Fast Current Velocities Research Articles

The Role of Current and Light in Explaining the Habitat Distribution of the Lotic Snail Elimia semicarinata (Say)

We sampled Doe Run, Kentucky to search for habitat-mediated differences in the abundance and size distribution of a pleurocerid grazer, Elimia semicarinata, predicted by the literature. Adult density was 3× greater in a slow-flow, sunny habitat, than in faster flowing or shaded habitats where densities were similar. Adult size was greatest in slow-flow habitats, and smallest in habitats with faster current velocities. In comparison, juvenile densities were greater in habitats with faster current velocities. Linear regressions indicated that both adult density and size were negatively related to current velocity, but that juvenile abundance was positively related to current velocity; none of the variables were significantly affected by light levels. Periphyton biomass (both chlorophyll a concentration and ash-free dry mass) was generally greater in slow-flow, sunny habitats, and lower in habitats with faster current velocities, suggesting current velocity may indirectly affect snail size distributions by altering food resources. Differences in gastropod size and density were maintained among habitats even though a field experiment suggested rapid colonization rates in all habitats. An experiment with in situ flow baffles revealed that the number and size of snails colonizing flow refugia increased only in habitats with faster current velocities. Taken together, our results suggest that adults may select flow refugia, while juveniles avoid them, and that pleurocerid population dynamics are influenced by current velocity directly by shear stress, or indirectly by effects of current velocity on periphyton biomass. Future studies of grazer-periphyton interactions should take such complexities into account.

Phenotypic Plasticity in a Suspension-Feeding Insect, Simulium lundstromi (Diptera: Simuliidae), in Response to Current Velocity

The morphology of the labral fans of blackfly larvae is intimately interrelated with the lotic habitats in which they live. Marked seasonal variations in the primary fan morphology of Simulium lundstromi were found in a natural population. In separate experiments, larvae of the overwintering and summer generations were reared at two different current velocities. For both seasons, larvae living in slow velocity (8 cm s -1 ) flumes developed larger primary fans with wider distance between individual rays, and longer stems than those exposed to fast current velocities (31-35 cm s -1 ). These morphological adaptations apparently serve to enable feeding at different flow regimes by balancing particle encounter rates with malfunction of the fans caused by the effects of high drag. However, larvae of both generations had low survival rates and long development times at slow current velocities compared with those in faster flow, because the morphological modifications could not compensate completely for the reduced delivery rate of food particles resulting from the low current velocity. The observed plasticity of fan morphology in response to variation in current velocity is consistent with the natural conditions found in the stream where the larvae lived. This suggests that phenotypic plasticity in blackfly larvae has evolved in response to the intrinsically heterogeneous nature of running water environments.

Patterns of Microhabitat Use Among Four Species of Darters in Three Appalachian Streams

-We used snorkeling techniques to examine patterns of microhabitat use among four species of darters-Etheostoma flabellare, E. blennioides, Percina gymnocephala and the potentially threatened E. osburni-in three West Virginia streams. Sympatric darter species were generally segregated in each stream, based on microhabitat use variables of mean depth, current velocity and substrate type. In all three streams-the East Fork of the Greenbrier River, the Cherry River and Laurel Creek-E. osburni was observed in fast current velocities and rock substrate in water depths ranging from 20 to 30 cm. In the East Fork of the Greenbrier River and Laurel Creek, E.fiabellare was common in slower velocities over predominantly cobble substrate. Percina gymnocephala and E. blennioides were spatially segregated from E. osburni on the basis of water column depth. Differences in habitat use may be related to morphological differences between species.

Interaction between the effects of Substratun, Velocity and location on Stream Benthos: and experiment

Patches of large and small pebbles were created in three riffles (fast current velocities) and three pools (slow velocities). It was expected that patches with different sizes of pebbles in the two velocity regimes would vary in the entrapment of fine sediments and organic matter, which in turn would result in differences in benthic community structure. This was not the case, for although deposition of fine material was greater in pools, there were appreciable location-specific differences in the fauna unrelated to the variables monitored in the experiment. Functional feeding groups did not respond predictably to the distribution of detritus. Generally, the community was least influenced by substratum size, with any differences being inconsistent across locations. Most other substratum effects were attributable to the presence of epilithon on undisturbed control patches. Velocity was the most influential factor, with riffles having higher total abundances and higher species richness. Some taxa showed strong location- specific differences. At the level of a small patch of pebbles, the colonization dynamics of the fauna are probably a mixture of species- and location-specific dispersal and selection mechanisms. At larger spatial scales, however, community structure is more predictable, with pools differing substantially from riffles.

PERFORMANCE TESTS OF THREE FAST CURRENT OIL RECOVERY DEVICES1

ABSTRACT Presently, the effective removal of oil spills is limited to current speeds of less than one to two knots. To be able to effectively recover spilled oil in areas of higher current speeds, the Coast Guard has a development effort underway for obtaining such a device. The first stage of the development program included a competitive evaluation of small scale models of seven different fast current oil recovery concepts. The two most promising concepts have now been developed into large scale models. These two devices plus a third device which evolved from a parallel state-of-the-art evaluation program were tested during the summer of 1976 at the Environmental Protection Agency's Oil and Hazardous Materials Simulated Environmental Test Tank (OHMSETT). The Shell ZRV large scale model performed well in fast-current velocities in both calm seas and in a wave train. The Seaward Streaming Fiber Recovery Device performed well in fast currents in calm conditions but performed poorly in waves. The French Cyclonet 050 provided fair performance in medium currents and in calm conditions but gave poor performance when waves were present.

Brood Habitat of the Hooded Merganser

Twenty-one broods of hooded mergansers (Lophodytes cucullatus) in northern Wisconsin were studied from May 1, 1967, to August 14, 1967, to determine the habitat types preferred by broods. Our results and an extensive literature review indicate that rivers and streams are an important component of the hooded merganser's brood habitat. Specifically, in Wisconsin, rivers with high levels of food resources, fast current velocities (0.80-0.93 ft/second), wide (40-60 ft), and moderately deep (1-2 ft) channels, with cobbled bottoms, and heavy surrounding cover of mixed hardwoods were used most by merganser broods.