Constant Flow Regime Research Articles

THE EFFECT OF HYDROLOGICAL DISTURBANCE ON THE IMPACT OF A BENTHIC INVERTEBRATE PREDATOR

The harsh–benign model of community dynamics predicts that the impact of predation will decline as abiotic conditions become more stressful to biota. Experiments were conducted to determine whether hydrological disturbance altered the impact of an invertebrate predator in stream benthic communities. The impact of a predatory stonefly, Cosmioperla kuna, on its mayfly prey was measured in experimental stream channels receiving constant or variable flow (flooding) regimes over a one-week period. Contrary to predictions of the harsh–benign hypothesis, the impact of Cosmioperla on its two major prey taxa was either unchanged or increased by artificial floods, despite increased predator emigration from variable-flow channels. Predator impacts in variable-flow treatments were apparently strongly influenced by predator-induced prey emigration during floods. The results of this study show that nonlethal predator effects may be important during abiotic disturbance, and that it may not be reasonable to predict the impact of predation solely on the basis of the relative tolerances of predators and prey to prevailing abiotic conditions.

Acceleration of Pine Island and Thwaites Glaciers, West Antarctica

AbstractRecent satellite investigations revealed that in the 1990s the grounding line of Pine Island and Thwaites Glaciers, West Antarctica, retreated several km, the ice surface on the interior of the basins lowered 10 cm a–1, and Pine Island Glacier thinned 1.6 ma–1. These observations, however, were not sufficient to determine the cause of the changes. Here, we present satellite radar interferometry data that show the thinning and retreat of Pine Island Glacier are caused by an acceleration of ice flow of about 18 ± 2% in 8 years. Thwaites Glacier maintained a nearly constant flow regime at its center, but widened along the sides, and increased its 30 ± 15% mass deficit by another 4% in 4 years. The combined mass loss from both glaciers, if correct, contributes an estimated 0.08 ± 0.03 mma–1 global sea-level rise in 2000.

The Intermediate Disturbance Hypothesis: application of this concept to the response of epilithon in a regulated Mediterranean river (Lower-Durance, southeastern France)

Hydrological regime is responsible for the most significant disturbances occurring in the regulated lower part of the River Durance. The present study was an attempt at determining the response of epilithon to the hydrodynamic disturbances occurring in this river. Three patterns of hydrodynamic disturbance resulting from three different types of regime were analysed. Under low stable compensation flow regimes, disturbance frequency and intensity were considered to be low. Under constant release flow regimes, disturbance frequency and intensity were considered to be severe. High compensation flow regimes with infrequent releases were considered intermediate. The validity of the Intermediate Disturbance Hypothesis (IDH) was confirmed for the number of algal species and the autotrophic index (an index for estimating the autotrophic versus heterotrophic balance). The results show that when the disturbance was of intermediate severity, the autotrophic and heterotrophic communities were balanced, which was not the case at either low or high hydrodynamic disturbance levels. The results allow to define the habitat of the epilithic algal species. Colonizer and competitor species were identified on the basis of the IDH. Several obviously ubiquious and resistant species were recorded at all three disturbance levels.

Flow around the afterbody of a plate in a longitudinal gas stream with transverse injection from the lateral surface

The flow around the afterbody of a plate of finite thickness in a supersonic gas stream is investigated on the basis of a numerical solution of the time-dependent Navier-Stokes equations for a compressible viscous heat-conducting gas. The change in the flow pattern with the onset of transverse slot injection from the body surface in the vicinity of the base section is studied. For constant supersonic injection, both steady and unsteady flow regimes could be obtained depending on the values of certain relevant parameters.

Species richness and spatial variation in fish assemblage structure in two rivers of the Wet Tropics of northern Queensland, Australia

Fish assemblages were sampled at 22 sites within the Mulgrave and South Johnstone Rivers of the Wet Tropics World Heritage Area, north Queensland. Flow regimes of these rivers are highly predictable, by Australian standards, due to low annual and seasonal variability. A gradual downstream change in fish assemblage structure, correlated with gradual change in habitat, substrate and type of in-stream cover, was observed in the Mulgrave River but not the South Johnstone. A reduced species richness was observed in the South Johnstone relative to the Mulgrave probably due to the effect of two high gradient sections located in the former river and a more diverse array of habitat types present in the latter. Both rivers contained more species than other tropical Australian rivers of greater size. Possible reasons for this included the constant and predictable flow regime and the greater diversity of habitats found in rivers of the Wet Tropics compared to other tropical Australian rivers.

Ecology of alpine streams

SUMMARY1. This review examines ecological conditions and zoobenthic communities of kryal, krenal and rhithral streams of the alpine zone. Altitudinal and biogeographical faunal patterns are also analysed.2. Kryal segments, fed by glacial meltwater, are characterized by low temperatures (Tmax4°C) and large diel flow fluctuations in summer. The water may be clear or turbid from suspended rock flour. Fishes and higher plants are absent. The macroalga Hydrurus foetidus may be abundant in kryal and other alpine stream types of the Holarctic. The highly restricted cosmopolitan fauna of glacial brooks consists of diamesine chironomids, sometimes accompanied by simuliids. Sparse food resources include algae and allochthonous (aeolian) organic matter.3. Rhithral segments in alpine catchments are characterized by soft water, a hydrograph dominated by an extended period of snowmelt runoff, and a broader temperature range than kryal or krenal biotopes. Bryophytes, macroalgae (chrysophytes, chlorophytes, cyanophytes, rhodophytes) and epiphytic and epilithic diatoms constitute the flora. A relatively diverse zoobenthos includes four orders of insects (Flecoptera, Ephemeroptera, Trichoptera, Diptera), turbellarians, acarines, oligochaetes and nematodes.4. Krenal segments, fed by groundwater, are typically calcareous with summer‐cool and winter‐warm thermal conditions, high water clarity, and constant flow regimes. Bryophytes and macroafgae are accompanied by a rich diatom flora. The zoobenthos consists of a composite of kryal and rhithral elements with few crenobionts. Zoobenthos species richness values are intermediate between those of kryal and rhithral segments, whereas densities in perennial, well‐oxygenated springbrooks far exceed those in other alpine stream types.5. Downstream faunal changes are most predictable in kryal segments where chironomids of the genus Diamesa are the predominant, if not sole, members of the zoobenthos in the upper zone of glacial brooks, the metakryal. Where Tmax exceeds about 2°C the transition to the hypokryal occurs and Diamesa is co‐dominant with simuliids. These largely stenozonal headwater forms decline downstream where Tmax exceeds about 4°C, concomitant with a marked increase in the euryzonal mountain fauna.6. Species occurring in alpine rhithral biotopes tend to be euryzonal forms at their upper alrirudinal limits, whereas the lower elevation mountain stream fauna consists of species with narrower distribution limits. There is, however, a precipitous drop in mean altitudinal range from the alpine rhithral to the kryat because of the stenozonal nature of the glacial brook fauna.7. The view that effects of temperature on generation time and mutation rate determine the speed at which selection proceeds is consistent with altitudinal species richness patterns exhibited by zoobenthos along the alrirudinal gradient and may provide an evolutionary explanation for the low faunal diversity in alpine headwaters.8. With increasing altitude, mountain ‘islands’ become progressively insular as area decreases and isolation increases. For a cold‐adapted stream fauna the insular nature of mountain tops is greatest in the tropics. Nonetheless, alpine stream faunas generally

Relative Importance of Mechanisms Determining Decomposition in a Southeastern Blackwater Stream

-Chemical inhibitors were used to separate the effects and determine the relative importance of microbial degradation, flow-related fragmentation, and shredder fragmentation on sweet gum (Liquidambar styraciflua) decomposition rates in Upper Three Runs, in South Carolina. We correlated several abiotic and biotic variables (current velocity, accumulation of inorganic and fine particulate organic matter, water depth, bacterial density and shredder biomass) with the decomposition of individual sweet gum leaf packs. We also surveyed the biomass and density of shredders in natural leaf accumulations and in constructed leaf packs to help determine the importance of shredders in decomposition. Except for accumulated sediments (inorganic and fine particulate organic matter, FPOM), none of the independent variables, including base-flow current velocity and shredder biomass, were significantly correlated with decomposition of individual sweet gum leaf packs. Sediment accumulation was inversely related to decomposition rates. Experimental analyses suggested that microbial degradation dominated the decomposition processes. A constant flow regime characterized by low current velocities, plus a depauperate shredder abundance, accounted for the relatively minor role of shredders and flow-related fragmentation.

Flow regime of the Lambert Glacier-Amery Ice Shelf system, Antarctica: structural evidence from Landsat imagery

High-resolution visible and near-infrared satellite imagery provides a means of investigating the structural glaciology, and in turn the dynamics, of large ice masses. The Lambert Glacier-Amery Ice Shelf system is one of the largest ice drainage basins in Antarctica and has previously yielded conflicting evidence concerning its dynamic behaviour: either that the system has a propensity for surging or that it has a constant flow regime. Digital manipulation of Landsat imagery allows analysis of the structure of the glacier system, showing longitudinal foliation, medial moraines and crevasse patterns that provide no evidence of surging behavior during the residence time of ice in the glacier system.

Flow regime of the Lambert Glacier-Amery Ice Shelf system, Antarctica: structural evidence from Landsat imagery

High-resolution visible and near-infrared satellite imagery provides a means of investigating the structural glaciology, and in turn the dynamics, of large ice masses. The Lambert Glacier-Amery Ice Shelf system is one of the largest ice drainage basins in Antarctica and has previously yielded conflicting evidence concerning its dynamic behaviour: either that the system has a propensity for surging or that it has a constant flow regime. Digital manipulation of Landsat imagery allows analysis of the structure of the glacier system, showing longitudinal foliation, medial moraines and crevasse patterns that provide no evidence of surging behavior during the residence time of ice in the glacier system.

Flow regime of the Lambert Glacier-Amery Ice Shelf system, Antarctica: structural evidence from Landsat imagery

High-resolution visible and near-infrared satellite imagery provides a means of investigating the structural glaciology, and in turn the dynamics, of large ice masses. The Lambert Glacier-Amery Ice Shelf system is one of the largest ice drainage basins in Antarctica and has previously yielded conflicting evidence concerning its dynamic behaviour: either that the system has a propensity for surging or that it has a constant flow regime. Digital manipulation of Landsat imagery allows analysis of the structure of the glacier system, showing longitudinal foliation, medial moraines and crevasse patterns that provide no evidence of surging behavior during the residence time of ice in the glacier system.

Strain and kinematic analysis in general shear zones

We present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear, and thus provide a framework in which data previously considered contradictory may be understood. Rigid and deformable porphyroclast systems, including σ, δ and complex σ-δ grains are potential indicators of both strain and flow. The shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes. General shear is divided into two fields: sub-simple shear, in which the rotational component of the strain is less than that for simple shear, and super-simple shear, in which the rotational component is greater than for simple shear. Sub-simple shear may involve narrowing or broadening of shear zones. Super-simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts, but must be enclosed by regimes of sub-simple shear. The polar Mohr constructions for finite deformation and flow are useful to analyze general shear in theory. The hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number, W n. This number represents the relative contributions of pure and simple shear in steady flow. In nature, deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime. We therefore introduce the concept of accelerating deformation and analyze the implications of non-steady flow for the shearing histories of deformed objects.

Influence of Flow Regime on Life History, Production, and Genetic Structure of Baetis tricaudatus (Ephemeroptera) and Hesperoperla pacifica (Plecoptera)

Life histories, annual production, and genetic structure for two insect species were examined for two adjacent streams that differ in flow regime. Birch Creek had a mesic groundwater (seasonally constant) flow regime; Little Lost River had a snowmelt (seasonally cyclic) flow regime. Baetis tricaudatus was multivoltine, whereas Hesperoperla pacifica had a life cycle longer than one year. The life histories of B. tricaudatus were similar between streams, but mean biomass was greater in Birch Creek. Gene frequencies of B. tricaudatus also were similar between streams, Nei's genetic distance being only 0.011. Expected heterozygosities and population polymorphisms were higher in the Little Lost River. In contrast, the life histories of H. pacifica were different between streams, emergence being later in the Little Lost River. This difference could be explained by temperature. However, the genetic structure of H. pacifica showed the same pattern as B. tricaudatus with more polymorphisms and higher heterozygosities occurring in the Little Lost River. Nei's genetic distance between the H. pacifica populations was 0.054. These data support the idea that populations exhibit greater genetic variability in more variable environments than populations in relatively more constant environments.

Urban Storm Water Discharges: Effects upon Communities of Sessile Diatoms and Macro-Invertebrates

From 1985 to 1987, long-term and more or less permanent effects of discharges from combined or separate sewer systems on communities of sessile diatoms and macro-invertebrates in receiving waters have been studied. Sessile diatoms and/or macro-invertebrates have been investigated on 46 locations, spread all over The Netherlands. The results were related to the type of sewer system, the discharges, and the characteristics of the receiving water, and compared with results from sample(s) taken from a corresponding water not influenced by sewer overflows, the reference water. In general, communities of sessile diatoms and macro-invertebrates indicate a more severe organic pollution and disturbance of receiving waters compared with reference waters. In the immediate vicinity of the overflows these communities were more disturbed than at some distance. In small ditches, effects were more pronounced compared with large waterbodies and waters with a constant flow regime. Finally, effects of combined sewer overflows were more pronounced than effects of discharges from separate sewer systems, except for locations in industrial areas.

Single bubble formation at orifices submerged in viscous liquids

AbstractThis paper concerns the slow formation of gas bubbles at circular orifices submerged in liquids with viscosities ranging from 10 to 1000 poise. A mathematical model is developed for predicting the bubble lift‐off size as a function of, basically, Froude, Weber and Reynolds numbers; it is analytical and does not depend on semi‐empirical coefficients.To check the validity of this model, experiments involving various gas flow rates and orifice diameters were performed in several liquids. The model consistently underestimates the experimentally obtained bubble size; the error of estimate varies from 10 to 25%. For bubble formation in a regime between the constant flow and constant pressure regimes, both the chamber pressure and the flow rate into the bubble vary. Furthermore, the instantaneous gas flow rate into the bubble can be many times greater than the average flow rate in the piping far upstream of the orifice exit. The former flow rate is important in determining the forces acting on the bubble and a method is given for obtaining its average value.