Autumn use of woody snags by fishes in backwater and channel border habitats of a large river

Snags are important to fish communities in small rivers and streams, but their importance to fishes in large rivers has not been investigated. This study examined snag use by fishes during autumn in backwater and channel border habitats in the upper Mississippi River, and compared these to fish communities in reference sites without snags. Species assemblages differed significantly between backwater and channel border habitats, and between snag and reference sites within the channel border, likely responding to differences in substrate, depth, and current velocity. In both habitats, average fish biomass and abundance were higher (2 to 50 ×) at snag sites than at reference sites, but these differences were significant only for channel border biomass. Fish taxa richness differed between backwater and channel border habitats, but not between snag and reference sites. Most large piscivorous fishes (e.g., Micropterus spp., Stizostedion spp.), several insectivorous fishes (Lepomis macrochirus, Ambloplites rupestris, Minytrema melanops), and a few prey fishes (L. macrochirus, Notropis atherinoides) were significantly more abundant at snag sites than at reference sites, suggesting active selection of snags for foraging or protection. Snag quality, as assessed by a snag rating index, had a direct effect on attracting fish communities with greater biomass, especially within the channel border habitat. These results indicate that snags are important habitat for fish communities in both backwaters and channel border habitats of the upper Mississippi River.     

Non-wadeable river bioassessment: spatial variation of benthic diatom assemblages in Pacific Northwest rivers,USA

Current bioassessment efforts are focused on small wadeable streams, at least partly because assessing ecological conditions in non-wadeable large rivers poses many additional challenges. In this study, we sampled 20 sites in each of seven large rivers in the Pacific Northwest, USA, to characterize variation of benthic diatom assemblages among and within rivers relative to environmental conditions. Analysis of similarity (ANOSIM) indicated that diatom assemblages were significantly different among all the seven rivers draining different ecoregions. Longitudinal patterns in diatom assemblages showed river-specific features. Bray–Curtis dissimilarity index values did not increase as a function of spatial distance among the sampled reaches within any river but the Malheur. Standardized Mantel r of association between assemblage similarity and spatial distance among sites ranged from a high of 0.69 (Malheur) to a low of 0.18 (Chehalis). In the Malheur River, % monoraphids, nitrogen-tolerant taxa, and beta-mesosaprobous taxa all decreased longitudinally while % motile taxa, especially Nitzschia, showed an opposite trend, reflecting a strong in-stream water quality gradient. Similar longitudinal trends in water quality were observed in other rivers but benthic diatom assemblages showed either weak response patterns or no patterns. Our study indicated that benthic diatom assemblages can clearly reflect among-river factors. The relationships between benthic diatom assemblages and water quality within each river may depend on the strength of the water quality gradients, interactive effects of water quality and habitat conditions, and diatom sampling design.     

In situ experiments on predatory regulation of a bivalve mollusc (Dreissena polymorpha) in the Mississippi and Ohio Rivers

1. In situ exclosure experiments in the Mississippi and Ohio Rivers determined the importance of fish predation in regulating zebra mussels (Dreissena polymorpha), an increasingly important constituent of the benthic invertebrate assemblages in both rivers. 2. We evaluated the effects of predatory fish on the density, biomass and size distribution of zebra mussels in a floodplain reach of the upper Mississippi River and in a naturally constrained reach of the Ohio River. Fifty, six-sided, predator-exclusion cages and fifty ‘partial’ cages (mesh at the upstream end only) were deployed, with half the cages containing willow snags and half clay tiles suspended 12–16 cm above the bottom. A single snag or tile sample unit was removed from each cage at approximately monthly intervals from July to October 1994. Types and relative abundances of molluscivorous fish were evaluated by electrofishing near the cages in both rivers. Actual and potential recruitment of young zebra mussels on to the substrata were measured using benthic samples in both rivers and estimated (Ohio River only) from counts of planktonic veligers. 3. Zebra mussels were consumed by at least three fish species in the upper Mississippi River (mostly carp, Cyprinus carpio, and redhorse suckers, Moxostoma sp.) and five species in the Ohio River (primarily smallmouth buffalo, Ictiobus bubalus, and channel catfish, Ictalurus punctatus), but potential recruitment seemed adequate to replace consumed mussels, at least in the Ohio River. The number of juvenile benthic mussels showed no apparent link with the density of veligers soon after initiation of reproduction. Recruitment of juveniles on snags and tiles was not affected by cage type (thus eliminating a potentially confounding ‘cage effect’). 4. Fish significantly influenced mussel populations, but the impact was often greatest among low density populations in the upper Mississippi. Density and biomass differed in both rivers for cage type (higher inside cages), substratum (greater on tiles), and date (increased over time). Presumed size-selective predation was present in the Mississippi (greater on larger size classes) but was not evident in the Ohio. We hypothesize that fish in the Mississippi can more easily select larger prey from the low density populations; whereas size-selective predation on tightly packed zebra mussels in the Ohio would be difficult. 5. Although fish can reduce numbers of Dreissena polymorpha in the two rivers, current levels of fish predation seem insufficient to regulate zebra mussel densities because of its great reproductive capacity. The recent invasion of zebra mussels, however, could lead to larger fish populations while promoting greater carbon retention and overall ecosystem secondary production.     

Benthic, Drifting and Marginal Macroinvertebrate Assemblages in a Lowland River: Temporal and Spatial Variations and Size Structure

Aquatic macroinvertebrates living in anastomosing lowland rivers use different habitats and respond differently to the hydrological regime. In this paper, the structure and composition of benthic, drifting and marginal macroinvertebrate assemblages are analyzed in the lowland river Ctalamochita (Córdoba, Argentina). The assemblages were studied in an annual cycle; a comparison among the composition of benthos, drift and marginal fauna was carried out; and size structure of the assemblages was characterized. Samples were obtained from two sites: a rural and an urban site. In total 73 taxa of aquatic macroinvertebrates were collected. Benthos was characterized by Chironomidae and Oligochaeta; marginal fauna was mainly constituted by Coleoptera, Heteroptera, Decapoda, the Trichoptera Nectopsyche sp., Ephemeroptera and Odonata. Drifting assemblage was composed by macroinvertebrates from local and remote upstream benthos, and from the marginal zone. Marginal fauna diversity was higher than benthos and drift. Total biomass of the assemblages pooled together was relatively equitably among size classes. Larger size classes consisted of organisms from the marginal zone whereas the smallest ones were composed by benthic and drifting organisms. In the study area there is habitat partitioning in the lateral dimension of the river. Marginal fauna was more diverse due to the asymmetry of transport and deposit processes, which generate a heterogeneous habitat in the bankside. The relation between fine substrate and high current velocity determines an unstable habitat in the central channel, which makes colonization by benthic macroinvertebrates difficult.     

Temporal trends in algae, benthic invertebrate, and fish assemblages in streams and rivers draining basins of varying land use in the south-central United States, 1993–2007

Site-specific temporal trends in algae, benthic invertebrate, and fish assemblages were investigated in 15 streams and rivers draining basins of varying land use in the south-central United States from 1993–2007. A multivariate approach was used to identify sites with statistically significant trends in aquatic assemblages which were then tested for correlations with assemblage metrics and abiotic environmental variables (climate, water quality, streamflow, and physical habitat). Significant temporal trends in one or more of the aquatic assemblages were identified at more than half (eight of 15) of the streams in the study. Assemblage metrics and abiotic environmental variables found to be significantly correlated with aquatic assemblages differed between land use categories. For example, algal assemblages at undeveloped sites were associated with physical habitat, while algal assemblages at more anthropogenically altered sites (agricultural and urban) were associated with nutrient and streamflow metrics. In urban stream sites results indicate that streamflow metrics may act as important controls on water quality conditions, as represented by aquatic assemblage metrics. The site-specific identification of biotic trends and abiotic–biotic relations presented here will provide valuable information that can inform interpretation of continued monitoring data and the design of future studies. In addition, the subsets of abiotic variables identified as potentially important drivers of change in aquatic assemblages provide policy makers and resource managers with information that will assist in the design and implementation of monitoring programs aimed at the protection of aquatic resources.     

Longitudinal changes in macroinvertebrate assemblages along a glacial river system in central Iceland

1. Macroinvertebrate assemblages were studied in the glacial river West-Jökulsá, originating from the Hofsjökull Ice Cap in central Iceland at an altitude of 860 m. Sampling sites were distributed from the source to 45 km downstream at 160 m a.s.l. Comparative studies were carried out on non-glacial rivers and tributaries in the area, at similar altitudes and distances from the glacial source.
2. Detrended correspondence analysis (DCA) demonstrated that species composition of benthic macroinvertebrates was related to the distance from the glacier. Assemblages at sampling sites furthest from the glacier were similar in species composition to sites in non-glacial rivers. Temporal variation was small compared with longitudinal zonation.
3. Based on canonical correspondence analysis (CCA) of data from the main glacial river, distance from the glacier, altitude, bryophyte biomass and the Pfankuch Index of channel stability were the measured explanatory variables having a significant effect on the structure of macroinvertebrate assemblages, accounting for 31% of the total variation in the data set. When data from all the rivers were analysed, altitude, bryophyte biomass, channel slope, suspended sediment concentration and maximum water temperature explained 21% of the variance.
4. Macroinvertebrate communities were in general agreement with the predictions of the conceptual model of Milner & Petts (1994) for the upstream reaches. The assemblages consisted mainly of Orthocladiinae and Diamesinae (Chironomidae), although other taxa such as Simuliidae, Plecoptera and Trichoptera were also found in low numbers. Shredders were lacking from the benthic communities, apparently because of continued glacial influence in the river even 45 km downstream from the glacier and lack of allochthononus inputs from riparian vegetation.     

Substrate specificity,environmental degradation and disturbance structuring macroinvertebrate assemblages in neotropical streams

Structure and composition of benthic macroinvertebrate assemblages were investigated in seven sampling sites with a gradient of environmental integrity and water quality conditions. Composite samples of the four most representative substrates were collected in order to characterize the riffle-pool dynamic in each sampling site. Spatial and temporal variability of macroinvertebrate assemblages were analyzed at two scales: using substrates and grouping samples for comparing sampling sites. Distribution of macroinvertebrates was influenced primarily by substrate type, but also by environmental integrity, water quality and sampling period. Species occurrence was highly dependent on substrate type. At local spatial scale, environmental degradation measured by the Riparian Channel Environmental Inventory and water chemistry were the determinants of assemblage patterns. We evaluated to which extent the substrates were influenced by environmental integrity and water chemistry, and we found that degradation influenced significantly the macroinvertebrate fauna on the four substrate types, although they were not responding to the same variables. Our results show that qualitatively communities were not influenced by seasonal changes, but abundance was stochastically dependent on rainfall.     

Characterization of diatom assemblages in mid-altitude streams of NW Italy

Following the European Water Framework Directive, this study aims to be the first step to (i) identify diatom type assemblages in unpolluted streams in NW Italy, and (ii) find which ecological factors explain most of the variation. To achieve this, we collected physical, chemical and benthic community data from four streams in NW Italy from 2001 to 2004, for a total of 72 samples. All sampling sites were between 200 m a.s.l. and 800 m a.s.l., but differed in the dominant lithological substrate, i.e. alluvial or siliceous. Relationships between diatom communities and environmental factors were examined using canonical correspondence analysis (CCA), while Indicator Species Analysis was used to define characterizing species and accompanying species of three environmental groups identified by CCA: (1) high water quality and medium saline content, (2) high water quality and low saline content, (3) poor water quality. The diatom assemblages of the three groups of sites differed significantly, as shown by the Multi-Response Permutation Procedure. There were strong correlations between diatoms and environmental factors, especially chlorides (also highly correlated with sulphates and carbonate hardness), nitrate concentration and conductivity. The group 1 assemblage was typical of the alluvial Alpine streams with medium saline content and was characterized by mostly oligosaprobic/β-mesosaprobic taxa such as Cymbella affinis, Diatoma ehrenbergii and Staurosira pinnata. The species assemblage found in the siliceous Alpine rivers with good water quality make them suitable reference sites for a benthic diatom community. Electronic Supplementary Material Supplementary material is available for this article at and accessible for authorised users Handling editor: K. Martens     

The significance of littoral and shoreline habitat integrity to the conservation of lacustrine damselflies (Odonata)

Human development of pond and lake shorelines may significantly impact native lacustrine biota including a variety of aquatic macroinvertebrate groups. In an effort to better understand the habitat associations and sensitivities of lacustrine damselflies (Odonata: Zygoptera), we sampled adults in littoral macrophyte habitat during two flight periods at 35 randomly selected pond and lake sites in southern Maine during 2000 and 2001. Data were also collected to help characterize water body, shoreline disturbance, and aquatic vegetation at each study site. Nonmetric multidimensional scaling was used for ordination of damselfly assemblages, and coordinates from the most stable solution were related to site variables using forward stepwise multiple regression. Our results suggest that the diversity and composition of damselfly assemblages is related to the abundance and richness of littoral zone macrophytes, extent of riparian disturbance, benthic substrate granularity, and lake productivity; all variables subject to anthropogenic degradation on excessively developed waterbodies. Additionally, we developed a Habitat Tolerance Index useful for distinguishing between relative habitat specialists and generalists from among a diverse assemblage of 19 lacustrine species. Finally, species-specific damselfly associations with multiple genera of floating and emergent macrophytes were assessed using both nonparametric correlation and multiplicative regression yielding significant relationships for 17 species, including two damselflies of global conservation concern (Enallagma laterale and E. pictum). We conclude that the protection of littoral and shoreline habitat integrity, with special emphasis on emergent and floating macrophytes, is critical to the conservation of lacustrine biodiversity.     

Links Between Anthropogenic Perturbations and Benthic Macroinvertebrate Assemblages in Afromontane Forest Streams in Uganda

Relationships between environmental variables and benthic macroinvertebrate assemblages were investigated among several sites that varied in disturbance history in Bwindi Impenetrable National Park, an Afromontane site in East Africa. Environmental variables were correlated with the level of past catchment disturbance – logging, agricultural encroachment, and present tourism activity. For example, sites in medium and high disturbance categories had higher values of specific conductance and lower water transparency than low disturbance category sites, these environmental variables may therefore act indicators of ecological quality of rivers. Environmental variables such as conductivity and water transparency were found to be good predictors of benthic macroinvertebrate assemblages, with anthropogenically stressed sites having lower diversity than the reference sites. Impacted sites were dominated by tolerant taxa such as chironomid and leeches, while ‘clean water’ taxa such as Ephemeroptera, Plecoptera and Trichoptera dominated at minimally impacted sites. Comparison of sites with different disturbance histories provided evidence for differences in benthic macroinvertebrate communities that reflect the state of forest restoration and recovery. We recommend quarterly monitoring of water quality to act as an early warning system of deterioration and tracking ecological recovery of previously impacted sites.     

Regional and local drivers of macroinvertebrate assemblages in boreal springs

Aim To identify the most important environmental drivers of benthic macroinvertebrate assemblages in boreal springs at different spatial scales, and to assess how well benthic assemblages correspond to terrestrially derived ecoregions. Location Finland. Methods Benthic invertebrates were sampled from 153 springs across four boreal ecoregions of Finland, and these data were used to analyse patterns in assemblage variation in relation to environmental factors. Species data were classified using hierarchical divisive clustering (twinspan ) and ordinated using non‐metric multidimensional scaling. The prediction success of the species and environmental data into a priori (ecoregions) and a posteriori (twinspan ) groups was compared using discriminant function analysis. Indicator species analysis was used to identify indicator taxa for both a priori and a posteriori assemblage types. Results The main patterns in assemblage clusters were related to large‐scale geographical variation in temperature. A secondary gradient in species data reflected variation in local habitat structure, particularly abundance of minerogenic spring brooks. Water chemistry variables were only weakly related to assemblage variation. Several indicator species representing southern faunistic elements in boreal springs were identified. Discriminant function analysis showed poorer success in classifying sites into ecoregions based on environmental than on species data. Similarly, when classifying springs into the twinspan groups, classification based on species data vastly outperformed that based on environmental data. Main conclusions A latitudinal zonation pattern of spring assemblages driven by regional thermal conditions is documented, closely paralleling corresponding latitudinal patterns in both terrestrial and freshwater assemblages in Fennoscandia. The importance of local‐scale environmental variables increased with decreasing spatial extent. Ecoregions provide an initial stratification scheme for the bioassessment of benthic macroinvertebrates of North European springs. Our results imply that climate warming, landscape disturbance and degradation of spring habitat pose serious threats to spring biodiversity in northern Europe, especially to its already threatened southern faunistic elements.     

Spatial autocorrelation of assemblages of benthic invertebrates and its relationship to environmental factors in two upland rivers in southeastern Australia

The nature of spatial autocorrelation of biota may reveal much about underlying ecological and biological factors responsible for producing those patterns, especially dispersal processes (drift, adult flight, etc.). We report here on assemblage‐level autocorrelation in the benthic‐invertebrate assemblages (retained in sieves of 300 µm mesh) of riffles in two adjacent, relatively pristine rivers in southeastern Victoria, Australia (40‐km reaches of the Wellington and Wonnangatta Rivers). These are related to patterns of autocorrelation in physical and catchment conditions (‘environmental variables’) in the vicinity of the sampling points. Both the invertebrate assemblages and environmental variables were autocorrelated at small scales (= 8 km) in the Wellington River in one of the sampling years (1996). Dissimilarities of invertebrate assemblages were correlated with dissimilarities of environmental variables in both sampling years (1996 and 1997) in that river. Environmental variables were autocorrelated in the Wonnangatta River, but this was not expressed as autocorrelation in the assemblages of invertebrates, which were not autocorrelated at any scale studied. Individual environmental variables showed different spatial patterns between the two rivers. These results suggest that individual rivers have their own idiosyncratic patterns and one cannot assume that even similar, geographically adjacent rivers will have the same patterns, which is a difficulty for ecological assessment and restoration.     

Impact of the longitudinal and seasonal changes of the water quality on the benthic macroinvertebrate assemblages of the Andorran streams

The ecological quality of the Andorran streams was assessed in 1998-1999, based on the survey of the water chemistry and the benthic macroinvertebrate assemblages. Two types of modification of the water quality were observed in the Andorran rivers: (i) a progressive degradation along the longitudinal gradient with a chronic degradation in the lower water courses; (ii) a seasonal modification in the mid-elevation sites. Two responses of the benthic macroinvertebrate assemblages to these disturbances were observed: an extreme simplification of the composition and a change of the trophic structure of the assemblages in the more impacted sites.     

Epilithic diatoms as indicators in tropical African rivers (Lake Victoria catchment)

We investigated epilithic diatoms in rivers draining to the Nyanza Bay in Lake Victoria (Kenya) with the aim of determining environmental gradients in the assemblages and testing the usefulness of diatom metrics from temperate regions. Spatial and temporal variations of assemblages were studied in 12 sites of three rivers. Kibos, Nyando, and Kisat rivers contained 224 diatom taxa collected on seven sampling occasions over 4 years. Species richness showed a marginal decrease downstream and was the lowest at sites with high conductivity and ammonia–nitrogen levels. Two-Way Indicator Species Analysis and Canonical Correspondence Analysis revealed two major groups of river sites. Conductivity, alkalinity, turbidity, dissolved oxygen, and silicate were the most important variables influencing species distribution. Ecological diatom metrics of temperate regions and the Specific Pollution sensitivity Index showed good relationships with environmental variables. Both diatom assemblages and averaged indicator values were strong in predicting sites of ecological deterioration and in differentiating an upstream site of better quality (drinking water supply of Kisumu), thereby confirming epilithic diatoms as suitable water quality indicators in equatorial rivers. The use of metrics initially designed for temperate rivers, however, appears less valuable in good quality tropical rivers because potential indicators are not considered.     

The effects of land use on environmental features and functional organization of macroinvertebrate communities in Patagonian low order streams

Benthic invertebrates, water quality variables, chlorophyll a and particulate organic matter (POM) were studied in 18 sites of mountain streams in Patagonia (Argentina) subjected to six different land uses: native forest, pine plantation, pasture, harvest forest, urban and reference urban. Three streams of each land use were studied in March 2006. Macroinvertebrates were sampled in three riffles and three pools (n = 108) and biomass of detrital fractions of POM were quantified. Overall benthic POM biomass was higher at native and harvest forest than pastures, whereas fine fraction (FPOM) was higher in harvest forest than in pastures. Regarding to autotrophic subsidies bryophytes were the only that changed consistently among uses. These differences in energy resources were correlated with changes in community attributes. Shredder richness was clearly higher at native and harvest forest than exotic pine plantations, collector gatherers density was consistently high at harvest sites, and total density was significantly higher at urban and harvest forest. Multidimensional scaling ordination based on macroinvertebrate density data showed a clear separation of forested (either native or exotic species) from riparian modified areas (pasture, urban and harvest sites). Environmental variables having explanation power on macroinvertebrate assemblages were mostly related with: detritus availability (wood and leaves biomass) and impairment (total phosphorous and % sand). These results confirm that macroinvertebrate assemblage structure in Patagonian low order streams can be altered by land use practices. Among guild structure measures, those indicators based on benthic community functional attributes, shredders richness and collectors density, resulted good candidates to assess land use impacts. On account of riparian corridor management may be critical to the distribution of benthic taxa, the maintenance of good conditions of vegetation adjacent to rivers will enhance water quality and the environment for highly endemic headwater communities of Patagonian streams.     

Associations between fish assemblages and environmental factors for Mediterranean-type rivers during summer

The structure of summer fish assemblages was examined along longitudinal gradients in 31 Mediterranean-type rivers of the middle Guadiana basin (south-west Iberian Peninsula), using data from 157 sites including small streams to deep rivers. An ordination analysis, based on 16 variables, was applied to species presence, using principal component and canonical correspondence analysis. The results for the habitat data were compared with those for the biological data using a Mantel analysis, and the agreement was highly significant. Spatial structure was considered by partitioning the total variability among the environmental and geographical variables. The fish assemblages showed longitudinal zoning during the summer, with species distributed over gradients of habitat size (depth), water quality (current and physico-chemical variables), and cover (substratum and vegetation), according to their adult size and life history. The size of the habitat that remained available in summer had the greatest biological effect, being the most important factor explaining fish species distribution and assemblage structure during this stressing season. Strictly spatial variation was low, but there was still a high residual variation. Habitat associations and life-history strategies are discussed for native and exotic species.     

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.     

Effects of a pulp and paper mill on the ecology of the La Trobe River,Victoria, Australia

Four riverine animal communities were measured to assess the impact of extensively treated wastewater from a pulp and paper mill on the lower La Trobe River in Victoria, Australia. Benthic macroinvertebrates in channel and bankside habitats were sampled using a new air-lift corer. Population density was expressed in relation to substrate volume. Other communities measured at five sites upstream and downstream of the mill's wastewater outfall were the zooplankton, and the animals associated with submerged littoral vegetation. Ten environmental variables were also measured during the two sampling periods.A total of 50 benthic macro-invertebrate taxa were dominated by Oligochaeta, Chironomidae and Bivalvia. Benthic communities upstream and downstream of the outfall were very similar. Benthic samples showed large unexplained variation between stations and seasons, despite the similarity of stations and the stratified sampling design, but within-sample variation was small. There was some evidence that benthic faunal patchiness was associated with patterns of stream-bed scouring and deposition in periods of high flow. Littoral samples collected 28 taxa, dominated by Decapoda and Hemiptera. The benthic and littoral communities were quite distinct, with only three species common to both.Only two of the biological and environmental variables responded to wastewater from the mill: total dissolved solids rose by 20–25% over upstream levels; and zooplankton density increased by 2–3 orders of magnitude. It was concluded that wastewater treatment had successfully avoided the major environmental problems often associated with pulp and paper mills.     

Development of a regional macroinvertebrate index for large river bioassessment

Large river bioassessment protocols lag far behind those of wadeable streams and often rely on fish assemblages of individual rivers. We developed a regional macroinvertebrate index and assessed relative condition of six large river tributaries to the upper Mississippi and Ohio rivers, Midwest USA. In 2004 and 2005, benthic macroinvertebrates, water chemistry, and habitat data were collected from randomly selected sites on each of the St. Croix, Wisconsin, Minnesota, Scioto, Wabash, and Illinois rivers. We first identified the human disturbance gradient using principal components analysis (PCA) of abiotic data. From the PCA, least disturbed sites showed strong separation from stressed sites along a gradient contrasting high water clarity, canopy cover, habitat scores, and plant-based substrates at one end and higher conductivity and nutrient concentrations at the other. Evaluation of 97 benthic metrics identified those with good range, responsiveness, and relative scope of impairment, as well as redundancies with other metrics. The final index was composed of Diptera taxa richness, EPT taxa richness, Coleoptera taxa richness, percent oligochaete and leech taxa, percent collector-filterer individuals, predator taxa richness, percent burrower taxa, tolerant taxa richness, and percent facultative individuals. Each of the selected metrics was scored using upper and lower thresholds based on all sites, and averaging across the nine metric scores, we obtained the Non-wadeable Macroinvertebrate Assemblage Condition Index (NMACI). The NMACI showed a strong response to disturbance using a validation data set and was highly correlated with non-metric multidimensional scaling (NMDS) ordination axes of benthic taxa. The cumulative distribution function of index scores for each river showed qualitative differences in condition among rivers. NMACI scores were highest for the federally protected St. Croix River and lowest for the Illinois River. Other rivers were intermediate and generally reflected the mixture of land use types within individual basins. Use of regional reference sites, though setting a high level of expectation, provides a valuable frame of reference for the potential of large river benthic communities that will aid management and restoration efforts.