The relationship between land use and physicochemistry, food resources and macroinvertebrate communities in tributaries of the Taieri River, New Zealand: a hierarchically scaled approach

1. The relationship between land use and stream conditions was investigated, including physicochemistry, the availability of primary food resources and species richness, species composition and trophic structure of stream macroinvertebrate communities. The survey involved eight subcatchments of the Taieri River (New Zealand) encompassing reasonably homogeneous examples of four major land uses: native forest, native tussock grassland, plantations of introduced pine and agricultural pasture.
2. Each land use was represented by two subcatchments, each subcatchment by two to four tributaries, and each tributary by two to three sampling sites. These three sampling scales each represent typical designs for stream community studies. By recording responses at all scales, it can be determined explicitly whether the scale of sampling influences interpretation of community structure.
3. Elevation, riffle length, proportion of large substrata in the bed, total phosphorus and alkalinity were significantly related to land use, as were canopy cover and the relative abundance of leaves and wood in the streams. Principal components analysis of invertebrate density data identified nine orthogonal community types, the distributions of two of which were significantly related to land use. The role played by browsers and shredders in the stream community depended on land use.
4. Primary analysis was at the level of the tributary. When it focused on sites within tributaries, more variables were related to land use and at a higher level of significance. This was largely a result of enhanced statistical power due to increased replication. When whole subcatchments were the focus of attention, statistical power was so low, even with six to eleven subsamples to generate overall means, that few significant patterns could be identified. However, the community patterns that were revealed were similar whatever the scale of sampling.     

Identifying the scales of variability in stream macroinvertebrate abundance, functional composition and assemblage structure

1. Many natural ecosystems are heterogeneous at scales ranging from microhabitats to landscapes. Running waters are no exception in this regard, and their environmental heterogeneity is reflected in the distribution and abundance of stream organisms across multiple spatial scales. 2. We studied patchiness in benthic macroinvertebrate abundance and functional feeding group (FFG) composition at three spatial scales in a boreal river system. Our sampling design incorporated a set of fully nested scales, with three tributaries, two stream sections (orders) within each tributary, three riffles within each section and ten benthic samples in each riffle. 3. According to nested anova s, most of the variation in total macroinvertebrate abundance, abundances of FFGs, and number of taxa was accounted for by the among‐riffle and among‐sample scales. Such small‐scale variability reflected similar patterns of variation in in‐stream variables (moss cover, particle size, current velocity and depth). Scraper abundance, however, varied most at the scale of stream sections, probably mirroring variation in canopy cover. 4. Tributaries and stream sections within tributaries differed significantly in the structure and FFG composition of the macroinvertebrate assemblages. Furthermore, riffles in headwater (second order) sections were more variable than those in higher order (third order) sections. 5. Stream biomonitoring programs should consider this kind of scale‐dependent variability in assemblage characteristics because: (i) small‐scale variability in abundance suggests that a few replicate samples are not enough to capture macroinvertebrate assemblage variability present at a site, and (ii) riffles from the same stream may support widely differing benthic assemblages.     

Ecological relationships between stream communities and spatial scale: implications for designing catchment-level monitoring programmes

1. Stream communities are structured by factors acting over multiple spatial and temporal scales. Identifying what factors are driving spatial patterns in stream communities is a central aim of ecology.
2. Here we used two large European data sets of fish, invertebrates, macrophytes, benthic diatoms and environmental data in two stream groups (lowland and mountain) to determine the importance of variables at different spatial scales (geographical, regional, local) on community structure.
3. Both geographical position and ecoregion were selected first in canonical correspondence analysis (CCA), clearly showing the broad spatial gradients covered in the data set. Secondary predictors (after accounting for spatial and/or ecoregion effects) were similar between stream groups and among the four organism groups. In particular, conductivity and N concentration were strong predictors reflecting catchment land use.
4. Using partial CCA, we assessed the individual importance of the three spatial scales on the community structure of the four organism groups in the two stream groups. The majority of among-site variability (22–29%) was accounted for by local scale variables (e.g. water chemistry and substratum type), with regional and spatial variables accounting 11–13% and 5–6%, respectively. Our findings indicate that the four organism groups are responding similarly to the different levels of spatial scale, implying much redundancy which should be consider when implementing studies of bioassessment.     

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 communities in a conifer‐afforested catchment in Ireland: relationships to physico‐chemical and biotic factors

1. The influence of land use and physico-chemical factors on stream macroinvertebrates was analysed at fifteen sites over a 2-year period in a single conifer-afforested catchment in Ireland, in an area subject to very low levels of atmospheric pollution. 2. Macroinvertebrate assemblages were classified using two-way indicator species analysis into five major groupings that were related to distance from headwaters and land use. Trends in macroinvertebrate community composition were related to changes in physico-chemical and biotic characteristics of the river and its tributaries using canonical correspondence analysis. 3. Local ecological factors (e.g. acid water, moss, shading or agricultural runoff), longitudinal trends in stream physico-chemistry (related to distance from headwaters, geology and land use) and season (related to life history patterns of the invertebrates) were the explanatory variables of spatio-temporal patterns in macroinvertebrate community composition in the catchment. 4. Spatial variation in macroinvertebrate density, taxon richness, diversity and evenness was investigated in relation to environmental characteristics of the study sites using Spearman’s rank correlation, principal components analysis and stepwise multiple regression. Invertebrate density and richness increased with distance from the headwater and associated increases in pH, water hardness and nutrients. Macroinvertebrate density and richness also increased with increasing moss weight. Invertebrate diversity and evenness increased with shading of the channel. 5. The increase in macroinvertebrate density and richness and changes in community composition were particularly marked over a relatively short (1.2 km) distance in one tributary, and were concurrent with a rapid increase in stream pH of 1.7 units. 6. Although macroinvertebrate communities at conifer-afforested sites were not impoverished in the same way as those in some other parts of Europe, they differed from the communities found above and below the plantation. This appeared to be owing to the primary importance of local ecological factors and the effect that the longitudinal position of these forest sites within the river system had on their physico-chemical and biotic nature.     

Genetic structure of a native cyprinid in a reservoir‐altered stream network

1. Reservoirs modify riverine ecosystems worldwide, and often with deleterious impacts on native biota. The immediate effects of reservoirs on native fish species below dams and in impounded reaches have received considerable attention, but it is unclear how reservoirs may affect fish species at larger spatial and temporal scales. Documented declines of stream fish populations in direct tributaries of reservoirs suggest reservoir pools may reduce gene flow among historically connected populations. 2. Because of increased predator densities in reservoirs and the extent of habitat alteration in impounded reaches, I predicted reservoir habitats would reduce gene flow among small‐bodied fish populations separated by reservoir habitat. I used microsatellite markers to assess the spatial genetic structure of populations of the red shiner (Cyprinella lutrensis), in a reservoir‐fragmented stream network (Lake Texoma, U.S.A.). I also tested the prediction that populations in two direct tributaries that have experienced population declines would have low genetic diversity. Individuals were collected from six sites upstream of the reservoir, three sites in the reservoir and three sites in direct tributaries of the reservoir during 2008 and 2009. 3. Results indicate that most populations were isolated by distance with little divergence among populations. In one direct tributary population, however, there was substantial genetic divergence, and genetic diversity was significantly lower than in other populations. Gene flow also seemed to be lower in reservoir habitats than in intact stream habitats, suggesting reservoir habitats may be reducing gene flow among the reservoir‐separated populations. These results indicate that reservoirs may reduce gene flow among reservoir‐fragmented stream fish populations, altering the evolutionary trajectories of fragmented populations.     

The relationships among three habitat scales and stream benthic invertebrate community structure

1. The relationships between three habitat scales and lotic invertebrate species composition were investigated for the 15 540 km² Yakima River basin in south-central Washington, U.S.A.
2. The three spatial scales were sample (the sampled riffle), reach (a length of ten–twenty stream widths) and segment (a length of stream of nearly uniform slope and valley form having no change in stream order).
3. Physical variables were highly correlated between scales and expressed a relationship between altitude, basin form and small-scale physical structure.
4. Multiple discriminant function analyses indicated that segment- and reach-scale variables discriminated among species-defined groups better than sample-scale variables.
5. Species composition varied along a complex altitudinal gradient of changing basin form and resultant land use.
6. There was no clear relationship between species richness and altitude on a site basis. However, when viewed at the basin scale, maximum richness was observed at the transition between montane and valley sites.     

Contemporary Land Change Alters Fish Communities in a San Francisco Bay Watershed,California, U.S.A.

Urbanization is one of the leading threats to freshwater biodiversity, and urban regions continue to expand globally. Here we examined the relationship between recent urbanization and shifts in stream fish communities. We sampled fishes at 32 sites in the Alameda Creek Watershed, near San Francisco, California, in 1993–1994 and again in 2009, and we quantified univariate and multivariate changes in fish communities between the sampling periods. Sampling sites were classified into those downstream of a rapidly urbanizing area (“urbanized sites”), and those found in less impacted areas (“low-impacted sites”). We calculated the change from non-urban to urban land cover between 1993 and 2009 at two scales for each site (the total watershed and a 3km buffer zone immediately upstream of each site). Neither the mean relative abundance of native fish nor nonnative species richness changed significantly between the survey periods. However, we observed significant changes in fish community composition (as measured by Bray-Curtis dissimilarity) and a decrease in native species richness between the sampling periods at urbanized sites, but not at low-impacted sites. Moreover, the relative abundance of one native cyprinid (Lavinia symmetricus) decreased at the urbanized sites but not at low-impacted sites. Increased urbanization was associated with changes in the fish community, and this relationship was strongest at the smaller (3km buffer) scale. Our results suggest that ongoing land change alters fish communities and that contemporary resurveys are an important tool for examining how freshwater taxa are responding to recent environmental change.     

Scale-dependent effects of fine sediments on temperate headwater invertebrates

1. Anthropogenic activities can increase fine sediment supply to streams over multiple spatial and temporal extents. Identifying the processes responsible, and the scale at which any effects on stream organisms become evident, are key management needs, but appropriately scaled surveys are surprisingly few. 2. We surveyed macroinvertebrates and superficial fine sediments at two spatial resolutions (reach‐ and patch‐scale) in tributaries of the River Usk, a temperate, montane catchment in rural Wales (U.K.). Land use, habitat and geomorphological character were measured on‐site or derived from an existing database (=Fluvial Audit). We aimed to identify: (i) how in‐stream sediments varied with land use and associated geomorphology; (ii) likely consequences for macroinvertebrates and (iii) any scale‐dependence in relationships between macroinvertebrates and sediment character. 3. At both the reach‐ and patch‐scales, bed cover by fine sediment was related directly to the extent of eroding banks 500 m upstream. In turn, sedimentation and bank erosion were negatively correlated with catchment or riparian woodland extent. 4. At the reach scale, macroinvertebrate composition varied with catchment land use and stream chemistry, with richness declining as rough grazing or woodland was replaced by improved grassland. There was no response to deposited sediment except for weak increase in the relative abundance of oligochaetes. 5. By contrast, at the patch scale, fine sediments were accompanied by pronounced changes in invertebrate composition, and we ranked the 27 most common taxa according to their apparent sediment tolerance. General estimating equations showed that total and Ephemeroptera, Plecoptera and Trichoptera richness decreased significantly by 20% and 25% at the most sediment impacted sites (30% cover) by comparison with sediment‐free sites. 6. We conclude that sediment deposition in the upper Usk system mostly reflects local bank erosion, with riparian woodland likely to mediate this process through bank stability. Fine sediment release had marked ecological effects, but these were detectable only at patch‐to‐patch scales. We suggest that investigation of localized sediment release in streams will benefit from scale‐dependent or scale‐specific sampling, and some effects could go undetected unless sample resolution is selected carefully.     

Dispersal and recruitment of Tasiagma ciliata (Trichoptera: Tasimiidae) in rainforest streams, south-eastern Australia

1. This study examined genetic variation within and among populations of the caddis fly Tasiagma ciliata (Tasimiidae: Trichoptera) from rainforest streams in south-east Queensland, Australia.
2. Very low levels of genetic differentiation at large spatial scales, between subcatchments and between catchments, indicated that dispersal by the winged adults is widespread. However, significant genetic differentiation at the smallest spatial scale examined, within reaches in a single stream, suggested limited movement by larvae within streams.
3. A patchy distribution of deviations from Hardy–Weinberg equilibrium and differences in patterns among allozyme loci suggested that populations in particular reaches were the result of only a few matings.
4. These results are surprising, given the large numbers of larvae present within a single reach. We suggest that stochastic effects of recruitment may underlie much of the spatial and temporal variation in population numbers in these rainforest streams.     

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.     

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     

Importance of scale,land‐use,and stream network properties for riparian plant communities along an urban gradient

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Alien and native plants show contrasting responses to climate and land use in Europe

Aim We tested whether the distribution and cover of alien plant species in Europe was related to human disturbance and microclimate. Location Surveys were conducted at 13 sites across Europe, each containing a pair of landscapes with different land‐use intensities. Methods Sampling locations were chosen based on land use and microclimate at two scales: land use was characterized at the patch and landscape scale; climate was expressed as regional and local temperature. The slope of each sample location was derived from a digital elevation model. Cover of plant species was measured using point counts and analysed using mixed effect models. Species were classified as native, archaeophytes and neophytes (pre‐ versus post‐ad 1500 immigrants). Due to the zero inflation observed in the alien groups, their cover was analysed conditional on their presence. Results Anthropogenic disturbance was a significant explanatory variable, increasing the presence and cover of alien species and decreasing the cover of native species. Alien presence was increased in sites under agricultural management, while their cover responded to land use at both local and landscape scales (and to their interaction), such that only natural habitats in semi‐natural landscapes had low alien cover. Microclimate was important for neophytes, with presence concentrated around mesic conditions. Slope was relevant for archaeophytes and native species, suppressing the former group and promoting the latter one. Main conclusions We found that, at the European scale, the distribution of alien plants is related to anthropogenic disturbance more than to microclimatic differences. The presence of neophytes, however, was influenced by climate at local and regional scales, with the highest incidence under mesic conditions. The different patterns observed for the presence and cover of alien species suggest different mechanisms acting during their establishment and spread. They also suggest that to counteract the expansion of alien species natural habitats may need to be maintained at landscape scales.     

Covariation of stream community structure and biomass of algae, invertebrates and fish with forest cover at multiple spatial scales

1. To evaluate the spatial extent of the effects of forest cover on stream ecosystems, we measured algae, invertebrate, and fish biomass and invertebrate and fish community structure in 38 small first- to third-order streams in the National Capital Region of Canada along with forest cover at different spatial scales.
2. We considered 55 spatial scales of forest cover including several buffer widths (doubling 10–320 m) and lengths (doubling 10–1280 m, entire riparian distance upstream from sampling area) and entire catchments to determine which spatial scale maximized the correlation with biomass and metrics of community structure.
3. The proportion of variability in biomass and structural metrics explained by forest cover generally increased with increasing scale, suggesting that catchment-wide disturbances are the most influential determinants of benthic and fish communities.
4. Catchment forest cover explained more variation in algal (adjusted r ²   =   0.54), invertebrate (adjusted r ²   =   0.51) and fish (adjusted r ²   =   0.33) biomass than structural metrics of invertebrates and fish (adjusted r ²   =   0.08–0.27).
5. Analyses of the partial effects of forest cover at three scales (reach, riparian and the entire catchment) on biomass and community structure metrics identified catchment and reach scales as being most influential and never detected a significant partial effect of forest cover at the riparian scale.
6. These results suggest that maintenance or protection of reach and riparian buffers alone will not sufficiently protect stream function and structure from catchment-wide impacts.     

The influence of chemistry and habitat features on the microcrustacea of some upland Welsh streams

SUMMARY. 1. Microcrustaceans were sampled during September 1990 from three microhabitats (margins, stony riffles and gravel) at thirteen stream sites in mid-Wales.
2. Patterns in the distribution, abundance and community structure of microcrustacean taxa were related to stream chemistry, physiography, substratum composition and marginal habitat structure. Patterns of distribution between microhabitats were also assessed.
3. Chemical variables were the strongest correlates with microcrustacean parameters. Total numbers of microcrustaceans and harpacticoid copepods were reduced at sites with high aluminium concentrations, and ostracods were scarce or absent at the most acidic sites. In contrast, cyclopoid copepods were more abundant and species rich at low pH.
4. Microcrustacean communities were most species rich at sites with a high percentage cover of macrophytes on the substratum. Cladoceran species richness and abundance, and the abundance of several microcrustacean species, were also positively correlated with percentage macrophyte cover.
5. Three site groupings produced by TWINSPAN classification were primarily related to percentage macrophyte cover and marginal habitat structure, with chemistry and land use also of importance.
6. Total microcrustacean abundance was highest in margins, but of all the species, only the harpacticoid Bryocamptus cuspidatus showed a strong microhabitat preference.     

The relationships among three habitat scales and stream benthic invertebrate community structure

1. The relationships between three habitat scales and lotic invertebrate species composition were investigated for the 15 540 km² Yakima River basin in south-central Washington, U.S.A.
2. The three spatial scales were sample (the sampled riffle), reach (a length of ten–twenty stream widths) and segment (a length of stream of nearly uniform slope and valley form having no change in stream order).
3. Physical variables were highly correlated between scales and expressed a relationship between altitude, basin form and small-scale physical structure.
4. Multiple discriminant function analyses indicated that segment- and reach-scale variables discriminated among species-defined groups better than sample-scale variables.
5. Species composition varied along a complex altitudinal gradient of changing basin form and resultant land use.
6. There was no clear relationship between species richness and altitude on a site basis. However, when viewed at the basin scale, maximum richness was observed at the transition between montane and valley sites.