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- 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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Use of the continuity principle to evaluate water processing rate of suspension-feeding mosquito larvae
- 1999
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Ingår i: Journal of the American Mosquito Control Association. - 8756-971X .- 1943-6270. ; 15:2, s. 228-237
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Tidskriftsartikel (refereegranskat)abstract
- Water processing rates of active suspension-feeding larvae of Culiseta morsitans and Cities quinquefasciatus 2nd and 4th instars were estimated through video image analysis of the conical jet flow driving the large recirculation patterns surrounding the organisms. In accordance with the principle of continuity, individual processing rates (PRs) were assessed by averaging a series of consecutive flow rates (Q(x)) defined as the product of the water velocity (U-x) and the associated cross-sectional area (A(x)) along a transect passing through the center of the delineated jet flow. Results clearly show very tight adherence to the principle of continuity. They also demonstrate that, although extreme care must be taken when streamtube delineation is performed, the methodology used can generate reliable assessment of individual processing rates regardless of the instars or species studied. The small coefficient of variation observed in assessing PR at the larval level further underlines the consistency of the method. Significant differences in water processing rates were observed for different species and instars. These could partially be related to body size, head width, and the length of the lateral palatal brushes (LPBs, which are the structures involved in the production of the water jet. Assessment of the jet velocity at the feeding groove level suggests the keg role of LPB beating frequency in the jet intensity, and consequently the magnitude of the processing rate. Analysis of data further indicates that obligate suspension feeders such as Cs. morsitans must sustain a larger flow pattern around the larvae to ensure sufficient particle entrapment than facultative suspension feeders (or even brushers) such as Cs. quinquefasciatus.
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| 3. |
- Vought, Lena B. M., et al.
(författare)
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Effect of riparian structure, temperature and channel morphometry on detritus processing in channelized and natural woodland streams in southern Sweden
- 1998
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Ingår i: Aquatic conservation. - 1052-7613 .- 1099-0755. ; 8:2, s. 273-285
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Tidskriftsartikel (refereegranskat)abstract
- 1. Ten south Swedish streams were selected to represent two distinct types—natural woodland streams and channelized streams. Measurements were made on leaching, decomposition and microbial respiration of the dominant riparian vegetation (European Black Alder), structure of the benthic macroinvertebrate community, macroinvertebrates inhabiting leaf material, channel morphometry, macrophyte composition, water chemistry and total accumulated degree days.2. Leaf decomposition rates were not significantly different when channelized streams were compared with natural woodland streams. In channelized streams the average decomposition rate was −0.0556±0.0337 (±S.D.) day−1 compared with −0.0457±0.0115 day−1 in natural woodland streams.3. There was significantly higher variation in leaf decomposition among the five channelized streams compared with the five natural streams (F–test, p<0.05). This was mainly due to extremely high decomposition rates in channelized streams colonized by emergent macrophytes.4. Alder decomposition rates were low in channelized streams without macrophytes (−0.0053 °day−1), intermediate in natural streams (−0.0087 °day−1), and high in channelized streams with macrophytes (−0.0136 °day−1).5. The shredder functional group ranged from 13 to 70% of the benthic community in the natural streams. Channelized streams had a more variable shredder population ranging from 0.5 to 80%. The highest values were found in channelized streams that had become colonized by macrophytes.6. There was a significant difference in total accumulated degree days between the channelized (256 °day) and natural woodland streams (209 °day). This is most likely an effect of drainage tiles contributing warmer groundwater to the channelized streams during fall.7. It is concluded that, contrary to the prevailing conceptual model of stream systems, decomposition rates and macroinvertebrate functions are not necessarily reduced in streams without riparian vegetation. The loss of the riparian canopy can stimulate emergent macrophytes which will provide autochthonous detritus for benthic communities. This will change benthic community structure and the life cycle strategies present.
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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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| 5. |
- Vought, Lena B. M., et al.
(författare)
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Structure and function of buffer strips from a water-quality perspective in agricultural landscapes
- 1995
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Ingår i: Landscape and Urban Planning. - 0169-2046 .- 1872-6062. ; 31:1-3, s. 323-331
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Tidskriftsartikel (refereegranskat)abstract
- Buffer strips can greatly improve the water quality of nearby agricultural streams by reducing nutrient leaching in groundwater and surface water runoff, even though they comprise little of the total catchment area. Hence, vegetated buffer zones located along streams and in the upland portions of the catchment can minimize erosion or trap sediments in surface runoff and thereby decrease phosphorus loading in surface water. For example, a buffer strip 10 m wide can reduce the phosphorus load, typically bound to sediment, by as much as 95%. Moreover, both natural and constructed riparian forests and wetlands may create conditions favorable for nitrogen transformation/removal by soil microbial processes such as denitrification, with as much as 100% of the nitrate being removed in these zones.In addition to nutrient removal, buffer strips will increase the diversity of flora and fauna in the otherwise monocultural landscape. The vegetation along the stream will also stabilize the stream banks and improve habitat for both fish and invertebrates within the stream.
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| 6. |
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