Effects of dispersed recreational activities on the microbiological quality of forest surface water.
(1/591)
The microbiological quality of forest surface waters in the Greenwater River watershed was examined to investigate the influence of heavy motorized camping in an area with no sanitary facilities. Indicator densities increased during weekend human-use periods when compared to weekdays. Increases in indicator densities were also noted downstream from heavily used camping areas when compared to upstream sites. Seasonal, weekly, and diurnal fluctuations in indicator densities were observed. This study suggests that potential health hazards exist in this watershed during periods of human use. (+info)
Incidence and causes of tenosynovitis of the wrist extensors in long distance paddle canoeists.
(2/591)
OBJECTIVES: To investigate the incidence and causes of acute tenosynovitis of the forearm of long distance canoeists. METHOD: A systematic sample of canoeists competing in four canoe marathons were interviewed. The interview included questions about the presence and severity of pain in the forearm and average training distances. Features of the paddles and canoes were determined. RESULTS: An average of 23% of the competitors in each race developed this condition. The incidence was significantly higher in the dominant than the nondominant hand but was unrelated to the type of canoe and the angle of the paddle blades. Canoeists who covered more than 100 km a week for eight weeks preceding the race had a significantly lower incidence of tenosynovitis than those who trained less. Environmental conditions during racing, including fast flowing water, high winds, and choppy waters, and the paddling techniques, especially hyperextension of the wrist during the pushing phase of the stroke, were both related to the incidence of tenosynovitis. CONCLUSION: Tenosynovitis is a common injury in long distance canoeists. The study suggests that development of tenosynovitis is not related to the equipment used, but is probably caused by difficult paddling conditions, in particular uneven surface conditions, which may cause an altered paddling style. However, a number of factors can affect canoeing style. Level of fitness and the ability to balance even a less stable canoe, thereby maintaining optimum paddling style without repeated eccentric loading of the forearm tendons to limit hyperextension of the wrist, would seem to be important. (+info)
The aerodynamics and hydrodynamics of plants.
(3/591)
Because they grow away from their substratum to compete for light, plants have to withstand hydrodynamic or aerodynamic drag. Both water and land plants reconfigure in response to this drag, and this is presumed to reduce the risk of mechanical failure. However, there is little unequivocal evidence of drag reduction in large trees as a result of reconfiguration. Land plants must also transport water internally to their tissues, and many have developed xylem tracheids and vessels that help speed up this process. Recent evidence that tree height is limited by water supply suggests that water transport efficiency must be a crucial element in tree design. However, the resistance of many parts of the xylem is still unknown. More focused work is urgently required to shed light on the evolution and ecology of plants in relation to the flow of fluids. (+info)
Limits to optimization: fluid dynamics, adhesive strength and the evolution of shape in limpet shells.
(4/591)
Limpets are commonly found on wave-swept rocky shores, where they may be subjected to water velocities in excess of 20 m s(-1). These extreme flows can impose large forces (lift and drag), challenging the animal's ability to adhere to the substratum. It is commonly thought that the conical shape of limpet shells has evolved in part to reduce these hydrodynamic forces while providing a large aperture for adhesion. This study documents how lift and drag actually vary with the shape of limpet-like models and uses these data to explore the potential of hydrodynamic forces to serve as a selective factor in the evolution of limpet shell morphology. At a low ratio of shell height to shell radius, lift is the dominant force, while at high ratios of height to radius drag is dominant. The risk of dislodgment is minimized when the ratio of height to radius is 1.06 and the apex is in the center of the shell. Real limpets are seldom optimally shaped, however, with a typical height-to-radius ratio of 0.68 and an apex well anterior of the shell's center. The disparity between the actual and the hydrodynamically optimal shape of shells may be due to the high tenacity of limpets' adhesive system. Most limpets adhere to the substratum so strongly that they are unlikely to be dislodged by lift or drag regardless of the shape of their shell. The evolution of a tenacious adhesion system (perhaps in response to predation) has thus preempted selection for a hydrodynamically optimal shell, allowing the shell to respond to alternative selective factors. (+info)
Hydrodynamics, shell shape, behavior and survivorship in the owl limpet Lottia gigantea.
(5/591)
On wave-swept rocky shores, limpets are subjected to water velocities in excess of 20 m s(-1), which may impose large hydrodynamic forces. Despite the extreme severity of this flow environment, predictions from conical models suggest that limpets' shells are typically far from the optimal shape that would minimize the risk of dislodgment, a deviation that is allowed by the high tenacity of the limpets' adhesive system. In this study, we test this conclusion using an actual limpet. The shell of Lottia gigantea differs substantially from the hydrodynamic optimum in that its apex is displaced anteriorly to form a plough, which is used to defend the limpet's territory. The hydrodynamic effects of this shape are similar to those observed in conical models: the animal experiences an increased lift when facing into the flow and a decreased lift when the flow is at its back. However, neither effect has a substantial impact on the risk of dislodgment. When the animal is stationary, its adhesion to the substratum is very strong, and its risk of being dislodged is small regardless of its orientation to the flow and despite its sub-optimal shape. In contrast, when the animal is crawling rapidly, its adhesion is substantially decreased, and it would probably be dislodged by rapid flow even if the shell were shaped optimally. The risk of dislodgment by waves is therefore functionally independent of shell shape. In essence, despite the extremely high water velocities to which this species is subjected, its shell has had the 'permission' of the flow environment to respond to other selective factors, in particular those associated with its aggressive, territorial behavior. The result is a shell that is both a potent territorial weapon and a functional (albeit less than optimal) hydrodynamic shape. (+info)
Stomatopod antennule design: the asymmetry, sampling efficiency and ontogeny of olfactory flicking.
(6/591)
Many crustaceans detect odors from distant sources using chemosensory sensilla (aesthetascs) on their antennules. The greater the flow of water through arrays of aesthetascs, the faster the access of odorant to receptors inside the aesthetascs. Stomatopods facilitate odorant access by flicking their antennules, thus increasing the relative velocity of the water reaching their aesthetascs. We used dynamically scaled physical models to investigate how aesthetasc size and spacing and antennule flicking velocity affect flow penetration into the simple aesthetasc arrays of the stomatopod Gonodactylaceus mutatus. Particle image velocimetry of flow fields near models of juvenile and adult antennules revealed that velocity gradients around the aesthetascs are steeper during the outward part of the flick than during the return stroke and that the velocity gradients are steeper at the aesthetasc tips than at their bases. More fluid per unit time flows between aesthetasc rows during the outward stroke than during the return stroke, ensuring that odor sampling is pulsatile. During flicking, velocity gradients are steeper near adult aesthetascs than near juvenile aesthetascs, and adults process more fluid per unit time than juveniles. The resulting differences in odorant access can be related to size- and age-dependent changes in stomatopod ecology. (+info)
Sensory processing of water currents by fishes.
(7/591)
Water currents are extremely important in the aquatic environment and play a very significant role in the lives of fishes. Sensory processing of water currents involves a number of sensory modalities including the inner ear, vision, tactile sense and the mechanosensory lateral line. The inner ear will detect whole-body accelerations generated by changes in flow, or by turbulence, whereas visual and tactile inputs will signal translational movement with respect to an external visual or tactile reference frame. The superficial neuromasts of the mechanosensory lateral line detect flow over the surface of the body and have the appropriate anatomical distribution and physiological properties to signal the strength and the direction of flow and, hence, contribute to the detection of regional differences in flow over different parts of the body. (+info)
Upwelling intensification as part of the Pliocene-Pleistocene climate transition.
(8/591)
A deep-sea sediment core underlying the Benguela upwelling system off southwest Africa provides a continuous time series of sea surface temperature (SST) for the past 4.5 million years. Our results indicate that temperatures in the region have declined by about 10 degrees C since 3.2 million years ago. Records of paleoproductivity suggest that this cooling was associated with an increase in wind-driven upwelling tied to a shift from relatively stable global warmth during the mid-Pliocene to the high-amplitude glacial-interglacial cycles of the late Quaternary. These observations imply that Atlantic Ocean surface water circulation was radically different during the mid-Pliocene. (+info)