Replicate Streams Research Articles

Density‐dependent diet composition of juvenile Atlantic salmon (Salmo salar)

Abstract – Decreases in body growth with increasing population density may be caused by reduced prey delivery rate. However, changes in food quality because of an increasing inclusion of suboptimal prey in the diet may also contribute to such effects. Here, we test for density‐dependent diet composition by creating spatial variation in Atlantic salmon young‐of‐the‐year (YOY) density in three replicate streams and obtain detailed information on individual positions (±1 m) and diet. Diet breadth with respect to prey size increased with increasing local density for the two most common prey types (Chironomidae and Ephemeroptera). For the largest prey type (Ephemeroptera), there was also an increase in mean prey size with increasing density, suggesting that YOY salmon preferentially utilise the smaller prey among those available. According to optimal foraging theory, changes in diet with increasing local density are likely to come at an energetic cost and hence may contribute to the commonly observed density‐dependent growth of juvenile salmonids.

The spatial scale of density-dependent growth and implications for dispersal from nests in juvenile Atlantic salmon

By dispersing from localized aggregations of recruits, individuals may obtain energetic benefits due to reduced experienced density. However, this will depend on the spatial scale over which individuals compete. Here, we quantify this scale for juvenile Atlantic salmon (Salmo salar) following emergence and dispersal from nests. A single nest was placed in each of ten replicate streams during winter, and information on the individual positions (±1 m) and the body sizes of the resulting young-of-the-year (YOY) juveniles was obtained by sampling during the summer. In six of the ten streams, model comparisons suggested that individual body size was most closely related to the density within a mean distance of 11 m (range 2–26 m). A link between body size and density on such a restricted spatial scale suggests that dispersal from nests confers energetic benefits that can counterbalance any survival costs. For the four remaining streams, which had a high abundance of trout and older salmon cohorts, no single spatial scale could best describe the relation between YOY density and body size. Energetic benefits of dispersal associated with reduced local density therefore appear to depend on the abundance of competing cohorts or species, which have spatial distributions that are less predictable in terms of distance from nests. Thus, given a trade-off between costs and benefits associated with dispersal, and variation in benefits among environments, we predict an evolving and/or phenotypically plastic growth rate threshold which determines when an individual decides to disperse from areas of high local density.

Comparison of visual survey and seining methods for estimating abundance of an endangered, benthic stream fish

We compared visual survey and seining methods for estimating abundance of endangered Okaloosa darters, Etheostoma okaloosae, in 12 replicate stream reaches during August 2001. For each 20-m stream reach, two divers systematically located and marked the position of darters and then a second crew of three to five people came through with a small-mesh seine and exhaustively sampled the same area. Visual surveys required little extra time to complete. Visual counts (24.2 ± 12.0; mean ± one SD) considerably exceeded seine captures (7.4 ± 4.8), and counts from the two methods were uncorrelated. Visual surveys, but not seines, detected the presence of Okaloosa darters at one site with low population densities. In 2003, we performed a depletion removal study in 10 replicate stream reaches to assess the accuracy of the visual survey method. Visual surveys detected 59% of Okaloosa darters present, and visual counts and removal estimates were positively correlated. Taken together, our comparisons indicate that visual surveys more accurately and precisely estimate abundance of Okaloosa darters than seining and more reliably detect presence at low population densities. We recommend evaluation of visual survey methods when designing programs to monitor abundance of benthic fishes in clear streams, especially for threatened and endangered species that may be sensitive to handling and habitat disturbance.

Hierarchical patterns of invertebrate assemblage structure in stony upland streams change with time and flow permanence

Summary1. Studies in several parts of the world have examined variation in univariate descriptors of macroinvertebrate assemblage structure in perennially flowing stony streams across hierarchies of spatial scale using nested analyses of variance. However, few have investigated whether this spatial variation changes with time or whether these results are representative of habitats other than riffles or of other stream types, such as intermittently flowing streams.2. We describe patterns in taxon richness and abundance from two sets of samples from stony streams in the Otway Range and the Grampians Range, Victoria, Australia, collected using hierarchical designs. Sampling of riffles was repeated in the Otways, to determine whether spatial patterns were consistent among times. In the Grampians, spatial patterns were compared between intermittent and perennially flowing streams (stream type) by sampling pools.3. In the Otways streams, most variation in the dependent variables occurred between sample units. Patterns of variation among the other scales (streams, segments, riffles, groups of stones) were not consistent between sampling times, suggesting that they may have little ecological significance.4. In the Grampians streams, variation in macroinvertebrate taxon richness and abundance differed significantly between replicate streams within each stream type but not between stream types or pools. The largest source of variation in taxon richness was stream type. Little variation occurred among sample units.5. The pattern of most variation occurring among sample units is robust both to differences in the method of sampling and different dependent variables among studies and increasingly appears to be a property of riffles in stony, perennial upland streams. High variation among sample units (residual variation) limits the explanatory power of linear models and therefore, where samples are from a single sampling time, small but significant components of variation are unlikely to represent features of assemblage structure that will be stable over time.

Laboratory and field responses to cadmium: an experimental study in effluent-dominated stream mesocosms.

Although select stream flows in the southwestern United States are dominated by effluent discharges, metal hazards have not been experimentally evaluated in effluent-dominated streams. Lotic mesocosms were designed to assess cadmium effects on multiple levels of biological organization, to determine relevance to regulatory criteria of standard laboratory toxicity tests, and to link laboratory tests to stream responses. Replicate streams were treated with 15 or 143 microg/L Cd during a 10-d study. Streams were sampled on days 0 and 10 for benthic macroinvertebrates, periphyton, and ecosystem metabolism. Concurrent Ceriodaphnia dubia and Pimephales promelas laboratory tests were performed with water from streams. Individual organism, population, and community response variables were affected by 143 microg/L Cd but not by the I5-microg/L treatment level. A biotic ligand model for cadmium predicted a 48-h median effective concentration (EC50) value of 280 microg/L Cd for C. dubia in these effluent-dominated streams: an EC50 value of 38.3 microg/L Cd was estimated for C. dubia in tests performed with reconstituted hard water. Our findings generally support use of the biotic ligand model for establishing site-specific, acute water quality criteria for cadmium. However, future effluent-dominated stream research is required to evaluate relationships between chronic cadmium exposure and organismal and community responses.

A biological assessment of best management practice effectiveness during intensive silviculture and forest chemical application

A multi-year study was conducted to evaluate the effectiveness of Florida's Best Management Practices (BMPs) for protecting aquatic ecosystems during intensive forestry operations and forest chemical applications. Five silviculture sites adjacent to stream systems were selected for study from major eco-regions of the state. Replicate stream bioassessments, using a multimetric approach (the Stream Condition Index), were conducted as part of a `before-after, control-impact' (BACI) study design. Bioassessment stations were established above and below the treatment area to determine pre-treatment reference and test conditions. Silviculture treatments of clearcut harvesting, intensive mechanical site preparation and machine planting were then completed, during which all applicable BMPs were adhered to. In addition, two sites received an herbicide application and one site was fertilized. Following the treatments, the sites were re-sampled at the same points both one year, and two years after the first bioassessment. No significant differences in the SCI were observed between the reference and test portions of the streams that could be attributed to the silviculture operations using BMPs. Hence, the study showed that BMPs provided protection to adjacent stream ecosystems, even during intensive silviculture and forest chemical applications.

Spatial and temporal variability in the structure of invertebrate assemblages in control stream mesocosms

Outdoor stream mesocosm studies conducted between 1992 and 1996 at two facilities enabled the investigation of structural variability in invertebrate assemblages within and between studies. Temporal variability of benthic invertebrate assemblages between eight replicate streams within a study was assessed in a 28-day mesocosm study without chemical treatment. Cluster analysis, non-metric multidimensional scaling, and principal component analysis each showed the untreated assemblages as structurally distinct groups on the three sampling days. The assemblages between the eight replicate streams showed >88% Bray–Curtis similarity at any one time during the study. In addition, pre-treatment data from a series of four studies conducted at one facility were used to examine structural variability in the starting benthic invertebrate assemblages between studies. Invertebrate assemblages were structurally distinct at the start of each mesocosm study conducted in different years at the same facility and the taxa responsible for differences in the assemblages were also different each year. The implications of temporal and spatial variability in benthic invertebrate assemblages within and between mesocosm studies with regards to species sensitivity and study repeatability should be considered when results of such studies are used in risk assessment.

Allocation of effort in stream food-web studies: the best compromise?

The amount and allocation of effort needed to characterize stream food webs was investigated in five replicate streams. Two areas were considered:analysis of community composition (number of individuals sampled)and of diets (number of individuals gutted per animal taxon). Food webs were described by use of consistent methodology, then the effort was retrospectively reduced by considering half of the gut samples (halving dietary analysis effort)and by successively reducing the number of individuals included. Food webs with a reduced number of individuals overestimated connectance and prey:predator ratios, and underestimated species richness, links per species and mean chain lengths. These changes were due to loss of some invertebrate predator species when effort was reduced. In contrast, for dietary analysis the amount of effort expended on non-predatory invertebrates was more influential; halving effort in dietary analysis of non-predatory taxa reduced estimates of connectance and links per species. This study suggests that the effort needed to produce a reasonable estimate is highly dependent on the food-web attribute in question, and that aiming for equity of effort across taxonomic groups is as important as expending greater effort in general.

The effects of a C12–13 linear alcohol ethoxylate surfactant on periphyton, macrophytes, invertebrates and fish in stream mesocosms

AbstractThe ecological effects of a C12–13 linear alcohol ethoxylate (LAE) were studied in stream mesocosms. The surfactant has an average distribution of six and one‐half ethylene oxide groups per mole of alcohol. Responses of periphyton, macrophytes, invertebrates, and fish were examined and used to estimate a mesocosm‐predicted no‐observable‐effect concentration (NOEC). The stream mesocosm experiment consisted of a 2‐week period of natural colonization, a 30‐d treatment period, and a 2‐week post‐treatment period. Four surfactant concentrations in duplicate streams were used along with two untreated control streams. Surfactant concentrations were delivered to the streams with no apparent loss during the 17‐min transit time. The structural integrity of the surfactant was also maintained with no observed differences between the head, middle, or tail sections of individual streams. Average measured concentrations of LAE for replicate streams were 0.32, 0.88, 1.99, and 5.15 mg/L. Periphyton and Myriophyllum aquaticum did not show significant effects. The no‐observed‐effect concentration (NOEC) for all periphyton and M. aquaticum parameters was 5.15 mg/L, the highest concentration tested. Statistically significant effects were observed on Simuliidae, Copepoda, and Cladocera densities during the treatment period in all exposure concentrations. Thus, the lowest‐observed‐effect concentration (LOEC) for invertebrate densities was 0.32 mg/L. Drifting invertebrates did not show significant LAE effects; however, increased numbers of invertebrates drifted in the 5.15‐mg/L streams compared to controls. The 30‐d LC50 for farm‐raised and University‐cultured fathead minnows was similar at 1.27 mg/L. The 30‐d survival NOEC and LOEC for both populations of fish were 0.88 mg/L and 1.99 mg/L, respectively. There were no significant effects on reproduction in University‐cultured fathead minnow. Fathead minnow reproductive behavior and feeding behavior were most susceptible to surfactant exposure with a NOEC of 0.32 mg/L. Bluegill sunfish survival responded similarly to the LAE as fathead minnow with a 30‐d NOEC of 0.88 mg/L. No sublethal effects on juvenile bluegill growth were observed in this study. For primarily regulatory purposes, a “mesocosm NOEC” of 0.28 mg/L was derived for use in risk assessment.

Assessing the Effects of a C14–15Linear Alcohol Ethoxylate Surfactant in Stream Mesocosms

Fish, benthic macroinvertebrate, and plant responses to 30-day exposures of C14–15linear alcohol ethoxylate surfactant with an average of 7 mol of ethylene oxide (LAE) were measured in flowthrough stream mesocosms. Replicate stream mesocosms were treated in two experiments with concentrations of LAE ranging from 80 to 550 μg/liter. Macroinvertebrates were relatively insensitive with the exception of Simuliidae density which was significantly affected at 160 μg/liter. Fathead minnow (Pimephales promelas R.) reproduction was significantly reduced at >280 μg/liter and larval survival decreased significantly at 330 μg/liter. Growth and mortality of bluegill sunfish (Lepomis macrochirus L.) were not affected at the highest exposure concentration of 330 μg/liter in the first experiment. No ecologically significant effects were observed for vascular aquatic plants or periphyton. The laboratory and stream mesocosm results were similar with NOECs ranging between 80 and 550 μg/liter surfactant. The study provided data for an improved risk assessment of this nonionic surfactant, by reducing the uncertainty associated with extrapolation from laboratory data.

The Effects of a Chronic Application of Chlorpyrifos on the Macroinvertebrate Fauna in an Outdoor Artificial Stream System: Species Responses

An outdoor artificial stream system was used to examine the effects of a chronic application of the organophosphate pesticide chlorpyrifos on the invertebrate fauna of the system. Two replicate streams received chlorpyrifos for 21 days at the high dose (5 μg · liter −1) or low dose (0.1 μg · liter −1) or only the carrier solution with which chlorpyrifos is mixed for commercial sale (1,1,1-trichloroethane and xylene). Streams behaved as replicates with respect to five water quality parameters. Seventy-four nonchironomid and 24 chironomid taxa were recorded during the study. The number of taxa and total invertebrate abundance were significantly reduced by both high and low doses of the pesticide. Shannon-Weaver diversity was also reduced by both high and low doses of the pesticide whereas evenness increased in high dose streams. The individual abundances of 9/36 nonchironomid and 13/19 chironomid taxa were significantly reduced by pesticide application; the abundance of one taxon, the gastropod Physastra, increased. The biomass of periphyton in the streams was affected by changes in the abundance of chironomid grazers and Physastra, and the slow recovery of grazers from mortality due to chlorpyrifos appeared to result in a higher biomass of periphyton in the high dose streams than in controls and low dose streams 21 days after dosing ceased. Inverse relationships between the amounts of fine particulate organic matter (FPOM) and the sum of the numbers of all taxa of collector-gatherers (as well as numbers of four individual taxa) were interpreted as disruption of the processing of FPOM by members of this trophic group following toxic effects of chlorpyrifos. The implications of the study for biological monitoring of the direct and indirect effects of chronic doses of chlorpyrifos on streams are discussed, and the use of chironomid larvae and periphyton in biomonitoring to detect pesticide impacts is particularly recommended.

Lotic Ecosystem Response to a Chlorine Disturbance.

The influence of repeated chlorine additions on the resistance and resilience of laboratory stream ecosystems was investigated. Prior to the disturbance, four treatments were imposed on eight laboratory streams in a 2 x 2 factorial design, resulting in two replicate streams per treatment. Treatments included two circulation regimes (once-through or 98% recirculated) and two levels of grazer density (1000 individuals/m2 or 0 individuals/m2 , using the snail Elimia clavaeformis). Resistance of periphyton biomass to an initial set of chlorine additions was greater in once-through than recirculated streams. Periphyton resistance following a second set of chlorine additions was greater in streams without snails compared to those with snails. This appeared to be a biomass-mediated response; the greater biomass levels in no-snail streams provided a larger buffer to the oxidizing action of chlorine. Resilience of most structural parameters and area-specific carbon-fixation rates was not influenced to a significant degree either by flow regime or snail density. Resilience of chlorophyll-specific carbon fixation and exoproteolytic activity (an index of microbial activity) was greater in recirculated streams compared to once-through streams, but only when snails were present. Over the entire experimental period (15 wk), most structural parameters and area-specific carbon fixation rates were significantly greater in (1) streams without snails compared to those with them and (2) streams with once-through circulation compared to those that were recirculated, but only for those streams with snails. Our chlorine additions appeared to have relatively little influence on snails, and snail growth over the experiment was significantly greater in once-through compared to recirculated streams. These data are consistent with other findings that total residual chlorine concentrations of <1.0 mg/L can significantly affect periphyton structure and function. However, nutrient cycling rates appeared to be little affected by the chlorine perturbation, which allowed recirculated systems to recover faster than predicted. The findings from this study suggest the periphyton mat physiognomy and integrity strongly influence system resistance (due to buffering capacity) and resilience (because of nutrient cycling).

Influence of Nutrients and Grazing on the Response of Stream Periphyton Communities to a Scour Disturbance

We examined the effect of nutrient input and grazing intensity on resistance and resilience of periphyton communities in laboratory streams to a scour disturbance. Previous theoretical studies using stream models indicated that resilience of nutrient-limited streams, as defined by the return time to the initial state, is strongly related to the residence time of nutrients in the system and to the presence of herbivores. To experimentally test this prediction we established two levels of nutrient input by altering the flow regime (once-through flow and 98% recirculated flow) and two levels of grazing intensity by the presence or absence of the snail Elimia clavaeformis, resulting in a 2 × 2 factorial design with two replicate streams per treatment. After the streams reached an approximately stable level of periphyton biomass, a scour disturbance was imposed on all streams. Measures of the resistance and resilience of the periphyton to this disturbance were made. The resistance of most structural characteristics of the periphyton was significantly higher in streams with snails than in streams without snails. Nutrient input had little effect on resistance of all periphyton characteristics. Resilience was measured by two parameters: rate of increase of a particular characteristic over time following the disturbance (r), and time to return to the pre-disturbance state (T_s). The experimental results on resilience were complex. In general, high grazing intensity resulted in low values of r for most periphyton characteristics, but also shorter T_s for some characteristics. The shorter T_s values were attributed to lower pre-disturbance biomass and metabolism in the streams with snails compensating for lower r for these characteristics following the disturbance. Contrary to model predictions, low nutrient input generally did not result in low resilience for most characteristics in the streams without snails, probably because increased nutrient recycling compensated for low inputs. However, for the streams with snails, resilience of most periphyton characteristics was lower in streams with low nutrient input compared with streams with higher nutrient input. This contrast in resilience suggests a positive feedback between biomass accrual and nutrient recycling that helps maintain high productivity despite low nutrient inputs during recovery of stream periphyton communities from disturbance.

Response of the microflora in outdoor experimental streams to pentachlorophenol: environmental factors.

The 2nd year of a 2-year study of the fate of pentachlorophenol in outdoor artificial streams focused on details of microbial degradation by a combination of in situ and laboratory measurements. Replicate streams were dosed continuously at pentachlorophenol concentrations of 0, 48, and 144 micrograms/L, respectively, for an 88-d period during the summer of 1983. Pentachlorophenol was degraded both aerobically and anaerobically. Aerobic degradation was more rapid than anaerobic degradation. Mineralization of pentachlorophenol was concommitant with pentachlorophenol disappearance under aerobic conditions, but lagged behind loss of the parent molecule under anaerobic conditions. Biodegradation in the streams, or in specific stream compartments such as the sediment or water column, was characterized by an adaptation period (3-5 weeks for the stream as a whole, and reproducible from the previous year), which was inversely dependent on the concentration of pentachlorophenol and microbial biomass. The adaptation in the streams could be attributed to the time necessary for selective enrichment of an initially low population of pentachlorophenol degraders on surface compartments. The extent of biodegradation in the streams (percent loss of initial concentration of pentachlorophenol) increased with increasing pentachlorophenol input, which was explicable by an increase in the pentachlorophenol degrader population with increasing pentachlorophenol concentration. The sediment zone most significant to overall pentachlorophenol biodegradation was the top 0.5- to 1-cm layer as shown by pentachlorophenol migration rates and depth profiles of degrader density within the sediment. Pentachlorophenol profiles in sediment cores taken during and after the adaptation period for degradation showed that diffusion of pentachlorophenol into the sediment was rate limiting to degradation in this compartment.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of varying discharge on the downstream movement of salmon fry, Oncorhynchus tshawytscha Walbaum

Some of the consequences of varying flows on the downstream migration of salmon fry were investigated in five replicate streams adjacent to the lower Waitaki River, New Zealand. Fluctuating discharge appeared to increase the number of fry moving downstream, provided that mean water velocities at peak flows exceeded 25 cms−1’and that some fry were migrating out of the streams anyway. Salmonids appear to have a lengthier flow–sensitive period than has been proposed in the literature. Research is required to determine whether recently emerged fry that leave parental spawning streams in New Zealand disperse immediately to the ocean or develop and grow for extended periods en route. It may sometimes be feasible and worthwhile to minimize stream flow variations to encourage fry to remain longer in fresh water.

The effect of grazing intensity on phosphorus spiralling in autotropic streams.

The effect of grazing on primary productivity and phosphorus cycling in autotrophic streams was studied using the snail Goniobasis clavaeformes. Snails were added to each of three replicate laboratory stream channels, receiving once-through flow of groundwater, in densities of 2.1, 3.0, and 4.2 g ash free dry mass (AFDM)/m2. A fourth channel received no snails and served as an ungrazed control.Presence of snail grazers resulted in a large reduction in aufwuchs biomass, primary productivity, and biotic phosphorus uptake; a modest reduction in fine particulate organic matter (FPOM); and an increase in the fraction of stream particulate organic matter (POM) exported as seston. Although primary production and aufwuchs biomass continued to decline with increasing snail density, phosphorus uptake increased. This increased phosphorus uptake is attributed to abiotic sorption to inorganic surfaces exposed as a result of efficient removal of aufwuchs at high snail densities. Although snail densities were chosen to bracket the density measured in a natural stream, the experimental densities may result in considerably higher grazing pressure on aufwuchs due to the absence of alternate food sources (e.g., coarse particulate organic matter) usually found in natural streams.Presence of snail grazers increased the spiralling length of phosphorus, primarily by reducing aufwuchs biomass and consequently reducing uptake of phosphorus from the water. Presence of snails also increased downstream transport velocity of phosphorus bound to organic particles. These results follow the patterns predicted in a previous theoretical analysis for mildly phosphorus-limited streams.