Development of dual fish multi-metric indices of biological condition for streams with characteristic thermal gradients and low species richness

Biological indicators based on fish assemblage characteristics are used to assess stream condition worldwide. Fish-based bioassessment poses challenges in Southern New England, the USA, due to the effects of within-watershed thermal gradients on fish assemblage types, low regional species richness, and lack of minimally disturbed sites. Dual multi-metric indices (MMI) of biological condition were developed for wadeable streams based on fish assemblage characteristics sampled across watershed landscapes with varying levels of human disturbance. A coldwater MMI was developed using streams with drainage area of ≤15 km², and a mixed-water MMI for streams with drainage areas of >15 km². For each MMI development, candidate metrics represented by ecological classes were sequentially tested by metric range, within-year precision, correlation with stream size, responsiveness to landscape-level human disturbances, and redundancy. Resultant coldwater and mixed-water MMI were composed of 5 and 7 metrics, respectively. Stream sites tended to score similarly when the two MMI were applied to transitional sites, i.e., drainage areas of 5–40 km². However, some sites received high scores from the mixed-water MMI and intermediate scores from the coldwater MMI. It was thus difficult to ascertain high-quality mixed-water streams from potential coldwater streams which currently support mixed-water assemblages due to ecological degradation. High-quality coldwater streams were restricted to stream sites with drainage areas ≤15 km². The newly developed fish-based MMI will serve as a useful management tool and the dual-MMI development approach may be applicable to other regions with thermal gradients that transition from coldwater to warmwater within watersheds.     

Isotopic metrics as a tool for assessing the effects of mine pollution on stream food webs

Most tools used to assess pollution impacts are based on structural, or less frequently, functional aspects of biotic communities. However, the application of measures that take a food web approach to understand the effects of stress on stream ecosystems offers a new perspective and promising insights. We assessed quantitative isotopic metrics, which describe characteristics of food web structure, as indicators of acid mine drainage (AMD) in 12 streams along a stress gradient and compared these metrics with traditional structural and functional metrics. The gradient ranged from highly stressed (pH < 3) streams with elevated concentrations of dissolved metals (Fe and Al) to moderately acidic streams (pH 3.6–4.9) with substrata coated in metal hydroxide precipitates and circumneutral reference streams. Key differences in food web structure were detected by the isotopic metrics. Specifically, fewer trophic levels and reduced trophic diversity characterized food webs in all mining impacted streams but the differences were not significant along the gradient. In contrast, most structural and functional metrics were significant predictors of AMD as stress increased. Therefore, our results suggest that isotopic metrics offer little advantage over traditional metrics in terms of detecting impacts for biomonitoring purposes. However, they do provide additional insights into how whole food webs are disrupted, and are likely to be more useful for guiding stream management and rehabilitation strategies.     

Towards rapid bioassessment of wadeable streams in Brazil: Development of the Guapiaçu-Macau Multimetric Index (GMMI) based on benthic macroinvertebrates

We developed a multimetric index based on macroinvertebrates to assess ecological condition of wadeable streams in Rio de Janeiro State, southeast Brazil. To do so we used a set of 12 reference and 12 severely impaired sites sampled in the summer wet season as calibration sites. Nine metrics were selected based on their abilities to distinguish between reference and impaired sites and their independence from other metrics. Metrics retained in the final index were: family richness; Trichoptera family richness; Shannon family diversity; % Plecoptera individuals; % Ephemeroptera, Plecoptera and Trichoptera (EPT) individuals; % mollusk and Diptera individuals; % shredder individuals; proportion Chironomidae/Diptera individuals; and proportion Hydropsychidae/Trichoptera individuals. The final 9 metrics were standardized; then the Guapiaçu-Macau Multimetric Index (GMMI) was calculated, yielding a final index score ranging from 0 to 100. We validated the index through use of 19 sites subject to different levels of impairment, sampled both in summer and in winter. Our final multimetric index distinguished well between different levels of impairment and was strongly correlated with other disturbance measures. Temporal stability was also tested through use of 8 sites that were sampled in both seasons, and results showed no significant changes in the index final score among seasons. Our research represents one of the first initiatives in Brazil to develop a multimetric index for use in a spatially extensive bioassessment program extending across substantial natural and disturbance gradients. It can be a useful tool to help conserve streams in Atlantic forest conservation areas. We suggest that the methodology established here offers a foundation for similar index development and assessments in Brazil.     

Mayfly bioindicator thresholds for several anthropogenic disturbances in neotropical savanna streams

Anthropogenic disturbances are widely recognized as major threats to terrestrial and aquatic biodiversity worldwide, including areas located in non-forest ecosystems. Headwater streams in the neotropical savanna are severely threatened by large-scale landscape changes that degrade local habitat characteristics and lead to biodiversity loss. The objective of our study was to evaluate Ephemeroptera assemblages as bioindicators of catchment land use and cover, local streambed and riparian vegetation conditions, and instream water quality. To do so, we sampled mayfly nymphs in 184 stream sites across a broad disturbance gradient in four hydrologic units of the Brazilian neotropical savanna. We selected seven metrics without significant co-variation with natural variability: % catchment urban, riparian vegetation condition index (RCOND), human disturbances of the stream channel and riparian zone (W1_HALL), substrate mean embeddedness (XEMBED), dissolved oxygen (mg L⁻¹), pH, and total phosphorus (mg L⁻¹). We ran threshold indicator taxa analysis (TITAN) for each disturbance metric to detect change points in mayfly genera responses (whether sensitive or tolerant) and assemblage turnover pattern. TITAN showed that 20 of the 39 genera found were robust bioindicators (based on purity and reliability values >0.95), sixteen of them being sensitive to increased disturbance. The most sensitive genera were Tricorythopsis (Leptohyphidae) and Camelobaetidius (Baetidae), showing decreased abundance to most disturbance metrics. We found a turnover pattern of mayfly genera in response to W1_HALL in a narrow variation range. For total phosphorus, the benchmark value defined in Brazilian Federal Legislation is higher than the turnover threshold of several mayfly genera. This indicates that we will lose many sensitive genera even within the limits imposed by national environmental legislation. The indicator taxa approach, based on multiple taxa rather than univariate metrics or single indicator species, demonstrates the value of quantitative ecological information for conserving and managing freshwater ecosystems globally.     

Effects of livestock exclusion on in‐stream habitat and benthic invertebrate assemblages in montane streams

1. Stream and riparian ecosystems in arid montane areas, like the interior western United States, are often just narrow mesic strands, but support diverse and productive habitats. Meadows along many such streams have long been used for rangeland grazing, and, while impacts to riparian areas are relatively well known, the effect of livestock grazing on aquatic life in streams has received less attention. 2. Attempts to link grazing impacts to disturbance have been hindered by the lack of spatial and temporal replication. In this study, we compared channel features and benthic macroinvertebrate communities (i) between 16 stream reaches on two grazed allotments and between 22 reaches on two allotments where livestock had been completely removed for 4 years, (ii) before and after the 4‐year grazing respite at a subset of eight sites and (iii) inside and outside of small‐scale fenced grazing exclosures (eight pairings; 10+ year exclosures) in the meadows of the Golden Trout Wilderness, California (U.S.A.). 3. We evaluated grazing disturbance at the reach scale in terms of the effects of livestock trampling on per cent bank erosion and found that macroinvertebrate richness metrics were negatively correlated with bank erosion, while the percentage of tolerant taxa increased. 4. All macroinvertebrate richness metrics were significantly lower in grazed areas. Bank angle, temperature, fine sediment cover and erosion were higher in grazed areas, while riparian cover was lower. Regression models identified riparian cover, in‐stream substratum, bank conditions and bankfull width‐to‐depth ratios as the most important for explaining variability in macroinvertebrate richness metrics. 5. Small‐scale grazing exclosures showed no improvements for in‐stream communities and only moderate positive effects on riparian vegetation. In contrast, metrics of macroinvertebrate richness increased significantly after a 4‐year period of no grazing. 6. The success of grazing removal reported here suggests that short‐term removal of livestock at the larger, allotment meadow spatial scale is more effective than long‐term, but small‐scale, local riparian area fencing, and yields promising results in achieving stream channel, riparian and aquatic biological recovery.     

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.     

Diversity and functions of leaf-decaying fungi in human-altered streams

1. Stream conditions have been evaluated using leaf breakdown, and aquatic hyphomycetes are a diverse group of fungal decomposers which contribute to this process. 2. In field surveys of three pairs of impact‐control stream sites we assessed the effect of eutrophication, mine pollution and modification of riparian vegetation on alder leaf breakdown rate in coarse and fine mesh bags and on mycelial biomass, spore production and species diversity of leaf‐colonizing fungi. 3. In addition, we gathered published information on the response of leaf‐colonizing fungi to these three types of perturbations. We conducted a meta‐analysis of 23 published papers to look for consistent patterns across studies and to determine the relevance of four fungal‐based metrics (microbial breakdown rate, maximum spore production, maximum mycelial biomass and total species richness) to detect stream impairment. 4. In our field surveys, leaf breakdown rates in coarse mesh bags were lower at impact than at paired control sites regardless of perturbation type. A similar trend was observed for leaf breakdown rates in fine mesh bags. Mycelial biomass and spore production were higher in the eutrophied stream than in the control stream. Spore production was depressed in the mine polluted stream, while it was slightly enhanced in the stream affected by forestry. Fungal diversity tended to be lower at impact than at paired control sites, though the mean and cumulative species richness values were often inconsistent. 5. Results of the meta‐analysis confirmed that mine pollution reduces fungal diversity and performance. Eutrophication was not found to affect microbial breakdown rate, maximum spore production and maximum mycelial biomass in a predictable manner because both positive and negative effects were reported in the literature. However, fungal species richness was consistently reduced in eutrophied streams. Modification of riparian vegetation had at most a small stimulating effect on maximum spore production. Among the four fungal‐based metrics included in the meta‐analysis, maximum spore production emerged as the most sensitive indicator of human impact on streams. 6. Taken together, our findings indicate that human activities can affect the diversity and functions of aquatic hyphomycetes in streams. We also show that leaf breakdown rate and simple fungal‐based metrics, such as spore production, are relevant to assess stream condition.     

Effects of oil palm plantations on habitat structure and fish assemblages in Amazon streams

The aim of this research is to assess the effects of oil palm plantations on stream habitat and their fish assemblage diversity. We hypothesize that streams which drain through oil palm plantations tend to be less heterogeneous, limiting the occurrence of many species, than streams that drain through forest fragments, which support higher fish diversity. A total of 17 streams were sampled; eight in forest fragments and nine in oil palm plantations. Environmental and biological variables were sampled along 150 m stretch in each stream. Of the 242 environmental variables measured, ten were considered important to assess the condition of structural habitat, and out of these variables, four were considered relevant in the distinction between streams in oil palm plantations and forest fragments. A total of 7245 fishes were collected, belonging to 63 species. Unlike our original hypothesis, the species richness did not differ between forest fragment and oil palm plantations streams, showing that it is not a good divert measure in streams disturbance assessment. However, fish assemblages differed in species composition, and 56 species were recorded in oil palm plantation streams, while 44 species were recorded in forest fragments streams. Some species were identified as indicators of either altered (Aequidens tetramerus and Apistogramma agassizii) or undisturbed areas (Helogenes marmoratus). Overall, oil palm plantations were proven to change stream habitat structure and fish species distribution, corroborating other studies that have evidenced changes in patterns of biological community structure due to impacts by different land uses.     

Deforestation and Benthic Indicators: How Much Vegetation Cover Is Needed to Sustain Healthy Andean Streams?

Deforestation in the tropical Andes is affecting ecological conditions of streams, and determination of how much forest should be retained is a pressing task for conservation, restoration and management strategies. We calculated and analyzed eight benthic metrics (structural, compositional and water quality indices) and a physical-chemical composite index with gradients of vegetation cover to assess the effects of deforestation on macroinvertebrate communities and water quality of 23 streams in southern Ecuadorian Andes. Using a geographical information system (GIS), we quantified vegetation cover at three spatial scales: the entire catchment, the riparian buffer of 30 m width extending the entire stream length, and the local scale defined for a stream reach of 100 m in length and similar buffer width. Macroinvertebrate and water quality metrics had the strongest relationships with vegetation cover at catchment and riparian scales, while vegetation cover did not show any association with the macroinvertebrate metrics at local scale. At catchment scale, the water quality metrics indicate that ecological condition of Andean streams is good when vegetation cover is over 70%. Further, macroinvertebrate community assemblages were more diverse and related in catchments largely covered by native vegetation (>70%). Our results suggest that retaining an important quantity of native vegetation cover within the catchments and a linkage between headwater and riparian forests help to maintain and improve stream biodiversity and water quality in Andean streams affected by deforestation. This research proposes that a strong regulation focused to the management of riparian buffers can be successful when decision making is addressed to conservation/restoration of Andean catchments.     

Wetlands serve as natural sources for improvement of stream ecosystem health in regions affected by acid deposition

For over 40 years, acid deposition has been recognized as a serious international environmental problem, but efforts to restore acidified streams and biota have had limited success. The need to better understand the effects of different sources of acidity on streams has become more pressing with the recent increases in surface water organic acids, or ‘brownification,’ associated with climate change and decreased inorganic acid deposition. Here, we carried out a large scale multi‐seasonal investigation in the Adirondacks, one of the most acid‐impacted regions in the United States, to assess how acid stream producers respond to local and watershed influences and whether these influences can be used in acidification remediation. We explored the pathways of wetland control on aluminum chemistry and diatom taxonomic and functional composition. We demonstrate that streams with larger watershed wetlands have higher organic content, lower concentrations of acidic anions, and lower ratios of inorganic to organic monomeric aluminum, all beneficial for diatom biodiversity and guilds producing high biomass. Although brownification has been viewed as a form of pollution, our results indicate that it may be a stimulating force for biofilm producers with potentially positive consequences for higher trophic levels. Our research also reveals that the mechanism of watershed control of local stream diatom biodiversity through wetland export of organic matter is universal in running waters, operating not only in hard streams, as previously reported, but also in acid streams. Our findings that the negative impacts of acid deposition on Adirondack stream chemistry and biota can be mitigated by wetlands have important implications for biodiversity conservation and stream ecosystem management. Future acidification research should focus on the potential for wetlands to improve stream ecosystem health in acid‐impacted regions and their direct use in stream restoration, for example, through stream rechanneling or wetland construction in appropriate hydrologic settings.     

Assessment of biotic condition of Atlantic Rain Forest streams: A fish-based multimetric approach

We developed a preliminary fish-based multimetric index (MMI) to assess biotic condition of Atlantic Rain Forest streams in Southeastern Brazil. We used least-disturbed sites as proxies of reference conditions for metric development. To determine the disturbance gradient we used an Integrated Disturbance Index (IDI) that summarized the multiple disturbances measured at local/regional catchment scales in a single index, describing the totality of exposure of the streams to human pressures. For our 48 sites, nine were least-disturbed (IDI < 0.25), five were most-disturbed (IDI > 1.35) and 34 were intermediate. Initially, we considered 41 candidate metrics selected primarily from previous studies. We screened this pool of candidate metrics using a series of tests: range test, signal-to-noise test, correlation with natural gradients, responsiveness test, and redundancy test. After screening, we selected six metrics for the MMI: % Characiform individuals, % water column native individuals, % benthic invertivorous individuals, % tolerant species, % intolerant species, and % detritivorous individuals. Metrics such as diversity, dominance, species richness and biomass that have been historically used for assessing ecosystem condition failed one or more screening tests. We conclude that an IDI and rigorous metric screening are critical to the MMI development process and for meaningful assessments of stream condition.     

Comparison of watershed disturbance predictive models for stream benthic macroinvertebrates for three distinct ecoregions in western US

The successful use of macroinvertebrates as indicators of stream condition in bioassessments has led to heightened interest throughout the scientific community in the prediction of stream condition. For example, predictive models are increasingly being developed that use measures of watershed disturbance, including urban and agricultural land-use, as explanatory variables to predict various metrics of biological condition such as richness, tolerance, percent predators, index of biotic integrity, functional species traits, or even ordination axes scores. Our primary intent was to determine if effective models could be developed using watershed characteristics of disturbance to predict macroinvertebrate metrics among disparate and widely separated ecoregions. We aggregated macroinvertebrate data from universities and state and federal agencies in order to assemble stream data sets of high enough density appropriate for modeling in three distinct ecoregions in Oregon and California. Extensive review and quality assurance of macroinvertebrate sampling protocols, laboratory subsample counts and taxonomic resolution was completed to assure data comparability. We used widely available digital coverages of land-use and land-cover data summarized at the watershed and riparian scale as explanatory variables to predict macroinvertebrate metrics commonly used by state resource managers to assess stream condition. The “best” multiple linear regression models from each region required only two or three explanatory variables to model macroinvertebrate metrics and explained 41–74% of the variation. In each region the best model contained some measure of urban and/or agricultural land-use, yet often the model was improved by including a natural explanatory variable such as mean annual precipitation or mean watershed slope. Two macroinvertebrate metrics were common among all three regions, the metric that summarizes the richness of tolerant macroinvertebrates (RICHTOL) and some form of EPT (Ephemeroptera, Plecoptera, and Trichoptera) richness. Best models were developed for the same two invertebrate metrics even though the geographic regions reflect distinct differences in precipitation, geology, elevation, slope, population density, and land-use. With further development, models like these can be used to elicit better causal linkages to stream biological attributes or condition and can be used by researchers or managers to predict biological indicators of stream condition at unsampled sites.     

Macroinvertebrate community structure,secondary production and trophic‐level dynamics in urban streams affected by non‐point‐source pollution

1. Despite non‐point‐source (NPS) pollution being perhaps the most ubiquitous stressor affecting urban streams, there is a lack of research assessing how urban NPS pollution affects stream ecosystems. We used a natural experimental design approach to assess how stream macroinvertebrate community structure, secondary production and trophic structure are influenced by urban NPS pollution in six streams. 2. Differences in macroinvertebrate community structure and secondary production among sites were highly correlated with stream‐water specific conductivity and dissolved inorganic phosphorus (DIP) concentrations. Macroinvertebrate richness, the Shannon diversity index and the Shannon evenness index were all negatively correlated with specific conductivity. These patterns were driven by differences in the richness and production of EPT and other intolerant taxa. Production of the five most productive taxa, tolerant taxa, non‐insect taxa and primary consumers were all positively correlated with stream‐water DIP. 3. Despite the positive correlation between primary consumer production and DIP, there was no correlation between macroinvertebrate predator production and either total or primary consumer macroinvertebrate production. This was observed because DIP was positively correlated with the production of non‐insect macroinvertebrate taxa assumed to be relatively unavailable for macroinvertebrate predator consumption. After removing production of these taxa, we observed a strong positive correlation between macroinvertebrate predator production and production of available prey. 4. Our results suggest that urban NPS pollution not only affects macroinvertebrate community structure, but also alters secondary production and trophic‐level dynamics. Differences in taxon production in our study indicate the potential for altered energy flow through stream food webs and potential effects on subsidies of aquatic insect prey to riparian food webs.     

Effects of in situ phosphorus enrichment on the benthos in a subalpine karst stream and implications for bioassessment in nature reserves

Park managers in nature reserves need scientifically defensible and operationally feasible ecological indicators to better manage protected areas for both nature conservation and tourism. Such needs are much more urgent in karst aquatic ecosystems where spectacular natural scenic wonders attract millions of visitors to natural areas with streams and lakes that are particularly vulnerable to nutrient pollution. To identify a set of biotic indicators of phosphorus (P) pollution in a karst stream, we conducted an in situ P enrichment experiment in a nearly pristine karst stream located at a UNESCO world heritage site in China. Our results show that both benthic algal assemblages and macroinvertebrates were sensitive to P enrichment. Changes in diatoms (e.g., Achnanthidium minutissimum, Delicata delicatula) and macroinvertebrates (e.g., collectors) were indicative of P enrichment. The color change of travertine bryophyte beds from creamy white to green was largely due to increase in filamentous green algae such as Zygnema sp., which may provide a visual cue for P enrichment and pollution. Our findings, in conjunction with further studies that directly link these indicators with human disturbance (e.g., tourist activities) throughout the park, could improve the operation of park managers in minimizing tourist-induced nutrient pollution and in operationalizing these indicators in the current environmental monitoring and assessment program.     

Identifying indicators and quantifying large-scale effects of dams on fishes

Although localized effects of individual dams on stream fish assemblages have been relatively well-studied, less is known about the effects of multiple dams within a stream network on fishes and the patterns that emerge when the combined effects of individual and multiple dams are viewed across entire river basins, ecoregions, and states. This study evaluated multiple stream network fragmentation metrics representing localized (e.g., distance-to-dams) and cumulative (e.g., total upstream reservoir storage) dam influences on streams in Michigan, Wisconsin, and Minnesota, developing an approach for identifying suitable fish indicators of dam effects. We used change point and correlation analyses to determine associations of stream fish catch per unit effort and various stream network fragmentation metrics with data from more than 2000 fish survey sites stratified by stream size, thermal regime, and ecoregion. Of the identified indicator species, predominantly warmwater, large river, and/or lentic species were positively associated with stream network fragmentation, whereas cold and coolwater lotic species were negatively associated with fragmentation. These results suggest a combination of downstream thermal effects and upstream influences from impoundments generated by dams. Variance partitioning analyses based on identified indicator species revealed greater upstream-dominated dam influences in headwaters than mid-sized streams, and a greater relative influence of dams vs. other non-dam anthropogenic influences in cold streams than warm streams. Overall, a combination of localized and cumulative fragmentation metrics, as well as upstream and downstream-oriented measures, were influential in indicator species responses, emphasizing the importance of selecting a diversity of fragmentation metrics when assessing effects of dams on stream fishes. Understanding multiple dam influences on stream fishes, including localized effects from individual dams and cumulative effects from all dams within a river basin, would provide useful information for a variety of management activities, including dam operation and dam removal prioritization. Dams significantly affect conservation and management options for stream fishes, with identification of multi-scale dam influences on fishes being critical to restoration and maintenance of aquatic biodiversity throughout the world.     

MULTIVARIATE ANALYSIS OF PERIPHYTON ASSEMBLAGES IN RELATION TO ENVIRONMENTAL GRADIENTS IN COLORADO ROCKY MOUNTAIN STREAMS 1

We assessed relationships between chemical and physical characteristics and periphyton assemblages in stream reaches of the mineral belt in the Southern Rockies ecoregion of Colorado, United States. Using canonical ordination analyses, we contrasted results wherein assemblage structure was assessed using community metrics or species abundances. Our objectives were to identify community metrics or individual species diagnostic of the primary environmental stressors in these streams, to compare the sensitivity of these two approaches to determining the primary stressors, and to determine how these approaches may be used to differentiate the effects of these environmental stressors from other gradients. For periphyton metrics, the first axis extracted by redundancy analysis correlated with total phosphorus, substrate coarseness and embeddedness, and riparian vegetation condition, whereas the second axis correlated with dissolved metals. For species abundances, the three axes extracted by canonical correspondence analysis (CCA) were correlated with (1) stream size and types of in‐stream habitats; (2) total phosphorus, dissolved ions, and riparian disturbance by agriculture; and (3) sediment coarseness and embeddedness and riparian vegetation condition. Concentrations of dissolved metals were not correlated with the CCA axes. Analyses of species abundances were sensitive to effects associated with nutrients, substrates, and riparian vegetation, whereas analyses of periphyton metrics were sensitive not only to these nutrient and physical habitat effects but also to toxicological effects associated with metals. As a result, the analyses of periphyton metrics may be used to identify which metrics would be useful for a periphyton index of biotic integrity and would also be individually diagnostic of the larger scale stressors in these streams, nutrient, substrate, and riparian vegetation effects of livestock grazing and increased metal concentrations associated with metal mining.     

Using modelled stream temperatures to predict macro‐spatial patterns of stream invertebrate biodiversity

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Leaf‐litter colonisation and breakdown in relation to stream typology: insights from Mediterranean low‐order streams

1. Scant information is available on leaf breakdown in streams of arid and semiarid regions, including the Mediterranean, where environmental heterogeneity can be high and the relationship between stream characteristics and leaf breakdown is poorly known. We tested the hypotheses that differences in leaf breakdown metrics would be substantially higher between mountain and lowland Mediterranean streams than among streams within each subregion and that variability among streams would be substantially higher in the lowlands, because permanent reaches in the semiarid lowland streams are rare and isolated. 2. We compared leaf breakdown and associated dynamics of nutrients, fungi and invertebrates in low‐order Mediterranean streams draining sub‐humid forests in the Sierra Nevada Mountains and nearby semiarid lowlands of south‐eastern Spain. Streams differed between the two subregions mainly in water ion content, temperature and riparian tree cover. We detected higher environmental heterogeneity among streams within the lowlands compared to the Sierra Nevada mountain range. In the lowlands, breakdown coefficients (k) of alder leaves spanned almost the entire range reported for this species from temperate streams, overlapping with less variable breakdown coefficients in the Sierra Nevada. 3. The high variability of k values among the lowland sites appeared to be caused primarily by variability in the composition and abundance of a few leaf‐consuming invertebrate taxa, particularly the snail Melanopsis praemorsa. Fungal and nutrient dynamics were less variable among sites within each subregion. 4. These results indicate that the critical condition for stream functional assessment of well‐constrained breakdown rates, or related metrics, could be met at reference sites within homogenous bio‐geo‐climatic regions such as the Sierra Nevada. By contrast, in heterogeneous areas such as the semiarid lowland streams, natural variability of breakdown rates can greatly exceed the magnitude of effects expected in response to anthropogenic disturbances.     

Assessment of streams of the eastern United States using a periphyton index of biotic integrity

Benthic algae were collected from 272 eastern United States streams and rivers and analyzed for diatom species richness and dominance, the relative abundance of acidobiontic, eutraphentic, and motile diatoms, standing crops of chlorophyll and biomass, and alkaline phosphatase activity. These data were used to calculate a periphyton index of biotic integrity (PIBI), and values of the index were compared among reference, moderately impacted, and disturbed streams. The level of disturbance was based on stream chemistry, riparian disturbance, or a combined classification. Analyses of variance showed that PIBI was significantly higher in reference streams for all classifications. The PIBI and its metrics were correlated with many of the chemistry and habitat variables, and canonical correlation analysis revealed three significant environmental gradients which extracted 84% of the variance in the PIBI and its metrics. We used the mean 75th, 25th, and 5th percentile scores from the reference sites to set thresholds for excellent, good, fair, or poor condition. Applying these criteria to the cumulative distribution of total stream length in the region, we found that 4.3% of the stream length was in excellent condition; 20.8% in good condition; 56.4% in fair condition; and 18.5% in poor condition. The sensitivity of the PIBI and its component metrics to environmental stressors supports the use of this index for monitoring ecological conditions in streams in the eastern United States and as a tool to aid in diagnosing the causes of their impairment.