Micro-environmental characteristics of filamentous algal communities in flowing freshwaters

SUMMARY. 1. Filamentous algae in flowing freshwaters can represent a spatially and temporally distinct sub-habitat for epiphytic diatom communities. This sub-habitat is described in a low discharge, spring-fed stream with extensive filamentous green algal mats, and in a tuft of Cladophora glomerata (L.) Kützing from a large river.
2. Oxygen micro-electrodes, a thermistor current velocity probe, a standard pH probe and water chemistry were employed to assess spatial heterogeneity. Temporal patterns of epiphyte colonization were evaluated on filamentous artificial substrates.
3. There were steep spatial gradients in the low discharge stream. At mid-day, O₂ ranged from 0–1.5 times air-saturated O₂ concentrations, pH varied from 7.25–8.0, and current velocity spanned 0–0.5 m s⁻¹. Areas near the surface of algal mats had high O₂, pH and current velocity. These patterns were correlated with epiphyte community structure.
4. In the interior of C. glomerata tufts O₂ concentration was raised and current velocity depressed compared to the surrounding water, even when external current velocity was as high as 0.4 m s⁻¹.
5. After thirty-five days of colonization of artificial substrate in the low discharge environment, epiphyte communities were similar to those on filamentous atgae. Epiphyte diversity on artificial substrates subsequently decreased compared to natural substrates as did the similarity between the types on substrates, suggesting that microscale renewal of epiphyte habitat (growth of filamentous algae) maintains high epiphytic diversity.     

Downstream increase in the abundance and heterotrophic activity of suspended bacteria in an intermittent calcareous headstream

SUMMARY. 1. Concentration of total bacteria, and heterotrophic activity (as turnover rate for glucose assimilation), in the water of an intermittent spring-fed calcareous headstream, increased with distance from the source to 1600 m.
2. This increase was gradual rather than stepwise and might be due to release of bacteria from submerged vegetation and the stream bed, and to input of terrestrial bacteria with groundwater.
3. The increment per unit length of stream was greatest in summer when aquatic vegetation was most abundant and discharge was low.
4. When the stream was partly dry, isolated peaks of suspended bacteria occurred and there was no regular downstream increase.
5. A lesser spring which upwelled into a natural basin consistently contained more suspended bacteria than the principal source, which was an artificial culvert.     

Initial colonization of periphyton on natural and artificial apices of Myriophyllum heterophyllum Michx

SUMMARY. 1. The initial colonization of periphyton on natural and artificial apices of Myriophyllum heterophyllum Michx was compared at three depths in the littoral zone of Lake Winnipesaukee, a soft-water New England lake. After a 1 week incubation period, the apices were sampled and the periphyton was removed and counted as numbers of periphyton organisms per centimetre of stem.
2. Initial colonization on both substrates was characterized by diatoms, particularly small single-celled species, throughout the spring and summer. Blue-green and green algae occurred in low numbers on both substrates during mid-summer, usually forming a greater percentage of the population of the natural apices. Blooms of the green alga Zygnema sp. dominated both substrates in late August.
3. Community composition generally did not differ significantly by depth or substrate on the natural and artificial apices: however, total abundance was significantly greater on the natural apices. M. heterophyllum appeared to serve as a neutral substrate in terms of community composition but had a positive effect on the total numbers of algae.     

Field experiments on the mobility of benthic invertebrates in a southern English stream

1. In each of twenty-six week-long experiments, the colonization by macroinvertebrates of boxes of natural sediment in a stony stream was measured. The experiments took place between February and November 1992 and environmental conditions prevailing during the weeks (particularly discharge and temperature) differed widely.
2. Colonization rate also varied widely between the weekly experiments and was sensitive to discharge, temperature and background benthic density, depending on the taxa considered.
3. A 'mobility index' measured colonization rate independently of background benthic density. This index was most strongly and positively correlated with discharge for the abundant stonefly Leuctra nigra, the net-spinning caddis Plectrocnemia conspersa and the Chironomidae, perhaps indicating that their mobility is physically driven by the influence of flow on drift.
4. Mobility in a second stonefly ( Nemurella pictetii ) was greatest in summer, when flows were low but temperature was high. Peak mobility in this species occurred during an ochreous bloom on the stream bed. It is likely the mobility of N. pictetii is more active than the other taxa.
5. There were thus differences among taxa in their mobility at baseflow and in their susceptibility to flow fluctuations. The population consequences of differences in mobility among taxa are discussed.     

Rapid biological assessment charts the recovery of stream macroinvertebrate assemblages after sewage discharges cease

Rapid biological assessment (RBA) methods involving non-quantitative sampling of aquatic macroinvertebrates, sub-sampling of only a proportion of the organisms collected, and identification only to genus-level were used to assess responses over up to 7 years following the cessation of discharges from five sewage treatment plants into small streams in the Blue Mountains, Australia, and an increased volume of discharge into another stream. Multivariate analysis (ordination and analysis of similarities) did not always show an obvious recovery after discharge cessation: assemblages sampled upstream and downstream of discharge points were not always clearly closer in ordination space after cessation than before and statistically significant differences between upstream and downstream assemblages generally remained after cessation, apparently because of natural medium-scale spatial variability. However, the tolerance-based SIGNAL-SG biotic index demonstrated some recovery in all cases of discharge cessation, and a lag in recovery of about a year. A lesser recovery in the more urbanised catchments was attributed to persistent pollution from sources other than treatment plant discharges. The biotic index also revealed subtle biological change that was not predictable from monitoring data on nutrient concentrations. The SIGNAL-SG biotic index derived from RBA sampling provides an easily communicated measure of the effectiveness of investment in abatement of sewage impacts on stream macroinvertebrates in the Blue Mountains.     

Temporal changes in replicated experimental stream fish assemblages: predictable or not?

Summary 1. Natural aquatic communities or habitats cannot be fully replicated in the wild, so little is known about how initially identical communities might change over time, or the extent to which observed changes in community structure are caused by internal factors (such as interspecific interactions or traits of individual species) versus factors external to the local community (such as abiotic disturbances or invasions of new species).
2. We quantified changes in seven initially identical fish assemblages, in habitats that were as similar as possible, in seminatural artificial streams in a 388-day trial (May 1998 to May 1999), and compared the change to that in fish assemblages in small pools of a natural stream during a year. The experimental design excluded floods, droughts, immigration or emigration. The experimental fish communities diverged significantly in composition and exhibited dissimilar trajectories in multivariate species space. Divergence among the assemblages increased from May through August, but not thereafter.
3. Differences among the experimental assemblages were influenced by differences that developed during the year in algae cover and in potential predation (due to differential survival of sunfish among units).
4. In the natural stream, fish assemblages in small pools changed more than those in the experimental units, suggesting that in natural assemblages external factors exacerbated temporal variation.
5. Our finding that initially identical assemblages, isolated from most external factors, would diverge in the structure of fish assemblages over time suggests a lack of strong internal, deterministic controls in the assemblages, and that idiosyncratic or stochastic components (chance encounters among species; vagaries in changes in the local habitat) even within habitat patches can play an important role in assemblage structure in natural systems.     

Longitude variability of macrobenthos in the streams of Central European Russia

The changes in macrobenthos community depended on changes in stream discharge (from 0.001 m3/sec to 100 m3/sec) were studied on the basis of data from 254 stations of 180 streams located in the centre of European part of Russia. While discharge of stream increases community composition changes considerably. Species diversity increases from 12 to 47 species per station with the increase in stream size. Moreover, the diversity of almost all groups, discerned according habitat or trophic position and main taxonomic groups (with the exception of Plecoptera and Diptera) increases with the increase in stream discharge. The diversity of lithorheophilic species and species inhabiting soft substrates is higher in small streams, whereas phitophilic species are more diverse in large streams. With the increase in stream size the percent of algophagous and filter feeders increases, percent of carnivorous remains the same and the percent of detritophages decreases. The relative role of invertebrates macrotaxons change with the stream size: in the smallest streams the diversity is the highest among Diptera, Trichoptera and Plecoptera, in medium-size streams--among Trichoptera, Ephemeroptera and Diptera, in large streams--in Ephemeroptera, Gastropoda and Trichoptera. In some groups some species replace other (close-related) in parallel with change in stream discharge however in general this tendency is weak. The index of saprobic conditions increases with the increase in stream size from 1.6-1.7 to 2.3-2.4. In small streams the saprobic conditions are very different whereas large streams have tendency to be at beta-mesosaprobic level. Cluster analysis reveal four size classes of streams. Peculiarities of habitat and macrobenthos fauna of these classes are described.     

Leaf-pack dynamics in a southern African mountain stream

SUMMARY 1. The occurrence, composition and invertebrate fauna of naturally-occurring leaf packs were studied over 24 months in Langrivier, a second-order mountain stream in the south-western Cape, South Africa. Langrivier is shallow and fast-flowing and stores very low levels of allochthonous detritus, although natural leaf packs form an obvious part of the energy base in the stream throughout the year. 2. The occurrence and size of the packs were influenced mainly by stream discharge and by the timing and character of leaf fall from riparian trees. Packs were smallest (minimum dry mass 17 g, minimum volume 1.7–10^?5 m³) in winter when discharge was high, and largest (maximum dry mass 191 g, maximum volume 4.2–10^?3 m³) in spring when discharge decreased and leaf fall from the evergreen riparian trees began. Through the year the packs covered a mean 0.41 % of the stream bed and had a mean abundance of 0.46 packs m^?2 of stream bed. They were ephemeral, lasting on average <1.7 months and yet accounted for 29% of the stored detritus in the system. Wood was the dominant component of packs, and leaves at ali stages of decomposition were present throughout the year. 3. The ratio of numbers of invertebrates in packs: numbers of individuals in the benthos was very low (0.002–0.030), presumably because of the rarity and small size of the packs. Nevertheless, the density of invertebrates per unit area covered by leaf packs was consistently much higher than the density in an equivalent area of the benthos, except during peak leaf fall (October to December). 4. Experiments were undertaken with artificial leaf packs in order to determine the extent to which these simulated natural packs. Although both natural and artificial leaf packs contained a high proportion of Plecoptera (46% and 29% respectively), the natural packs contained high numbers of simuliid larvae (33% of total), whereas artificial packs had a high percentage of chironomid larvae (62%), Several other taxa regularly occurred in both types of pack but in very low numbers. In addition,     

Physico-chemistry and aquatic insects of a glacier-fed and a spring-fed alpine stream

1. Physico-chemical conditions and benthic macroinvertebrates were studied in two adjacent alpine streams in the Tyrolean Alps, Austria, for 2 years, and aquatic insect emergence was recorded for 1 year.
2. In the spring-fed system, maximum discharge and increased concentrations of suspended solids, nitrate and particulate phosphorus occurred during snowmelt in June. In the glacier-fed stream, high discharge and strong diel fluctuations in flow and concentrations of suspended solids created a harsh and unstable environment during summer. Glacial ablation, variation in groundwater inflow, and water inputs from tributaries draining calcareous rocks caused water chemistry to vary both seasonally and longitudinally in glacier-fed Rotmoosache.
3. A total of 126 aquatic or semi-aquatic invertebrate taxa were collected, 94 of which were found in the glacier-fed stream and 120 in the spring-fed stream. Chironomid abundance was 2–8 times and taxa richness 2–3 times lower in the glacier-fed stream than in the spring-fed stream, as was the number of chironomid taxa (72 versus 93 total).
4. These results broadly support the conceptual model by Milner & Petts (1994) concerning glacier-fed stream systems. However, single samples and seasonal means showed relatively high invertebrate abundance and richness, especially during winter, indicating a considerable degree of spatial and temporal variability.
5. We suggest that the seasonal shifts from harsh environmental conditions in summer to less severe conditions in autumn and a rather constant environment in winter are an important factor affecting larval development, life-history patterns and the maintenance of relatively high levels of diversity and productivity in glacier-fed streams.     

Use of Protozoan Communities to Predict Environmental Effects of Pollutants1

ABSTRACT. This study compared the response of protozoan communities colonizing artificial substrates to complex effluents in laboratory microecosystems and validated laboratory predictions using similar sampling methods in the field. Sampling stations were established on a small stream receiving heavy metal and sewage treatment plant effluents. Water from each station was used as a test medium to test the colonization of polyurethane foam artificial substrates in laboratory microecosystems. The heterotrophic index (HI), the ratio of total community biomass to chlorophyll biomass, was also measured. Field colonization trials and HI determinations were carried out at each sampling station. There was a strong negative relationship between the number of species colonizing artificial substrates and the total metal concentration of the water at each station; protozoan colonization was severely depressed at the highest metal concentrations (>400 μg/liter) and recovered at downstream stations where dilution had taken place. The HI differentiated stations receiving high heavy metal concentrations in the field from those recovering from heavy metal influences. Effect concentrations based on laboratory experiments predicted that the concentration of total heavy metal that would produce a 5% decrease in species number (EC5) was 18 μg/liter, approximately the background concentration found in the stream studied. These experiments demonstrated that laboratory microecosystems or microcosms can be used to predict effects in the field accurately.     

Field experiments on flow refugia in streams

1. Field experiments were carried out to determine whether animals move into areas of low shear stress during periods of peak flow and therefore avoid hydraulic disturbance.
2. Flow at the scale of 0.05 m² patches was reduced experimentally by creating artificial 'refugia'. Invertebrate colonization of cages with 1.1 mm mesh sides, which provided such potential refugia by reducing hydraulic forces within the cage, was compared with colonization of cages with coarser (15 mm) mesh which did not restrict the flow.
3. Colonization of these cages was tested over a series of weekly periods in two different streams. Nine trials were completed in a stream with abundant natural flow refugia (Broadstone Stream, SE England), and during three of these trials strong spates occurred. Six trials were completed in a stream with comparatively few natural flow refugia (Dargall Lane, SW Scotland), and peak flows were relatively less.
4. In Broadstone Stream, the relative colonization of refugium cages was greatest during periods of peak flow, suggesting animals had used these low-flow areas as refugia during spates. Use of the artificial refugia did not occur in Dargall Lane, at least at the flows achieved during the trials.
5. Our results are consistent with the hypothesis that stream invertebrates accumulate in refugia during high flow disturbances. Whether their distribution among patches is altered by active or passive means remains unclear.     

Why,when and how do fish populations decline,collapse and recover? The example of brown trout (Salmo trutta) in Rio Chaballos (northwestern Spain)

1. Around the year 2000, historically abundant populations of brown trout ( Salmo trutta ) and Atlantic salmon ( S. salar ) co-occurring in rivers flowing along the Cantabrian corridor of north-western Spain showed a dramatic decline to alarming levels. For one reason or another, fishing was not banned and fishing pressure continued to reduce the few survivors. Unexpectedly, the populations recovered 'naturally' in a very short time period to the extent that in 2004–06 numbers had attained population sizes comparable to those of the mid 1980s.
2. The population of brown trout in Rio Chaballos showed a boom-and-bust pattern concurrent with those observed across broader geographical scales. This study revisits a 22-year data set to explore the nature of the severe decline and rapid recovery of this population.
3. Recruitment was related to stream discharge in March that covers the emergence period and the earliest search stages for food. Coefficients of variation for discharge and recruitment increased over the years and were highly correlated with each other, demonstrating that increased temporal variability in recruitment is strongly linked to increased variability in stream discharge. In turn, recruitment appears to be the major determinant of year-class strength and hence, of population size.
4. A number of factors appeared to operate as resilience mechanisms, permitting the population to increase rapidly when environmental conditions are optimal. These include strong recruitment-discharge relationships, short life-span, small stocks of eggs or offspring required to fill the amount of space suitable for the youngest juveniles and a few females surviving to spawn for a second time.
5. Implications for fishery management and conservation are discussed in the context of the expectation that these populations will vary over the coming years within ranges similar to those in this study.     

Sexual dimorphism in Gammarus pulex: the effect of current flow on pre-copula pair formation

SUMMARY. 1. Male Gammarus pulex (L.) are typically twice as heavy as females in field caught pre-copula pairs and mating is positively size assortative. Earlier work had shown that relatively large males can swim in pre-copula at higher current speeds than males that are relatively small compared with their mates. We describe experiments on pair formation in the laboratory, in static water and in an artificial stream.
2. Pairs formed in the artificial stream had a significantly higher weight ratio than either those formed in static water or those caught in the field. In both experimental conditions, males in pairs were significantly larger than singles. In the stream, the weight ratio of pairs increased with formation sequence due to a significant decrease in the size of selected females.
3. It is concluded that these results are consistent with the hypothesis that the relatively large size of paired male G. pulex is a product of mechanical constraints rather than male–male competition.     

Influence of ultraviolet-B radiation on the drift response of stream invertebrates

1. Recent studies have shown that ultraviolet (UV) radiation (280–400 nm) has increased by ≈ 8% in temperate regions over the past decade, but little effort has been devoted to understanding the ecological effects on temperate ecosystems. This research examined the effects of artificial ultraviolet-B (UVB; 280–320 nm) radiation on the drift response of immature stream insects in laboratory microcosms.
2. Two experiments involved natural populations of stream invertebrates, collected from the Cache la Poudre River (September 1994) and the Arkansas River (October 1995) in Colorado. UVB lamps were turned on from 10.00 to 14.00 h each day, and drifting animals were collected on days 1, 3, 5 and 7 during the exposure period. Levels of artificial UVB used in these experiments were similar to levels that stream organisms experience during clear, mid-day conditions at Fort Collins, Colorado (longitude 105°30'; latitude 40°35').
3. Drift was significantly higher in microcosms exposed to UVB than in controls and was dominated by Baetis sp. (Ephemeroptera: Baetidae), Trichoptera (caddisflies) and Simulium sp. (Diptera: Simuliidae). The increased drift of some stream invertebrates in UVB-exposed streams may be a behavioural response and/or a result of injury.
4. Stream organisms may be particularly sensitive to predicted increases in UV radiation, because streams are generally shallow with clear water. As a result of this potential sensitivity, we recommend that research be directed to understanding the ecological effects of UV radiation on these habitats.     

Influence of ultraviolet-B radiation on the drift response of stream invertebrates

1. Recent studies have shown that ultraviolet (UV) radiation (280–400 nm) has increased by ≈ 8% in temperate regions over the past decade, but little effort has been devoted to understanding the ecological effects on temperate ecosystems. This research examined the effects of artificial ultraviolet-B (UVB; 280–320 nm) radiation on the drift response of immature stream insects in laboratory microcosms.
2. Two experiments involved natural populations of stream invertebrates, collected from the Cache la Poudre River (September 1994) and the Arkansas River (October 1995) in Colorado. UVB lamps were turned on from 10.00 to 14.00 h each day, and drifting animals were collected on days 1, 3, 5 and 7 during the exposure period. Levels of artificial UVB used in these experiments were similar to levels that stream organisms experience during clear, mid-day conditions at Fort Collins, Colorado (longitude 105°30'; latitude 40°35').
3. Drift was significantly higher in microcosms exposed to UVB than in controls and was dominated by Baetis sp. (Ephemeroptera: Baetidae), Trichoptera (caddisflies) and Simulium sp. (Diptera: Simuliidae). The increased drift of some stream invertebrates in UVB-exposed streams may be a behavioural response and/or a result of injury.
4. Stream organisms may be particularly sensitive to predicted increases in UV radiation, because streams are generally shallow with clear water. As a result of this potential sensitivity, we recommend that research be directed to understanding the ecological effects of UV radiation on these habitats.     

Factors affecting the microdistribution of Gammarus pulex (Amphipoda): an experimental study

SUMMARY. 1. The tnierodistribution of Gammarus species is size assortative: larger animals are associated with larger substrate particles. Using an artificial stream with scrubbed substrate we investigate the hypothesis that the assortative mechanism is stimulated by current avoidance rather than food searching.
2. In uniformly mixed substrate, G. pulex tend to move upstream, but in patchy substrate they are found in a predictable substrate grade. There is no discrimination between patches by different size classes of G. pulex in static water. The size assortative field pattern can only be reproduced under flow conditions in the laboratory. It occurs in the absence of food and irrespective of the sequence or location of substrate patches.
3. As density increases, G. pulex are displaced from the optimal patches but move into the open stream rather than into the cover of alternative patch types.
4. We discuss the significance of these results and suggest that some earlier models explaining mechanisms for microdistribution patterns tnay have been unnecessarily complex. Contrasts between natural and simulated stream situations and their experimental advantages are noted.     

Establishing and maintaining laboratory-based microcosms of riffle insect communities: their potential for multispecies toxicity tests

The purpose of this study was to determine which of the following artificial stream designs would be most logistically simple yet effective in maintaining riffle insects during a 30 d bioassay: 1) static and no current (S-NC); 2) flow-through and no current (FT-NC); 3) static with current (S-C); or 4) flow-through with current (FT-C). Flow-through and current, when provided, were 12 ml min^–1 and 30 cm sec^–1, respectively. Streams were covered by emergence traps, and daylight equivalent lights provided a natural photoperiod. The four stream designs were evaluated in triplicate based on changes in insect species-abundances after 30 d. Test organisms were transferred to the artificial streams in rock-filled containers previously colonized for 30 d in a third-order mountain stream riffle. Additional colonized substrates were sampled immediately to provide an estimate of initial densities placed in the artificial streams. Hess samples were taken directly from the source riffle to evaluate how well the artificial substrates reflected species-abundances on the natural substrate. Adults were collected from the artificial streams every 48–72 h to determine the percentage of initial densities that emerged. After 30 d (7 Aug–6 Sept, 1986), all organisms remaining in the streams were censused. Designs were evaluated using combined densities of adults and young.Relative to benthic samples taken directly from the source riffle, the artificial substrates selected for collector-filterers and against collector-gatherers. The FT-C and S-C stream designs maintained most taxa at or above initial densities, and even in the FT-NC and S-NC streams densities of some taxa were not significantly different (P 0.05) from initial densities. Emergent adults comprised a large proportion of mayfly and chironomid densities and must be monitored during bioassays with aquatic insects. These results indicate that microcosms of riffle insect communities can be maintained for at least 30 d with moderate current and minimal flow-through.     

The role of fungi in the diet of the amphipod Gammarus pulex (L.): an enzymatic study

SUMMARY. 1. Sets of ten Gammarus pulex fed on controlled diets of sterile alder leaves, or fungal mycelium, or alder leaves incubated for 10 days with an aquatic hyphomycete, were assayed for cellulase, β-1,3-glucanase an d chiitinase activity and compared with (a) animals taken directly from the stream, (b) animals starved for 2 days, and (c) enzyme activity in fungal mycelium.
2. Gut enzyme activity was compared on natural substrates of sterile leaves, mycelium and inoculated leaves as well as on model substrates.
3. G. pulex secretes an endogenous coupled cellulase system capable of degrading native cellulose in plant cell walls. It also secretes β-1,3-glucanase and chitinase capable of degrading fungal cell walls thus affording access for gut enzymes to cell contents.
4. Secretion of enzymes active on native cellulose is enhanced on a diet of leaves already partially degraded by fungal enzymes. Gut enzymes extract more reducing sugar from this substrate than from sterile leaves. Specific enzyme secretion is enhanced by the presence in the diet of exposed, accessible substrates. Fungal enzymes do not appear to contribute to the digestive processes of G. pulex.     

Effects of experimentally enhanced flows on fishes of a small Texas (U.S.A.) stream: assessing the impact of interbasin transfer

1. Completion of a large interbasin water transfer system in northern Texas (U.S.A.) provided the opportunity to test the effects of pre-planned, experimental increases (≈×30) in flow on the fish fauna of a small, low-gradient, natural stream that was included as part of the conveyance system. Water from Lake Texoma (Red River basin) was pumped via a 16-km pipeline to the headwaters of Sister Grove Creek (Trinity River basin), which then carried the donor water 50 km downstream to Lake Lavon.
2. Baseline (pre-transfer) data on the composition of fish assemblages at seven stations on the creek or at its confluence with the receiving reservoir were collected monthly for 3 years, and similar data were collected for 2 years during and after trial flows of Lake Texoma water to Sister Grove Creek. We also documented fish abundance at five creek stations immediately before and after three trial flow periods of 10–14 days each in summer and autumn.
3. Multivariate analysis of all routine monthly samples over the 5-year pre- and post-transfer period showed moderate changes in the fish fauna of the creek after initiation of the trial flows. Samples taken within a week before and after the artificial high flows showed little overall change in abundance of individual fish species, but at some stations the quantitative or qualitative change in composition of the local assemblage was substantial.
4. The trial flows lasted 2 weeks or less. Long-term effects of water transfer on the fish fauna of Sister Grove Creek can only be determined after the conveyance system goes into normal operation, with periods of artificial flow of longer duration.     

An application of the plaster dissolution method for quantifying water velocity in the shallow hyporheic zone of an Appalachian stream system

1. A method for quantifying interstitial water velocity based on the dissolution rate of plaster of Paris standards was developed as part of a study of vertical, longitudinal (1–4 order sites) and seasonal variation in the biotic and physical characteristics of the shallow hyporheic zone (0–30 cm) of a headwater stream system in West Virginia, U.S.A.
2. A calibration model was developed using a water velocity simulation tank to relate mass loss of plaster standards to water velocity and temperature. The model was then used to calculate water velocity through artificial substrata embedded in the shallow hyporheic zone of four stream reaches based on in situ mass loss of plaster standards.
3. Water velocity in the hyporheic zone increased with stream order, was highest in early spring and winter during high stream base flows, and decreased with depth into the substratum. There was a strong interaction between depth and season: during periods of high stream discharge, water velocity through the upper level of the shallow hyporheic zone (0–10 cm into the substrate) increased disproportionately more than velocity at greater depths. Mean interstitial velocity in March ranged from 0 cm s^–1 in the lowest level (20–30 cm) to 3.5 cm s^–1 at the upper level (0–10 cm) at the first‐order site, and from 2.5 cm s^–1 (20–30 cm) to 9.5 cm s^–1 (0–10 cm s^–1) at the fourth‐order site. Gradients in stream discharge and sediment permeability accounted for treatment effects.
4. Use of calibrated data improved the ability to resolve among‐season differences in interstitial water movement over the use of uncalibrated mass loss data. For some applications of the plaster standard method, empirical calibration may not be necessary.