SPATIAL PATTERNS AND ECOLOGICAL DETERMINANTS OF BENTHIC ALGAL ASSEMBLAGES IN MID-ATLANTIC STREAMS, USA

We attempted to identify spatial patterns and determinants for benthic algal assemblages in Mid-Atlantic streams. Periphyton, water chemistry, stream physical habitat, riparian conditions, and land cover/use in watersheds were characterized at 89 randomly selected stream sites in the Mid-Atlantic region. Cluster analysis (TWINSPAN) partitioned all sites into six groups on the basis of diatom species composition. Stepwise discriminant function analysis indicated that these diatom groups can be best separated by watershed land cover/use (percentage forest cover), water temperature, and riparian conditions (riparian agricultural activities). However, the diatom-based stream classification did not correspond to Omernik's ecoregional classification. Algal biomass measured as chl a can be related to nutrients in habitats where other factors do not constrain accumulation. A regression tree model indicated that chl a concentrations in the Mid-Atlantic streams can be best predicted by conductivity, stream slope, total phosphorus, total nitrogen, and riparian canopy coverage. Our data suggest that broad spatial patterns of benthic diatom assemblages can be predicted both by coarse-scale factors, such as land cover/use in watersheds, and by site-specific factors, such as riparian conditions. However, algal biomass measured as chl a was less predictable using a simple regression approach. The regression tree model was effective for showing that ecological determinants of chl a were hierarchical in the Mid-Atlantic streams.     

Concordance among stream assemblages and spatial autocorrelation along a fragmented gradient

Patterns of spatial autocorrelation of biota and distributional similarity (concordance) between assemblages of different organism groups have important implications in both theoretical ecology and biodiversity conservation. Here we report environmental gradients and spatial distribution patterns of taxonomic composition among stream fish, benthic macroinvertebrate, and diatom assemblages along a fragmented stream in south‐western France. We quantified spatial patterns of lotic assemblage structure along this stream, and we tested for concordance in distribution patterns among the three taxonomic groups. Our results showed that both environmental characteristics and stream assemblages were spatially autocorrelated. For stream fish and diatom assemblages, these patterns reflected assemblage changes along the longitudinal stream gradient, whereas environmental variables and benthic macroinvertebrates exhibited a more patchy spatial pattern. Cross‐taxa concordance was significant between stream fish and diatoms, and between stream fish and benthic macroinvertebrates. The assemblage concordance between stream fish and diatoms could be attributed to similar responses along the longitudinal gradient, whereas those between stream fish and benthic macroinvertebrates may result from biotic interactions. Based on potential dispersal capacities of taxa, our results validated the hypotheses that weakly dispersing taxa exhibit greater concordance than highly dispersing ones and that dispersal capacities affect how taxonomic groups respond to their local environment. Both diatoms and highly dispersing stream fish were affected by stream fragmentation (i.e. the number of dams between sites), while the effect of fragmentation was not significant for invertebrates that fly well in their adult stage, thus emphasizing the importance of the way of dispersal. These results suggest that addressing the effects of dispersal capacity on stream assemblage patterns is crucial to identifying mechanisms behind patterns and to better understanding the determinants of stream biodiversity.     

Effects of physico-chemistry, land use and hydromorphology on three riverine organism groups: a comparative analysis with monitoring data from Germany and Austria

The majority of studies comparing the response of biotic metrics to environmental stress in rivers are based on relatively small, homogeneous datasets resulting from research projects. Here, we used a large dataset from Austrian and German national river monitoring programmes (2,302 sites) to analyse the response of fish, diatom and macroinvertebrate metrics to four stressors acting at different scales (hydromorphology, physico-chemistry, riparian and catchment land use). Nutrient enrichment and catchment land use were the main discriminating stressors for all organism groups, over-ruling the effects of hydromorphological stress on the site scale. The response of fish metrics to stress was generally low, while macroinvertebrate metrics performed best. The Trophic Diatom Index (TDI) responded most strongly to all stressors in the mountain streams, while different metrics were responsive in the lowlands. Our results suggest that many rivers are still considerably affected by nutrient enrichment (eutrophication), which might directly point at implications of catchment land use. We conclude that monitoring datasets are well-suited to detect major broad-scale trends of degradation and their impact on riverine assemblages, while the more subtle effects of local-scale stressors require stream type-specific approaches.     

Comparative study of monitoring South-Finnish rivers and streams using macroinvertebrate and benthic diatom community structure

In southern Finland, most of the rivers are turbid and suffer from eutrophication and leaching of suspended solids from diffuse sources. We first related benthic diatom and macroinvertebrate structure to environmental factors using direct ordination. Second, benthic diatoms and macroinvertebrates were simultaneously sampled in several South-Finnish rivers and streams to compare two monitoring methods. The study sites constituted of some large, moderately nutrient rich rivers and some smaller, less eutrophic streams situated on the south coast of Finland. Diatom species distribution was most affected by conductivity, total P and latitude. Species distribution of macroinvertebrates was mostly related to channel width, conductivity and pH. For diatoms, separation of community structure between sampling stations was clear, but corresponding macroinvertebrate communities were more similar to each other. Correlation between diatom and macroinvertebrate pollution indices was rather low and insignificant (r = 0.28). As a whole, variation of macroinvertebrate index values (CV = 4.7%) among replicate samples was slightly lower than for diatom index (CV = 6.0%). On the contrary, community similarity between the replicate samples was slightly lower among macroinvertebrates (r = 0.770) due probably to their larger local scale spatial variation, sampling of more habitats and lower density compared to diatoms (r = 0.874). In conclusion, multiple pressures affecting the river ecosystems at different spatial and temporal scales should lead to choosing more than one biological monitoring method with clearly identifiable responses.     

Diatom Assemblages and their Associations with Environmental Variables in Oregon Coast Range Streams, USA

The Oregon Coast Range, rich in natural resources, is under increasing pressure from rapid development. The purpose of this study was to examine diatom species patterns in relation to environmental variables in streams of this region. Diatoms, water quality, physical habitat and watershed characteristics were assessed for 33 randomly selected stream sites. Watershed size, elevation, geology, vegetation and stream morphology varied substantially among sites. Streams were characterized by dilute water chemistry and a low percent of fine substrate. A total of 80 diatom taxa were identified. Taxa richness was low throughout the region (median 15, range 10–26). Assemblages were dominated by two adnate species, Achnanthidium minutissimum and Achnanthes pyrenaicum. Diatoms sensitive to organic pollution dominated the assemblages at all sites (median 85%). Non-metric multidimensional scaling (NMDS) and correlational analysis showed quantitative relationships between diatom assemblages and environmental variables. NMDS axes were significantly correlated with watershed area, watershed geology, conductivity, total nitrogen, total solids and stream width. Diatom-based site classification (Two-way Indicators Species Analysis, (TWINSPAN)) yielded 4 discrete groups that displayed weak correlations with environmental variables. When stream sites were classified by dominant watershed geology, overall diatom assemblages between groups were significantly different (Analysis of Similarity (ANOSIM) global R = 0.19, p < 0.05). Our results suggest that streams in the coastal region are in relatively good condition. High natural variability in stream conditions in the Oregon Coast Range ecoregion may obscure quantitative relationships between environmental variables and diatom assemblages. A bioassessment protocol that classifies sites by major landscape variables and selects streams along the major human disturbance gradient might allow for detection of early signs of human disturbance in environmentally heterogeneous regions, such as the Pacific Northwest.     

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.     

Choice of biota in stream assessment and monitoring programs in tropical streams: A comparison of diatoms,macroinvertebrates and fish

The objective of this study was to compare the responses of diatoms, macroinvertebrates and fish to agriculture, urbanization and mining in the Manyame River Basin. Water quality sampling and benthic diatom, macroinvertebrate and fish community data were collected in April (end of the rain season) and September (dry season) 2013 at 44 sampling stations spread out across three land-use categories: commercial agricultural, communal agricultural and urban-mining areas. Commercial agricultural areas were relatively pristine as they were characterized by mature deciduous riparian forest strips which acted as riparian buffers thus protecting water resources from nonpoint source pollution. In communal agricultural areas a combination of poor agricultural practices (stream bank cultivation, overgrazing, soil erosions) and high human population densities had negative effects on water quality of streams draining these areas. Streams in urban-mining areas were highly stressed, being impacted primarily by physical habitat degradation and both point and nonpoint sources of pollution. A suite of environmental variables that varied with land-use pattern was assessed to find the combination of variables that best explained patterns of biota community composition. Community metrics i.e. the Trophic Diatom Index (TDI) based on diatoms, the South African Scoring system version 5 (SASS 5) based on macroinvertebrates and the Fish Assemblage Integrity Index (FAII) were used to determine the ecological status of study streams in relation to human-induced stressors. Data were also subjected to multivariate statistical techniques; canonical correspondence analysis (CCA), mantel test and cluster analysis to determine environmental gradients along which the diatom, macroinvertebrate and fish assemblages were distributed as well as to elucidate hypothesized differences in response to stressors among communities per land-use type. Using CCA, we assessed the individual importance of a set of environmental variables on each biotic community structure. ANOVA, showed a significant difference (p < 0.05) in physical and chemical variables among commercial agricultural, communal agricultural and urban-mining sampling stations with no significant differences (p > 0.05) between the 2 sampling periods. Based on CCAs carried out using individual variables, the strengths of relationships between diatoms and macroinvertebrates was generally high for nutrient levels, organic and metal pollution and other variables. However, fish assemblages showed a relatively low association with all water quality variables in the study; this might be explained by the high abundance of omnivores and air breathers which are able to tolerate a variety of environmental conditions. These patterns were also confirmed by the mantel test as well as the other CCAs carried out to investigate the simultaneous effects of environmental variables. These findings indicate that diatoms are more powerful indicators in accessing ecological stream/river quality and have potential for application in routine monitoring programs in tropical streams.     

Different roles of environmental variables and spatial factors in structuring stream benthic diatom and macroinvertebrate in Yangtze River Delta,China

Exploring the relative contribution of spatial factors and environmental variables in shaping communities is of widespread interest in biodiversity conservation and environmental management. Stream communities are hierarchically regulated by environmental variables over multiple spatial scales, and the reaction of different organisms to stressors are still equivocal. We sampled both macroinvertebrates and diatom at 80 sites and additional 10 sites for macroinvertebrates, field measured and laboratory analyzed environmental variables, from the tributaries of Qiantang River, Yangtze River Delta China in 2011. We used PCNM (principal coordinates of neighbor matrices) to generate spatial predictors. We applied redundancy analysis and variation partitioning procedures to identify key spatial and environmental factors, and to quantify their relative roles in shaping diatom and macroinvertebrate assemblages. Our results demonstrated the role of spatial and environmental variables differed in shaping benthic diatom and macroinvertebrate. Diatom assemblage variations were better explained by spatial factors, however macroinvertebrate assemblage variations were better explained by environmental variables. In terms of environmental variables, catchment scale variables (e.g., land use estimators, land use diversity) played the primary role in determining the patterns of both diatom and macroinvertebrate assemblages, whereas the influence of reach-scale variables (e.g., pH, substrates, and nutrients) appeared less. However, nutrients were the stronger factors influencing benthic diatom, whereas physical habitat (e.g., substrates) played more important role than water chemistry in structuring macroinvertebrates. Our results provided more evidence to the incorporation of spatial factors interpreting spatial patterns of stream organisms, and highlighted the useful of multiple organisms and environmental variables at different spatial scales in diagnosing mechanism of stream degradation and in building a sound stream conditions monitoring program for Yangtze River Delta.     

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.     

Beta diversity of stream diatoms at two hierarchical spatial scales: implications for biomonitoring

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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.     

Should only live diatoms be used in the bioassessment of small mountain streams?

It is unclear whether differentiating live and dead diatoms would enhance the accuracy and precision of diatom-based stream bioassessment. We collected benthic diatom samples from 25 stream sites in the Northern Oregon Coast ecoregion. We counted live diatoms (cells with visible chloroplasts) and then compared the counts with those generated using the conventional method (clean counts). Non-metric multidimensional scaling (NMDS) showed that the diatom assemblages generated from the two counts were overall similar. The relationships between the two diatom assemblages (summarized as NMDS ordination axes) and the environmental variables were also similar. Both assemblages correlated well with in-stream physical habitat conditions (e.g., channel dimensions, substrate types, and canopy cover). The conventional diatom method provides taxonomic confidence while the live diatom count offers ecological reliability. Both methods can be used in bioassessment based on specific assessment objectives. Handling editor: J. Saros     

Macroinvertebrate species and assemblages in the headwater streams of the River Tyne,northern England in relation to land cover and other environmental variables

The macroinvertebrate species and assemblages of headwater streams of the River Tyne catchment in northern England were classified and their relationship with environmental variables based on stream structure, water acidity, distance from source and land cover investigated using constrained ordination and logistic regression. Fuzzy classification of data from 322 stream sites generated five assemblages. Stream structure, quantified as an exposure index, was found to be the most important environmental variable, with water acidity also important. Distance from source and land cover had less influence on species and assemblage distribution. A considerable amount of variation in assemblage distribution was explained using a two-variable logistic regression with stream structure (exposure index) and water acidity (pH) in a template. Site structure and water acidity appeared to be related to drift, geology and topography with little anthropogenic influence. The applicability of the habitat template concept for explaining the distribution of stream macroinvertebrates is discussed.     

Using Diatom Assemblages to Assess Urban Stream Conditions

We characterized changes in diatom assemblages along an urban-to-rural gradient to assess impacts of urbanization on stream conditions. Diatoms, water chemistry, and physical variables of riffles at 19 urban and 28 rural stream sites were sampled and assessed during the summer base flow period. Near stream land use was characterized using GIS. In addition, one urban and one rural site were sampled monthly throughout a year to assess temporal variation of diatom assemblages between the urban and rural stream sites. Canonical correspondence analysis (CCA) showed that the 1st ordination axis distinctly separated rural and urban sites. This axis was correlated with conductivity (r = 0.75) and % near-stream commercial/industrial land use (r = 0.55). TWINSPAN classified all sites into four groups based on diatom assemblages. These diatom-based site groups were significantly different in water chemistry (e.g., conductivity, dissolved nutrients), physical habitat (e.g., % stream substrate as fines), and near-stream land use. CCA on the temporal diatom data set showed that diatom assemblages had high seasonal variation along the 2nd axis in both urban and rural sites, however, rural and urban sites were well separated along the 1st ordination axis. Our results suggest that changes in diatom assemblages respond to urban impacts on stream conditions.     

Relationship of fish and macroinvertebrate communities in the mid-Atlantic uplands: Implications for integrated assessments

Indices developed for stream bioassessment are typically based on either fish or macroinvertebrate assemblages. These indices consist of metrics which subsume attributes of various species into aggregate measures reflecting community-level ecological responses to disturbance. However, little is known about the relationship between fish and macroinvertebrate metrics, or about how ecological health assessments are affected by assemblage-specific responses to disturbance. We used principal component analysis (PCA) and regression analysis of existing fish (n = 371) and macroinvertebrate (n = 442) stream bioassessment data from a multi-source dataset to determine broad scale, within-assemblage metric patterns, and to examine the intercorrelation of fish and macroinvertebrate metrics (n = 246) and their response to watershed area and land use/land cover gradients. Fish and macroinvertebrate metrics expressed as principal components (PCs) accounted for 72.4 and 85.4% of dataset variance, respectively, with PC-metric patterns reflecting aspects of stream impairment including water and habitat quality. Model components predicting fish metric response differed among fish PCs, with watershed area and macroinvertebrate metric response strongly correlated with the first fish PC, and remaining fish PC models consisting of watershed area, land use, and macroinvertebrate PCs. Correlation between fish and macroinvertebrate PCs, and models relating fish and macroinvertebrate PCs generally explained less variation (13–27%) than metric response models of fish (25–34%) and macroinvertebrates (8–38%) to watershed area and land use/land cover variables. Best-response models integrating fish and macroinvertebrate PCs, watershed area, and land use/land cover variables accounted for the greatest variation in fish PCs (32–50%) across sites. Because fish and macroinvertebrate metrics provide different information on ecological condition, integrated use of information from multiple groups may be appropriate when developing monitoring programs.     

Relationships Between Environmental Variables and Benthic Diatom Assemblages in California Central Valley Streams (USA)

This study examines distributional patterns of benthic diatom assemblages in relation to environmental characteristics in streams and rivers in the California Central Valley ecoregion. Benthic diatoms, water quality, and physical habitat conditions were characterized from 53 randomly selected sites. The stream sites were characterized by low mid-channel canopy cover and high channel substrate embeddedness. The waters at these sites were enriched with minerals and turbidity varied from 1.3 to 185.0 NTU with an average of 13.5 NTU. A total of 249 diatom taxa were identified. Average taxa richness was 41 with a range of 7–76. The assemblages were dominated by Staurosira construens (11%), Epithemia sorex (8%), Cocconeis placentula (7%), and Nitzschia amphibia (6%). Multivariate analyses (cluster analysis, classification tree analysis, and canonical correspondence analysis) all showed that benthic diatom assemblages were mainly affected by channel morphology, in-stream habitat, and riparian conditions. The 1st CCA axis negatively correlated with mean wetted channel width (r = −0.66) and thalweg depth (r = −0.65) (Table 4). The 2nd axis correlated with % coarse substrates (r=0.60). Our results suggest that benthic diatoms can be used for assessing physical habitat alterations in streams.     

Catchment land cover as a proxy for macroinvertebrate assemblage structure in Carpathian Mountain streams

We compared land cover, riparian vegetation, and instream habitat characteristics with stream macroinvertebrate assemblages in 25 catchments in the Carpathian Mountains in Central Europe. This study area was particularly selected because of its diverse history of forest and agricultural ecosystems linked to geopolitical dynamic, which provide a suite of unique landscape scale, land cover settings in one ecoregion. Canonical Correspondence Analysis (CCA) showed that variation in composition and structure of macroinvertebrate assemblages was primarily related to four land cover types, and not to riparian or instream habitat. These were the portions in the catchment areas of (1) broadleaved forest, (2) fine-grained agricultural landscape mosaic with scattered trees (e.g., pre-industrial cultural landscape), (3) mixed forest, and (4) natural grassland without trees. Principal Component Analysis (PCA) suggested that land cover types and stream channel substrates co-varied. The PCA also showed that chemical variables, including organic carbon, had higher values in the agricultural landscape compared to natural forests. The major source of variation among taxa in streams was higher abundance of Diptera in agricultural landscapes and of Plecoptera, Coleoptera, Trichoptera, and Amphipoda in forests. Gastropoda and Oligochaeta were more abundant in open, fine-grained agricultural landscape mosaics with scattered trees. Ephemeroptera taxa were quite indifferent to these gradients in catchment land cover, but showed a tendency of being more abundant in the pre-industrial cultural landscape. Our findings suggest that land cover can be used as a proxy of the composition and structure of macroinvertebrate assemblages. This means that land use management at the catchment scale is needed for efficient conservation and recovery of stream invertebrate communities.     

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.     

Biotelemetry of crustacean decapods: sampling design,statistical analysis,and interpretation of data

Lotic systems in many regions of the country have experienced habitat degradation and biodiversity loss due to agricultural activity and urbanization. Southeastern Michigan is no exception, as agriculture in the River Raisin watershed and increased urbanization in the Huron River watershed threatens both systems. To further understand the ecological impact of land use on trophic interactions in Midwestern streams and assess the use of a selected set of weighted, quantitative food web metrics as a tool for investigating the influence of anthropogenic disturbance on these systems we compared summer food webs for nine second-order streams. All streams were categorized as developed, undeveloped, or agricultural based on land cover data. Developed and undeveloped streams were located in the Huron River watershed and agricultural streams were located in the River Raisin watershed. Reach-level habitat quality was also assessed at each study site using the EPA’s Rapid Habitat Assessment. Fish diets (n = 410) were analyzed to create summer food webs for each site. Comparisons of food webs were made using a suite of weighted, quantitative metrics to identify differences in fish–macroinvertebrate interactions across streams with differing land cover at the sub-basin scale and habitat quality at the local scale. Although undeveloped streams had higher species richness and less habitat degradation, no significant patterns were observed in the quantitative metrics across the three stream categories or based on reach-level habitat conditions. Decapoda, terrestrial Hymenoptera, and Chironomidae were the primary prey taxa in all stream categories. Decapods accounted for the majority of biomass consumed and the pattern of this consumption strongly influenced metric scores. The suite of quantitative metrics tested in this study did not detect significant differences in fish–macroinvertebrate food webs across land use categories, likely in part due to the dominance of a large, tolerant prey taxa in fish diets, regardless of land use and local habitat quality.     

Spatial and temporal variation in fish assemblages of drying stream pools: The role of abiotic and biotic factors

Droughts and summer drying create unusual temporary aquatic habitats in the form of isolated pools in many small streams around the world. To examine spatial and temporal variation in fish community structure of drying stream pools, their relation to abiotic environmental variables, and associations among species, fish were sampled during summer 1995 and 1996 from pools of four streams in the Ozark mountains, Arkansas, USA. Redundancy analysis of physical-chemical variables showed significant differences among stream sites, but no significant difference between years or stream site by year interaction. Stream sites separated consistently along axes one (habitat heterogeneity) and two (temperature/canopy cover) in both years. Redundancy analysis of fish species-size class densities showed a significant stream site by year interaction. Groupings of stream sites based on fish assemblages were not well explained by physical-chemical variables measured at the pool scale, but were related to location within the drainage basin, and these groupings differed between years. There were 27 (15.8%) and 10 (5.8%) significant associations found among fish species-size classes in 1995 and 1996, respectively, and all but two significant associations in 1995 were positive. Pool depth, habitat heterogeneity, pool size and dissolved oxygen/canopy cover were important local abiotic factors depending on response variables examined. In both years, large fish total density, large central stoneroller density (80 mm TL), and small sunfish (<80 mm TL) density were positively related to pool depth. Otherwise, there was no consistent relationship between physical-chemical variables and dependent variables (fish density and species richness) within a year or between years for a given dependent variable. These results support the hypothesis that local abiotic factors are important in structuring fish assemblages in harsh environments, but the importance of those factors varies temporally, and regional influences appear to override local abiotic conditions as factors structuring fish assemblages in drying stream pools. Predation by terrestrial vertebrates may also be an important factor structuring these fish assemblages that has been largely overlooked.