Structural and functional responses of benthic macroinvertebrates to acid precipitation in two forested headwater streams (Vosges Mountains, northeastern France)

From December 1996 to August 1997, beech litter breakdown and stream benthic macroinvertebrate communities were investigated to assess the effects of acidic precipitation on community structure and function in two second-order headwater streams of the Vosges Mountains (NE France). Because of microscale changes in bedrock mineral composition, one of the streams was acidified (mean pH=4.53, mean total Al=421 g.l^-1) and the other circum-neutral (mean pH=7.23, mean total Al=36 g.l^-1). Results showed that both litter breakdown rate and macroinvertebrate community structure were drastically affected under acidic conditions. The rate of leaf litter breakdown decreased by nine times in the acidic stream. Benthic sampling showed that scrapers were totally eradicated and both gathering and filtering collectors were drastically reduced. Such drastic effects appear to be the consequences of the toxicity of acid water including both proton and aluminum toxicity. A decrease in shredder abundance and a shift from the efficient acid-sensitive Amphipoda Gammarus fossarum to acid-tolerant Nemouroidea (mainly Leuctra sp.) was observed in the acidic stream. Our results indicate that freshwater acidification significantly alters the action of shredders processing leaf litter in the acidic stream. Consequently, interactions between structural and functional responses to acidification probably have profound consequences on the efficiency of acidified stream ecosystems, which in return may alter downstream functioning.     

Responses of benthic macroinvertebrates in small intermittent streams to silvicultural practices

We examined macroinvertebrate communities in small(0.1-1.0 m²) pools of intermittent streams (alwayscontainingsome water but without perennial flow) with small watersheds(2-6 ha) subjected to five types of forest harvest to assesspotential impacts of the different harvest methods. Bufferstrips10 m wide were left on each side of the streams. Each harvesttreatment was coupled with a similar unharvested referencestand.An incomplete block design included three 0.05 m² vacuumsamples from each treatment paired with three from theadjacentreferences. There was a high degree of similarity amongreferencesfor parameters other than taxonomic composition (e.g.macroinvertebrate density, number of species, Shannondiversity,functional groups, etc.). Statistically significantdifferenceswere found between references and treatments and among harvestmethods but the responses varied among response variables(density,Shannon-Weiner diversity, species composition), differentspeciesassemblages (all invertebrates, chironomids,Ephemeroptera-Plecoptera-Trichoptera [EPT], isopods), andfunctional group categories (shredders, collector-gatherers).Wecollected 56 taxa, 7–16 per site, with low communitysimilarity(mean Jaccards=0.18, mean Bray-Curtis percentdissimilarity=81). The most severe harvest treatmentsresultedin the highest diversities of total invertebrates in thesesmallspring pool communities.     

A method to estimate the population size of benthic macroinvertebrates in streams

Summary A method is described by which samples of stream macroinvertebrates can be linked to the roughness of the substratum, the water depth, the velocity, and to a combination of these factors, i.e., Froude number and thickness of the laminar sublayer, at the exact point of sampling. The abundance of Odagmia ornata (Diptera: Simuliidae), the species considered in this study, was not related to roughness, but depended with increasing significance on depth, velocity, Froude number, and laminar sublayer. Therefore, it is suggested that the population size of stream macroinvertebrates can be estimated using the relationships between abundance and the most suitable hydrodynamic factor. For this purpose it is necessary only to measure the physical factors and then to calculate the abundance, using both these measurements and the abundance-hydrodynamic factor relationships formerly established.A longer section of a stream with a relatively wide range of habitats was sampled for 1 week, during which the new method yielded results that reached the level of accuracy per sampling effort obtained to date only when a narrower range of habitats was sampled, usually only one stream riffle. Under the latter conditions, the new method is suggested to yield results of increased accuracy, particularly if samples are taken within a short period.     

Modelling the hydraulic preferences of benthic macroinvertebrates in small European streams

1. Relating processes occurring at a local scale to the natural variability of ecosystems at a larger scale requires the design of predictive models both to orientate stream management and to predict the effects of larger scale disturbances such as climate changes. Our study contributes to this effort by providing detailed models of the hydraulic preferences of 151 invertebrate taxa, mostly identified at the species level. We used an extensive data set comprising 580 invertebrate samples collected using a Surber net from nine sites of second and third order streams during one, two or three surveys at each site. We used nested non‐linear mixed models to relate taxon local densities to bed shear stresses estimated from FliesswasserStammTisch hemisphere numbers. 2. An average model by taxon, i.e. independent from surveys, globally explained 25% of the density variations of taxa within surveys. A quadratic relationship existed between the average preferences and the niche breadth of taxa, indicating that taxa preferring extreme hemisphere numbers had a reduced hydraulic niche breadth. A more complete model, where taxa preferences vary across surveys, globally explained 38% of the variation of taxa densities within surveys. Variations in preferences across surveys were weak for taxa preferring extreme hemisphere numbers. 3. There was a significant taxonomic effect on preferences computed from the complete model. By contrast, season, site, average hemisphere number within a survey and average density of taxa within a survey used as covariates did not consistently explain shifts in taxon hydraulic preferences across surveys. 4. The average hydraulic preferences of taxa obtained from the extensive data set were well correlated to those obtained from two additional independent data sets collected in other regions. The consistency of taxon preferences across regions supports the use of regional preference curves for estimating the impact of river management on invertebrate communities. By contrast, the hydraulic niche breadths of taxa computed from the different data sets were not related.     

Use of benthic macroinvertebrates to assess the biological status of Pampean streams in Argentina

Macro-invertebrate communities and environmental variables were assessed seasonally for two years in seven streams in North-Eastern of Buenos Aires province (Argentina) in order to analyse changes in their structure and composition in relation with the quality of the water. The study includes pristine streams and others affected by urban and industrial effluents with high conductivity, nitrates, nitrites, phosphates and low oxygen content. Organisms with well-known pollution tolerance were identified to assess biological water quality, using a new Biotic Index (IBPAMP: Biotic Index for PAMPean rivers and streams) in comparison with other existing biotic indices. The usefulness of principal component analysis (PCA) and correlation matrices were examined to evaluate the efficiency of the method to assess disturbances. In general IBPAMP did well correlate with several classical measures of biological water quality (taxon richness, diversity and several biotic indices). The El Gato stream was the most disturbed ecosystem among all studied sites. It was characterised by low dissolved oxygen levels, high turbidity in the middle course, high BOD5 (>30 mg l^–1) and COD (>40 mg l^–1) values. The Buñirigo stream has a bad quality in the industrial area, but varying according to the dry and wet periods. In general, in the mountainous areas the water quality of streams was good with the exception of the stations located downstream of cities like Ayacucho on the Tandileofú stream.     

Distribution of benthic macroinvertebrates in an artificially destratified reservoir

A total of 76 taxa of benthic macroinvertebrates as collected from Ham's Lake, Oklahoma, during 1974 and 1975. The composition and density of the benthic assemblage was similar to that of other Oklahoma reservoirs. The number of species and density of macroinvertebrates decreased from March to the end of July, 1975 Species diversity and biomass did not change significantly with time. Number of species and species diversity decreased with depth on all sampling periods. The most pronounced changes occurred between 4 and 5 m during periods of thermal stratification and hypolimnion anoxia. Artificial destratification removed the thermocline from Ham's Lake within 2 wk. More gradually, the deep waters were reoxygenated. Destratification did not substantially alter the depth distribution of benthic macroinvertebrates until oxygen level of the deep water was increased. Research supported with funds from the Oklahoma Water Resources Research Institute and the Bureau of Reclamation.     

Food resources of shredders and other benthic macroinvertebrates in relation to shading conditions in tropical Hong Kong streams

1. Gut content analyses (GCA) of benthic macroinvertebrates, supplemented by carbon and nitrogen stable isotope analyses (SIA), were used to determine the relative contribution of leaf litter and autochthonous food sources to consumer biomass in five shaded and five unshaded streams in tropical Hong Kong. 2. Only four obligate shredders and two facultative shredders were identified out of 58 morphospecies dissected. Non‐shredder taxa consumed little (<23% food eaten) coarse particulate organic matter (CPOM) in spite of its abundance in streams, and GCA revealed that fine particulate organic matter was the major food (25–99%) of most primary consumers. 3. Stable isotope analysis results were in general agreement with the findings of GCA, and confirmed that three of the four obligate shredders had a high dependence (55–78% of assimilated carbon) on CPOM. 4. Autochthonous energy sources were important in all streams: non‐shredding primary consumers examined, which accounted for 72% of total macroinvertebrate abundance in shaded streams, derived (on average) 61% of their biomass from autochthonous foods; the equivalent values for unshaded streams were 72% (abundance) and 71% (biomass).     

Effects of flow and refugia on drift loss of benthic macroinvertebrates: implications for habitat restoration in lowland streams

• 1 Current stream restoration practices are rarely based on sufficient knowledge of the physical-habitat requirements of the biota. In this study the drift loss of two lowland stream benthic macroinvertebrates, Gammarus pulex (L.) (Amphipoda, Crustacea) and Ephemerella ignita (Poda) (Ephemeroptera, Insecta), was investigated over gradients of flow forces and abundance of woody debris in laboratory flume experiments.
• 2 The losses by drift of E. ignita and G. pulex increased significantly at median flume shear stresses of approximately 11 and 31 dyn cm^?2, respectively.
• 3 Above these critical shear-stress values the population losses of both species significantly decreased with increasing abundance of stationary woody debris.
• 4 Ephemerella ignita exhibited high population loss in the first period of hydraulic disturbance. Gammarus pulex was affected in a different way, showing an almost constant population loss over time. In contrast to E. ignita, G. pulex used the refugium ‘woody debris’ actively and more efficiently.
• 5 Restoration concepts of lowland running waters have to consider hydraulic disturbance by flow as a key element for potential benthic community recovery.
• 6 Woody debris in the baseflow channel of lowland streams appears to mitigate the impact of hydraulic disturbance to benthic macroinvertebrates caused by rising discharge.

     

Variability and convergence in benthic communities along the longitudinal gradients of four physically similar Rocky Mountain streams

1. High‐gradient mountain streams are ideal for studying longitudinal biological patterns, although the degree of similarity in the biological gradient among physically similar streams in a region is poorly known. Our first objective was to evaluate variability in benthic communities along four streams in the central Rocky Mountains of Colorado. We analysed the relative influence of longitudinal position versus reach‐scale physical variables on community structure and measured community similarity at comparable longitudinal positions on the four streams. 2. Our second objective was to evaluate the relative utility of taxonomically versus functionally defined communities to characterise assemblage structure: are taxonomic patterns more predictable along the gradient than are patterns of ecologically important species traits? 3. Redundancy analyses (RDA), including measures of both reach‐scale environmental variables (substratum properties, periphytic cover, local channel slope) and longitudinal position (altitude, stream size), confirmed that the longitudinal position of a site was most important in determining taxonomic composition. Functional community structure was also influenced by longitudinal position, but reach‐scale variables (especially periphyton and median particle size) were of greater importance. 4. Redundancy analyses explained 29.3% of total taxonomic variance and 26.0% of functional variance, indicating that defining assemblages functionally provides no greater understanding of community patterns given several known environmental variables. Strict longitudinal limits of taxa, the presumably identical regional species pool across our sites, and/or trade‐offs among different types of species traits probably explain this result. 5. Redundancy analyses did suggest, however, that traits related to longer life (semivoltinism, long‐lived adults, and slow larval development) were more common downstream, while long‐distance dispersal ability and high fecundity were associated with higher altitude and its associated harsher conditions. 6. When sampling sites were grouped into three ecological zones defined by altitude, mean community similarity (measured both taxonomically and functionally) was lowest across streams at the highest altitude. This pattern could be driven by increased insularity of alpine‐zone streams, resulting from a combination of harsh terrestrial environment, lack of hydrological connectivity, and limited species ranges along the longitudinal continuum.     

Measuring and controlling data quality in biological assemblage surveys with special reference to stream benthic macroinvertebrates

1. Biological assemblage surveys primarily aim to characterise species composition and relative abundance at one or more spatial or temporal scales. Data interpretation and conclusions are dependent on how well samples characterise the assemblage of interest. 2. Conventional measures of data quality, e.g. standard deviations or coefficients of variation, were designed for single variable estimation, and they are either insufficient or invalid for assessing the quality of data describing entire assemblages. Similarity indices take species composition and relative abundance into account and may be used to effectively measure and control the quality of data used to characterise assemblage structure. 3. The average Jaccard coefficient (JC) calculated across multiple pairs of replicate samples, i.e. autosimilarity JC (AJC), is conceptually and numerically related to the average coefficient of variation in the densities of all species recorded, a measure of sampling precision, and to the proportion of total species richness sampled, a measure of sampling accuracy. 4. We explored how AJC can be used to assess the effect of different potential sources of error on the quality of assemblage survey data, including the sampling effort used both within regions and at individual sites, the individuals collecting samples, sub‐sampling procedures, and consistency of taxon identification. 5. We found that the autosimilarity‐based approach overcomes most weaknesses associated with conventional measures of data quality and can be used to effectively measure and control the quality of assemblage survey data.     

Biological and ecological traits of benthic freshwater macroinvertebrates: relationships and definition of groups with similar traits

• 1 Relating species traits to habitat characteristics can provide important insights into the structure and functioning of stream communities. However, trade‐offs among species traits make it difficult to predict accurately the functional diversity of freshwater communities. Many authors have pointed to the value of working with groups of organisms as similar as possible in terms of relationships among traits and have called for definition of groups of organisms with similar suites of attributes.
• 2 We used multivariate analyses to examine separately the relationships among 11 biological traits and among 11 ecological traits of 472 benthic macroinvertebrate taxa (mainly genera). The main objective was to demonstrate (1) potential trade‐offs among traits; (2) the importance of the different traits to separate systematic units or functional groupings; and (3) uniform functional groups of taxa that should allow a more effective use of macroinvertebrate biological and ecological traits.
• 3 We defined eight groups and 15 subgroups according to a biological trait ordination which highlighted size (large to small), reproductive traits (K to r strategists), food (animal to plant material) and feeding habits (predator to scraper and/or deposit feeder) as ‘significant’ factors determining the ordination of taxa. This ordination partly preserved phylogenetic relationships among groups.
• 4 Seven ecological groups and 13 ecological subgroups included organisms with combinations of traits which should be successively more adequate in habitats from the main channel to temporary waters, and from the crenon to the potamic sections of rivers, and to systems situated outside the river floodplain. These gradients corresponded to a gradual shift from (1) rheophilic organisms that lived in the main channel of cold oligotrophic mountain streams to (2) animals that preferred eutrophic habitats of still or temporary waters in lowlands. The groups with similar ecological traits had a more diverse systematic structure than those with similar biological traits.
• 5 Monitoring and assessment tools for the management of water resources are generally more effective if they are based on a clear understanding of the mechanisms that lead to the presence or absence of species groups in the environment. We believe that groups with similar relationships among their species traits may be useful in developing tools that measure the functional diversity of communities.

     

Dissolved oxygen concentration and diversity of benthic macroinvertebrates in an artificially destratified lake

Changes in species composition and diversity of benthic macroinvertebrates during summer and fall were compared in an area of a lake artificially destratified and in an arm not destratified. Numbers of species, diversity, and density were significantly correlated with the concentration of dissolved oxygen, while none of the biotic variables were correlated with temperature.Research supported with funds from the Oklahoma Water Resources Research Institute     

The fate of assimilated nitrogen in streams: an in situ benthic chamber study

1. Nitrogen (N) processing in streams has been investigated using whole‐stream ¹⁵N addition experiments that, in general, have found that a large proportion of added nitrate removed from the water column appears to be assimilated by the stream benthos. The long‐term fate of this retained N is unknown, and of particular interest is the possibility that it becomes denitrified through coupled mineralisation–nitrification–denitrification processes (indirect denitrification). 2. We used in situ chambers to produce highly ¹⁵N‐enriched benthic biofilms and removed the chambers to allow biofilms to interact with ambient stream conditions. Nitrogen assimilation and direct denitrification were estimated from the first chamber deployment. Chambers were periodically reinstalled over 4 weeks to measure tracer ¹⁵N in ammonium (), nitrate () and dinitrogen (N₂), from which we estimated subsequent rates of biotic N transformations, including N mineralisation (ammonification), nitrification and indirect denitrification. We also estimated rates of depuration of ¹⁵N tracer from benthic biomass compartments. 3. Nitrate uptake was roughly equivalent in the sand and cobble habitats that dominated the stream. Direct denitrification (denitrification of from the water column) was an order of magnitude higher in cobble habitats than in sand habitats, accounting for c. 26 and 2% of total nitrate uptake in cobble and sand, respectively. 4. Mean residence times of actively cycling organic N in stream benthos (algae and microbes) were 16 days in cobble habitats and 9 days in sand habitats. The difference between habitat types was driven by the influence of N residence time in epilithic biofilms (18 days) on cobbles. 5. Release of enriched ¹⁵ was the primary flux of remineralised N, while release of enriched ¹⁵ was an order of magnitude less. We detected slight ¹⁵N enrichment in dissolved nitrogen gas (N₂) in post‐enrichment sampling, indicating that indirect denitrification was taking place. However, indirect denitrification accounted for <0.1% of the assimilated N. 6. These experiments agree with results of whole‐stream ¹⁵N additions, in that most added N was assimilated rather than directly denitrified. Assimilation was primarily a short‐term N retention mechanism in this stream, and indirect denitrification of assimilated N accounted for only a minor proportion of the observed ¹⁵N loss over time. 7. Remaining possible fates include export of N as particulate organic matter, which may lead to additional storage of assimilated N in downstream habitats, and consumption by grazers.     

Development of an Index of Trophic Completeness for benthic macroinvertebrate communities in flowing waters

The analysis of the trophic structure of benthic macroinvertebrate communities can be used in biological assessments of the condition of river ecosystems. Using the trophic, or functional approach, the Index of Trophic Completeness (ITC) was developed. The goal was to overcome the problems and drawbacks of using conventional diversity or biotic indices in biological assessments of rivers, such as limitation to distinct geographical regions or focus on species richness without regard for ecosystem functioning. Following an extensive review of the literature on the trophic characteristics of benthic macroinvertebrates, a large number of species (±300) were characterized according to a number of trophic criteria: plant:animal ratio in the diet, feeding mechanism, food size, food acquisition behaviour, and energy and substance transfers. On the basis of their trophic characteristics, the species could be divided into 12 trophic groups. After examination of data from geographically diverse rivers, it was concluded that any undisturbed riverine benthic macroinvertebrate community should be represented by members of each of these 12 trophic groups, with each group fulfilling a function in the benthic community. Being a community which plays a central role in the functioning of the aquatic ecosystem, the benthic invertebrates are expected to respond to disturbances to the hydrobiocoenose. The outcome of an ITC assessment is clearly presentable in the form of a pie graph with 12 wedges, each representing one of the 12 defined trophic groups. Functionally complete communities are represented by 12 wedges; a blank wedge indicates that a trophic group is not represented. This paper describes the preliminary developments in the ITC method, its potential as a biological assessment method in rivers in different geographical zones, and presents examples of trial mappings of Russian and European rivers. The application of the ITC to these rivers demonstrated the absence of ITC trophic groups at sites under the influence of anthropogenic activity.     

Birch leaf processing and associated macroinvertebrates in an acidified lake subjected to liming

In connection with the liming of an acid lake in southern Norway, a series of litter bags was placed in a pH-gradient in the limed lake and a nearby unlimed lake. During the experiments, which lasted two years, no significant differences in decomposition rates between the various localities at the same depth were noticed. The chironomid collector Tanytarsus pallidicornis was the dominant invertebrate species in the benthic samples. This demonstrates the importance of fine particulate organic matter as a food source in the lake. Collector dominance was lower in the leaf packs, which consisted mostly of coarse particulate organic matter. A poor fauna of detritus grazers probably contributed to the unchanged rates of decomposition of the leaves after liming.     

Performance of eDNA assays to detect and quantify an elusive benthic fish in upland streams

The sensitivity and specificity of eDNA-based monitoring, coupled with its potential utility to estimate population density or biomass, makes it a useful tool in invasive species management. In this study, we investigated the potential of the eDNA method to improve the detection of the elusive invasive fish, oriental weatherloach (Misgurnus anguillicaudatus), in a river system where a density gradient of the species occurs. We compared detection rates between eDNA and conventional monitoring methods and examined the relationship between eDNA and abundance in a flowing environment. The eDNA method had a higher site detection rate than conventional methods (63 vs. 38%). Weatherloach eDNA was detected at all sites where the fish has been previously caught and none of the sites where the species has not been caught for the past 7 years. There was an increasing density trend going downstream based on long-term conventional monitoring, but the eDNA concentration in water samples reflected this trend only in a continuous section of the river where impoundments were absent. We did not find a positive relationship between eDNA concentration and contemporary abundance estimates in our study area. A high eDNA concentration was recorded at a site (DVC) which was designated a low density site based on long-term catch data. This discrepancy was a likely result of physical habitat characteristics which influenced the efficiency of the conventional methods used. This study highlighted the challenges of inferring density from eDNA data in flowing water because habitat features may confound results, necessitating careful consideration for results to be useful to management.     

An expert system to estimate the pesticide contamination of small streams using benthic macroinvertebrates as bioindicators II. The knowledge base of LIMPACT

The development and the evaluation of a biological indicator system for pesticide pollution in streams are presented. For small headwater streams with an agricultural catchment area, the expert system LIMPACT estimates the pesticide contamination according to the four classes: Not Detected (ND), Low (L), Moderate (M) and High (H) contamination without any specification of the chemical agents. The input parameters are the abundance data of benthic macroinvertebrate taxa within four time frames in a year (March/April, May/June, July/August, September/October) and nine basic water-quality and morphological parameters. The heuristic knowledge base was developed with the shell-kit D3 and contains 921 diagnostic rules with scores either to establish or to de-establish a diagnosis. The 418 rules had less than three symptoms, and only 47 rules had more than four symptoms in their rule condition. We differentiate between positive indicator (PI) taxa, which indicate contamination by high abundance values and positive abundance dynamics, and negative indicator (NI) taxa, a high abundance of which rules out contamination and indicates an uncontaminated site. We analysed 39 taxa and found 13 positive and 24 negative indicators. The database comprises 157 investigations per stream and year with rainfall event-controlled pesticide sampling and repeated benthic sampling as described in Part 1 [Ecol. Indicators, this issue]. For the evaluation of LIMPACT, we used the same cases. The correct class for the 157 investigations per stream and year is established by LIMPACT in 66.7–85.5% of the cases, with better results for uncontaminated sites. The overall alpha error probability (false positive) is 9.6% while the beta error probability (false negative) varied between 0 and 8% depending on the contamination class. If each stream is considered only once in the system (n=104), the correct diagnosis is established by LIMPACT in 51.9–88.6% of the cases. In most of the remaining cases no diagnosis is established instead of a wrong one.