Outdoor Stream Channels Research Articles

Dead or alive — Old empty shells do not prompt false‐positive results in environmental DNA surveys targeting the freshwater pearl mussel (Margaritifera margaritifera L.)

Abstract Environmental DNA (eDNA) from water samples is increasingly used to detect the presence and distribution of species in aquatic ecosystems. However, before implementing eDNA in monitoring programmes, various species‐specific sampling or analytical issues remain to be resolved in order to minimize frequencies of false‐positive and ‐negative results. For example, empty shells from freshwater pearl mussels (Margaritifera margaritifera) contain extractable DNA (chemical extraction from ground‐up shells) suggesting a risk of false‐positive samples at stream sites with extinct populations but with empty shell material remaining. The aim of this study was to investigate whether empty and naturally degrading shells from M. margaritifera can cause false‐positive eDNA signals in water samples. Water samples were collected from outdoor stream channels (in Lemming, Denmark) with living freshwater pearl mussels or empty shell material (density ~10 individuals m−2) during a 3‐week experimental period. Living freshwater pearl mussels were collected from Hemgravs stream in Sweden and transported to Denmark according to permissions granted by the Swedish and Danish authorities. All water samples from stream channels containing empty shells were negative for eDNA indicating that eDNA traces in stream water are most likely to originate from living individuals located upstream of the sampling site. Water samples collected from stream channels containing living individuals of M. margaritifera were consistently positive for eDNA except for one sample (interpreted as a false negative). The study shows that positive eDNA signals for freshwater pearl mussels most likely reflect the presence of living individuals. Consequently, we suggest that eDNA should be used to locate remaining population fragments of M. margaritifera in deep and turbulent streams, providing a platform for faster and more efficient decision making when launching investigative and mitigation initiatives.

Pesticide impacts on predator–prey interactions across two levels of organisation

In this study, we aimed to evaluate the effects of a short pulse exposure of the pyrethroid lambda-cyhalothrin (LC) on the predator and anti-predator behaviour of the same species; Gammarus pulex. Predator behaviour, at the level of the individual, was studied in indoor microcosms using video tracking equipment during simultaneous exposure of the predator (G. pulex) and its prey (Leuctra nigra) during 90min exposure of 1, 6.6 or 62.1ngL−1 LC. During an initial 30min of exposure, the predator and prey organisms were maintained physically separated, and the actual interaction was studied through the subsequent 60min of exposure. The anti-predator behaviour of G. pulex (drift suppression in response to the presence of brown trout) was studied in outdoor stream channels during a 90min pulse exposure to LC (7.4 or 79.5ngL−1) with, or without, brown trout. Based on survival curves for L. nigra we found that the mortality rate for L. nigra significantly decreased during exposure to 6.6 and 62.1ngL−1 LC (P<0.05 and P<0.001, respectively). We found no significant effects suggesting that G. pulex was repelled by contaminated prey items (P>0.05). We found that the exposure of G. pulex to 7.4 and 79.5ngL−1 LC significantly increased drift (from ∼0% to ∼100% in both treatments; P<0.001) independent of the presence of brown trout (P<0.05). In other words, the natural anti-predator behaviour of G. pulex was overruled by the stress response to LC exposure increasing G. pulex predation risk from drift feeding brown trouts. Our results show that the anti-predator and predator behaviour of G. pulex were significantly changed during exposure to very low and environmentally realistic LC concentrations and exposure duration. The potential implications for the field scenario are discussed.

Size at Implantation Affects Growth of Juvenile Steelhead Implanted with 12‐mm Passive Integrated Transponders

AbstractPassive integrated transponder (PIT) tags have led to greater understanding of fish growth, survival, predation, migration, behavior, and the effects of human‐caused environmental manipulation. Technological advances have reduced the size of PIT tags, permitting their implantation into smaller fish. To reap the benefits of PIT tag technology, implantation must not adversely impact growth, survival, or behavior. Steelhead Oncorhynchus mykiss parr reared in a natural‐like environment were implanted with 12‐mm PIT tags, and implantation effects on growth rate were measured. Steelhead had fork lengths ranging from 45 to 96 mm after 4 weeks of rearing in an outdoor stream channel. Thirty (17.4%) of the 172 steelhead parr that were under 74 mm at the time of PIT tag implantation had instantaneous growth rates of 0 [loge (g)]/d or less, while all parr (n = 72) over 75 mm exhibited positive growth rates. Logistic regression indicated that fork length at implantation was significantly related to the probability of positive growth rates (P &lt; 0.001). For steelhead parr that exceeded 74 mm at implantation, the probability of experiencing positive growth was greater than 95%. The data suggest that fork length of steelhead parr should be above 74 mm at implantation to minimize negative growth effects associated with 12‐mm PIT tags.

Non‐interactive effects of habitat complexity and adult crayfish on survival and growth of juvenile crayfish (Pacifastacus leniusculus)

Summary1. In a 1‐month outdoor stream channel experiment, we investigated the relative importance of habitat complexity (i.e. cobbled area) and the presence of adult signal crayfish (Pacifastacus leniusculus) males on the survival and growth of juveniles.2. In treatments with high habitat complexity, more juveniles survived, more were newly moulted and they had a higher specific growth rate (SGR) at the end of the experiment than juveniles in treatments with low habitat complexity. The presence of adult males did not affect survival, moulting stage or growth of the juveniles.3. The presence of adult males decreased juvenile activity during night. Juveniles in treatments with low habitat complexity were more active than juveniles in high habitat complexity during both day and night.4. There was no difference in total invertebrate biomass between treatments. However, some invertebrate taxa, such as Chironomidae larvae, were affected by habitat complexity or the presence of adult crayfish. Juvenile crayfish in all channels had consumed detritus, algae and Chironomidae larvae and there were no differences in gut contents or stable isotope signals (carbon and nitrogen) between treatments, indicating a similar diet among the juveniles across treatments. However, the biomass of chironomids was significantly higher in channels with adult crayfish present, indicating a decreased consumption of chironomids by juveniles in the presence of adults.5. Our results suggest that the recruitment of juvenile crayfish is mostly affected by habitat complexity. The competition for food and shelter and aggressive interactions between the juveniles were most pronounced in low habitat complexity, indicating that habitats with a good access to shelter will enhance recruitment of juvenile crayfish in streams.

Behaviour and growth of juvenile brown trout exposed to fluctuating flow

Abstract – Parr of brown trout (Salmo truttaL.) were exposed to constant or fluctuating water level and flow in artificial outdoor stream channels during 21 days in three consecutive runs, and their individual behaviour and social interactions were monitored. Despite the large variation in flow, no clear differences in growth, which was generally poor, and behaviour were found between treatments. The signs of a social structure in the stream channels were very subtle and there were no clear relation between growth rate and aggressive/dominant behaviour in any of the treatments in accordance with findings in studies of growth and dominance in the wild. Thus, in regulated rivers, daily fluctuations in flow and water level (hydropeaking) are not likely to alter the behaviour of juvenile brown trout or affect their energy turnover negatively. Several studies now indicate that if stranding can be avoided, hydropeaking has relatively small direct effects on stream salmonids. Therefore, future research should focus on cascading ecological effects that may influence the productivity of the ecosystems in regulated rivers.

The effect of food abundance on territory size and population density of juvenile steelhead trout (Oncorhynchus mykiss).

Optimal territory size models predict a decrease in territory size with increasing food abundance. However, most of these models may not be applicable to juvenile salmonids in streams, because they defend contiguous territories at high densities. The optimal size of a contiguous territory is predicted to (1) be independent of food abundance when food is rare and (2) decrease only when food abundance is high enough to induce a reduction in territory size below the contiguous optimum. To test these predictions, we raised equal densities of juvenile steelhead trout in outdoor stream channels over a 32-fold range of food abundance in the absence of emigration for 25 days. Increasing competition for scarce food resulted in increasing mortality, higher willingness to emigrate, higher variance in body mass, lower growth, lower population density and lower biomass. The size of territories decreased with increasing local population density, and increased with increasing body size. However, territory size did not change with food abundance, a result consistent with the prediction of a contiguous territory size model. On average, total salmonid biomass increased 5.7 times in response to the 32-fold increase in food abundance. Our data provide strong support for an earlier quantitative relationship between the abundance of stream salmonids and their food.

Effect of Depth and Substrate on Use of Stream Pools by Brown Trout

Abstract We tested how depth and cobble clusters affected pool use by brown trout Salmo trutta in four enclosures in a seminatural, outdoor stream channel. Into each enclosure, which consisted of a shallow, cobble-filled habitat and a deeper pool, we stocked eight brown trout 9–19 cm long that had been tagged with passive integrated transponders (PIT). Receiver antennae for the PIT tags were placed between the two habitats to allow continuous monitoring of movements of individual fish. We found that trout used pools to a greater extent at night than during the day. Alterations of depth and substrate had no effect on pool use at night. During the day, increasing water depth either alone or together with adding cobbles increased pool use, whereas cobble addition alone had no effect on pool use. We suggest that evaluations of physical habitat modifications in streams should include measurements of population responses as well as information on how, when, and which fish use newly created habitat structures.

Acute lethal and sublethal effects of a neem-based insecticide on nontarget aquatic insects in stream channels.

Extracts from seeds and leaves of the neem tree, Azadirachta indica, express insecticidal activity against a broad range of insect pests (Schmutterer and Singh 1995). The primary active ingredient in neem extracts is the triterpenoid, azadirachtin. Because several common forest pests are among the most susceptible insects to azadirachtin, the use of neem-based insecticides in Canadian forest pest management programs is being investigated (Isman et al. 1991; Helson et al. 1999). Insecticide applications to forests may result in some of the product entering nearby water bodies and it is therefore important to ensure that these insecticides do not post a risk of adverse effects on aquatic organisms. Small streams are particularly susceptible to contamination by runoff from adjacent sprayed areas because of low dilution potential, and from inadvertent overspray because they are difficult to avoid during aerial applications. We investigated the potential for adverse effects on stream insects by applying a neem-based insecticide to outdoor stream channels and measuring acute lethal and sublethal responses.

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.

Accumulation Dynamics of Triclopyr Ester in Aquatic Leaf Packs and Effects on Detritivorous Insects

AbstractPrevious field studies have demonstrated that residues of the herbicide, triclopyr butoxyethyl ester (3,5,6‐trichloro‐2‐pyridinyloxyacetic acid, butoxyethyl ester) (TBEE), can accumulate in submerged leaf material of aquatic systems at concentrations up to 20 times the maximum aqueous concentrations. Accumulated TBEE residues may pose a risk of adverse effects to detritivorous invertebrates inhabiting and using natural leaf packs. We examined the dynamics of TBEE accumulation and persistence in leaf materials of laboratory and outdoor aquatic systems, and determined the ecological significance of this in terms of effects on detritivorous insects and organic matter processing. Accumulations of TBEE in leaf packs of semi‐static laboratory microcosms were up to 80 times aqueous concentrations, and residues persisted for 4 to 5 d. Leaf material of flow‐through laboratory microcosms accumulated TBEE at much higher rates (up to 1000 times aqueous concentrations), but residues were cleared by 48 to 72 h. Accumulation and persistence in flow‐through units were dependent on water depth, velocity, and exposure duration. Accumulated TBEE residues were less in outdoor stream channels than in laboratory flow‐through units, probably because of losses through sorption to natural benthic material in the stream channels. Despite accumulations of TBEE in leaf packs at up to 90 mg kg−1 in systems treated at or near expected environmental concentrations, there was no significant mortality of detritivorous insects and no significant reductions in leaf consumption. Significant mortality and reduced feeding occurred only in systems treated at concentrations well above (up to 10 times) expected environmental concentrations.

Functional Effects of the Bacterial InsecticideBacillus thuringiensisvar.kurstakion Aquatic Microbial Communities

Epilithic microbial communities were colonized on leaf disks and exposed to commercial preparations ofBacillus thuringiensisvar.kurstaki(Btk) in aquatic microcosms. Responses in terms of microbial respiration, bacterial cell density, protozoan density, and microbial decomposition activity were measured. Test concentrations for treatments with Dipel 64AF and Dipel 8AF in microcosms were the expected environmental concentration (EEC) of 20 IU/ml, 100× the EEC, and 1000× the EEC. Bacterial cell density in the biofilm of leaf disks was significantly increased at concentrations as low as the EEC. There were no concomitant alterations in protozoan density. Microbial respiration was significantly increased, and decomposition activity was significantly decreased, but only at the artificially high concentration of 1000× the EEC. This effect was attributed to the spore–crystal component rather than formulation ingredients. Microbial decomposition of leaf material was also determined in outdoor stream channels treated at concentrations ranging from the EEC to 100× the EEC. Although there tended to be reduced decomposition activity in treated channels, there were no significant differences in mass loss of leaf material between treated and control channels. Various regression, classification, and ordination procedures were applied to the experimental data, and none indicated significant treatment effects. These results from laboratory and controlled field experiments indicate that contamination of watercourses with Btk is unlikely to result in significant adverse effects on microbial community function in terms of detrital decomposition.

Hexazinone effects on stream periphyton and invertebrate communities

AbstractExperiments were conducted in laboratory test chambers and outdoor stream channels to measure the effects of hexazinone on stream periphyton and macroinvertebrate communities. All experimental units were treated at the nominal concentration of 2.7 mg/L, which represents the maximum expected environmental concentration in water from forest vegetation management applications. In laboratory flow‐through tests, a 12‐h exposure of stream periphyton on natural substrates to hexazinone resulted in a significant reduction in net photosynthetic activity, but no significant effects on periphyton biomass (chlorophyl‐a concentration). Recovery from toxic effects was rapid, with no significant differences in photosynthetic activity among treated and control units within 3 h after the hexazinone concentrations were cleared. In stream channels treated for 12 h with hexazinone, there were no significant effects on periphyton biomass and no significant differences in invertebrate drift, compared to control channels. There were also no indications of adverse treatment effects on the invertebrate communities in the stream channels 14 d after the application. The treated and control channels differed in invertebrate community structure, as determined by a stepwise discriminant analysis [Wilks' lambda F equivalent (3,2) = 127.6, p = 0.007], and this was supported by a two‐way ANOVA which showed a significant difference in abundance of macroinvertebrates [F(1, 56) = 10.5, p = 0.002] between treated and control channels, averaged over all taxa. However, subsequent pairwise t tests, when adjusted for multiple comparisons, were unable to identify significant differences between treatment levels for any of the 14 taxa with sufficient data for analysis. Although not significant, the comparison of means showed that abundance of most taxa was higher in the treated channels than in the controls.

Spatial distribution, survival, and growth of sibling groups of juvenile coho salmon (Oncorhynchus kisutch) in an experimental stream channel

The spatial distribution, survival, and growth of two full-sibling families of coho salmon (Oncorhynchus kisutch) in an experimental outdoor stream channel were compared between the families and with the performance of one of the families in an allopatric control channel after 75 d of rearing. No difference in survival was observed between families (81.2% overall), but their spatial distributions in the channel differed markedly. One family or the other numerically dominated 5 of 7 riffle-pool habitat units within the sympatric treatment channel. The family that was larger at the beginning of the experiment (0.52 vs. 0.37 g mean mass) was also larger at the end (2.03 vs. 1.58 g). While there was little evidence of density-dependent growth overall, the growth of each family was correlated with the density of siblings in the unit. However, the larger bodied family showed negative density-dependent growth, whereas the smaller bodied family showed positive density-dependent growth. These patterns of distribution and growth may have arisen from sibling recognition or some other proximate mechanism such as assortative distribution based on size or interfamily variation in aggression. Regardless of the mechanism, intrapopulation variation in distribution and growth may lead to considerable variation in fitness among families because these factors affect success in subsequent freshwater and marine life history stages.

Toxicity of a New Molt-Inducing Insecticide (RH-5992) to Aquatic Macroinvertebrates

The molt-inducing insecticide RH-5992, a potent ecdysone agonist, is being evaluated for potential use in forestry to control defoliating lepidopterans. The possible adverse effects of RH-5992 on nontarget aquatic organisms were studied in two test systems. Acute lethal effects were determined for one aquatic amphipod and 11 species of aquatic insects in laboratory flowthrough toxicity tests. Lethal and behavioral effects (drift response) on the amphipod and 8 species of stream insects were also evaluated under natural environmental conditions and more realistic exposure regimes in outdoor stream channels. There were no significant effects on drift or survival of the test species exposed to RH-5992 at the maximum test concentration of 3.5 mg/liter (100× the worst-case expected environmental concentration) in laboratory toxicity tests and stream channel treatments. Mortality of the amphipod Gammarus sp. in one toxicity test was considered an artifact, because there was no significant mortality in subsequent tests at concentrations up to 7.0 mg/liter, or in stream channels treated at 3.5 mg/liter. Yellow birch leaves were sprayed with RH-5992 at a rate of 50 g/ha and tested for residual toxic effects on two species of shredding invertebrates in the outdoor stream channels. There was no feeding inhibition or lethal effect on either test species resulting from consumption of the contaminated foliage. The candidate insecticide RH-5992 does not appear to pose undue risk of direct adverse effects to aquatic macroinvertebrates, particularly in water bodies where residues are likely to be short lived following aerial applications (e.g., lotic systems).

Lethal and sublethal effects of Bacillus thuringiensis var. kurstaki on aquatic insects in laboratory bioassays and outdoor stream channels.

The microbial insecticide Bacillus thuringiensis is generally considered to be more environmentally acceptable than many broad-spectrum chemical insecticides (Laird et al. 1990), and Bacillus thuringinesis var. kurstaki (Btk) is now widely used in forest management for controlling defoliating insects (van Frankenhuyzen 1990). Broadscale applications of Btk to forested areas may result in contamination of watercourses, and may pose some hazard to aquatic organisms. Although the impact of B. thuringiensis var. israelensis (a dipteran-active serotype used for biting-fly control) on non-target aquatic fauna has been extensively investigated (e.g., Merritt et al. 1989), few published studies have reported the effects of Btk (the variety used in forest pest management) on aquatic invertebrates. Previous risk assessments of Btk to aquatic invertebrates have been largely based on static bioassays (Eidt 1985) and unpublished data from field investigations (Surgeoner and Farkas 1989). Our objective was to improve the risk assessment for stream insects exposed to Btk by providing further toxicity data for an array of insect taxa under more natural exposure regimes and environmental conditions. We conducted experiments to measure the acute lethal response of aquatic insects to Btk (Dipel 8AF) in recirculating laboratory bioassays, and to determine lethal and behavioural (drift) effects of Btk on aquatic insects in outdoor stream channels. MATERIALS AND METHODS Test organisms were collected from streams with an electroshocker and acclimated at the test sites for 24 hr before the treatments. No attempt was made to determine specific stages of development for the specimens, but most (except Taeniopteryx nivalis and some groups of Lepidostoma sp.) were in late or final instar. Btk was applied as formulated product (Dipel 8AF, Abbott Laboratories, Chicago, IL) at a maximum concentration of 600 IU/mL. As a means send reprint requests to D.P. Kreutzweiser at above address

Effects of the herbicides hexazinone and triclopyr ester on aquatic insects

Experiments were conducted to measure acute lethal response of aquatic insects to hexazinone (Velpar L) and triclopyr ester (Garlon 4) in flow-through laboratory bioassays, and to determine lethal and behavioral effects of these herbicides on insects in outdoor stream channels. No significant mortality ( χ 2 P > 0.05) occurred in 13 test species exposed to hexazinone in laboratory flow-through bioassays (1-hr exposure, 48-hr observation) at the maximum test concentration of 80 mg/liter. The survival of insects exposed to 80 mg/liter hexazinone in outdoor stream channels was likewise unaffected. Significant drift ( χ 2 P < 0.001) of Isonychia sp. occurred during a hexazinone treatment of the stream channels, but only at the maximum concentration of 80 mg/liter, and survival of the displaced isonychia sp. was not affected. In flow-through bioassays with triclopyr ester, 10 of 12 test species showed no significant mortality at concentrations greater than 80 mg/liter. Survival of Isogenoides sp. and Dolophilodes distinctus was significantly affected at less than 80 mg/liter. Lethal concentrations were estimated by probit analysis of concentration-response data (1-hr exposure, 48-hr observation) for Simulium sp. (LC 50 = 303 mg/liter), Isogenoides sp. (LC 50 = 61.7 mg/liter), and D. distinctus (LC 50 = 0.6 mg/liter). Triclopyr ester applications to the stream channels resulted in significant drift and mortality of D. distinctus at 3.2 mg/liter (no effects at 0.32 mg/liter), Isogenoides sp. at 32 mg/liter, and Hydropsyche sp. and Epeorus vitrea at 320 mg/liter. The risk to aquatic insects of these herbicides used in forest vegetation management is discussed.

Influence of Cover Complexity and Current Velocity on Winter Habitat Use by Juvenile Coho Salmon (Oncorhynchus kisutch)

Winter habitat use by juvenile coho salmon (Oncorhynchus kisutch) varied with cover type and flow level in outdoor stream channels. Cover utilization and the number of fish remaining in stream channels increased significantly as cover complexity increased. Most fish emigrated during a simulated freshet unless the most complex cover (low velocity, shade, and wood debris combined) was available. At both high and low flows, emigration occurred primarily during the rapid decline in light levels at twilight. Most coho formed aggregations beneath cover, exhibiting feeding and aggression at temperatures as low as 2.5 °C. We conclude that (1) social interactions, in concert with habitat features, influence the abundance of coho salmon within specific stream habitats in winter, and (2) structural complexity of wood debris is an important consideration for management practices designed to protect or enhance winter habitat for this species.