Lewis L. Osborne

Microhabitat Characteristics of Hydropsyche (Trichoptera:Hydropsychidae) and the Importance of Body Size

The effects of sedimentation, microhabitat velocity and flow patterns, and larval body size on the distribution of four species of net-spinning hydropsychid caddisflies (i.e., Hydropsyche betteni, H. sparna, H. cheilonis, and H. bronta) were examined in Jordan Creek, Illinois. Significantly more larvae occurred in hydraulically calibrated concrete artificial substrate notches with little or no sedimentation. Accumulation of sediment did not appear to adversely affect the larvae during the study, however, because no significant differences were found between the distributions of larvae and the distributions of notches among four categories of sedimentation. Most larvae were found inhabiting microhabitats with rapidly spiralling flow vortices reflecting the importance of microhabitat flow pattern on Hydropsyche larval distribution. No significant differences were found in the distributions of the four species among the microhabitat velocities inhabited, although some fifth-instar H. betteni, the largest of the four species studied, were found inhabiting velocities up to 35 cm/s, whereas the other species were restricted to velocities less than 25 cm/s. Within a species, larger larvae were found at higher velocities than smaller, less mature, larvae. These results suggest that larval body size and microhabitat flow pattern, rather than capture-net mesh size, influence the distribution of Hydropsyche larvae in Jordan Creek.

Colonization and recovery of lotic epilithic communities: A metabolic approach

Community respiration and net primary productivity measurements from precleaned and disturbed substrates of various sizes were collected to examine the colonization and recovery rates of lotic epilithic communities in situ. The assumptions and limitations of the technique for monitoring metabolic recovery are discussed. The results indicate that substrate size and heterogeneity affect the rates of metabolic recovery; metabolic recovery of the heterotrophic community component generally occurs before the autotrophic; following a physical disturbance 13–21 days are required for metabolic recovery while pre-cleaned mixed and homogenous large sized substrates require 15–21 days; a temporary summer metabolic equilibrium appears to exist in the Sheep River, the duration of which is dependent on abiotic environmental variables. Future metabolic studies should include structure and composition measurements to attain maximum information on the recovery of epilithic communities.

Characterization of benthic microhabitat: An experimental system for aquatic insects

An experimental system used to determine microhabitat current velocity and microhabitat selection by aquatic insects is described. The experimental system includes a microvelocity probe and a hydraulically calibrated artificial substrate. A thermistor velocity probe detects flow velocities to 0.5 m s−1 near the surface of substrates at locations inhabited by aquatic insects. The artificial substrate was designed to provide two major habitat types, highly turbulent vortex areas and regions with unidirectional, near laminar flow. Substrate calibration and microhabitat characteristics of the substrates are demonstrated. Experimental studies of Simulium sp. location on substrates indicated that while simuliid larvae are characteristic of lotic, erosional habitats, actual microhabitats selected are governed by substantially lower flow velocity.

The effects of a chlorinated discharge and a thermal outfall on the structure and composition of the aquatic macroinvertebrate communities in the sheep river, Alberta, Canada

Abstract Physico-chemical and biological samples were collected from 12 sampling stations over a 13-month period to assess the effects of a small towns chlorinated sewage discharge and a thermal discharge on the Sheep Rivers macroinvertebrate communities. During the study, the chlorinated effluent plume was restricted to the left third of the channel for approx. 0.5 km at which point the effluent was thoroughly mixed due to an abrupt change in channel direction. Within the concentrated 0.5 km chlorinated plume, total residual chlorine TRC concentrations periodically exceeded 5.0 mg l −1 . Stations were categorized into similar community assemblages on the basis of species abundance and composition using heirarchical cluster analysis. Stations immediately downstream of the thermal outfall and those within the chlorinated plume had distinctly different structure and were dominated by Oligochaeta. Multiple discriminant analysis indicated that temperature was the principle discriminating variable immediately below the thermal discharge while the chlorinated sewage (MCSE) variable was the most important discriminant function within the chlorinated effluent plume. Following complete mixing of the effluent plume within the stream channel (0.6 km downstream of outfall), macroinvertebrate structure and diversity improved, presumably due to nutrient enrichment and dilution of TRC below detectable levels.

Acute metabolic responses of lotic epilithic communities to total residual chlorine

Numerous workers have examined the effects of chlorine on individual e p i l i t h i c community components (e.g. , CAIRNS & PLAFKIN 1975; BROOKS & LIPTAK 1979), but l i t t l e attent ion has been given to the effects of residual chlorine on the whole l o t i c e p i l i t h i c community. Ep i l i t h i c organisms are those microf loral and fauna assemblages l i v ing on the surface of rocks; the primary cons t i t uents include bacteria, algae, fungi, and protozoans. Ep i l i t h i c communities are an important functional component of aquatic ecosystems. Thus, deter iorat ion of the community due to the introduction of a stress agent could dras t ica l l y impair the functional capabi l i t ie~ of the ent i re system. As the respirat ion rates of biological systems are re f lec t ive of energy flow through the system, and primary product iv i ty is a measure of carbon f ixat i o n c a p a b i l i t i e s , the purpose of th is invest igat ion was to determine the acute metabolic responses of l o t i c e p i l i t h i c communities to various concentrations of total residual chlorine (TRC).

Potential effects of three antibiotics on community respiration and production measurements

The effects of three commonly available antibiotics (tetracycline hydrochloride, streptomycin and neomycin sulfate) on the micro-Winkler and D.O. probe oxygen techniques and on the pH method of CO2 determination were investigated in the laboratory to assess potential effects on community metabolism measurements.All three antibiotics significantly altered O2 and CO2 concentrations through time. The results demonstrate that the use of the three antibiotics as bacterial respiratory inhibitors in community metabolism studies could cause significant overestimations of community respiration when measured as CO2, and significant underestimation of primary productivity and overestimation of respiration when measured as O2.