Effects of snow cover on the benthic fauna in a glacier-fed stream

1. Alpine streams above the tree line are covered by snow for 6–9 months a year. However, winter dynamics in these streams are poorly known. The annual patterns of macroinvertebrate assemblages were studied in a glacial stream in the Austrian Alps, providing information on conditions under the snow.
2. Snow cover influenced water temperature, the content of benthic organic matter and insect development. Taxa richness and abundance of macroinvertebrates did not show a pronounced seasonal pattern. The duration of the autumn period with stable stream beds was important in determining the abundance and composition of the winter fauna.
3. There were significant differences in species composition between summer and winter. Two potential strategies in larval survival were evident: adaptation to the extreme abiotic conditions in summer (e.g. Diamesa spp.) or avoidance of these conditions and development during winter (e.g. Ephemeroptera and Plecoptera).
4. A comparison of a stream reach with continuous snow cover and a stream reach that remained open throughout winter showed that conditions under snow are suboptimal. At the open stream site, with higher water temperatures and greater food supply (benthic organic matter content), abundance and taxa richness was higher and larval growth was faster. Several taxa were found exclusively at this site.
5. Winter conditions did not provide an entirely homogeneous environment, abiotic conditions changed rapidly, especially at the onset of snowfall and at snowmelt. Continuous monitoring is necessary to recognize spatial and temporal heterogeneity in winter environments and the fauna of alpine streams.     

Macroinvertebrate diversity in headwater streams: a review

1. Headwater streams are ubiquitous in the landscape and are important sources of water, sediments and biota for downstream reaches. They are critical sites for organic matter processing and nutrient cycling, and may be vital for maintaining the 'health' of whole river networks.
2. Macroinvertebrates are an important component of biodiversity in stream ecosystems and studies of macroinvertebrate diversity in headwater streams have mostly viewed stream systems as linear reaches rather than as networks, although the latter may be more appropriate to the study of diversity patterns in headwater systems.
3. Studies of macroinvertebrate diversity in headwater streams from around the world illustrated that taxonomic richness is highly variable among continents and regions, and studies addressing longitudinal changes in taxonomic richness of macroinvertebrates generally found highest richness in mid-order streams.
4. When stream systems are viewed as networks at the landscape-scale, α-diversity may be low in individual headwater streams but high β-diversity among headwater streams within catchments and among catchments may generate high γ-diversity.
5. Differing ability and opportunity for dispersal of macroinvertebrates, great physical habitat heterogeneity in headwater streams, and a wide range in local environmental conditions may all contribute to high β-diversity among headwater streams both within and among catchments.
6. Moving beyond linear conceptual models of stream ecosystems to consider the role that spatial structure of river networks might play in determining diversity patterns at the landscape scale is a promising avenue for future research.     

Leaf breakdown and associated macroinvertebrates in alpine glacial streams

1. The relationship between macroinvertebrate assemblages and the breakdown of alder [Alnus viridis (Chaix), Dc.] leaves was examined by exposing leaf packs in four streams in an alpine glacial floodplain over 8 months. Although glacially fed, the four sites (pro-glacial, glacial lake outlet, main channel, and a side-channel with a mix of water sources) differed physically and contained different benthic communities.
2. Leaf breakdown and associated fungal properties differed widely among sites. Leaf decay rate varied by an order of magnitude ( k ranged from 0.0029 to 0.0305 day^–1), and was fastest at the lake outlet (< 20% leaf mass remaining by day 45) and slowest at the pro-glacial site (> 75% remaining on day 45). Rapid processing at the lake outlet was because of the presence of Acrophylax zerberus Brauer, a shredding caddisfly.
3. There were few macroinvertebrate taxa at the pro-glacial site (two to four taxa present in packs) and leaf breakdown was attributed primarily to micro-organisms. Leuctra abundance in leaf packs was strongly correlated with fungal biomass but not with the sporulation activity of any specific aquatic hyphomycete. Other taxa, such as Baetis and chironomids, showed no relationship with any leaf characteristic, suggesting that leaf packs were used mainly as a habitat and not as a food resource.
4. The predatory stonefly Isoperla was significantly associated with the abundance of macroinvertebrate prey ( Baetis , Chironomidae and Leuctra ) in leaf packs at the main and side-channel sites. The results indicate that leaf breakdown can vary widely in alpine lotic environments, reflecting site-specific differences in habitat characteristics, and in macroinvertebrate and fungal composition.     

Groundwater influence on alpine stream ecosystems

1. Spatial and temporal variability of relative snow‐melt, glacier‐melt and groundwater contributions to streams play important roles in shaping alpine freshwater ecosystems. Although meltwater (particularly glacier‐fed) streams have received much attention in recent years, the influence of groundwater on alpine freshwater ecosystems remains poorly understood. 2. This study tested the hypotheses that increased groundwater contributions to meltwater‐dominated alpine streams would yield increases in water temperature, channel stability, electrical conductivity and particulate organic matter (POM) and decreases in suspended sediment concentration (SSC). These more favourable habitat conditions were hypothesised to result in increased macroinvertebrate abundance and diversity. 3. Groundwater contributions, physicochemical habitat variables and benthic macroinvertebrates were sampled throughout the 2002 and 2003 summer‐melt seasons in three streams in the French Pyrénées. 4. Increased groundwater contributions were significantly correlated with higher discharge, water temperature, electrical conductivity, POM and channel stability, but lower SSC. 5. Macroinvertebrate total abundance, taxonomic richness, number of Ephemeroptera, Plecoptera and Trichoptera genera, and per cent Plecoptera all increased significantly with greater groundwater contributions to streamflow. However, beta diversity and Trichoptera relative abundance decreased. 6. Abundance of most macroinvertebrate taxa was highest under groundwater‐dominated conditions but a gradient of optimum groundwater preferences was evident across all taxa. Some taxa were found only where groundwater contributions were low (i.e. in predominantly meltwater‐fed streams). 7. This study provides evidence that water source, physicochemical habitat and stream biota are strongly linked. Therefore, an interdisciplinary approach is necessary for future studies aiming to develop conservation strategies or predict the response of alpine river ecosystems to global climate change.     

Trends of macroinvertebrate community structure in glacier-fed rivers in relation to environmental conditions: a synthesis

1. Generalized additive models (GAMs) were used to predict macroinvertebrate taxonomic richness and individual taxon diversity at the reach level across seven European glacier-fed river sites from a set of 11 environmental variables. Maximum water temperature and channel stability were found to explain the most deviance in these models.
2. Using this information, and data from other recent studies of glacier-fed rivers, a modified conceptual model based on Milner & Petts (1994) is presented which predicts the occurrence of macroinvertebrate families and subfamilies as determined by maximum water temperature ( T _max) and channel stability. This deterministic model only applies to the summer meltwater period when abiotic variables drive community structure.
3. Where maximum water temperature is below 2 °C, Diamesinae chironomids are typically the sole inhabitants, but where T _max >2 °C but <4 °C Orthocladiinae are found and, where channels are more stable, Tipulidae and Oligochaeta also occur. Above 4 °C Perlodidae, Taeniopterygidae, Baetidae, Simuliidae and Empididae can be expected to be part of the glacier-fed river community, particularly in Europe.
4. At other times of the year when environmental conditions ameloriate, glacial rivers support higher macroinvertebrate abundance and diversity, with a number of taxa present that are not found during the summer melt period.
5. Dispersal constraints influence macroinvertebrate assemblages of many glacier-fed rivers located on islands and in some alpine areas.     

Concordance between ecotypes and macroinvertebrate assemblages in Mediterranean streams

1. According to the guidelines of the European Water Framework Directive, assessment of the ecological quality of streams and rivers should be based on ecotype-specific reference conditions. Here, we assess two approaches for establishing a typology for Mediterranean streams: a top-down approach using environmental variables and bottom-up approach using macroinvertebrate assemblages.
2. Classification of 162 sites using environmental variables resulted in five ecotypes: (i) temporary streams; (ii) evaporite calcareous streams at medium altitude; (iii) siliceous headwater streams at high altitude; (iv) calcareous headwater streams at medium to high altitude and (v) large watercourses.
3. Macroinvertebrate communities of minimally disturbed sites ( n  = 105), grouped using UPGMA (unweighted pair-group method using arithmetic averages) on Bray–Curtis similarities, were used to validate four of the five ecotypes obtained using environmental variables; ecotype 5, large watercourses, was not included as this group had no reference sites.
4. Analysis of similarities ( anosim ) showed that macroinvertebrate assemblage composition differed among three of the four ecotypes, resulting in differences between the bottom-up and top-down classification approaches. Siliceous streams were clearly different from the other three ecotypes, evaporite and calcareous ecotypes did not show large differences in macroinvertebrate assemblages and temporary streams formed a very heterogeneous group because of large variability in salinity and hydrology.
5. This study showed that stream classification schemes based on environmental variables need to be validated using biological variables. Furthermore, our findings indicate that special attention should be given to the classification of temporary streams.     

A hydrogeomorphological context for ecological research on alpine glacial rivers

1. This paper presents a framework for the analysis of glacial stream ecosystems based upon the hierarchy of physical processes that operate over timescales varying from diel to millennial. Linked conceptual models propose interrelationships between climate, hydrology and fluvial geomorphology in alpine catchments.
2. These conceptual models are illustrated using data from the Taillon/Gabiétous catchment, French Pyrénées. Secondary sources provide information concerning the long-term sequence of climatic and geomorphological controls on contemporary catchment processes. Detailed hydrogeomorphological field data collected over three consecutive summer melt seasons (1995–97) permit identification of marked changes in shorter-term (diel, seasonal and inter-annual) physical processes.
3. Clear differences in the response of water quality and quantity variables were observed between years as climatic conditions varied. In two of the three study years, a precipitation-driven regime was imposed upon the typical ablation-driven river discharge pattern in alpine streams. Clear changes in water quality and quantity were evident with increasing distance from the glacier: (i) discharge increased although specific discharge decreased markedly, (ii) the mean and variability in water temperature increased, and (iii) base concentrations of suspended solids decreased.
4. The physical processes incorporated in the conceptual models presented in this paper have ecological implications because they underpin a nested suite of disturbance regimes operating over timescales from diel to millennial.     

Macrobenthic invertebrate richness and composition along a latitudinal gradient of European glacier-fed streams

1. The influence of 11 environmental variables on benthic macroinvertebrate communities was examined in seven glacier-fed European streams ranging from Svalbard in the north to the Pyrenees in the south. Between 4 and 11 near-pristine reaches were studied on each stream in 1996–97.
2. Taxonomic richness, measured at the family or subfamily (for Chironomidae) levels for insects and higher levels for non-insects, increased with latitude from Svalbard (3 taxa) to the Pyrenees (29 taxa).
3. A Generalized Additive Model (GAM) incorporating channel stability [Pfankuch Index (PFAN)], tractive force, Froude number (FROU), water conductivity (COND), suspended solids (SUSP) concentration, and maximum temperature explained 79% of the total deviance of the taxonomic richness per reach. Water temperature and the PFAN of stability made the highest contribution to this deviance. In the model, richness response to temperature was positive linear, whereas the response to the PFAN was bell-shaped with an optimum at an intermediate level of stability.
4. Generalized Additive Models calculated for the 16 most frequent taxa explained between 25 (Tipulidae) and 79% (Heptageniidae) of the deviance. In 10 models, more than 50% of the deviance was explained and 11 models had cross-validation correlation ratios above 0.5. Maximum temperature, the PFAN, SUSP and tractive force (TRAC) were the most frequently incorporated explanatory variables. Season and substrate characteristics were very rarely incorporated.
5. Our results highlight the strong deterministic nature of zoobenthic communities in glacier-fed streams and the prominent role of water temperature and substrate stability in determining longitudinal patterns of macroinvertebrate community structure. The GAMs are proposed as a tool for predicting changes of zoobenthic communities in glacier-fed streams under climate or hydrological change scenarios.     

滇西北高山微水体与溪流生境底栖动物多样性和环境特征

高山微水体由于面积微小且通过地表径流形成串联结构常常被认为与高山溪流具有类似的生境, 然而由于这两类生境中环境因子与底栖动物多样性存在差异, 它们在生态系统中的作用可能完全不同。滇西北地区是全球生物多样性热点区域之一, 境内高山微水体和高山溪流分布密集, 在区域底栖生物多样性维持方面具有重要的功能, 然而目前对这两类高山淡水生态系统的研究较少。为了比较这两类生境环境因子的异同及其对底栖动物多样性的维持作用, 2015年6月, 作者在云南省怒江州贡山县的高山峡谷内, 对27个高山微水体和同区域分布的1条高山溪流(海拔高差500 m范围)的底栖动物多样性和水环境因子进行了实地调查。结果表明: (1)高山微水体和高山溪流底栖动物群落中优势分类单元种群数量均比较庞大, 而稀有分类单元数量较多且种群较小; (2)两种生境在环境因子、物种多样性、功能多样性和群落结构方面的差异明显, 高山溪流有较高的物种丰富度、物种多样性和功能多样性; (3)高山微水体底栖动物多样性的分布与水环境因子无关, 而高山溪流底栖动物多样性与群落结构的形成受到与流速关联的水环境因子和海拔的影响。因此, 高山微水体与高山溪流不能简单地视为类似的生境类型, 它们对区域底栖动物多样性和生态功能维持可能具有不同的作用。     

Benthic Algae in High Altitude Streams of the Alps – a Neglected Component of the Aquatic Biota

This is a review on benthic algae from streams situated above the tree line in the Alps. It integrates published and unpublished data from alpine streams in Austria and in the Trento Province (Northern Italy). The main focus is on the structural and taxonomic composition of benthic algae including macro- and micro-algae and their contribution to the epilithic biofilm and the stream food-web. The environmental conditions relevant to algae within the two major stream types, the glacial (glacier-fed) and non-glacial krenal (spring-fed) stream are discussed. The paper considers both the maximum possible structural complexity of transverse algae zonation in cascading alpine/subalpine stream segments, and the effects of glacial water on species richness in the Central Alps in Austria. Autecological data are given for 46 common diatoms from 42 sites in the Central Eastern and Southern Central Alps and for 30 algae in addition to diatoms for 22 streams in the Central Eastern Alps. Since data on responses of benthic algae to the harsh conditions in high altitude Alpine streams are very scarce, results from literature and the author’s experiences from these and other mountain stream types are synthesized to formulate major objectives for future research in benthic high altitude Alpine stream ecology.     

Stability and Persistence of Alpine Stream Macroinvertebrate Communities and the Role of Physicochemical Habitat Variables

Macroinvertebrate communities in alpine streams have rarely been examined over more than two consecutive years or at sub-monthly temporal resolution during the summer melt season, in relation to a range of stream physicochemical habitat measurements. This paper addresses these research gaps by investigating the inter- (late melt season, 1996–2003) and intra-annual (bi-weekly; June–September, 2002–2003) community compositional stability and persistence of three alpine streams fed from different water sources (snow, glaciers and groundwater) in the Taillon–Gabiétous catchment, French Pyrénées. Inter-annual community stability and persistence decreased from 1996 to 2003; however, groundwater stream communities changed less than those in the main glacial stream. Intra-annual community stability varied spatially and temporally, particularly in relation to water quality variables (water temperature and suspended sediment concentration); water quantity (stream discharge) was less important perhaps due to taxa possessing adaptations to flow variability. The 15 most abundant taxa were consistently more stable and persistent than the entire stream community suggesting a common pool of taxa in these streams. Overall, the results support the view that streams originating from different alpine water sources are characterised by distinct benthic macroinvertebrate assemblages, and demonstrate the value of sampling at nested temporal scales (inter-annual to bi-weekly) for understanding how these stream ecosystems function.     

Vulnerability of alpine stream biodiversity to shrinking glaciers and snowpacks

Climate change poses a considerable threat to the biodiversity of high latitude and altitude ecosystems, with alpine regions across the world already showing responses to warming. However, despite probable hydrological change as alpine glaciers and snowpacks shrink, links between alpine stream biota and reduced meltwater input are virtually unknown. Using data from the French Pyrénées, we demonstrate that taxonomic richness and total abundance of stream macroinvertebrates increase significantly as meltwater (snow melt and glacier melt) contributions to river flow decrease. Macroinvertebrate species showed a gradation of optimum meltwater conditions at which they persist. For example: Habroleptoides berthelemyi (Ephemeroptera), Perla grandis (Plecoptera) and Rhithrogena spp. (Ephemeroptera) increased in abundance when meltwater contributions to streamflow decrease, whereas in contrast, Rhyacophila angelieri (Trichoptera) and Diamesa latitarsis spp. (Diptera) decreased in abundance. Changes in alpine stream macroinvertebrate community composition as meltwater contributions decline were associated with lower suspended sediment concentration, and higher water temperature, electrical conductivity and pH. Our results suggest α diversity (at a site) of streams presently fed by meltwaters will increase with future meltwater reductions. However, β diversity (between‐sites) will be reduced as snow melt and glacier melt decrease because the habitat heterogeneity associated with spatiotemporal variability of water source contributions will become lower as meltwater contributions decline. Extinction of some endemic alpine aquatic species (such as the Pyrenean caddis fly R. angelieri) is predicted with reduced meltwater inputs, leading to decreases in γ diversity (region). Our identification of significant links between meltwater production and stream macroinvertebrate biodiversity has wider implications for the conservation of alpine river ecosystems under scenarios of climate change induced glacier and snowpack loss.     

Effects of forest fire on headwater stream macroinvertebrate communities in eastern Washington,U.S.A.

1. Recent increases in fire frequency in North America have focused interest on potential effects on adjacent ecosystems, including streams. Headwaters could be particularly affected because of their high connectivity to riparian and downstream aquatic ecosystems through aquatic invertebrate drift and emergence. 2. Headwater streams from replicated burned and control catchments were sampled in 2 years following an intense forest fire in northeastern Washington (U.S.A.). We compared differences in benthic, drift and emergent macroinvertebrate density, biomass and community composition between five burned and five unburned catchments (14–135 ha). 3. There were significantly higher macroinvertebrate densities in burned than control sites for all sample types. Macroinvertebrate biomass was greater at burned sites only from emergence samples; in benthic and drift samples there was no significant difference between burn and control sites. 4. For all sample types, diversity was lower in the burned catchments, and the macroinvertebrate community was dominated by chironomid midges. 5. Compared to the effects of fire in less disturbed ecosystems, this study illustrated that forest fire in a managed forest may have greater effects on headwater macroinvertebrate communities, influencing prey flow to adjacent terrestrial and downstream aquatic habitats for at least the first 2 years post‐fire.     

Microbial assemblages reflect environmental heterogeneity in alpine streams

Alpine streams are dynamic habitats harboring substantial biodiversity across small spatial extents. The diversity of alpine stream biota is largely reflective of environmental heterogeneity stemming from varying hydrological sources. Globally, alpine stream diversity is under threat as meltwater sources recede and stream conditions become increasingly homogeneous. Much attention has been devoted to macroinvertebrate diversity in alpine headwaters, yet to fully understand the breadth of climate change threats, a more thorough accounting of microbial diversity is needed. We characterized microbial diversity (specifically Bacteria and Archaea) of 13 streams in two disjunct Rocky Mountain subranges through 16S rRNA gene sequencing. Our study encompassed the spectrum of alpine stream sources (glaciers, snowfields, subterranean ice, and groundwater) and three microhabitats (ice, biofilms, and streamwater). We observed no difference in regional (γ) diversity between subranges but substantial differences in diversity among (β) stream types and microhabitats. Within‐stream (α) diversity was highest in groundwater‐fed springs, lowest in glacier‐fed streams, and positively correlated with water temperature for both streamwater and biofilm assemblages. We identified an underappreciated alpine stream type—the icy seep—that are fed by subterranean ice, exhibit cold temperatures (summer mean <2°C), moderate bed stability, and relatively high conductivity. Icy seeps will likely be important for combatting biodiversity losses as they contain similar microbial assemblages to streams fed by surface ice yet may be buffered against climate change by insulating debris cover. Our results show that the patterns of microbial diversity support an ominous trend for alpine stream biodiversity; as meltwater sources decline, stream communities will become more diverse locally, but regional diversity will be lost. Icy seeps, however, represent a source of optimism for the future of biodiversity in these imperiled ecosystems.     

Relationships between ecosystem metabolism, benthic macroinvertebrate densities, and environmental variables in a sub-arctic Alaskan river

Relationships between environmental variables, ecosystem metabolism, and benthos are not well understood in sub-arctic ecosystems. The goal of this study was to investigate environmental drivers of river ecosystem metabolism and macroinvertebrate density in a sub-arctic river. We estimated primary production and respiration rates, sampled benthic macroinvertebrates, and monitored light intensity, discharge rate, and nutrient concentrations in the Chena River, interior Alaska, over two summers. We employed Random Forests models to identify predictor variables for metabolism rates and benthic macroinvertebrate density and biomass, and calculated Spearman correlations between in-stream nutrient levels and metabolism rates. Models indicated that discharge and length of time between high water events were the most important factors measured for predicting metabolism rates. Discharge was the most important variable for predicting benthic macroinvertebrate density and biomass. Primary production rate peaked at intermediate discharge, respiration rate was lowest at the greatest time since last high water event, and benthic macroinvertebrate density was lowest at high discharge rates. The ratio of dissolved inorganic nitrogen to soluble reactive phosphorus ranged from 27:1 to 172:1. We found that discharge plays a key role in regulating stream ecosystem metabolism, but that low phosphorous levels also likely limit primary production in this sub-arctic stream.     

Using the salinity preferences of benthic macroinvertebrates to classify running waters in brackish marshes in Germany

Marshland streams along European coastlines are typically located in the transition zone from limnic to brackish conditions. They constitute a distinct and important stream type within the German stream typology, which is predominantly characterised by tidal influence and salinity. According to the Water Framework Directive (WFD) the basis for the abiotic classification of European transitional and coastal waters is the ‘Venice System’ (Weber, M., 2005. Ergebnisse der Bestandsaufnahme 2004 zur Umsetzung der europäischen Wasserrahmenrichtlinie (WRRL) in den Küstengewässern Mecklenburg-Vorpommerns. Rostocker Meeresbiol. Beitr. 14, 7–15). However, the extreme spatial and temporal variability in salinity and tidal influence determines and controls the macroinvertebrate communities of marshland river and stream ecosystems and hampers the application of the ‘Venice System’. Earlier, purely biotic classifications of brackish waters typically classify different brackish water zones, each with a specific macroinvertebrate community, and often yield unsatisfactory results due to the extensively dynamic abiotic factors found in marshland streams. In practice, the permanent impact of tidal charge means that stable salinity zones do not exist. This effect can than be intensified by freshwater discharges after heavy rainfall or high tides in combination with strong winds that hinder discharge into the open sea. To overcome the restricted applicability of abiotic and biotic classification systems, we present a scoring system for marshland streams that combines the abiotic salinity classes of the ‘Venice System’ with the salinity preferences of the macroinvertebrate community. This proposal is based on literature data for macroinvertebrate salinity tolerances and preferences. According to the 137 references that were evaluated, 151 macroinvertebrate taxa were classified into six salinity groups. In a second step, we applied this scoring scheme to empirical data from two official quality assessment surveys. These surveys had been carried out in ten estuary tributaries of German marshland areas in Lower Saxony and Schleswig-Holstein in order to implement the WFD. Applying the scoring system to these data revealed a clear (and expected) gradient that was not expressed in the abiotic data. Thus we conclude that the biotic salinity preferences of benthic macroinvertebrates are a useful baseline metric for the ecological assessment of marshland streams and other transitional waters. Regional revision and adaptation of taxonomic salinity preferences would broaden the applicability of this assessment to transitional waters worldwide.     

Macroinvertebrate communities in streams with contrasting water sources in the Japanese Alps

Alpine streams are typically fed from a range of water sources including glacial meltwater, snowmelt, groundwater flow, and surface rainfall runoff. These contributions are projected to shift with climate change, particularly in the Japanese Alps where snow is expected to decrease, but rainfall events increase. The overarching aim of the study was to understand the key variables driving macroinvertebrate community composition in groundwater and snowmelt‐fed streams (n = 6) in the Kamikochi region of the northern Japanese Alps (April–December 2017). Macroinvertebrate abundance, species richness, and diversity were not significantly different between the two stream types. Community structure, however, was different between groundwater and snowmelt‐fed streams with macroinvertebrate taxa specialized for the environmental conditions present in each system. Temporal variation in the abundance, species richness, and diversity of macroinvertebrate communities was also significantly different between groundwater and snowmelt streams over the study period, with snowmelt streams exhibiting far higher levels of variation. Two snowmelt streams considered perennial proved to be intermittent with periodic drying of the streambed, but the macroinvertebrates in these systems rebounded rapidly after flows resumed with no reduction in taxonomic diversity. These same streams, nevertheless, showed a major reduction in diversity and abundance following periods of high flow, indicating floods rather than periodic drying was a major driver of community structure. This conclusion was also supported from functional analyses, which showed that the more variable snowmelt streams were characterized by taxa with resistant, rather than resilient, life‐history traits. The findings demonstrate the potential for significant turnover in species composition with changing environmental conditions in Japanese alpine stream systems, with groundwater‐fed streams potentially more resilient to future changes in comparison to snowmelt‐fed streams.     

Assessing the influence of water and substratum quality on benthic macroinvertebrate communities in a metal-polluted stream: an experimental approach

SUMMARY 1. Field and laboratory experiments were conducted to assess the relative influence of water quality and substratum quality on benthic macroinvertebrate communities in the Animas River, a metal-polluted stream in south-western Colorado (U.S.A.).
2. A community-level in situ toxicity test measured direct effects of Animas River water on benthic invertebrates collected from a reference stream (Elk Creek). The effects of metal-contaminated biofilm were examined by comparing macroinvertebrate colonisation of clean and contaminated substrata placed in Elk Creek. A feeding experiment with the mayfly Baetis tricaudatus Dodds (Ephemeroptera: Baetidae) examined metal bioaccumulation and effects of metal-contaminated biofilm on growth and survival.
3. Animas River water was acutely toxic to most taxa, with greatest effects observed on mayflies (Heptageniidae, Ephemerellidae) and stoneflies (Taeniopterygidae and Capniidae).
4. Although Animas River biofilm was characterised by high concentrations of metals and low algal biomass, most taxa colonised substratum from the reference stream and the Animas River equally. The exceptions were Ephemerellidae, Taeniopterygidae and Simuliidae, which were less abundant on Animas River substratum. Mayflies grazing Animas River biofilm accumulated significantly more metals and showed reduced growth compared with organisms feeding on Elk Creek biofilm.
5. Results of our experiments demonstrated that effects of heavy metals on benthic community structure in the Animas River were complex, and that responses to metals in water and contaminated substratum were species-specific. Predicting recovery of benthic communities following remediation requires an understanding of these species-specific responses.     

Comparisons of benthic communities adjacent to riparian native eucalypt and introduced willow vegetation

1. Willows, Salix spp., have been widely introduced as a riparian species in temperate Australia and New Zealand. The present study was a broad-scale observational survey to document the differences between reaches of river lined with willows and native vegetation in the community structure of benthic invertebrates and the resources which these plants use.
2. Nine rivers in south-eastern Tasmania were examined on three occasions in autumn, spring and summer. Taxa were identified to family level, with the exception of Oligochaeta and Acarina, and benthic organic matter (CPOM and FPOM) and epilithic biomass were measured for each reach.
3. Taxon diversity and evenness were lower in willowed reaches in autumn, and total macroinvertebrate density and number of taxa were lowest in willowed reaches in summer. No differences in the fauna between willowed and native reaches were observed in spring. Measures of community similarity of the fauna in willowed and native reaches were significantly different in autumn and summer, but not in spring.
4. The taxa responsible for the significant differences seemed to be responding to differences in food availability and habitat quality in reaches of each vegetation type. Organic matter standing stock was higher in willowed reaches in autumn although the influence of these litter inputs on the fauna were not marked. Epilithon biomass was highest in autumn and spring in willowed reaches when shading in these reaches was least.
5.  The most marked differences between willowed and native reaches were during summer low flows, when the instream fauna appeared to be responding to changes to shading, water quality and the quality of the habitat.     

Predicting the macroinvertebrate faunas of rivers by multiple regression of biological and environmental differences

1.   The prediction of macroinvertebrate community composition in flowing waters from environmental data has enabled pollution assessments that take account of natural variability. Polluted sites are identified by discrepancies between the observed fauna and the fauna expected at an unpolluted site on the same type of river.
2.   The usual method of prediction involves a sequence of (a) classification of unpolluted reference sites by cluster analysis of macroinvertebrate community data (b) multiple discriminant analysis to relate site clusters to environmental variables, and (c) use of site clusters, discriminant functions and environmental data to estimate the probability of collection of each macroinvertebrate taxon at sites that are to be assessed (test sites).
3.   This paper describes an alternative method that does not require classification and predicts abundance rather than probability of occurrence. The main steps are (a) multiple regression of biological differences between pairs of reference sites on differences in physical variables (b) use of the multiple regression relationship to predict the biological similarity of a test site to each reference site, and (c) estimation of the expected fauna at the test site as a weighted mean of the faunas at the reference sites. The predicted similarities of the test site to each reference site are used to derive the weightings.
4.   The method is illustrated using macroinvertebrate and environmental data collected in the upper Murrumbidgee River catchment as part of Australia's Monitoring River Health Initiative. In comparison with a classification-based analysis of these data, macroinvertebrate indices generated by the new method showed a greater distinction between human-disturbed and undisturbed test sites, and a similar or higher degree of correlation with physical and chemical indicators of human disturbance.