Scales of spatiotemporal variability in macroinvertebrate abundance and diversity in monsoonal streams: detecting environmental change

1. We quantified spatial and temporal variability in benthic macroinvertebrate species richness, diversity and abundance in six unpolluted streams in monsoonal Hong Kong at different scales using a nested sampling design. The spatial scales were regions, stream sites and stream sections within sites; temporal scales were years (1997–99), seasons (dry versus wet seasons) and days within seasons. 2. Spatiotemporal variability in total abundance and species richness was greater during the wet season, especially at small scales, and tended to obscure site‐ and region‐scale differences, which were more conspicuous during the dry season. Total abundance and richness were greater in the dry season, reflecting the effects of spate‐induced disturbance during the wet season. Species diversity showed little variation at the seasonal scale, but variability at the site scale was apparent during both seasons. 3. Despite marked variations in monsoonal rainfall, inter‐year differences in macroinvertebrate richness and abundance at the site scale during the wet season were minor. Inter‐year differences were only evident during the dry season when streams were at base flow and biotic interactions may structure assemblages. 4. Small‐scale patchiness within riffles was the dominant spatial scale of variation in macroinvertebrate richness, total abundance and densities of common species, although site or region was important for some species. The proportion of total variance contributed by small‐scale spatial variability increased during the dry season, whereas temporal variability associated with days was greater during the wet season. 5. The observed patterns of spatiotemporal variation have implications for detection of environmental change or biomonitoring using macroinvertebrate indicators in streams in monsoonal regions. Sampling should be confined to the dry season or, in cases where more resources are available, make use of data from both dry and wet seasons. Sampling in more than one dry season is required to avoid the potentially confounding effects of inter‐year variation, although variability at that scale was relatively small.     

The Effect of Riffle-Scale Environmental Variability on Macroinvertebrate Assemblages in a Tropical Stream

In a tropical stream (at the Soberaní;a National Park, Panama), different environmental factors were quantified in riffle habitats (water characteristics: velocity, depth, turbulence, and direction; stone characteristics: surface area, sphericity, and degree of burial; and others: substrate type, and canopy cover). Characteristics of macroinvertebrate assemblages (mean density of individuals, mean taxon richness, and cumulative taxon richness in three stones at each riffle) were related to both mean values and variability of these environmental factors at riffle scale. Macroinvertebrate density was higher in shallow, fast flowing, stony riffles, with low variability in dominant substrate type. Taxon richness was also higher in shallow riffles with loose, not buried stones, and water direction more or less parallel to the bank. Environmental variability resulted as important as mean values of environmental factors to explain variation in macroinvertebrate assemblages. This is the first study, to our knowledge, that quantifies substratum variability and demonstrates its influence on macroinvertebrate assemblages in a tropical stream.     

Relations Between River Plant Richness in the Portuguese Floodplains and the Widespread Water Knotgrass <Emphasis Type="Italic">(Paspalum Paspalodes</Emphasis>)

We examined the variability of macroinvertebrate assemblage structure, species identities, and functional feeding group composition in relation to stream size, tributary position, and in-stream factors in a boreal watershed in Finland. Our study included three riffle sites in each of three stream sections in each of three stream size classes. Multi-response permutation procedure, indicator value method, and canonical correspondence analysis revealed clear differences in assemblage structure among the stream size classes, with a gradual increase of species richness as the stream size increased. Significant differences in assemblage structure were also found among the tributary river systems. The functional feeding group composition broadly followed the river continuum concept, i.e., headwaters were dominated by shredders, gatherers, or filterers, whereas scrapers increased in relative abundance with stream size. There was, however, considerable variation in the functional feeding group composition both among and within the headwater stream sections. Our findings refer to a strong influence of stream size on macroinvertebrate assemblages, but also factors prevailing at the scale of individual riffles should be considered in biodiversity conservation of lotic ecosystems.     

Scales of spatiotemporal variation in macroinvertebrate assemblage structure in monsoonal streams: the importance of season

1. We assessed the relative importance of different scales of spatial and temporal variability on benthic macroinvertebrate assemblage structure in six unpolluted streams in monsoonal Hong Kong using ordination and complementary multivariate analyses. The spatial scales were regions, sites (streams) and sections (riffles) within sites. The temporal scales were years (three, including one with unusually high rainfall), seasons (dry versus wet) and days within seasons. 2. Significant differences in assemblage structure were manifested at all temporal scales. Those at the site scale were most obvious, whereas demarcation of assemblage structure at the section (riffle) scale was smaller, and there was no significant regional differentiation in assemblage structure. Seasonal variability in assemblage structure was greater than that among years or days. 3. Inter‐year differences in assemblage structure were recorded at all sites, and were noted among all years at some sites but not at others. They were recorded more frequently during the dry season, although their occurrence (in pair‐wise comparisons between years) appeared to be related to differences in the monsoonal (wet season) rainfall. 4. Seasonal differences in assemblage structure were strongly evident at all sites. Inter‐site differences were more apparent during the dry season when local (site‐scale) influences on assemblages were stronger. By contrast, wet‐season samples were more variable because of spate‐induced disturbance, and inter‐site differentiation was less distinct. 5. Differences among days at all sites were relatively minor, but shifts attributable to repeated spate‐induced disturbance were evident at some sites during the wet season. 6. Differences at the section scale were recorded more frequently during the dry season, when the extent of within‐site variability among sections was higher, reflecting increased patchiness within sections resulting from increased substratum heterogeneity and/or greater intensity of biotic interactions. 7. Seasonal shifts in macroinvertebrate assemblage structure at a variety of scales in Hong Kong streams are likely to be attributable to monsoonal rains affecting the relative intensity of abiotic disturbance and biotic interactions in accordance with the harsh‐benign hypothesis.     

Spatial and Temporal Variation of Macroinvertebrate Drift in Two Neotropical Streams1

The detection of spatial variation in macroinvertebrate drift depends on the spatial scale of investigation in streams of the La Selva Biological Station, Costa Rica. Drift samples were taken in a spatially nested design, with two streams, two reaches per stream, two riffles per reach, and four replicate samples per riffle. Drift showed little variation among streams, but varied significantly at the scales of reach and riffle, with variation among samples also high. In addition, sampling took place at two temporal scales: diel and at two different periods that differed in rainfall conditions. Drift diel periodicity was a clear pattern, while only density of individuals varied among sampling periods. This is the first study of macroinvertebrate drift at multiple spatial scales, despite the recognition that multi‐scale studies are essential for a more complete understanding of community patterns and processes.     

Multiscale patterns of spatial variation in stream macroinvertebrate communities

Our ability to detect patterns of variation of communities depends on the spatial scale of observation. I examined the spatial variation of macroinvertebrate community structure: abundance, richness, evenness, percentage of Ephemeroptera, Plecoptera and Trichoptera (EPT), and taxonomic composition across a wide range of spatial scales in two mountain streams. In a nested design, three segments were selected within each basin, three riffles within each segment, three sections within each riffle, and three samples within each section. Significant variation of communities occurred mainly at sample and riffle scales, although different community characteristics may vary at different scales. Environmental factors were strongly related to communities, but these relationships depended on spatial scale in many cases, suggesting that the influence of the environment is ultimately regulated by the grain and extent of organisms. This study highlights the importance of multiscale studies to obtain a complete understanding of the spatial variation of macroinvertebrate communities and their relationship with the environment.     

Testing for temporal coherence across spatial extents: the roles of climate and local factors in regulating stream macroinvertebrate community dynamics

Temporal coherence or spatial synchrony refers to the tendency of population, community or ecosystem dynamics to behave similarly among locations through time as a result of spatially‐correlated environmental stochasticity (Moran effect), dispersal or trophic interactions. While terrestrial studies have treated synchrony mainly as a population‐level concept, the majority of freshwater studies have focused on community‐level patterns, particularly in lake planktonic communities. We used spatially and temporally hierarchical data on benthic stream invertebrates across six years, with three seasonal samples a year, in 11 boreal streams to assess temporal coherence at three spatial extents: 1) among regions (watersheds), 2) among streams within a region, and 3) among riffles within a stream, using the average of correlation coefficients for stream/riffle pairs across years. Our results revealed the primacy of strongly synchronized climatic factors (precipitation, air temperature) in inducing temporal coherence of macroinvertebrate assemblages across geographically distinct sites (i.e. Moran effect). Coherence tended to decrease with increasing spatial extent, but positive coherence was detected for most biological variables even at the largest extent (about 350 km). The generally high level of coherence reflected the strong seasonality of boreal freshwater communities. A hydrologically exceptional year enhanced the synchrony of biological variables, particularly total macroinvertebrate abundance. Regionally low precipitation in that year led to a substantial decrease in benthic densities across a broad spatial extent, followed by a rapid post‐drought recovery. Coherence at the among‐riffle (within‐stream) extent was lower than expected, implying that local‐scale habitat filters determine community dynamics at smaller spatial extents. Thus, temporal coherence of stream benthic communities appears to be controlled by partly different processes at different spatial scales.     

Relationships between deforestation, riparian forest buffers and benthic macroinvertebrates in neotropical headwater streams

1. Few studies have evaluated the effectiveness of riparian buffers in the tropics, despite their potential to reduce the impacts of deforestation on stream communities. We examined macroinvertebrate assemblages and stream habitat characteristics in small lowland streams in southeastern Costa Rica to assess the impacts of deforestation on benthic communities and the influence of riparian forest buffers on these effects. Three different stream reach types were compared in the study: (i) forested reference reaches, (ii) stream reaches adjacent to pasture with a riparian forest buffer at least 15 m in width on both banks and (iii) stream reaches adjacent to pasture without a riparian forest buffer. 2. Comparisons between forest and pasture reaches suggest that deforestation, even at a very local scale, can alter the taxonomic composition of benthic macroinvertebrate assemblages, reduce macroinvertebrate diversity and eliminate the most sensitive taxa. The presence of a riparian forest buffer appeared to significantly reduce the effects of deforestation on benthic communities, as macroinvertebrate diversity and assemblage structure in forest buffer reaches were generally very similar to those in forested reference reaches. One forest buffer reach was clearly an exception to this pattern, despite the presence of a wide riparian buffer. 3. The taxonomic structure of macroinvertebrate assemblages differed between pool and riffle habitats, but contrasts among the three reach types in our study were consistent across the two habitats. Differences among reach types also persisted across three sampling periods during our 15‐month study. 4. Among the environmental variables we measured, only stream water temperature varied significantly among reach types, but trends in periphyton abundance and stream sedimentation may have contributed to observed differences in macroinvertebrate assemblage structure. 5. Forest cover was high in all of our study catchments, and more research is needed to determine whether riparian forest buffers will sustain similar functions in more extensively deforested landscapes. Nevertheless, our results provide support for Costa Rican regulations protecting riparian forests and suggest that proper riparian management could significantly reduce the impacts of deforestation on benthic communities in tropical streams.     

The contribution of riffles and riverine wetlands to benthic macroinvertebrate biodiversity

Benthic macroinvertebrates collected in biomonitoring programs are a potentially valuable source of biodiversity information for conservation planning in river ecosystems. Biomonitoring samples often focus on riffles; however, we have only partially assessed the extent to which riffle biodiversity patterns reflect those of other river habitats, particularly riverine wetlands. Using a standard biomonitoring protocol, we assessed the richness, composition and magnitude of variation of macroinvertebrate assemblages in riffles across 18 sites in the Nashwaak river catchment, and compared these to samples from adjacent riverine wetlands. Despite containing on average fewer taxa per site than riffles, riverine wetlands demonstrated similar levels of taxon richness at the catchment scale. There was strong assemblage separation between habitat types, and riverine wetlands displayed significantly greater assemblage variation than riffles. Riffles and riverine wetlands did not demonstrate significant correlations in terms of taxon richness or assemblage variation, though this may be partially due to the scale at which we collected observations. Principal component analysis with vector fitting suggested that (log) sub-catchment area was an important factor structuring riffle assemblages, while depth was potentially important for riverine wetland assemblages. We discuss the implications of these results for the use of biomonitoring data in systematic conservation planning, and identify future research that will improve our understanding of the role riverine wetlands play in maintaining catchment biodiversity and ecosystem processes.     

山地河流浅滩深潭生境大型底栖动物群落比较研究——以重庆开县东河为例

浅滩和深潭是山地河流中常见的河流生境结构。2011年7月,在重庆开县东河上游双河口-杉木桥河段,选择21个浅滩和深潭,调查大型底栖动物,研究影响不同生境中底栖动物组成、分布和多样性的生态机理。结果表明:调查河段浅滩和深潭中大型底栖动物分别为31种和24种,密度分别为450.62 个/m²和86.24 个/m²,生物量分别为2.88 g/m²和0.55 g/m²。浅滩有指示种11种,即纹石蛾(Hydropsyche sp.)、假蜉(Iron sp.)、假二翅蜉(Pseudocloeon sp.)、舌石蛾(Glossosoma sp.)、高翔蜉(Epeorus sp.1)、背刺蜉(Notacanthurus sp.)、Heterocloeon sp、锯形蜉(Serratella sp.)、朝大蚊(Antocha sp.)、等蜉(Isonychia sp.)、溪颏蜉(Rhithrogena sp.)。深潭指示种仅蜉蝣(Ephemera sp.)和黑大蚊(Hexatoma sp.)两种。刮食者为两类生境的优势功能摄食类群。浅滩中滤食者和刮食者比例显著高于深潭,而收集者和捕食者显著低于深潭。两类生境中大型底栖动物群落结构差异显著。浅滩中大型底栖动物的密度、生物量、丰富度指数、Shannon-Wiener 指数、改进的Shannon-Wiener指数均明显高于深潭。受地貌形态、水力特征和冲淤变化规律影响的生境稳定性和异质性差异是导致大型底栖动物群落差异的主要原因。     

Hydraulic microhabitats and the distribution of macroinvertebrate assemblages in riffles

1. The influence of hydraulic conditions on the spatial distribution of macroinvertebrate assemblages was investigated in three riffles in a perennial Australian river. 2. Velocity, depth and variability of substrate roughness were measured at each of 56 macroinvertebrate sampling locations. Complex hydraulic variables (roughness Reynolds number, shear velocity, Froude number) were calculated from combinations of two or three of the directly measured variables. The biological significance of directly measured and complex hydraulic variables was determined by a combination of univariate and multivariate statistical procedures. 3. Macroinvertebrate abundance, number of taxa and community composition were significantly different between the identified roughness Reynolds number, Froude number, velocity and shear velocity microhabitats throughout the studied riffles. 4. Regression analysis showed macroinvertebrate abundance and number of taxa were negatively related to roughness Reynolds number, shear velocity, velocity and Froude number. Depth was negatively related to abundance. In general, the majority of the macroinvertebrate community preferred the areas of riffles with the lowest near‐bed turbulence. 5. Roughness Reynolds number explained more of the spatial variation in invertebrate abundance, number of taxa and community composition than the other hydraulic variables, either directly measured or calculated. Of the directly measured variables, velocity had the greatest explanatory power, which was marginally less than roughness Reynolds number and shear velocity. 6. This study demonstrated that small‐scale differences in hydraulic conditions created by combinations of velocity, depth and substrate roughness have an important role in the spatial distribution of macroinvertebrate assemblages in riffle habitats.     

Relationships between land use, spatial scale and stream macroinvertebrate communities

1. The structure of lotic macroinvertebrate communities may be strongly influenced by land‐use practices within catchments. However, the relative magnitude of influence on the benthos may depend upon the spatial arrangement of different land uses in the catchment. 2. We examined the influence of land‐cover patterns on in‐stream physico‐chemical features and macroinvertebrate assemblages in nine southern Appalachian headwater basins characterized by a mixture of land‐use practices. Using a geographical information system (GIS)/remote sensing approach, we quantified land‐cover at five spatial scales; the entire catchment, the riparian corridor, and three riparian ‘sub‐corridors’ extending 200, 1000 and 2000 m upstream of sampling reaches. 3. Stream water chemistry was generally related to features at the catchment scale. Conversely, stream temperature and substratum characteristics were strongly influenced by land‐cover patterns at the riparian corridor and sub‐corridor scales. 4. Macroinvertebrate assemblage structure was quantified using the slope of rank‐abundance plots, and further described using diversity and evenness indices. Taxon richness ranged from 24 to 54 among sites, and the analysis of rank‐abundance curves defined three distinct groups with high, medium and low diversity. In general, other macroinvertebrate indices were in accord with rank‐abundance groups, with richness and evenness decreasing among sites with maximum stream temperature. 5. Macroinvertebrate indices were most closely related to land‐cover patterns evaluated at the 200 m sub‐corridor scale, suggesting that local, streamside development effectively alters assemblage structure. 6. Results suggest that differences in macroinvertebrate assemblage structure can be explained by land‐cover patterns when appropriate spatial scales are employed. In addition, the influence of riparian forest patches on in‐stream habitat features (e.g. the thermal regime) may be critical to the distribution of many taxa in headwater streams draining catchments with mixed land‐use practices.     

Stream macroinvertebrate response to catchment urbanisation (Georgia, U.S.A.)

SUMMARY 1. The effects of catchment urbanisation on water quality were examined for 30 streams (stratified into 15, 50 and 100 km² ± 25% catchments) in the Etowah River basin, Georgia, U.S.A. We examined relationships between land cover (implying cover and use) in these catchments (e.g. urban, forest and agriculture) and macroinvertebrate assemblage attributes using several previously published indices to summarise macroinvertebrate response. Based on a priori predictions as to mechanisms of biotic impairment under changing land cover, additional measurements were made to assess geomorphology, hydrology and chemistry in each stream. 2. We found strong relationships between catchment land cover and stream biota. Taxon richness and other biotic indices that reflected good water quality were negatively related to urban land cover and positively related to forest land cover. Urban land cover alone explained 29–38% of the variation in some macroinvertebrate indices. Reduced water quality was detectable at c. >15% urban land cover. 3. Urban land cover correlated with a number of geomorphic variables such as stream bed sediment size (–) and total suspended solids (+) as well as a number of water chemistry variables including nitrogen and phosphorus concentrations (+), specific conductance (+) and turbidity (+). Biotic indices were better predicted by these reach scale variables than single, catchment scale land cover variables. Multiple regression models explained 69% of variation in total taxon richness and 78% of the variation in the Invertebrate Community Index (ICI) using phi variability, specific conductance and depth, and riffle phi, specific conductance and phi variability, respectively. 4. Indirect ordination analysis was used to describe assemblage and functional group changes among sites and corroborate which environmental variables were most important in driving differences in macroinvertebrate assemblages. The first axis in a non‐metric multidimensional scaling ordination was highly related to environmental variables (slope, specific conductance, phi variability; adj. R²=0.83) that were also important in our multiple regression models. 5. Catchment urbanisation resulted in less diverse and more tolerant stream macroinvertebrate assemblages via increased sediment transport, reduced stream bed sediment size and increased solutes. The biotic indices that were most sensitive to environmental variation were taxon richness, EPT richness and the ICI. Our results were largely consistent over the range in basin size we tested.     

Hierarchical structure of stream ecosystems: consequences for bioassessment

It has long been recognized that communities and their ecosystems are structured at several, nested spatial scales. But identifying the appropriate scale(s) to collect, analyse and interpret data to answer specific questions about ecosystems has been a vexing problem for ecologists. We collected observations of the benthic invertebrate community and its environment in 10 primarily agricultural tributary streams of the Thames River in southwestern Ontario, Canada. Within each stream we sampled two reaches, in each reach we sampled three riffles, and in each riffle we took three kick samples of invertebrates and characterized the substrate environment. We also characterized the habitat at each of the 20 reaches (10 streams × 2 reaches/stream). Most of the variability in the stream invertebrate community structure (as described with taxonomic richness and the biotic index of tolerance, as well as by the Bray-Curtis distance of the community composition from the mean at a spatial scale) was at larger spatial scales of among streams and between riffles. Much of the substrate and habitat variation was also at the larger spatial scales, as were correlations between the biota and the environment of the benthic invertebrate community. We concluded that for the purposes of bioassessment, characterization of one reach per stream is sufficient, at least in this context, for describing a stream and evaluating its health. Handling editor: R. Norris     

Comparative Environmental Assessment in the Studies of Benthic Diatom,Macroinvertebrate, and Fish Communities

Community response to environmental gradients operating at hierarchical scales was assessed in studies of benthic diatoms, macroinvertebrates and fish from 44 stream sites in the New York City watershed. Hierarchical cluster analysis (TWINSPAN) of diatoms and fish partitioned the study sites into four groups, i.e., acid streams, reservoir outlets and wetland streams, large eutrophic streams, and small eutrophic streams; macroinvertebrate TWINSPAN distinguished an additional group of silty eutrophic streams. The correspondence among the three assemblage TWINSPAN groupings was moderate, ranging from 51 to 57%. The similarity across the four major group types was the highest among large eutrophic stream and acid stream assemblages, and the lowest among small eutrophic stream assemblages. Stepwise discriminant function analysis revealed that environmental factors discriminated most effectively the diatom grouping and least effectively the fish grouping. The best environmental predictors for diatom and macroinvertebrate grouping were conductance and percent surface water, while population density was most powerful in separating the fish groups. Carbaryl was the only pesticide that correlated with macroinvertebrate grouping. Partial redundancy analyses suggested a differential dependence of freshwater communities on the scale of the environmental factors to which they respond. The role of small‐scale habitat and habitatland cover/land use interaction steadily increased across the diatom, macroinvertebrate, and fish assemblages, whereas the effect of large‐scale land cover/land use declined.     

The quantification of local substrate heterogeneity in streams and its significance for macroinvertebrate assemblages

The effect of substrate heterogeneity on the structure of stream macroinvertebrate assemblages (total abundance, taxon richness, and evenness) is still not clear, but this could be due to the lack of standard methods for quantifying substrate heterogeneity. An accurate quantification of substrate heterogeneity was obtained from photographs of sampled areas (each 225 cm²), which were used to create maps that were subsequently digitized and analyzed using image analysis software. These maps allowed the calculation of multiple metrics quantifying two aspects of substrate heterogeneity: composition and spatial configuration of substrate patches. The diversity of substrate types (calculated as the Shannon diversity index), and the heterogeneity of patch compactness (calculated as the coefficient of variation of the relationship between patch dimensions) were the metrics explaining more biotic variance at the sample scale, but at higher scales there were no relationships between assemblage structure and substrate heterogeneity. Most variation in substrate heterogeneity occurred at the sample scale, while some metrics varied significantly at riffle or segment scales; these patterns of variation match those of macroinvertebrate assemblages, which had been previously studied. The importance of quantifying substrate heterogeneity and considering the spatial scales of its study are discussed.     

Relationships between fishes and habitat in rainforest streams in Sabah, Malaysia

Distinct fish assemblages were found at the mesohabitat scale in 14 streams in eastern Sabah, Malaysia. Sites were designated a priori as pool, run or riffle on the basis of physical habitat structure and properties. Principal components analysis of physical habitat data confirmed the validity of the a priori designation with a major axis of three correlated variables: water velocity, depth and substratum type. Canonical discriminant analysis on fish abundance and biomass data confirmed the existence of a specialized assemblage of fishes from riffle areas of all streams. Overall, pool and run assemblages were highly variable, dependent on stream size, but also variable between streams of the same size. Multiple regression of species richness, diversity, abundance and biomass data on principal components revealed significant but low correlations with measured habitat variables. Riffle habitats showed lower species richness and diversity but high abundance. The fish assemblage in riffles was dominated by balitorid species, specialized for fast-water conditions. Pool assemblages had the highest species diversity and were dominated by cyprinid species of a number of morphological and ecological guilds. Run assemblages were intermediate in assemblage characteristics between riffle and pool assemblages. Between-stream variation in assemblage composition was less than within-stream variation. Of 38 species collected, seven could be designated as riffle specialists, 18 as pool specialists and 13 as ubiquitous, although most of the latter showed size-specific habitat use with larger size classes found in slower, deeper water.     

Scale and the detection of land-use effects on morphology, vegetation and macroinvertebrate communities of grassland streams

1. Land‐use studies are challenging because of the difficulty of finding catchments that can be used as replicates and because land‐use effects may be obscured by sources of variance acting over spatial scales smaller than the catchment. To determine the extent to which land‐use effects on stream ecosystems are scale dependent, we designed a whole‐catchment study of six matched pairs (pasture versus native tussock) of second‐order stream catchments, taking replicate samples from replicate bedforms (pools and riffles) in each stream. 2. Pasture streams had a smaller representation of endemic riparian plant species, particularly tussock grasses, higher bank erosion, a somewhat deeper layer of fine sediment, lower water velocities in riffles, less moss cover and higher macroinvertebrate biodiversity. At the bedform scale, suspendable inorganic sediment (SIS) was higher in pools than riffles and in pasture streams there was a negative relationship between SIS and the percentage of the bed free of overhanging vegetation. Differences between stream reaches (including any interactions between land use and stream pair) were significant for SIS, substrate depth and characteristics of riparian vegetation. There were also significant differences between replicate bedforms in the same stream reaches in percentage exotic species in overhanging vegetation, percentage moss cover, QMCI (Quantitative Macroinvertebrate Community Index – a macroinvertebrate‐based stream health index) and macroinvertebrate density. 3. Significant differences among stream reaches and among replicate bedform units within the same reach, as well as interactions between these spatial units and land‐use effects, are neither trivial nor ‘noise’ but represent real differences among spatial units that typically are unaccounted for in stream studies. Our multi‐scale study design, accompanied by an investigation of the explanatory power of different factors operating at different scales, provides an improved understanding of variability in nature.