Outdoor Experimental Channels Research Articles

Flow structure around an actual willow patch under different depth conditions

Vegetation is one of the key factors in river management where environmental aspects as well as flood protection should be taken into consideration. Because of this, numerous studies have been done including experiments and hydrodynamic modelling. Because most of experimental studies were made in indoor laboratory flumes with artificial trees, there are still limitations in transfer of their result to actual channels. REC (River Experiment Center) of Korea has been operating three real-scale, nature-like outdoor experimental channels. In a straight channel, several 4x2 m actual willow patches were planted and have been grown last three years for studies on flow vegetation interaction. A set of intensive flow measurement was made around the first upstream willow patch using ADVs together with measurement of vegetation properties. The experiments were made under several different depth conditions simulating snow-melt and flash-flood. Distribution of flow around and through the patch was characterized along with vertical profiles. The results of the experiment enhance understanding on interaction of flow and actual vegetation in a natural channel and may also provide information on flow resistance used for hydrodynamic modelling and validation.

Shifts in microbial community structure and function in stream sediments during experimentally simulated riparian succession

Successional changes of terrestrial vegetation can profoundly influence stream ecosystem structure and function. We hypothesized that microbial enzyme production and community structure in stream beds depend on terrestrial litter inputs that reflect different stages of riparian succession. Outdoor experimental channels were supplied with leaf-litter of varying quantities and qualities to mimic litter supply during five successional stages: (1) an initial biofilm stage; (2) an open-land stage with grass litter; (3) a transitional stage with mixed grass and birch litter; (4) an early forest stage with birch litter; and (5) an advanced forest stage with 2.5 × the amount of birch litter. Mean potential activities of nitrogen- and phosphorus-acquiring enzymes in sediments (20.7 and 67.3 μmol g(-1) dry mass) were 12-70 times greater than those of carbon-acquiring enzymes (0.96-1.71 μmol g(-1) dry mass), with the former reduced 1.3-8.3-fold in channels with tree litter. These patterns could suggest gradually diminishing nutrient limitation of microbial activity during riparian succession, potentially linked both to an increasing supply by the added litter and to a lower nutrient demand as algal biomass and labile carbon supply by photosynthetic exudates declined. As the observed shifts in nutrient-acquiring enzymes were reflected in changes of sediment microbial communities, these results indicate that both the type and density of terrestrial vegetation control microbial community structure and function in stream sediments, particularly enzyme production related to nutrient cycling.

Fungal importance extends beyond litter decomposition in experimental early‐successional streams

Fungi are important decomposers of leaf litter in streams and may have knock-on effects on other microbes and carbon cycling. To elucidate such potential effects, we designed an experiment in outdoor experimental channels simulating sand-bottom streams in an early-successional state. We hypothesized that the presence of fungi would enhance overall microbial activity, accompanied by shifts in the microbial communities associated not only with leaf litter but also with sediments. Fifteen experimental channels received sterile sandy sediment, minimal amounts of leaf litter, and one of four inocula containing either (i) fungi and bacteria, or (ii) bacteria only, or (iii) no microorganisms, or (iv) killed microorganisms. Subsequently, we let water from an early-successional catchment circulate through the channels for 5 weeks. Whole-stream metabolism and microbial respiration associated with leaf litter were higher in the channels inoculated with fungi, reflecting higher fungal activity on leaves. Bacterial communities on leaves were also significantly affected. Similarly, increases in net primary production, sediment microbial respiration and chlorophyll a content on the sediment surface were greatest in the channels receiving a fungal inoculum. These results point to a major role of fungal communities in stream ecosystems beyond the well-established direct involvement in leaf litter decomposition.

Impact of lambda-cyhalothrin on a macroinvertebrate assemblage in outdoor experimental channels: Implications for ecosystem functioning

In this study, the impact of a single pulse of the pyrethroid lambda-cyhalothrin was tested on a macroinvertebrate assemblage consisting of Gammarus pulex, Leuctra nigra, Heptagenia sulphurea and Ancylus fluviatilis in outdoor experimental stream channels. Channels (4 m long, 0.1 m wide) were groundwater fed and had natural substratum. Macroinvertebrates were exposed to 10.65 or 106.5 ng L −1 lambda cyhalothrin for 90 min in the laboratory and after 24 h introduced to the experimental stream channels with four replicates of each treatment and controls. Drift samples were taken with 24-h interval for 10 days and behaviour of drifted macroinvertebrates was assessed. Microalgae biomass was measured on days 1, 5, 8 and 10 along with leaf litter decomposition using leaf packs of beech ( Fagus sylvatica). Numbers of drifting G. pulex and L. nigra with reduced mobility increased significantly with concentration of lambda-cyhalothrin. Increase of algal biomass was significantly greater in stream channels with macroinvertebrates exposed to 106.5 ng L −1 compared to controls and 10.65 ng L −1 treatments. Accrual of microalgal biomass was significantly higher in the high concentration treatment and decomposition of leaf litter was significantly greater in control channels compared to channels with exposed macroinvertebrates. This study may apply valuable knowledge to the understanding and assessment of how pyrethroids impact ecosystem functioning in streams.

Stream macroinvertebrate drift response to pulsed exposure of the synthetic pyrethroid lambda‐cyhalothrin

Outdoor experimental channels were used to study the behavioral changes of stream macroinvertebrates exposed to a pulse of the pyrethroid insecticide lambda-cyhalothrin. The primary end point was the number of macroinvertebrates drifting, but the mobility of macroinvertebrates caught in the drift also was assessed. A specified number of two insect species, Baetis rhodani and Leuctra fusca/digitata, and of the amphipod Gammarus pulex were introduced into small replicated subsections of the experimental channels. Macroinvertebrates were allowed to acclimatize for 26 h prior to a 60-min pulsed exposure to lambda-cyhalothrin. Measurement was initiated 2 h before pesticide application and continued for the following 24 h. Pulse concentrations of lambda-cyhalothrin of 0.001, 0.01, 0.1, and 1.0 microg L(-1) were applied, and each experiment was replicated 8 times. All three species responded to the pesticide pulse with catastrophic drift. The 0.001 microg L(-1) treatment caused a significant increase in the drift of Gammarus, whereas the drift response threshold was 0.01 microg L(-1) for the two insect species. Drift response onset followed the applied pulse concentration, with the highest concentrations resulting in more individuals of all species entering drift at an early stage. The majority of individuals caught in drift samples during low concentrations showed no change in mobility. At the two highest concentrations, however, both Baetis and Leuctra were in the process of being immobilized, with Leuctra the more sensitive of the two. In contrast, only a few of the Gammarus individuals caught showed changes in mobility after the high-concentration treatments. The present study shows that lambda-cyhalothrin is a potential hazard for macroinvertebrate populations in headwater streams. The clear species-specific responses indicate that sublethal doses have the potential to change the macroinvertebrate community structure.

Predation Threat Affects Behaviour and Habitat Use by Hatchery Brown Trout (Salmo Trutta L.) Juveniles

The effect of predation threat on behaviour and habitat use by brown trout (Salmo trutta L.) juveniles were studied in four indoor and six outdoor experimental channels. Northern pike (Esox lucius L.) was used as a predator. Brown trout were more active during the night compared to day, but in the presence of pike the increase in activity was less than in treatments without predator. Aggressive interactions between trout were higher during the day when pike was absent. In the presence of pike trout tended to use more coarse substrate classes as subdominant habitat suggesting increased use of cover and also higher or lower water depths. Our results increase knowledge of the effects of predation threat on habitat selection and behaviour by brown trout.

Behavioral Responses ofDrunella coloradensis(Ephemeroptera) Nymphs to Short-Term pH Reductions

Behavioral responses of Drunella coloradensis nymphs were examined in outdoor experimental stream channels after pH reductions of 1 and 2 pH units below ambient. The severity of pH decline below the ambient of 7.8 influenced the behavior patterns displayed by nymphs. At pH 7.01 (an intermediate pH decline) nymphs sat less frequently and burrowed more than controls. Burrowing behavior frequency returned to control levels and drifting and crawling behaviors increased relative to controls at pH 6.02. Ventilatory behaviors increased with pH decline, but were independent of the severity of acidity increases. These results suggest that individual behaviors may offer a more sensitive indicator of sub-acute stress in aquatic insect communities than population or community monitoring. Behaviors leading to increased activity levels in stream insects may have community-level effects via changes in predator–prey encounter rates or increased susceptibility to passive drift. These potential changes are discussed in reference to monitoring for acidification effects.

Resistance and Resilience of Lotic Algal Communities: Importance of Disturbance Timing and Current

We examined effects of disturbance timing on resistance and resilience of epilithic algal communities growing in fast— (29 cm/s) and slow— (12 cm/s) current outdoor experimental stream channels in Kentucky, USA that were either left undisturbed (control) over 33 d following a simulated spate, or were subjected to an additional spate after either 9, 18, 27, 33 d. On day 33, all channels were subjected to a final spate to assess effects of short—term disturbance history on resistance, independently of seasonal influences. Succession proceeded from a sparsely populated community dominated by a small, monoraphid diatom (Achnanthes minutissima) immediately after the initial spate, to dominance by dense floating mats of filamentous green algae (Zygnematales: Mougeotia and Spirogyra) and Synedra spp. by day 21—24. Resistance was generally lower in slow—current communities, both in terms of cell—density reduction and displacement of taxonomic structure, than in fast—current communities. Resistance in slow—current communities varied temporally, with communities least resistant on day 18, when community composition and physiognomy was changing rapidly, and on day 33, when green algal mats began to senesce. On day 33, slow—current communities that had not been recently disturbed (control, D9) exhibited greatest spate—induced loss of algal biomass. Additionally, slow—current communities with high pre—disturbance phaeophytin content (an indicator of algal senescence) also changed most in diatom assemblage structure across the final spate. No such relationship was noted in fast current, suggesting that autogenic factors influenced communities in slow current more than those in fast. Resilience was higher in slow—current communities than in fast current, with disturbed communities reaching biomass and taxonomic structure similar to controls after 3—9 d. High resilience in slow current resulted from enhanced reproduction in some populations following spate—induced biomass reduction and presumed release from nutrient and light limitation, and low shear stress relative to fast—current channels where biomass accrual was limited by current. Interactions between disturbance timing, successional state, and habitat affect the susceptibility of epilithic algal communities to disturbance and likely influence temporal and spatial heterogeneity in stream ecosystems.

Post-spate development of epilithic algal communities in different current environments

Development of epilithic algal communities was monitored in fast- (29 cm∙s−1) and slow-current (12 cm∙s−1) outdoor experimental stream channels for 33 d following a simulated spate. Disturbance reduced diatom densities in both current regimes to equal levels, but recovery was more rapid in slow current. Maximum algal abundances, which seemed to reach carrying capacity in both current environments, were lower in fast current than in slow. The percentage of live cells in diatom assemblages decreased during community development. The small, monoraphid diatom Achnanthes minutissima Kütz. dominated communities in both current regimes from 0 to 12 d, principally because of its persistence on substrata through disturbance. Post-spate diatom accumulation was more rapid in slow current, presumably due to higher cell export in fast current. Differences in community structure between current regimes during early (0–6 d) recovery were attributed to differences in attachment strength and growth form of persistent species. In both current regimes, initial dominance by A. minutissima shifted to dominance by Synedra spp. and dense, floating mats of zygnematalean green algae. Zygnematalean mats enhanced diatom deposition and probably reduced water-column nutrient concentrations, altered light availability, and increased habitat heterogeneity. Zygnematalean proliferation affected diatom succession in slow but not in fast currents, suggesting that autogenic changes were more pronounced in slow-current habitats. Key words: benthic algae, current, disturbance, recovery, streams, succession.

SUBSTRATUM CONDITIONING AND DIATOM COLONIZATION IN DIFFERENT CURRENT REGIMES1

ABSTRACTShort‐term (3 day) diatom colonization of clean ceramic tiles and tiles conditioned with a thin, nonalgal biofilm was examined in fast‐ and slow‐current outdoor experimental stream channels to assess effects of organic conditioning and current regime on diatom colonization. Colonization rates onto unconditioned tiles were 10 times lower in fast current that in slow. Substratum conditioning reduced the effects of current because organic conditioning of tiles significantly enhanced colonization in fast current, but not in slow current. Two diatom taxa (Nitzschia acicularis W. Sm. and Synedra radians Kütz) colonized unconditioned tiles more rapidly than conditioned tiles in slow current, suggesting the existence of negative interactions between these diatoms and bacteria and/or organics in conditioning films.

Temperature Influences on Adult Size, Development, and Reproductive Potential of Aquatic Diptera

Elevated temperature (2.5 and 4.0 °C) resulted in smaller body size of stream Diptera in outdoor experimental channels, and this trend applied to both predator and detritivore trophic groups. Comparison of cumulative emergence curves using the Kolmogorov–Smirnov test showed that most species developed more quickly in the heated channels; this led to greater overall survivorship. Reproductive potential, estimated from ovary area, did not change with body size for Conchapelopia aleta, Polypedilum aviceps, and Stempellinella brevis, and did so only weakly for Parametriocnemus lundbecki. In addition, females decreased in size more than males in the heated channels. Somatic growth appeared to be sacrificed to maintain reproductive potential, although loss of energy reserves could reduce the length of the reproductive stage. In balance, the aquatic Diptera demonstrated resistance to thermal elevation in the summer, even though ambient temperatures approached 30 °C. This may partially account for the group's ability to grow and develop throughout the year in extremely varied temperate environments.

An experimental study on the effect of elevated temperature on the heterotrophic and autotrophic food resources of aquatic insects in a forested stream

The effect of temperature on the heterotrophic and autotrophic food resources of aquatic insects was investigated in outdoor experimental channels and in the laboratory. Elevated temperatures in outdoor channels resulted in accelerated decay rates and accumulation of organic layers on introduced tiles. Heterotrophic activity (substrate respiration) increased with temperature in the laboratory for leaf strips, flocculent organic matter, and stone surface organic layers. Autotrophic activity (substrate photosynthesis) was greater in the laboratory for flocculent detritus (per milligram ash-free dry weight) than for stone surface organic layers. These results indicate that the primary food resources of shredder, collector, and scraper functional guilds are enhanced by elevated temperature, but also suggest that coarse particulate organic matter may disappear from the stream more quickly. The results also point out that substantial autotrophic activity occurs within flocculent organic detritus.

Revised Estimates of Growth Requirements and Lethal Temperature Limits of Juvenile Walleyes

Abstract The optimum temperature for growth of juvenile walleyes (Stizostedion vitreum) was estimated by rearing fish under a low light intensity (i.e., 5 1x). The upper lethal temperature was estimated by slowly raising the acclimation temperature 0.5°C/d until death occurred. The estimates of 26°C and 34.1°C, respectively, were similar to those observed for juvenile walleyes in outdoor experimental channels, but were higher than those determined in the laboratory by one of the present authors for Minnesota walleyes. Some possible sources of error include the light intensity differences between experiments, which can influence predator-prey interactions (ration levels) in laboratory tanks, and the methods of fish acclimation to lethal temperature.

Effects of pentachlorophenol on invertebrates and fish in outdoor experimental channels

Pentachlorophenol (PCP) was selected to assess the applicability of a toxicant criterion concentration for protecting aquatic communities in outdoor experimental channels. The criterion concentration was derived from on site laboratory bioassays. In 1982 three channels were continuously dosed with PCP for 12 wk at nominal concentrations of 48 μg/l (low, criterion level), 144 μg/l (medium, 3 × criterion) and 432 μg/l (high, 9 × criterion). In 1983 the low and medium treatments were repeated for 12 wk. Each year an untreated channel served as control. Invertebrate responses measured were changes in density, community composition and drift; fish responses were changes in survival, growth, reproduction and larval drift. Some ecosystem effects were detected at all treatment levels with fish being the most sensitive animals. Microinvertebrate densities were lower in the medium PCP channel than the control. Survival of the snail Physa gyrina was substantially reduced in the high treatment channel; no other macroinvertebrates were adversely affected by the toxicant. All fathead minnows and bluegill sunfish stocked in the high treatment channel died within the first 8 days of dosing. Fish survival was similar in all remaining channels. Fish growth and larval drift were lower in the treated channels than in the control channels and spawning was reduced in the medium dose channels. The numbers of fathead minnows collected both years from the medium dose channels were lower than the criterion and control channels. Highest numbers of bluegills were recovered from the control channels. The study indicated that the criterion concentration derived from laboratory tests did not fully protect the animals in the experimental channels.

Periphytic oxygen production in outdoor experimental channels

The contribution of periphytic oxygen was quantified in outdoor artificial streams. A factorial design was employed to determine the effect of stream velocity and light on periphytic growth, measured as chlorophyll α. Results showed that periphytic oxygen production can be estimated by the equation: mg O 2h −1 mg Chl a =0.85 × 10 −4 × Light Intensity (ft. candles) + 0.061 =0.91 × 10 −3 × Light Intensity (1x) + 0.061 for light intensities to 5000 ft-candles (53,800 lx). Stream velocity was found to be statistically insignificant in affecting oxygen production, but was a factor in periphyton accural and species composition. Gross oxygen production exceeded respiration by a factor of three.

Effects of diazinon on macroinvertebrates and insect emergence in outdoor experimental channels

Effects of diazinon on macroinvertebrates were assessed in three outdoor experimental channels from mid-May to mid-September, 1980. One channel served as a control and two channels as low and high treatments. Three dosing regimes were employed. The low and high treatment channels were continuously dosed for 12 wk to nominal concentrations of 0.3 and 3 μg/l, then increased to 6 and 12 μg/l for 4 wk, then the high treatment was increased to 30 μg/l with the low treatment channel returned to ambient. Diazinon concentrations did not reach the intended levels during the latter two dosing regimes. No consistent interchannel differences were observed in total macroinvertebrate abundance or in species diversity induces. Effects were noted at the lowest concentration for amphipods and insects. As diazinon concentrations were increased interchannel community structure changes became more pronounced. Elevated drift, especially amphipods and snails, occurred in the treated channels 4 wk after dosing began and following the increases in concentrations. Total numbers and species of insects emerging from the three channels were not greatly different but lower numbers of mayflies and damselflies emerged from the treated channels. Tolerance of macroinvertebrates to diazinon were as follows: flatworms, physid snails, isopods and chironomids most tolerant; leeches and the amphipod Crangonyx less tolerant; the amphipod Hyalella, mayflies, caddisflies and damselflies sensitive.

Effect of P-Cresol on Leaf Decomposition and Invertebrate Colonization in Experimental Outdoor Streams

In 1980, outdoor experimental stream channels at Monticello, Minnesota were continuously dosed for 24 and later 48 h with 8 mg/L p-cresol, a toxic phenolic by-product of coal gasification. The dosage, based on laboratory studies by the Environmental Protection Agency, was expected to stress but not to kill fish and invertebrates in the channels. Two unexpected results occurred: (1) severe depressions in dissolved oxygen (less than 1 mg/L), and (2) mortality to some fish and invertebrate species in the experimental versus reference channels. Because the direct effects on the aquatic ecosystem were inseparable from the indirect effect of reduced dissolved oxygen, two types of dosing regimes were designed in 1981 to partially uncouple the direct from the indirect effects. First, a continuous dose at 8 mg/L for 96 h was administered, then a second intermittent dose at 8 mg/L with temporary cessations when reductions in dissolved oxygen occurred. Leafpacks were placed in experimental and reference channels to monitor community level responses to the toxicant under severe long-term and under moderate short-term dissolved oxygen depletions. Biotic responses to the intermittent dose schedule were less severe than biotic responses to the continuous dose. The intermittently dosed experimental channel and its reference channel were more similar to each other than was the continuously dosed channel as compared with its reference channel with respect to: (1) invertebrate colonization patterns, (2) invertebrate biomass changes over time and (3) leaf biomass changes over time. During the continuous dose, some invertebrate species that were rare colonists on leafpacks became highly abundant (leeches and isopods); other normal colonists became extremely abundant (snails and flat-worms) or diminished (freshwater scuds). These changes in colonization patterns significantly altered biomass of invertebrates on leafpacks over time. Leaf biomass losses were similar over time except in the continuously dosed channel where swamp poplar leaf losses (Populus deltoides Marsh) were significantly smaller during and shortly after the dose.

Acidification effects on macroinvertebrates and fathead minnows ( Pimephales promelas) in outdoor experimental channels

Three outdoor experimental channels at the U.S. EPA Monticello (Minnesota) Ecological Research Station were employed to assess in the field acidification effects on macroinvertebrate communities and populations of fathead minnows ( Pimephales promelas). One channel served as ambient (pH 8), the second was acidified with sulfuric acid to pH 6 and the third to pH 5 for 17 weeks. Acidification did not markedly increase toxic metal concentrations in the channels; however, there was some evidence of possible mercury mobilization. Benthic macroinvertebrate densities were lower in the acidified channels during most of the study and final diversity indices were 2.1, 1.7 and 1.2 in the ambient, pH 6 and pH 5 channels, respectively. Drift of amphipods and leeches was stimulated in the pH 5 channel early in the study. The number of insect taxa and percentages emerging from the ambient, pH 6 and pH 5 channels, respectively, were 30 and 56%, 28 and 31%, and 18 and 13%. Macroinvertebrate tolerance to the acidification was classified as follows: damselflies, isopods and leeches most tolerant; chironomids, some amphipods ( Crangonyx) and flatworms of intermediate tolerance; and other amphipods ( Hyalella azteca) and snails ( Physa gyrina) most sensitive. Fathead minnow spawning and embryo production were similar in the ambient and pH 6 channels with little spawning and no eyed-embryos found in the pH 5 channel. Newly-hatched larval fish did not survive to the juvenile stage in the pH 6 channel. Continued acidification would likely have further decreased the diversity of the macroinvertebrate community, increased relative abundance of more tolerant species, and caused extinction of the minnow population.

Effect of elevated water temperature on macroinvertebrate communities in outdoor experimental channels

Macroinvertebrates were sampled monthly from December 1976 to September 1977 in two 520m long outdoor experimental channels. One channel was maintained at ambient seasonal Mississippi River water temperatures and the other 10°C higher. Maximum water temperature reached 31.0°C in the ambient and 40.8°C in the heated channel. Elevated temperature seasonally altered macroinvertebrate abundance and life history in the channels. Few animals were found in the heated channel during the period of maximum water temperature. Most macroinvertebrate density and composition differences were confined to the channel riffles rather than the pools. Peak total density in the heated channel riffles occurred 3 or 4 weeks before the ambient channel. Total macroinvertebrate density was appreciably higher in the heated channel riffles during the winter and spring months and in the ambient channel riffles during the summer months. This seasonal alteration was due to composition differences of several identified taxa. Reproductive periods for one snail and one isopod species began approx. 2 and 3 months earlier in the heated channel than in the ambient channel. No marked change occurred in the reproductive activities of an amphipod in the two channels.

Effect of elevated water temperature on insect emergence in outdoor experimental channels

Emergence of adult aquatic insects was determined weekly with plexiglass traps positioned in two outdoor experimental channels from April through August 1977. One channel was seasonal Mississippi River water temperature and the other maintained at 10°C higher. Maximum water temperatures reached 31·0°C in the ambient and 40·8°C in the heated channel. Chironomids comprised 84% of the insects collected in both channels. Percentage composition differed between the ambient and heated channels for the chironomid taxa while the mayfly, damselfly and caddisfly taxa were more similar. The temperature in the heated channel (10°C above ambient) advanced the emergence of two Chironominae, one Orthocladiinae, one Ceratopogonidae and one Zygopteran species by one to four weeks. Few insects emerged from the heated channel during the period of maximum temperature. Insect emergence was spatially distributed throughout each channel even though dissolved oxygen concentrations were near zero at sunrise and supersaturated at mid-afternoon hours at downstream stations.