Experimental Stream Channels Research Articles

Sediment addition reduces the importance of predation on ecosystem functions in experimental stream channels

Sedimentation is a pervasive cause of biological impairment in streams, and predation exerts strong control over lower trophic levels. However, studies combining these two factors are lacking. In a factorial experiment in flow-through channels, addition of sand (<0.5 mm) and predatory stoneflies (Perlidae) caused independent effects on benthic invertebrates, algal biomass, and leaf breakdown. Sand reduced invertebrate density by 55% and also reduced leaf breakdown and algal biomass. Predators reduced invertebrate densities by 40%, with the strongest impact on algal-feeding invertebrates. Predators also decreased densities of leaf-shredding invertebrates and reduced leaf breakdown, thereby inducing a trophic cascade via detritus-based food web. The two treatments exhibited an antagonistic interaction whereby sand obscured any effect of predators on algae, indicating that an abiotic stress may modify a trophic cascade. By contrast, we found no support for synergistic interactions between sand and predation. The strong effects of sedimentation on key ecosystem processes illustrate that stream management needs to exploit riparian and in-stream measures to reduce sediment inputs to headwater streams.

Effect of fine wood on juvenile brown trout behaviour in experimental stream channels

AbstractIn‐stream wood can increase shelter availability and prey abundance for stream‐living fish such as brown trout, Salmo trutta, but the input of wood to streams has decreased in recent years due to harvesting of riparian vegetation. During the last decades, fine wood (FW) has been increasingly used for biofuel, and the input of FW to streams may therefore decrease. Although effects of in‐stream FW have not been studied as extensively as those of large wood (LW), it is probably important as shelter for small‐sized trout. In a laboratory stream experiment, we tested the behavioural response of young‐of‐the‐year wild brown trout to three densities of FW, with trout tested alone and in groups of four. Video recordings were used to measure the proportion of time allocated to sheltering, cruising and foraging, as well as the number of aggressive interactions and prey attacks. Cruising activity increased with decreasing FW density and was higher in the four‐fish groups than when fish were alone. Foraging decreased and time spent sheltering in FW increased with increasing FW density. Our study shows that juvenile trout activity is higher in higher fish densities and that trout response to FW is related to FW density and differs from the response to LW as reported by others.

Low‐to‐moderate nitrogen and phosphorus concentrations accelerate microbially driven litter breakdown rates

Particulate organic matter (POM) processing is an important driver of aquatic ecosystem productivity that is sensitive to nutrient enrichment and.drives ecosystem carbon (C) loss. Although studies of single concentrations of nitrogen (N) or phosphorus (P) have shown effects at relatively low concentrations, responses of litter breakdown rates along gradients of low-to-moderate N and P concentrations are needed to establish likely interdependent effects of dual N and P enrichment on baseline activity in stream ecosystems. We established 25 combinations of dissolved inorganic N (DIN; 55-545 µg/L) and soluble reactive P (SRP; 4-86 µg/L) concentrations with corresponding N:P molar ratios of 2-127 in experimental stream channels. We excluded macroinvertebrates, focusing on microbially driven breakdown of maple (Acer rubrum L.) and rhododendron (Rhododendron maximum L.) leaf litter. Breakdown rates, k, per day (d-1) and per degree-day (dd-l), increased by up to 6X for maple and 12× for rhododendron over our N and P enrichment gradient compared to rates at low ambient N and P concentrations. The best models of k (d- and dd-1) included litter species identity and N and P concentrations; there was evidence for both additive and interactive effects of N and P. Models explaining variation in k dd-1 were supported by N and P for both maple and rhododendron (R =0.67 and 0.33, respectively). Residuals in the relationship between k dd-1 and N concentration were largely explained by P, but residuals for k dd-1 and P. concentration were less adequately explained by N. Breakdown rates were more closely related to nutrient concentrations than variables associated with measurements of two mechanistic parameters associated with C loss (fungal biomass and microbial respiration rate). We also determined the effects of nutrient addition on litter C: nutrient stoichiometry and found reductions in litter C:N and C:P along our experimental nutrient gradient. Our results indicate that microbially driven litter processing rates increase across low-to-moderate nutrient gradients that are now common throughout human-modified landscapes.

Seasonal Effects of Hydropeaking on Growth, Energetics and Movement of Juvenile Atlantic Salmon (Salmo Salar)

The performance and movements of juvenile Atlantic salmon Salmo salar exposed to variable water discharge (simulating hydropeaking) but with a stable water-covered area were studied in six experimental stream channels, both during the winter and summer. Thirty fish were stocked into each channel, and the growth, body fat and movements of the fish were followed for about 2.5 months in each season. During the winter, no effect of hydropeaking was documented on performance or movement. In the summer, fish experiencing hydropeaking had lower body mass, lower body fat, and higher movement rates than the control fish. In general, effect sizes were small, and the rapid and frequent changes in water discharge and water level in the present study had small effects on the performance of juvenile Atlantic salmon. The cumulative long-term effect at the population level is unknown, but a reduced growth rate of 10% and a reduction in body fat of 16% in the hydropeaking experiments in the summer might to some extent translate into increased smolt age and lower overwintering survival. Copyright © 2014 John Wiley & Sons, Ltd.

Are host–parasite interactions influenced by adaptation to predators? A test with guppies and Gyrodactylus in experimental stream channels

Natural populations often face multiple mortality sources. Adaptive responses to one mortality source might also be beneficial with respect to other sources of mortality, resulting in "reinforcing adaptations"; or they might be detrimental with respect to other sources of mortality, resulting in "conflicting adaptations". We explored these possibilities by testing experimentally if the responses of guppies (Poecilia reticulata) to the monogenean ectoparasitic worm Gyrodactylus differed between populations adapted to different predation regimes. In experimental stream channels designed to replicate the natural environment, we exposed eight guppy populations (high-predation and low-predation populations from each of four separate rivers) either to their local Gyrodactylus parasites (infection treatment) or to the absence of those parasites (control). We found that infection dynamics varied dramatically among populations in a repeatable fashion, but that this variation was not related to the predation regime of origin. Consistent with previous work, high-predation guppy females gained more mass, had lower reproductive investment, and had more but smaller embryos than did low-predation females. Relative to control (no parasite) channels, guppies from treatment (infected) channels gained less mass but produced similar numbers and sizes of embryos-and thus had a higher reproductive effort. However, no interaction was evident between infection treatment and predation regime. We conclude that parasitism by Gyrodactylus and predation are both likely selective forces for guppies, but that adaptation to predation does not have an obvious deterministic effect on host-parasite dynamics or on life-history traits of female guppies.

Effects of Hatchery Fish Density on Emigration, Growth, Survival, and Predation Risk of Natural Steelhead Parr in an Experimental Stream Channel

AbstractHatchery supplementation of steelhead Oncorhynchus mykiss raises concerns about the impacts on natural populations, including reduced growth and survival, displacement, and increased predation. The potential risks may be density dependent. We examined how hatchery stocking density and the opportunity to emigrate affect the responses of natural steelhead parr in an experimental stream channel and after 15 d found no density‐dependent effects on growth, emigration, or survival at densities ranging from 1–6 hatchery parr/m2. The opportunity for steelhead parr to emigrate reduced predation by coastal cutthroat trout O. clarkii clarkii on both hatchery and natural steelhead parr. The cutthroat trout exhibited a type‐I functional response (constant predation rate with increased prey density) for the hatchery and composite populations. In contrast, the predation rate on natural parr decreased as hatchery stocking density increased. Supplementation with hatchery parr at any experimental stocking density reduced the final natural parr density. This decline was explained by increased emigration from the supplemented groups. Natural parr had higher mean instantaneous growth rates than hatchery parr. The proportion of parr emigrating decreased as parr size increased over successive experimental trials. Smaller parr had lower survival and suffered higher predation. The final density of the composite population, a measure of supplementation effectiveness, increased with the hatchery steelhead stocking rate. Our results indicate that stocking larger hatchery parr (over 50 d postemergence) at densities within the carrying capacity would have low short‐term impact on the growth, survival, and emigration of natural parr while increasing the density of the composite population; in addition, a stocking density greater than 3 fish/m2 might be a good starting point for the evaluation of parr stocking in natural streams.Received June 28, 2010; accepted December 30, 2010

Multiple stressors in agricultural streams: interactions among sediment addition, nutrient enrichment and water abstraction

1. Many ecosystems are influenced simultaneously by multiple stressors, and the consequences of stressors are often unpredictable on the basis of knowledge of single effects. Agriculture affects streams world-wide via nutrient enrichment, elevated fine sediment and water abstraction for irrigation, but the combined impacts of these stressors are unknown. 2. We manipulated all three stressors simultaneously in an 18-day experiment and determined their individual and pair-wise combined effects on benthic invertebrates, algal biomass and leaf decay. We added nutrients (phosphorus plus nitrogen) and/or fine sediment (grain size 0·2 mm) to 18 experimental stream channels (dimensions 250 × 15 × 15 cm) supplied with water from a nearby stream. Three sediment and three nutrient treatments (high, intermediate, natural) were applied to each of six channels while flow was reduced by 80% in half the channels. Invertebrates (composition, abundance) and algae (chlorophyll a) were assayed using ceramic tile substrata and leaf decay was assayed using bundled leaves of a native shrub. Invertebrates colonizing leaf packs were also sampled. 3. Effects of sediment addition and flow reduction on biological response parameters were twice as common as nutrient enrichment effects. Nutrient enrichment increased total invertebrate abundance on tiles, algal biomass accrual and leaf decay rates, whereas both sediment addition (at the highest level) and flow reduction had mostly negative effects (e.g. reduced algal biomass, invertebrate abundance and/or taxonomic richness). 4. Stressors interacted often, and interactions between sediment and flow were particularly common. The negative impact of added sediment on aquatic biota was stronger at reduced flow, especially on tile substrata that were more exposed to the current than leaf-pack substrata. 5. Synthesis and applications. Our key findings imply that abstracting water from a stream already subjected to high fine sediment inputs may have far worse effects on the invertebrate fauna than abstraction from a similar stream with lower sediment levels. Aquatic resource managers should be aware of this important interaction between multiple stressors.

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.

Winter behaviour of juvenile Atlantic salmon Salmo salar L. in experimental stream channels: effect of substratum size and full ice cover on spatial distribution and activity pattern

Activity and choice of areas offering different cover (substratum or surface ice) for juvenile Atlantic salmon Salmo salar were studied in experimental stream channels during winter. Channels were completely ice covered between December and March. During this period, the ice thickness increased from 50 to 300 mm after which 50% of the ice was experimentally removed and followed by c. 2·5‐fold increase in discharge to simulate the effects of spring flood. Large substrata provided preferred habitats but areas with small substratum sizes were also used when full surface ice provided above‐stream cover and the stream discharge was relatively low. The fish remained nocturnal throughout the study but the level of day activity significantly increased as the surface ice became thicker. Maximum movement distance during a 24 h period and homing‐at‐dawn behaviour remained at a constant level throughout the main winter, but significantly changed during the simulated spring flood (mean ±s.e. maximum extent of movements within 24 h increased from 1·1 ± 0·1 to 3·0 ± 0·5 m; homing behaviour decreased from the highest level of 89·3 to 34·6% during spring flood). Overwinter survival was high (92·9%). Relative mass increase during the study ranged from –8·3 to 28·5%, and 84% of the juvenile Atlantic salmon gained mass. The highest rates of mass increase were associated with frequent movements between areas of different substratum size. The results indicate that during winter: (1) Atlantic salmon parr preferred large substratum cover compared with surface ice cover at the fish densities studied here, (2) juvenile Atlantic salmon were predominantly nocturnal but diurnal activity increased as surface ice became thicker and (3) increase in water discharge during spring altered the behaviour of juvenile Atlantic salmon and may have caused additional habitat shifts.

Ontogenetic shifts in drift periodicity and benthic dispersal in elmid beetles

Summary1. There is a paucity of information on ontogenetic changes in the dispersal of benthic invertebrates, which is an important aspect of their ecology. This study quantifies ontogenetic changes in diel periodicity in drift, and in upstream–downstream dispersal on the substratum for Elmis aenea, Oulimnius tuberculatus, Esolus parallelepipedus and Limnius volkmari (Coleoptera: Elmidae). Three drift nets were emptied every 3 h over 24 h in each month (October 1965–December 1968) at two contrasting sites: one in a deep section with abundant macrophytes, the other in a shallow stony riffle. Comparisons of periodicity between life‐stages of the same species were limited to months when numbers in the drift were highest. Dispersal was evaluated in six experimental stream channels, placed above the stream, with initial numbers of each life‐stage varying from 20 to 80.2. Drift numbers were always highest at night with few or no animals in the day samples. Ontogenetic shifts in diel periodicity were similar for all four species. Drift catches were similar throughout the night for the early and intermediate larval instars and for mature adults, but were highest in the early hours of the night with a gradual decline thereafter for later larval instars and immature adults. These patterns were unaffected by a severe spate, even though drift numbers increased considerably.3. Dispersal was density‐independent; the number of dispersing animals was a constant proportion of the initial number for each life‐stage. The relationship between dispersal distance and the number of animals travelling that distance was well described by an inverse power function. Median and maximum distances (m day−1) were estimated for each life‐stage.4. Ontogenetic shifts in dispersal in the stream channels matched those shown in diel drift periodicity. For all four species, the later larval instars and immature adults showed little movement in either direction, whereas early and intermediate larval instars and mature adults dispersed predominantly upstream, adults travelling further than any other life‐stage.5. Ontogenetic shifts in diel drift periodicity and dispersal were related to seasonal changes in drift density and critical periods in the life cycle. Such shifts have not been quantified in other stream invertebrates, but should be considered when evaluating the role of dispersal in their population dynamics and their colonization ability.

Pathways of N and C uptake and transfer in stream food webs: an isotope enrichment experiment

AbstractLanduse change alters the quantity and supply of stream energy resources from allochthonous (catchment-derived) to autochthonous (stream-derived) sources. This alteration has prompted the need for better understanding of C and N pathways through stream food webs. We added stable 15N-NH4 and 13C-acetate isotopes as tracers to experimental stream channels containing 1 of 4 key basal food resources: autotrophic epilithon, heterotrophic epilithon, fine particulate organic matter (FPOM), and coarse particulate organic matter (CPOM). Our goal was to evaluate the importance of these foods to 2 scrapers (Deleatidium sp. [mayfly] and Potamopyrgus antipodarum [snail]) and a facultative shredder (Olinga feredayi [caddisfly]). A 5th potential food source, new heterotrophic biofilm, grew on all surfaces during the course of the experiment. Isotope levels in the food resources and the invertebrates were measured weekly during the 3-wk isotope addition and for 2 wk after the addition. Changes in nutrient concent...

Food abundance and fish density alters habitat selection, growth, and habitat suitability curves for juvenile coho salmon (Oncorhynchus kisutch)

To understand how fish density and food availability affect habitat selection and growth of juvenile coho salmon (Oncorhynchus kisutch), we manipulated fish density (2–12 fish·m–2) and natural invertebrate drift (0.047–0.99 mg·m–3) in 12 experimental stream channels constructed in a side-channel of Chapman Creek, British Columbia. Increased food resulted in increased growth of both dominant and subdominant fish and a shift to higher average focal velocities (from 6.5 to 8.4 cm·s–1) with maximum growth in the range of 10–12 cm·s–1. Increased food appears to permit juvenile coho to exploit higher velocity microhabitats that might otherwise be bioenergetically unsuitable at lower food levels. Increased fish density resulted in lower growth of subdominant but not of dominant fish and a general displacement of fish to both higher and lower focal velocities. The shapes of habitat suitability curves were sensitive to food abundance, implying that differences in food availability may affect transferability of habitat suitability curves between streams of different productivity. While habitat suitability curves captured the change in extent of available habitat following prey enrichment, actual increases in growth rate with enrichment (i.e., changes in habitat quality) were poorly represented by habitat suitability values and better represented by bioenergetic model predictions.

Macroinvertebrate Responses to Algal and Bacterial Manipulations in Streams

Our study was designed to assess the relative importance of algae and bacteria as sources of energy for stream macroinvertebrates. In one experiment, we manipulated algae by artificially shading six sections in each of two streams, one stream with an open canopy (clear-cut drainage basin) and the other with a closed canopy (forested drainage basin); both streams were in Hubbard Brook Experimental Forest, New Hampshire, USA. Chlorophyll a concentrations were reduced from 0.2 to 0.05 μg/cm2 in artificially shaded sections of both streams. However, macroinvertebrates showed no response to these algal manipulations in either the clear-cut or forested stream. Nutrient concentrations (N and P) were low and limiting to primary production in both the clear-cut and forested streams. Additionally, both streams had relatively low macroinvertebrate densities suggesting bottom-up controls were important in macroinvertebrate abundance. However, the forested stream did have higher macroinvertebrate densities presumably because of higher inputs of coarse particulate organic matter from the riparian vegetation. In a second experiment, in Augusta Creek, Michigan, we manipulated both algae and bacteria. To reduce algae, we artificially shaded experimental stream channels so that chlorophyll a was reduced from natural levels of 3.0–5.6 to 0.4–0.7 μg/cm2. Half of the shaded channels had dissolved organic carbon (DOC – sucrose) dripped into them to raise DOC levels by 2–3 mg/l and thus stimulate bacterial abundance. Open channels, with higher algal abundance, had higher densities of Ephemerella, but only in November when nymphs were larger. Channels with increased DOC had higher bacterial abundances, higher densities of Chironomidae and lower densities of Heptageniidae. Several other macroinvertebrate taxa that were at relatively low abundance in our samples showed no significant response to these manipulations. Our results suggest that early instar Ephemerella may not rely as heavily on algae as later instars. Also, certain taxa were able to use the heterotrophic microbial community, especially chironomids which increased in numbers when bacterial density increased; thus, the bacterial carbon source may be more important to some stream macroinvertebrates than previous studies have suggested.

THE EFFECT OF HYDROLOGICAL DISTURBANCE ON THE IMPACT OF A BENTHIC INVERTEBRATE PREDATOR

The harsh–benign model of community dynamics predicts that the impact of predation will decline as abiotic conditions become more stressful to biota. Experiments were conducted to determine whether hydrological disturbance altered the impact of an invertebrate predator in stream benthic communities. The impact of a predatory stonefly, Cosmioperla kuna, on its mayfly prey was measured in experimental stream channels receiving constant or variable flow (flooding) regimes over a one-week period. Contrary to predictions of the harsh–benign hypothesis, the impact of Cosmioperla on its two major prey taxa was either unchanged or increased by artificial floods, despite increased predator emigration from variable-flow channels. Predator impacts in variable-flow treatments were apparently strongly influenced by predator-induced prey emigration during floods. The results of this study show that nonlethal predator effects may be important during abiotic disturbance, and that it may not be reasonable to predict the impact of predation solely on the basis of the relative tolerances of predators and prey to prevailing abiotic conditions.

The effect of visual isolation on territory size and population density of juvenile rainbow trout (Oncorhynchus mykiss)

Visibility is thought to affect the territory size of visually oriented animals but there have been few experimental tests of the hypothesis. We re-examined the relationship between visibility and territory size in juvenile salmonids to test the hypothesis that increasing habitat heterogeneity results in a reduction in territory size and consequently in higher population densities. Equal densities of young-of-the-year rainbow trout (Oncorhynchus mykiss) were stocked in two experimental treatments with low visibility and a control treatment with high visibility. Visibility was decreased by placing large stones or plywood dividers onto the substrate of experimental stream channels. As predicted, the size of individual territories decreased with decreasing visibility of the habitat. However, the treatments did not differ significantly in population density or growth rate of the fish. While this study confirms the inverse relationship between habitat visibility and territory size, the decrease in territory size did not produce an increase in population density of juvenile salmonids.

Use of electricity to inhibit macroinvertebrate grazing of epilithon in experimental treatments in flowing waters

Electricity delivered from a modified electric fence charger was used successfully to reduce grazing pressure on epilithon within experimental stream channels in the field without influencing flow through the channels. Laboratory experiments demonstrated that the presence of an electrical field similar to that used in the stream channels did not significantly influence epilithon biomass. Although more macroinvertebrates were collected from channels receiving electricity than those without, the much higher epilithon standing crop, measured as chlorophyll a (7–30× higher) and ash-free dry mass (3–5× higher), within electrified channels suggested that animals not excluded were insignificant grazers. Taxonomic composition in stream channels without electricity was similar to the river, both with 60–70% mayflies and 7–15% Diptera. In contrast, channels with electricity had 3–25% mayflies and 60–80% Diptera. Electricity proved to be an efficient way of reducing grazing pressure on epilithon through changes in the composition of invertebrate grazers.

Is the distribution, growth and survival of juvenile salmonids sex biased? Negative results for coho salmon in an experimental stream channel

There were no sex‐related differences in spatial distribution, abundance or growth of juvenile coho salmon Oncorhynchus kisutch from two full‐sibling families after 75 days rearing in an outdoor stream channel. These findings are not consistent with recent reports that aggressiveness and spatial distribution differ between males and females in juveniles of other streamdwelling salmonid species.

Is the distribution, growth and survival of juvenile salmonids sex biased? Negative results for coho salmon in an experimental stream channel

Is the distribution, growth and survival of juvenile salmonids sex biased? Negative results for coho salmon in an experimental stream channel

Effects of woody debris on the growth and behaviour of brown trout in experimental stream channels

We examined the effects of woody debris on the growth and behaviour of brown trout (Salmo trutta) in experimental stream channels. Two types of habitat were used in the study: a complex habitat created by placing woody debris on a gravel bed and a uniform habitat consisting of a gravel bed only. The experiment was run both outdoors with wild fish that fed on natural invertebrate drift and indoors with hatchery fish that were fed artificial food. In both treatments most of the fish lost mass. In all trials, however, the fish in the woody debris channel lost less mass than the fish in the control channel. Study of the fishes' behaviour revealed less swimming activity, less aggression, and less feeding activity in the woody debris channel than in the control channel. The results of this study indicate that the presence of woody debris decreases intraspecific competition through visual isolation, allowing fish to reduce aggressive interactions and energy expenditure.

Effects of woody debris on the growth and behaviour of brown trout in experimental stream channels

Effects of woody debris on the growth and behaviour of brown trout in experimental stream channels