Groundwater influence on alpine stream ecosystems

1. Spatial and temporal variability of relative snow‐melt, glacier‐melt and groundwater contributions to streams play important roles in shaping alpine freshwater ecosystems. Although meltwater (particularly glacier‐fed) streams have received much attention in recent years, the influence of groundwater on alpine freshwater ecosystems remains poorly understood. 2. This study tested the hypotheses that increased groundwater contributions to meltwater‐dominated alpine streams would yield increases in water temperature, channel stability, electrical conductivity and particulate organic matter (POM) and decreases in suspended sediment concentration (SSC). These more favourable habitat conditions were hypothesised to result in increased macroinvertebrate abundance and diversity. 3. Groundwater contributions, physicochemical habitat variables and benthic macroinvertebrates were sampled throughout the 2002 and 2003 summer‐melt seasons in three streams in the French Pyrénées. 4. Increased groundwater contributions were significantly correlated with higher discharge, water temperature, electrical conductivity, POM and channel stability, but lower SSC. 5. Macroinvertebrate total abundance, taxonomic richness, number of Ephemeroptera, Plecoptera and Trichoptera genera, and per cent Plecoptera all increased significantly with greater groundwater contributions to streamflow. However, beta diversity and Trichoptera relative abundance decreased. 6. Abundance of most macroinvertebrate taxa was highest under groundwater‐dominated conditions but a gradient of optimum groundwater preferences was evident across all taxa. Some taxa were found only where groundwater contributions were low (i.e. in predominantly meltwater‐fed streams). 7. This study provides evidence that water source, physicochemical habitat and stream biota are strongly linked. Therefore, an interdisciplinary approach is necessary for future studies aiming to develop conservation strategies or predict the response of alpine river ecosystems to global climate change.     

Community structure of benthic invertebrates in interior Alaskan (USA) streams and rivers

Taxonomic composition of benthic invertebrates in interior Alaskan streams and rivers is summarized from published and unpublished data. Diptera dominate the Alaskan stream fauna and constitute a larger proportion of the benthos in Alaskan streams than in streams of temperate North America. Plecoptera and Ephemeroptera are the next most abundant in Alaskan streams with Trichoptera generally very scarce. Several orders that occur regularly in streams of temperate North America are absent (or in very low abundance) in interior Alaskan streams: Hemiptera, Odonata, Megaloptera, Coleoptera. Net-spinning caddisflies, burrowing mayflies, and several families of stoneflies (Pteronarcyidae, Peltoperlidae and Perlidae) are conspicuous by their absence or extreme scarcity. Taxonomic composition varies significantly among hydrologic regions (major watersheds) and among stream types (springs, headwater streams, small rivers, and large rivers). Only two taxa (Chironomidae and Nemouridae) significantly increase in proportional contribution from south to north while many taxa decrease.     

Relationship between benthic insects (Ephemeroptera, Plecoptera, Coleoptera, Trichoptera) and temperature in small and medium-sized streams in Germany: A multivariate study

Benthic insect communities (Ephemeroptera, Plecoptera, Coleoptera, Trichoptera) were studied together with water temperature and environmental parameters in streams between June 2000 and June 2001. The sampling area consisted of 20 sites in small and medium-sized streams located in the lower mountainous area of Central Europe. Temperature was recorded nearly continuously and several physicochemical and environmental variables were assessed. Macroinvertebrates were sampled both in spring and summer. Data-sets of species abundance and occurrence were analysed using multivariate techniques and were correlated to the thermal and environmental conditions of the streams. The temperature preferences of the species were compared to published data-sets on their autecological characteristics. Up to 29% of the variability in the Ephemeroptera, Plecoptera, Trichoptera and Coleoptera community was explained by summer temperature variation in the data-sets for both small and medium-sized streams. A smaller, but significant part of the variability in species distribution was explained by conductivity, substratum type, and the percent coverage of local riparian forest. Compared to small streams, temperature was less important for the macroinvertebrate composition in medium-sized streams. This result is likely due to the more tolerant, eurythermic species composition in larger streams. A total of 33 Ephemeroptera, Plecoptera, Coleoptera and Trichoptera taxa were positively correlated and 28 taxa were negatively correlated to summer temperature patterns. The temperature preferences of taxa considered in this study were related to species traits, such as egg dormancies and life cycle plasticity.     

Benthic macroinvertebrate communities of intermittent streams in the middle reaches of the Guadiana Basin (Portugal)

The Guadiana River has an irregular hydrological regime, with severe droughts and floods, but little is known about how aquatic fauna respond to these natural events. Macroinvertebrate data and environmental information were collected at seven sites from three tributaries in the middle reaches of the Guadiana River, approximately every 3 months from April 1995 to April 1997. Despite considerable annual variation in discharge (related to duration of flood and drought periods), the number of macroinvertebrates found was consistently high. Diptera represented the major proportion of the benthic fauna (73.2%) followed by Ephemeroptera (10.3%), Coleoptera (4.1%) and Trichoptera (3.1%). Canonical correspondence analysis (CCA) was used to evaluate the relationships between taxa density and habitat variables. Generally, Plecoptera and Ephemeroptera were found in the upstream sampling sites. Wider and deeper sites were associated with the presence of Diptera and were least diverse. High values for both the Shannon-Wiener diversity index and the average score per taxon were usually found at upstream sites where Ephemeroptera and Plecoptera predominated. The data suggest that macroinvertebrates have a great capacity to recover rapidly from severe drought periods, both in terms of taxonomic diversity and number of individuals.     

Louisiana waterthrushes (Seiurus motacilla) and habitat assessments as cost-effective indicators of instream biotic integrity

1. Benthic stream animals, in particular macroinvertebrates, are good indicators of water quality, but sampling can be laborious to obtain accurate indices of biotic integrity. Thus, tools for bioassessment that include measurements other than macroinvertebrates would be valuable additions to volunteer monitoring protocols. 2. We evaluated the usefulness of a stream‐dependent songbird, the Louisiana waterthrush (waterthrush, Seiurus motacilla) and the Environmental Protection Agency Visual Habitat Assessment (EPA VHA) as indicators of the macrobenthos community in headwater streams of the Georgia Piedmont, U.S.A. We sampled macrobenthos, surveyed waterthrushes and measured habitat characteristics along 39 headwater reaches across 17 catchments ranging from forested to heavily urbanised or grazed by cattle. 3. Of the indicators considered, waterthrush occupancy was best for predicting relative abundances of macrobenthic taxa, while the EPA VHA was best for predicting Ephemeroptera–Plecoptera–Trichoptera (EPT) richness. Individual components of EPA VHA scores were much less useful as indicators of EPT richness and % EPT when compared with the total score. Waterthrushes were found along streams with higher % EPT, a lower Family Biotic Index (FBI) values and greater macrobenthos biomass. 4. While macroinvertebrates remain one of the most direct indicators of stream water quality, stream bird surveys and reach‐scale habitat assessments can serve as cost‐effective indicators of benthic macroinvertebrate communities. Using stream‐dependent birds as an early warning signal for degradation of stream biotic integrity could improve the efficacy of catchment monitoring programmes in detecting and identifying perturbations within the catchment.     

The invertebrate fauna of the streams in Øvre Heimdalen

The lotic communities in Øvre Heimdalen were completely dominated by insects. The species distribution of stoneflies (Plecoptera), mayflies (Ephemeroptera) and caddisflies (Trichoptera) is given together with autecological notes on the Plecoptera and certain other major species. The species distribution of these groups, especially the Plecoptera, was clearly related to the deciduous vegetation along the streams. There was a reduction in species parallel to a reduction in Salix vegetation.
The main inlet stream to the lake, Øvre Heimdalsvatn, the outlet and the outlet stream had different faunal compositions. The inlet fauna consisted to a large extent of winter growing species, mainly detritus feeders, while the outlet and outlet stream had a fauna dominated by summer growing species, several of which were filter feeders.     

Distribution of the macrobenthos fauna in the Ola River basin,northern coast of the Sea of Okhotsk

The taxonomic composition of the macrobenthos fauna and its distribution in the main stream and tributaries of the mid-size salmon Ola River, the northern coast of the Sea of Okhotsk, were investigated for the first time. In the Ola River basin, 253 taxa of benthic invertebrates belonging to 3 phyla (Plathelminthes, Annelida, and Arthropoda) and 5 classes (Turbellaria, Clitellata, Crustacea, Arachnida, and Insecta) were revealed. Mayflies (Ephemeroptera), stoneflies (Plecoptera), caddisflies (Trichoptera), and midges (Chironomidae, Diptera) showed the highest species richness and dominated the benthic communities. Chironomidae comprised most of the fauna: 140 species and species groups, or more than 55% of the total diversity. The shares of identified species of mayflies, stoneflies, and caddisflies were subequal. Analysis of hydromorphological characteristics and the composition of aquatic insect families showed that all the areas surveyed in the Ola River basin were rhithral while the macrobenthos fauna represented there belonged to rhithron. The classification obtained by cluster analysis showed spatial heterogeneity in the distribution of the benthic fauna along the Ola River, related to changes in water temperature, slope, and altitude. The heterogeneous fauna distribution and the corresponding change in stable hydromorphological features indicated the existence of the typical epi-, meta-, and hyporhithral subzones whose boundaries were difficult to distinguish. However, the rhithral subzones selected were characterized by the habitat selectivity of certain taxa and by peculiar species richness values, thus emphasizing their individuality.     

Vulnerability of alpine stream biodiversity to shrinking glaciers and snowpacks

Climate change poses a considerable threat to the biodiversity of high latitude and altitude ecosystems, with alpine regions across the world already showing responses to warming. However, despite probable hydrological change as alpine glaciers and snowpacks shrink, links between alpine stream biota and reduced meltwater input are virtually unknown. Using data from the French Pyrénées, we demonstrate that taxonomic richness and total abundance of stream macroinvertebrates increase significantly as meltwater (snow melt and glacier melt) contributions to river flow decrease. Macroinvertebrate species showed a gradation of optimum meltwater conditions at which they persist. For example: Habroleptoides berthelemyi (Ephemeroptera), Perla grandis (Plecoptera) and Rhithrogena spp. (Ephemeroptera) increased in abundance when meltwater contributions to streamflow decrease, whereas in contrast, Rhyacophila angelieri (Trichoptera) and Diamesa latitarsis spp. (Diptera) decreased in abundance. Changes in alpine stream macroinvertebrate community composition as meltwater contributions decline were associated with lower suspended sediment concentration, and higher water temperature, electrical conductivity and pH. Our results suggest α diversity (at a site) of streams presently fed by meltwaters will increase with future meltwater reductions. However, β diversity (between‐sites) will be reduced as snow melt and glacier melt decrease because the habitat heterogeneity associated with spatiotemporal variability of water source contributions will become lower as meltwater contributions decline. Extinction of some endemic alpine aquatic species (such as the Pyrenean caddis fly R. angelieri) is predicted with reduced meltwater inputs, leading to decreases in γ diversity (region). Our identification of significant links between meltwater production and stream macroinvertebrate biodiversity has wider implications for the conservation of alpine river ecosystems under scenarios of climate change induced glacier and snowpack loss.     

Colonization and ecological development of new streams in Glacier Bay National Park, Alaska

SUMMARY 1. Colonization and ecological development of postglacial freshwater communities was investigated in Glacier Bay National Park, south-eastern Alaska, following the rapid recession of a Neo-glacial ice sheet within the last 250 years.
2. Environmental variables shown to be most significant in stream development were temperature, flow regime and sedimentation.
3. The Chironomidae (Diptera) were the pioneer invertebrate colonizers of newly emergent streams arising as meltwater from receding ice sheets and displayed a distinct pattern of succession with stream maturity.
4. Ephemeroptera and Plecoptera colonized warmer clearwater streams, but Trichoptera had a minimal role in invertebrate community development.
5. Establishment and production of salmonid fish populations in the new streams related principally to stream flow and sediment characteristics.
6. Future pathways along which the streams may develop is probably dependent on the degree of large organic debris input.
7. Stream development, structure and function are summarized including reference to theories of ecosystem development, ecological succession and community stability.     

Scale-dependence of the correlation between human population and the species richness of stream macro-invertebrates

Recent biogeographical studies have shown positive correlations between plant/vertebrate species richness and human population presence. The same pattern has been reported for Ephemeroptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies) (EPT) amongst European countries. This is surprising as EPT are bio-indicators of stream pollution and most local studies report higher species richness of these macro-invertebrates where human influences on water quality are lower. Using a newly collated taxonomic dataset, we studied whether the species richness of EPT is related to human population size at finer resolutions (Italy's regions, provinces and 10×10 km² UTM cells) controlling for sampling effort, variations in area and for spatial autocorrelation. At all study grains, observed EPT species richness was strongly correlated to the number of records available for the same taxon. At the regional level, the observed number of Ephemeroptera and Plecoptera species significantly increased with increasing human population size. At the provincial level, observed species richness decreased significantly with increasing human population size for Ephemeroptera and did not vary significantly for Plecoptera and Trichoptera. At the finest grain scale, there were significant negative correlations of observed Ephemeroptera and Trichoptera species richness with human population size, although the proportion of variance explained was very low. These results were broadly confirmed when analyzing the estimated number of species using the formula of Chao2. Our analysis confirms the scale-dependence of the human population–biodiversity correlation. Over broad scales more populated regions tend to have more species than less populated ones. Restricting the study grain, the positive EPT species–people relationship disappears and turns into a negative one. Our findings suggest a challenge also for the conservation of regional EPT diversity.     

A comparison of benthic macroinvertebrate assemblages among different types of alpine streams

1. Benthic macroinvertebrate assemblages were compared among a diverse array of first‐order alpine tundra streams of the Swiss Alps. 2. A principal components analysis separated sites into three main groups: rhithral streams, rhithral lake outlets, and kryal sites including outlets and streams. Rhithral streams contained the most diverse and taxon rich assemblages, being colonised by both non‐insect taxa and Ephemeroptera, Plecoptera, Trichoptera and Diptera. 3. Rhithral lake outlets supported high densities of non‐insect taxa such as Oligochaeta, Nemathelminthes and crustaceans. Despite low taxon richness, kryal sites had high Ephemeroptera and Plecoptera abundances. Chironomidae were most common at all sites. 4. Collector‐gatherers were dominant at all sites, whereas filter‐feeders were rare. Scrapers and shredders were more common in streams than lake outlets. 5. Water temperature and algal standing crops were higher at rhithral lake outlets than rhithral streams, perhaps providing more favourable habitat for non‐insect taxa. Glacial runoff was the dominant factor influencing macroinvertebrate assemblages of kryal streams and kryal lake outlets. Alpine lakes influenced the environmental conditions of their outlets and, consequently, their macroinvertebrate assemblages unless being constrained by a glacial influence.     

Climatic and Catchment-Scale Predictors of Chinese Stream Insect Richness Differ between Taxonomic Groups

Little work has been done on large-scale patterns of stream insect richness in China. We explored the influence of climatic and catchment-scale factors on stream insect (Ephemeroptera, Plecoptera, Trichoptera; EPT) richness across mid-latitude China. We assessed the predictive ability of climatic, catchment land cover and physical structure variables on genus richness of EPT, both individually and combined, in 80 mid-latitude Chinese streams, spanning a 3899-m altitudinal gradient. We performed analyses using boosted regression trees and explored the nature of their influence on richness patterns. The relative importance of climate, land cover, and physical factors on stream insect richness varied considerably between the three orders, and while important for Ephemeroptera and Plecoptera, latitude did not improve model fit for any of the groups. EPT richness was linked with areas comprising high forest cover, elevation and slope, large catchments and low temperatures. Ephemeroptera favoured areas with high forest cover, medium-to-large catchment sizes, high temperature seasonality, and low potential evapotranspiration. Plecoptera richness was linked with low temperature seasonality and annual mean, and high slope, elevation and warm-season rainfall. Finally, Trichoptera favoured high elevation areas, with high forest cover, and low mean annual temperature, seasonality and aridity. Our findings highlight the variable role that catchment land cover, physical properties and climatic influences have on stream insect richness. This is one of the first studies of its kind in Chinese streams, thus we set the scene for more in-depth assessments of stream insect richness across broader spatial scales in China, but stress the importance of improving data availability and consistency through time.     

Invertebrate fauna of ephemeral streams on Hauturu-o-Toi/Little Barrier Island in northern New Zealand

ABSTRACT

The invertebrate fauna of five ephemeral forest streams on Hauturu-o-Toi/Little Barrier Island in northern New Zealand was assessed in January 2014. Low summer flows restricted benthic sampling largely to pools that would, during periods of ‘normal’ flow, be main-channel riffle/run habitat. Additionally, adult stages of aquatic insects were sampled by light trapping. Fifty-three aquatic species/morphospecies were recorded during the study, including 25 new records, bringing total island species richness to 65. The fauna was dominated by Ephemeroptera and Trichoptera; species richness of Plecoptera and Diptera was low, and only single species of Mollusca and Crustacea were recorded. Species found were either common with broad New Zealand distributions, or species restricted to the North Island. No species was endemic to the island. Faunal comparisons with adjacent mainland streams indicated the island had similar assemblages of core taxa, but generally lower species richness, likely resulting from physiographic differences found there.     

The macrobenthos of the pristine stream, Skiftesåa, Høylandet, Norway

The species composition of aquatic insects in theboreal stream, Skiftesåa, was investigated usingemergence traps, Malaise traps and kick samples. Atleast 13 Ephemeroptera, 16 Plecoptera, 25 Trichopteraand 120 Chironomidae species were recorded. This faunais representative for non-polluted, northern streams.The production of macrobenthos was estimated to beonly about 1 g dry weight per year and m²,possibly due to the fluctuating flow of water.     

Aquatic insect faunas and communities of a mountain stream in Sapa Highland,northern Vietnam

Aquatic insect communities were investigated from the Muonghoa Stream in the Sapa Highland (highest peak 3,143 m), a subtropical mountain stream in northern Vietnam. Field investigations for quantitative (Surber net 50 cm × 50 cm, mesh size 0.2 mm, riffle and pool/run) and qualitative (hand net, mesh size 1 mm) sampling were conducted at nine sites along the watercourse between 27 November and 2 December 2005. As a result, a total of 216 species (the majority of them undescribed) belonging to 139 genera, 61 families, and nine orders were recognized: 53 Ephemeroptera species (24.5%), nine Odonata species (4.2%), 15 Plecoptera species (6.9%), seven Hemiptera species (3.2%), 35 Coleoptera species (16.2%), one Megaloptera species (0.5%), 29 Diptera species (13.4%), 66 Trichoptera species (30.6%), and one Lepidoptera species (0.5%). Trichoptera, Ephemeroptera, and Coleoptera represented the major aquatic insect groups with regard to taxonomic and individual richness, whereas Hemiptera and Odonata were relatively less diverse and abundant than in studies of other tropical Southeast Asian streams. The dominance, richness, and diversity indices (H′) fell within the following ranges [mean ± standard deviation (SD)]: 0.18–0.76 (0.42 ± 0.19), 4.13–9.19 (7.06 ± 1.45), and 1.61–3.22 (2.67 ± 0.55), respectively. Riffle habitats generally yielded numbers of aquatic insect species and individuals approximately twice that sampled in pool/run habitats. Shredders were relatively larger in proportion within the headwater reach, whereas scrapers and collector-gatherers were more abundant in the middle and lower stream reaches. This functional feeding group composition is characteristic of temperate streams in East Asia. The results of detrended correspondence analysis and Bray–Curtis cluster analysis indicated that aquatic insect compositions at the sampling sites were very reflective of the reach characteristics, which evidence gradual changes with altitude and stream order along the stream watercourse. This is the first comprehensive investigation of aquatic insects in highland Southeast Asian regions.     

Does freshwater macroinvertebrate diversity along a pH‐gradient reflect adaptation to low pH?

1. The impacts of anthropogenic surface water acidification are much better known than those of natural acidity. Recent studies have indicated biodiversity is not degraded and species composition unaltered in naturally acidic compared to circumneutral watercourses.
2. Here, we use a geographically extensive dataset comprising sites in more than 200 Swedish streams to test whether the lack of effects on macroinvertebrate species diversity is due to exaptation and adaptation to natural acidity.
3. To this end, we modelled pH associated with spring flood episodes, which inflict the most challenging hydrochemical conditions to the biota. We compared taxonomic richness and species composition along the modelled pH gradient in northern Sweden, where acidity is largely natural, with southern Sweden, a region influenced by significant anthropogenic acidification.
4. We found Plecoptera richness did not respond to varying pH either in northern or southern Sweden. Ephemeroptera richness was sensitive to pH in both regions, while that of Trichoptera increased with increasing pH in southern Sweden, but decreased in the north. The taxonomic composition of Plecoptera changed along the pH gradient in both regions, whereas that of Ephemeroptera and Trichoptera changed more strongly with pH in southern Sweden.
5. Our results support the hypothesis that stream invertebrates are able to tolerate low pH through exaptation or adaptation, but that this capability varies among taxonomic groups.     

An enigmatic heteronemertean from the Gulf of Mexico

The effects of acid (HNO3) on drift and survival of benthic invertebrate communities were assessed in stream microcosms over a 7-day exposure period. Communities were obtained from the Cache la Poudre River, Colorado, using artificial substrates colonized in the stream for 30 days and then transferred to stream microcosms. Streams receiving the highest acid concentration (pH 4.0) contained significantly fewer individuals ( F = 378.42, p < 0.0001) and taxa ( F = 7.8, p = 0.0123) at the end of the experiment compared to the other two treatments (pH 5.5, 6.5) and the control (pH 7.4). Reduced macroinvertebrate abundance resulted primarily from reduced abundance of mayflies (Ephemeroptera) which were particularly sensitive. Comparisons of Plecoptera, Trichoptera, and Diptera abundances showed no statistically significant differences among treatments. Analysis of invertebrate drift samples, collected after 2, 6, 18, and 42 h exposure, revealed that percent drift in the most acidic streams was nine times that of control streams. Ephemeroptera was the only aquatic insect order to exhibit a significant drift response, and timing and magnitude of responses varied among mayfly taxa. Differences in sensitivity to acid among aquatic insect orders observed in our experimental streams were similar to those reported from field studies in other regions. Effects of acid on drift and survival of benthic invertebrate communities were also similar to effects of heavy metals, one of the primary water quality concerns in the Rocky Mountain region. These results suggest a general pattern of responses to chemical stressors in benthic communities from Rocky Mountain streams. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effects of geothermal water inflow on longitudinal changes in benthic macroinvertebrate community composition of a temperate stream

Studies of macroinvertebrate communities in thermal streams are highly geographically localized and mostly faunistical, making the efforts to understand in situ water thermal regime effects on those biocoenoses barely achievable. We examined the effects of geothermal water inflow on benthic macroinvertebrate community composition in a temperate stream. Environmental data analysis has shown that water temperature is a major factor determining the faunistical composition, especially downstream of the geothermal water inflow situated some 20 m upstream of locality V3. The increase in mean annual water temperature from 11.5±4.1 °C at locality V2 to 22.0±5.0 °C at locality V3 induced an enormous shift in community composition from a diverse one, composed mainly of Gammaridae, Simuliidae, Chironomidae, Trichoptera and Ephemeroptera, and to a lesser extent of Plecoptera, Coleoptera, other Diptera, Hirudinea, Odonata, Mollusca and Oligochaeta, to a uniform one strongly dominated by Chironomidae, Mollusca and Oligochaeta, comprising 98.9±0.5% of collected individuals. While the disappearance of Plecoptera and Ephemeroptera and the increase in representation of Mollusca and Oligochaeta at locality V3 might be solely explained by water temperature increase, in the case of Chironomidae the increase in water discharge and relatively high annual water temperature variation at locality V3 had additional positive effects. However, the latter factor induced disappearance of Gammaridae at locality V3. In addition to the increase in water temperature, increase of water velocity significantly determined the longitudinal dynamics of Coleoptera.     

The macro-invertebrate fauna of a small Andean stream

SUMMARY. The benthic fauna of a small headwater stream in the Amazon drainage in Ecuador was studied from August 1976 to July 1977. The sampling station was at an altitude of 3300 m in a typical paramo habitat of constant and cool temperatures. The fauna is dominated numerically by Hydracarina, Insecta, Copepoda and Oligochaeta, The major insect groups are Ephemeroptera, Plecoptera, Trichoptera, Elmidae (Coleoptera) and Chironomidae (Diptera). Benthos densities followed a bimodal pattern of rapid decreases and intervening gradual recoveries; similar patterns occur in most taxa, but are more pronounced in smaller animals such as Copepoda and Hydracarina. An analysis of the size-frequency distribution of three species of mayfly, two of stonefly and six of caddisfly suggest non-seasonal life-cycles except for Anacroneuria sp. Spates are thought to be the major factor regulating benthic densities in such non-seasonal environments.     

Variability in stream macroinvertebrates at multiple spatial scales

1. We intensively sampled 16 western Oregon streams to characterize: (1) the variability in macroinvertebrate assemblages at seven spatial scales; and (2) the change in taxon richness with increasing sampling effort. An analysis of variance (ANOVA) model calculated spatial variance components for taxon richness, total density, percent individuals of Ephemeroptera, Plecoptera and Trichoptera (EPT), percent dominance and Shannon diversity.
2. At the landscape level, ecoregion and among‐streams components dominated variance for most metrics, accounting for 43–72% of total variance. However, ecoregion accounted for very little variance in total density and 36% of the variance was attributable to differences between streams. For other metrics, variance components were more evenly divided between stream and ecoregion effects.
3. Within streams, approximately 70% of variance was associated with unstructured local spatial variation and not associated with habitat type or transect position. The remaining variance was typically split about evenly between habitat and transect. Sample position within a transect (left, centre or right) accounted for virtually none of the variance for any metric.
4. New taxa per stream increased rapidly with sampling effort with the first four to eight Surber samples (500–1000 individuals counted), then increased more gradually. After counting more than 50 samples, new taxa continued to be added in stream reaches that were 80 times as long as their mean wetted width. Thus taxon richness was highly dependent on sampling effort, and comparisons between sites or streams must be normalized for sampling effort.
5. Characterization of spatial variance structure is fundamental to designing sampling programmes where spatial comparisons range from local to regional scales. Differences in metric responses across spatial scales demonstrate the importance of designing sampling strategies and analyses capable of discerning differences at the scale of interest.