| 1. |
- Lacoursière, Jean O., 1958-
(författare)
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A laboratory study of fluid flow and microhabitat selection by larvae of Simulium vittatum (Diptera: Simuliidae)
- 1992
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Ingår i: Canadian Journal of Zoology. - 0008-4301 .- 1480-3283. ; 70:3, s. 582-596
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Tidskriftsartikel (refereegranskat)abstract
- Microhabitat selection by Simulium vittatum Zetterstedt larvae in a flume was studied at different mainstream velocities on two substrates; a thin flat plate parallel to the flow and a cylinder in cross flow. The results do not support the generally accepted assumptions that simuliid larvae keep within the boundary layer to avoid the direct influence of mainstream current and that they select the fastest velocity available when offered a longitudinal velocity gradient within their tolerance range. Instead, larvae gathered along the zone of boundary layer separation and remained along the stagnation line at the leading point of the cylinder when artificially positioned there. Further, under most conditions, larvae avoided zones of maximum surface shear stress. Larval reaction to hydraulic changes was immediate. It is hypothesized that S. vittatum larvae first scan the velocity profile at the substrate, initially moving toward increasing flow velocity (or water acceleration). They than cue on a steep velocity gradient along the body as part of the processes involved in choosing a location for suspension feeding.
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| 2. |
- Lacoursière, Jean O., 1958-, et al.
(författare)
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A small flume for studying the influence of hydrodynamic factors on benthic invertebrate behaviour
- 1990
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Ingår i: Journal of The North American Benthological Society. - 0887-3593 .- 1937-237X. ; 9:4, s. 358-367
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Tidskriftsartikel (refereegranskat)abstract
- A compact, versatile flume for studying the influence of hydrodynamic factors on the behaviour of benthic invertebrates is described. A range of lotic micro-environments can be simulated under controlled and replicable conditions by tailoring the velocity profile at the entrance of the test section. A specially designed diffuser composed of an array of adjustable horizontal rods allows tailored flow (e.g., zone of high shear stress, adjustable velocity gradient and turbulence level) to which organisms can be exposed. Water velocities of up to a maximum of 81.5 plus or minus 0.6 cm/s, with a turbulence intensity of 0.8% can be achieved. Simultaneous observations of flow and organism behaviours can be done by means of standard flow visualization techniques. Compact (72 cm long x 22 cm high x 10 cm wide; volume 10 L) and easily transportable, this flume is an inexpensive "desk-top" version of larger, more bulky systems, without sacrifice of performance and versatility.
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| 3. |
- Lacoursière, Jean O., 1958-, et al.
(författare)
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Fluid transmission and filtration efficiency of the labral fans of black fly larvae (Diptera: Simuliidae) : Hydrodynamic, morphological, and behavioural aspects
- 1993
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Ingår i: Canadian Journal of Zoology. - 0008-4301 .- 1480-3283. ; 71:1, s. 148-162
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Tidskriftsartikel (refereegranskat)abstract
- Body stance and water flow through the labral fans of suspension-feeding Simulium vittatum Zetterstedt larvae were examined using dead and live larvae. Transmission of flowing water through the fans were determined by means of dye injections. Feeding stance is the outcome of an active feedback process between flow forces and behavioural reactions that maintains the fans in an optimal filtering position. Fans responded to velocity increases through structural reconfiguration, which resulted in an increase in aperture size. As the velocity decreased, an increased fraction of the water directly approaching the fan aperture flowed around its perimeter, with no flow through the fans below 2.5 cm/s. Fluid transmission never exceeded 30-35%, even at velocities up to 50 cm/s. Calculations of suspension-feeding efficiency are reformulated to reflect labral fan transmission and behavioural components of the feeding process. Simulium vittatum larvae are consequently showed to be 4-26 times more efficient in filter feeding than has been previously assessed. The effect of flow on labral fan transmission is discussed in relation to known habitat choices and feeding behaviours of simuliid larvae.
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| 4. |
- Vought, Lena B. M., et al.
(författare)
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Nutrient retention in riparian ecotones
- 1994
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Ingår i: Ambio. - 0044-7447 .- 1654-7209. ; 23:6, s. 342-348
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Tidskriftsartikel (refereegranskat)abstract
- Nutrient retention mechanisms in riparian buffer strips are reviewed with emphasis on surface runoff and subsurface flows, the main pathways of exchanges between the stream and its surroundings. Unique physical and biogeochemical properties prevailing in these riparian ecotones dictate the flux of water, nutrients and other exogenous substances between the upland areas and the stream. Removal of nutrients from surface inflows is induced by deposition of sediment bound nutrients and exchange of dissolved nutrients with the soil/litter surface. Removal of nitrogen in subsurface flows can partly be explained by vegetation uptake, but the main mechanism for removal is usually denitrification. In channelized streams, the subsurface inflows have, in most cases, been altered to discharges via drainage tiles, with the exchange flows (water leaving and re-entering the open-channel via the stream bed and banks) being greatly decreased. Consequently, to improve nitrogen removal in these systems, these flows have to be intercepted or reestablished either through restoration of the old stream valley or through managed structures in the buffer strips.
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