is deposited will also increase with increasing discharge. This implies that fossil travertine deposits preserved well downstream of modern deposition limits are likely to have been formed under higher discharge regimes. Copyright © 2002 John Wiley & Sons, Ltd. [source] Influence of mapping resolution on assessments of stream and streamside conditions: lessons from coastal Oregon, USA,AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2009Ken Vance-Borland Abstract 1.Digital hydrographic data are commonly employed in research, planning, and monitoring for freshwater conservation, but hydrographic datasets differ in spatial resolution and accuracy of spatial representation, possibly leading to inaccurate conclusions or unsuitable policies for streams and streamside areas. 2.To examine and illustrate the potential for different hydrographic datasets to influence in-channel and streamside characterizations, a study area in the US Pacific Northwest was chosen because 1:100,000, 1:24,000, and densified 1:24,000 hydrography are available and widely used in research and management for several species of Pacific salmon and trout at risk. The potential was examined for differences among the digital hydrographic datasets in: (1) spatial extent to influence estimated abundances of fish habitat, streamside buffer conditions, and fish distributions; and (2) spatial position to influence estimated streamside buffer conditions and estimated stream gradient. 3.The analysis of spatial extent found the total stream length represented by the 1:100,000 hydrography was approximately one half that of 1:24,000 hydrography and only one fifth that of densified 1:24,000 hydrography. The 1:100,000 and 1:24,000 networks differed significantly for 13 out of 18 fish habitat attributes, and the three hydrographic datasets differed significantly for many characteristics in streamside buffers; fish distributions mapped at 1:24,000 added 6,14% of stream length to 1:100,000 distributions. The analysis of spatial position found few differences between the 1:100,000 and 1:24,000 hydrography in streamside buffer characteristics but significant differences in channel gradient. 4.Overall, hydrographic datasets differed only slightly in spatial position but differed in spatial extent to the point of representing different populations of streams. If species inhabiting larger streams (greater mean annual discharge) are of interest, then results derived from studies based on 1:100,000 hydrography should prove useful. However, higher-resolution hydrography can be critical when designing and implementing strategies to protect fish and other aquatic species at risk in smaller streams. Copyright © 2008 John Wiley & Sons, Ltd. [source] Genetic and morphological evidence for reproductive isolation between sympatric populations of Galaxias (Teleostei: Galaxiidae) in South Island, New ZealandBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2001JONATHAN M. WATERS New Zealand's South Island houses a flock of closely related stream-resident fish taxa (Galaxias vulgaris sensu lato), including a number of species recently described on the basis of subtle morphological differences. The taxonomic status of some members of the species complex remains uncertain. This study examines the degree of reproductive isolation between recently recognized morphotypes from Southland (G. ,southern', flatheads; G. gollumoides, roundheads) which co-occur in Bushy Creek, a tributary of the Mataura R. Although these morphotypes are broadly sympatric in Southland and Stewart Island, Bushy Creek is their only documented zone of contact. Molecular (microsatellite, isozyme and mtDNA markers) and morphological analyses of 139 fish samples across a 500-m transect (seven stations) reveal a cline from predominantly G. ,southern' (N=85) to predominantly G. gollumoides (JV=54), corresponding with a gradual increase in stream gradient. Multivariate analyses of genotypic and morphological data independently reveal distinct clusters that are completely congruent with mtDNA type, suggesting an absence of mtDNA introgression. Our data support the separate species status of G. ,southern' and G. gollumoides under both biological and phylogenetic species concepts. We suggest that the speciation of these taxa occurred in allopatry through independent losses of diadromy, with sympatry resulting from secondary contact. [source] Factors controlling the chemical evolution of travertine-depositing rivers of the Barkly karst, northern AustraliaHYDROLOGICAL PROCESSES, Issue 15 2002Russell N. Drysdale Abstract Groundwaters feeding travertine-depositing rivers of the northeastern segment of the Barkly karst (NW Queensland, Australia) are of comparable chemical composition, allowing a detailed investigation of how the rate of downstream chemical evolution varies from river to river. The discharge, pH, temperature, conductivity and major-ion concentrations of five rivers were determined by standard field and laboratory techniques. The results show that each river experiences similar patterns of downstream chemical evolution, with CO2 outgassing driving the waters to high levels of calcite supersaturation, which in turn leads to widespread calcium carbonate deposition. However, the rate at which the waters evolve, measured as the loss of CaCO3 per kilometre, varies from river to river, and depends primarily upon discharge at the time of sampling and stream gradient. For example, Louie Creek (Q = 0·11 m3 s,1) and Carl Creek (Q = 0·50 m3 s,1) have identical stream gradients, but the loss of CaCO3 per kilometre for Louie Creek is twice that of Carl Creek. The Gregory River (Q = 3·07 m3 s,1), O'Shanassy River (Q = 0·57 m3 s,1) and Lawn Hill Creek (Q = 0·72 m3 s,1) have very similar gradients, but the rate of hydrochemical evolution of the Gregory River is significantly less than either of the other two systems. The results have major implications for travertine deposition: the stream reach required for waters to evolve to critical levels of calcite supersaturation will, all others things being equal, increase with increasing discharge, and the length of reach over which travertine is deposited will also increase with increasing discharge. This implies that fossil travertine deposits preserved well downstream of modern deposition limits are likely to have been formed under higher discharge regimes. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||