Medium Gravel Research Articles

Microhabitat of Anthopotamus verticis (Ephemeroptera: Potamanthidae)

A field and laboratory study was designed to elucidate the microhabitat of the North American riverine mayfly Anthopotamus verticis (Say). Previous reports have suggested that these mayflies are surface sprawlers or clingers; but despite a flattened body shape that is often associated with sprawling or clinging benthos, our investigation showed that larvae of A. verticis burrow and inhabit the hyporheic biotope. Substrate particle size was found to be a primary limiting factor in the microdistribution of the larvae. When homogeneous substrates (either fine, medium, or coarse gravel, or small or large pebbles) were provided, small, mid-sized, and large larvae significantly preferred coarse gravel or small pebbles. Small larvae were better represented in coarse gravel, and large larvae were better represented in small pebbles. Vertical distribution was deeper in coarse gravel than in medium gravel, and smaller larvae were generally found deeper than large larvae. In the field, larvae occur in gravel or pebbles (excluding coarse sand or smaller particles) or mixed substrates, often at the interface of large rocks and finer substrates. Videomacroscopic examination also indicated larvae to be interstitial dwellers. Although relatively crude burrowers, larvae do use their tusks to excavate substrate, and their gills to generate interstitial current. We distinguish the fossorial behavior of Anthopotamus from most other ephemeroid mayflies because tube burrows are not formed. Minimum-sized interstices may be required for filter feeding and/or adequate ventilation, and may explain a deeper penetration of smaller larvae in finer substrates.

The character, structure and origin of the basal ice layer of a surge-type glacier

AbstractThe basal ice layer of surge-type Variegated Glacier, Alaska, appears to have formed by a combination of (i) open-system freezing of subglacial meltwaters over both rigid and unconsolidated substrates; (ii) apron over-riding during surge-induced glacier advance; (iii) incorporation of glacier ice by recumbent folding, thrust-faulting and nappe over-riding during down-glacier propagation of a surge front; and (iv) post-formational metamorphism involving recrystallization, partial internal melting and squeezing out of meltwaters and dissolved gases. Structural evidence and the characteristics of debris entrained in ice facies formed by basal freezing suggest that the layer includes a lower element formed under surge conditions and an upper element formed during the quiescent phase of a surge cycle. The lower element is depleted in comminution products and enriched in medium gravel, while the upper element contains comminution products but virtually no medium gravel. This distinction is attributed to the efficiency of bedrock fracture and meltwater flushing of comminution products under surge conditions. The basal ice layer thickens from <1 m to >13 m down-glacier in a manner consistent with the magnitude of horizontal shortening induced by the 1982–83 surge. Thickening is largely tectonic in origin, and the style and intensity of folding and thrust faulting change down-glacier as the magnitude of horizontal shortening increases. Tectonic processes associated with the down-glacier propagation of surge fronts therefore appear to be capable of creating thick basal ice layers which allow extensive supraglacial sedimentation of subglacially derived debris.

The character, structure and origin of the basal ice layer of a surge-type glacier

AbstractThe basal ice layer of surge-type Variegated Glacier, Alaska, appears to have formed by a combination of (i) open-system freezing of subglacial meltwaters over both rigid and unconsolidated substrates; (ii) apron over-riding during surge-induced glacier advance; (iii) incorporation of glacier ice by recumbent folding, thrust-faulting and nappe over-riding during down-glacier propagation of a surge front; and (iv) post-formational metamorphism involving recrystallization, partial internal melting and squeezing out of meltwaters and dissolved gases. Structural evidence and the characteristics of debris entrained in ice facies formed by basal freezing suggest that the layer includes a lower element formed under surge conditions and an upper element formed during the quiescent phase of a surge cycle. The lower element is depleted in comminution products and enriched in medium gravel, while the upper element contains comminution products but virtually no medium gravel. This distinction is attributed to the efficiency of bedrock fracture and meltwater flushing of comminution products under surge conditions. The basal ice layer thickens from <1 m to >13 m down-glacier in a manner consistent with the magnitude of horizontal shortening induced by the 1982–83 surge. Thickening is largely tectonic in origin, and the style and intensity of folding and thrust faulting change down-glacier as the magnitude of horizontal shortening increases. Tectonic processes associated with the down-glacier propagation of surge fronts therefore appear to be capable of creating thick basal ice layers which allow extensive supraglacial sedimentation of subglacially derived debris.

Stabilization of lateritic soils by extensible fibre reinforcement

Direct shear tests were run on samples of dry laterite sand and dry laterite gravel reinforced with different types of fibres. Both natural and synthetic fibres plus copper wires were tested. Test results showed that fibre reinforcement increases the peak strength and modifies the stress-deformation behaviour of laterites in a significant manner. It increases the peak shear strength and limits the amount of post peak reduction in shear resistance. Fibres increase significantly the angle of internal friction of the composite laterite. These shear strength increases were greatest for initial fibre orientations of 0° and 60° with respect to the shear surface while 120° orientation indicates the least for a laterite. Of all the various types of fibres used, inextensible earth reinforcements (high modulus metals) give the lower shear strengths relative to the extensible ones (i.e. low modulus geotextiles). The shear strength increases from coarse sand laterite through fine gravel laterite to medium gravel laterite and the shear strength is highest when the reinforcement is installed at 50% of the depth (mid point) of the sample (shear mould).

Differential Use of Stream Habitat by Spawning Catostomids

Spawning patterns of suckers (Catostomidae) in Deer Creek, Indiana, revealed differential use by species and age-size groups. In spring, white suckers (Catostomus commersoni) dominated headwaters, while redhorse (Moxostoma spp.) were more abundant downstream. Shorthead redhorse (M. macrolepidotum) were present only in main stem Deer Creek during spawning. Spawning groups of golden redhorse (M. erythrurum) and black redhorse (M. duquesnei) near the mouth of Deer Creek were significantly older and larger than those upstream in a first-order tributary. Spawning was not observed until water temperatures stayed above or near 10 C and until water levels were 20-60 cm deep over spawning shoals. Golden redhorse, shorthead redhorse and northern hog sucker (Hypentelium nigricans) spawned over medium gravel in riffles 30-60 cm deep with velocities of 0.4-0.9 m/sec. White sucker spawned over medium gravel at depths of 20-25 cm where velocity ranged from 0.50-0.59 m/sec. Creek chubsucker (Erimyzon oblongus) selected fine gravel in areas 50-75 cm deep having much slower velocity (0.10-0.24 m/sec). INTRODUCTION River tributaries serve as spawning and nursery areas for suckers (Catostomidae), but the effect of tributary spawning on maintaining river populations downstream is just beginning to be investigated. Previous reports (Thompson and Hunt, 1930; Trautman, 1957; Bowman, 1970; Larimore and Smith, 1963; Karr, 1975; Burr and Morris, 1977; Smith, 1977; Lake and Morrison, 1977) indicate that catostomids inhabiting rivers ascend smaller streams for spring spawning. The extent of upstream movements by adults and the degree to which resident and migrant suckers compete for stream spawning sites are unclear. Lack of specific information on the seasonal use of river tributaries hampers management efforts and an understanding of the potential impact of stream alteration on catostomid populations. Studies on catostomid spawning have shown some interspecific differences in the use of river tributaries. Black redhorse (Moxostoma duquesnei) and golden redhorse (M. erythrurum) in the streams and smaller rivers of Missouri and Ohio apparently move short distances for spawning (Bowman, 1970; Smith, 1977). Meyer (1962) found no evidence for the movement of golden redhorse, shorthead redhorse (M. macrolepidotum) or silver redhorse (M. anisurum) adults into a tributary of the Des Moines River, Iowa, during the spawning season. However, the abundance of adult silver redhorse and quillback (Carpiodes cyprinus) in a tributary of the Hocking River, Ohio, increased during spring, suggesting upstream movement into the tributary for spawning (Smith, 1977). Some specific measurements of spawning site characteristics for catostomids have been reported in recent literature. Black redhorse in Missouri spawn on riffles of rubble and gravel in 15-60 cm of water (Bowman, 1970). Spotted suckers spawn over course rubble in riffles 0.3-0.5 m deep with flow rates of 1.4 m3/sec and surface velocities of 1 Journal Paper no. 9585, Purdue Agricultural Experiment Station. 2 Present address: 120 Riverglade, Amherst, MA 01002.

Substrate size selection by stream invertebrates and the influence of sand

A field experiment showed that benthic invertebrates in running water exhibit preferences for different substrate particle sizes. Maximum numbers and biomass occurred on medium gravel (24.2‐mm mean diam), whereas diversity was greatest on large gravel (40.8 mm). Individual species fell into four groups: upper, medium, and lower size preference, and no preference. The addition of a limited quantity of sand to medium gravel affected only a few species.