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Specific leaf area (SLA) is one of the most widely researched plant traits, integrating multiple functions and reflecting plant resource acquisition strategies. However, the underlying mechanisms that drive temporal and spatial variation in SLA are still not clear. We used a combination of transect investigation and short-term manipulative experiments to identify patterns of variation in SLA over naturally occurring and simulated environmental gradients. We measured SLA of 631 species from the Tibetan (TP), Loess (LP), and Mongolian Plateaus (MP), where plant growth is limited by temperature, soil nutrient availability, and precipitation, respectively. In each plateau, we established an east–west transect of 10 sites, including meadow steppe (meadow), typical steppe (steppe), and desert steppe (desert) habitats. We further measured SLA of 15 species from the TP and MP, using manipulative experiments that altered temperature, precipitation and soil nitrogen levels. SLA ranged from 0.9 to 58.90 m2 kg−1 on average, and was significantly larger in desert than in meadow and steppe, except in the LP. Plants from the TP had significantly lower SLA than those from the LP and MP, but variation in SLA across the environmental gradients was small and consistent across the three plateaus. Conversely, the short-term manipulative experiments revealed that SLA increased with resource availability. Shifts in SLA across the broad environmental gradients was relatively small, and SLA had high sensitivity to short-term resource enrichment, suggesting that grassland species in these plateaus express divergent short- (acclimation) and long-term responses (adaptation) to the environment, which may be an important strategy for coping with ongoing shifts in climate.

The stomata control carbon and water vapor exchange between the leaves and atmosphere and may reflect plant adaptation to climate change to some extent. However, the spatial variation of stomatal traits on different sides of the leaves’ epidermis and their response to environmental changes remain unclear. Here, we measured stomatal density (SD), stomatal size (SS), and stomatal relative area (SRA) on both leaf surfaces of 181 plant species across an environmental gradient on the Loess Plateau. We calculated the proportion of stomatal traits between different epidermis surfaces of the leaves (abaxial and adaxial) and measured the total SD (SDtot), total SS (SStot), and total SRA (SRAtot) of the leaves as a whole. The SDtot, SStot, and SRAtot showed a log-normal distribution, differing across grassland types and plant functional groups, with a range of 22.57–890.09 stomata mm−2, 84.61–2022.81 μm2, and 0.51–43.71%, respectively. The SDtot, SStot, and SRAtot differed significantly between different grassland types. Meadow plants had larger SDtot, desert plants had larger SStot, and typical grassland plants had relatively larger SRAtot. The abaxial SD and SRA of the woody plants were significantly higher than those of herbaceous plants, but no significant differences were observed at the adaxial surface or for the overall leaf. A higher SDtot was correlated with a larger stomatal density ratio (R.SD) and smaller stomatal size ratio (R.SS). The R.SD, abaxial SD, abaxial SS, and adaxial SS were significantly correlated with environmental factors, but no such correlations were observed for the adaxial SD. These findings highlight the strong associations of stomatal traits with plant functional group and climate at a regional scale, representing the climatic adaptation strategies of stomatal traits across natural grassland communities.

The variation of phenotypic traits with environmental gradient can reveal the plant adapting strategies and predict reactions to future climate changes. However, it remains elusive, especially for alpine timberline tree species. To quantify the variation and explore the patterns of twig, leaf, stoma traits, and determine the scaling relationships along the topographic gradients, 576 current-year branches of Larix potaninii ssp. chinensis were collected and scaling relationships were analyzed. The results showed that the twig, leaf and stoma traits varied nonlinearly along altitudinal gradients (2900–3500 m) in both sunny and shady slopes, with a reversal point at about 3250 m, at which the optimum growth of twig length (78.53 mm), twig cross-sectional area (3.35 mm2), internode length (13.14 mm), leaf length (19.30 mm), specific leaf area (0.01 mm2mg−1), stomatal length (47.05 µm) and density (160.20 mm−2). In addition, the values of leafing intensity, leaf number and stomatal density on sunny slope, 1.52 mm−3, 88.79 and 160.20 mm−2 respectively, were higher than that on shady slope. Moreover, the relationships between leaf-twig traits were significantly correlative, and the leaf area-twig cross-sectional area and leaf intensity-leaf area scaling relationships were allometric (slope ≠ 1 or slope ≠ −1) and showed common slope with different y-intercept across altitudes and slope aspects (P

The use of functional trait analysis has been advocated to uncover the global mechanisms behind biodiversity responses to environmental variation, but the application of this approach to the Arctic macrobenthic community is underdeveloped relative to that used for other organism groups. Based on several summer surveys (July to September 2010, 2012, 2014 and 2016) in the Bering Sea, we used biological trait analysis (BTA) to quantify the composition and diversity of macrobenthic biological traits along an environmental gradient ranging from the shallowest portion of the continental shelf to the shelf break and deep basin. Our results show a clear shift in the macrobenthic functional composition through the application of abundance- and biomass-based measurements in six different subregions of the Bering Sea. The macrobenthic community of the south-western shelf and shelf break of the Bering Sea, an area with silty-sand sediment, was mainly composed of taxa characterized by high body flexibility, vermiform, and tube-dweller/burrower modalities or large, semi-motile, deposit feeder and flattened dorsally modalities. However, the community of the north-eastern shelf of the Bering Sea with sandy sediment was mainly characterized by organisms characterized as motile surface crawlers and carnivores/scavengers. Similar to the factors that determine the taxonomic distribution and composition of the macrobenthos, sediment composition and depth were found to be the main factors that affect the distribution of the macrobenthic functional structure in the study area. The species and functional diversity of the macrobenthos show a strong linear relationship, potentially indicating that the community exhibits relatively low functional redundancy and that the benthic ecosystem is vulnerable to species loss or regime shifts.

The use of borrowed indices to assess stream health has limitations and research suggests a need to develop more reliable regionally based indices that are sensitive to the relationship between taxa and environmental conditions. Implementing this is challenging in the Southern Hemisphere given the scarcity of diatom indices, specifically in sub-tropical areas. The purpose of this study was to develop a regionally based diatom index to assess freshwater lotic systems in sub-tropical eastern Australia and compare the results with borrowed indices to derive meaningful inferences on river health. A total of 119 epilithic diatom and water samples were collected during 2014–2015 from the Richmond River Catchment in Northern NSW Australia. Statistical analysis indicated that total phosphorus (TP) and total nitrogen (TN) were strong variables influencing the data set and subsequently TP was chosen as a nutrient proxy for the index. Analysis of diatoms resulted in TP sensitivity values (1–5) being assigned to 105 species with relative abundance of >1% in the data set. These species were used to calculate the Richmond River Diatom Index (RRDI) for 45 sites within the Catchment. The index effectively scored sites along the environmental gradient with sites in the upper catchment generally scoring lower (healthier) than the mid and lower catchment sites. The index compared positively with both the Diatom Species Index for Australian Rivers (DSIAR) (r = 0.76) and the Trophic Diatom Index (TDI) (r = 0.65). Further research is suggested to test the RRDI on independent sites in neighbouring catchments and develop class boundaries from the RRDI so that the index can be readily used by water managers to assess and monitor freshwater systems in sub-tropical Australia.

Limited predictability of cyanobacteria and algal harmful blooms (CyanoHABs) impairs the development of adequate water management programs. The Microcystis aeruginosa complex (MAC) is ubiquitous worldwide. Their large colony size and relatively low numerical abundance imply that MAC abundance and presence are usually underestimated in traditional phytoplankton quantifications, which are based on samples of small volume. The objective of this work was twofold: (a) evaluate four sampling strategies of increasing sampling size to detect MAC organisms and (b) asses the predictability of MAC presence using easy-to-measure environmental variables. Sampling strategies were (I) 5–25 mL sedimented water samples inspected under inverted light microscope; (II) 20 L of water samples inspected by on-board naked-eye; (III) samples collected by towing a 25 μm pore size net inspected under light microscope; (IV) naked-eye inspection of 1000–7000 L concentrated water samples collected using a 115 μm-pore plankton net. We evaluated these objectives in a large environmental gradient (800 km) from freshwater to marine water (salinity range = 0–33) covering a wide range of temperatures (10–33 °C), underwater turbidity (0–158 NTU) and wind intensity (0–8 ms −1 ). Classification Random Forest models (presence/absence of MAC organisms) were constructed and evaluated for each strategy by randomly partitioning data into training (2/3) and test (1/3) sets. A systematic increase in average accuracy (from 51 to 90%) and sensitivity (from 45 to 94%) towards methods with larger sampling size was found ( i.e. I–IV). The best obtained model showed a high accuracy (90%) and sensitivity (94%) to detect MAC presence. These results suggest that the presence of MAC organisms can be accurately predicted using easy-to-measure environmental variables once sampling size is adequate. The proposed methodology demands very low costs and could be readily incorporated in most water monitoring plans to provide early warning of MAC occurrence, even when there is a low biomass of organisms.

Testate amoeba communities are influenced by temporal variation in the productivity levels in the environment, and may be used as an indicator group for these changing conditions. Here, we analysed the effect of temporal variation in the levels of productivity variables on testate amoeba community of the upper Parana River floodplain. We evaluated the hypothesis that the frequency and abundance of the testate amoeba community change along an environmental gradient, with different taxa establishing at different points along the gradient in response to changes in the levels of productivity variables. We predicted that the number of species would increase and decrease at points associated with higher and lower levels of productivity variables, respectively. Testate amoeba species were sampled quarterly between 2000 and 2012 from six lakes in the upper Parana River floodplain, Brazil. We recorded 110 species belonging to 11 families. Threshold Indicator Taxa Analysis identified positive and negative significant shift points in response to the concentration of chlorophyll-a, total nitrogen, and total phosphorus on the frequency and abundance of the testate amoeba community. Our results indicated that change intervals in the levels of productivity variables were associated with the establishment of different taxa. The main bioindicator species of productivity were Difflugia acuminata, D. amphoralis, D. helvetica multilobata, D. kempny, D. lobostoma multilobata, D. parva, D. schurmanni, D. ventricosa, and Lesquereusia ovalis. These species were linked to the increase and decrease in the levels of productivity, confirming the ecological importance of the role of these organisms as bioindicators in aquatic ecosystems.

Questions Does the plant species composition of Thandiani sub Forests Division (TsFD) correlate with edaphic, topographic and climatic variables? Is it possible to identify different plant communities in relation to environmental gradients with special emphasis on indicator species? Can this approach to vegetation classification support conservation planning? Location Thandiani sub Forests Division, Western Himalayas. Methods Quantitative and qualitative characteristics of species along with environmental variables were measured using a randomly stratified design to identify the major plant communities and indicator species of the Thandiani sub Forests Division. Species composition was recorded in 10 × 2.5 × 2 and 0.5 × 0.5 m square plots for trees, shrubs and herbs, respectively. GPS, edaphic and topographic data were also recorded for each sample plot. A total of 1500 quadrats were established in 50 sampling stations along eight altitudinal transects encompassing eastern, western, northern and southern aspects (slopes). The altitudinal range of the study area was 1290 m to 2626 m above sea level using. The relationships between species composition and environmental variables were analyzed using Two Way Cluster Analysis (TWCA) and Indicator Species Analysis (ISA) via PCORD version 5. Results A total of 252 plant species belonging to 97 families were identified. TWCA and ISA recognized five plant communities. ISA additionally revealed that mountain slope aspect, soil pH and soil electrical conductivity were the strongest environmental factors (p ≤ 0.05) determining plant community composition and indicator species in each habitat. The results also show the strength of the environment-species relationship using Monte Carlo procedures. Conclusions An analysis of vegetation along an environmental gradient in the Thandiani sub Forests Division using the Braun-Blanquet approach confirmed by robust tools of multivariate statistics identified indicators of each sort of microclimatic zones/vegetation communities which could further be used in conservation planning and management not only in the area studied but in the adjacent regions exhibit similar sort of environmental conditions.

A range of factors may determine the structure of ecological communities in time and space, in particular niches, dispersal limits, and the evolutionary history of the species. In the last decades, the traditional focus of community ecology on species diversity and composition have been supplemented by approaches incorporating functional traits and phylogeny. Following this perspective, we evaluated the response pattern of adult damselflies and dragonflies (Odonata) along a gradient of environmental disturbance in Brazilian Amazonia, with the objective of identifying subgroups of species that respond in a similar manner to environmental filters. The study tested the hypothesis that the subgroups of species with similar responses to the environmental gradient are structured phylogenetically and will be morphologically more similar to one another than they are to the other species. Adult odonates were sampled in 98 Amazonian streams, 48 in the region of Santarem and Belterra and 50 in the municipality of Paragominas, both located in the Brazilian state of Para. The study was based on an ecological niche modeling approach and statistical significance testing methods to identify groups of species. These species groups (latent classes) were then associated with their morphological characteristics (Abdomen Length and Thorax Length) and phylogenetic relationships. Four latent classes, containing 34 species, were generated for each region. The latent classes of the Odonata formed along the gradient of anthropogenic impact had effects of phylogenetic proximity and the species' morphological similarity. Therefore, species belonging to the same latent class are more morphologically similar and have greater similarities in evolutionary history. It seems likely, however, that other processes may be important for the understanding of the structuring of the latent classes, such as intra- and interspecific relationships, environmental plasticity, and the history of land use. Both morphology and phylogeny are important for understanding species' responses to environmental gradients.

Ecological quality assessment of non-natural water bodies is, in contrast to natural systems, less developed and requires determining biological indicators that reliably reflect environmental conditions and anthropogenic pressures. This study was motivated to propose fish indicators appropriate for assessment of reservoir ecosystems in central Europe. We analysed changes in water quality, total biomass and the taxonomic, trophic and size composition of fish communities along the longitudinal axes of four elongated, deep-valley reservoirs. Due to high nutrient inputs from their catchments, the reservoirs exhibited pronounced within-system gradients in primary productivity and water transparency. Although fish communities were similar among the reservoirs and dominated by few native species, the community structure and biomass systematically changed along the longitudinal axes of the reservoirs. The biomass and proportion of planktivores/benthivores in the fish community were highest at eutrophic sites near the river inflow and declined substantially towards deep, more oligotrophic sites close to the dam. The biomass and proportion of piscivores significantly increased downstream within the reservoirs alongside improving water quality. At species level, perch Perca fluviatilis and bream Abramis brama responded most sensitively, although in opposite directions, to the longitudinal environmental gradient. The major longitudinal changes in fish community characteristics were found to be consistent between pelagic and benthic habitats. The results of this study suggest that fish communities are appropriate indicators of eutrophication and can be used for ecological quality assessment of non-natural lentic water bodies, such as reservoirs. Moreover, our results underline the necessity to consider within-system gradients in water quality and the fish community when planning sampling programmes for deep-valley reservoirs.

The usefulness of benthic multi-metric indices when assessing seafloor integrity across broad environmental gradients should be deliberated, as their lack of transparency might hide important sources of variation and fail to identify environmental change. This study compares the performance of two multi-metric indices; the Benthic Quality Index (BQI) and the Brackish water Benthic Index (BBI) between three sub-basins in the Baltic Sea. Both indices reflect the salinity-driven gradient in macroinvertebrate diversity and composition as well as changes in bottom water oxygen concentrations. The relative contribution of predictor variables for explaining index variation does, however, differ between sub-basins, resulting in the indices representing different aspects of the benthic community along the environmental gradient. This context-dependency is caused by inherent differences in benthic community characteristics between the sub-basins of the Baltic Sea, and how the communities are portrayed by the indices. An increased transparency of the importance of the different predictors for directing index values is needed for coherent classifications over broad environmental gradients, such as those occurring in large estuarine water bodies. Use of a weight of evidence table to combine multiple indicators would preserve transparency and be more likely to provide a robust assessment method that would detect seafloor degradation at an early stage.

The search for biological surrogate groups has been an active and contentious area of research. A surrogate group is defined as one that allows researchers to detect a known spatial and temporal environmental gradient and to represent the responses of other biological groups to those gradients. Using spatiotemporal zooplankton data from a near-pristine floodplain (the Araguaia River floodplain in Central Brazil), we first assessed the capacity of four zooplankton assemblages (Cladocera, Copepoda, Rotifera and Protozoa) to depict the effects of flooding. Second, we evaluated whether, during each hydrological period, ordination patterns derived from an assemblage matched those patterns shown by a second assemblage and by the environmental dataset. All four assemblages satisfactorily detected the environmental differences caused by the flood event. Most pairs of assemblages were significantly concordant. Additionally, the ordination patterns generated by these assemblages matched those generated by the environmental data. These results suggest that the patterns of concordance were mediated by similar responses to environmental gradients. However, the strengths of concordance between the assemblages, albeit significant, were low. Our results suggest the potential for use of the surrogacy approach in monitoring hydrological changes. However, due to the low strengths of concordance, the biodiversity pattern revealed by a specific assemblage is unlikely to be a good predictor of another. We also highlighted that conducting a formal meta-analysis on strengths of concordance between assemblages would be a promising avenue for further research.

Freshwater organisms face numerous stressors, such as nutrient enrichment, contaminant pollution, sedimentation and alterations in stream hydrology and habitat structure. One of the most significant and widespread stressors in European freshwaters is expected to be water pollution from intensive land use. However, the information on critical threshold concentrations at which taxa decline or increase in frequency and abundance is missing for the large majority of river benthic invertebrate taxa. The main aim was to determine ecological change points for benthic invertebrate taxa at which rapid alterations in species frequency and abundance occur as a consequence of relatively small changes in the environmental gradient. These change points can be interpreted as critical threshold concentrations. A total of 468 river benthic invertebrate taxa and nine physico-chemical variables describing the daytime dissolved oxygen, chloride, nutrient concentrations and organic load were analyzed. We selected 751 river sites from a nationwide range of locations in Germany for this investigation. Depending on the physico-chemical variable, between 20.6% and 48.8% of the total number of tested taxa were assigned with a valid change point. All taxa were assigned to negative or positive response groups depending on the response direction. Except for daytime dissolved oxygen, negative responding taxa are referred to as decreasers and positive responding taxa as increasers, respectively. In total, 25.8–100% of the decreasers’ change points were below (and above in the case of daytime dissolved oxygen) the background values defined as quality criteria for German rivers by the water authorities. This indicates that stricter quality criteria may need to be set to reach the good ecological status according to the European Water Framework Directive. The calculated daytime dissolved oxygen change points were essentially in line with the species saprobic values and taxon-specific change points for physico-chemical variables fit well with the data provided in other international studies. We deliver valuable knowledge about the sensitivities and response schemes of river benthic invertebrate species. This information is especially useful for the development of efficient management and policy tools to predict the likelihood of occurrence of individual species under different levels of anthropogenic impact.

The Laurentian Great Lakes coastal wetlands are highly productive and biologically diverse ecosystems. Ongoing environmental degradation and wetland loss have resulted in a number of restoration and conservation programs. To facilitate reporting on the health and recovery of these wetlands, various indices of ecological integrity have been developed to distill complex biotic community data into results that are easy to interpret and understand. The Index of Ecological Condition (IEC) approach uses a probabilistic framework to derive an index by fitting the observed assemblage of species based on species occurrence along an a priori environmental gradient. This study refines the original IEC by Howe et al. (2007a) using updated methodologies and focusing on marsh bird communities in lower Great Lakes coastal wetlands. The a priori environmental gradient was redeveloped using finer-scale (minimum mapping unit = 50 m2) landscape data than Howe et al. (2007a), including Phragmites australis as an invasive stressor, and incorporating measures of water quality and submerged aquatic vegetation as watershed-level disturbances. The environmental gradient showed a good relationship with known anthropogenic disturbances. Marsh bird communities were surveyed in lakes Erie and Ontario and wetland species with clear responses to the environmental gradient were selected for inclusion in the IEC. Where detection was low, species were grouped into multispecies guilds. The resulting IEC was comprised of 15 biotic response functions: 12 individual species and 3 species guilds, and was highly correlated with the a priori environmental gradient (R2 = 0.54). Species with strong positive responses included Canada Goose (Branta canadensis), Marsh Wren (Cistothorus palustris), Swamp Sparrow (Melospiza georgiana), and American Bittern (Botaurus lentiginosus). Pied-billed Grebe (Podilymbus podiceps) had a particularly strong response and was highly influential in the IEC. Great Egret (Ardea alba) was the only species with a negative relationship to the environmental gradient. The refined IEC performed well and provides easily understood output for coastal wetland practitioners in the lower Great Lakes, tasked with reporting on the ecological integrity of marsh bird communities.

The rapid urban population growth and coastal infrastructure development worldwide add dimensionality and complexity to the management process in sandy shores, and therefore the development of beach quality indices that take into account the increasing role of urbanization are particularly relevant. This work analyses the potential of human population density (HPD), nighttime lights and vegetation cover as indicators of urban impact on sandy beach biodiversity. Each indicator was tested against a large-scale 2-yr study of macrofaunal richness and physical characteristics along a strong environmental gradient defined by the widest estuary of the world, the Rio de la Plata. A negative linear relationship between HPD and the number of species was found. The amount of light recorded at night peaked at the most urbanized area in the coast, Montevideo city, and showed a negative relationship with macrofaunal richness. Vegetation cover, expressed through a normalized difference vegetation index, showed a weak positive relationship with species richness. Multiple linear regressions, combining urban indicators and physical characteristics as explanatory variables of macrofaunal richness, showed the best results when HPD and salinity range were combined. A regression tree explained 65% of deviance and had a structure coherent with previous results. Salinity was the dominant ecological driver: beaches with salinity ≥27.2 showed higher species richness, while beaches with less salinity and higher nighttime lights showed the lowest species richness. Random Forests selected salinity (mean and range) and HPD as the most informative variables to discriminate groups of beaches according to their macrobenthic richness. These results reflect that the salinity gradient is a macroscale driver that shapes species richness patterns along this coast, whereas the effects of urbanization are confined within the dominant large-scale environmental gradient. The identification of suitable urban indicators provided in this work constitutes the first step onto the development of more rigorous approaches to assess this globally relevant and long-lasting stressor.

Globally, river health is deteriorating due to increased anthropogenic pressures. Accurately assessing river health is crucial for the management of river resources with macroinvertebrates commonly used as biological indicators of ecological integrity. Complex biological data is made more straightforward using indices as they offer the ability to rapidly communicate complex science in a simple form. Management decisions are often based on the results of biological river health assessments, making the identification of the most appropriate, robust and sensitive macroinvertebrate-based index vital when undertaking catchment specific assessments. Selection of a macroinvertebrate-based index should rely on a scientific method rather than arbitrary selection criteria. This study aimed to compare the performance of several macroinvertebrate-based indices to identify the index or indices most appropriate to the Richmond River Catchment (RRC) in northern New South Wales, Australia. River health within the RRC is poor with a clear pollution gradient from upper to lower catchment sites. Six commonly used indices were calculated using family-level identification. The biological assessment supported the physicochemical results with a gradient in river health from upper to lower catchment. Family Richness and Family Richness Percent were assessed as the most usable indices. In studies that have restricted time, budget and expertise they will provide accurate but limited information on river health. SIGNAL2 was identified as the most valid index for assessing river health due to its overall sensitivity to changes in river health, and level of detail on anthropogenic impacts. The poor performance of the AUSRIVAS, EPT and BCI limits or precludes their use for river health assessment in the RRC. While this model for identification and selection of an appropriate macroinvertebrate-based index for catchment scale river health assessments was useful in this context, it needs to be improved with a larger dataset and a greater environmental gradient of river health to make a less subjective evaluation.

The classification of waterbodies under the Water Framework Directive is dependent on the ability of monitoring programmes to reflect habitat quality using biotic elements including benthic diatom communities. This study investigated the influence of specific riparian habitats, of mixed woodland, grassland and lake artificial structures such as jetties and slipways, on benthic diatom assemblages in nine lakes across gradients of total phosphorus, alkalinity and in the presence or absence of Dreissena polymorpha. The heterogeneity of the benthic diatom assemblages at riparian and lake scale was assessed by taking three replicates per site category per lake, following standard European Union protocols. Canonical correspondence analysis (CCA) and mixed effect modelling was used to investigate the main environmental controls on assemblage structure. Non-metric Multidimensional Scaling (NMDS) was used to examine patterns in assemblage structure. No single environmental gradient was found to control benthic diatom composition, with differences among assemblages influenced both by riparian habitat type within lakes and interaction of multiple environment gradients, including presence of D. polymorpha. Greater control was exerted on community structure at the lake than local riparian scale. The influence of scalar factors on diatom assemblages increased with increasing scale. We recommend that for effective monitoring and assessment of ecological status, standard sampling protocols should include localised littoral habitats with individual samples pooled across riparian habitat types, thereby accounting for both multiple environmental and spatial controls on community structure.

From autumn 2005 to spring 2008, a study focusing on the collection of Trichoptera larvae was conducted in the catchment of the Guadiamar River (SW Spain). The distribution of caddisfly species in relation with environmental factors was examined. Four groups of species were recognised according to the environmental gradient. A direct ordination analysis (CCA) used to describe assemblage changes among sites corroborated that conductivity, land-use, geomorphological gradient, and temporality were the variables that best explain the Trichoptera distribution, but to establish the relative influence of the land-use variables was difficult. On the other hand, mining pollution appeared to be the main factor explaining Trichoptera community structure. In April 1998 this river system underwent an accidental release of a large mass of toxic mine waste, which exterminated macroinvertebrates in the middle and lower parts and floodplain. Several years later, caddisfly communities in these areas were different from those of unaffected upper reaches. The species assemblage was especially poor in lower river reaches that underwent the permanent, diffuse urban and agricultural pollution. These conditions were tolerated only by Hydropsyche exocellata Dufour.

To assess the relative sensitivity of assessments using community metrics for macroinvertebrates, periphyton, and fish assemblages, we compared the results of three parallel assessments using these assemblages at 86 stream reaches sampled in 1994 and 1995 by the Regional Environmental Monitoring and Assessment Program (R-EMAP) in the mineralized zone or historical mining region of the Southern Rockies Ecoregion in Colorado. We contrasted assessments using community metrics for each taxa group selected to be diagnostic of the two large-scale stressor gradients identified in this ecoregion: discharges from historical hardrock metal mines and agriculture, particularly pasturing of livestock. While principal components analysis (PCA) extracted axes from the metrics for all three assemblages correlated with increased metal concentrations, the axes differed in their sensitivity to different environmental gradients. Two axes extracted from the fish metrics were correlated with dissolved metals, suspended solids, and sediment embeddedness or with sediment metals. Two axes extracted from the macroinvertebrate metrics partially separated these two stressor gradients, while the single correlated axis extracted from the periphyton metrics did not. The second macroinvertebrate PCA axis was correlated with an environmental gradient correlated both with agricultural effects and with stream size, as were the second and third periphyton PCA axes. The third fish PCA axis was correlated with stream size and slope, but was not sensitive to agricultural effects. Fish, macroinvertebrates, and periphyton differ in their sensitivity to different stressors, and combining metrics for these assemblages into a mixed assemblage index of biotic integrity may increase the utility of the multimetric approach to diagnose environmental stressors at impaired reaches.