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Different Flow Regimes (different + flow_regime)
Selected AbstractsThe effects of low summer flow on wild salmon (Salmo salar), trout (Salmo trutta) and grayling (Thymallus thymallus) in a small streamFRESHWATER BIOLOGY, Issue 12 2009W. D. RILEY Summary 1.,The effects of an experimentally imposed low summer flow on habitat use, displacement and survival of wild populations of juvenile salmon (Salmo salar), trout (Salmo trutta) and grayling (Thymallus thymallus) were investigated in a chalk stream. The habitat use and mobility of the fish in response to reduced flow was determined using passive integrated transponder-tag detector systems. 2.,Habitat use was compared to that available under different flow regimes. These consisted of an initial control phase of normal summer flow, an abrupt step change to 21 days of low flow, followed by a second control phase when normal summer flow was reinstated. First year (0+) salmon showed little change in their preferred substratum during low flow, whilst 1+ salmon increased their use of gravel and reduced that of mud during the day. Both 0+ and 1+ salmon were found in relatively deep water by day under low flow, whilst 1+ salmon preferred relatively shallow water at night. First year trout increased their use of gravel and reduced their use of mud and submerged tree roots under low flow, using relatively deep and fast flowing water by day. Older trout increased their use of gravel and occupied relatively deep, slow flowing water by day and relatively fast and shallow water at night. Grayling showed little change in their preferred substratum, but occupied relatively shallow water following the introduction of low flow. 3.,The range of movement of juvenile salmon increased at night under low flow, and was greater by day under normal flow. There was also an initial increase in the range of movement of 0+ trout following the introduction of low flow. Older trout initially moved less under low flow. With reduced flow, the range of movement by grayling increased significantly during the day. 4.,There was no net downstream displacement of any species with reduced flow, but the mortality rate in 0+ salmon, trout and grayling increased. This may be related to their small size and increased vulnerability to predation under low flow, and due to the reduction in depth and loss of the stream margins that are normally the preferred habitat of 0+ trout and grayling. 5.,The findings of this field study have implications for the management of braided, and highly regulated, chalk stream systems. In particular, they underline the importance of the stream margins as juvenile salmonid habitat, and suggest that a flow management strategy is required to mitigate for drought conditions. Such a strategy might include pre-emptive controls on abstraction and the maintenance of river flow via a prioritised route, predetermined using fish or habitat surveys, to minimise the effects of drought conditions on the more vulnerable or valued fish groups. [source] A simple model of hillslope response for overland flow generationHYDROLOGICAL PROCESSES, Issue 17 2001Professor Carmelo Agnese Abstract This paper deals with the derivation of the hydrological response of a hillslope on the assumption of quick runoff by surface runoff generation. By using the simple non-linear storage based model, first proposed by Horton, an analytical solution of the overland flow equations over a plane hillslope was derived. This solution establishes a generalization for different flow regimes of Horton's original solution, which is valid for the transitional flow regime only. The solution proposed was compared successfully with that of Horton and, for the turbulent flow regime, to the one derived from kinematic wave theory. This solution can be applied easily to both stationary and non-stationary rainfall excess events. An analytical solution for the instantaneous response function (IRF) was also derived. Finally, simple expressions to compute peak and time to peak of IRF are proposed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Vulnerability of age-0 pallid sturgeon Scaphirhynchus albus to fish predationJOURNAL OF APPLIED ICHTHYOLOGY, Issue 1 2010By W. E. French Summary Stocking is a commonly employed conservation strategy for endangered species such as the pallid sturgeon, Scaphirhynchus albus. However, decisions about when, where and at what size pallid sturgeon should be stocked are hindered because vulnerability of pallid sturgeon to fish predation is not known. The objective of this study was to evaluate the vulnerability of age-0 pallid sturgeon to predation by two Missouri River predators under different flow regimes, and in combination with alternative prey. To document vulnerability, age-0 pallid sturgeon (<100 mm) were offered to channel catfish Ictalurus punctatus and smallmouth bass Micropterus dolomieu in laboratory experiments. Selection of pallid sturgeon by both predators was measured by offering pallid sturgeon and an alternative prey, fathead minnows Pimephales promelas, in varying prey densities. Smallmouth bass consumed more age-0 pallid sturgeon (0.95 h,1) than did channel catfish (0.13 h,1), and predation rates did not differ between water velocities supporting sustained (0 m s,1) or prolonged swimming speeds (0.15 m s,1). Neither predator positively selected pallid sturgeon when alternative prey was available. Both predator species consumed more fathead minnows than pallid sturgeon across all prey density combinations. Results indicate that the vulnerability of age-0 pallid sturgeon to predation by channel catfish and smallmouth bass is low, especially in the presence of an alternative fish prey. [source] Seasonality of Competition in Early Development of Subtidal Encrusting CommunitiesMARINE ECOLOGY, Issue 3-4 2000Ben C. Maughan Abstract. Settlement panels immersed at Lough Hyne, County Cork, Ireland, at six stations with widely different flow regimes were retrieved at monthly intervals. Between 40 and 62 taxa were identified at each station during the study period. Percentage cover, number of interactions and number of recruits were recorded. Space occupied was found to vary more than 2.5 orders of magnitude between stations and seasons (0.3 , 82 %). Competition for space was most intense during summer, when recruitment was highest. More than 3600 interactions between pairs of species were recorded and competitive matrices are presented for the two stations with the most interactions. Both number of interactions and % cover were significantly higher at sites with greater water flow. The nature and the degree of competition varied between sites, with the most intense competition occurring in the very high flow sites with a large proportion of intraspecific encounters. Colonial species were more evident at the sites with high flow. Certain solitary species (notably Anomia ephippium and Pomatoceros spp.) were successful competitors in encounters with cheilostomatid bryozoans. Solitary species may prevent space monopolisation by the faster-growing bryozoans. ,Typical' early successional species, notably bryozoans such as Celleporella hyalina and Microporella ciliata, were more abundant at the more disturbed sites, implying either a larger adult population and/or preferential settlement of these species at such sites. [source] Sponge morphological diversity: a qualitative predictor of species diversity?AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2001James J. Bell Abstract 1.,To the non-specialist, problems are often associated with the quantification of sponge species diversity, as colour, shape and size can be highly variable within a single species. These variables can lead to an under-estimation of the contribution of sponges to the biodiversity of the benthos especially during biological surveys. 2.,Sponge species diversity (Shannon H, values), richness (mean number of species) and morphological diversity (Shannon H, values) were sampled at six sites (6 m depth intervals) on vertical (90°) and inclined surfaces (45°) experiencing different flow regimes at Lough Hyne Marine Nature Reserve (Ireland). Morphological diversity was sampled independently of species diversity. The time taken for the collection of both species and morphological diversity was recorded. 3.,Morphological diversity was positively correlated with both sponge species diversity (r2=0.87, p<0.05) and sponge species richness (r2=0.70, p<0.05). Linear regression was found to be significant for both the relationships (p<0.05 for each F -value). A sigmoidal relationship (r2=0.97, p<0.05) was found between morphological and species richness which proved to be significant (F -value 40.67, p<0.05). Separate Bray,Curtis dendrograms and correspondence analysis of morphological and species community compositions at the six sites showed very similar clustering and four major clusters were identified. 4.,The results of the present study indicate that sampling of sponge morphological diversity, rather than sponge species diversity and richness may be used as a qualitative estimate of sponge species diversity. Sampling of morphological diversity is much less time consuming, both in the field and laboratory, than collecting species diversity data and no specialist knowledge is required. Consideration is given to the use of such relationships in biological surveys and bio-monitoring. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||