Defining criteria to select reference sites in Mediterranean streams

The European Water Framework Directive establishes the need to define stream type-specific reference conditions to identify “high ecological status”. Methods for selecting reference sites using a priori criteria have been proposed by many authors. A review of these criteria revealed that the most relevant criteria for streams and rivers were those related to riparian vegetation, diffuse and point sources of pollution, river morphology and hydrological conditions and regulation. In this work, we propose 20 criteria that reflect the characteristics of Mediterranean streams and their most frequent disturbances for the selection of reference sites in Mediterranean streams in Spain. We studied 162 sites located in 33 Mediterranean basins belonging to five stream types. Of the locations, 57% were selected as a priori reference sites by having applied the proposed criteria. Reference sites were identified for all stream types except for “large watercourses” which includes the lower reaches of some rivers in this study area. This a priori selection of reference sites was subjected to validation using the macroinvertebrate community by applying of an IBMWP threshold, which is considered to be an indicator of undisturbed sites in Mediterranean streams. This approach determined that whole of this selection (100%) could be considered valid reference sites. Furthermore, we identified differences in the reference conditions for each stream type on the basis of macroinvertebrate assemblage composition. Handling editor: R. Bailey     

Prediction and assessment of local stream habitat features using large-scale catchment characteristics

1. Knowledge of what a habitat should be like, in the absence of the effects of human activities, is fundamental to local stream habitat assessment. It has been suggested that stream habitats are influenced by large-scale catchment features. This study aimed to identify these relationships so that local-scale habitat features could be predicted from larger-scale characteristics.
2. Fifty-one reference sites from the Upper Murrumbidgee River catchment, south-eastern Australia, were classified on the basis of the local features of their stream habitat. Large-scale variables, namely catchment area, stream length, relief ratio, alkalinity, percentage of volcanic rocks, percentage of metasediments, dominant geology and dominant soil type, provided sufficient information for classifying 69% of reference sites into appropriate reference site groups.
3. A model created using these large-scale catchment variables was able to predict the local habitat features that were expected (E) to occur at a site in the absence of the effects of human activities. These were compared with observed (O) local habitat features to provide an observed-to-expected (O/E) ratio, an assessment score of the habitat at a site. The departure of this ratio from 1 enables identification of those sites that may be impacted. A list of habitat features that are expected at a site can provide targets for habitat restoration or enhancement.
4. For impacted sites, when habitat assessment from the habitat predictive model was compared with biological assessment from the Australian River Assessment System (AUSRIVAS) predictive model, it was possible to identify whether habitat degradation or water quality degradation was the cause of biological impairment. Such assessment may make it possible to identify rehabilitation goals relevant to the biota.     

Temporal variability of stream bioassessments using benthic macroinvertebrates

1. When using benthic macroinvertebrate communities for bioassessment, temporal variation may influence judgement as to whether or not a site is degraded.
2. In a survey of sixteen reference and sixteen test sites in the upper Thames River catchment area (UTRCA) in south-western Ontario, Canada, consistent differences between summer and winter samples were found for taxon richness (increase; P = 0.06) and the Family Biotic Index (decrease; P = 0.11). A bioassessment based on these results would indicate better water quality in the same streams in winter relative to summer. No consistent pattern of seasonal difference was detected for Simpson's Diversity and Equitability, or percentage Dominant Taxon.
3. The Reference Condition Approach to bioassessment uses predictive modelling to explain variation in reference communities with the environmental conditions at these sites as predictors. The community at a test site is compared with that predicted by the model. Several predictive models were constructed using simple geographic and habitat characteristics (i.e. catchment area, distance to source, stream width, substrate and habitat diversity) as predictors. By including season of sampling in the models, we increased their predictive power and the ability of the bioassessment to detect degradation. The best results were achieved when separate predictive models were built for each sampling season.     

Habitat models for a riparian carabid beetle: their validity and applicability in the evaluation of river bank management

In order to assess the management success of river rehabilitation measurements it is necessary to have representative target species and objective statistical methods. In this study we, tested the validity of habitat suitability models for the riparian carabid beetle Bembidion velox in the evaluation of river bank management along the River Elbe, Germany. On the basis of seven independent data sets from different sites and years we have proven the robustness of logistic regression models with respect to their explanatory and predictive power and their applicability in the field. All models had robust explanatory power and described a strong association of B. velox with semi-terrestrial sandy open soil habitats. Transfers of model results for adult beetles to their larvae and vice versa were highly significant with “sand content” and “stem distance” as the main habitat factors for both life stages. To broaden the local explanatory power towards general predictions we performed model cross-validation in space and time. Spatial transfers produced models with excellent discrimination properties, measured by Area Under Curve (AUC) values of Receiver Operating Characteristics (ROC) plots, independent of sampling designs and trapping methodology. However, the applicability of habitat models for B. velox is defined by the validity period, as the availability of suitable habitats for this species is highly temporally variable and dependent on water level. Model transfers between species also demonstrated that the chosen target species is representative for carabids with similar distribution patterns, as the single species model had high predictive power for the occurrence of a multi-species carabid group.     

Quantitatively defining the conservation status of Natura 2000 forest habitats and improving management options for enhancing biodiversity

The main goal of Natura 2000 network is to guarantee the favourable conservation status of habitats and species ensuring European biodiversity. As a result, certain forest areas have been included in this network listed as 9230-Quercus pyrenaica habitat and 9340-Quercus ilex subsp. rotundifolia forest habitat. These areas were previously used for firewood extraction or livestock grazing and browsing. Nowadays these habitats are coppice forests with asexual regeneration, which is far from the desired conservation status. Traditional timber harvesting plans do not take account of the new objectives required for these Natura sites, which attempt to ensure biodiversity and recreational uses instead of simply focusing on timber production. This paper proposes a flexible methodology (applied to the study area “Dehesa Boyal” in ávila, Spain) for managing Natura 2000 forest sites by stands for sustainable forest management and the new requirements. The methodology has two phases. The first, “Division of the forest area into stands”, defines homogeneous patches of vegetation distinct in species composition, physiognomic structure and future management. The second, “Conservation status assessment of stands”, quantifies the conservation status of each previously classified stand considering a series of factors such as: functional health, restoration, floral richness and structure. A total value integrating the conservation status of stands is then calculated for the habitat. Both phases use Geographic Information System tools for managing information and visualizing results. The proposed methodology provides forest managers with a good knowledge of the territory and subsequently enables them to take appropriate conservation measures to maintain biodiversity.     

Distant land use affects terrestrial and aquatic habitats of high naturalness

Biotas from all ecosystems need to respond to factors that determine habitat suitability. These factors originate from different scales. Effects can be assumed to be hierarchical in the order large-scale geographic > regional > local > small-scale in-habitat factors. We aimed at the identification of general patterns by comparisons between ecosystems (forest floor snails, hololimnic stream macroinvertebrates) and across scales, and include potential seasonal effects. Sampling sites displayed signs of naturalness, such as high levels of deadwood accumulation in the forests, or a lack of artificial stream bed fixation plus a “good” to “high” score for the assemblage-derived Multimetric Index (MMI) in the streams. Terrestrial and aquatic assemblages of non-emergent taxa fluctuated independent of seasonal effects. They differed in their relative correlation with environmental matrices with quasi-concentric effects in forests, and longitudinal effects in streams. Large-scale factors, namely geographic position, strongly influenced assemblage turnover, but the effect is based on a high covariation between geographic position and environmental factors. We thus extracted variables that best explained species turnover after correcting for spatio-temporal effects. The terrestrial community assembling was habitat-based and mainly responded to soil acidification, distance to disturbances, and regional scale deforestation and deciduous/mixed forest cover. The stream assemblages were structured by regional pasture cover, organic pollution, regional deciduous forest cover and microlithal cover. Apparently, community assembly occurs along with changes in regional forest cover and the transport of nutrients and matter that can originate from a distance, irrespective of ecosystem and assumed “naturalness”.     

Estuary hydrogeomorphology affects carbon sources supporting aquatic consumers within and among ecological guilds

Diatom-based stream bioassessment is constantly being improved to meet the increasing demands of water quality management. This study examined whether percentage of live diatoms (PLD) in periphyton communities can be used as a metric of human disturbance in streams and rivers. The analyzed dataset (587 sites) was collected over the course of 3 years (2000–2002) from 12 Western US states (US EPA’s Environmental Monitoring and Assessment Program). The mean PLD in Western streams and rivers was low (34.50%) and highly variable (range 2.08–97.02%). It did not differ significantly between the Mountains (MT, 36.38%) and the Xeric (XE, 35.49%) ecoregions, but it was significantly (P < 0.05) greater than that in the Plains ecoregion (PL, 28.27%). PLD distinguished reference from impacted sites in the MT (P < 0.05) and somewhat in the PL (P = 0.05). However, PLD exhibited opposite patterns in the two ecoregions. It increased with human disturbance in the MT and decreased in the PL due to a potential subsidy-stress gradient of available resources. The different pattern may be largely interpreted by the quality of the reference conditions in each ecoregion. In the MT ecoregion, the selected reference sites may resemble very closely the natural state in this ecoregion. In contrast, human disturbance is much more pervasive in the low-land PL ecoregion and the “reference sites” may reflect the best attainable conditions in this ecoregion. PLD as a metric has potential for monitoring human disturbance of streams, if reference sites represent natural conditions and differing responses among regions are included in expected effects.     

The response of macroinvertebrate community taxa and functional groups to pollution along a heavily impacted river in Central Europe (Bílina River,Czech Republic)

Macroinvertebrate communities were investigated along a gradient of heavy industrial and municipal pollution in the highland Bílina River (Czech Republic). Physico-chemical determinants and ions were monitored and community analysis performed focusing on taxonomic composition, ecological functioning (feeder and dweller guilds) and water quality metrics, including saprobity index, BMWP and diversity. Impacted sites differed significantly from reference and from recovered stretches. Chemical data revealed two main pollution factors, (1) a “salinity determinant”, described best by conductivity and SO₄²⁻, and (2) an “organic pollution determinant”, represented best by O₂ concentrations and NO₂⁻, all varying locally and temporally. Some metrics and taxa showed significant correlations to abiotic parameters. Functional communities showed a stronger relationship to the “organic pollution determinant”, suggesting that elevated organic pollution had a dominating influence on functional community metrics; though other variables may also have an influence in this multistress environment. On the other hand, there were indications that the taxonomic community was more influenced by ion concentrations (“salinity determinant”). The gradient from reference sites to polluted sites was weaker in the final sampling campaign. The results presented here can be used as a reference for assessing future changes in environmental impact from pollution, being finer and more detailed than assessment according to the EU’s WFD.     

Two-scale modelling of Saponaria bellidifolia Sm. (Caryophyllaceae) abundance on limestone outcrops from its northern range periphery (Southeastern Carpathians)

We modelled the effect of habitat heterogeneity on the abundance of the submediterranean Saponaria bellidifolia, a red list species in Romania. The study was designed at two scales: 100 and 0.5 m². At larger scale, generalized additive models and canonical correspondence analysis were used to model the density of ramets, whereas at microscale, binomial logistic regression was employed to model the species’ occurrence. S. bellidifolia abundance responded sensitively to habitat type (classified as “grassy”, “rocky” and “scree”), rather than to microclimatic variables. At both scales, habitat type was the best predictor of ramet abundance, followed by slope and vegetation cover. At 0.5 m², soil depth was also a good predictor of species occurrence. The data revealed that screes are the most suitable habitats for hosting relatively large populations of this rare species, because of occasional natural disturbances and presumably lower interspecific competition.     

Predictive modelling of freshwater fish as a biomonitoring tool in New Zealand

SUMMARY 1. A challenge has been issued to ecologists to find quantitative ecological relationships that have predictive power. A predictive approach has been successful when applied to biomonitoring using stream invertebrates with the River Invertebrate Prediction and Classification System (RIVPACS). This approach, to our knowledge, has not been applied to freshwater fish assemblages.
2. This paper describes the initial results of the application of a regional predictive model of freshwater fish occurrence using 200 reference sites sampled in the Manawatu–Wanganui region of New Zealand over late summer/autumn 2000. In brief (i) sites were classified into biotic groups (ii) the physical and chemical characteristics that best describe variation among these groups were determined and (iii) the relationship between these environmental variables and fish communities was used to predict the fauna expected at a site.
3. Reference sites clustered into six groups based on fish density and community composition. Using 14 physical variables least influenced by human activities, a discriminant model allocated 70% of sites to the correct biological classification group. The variables that best separated the site groups were mainly large-scale variables including altitude, distance from the coast, lotic ecoregion and map co-ordinates.
4. The model was further validated by randomly removing 20% of the sites, rebuilding the model and then determining the number of removed sites correctly allocated to their original biotic groups using environmental variables. Using this process 67% of the removed sites were correctly reassigned to the six predetermined groups.
5. A further 30 sites were used to determine the ability of the model to detect anthropogenic impact. The observed over expected taxa ( O / E ) ratios were significantly lower than the reference site O / E ratios, indicating a response of the fish assemblages to the known stressors.     

Spatio-temporal changes in habitat potential of endangered freshwater fish in Japan

In recent years, biodiversity conservation and ecosystem restoration have been key issues of watershed management in many countries. To maintain or restore the environmental quality of watersheds, we need to assess the impact of anthropogenic changes on stream ecosystems with accuracy. In addition, watershed conservation planners have to make strategic plans and determine priorities of each conservation activity.

A new monitoring methodology to evaluate the change of habitat condition for freshwater fish based on a predictive habitat model using logistic regression was developed and applied to the whole of Japan. The main contributions of our approach were 1) the construction of a Geographical Information System (GIS) database that integrates many types of data, including freshwater fish species, water quality, habitat fragmentation by damming, geology, and climate; 2) spatial analysis for quantitative assessment and predictive habitat modeling using logistic regression to combine fish survey data and environmental habitat factors to determine critical and major habitat variables for each target fish; and 3) digital mapping and changes detection of fish habitat potential for targeted endangered fish species to show habitat distribution and spatio-temporal changes of habitat potential over a 25-year period (from 1977 to 2002). We found that predicted suitable habitat and actual fish habitat showed high overlap, and that habitat conditions and distribution patterns of target freshwater fish had been affected by major habitat variables to target species respectively.     

Effect of Seasonal Changes on Predictive Model Assessments of Streams Water Quality with Macroinvertebrates

In this study we investigate how seasonal variability in aquatic macroinvertebrate communities affects the performance of a predictive model developed to assess environmental quality. Macroinvertebrates were sampled from nine not visibly disturbed sites located in different streams of the Mondego catchment across a full year. Organisms were identified to the lowest practicable taxonomic level and their abundances recorded at three taxonomic levels (order, family and lowest level). The seasonal samples were examined with regard to seasonal variation using three predictive models at order, family and lowest taxonomic level. The models showed increasing effect of seasonal changes across taxonomic levels, from order to the lowest level. When using the current models samples should be taken in the same season as the reference sites were sampled. Furthermore, data from more reference sites should be added to the model in order to encompass sufficient natural variation and allow the use of the model in different seasons. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Experimental translocation of juvenile water voles in a Scottish lowland metapopulation

Population density affects dispersal success because residents can hinder or facilitate immigration into a new site, via a “social fence effect” or “social attraction” (or “conspecific attraction”), respectively. These mechanisms can affect the dynamics of fragmented populations and the success of translocations. However, information on the settlement behaviour of dispersers is rare. We conducted a manipulative field experiment using wild water voles, which exist in metapopulations along waterways in Scotland. We translocated 17 young of dispersal age into either an occupied site or a vacant site containing good habitat, which had recently become extinct due to a feral predator (American mink) moving through. We monitored the movements of translocated voles using radio telemetry. Translocated voles were less likely to settle in occupied sites with higher densities of residents, suggesting a possible social fence effect at high density. There was evidence of a social attraction mechanism, because voles never remained at new sites unless another individual arrived soon after translocation, and they were more likely to settle in occupied or colonised sites than vacant ones. Voles remained in the transient phase of dispersal for many days, and often followed a “stepping stone” trajectory, stopping for several days at successive sites. We suggest that trajectories followed by dispersing water voles, the time scale and long dispersal distances found in this species are conducive to locating conspecifics at low density and colonising vacant habitat. These results are encouraging for prospects of metapopulation persistence and future translocation success.     

Modelling occurrence of roach “Rutilus rutilus” in streams

The selection of suitable variables is the first and important issue for fish habitat requirements and stream/river management programs. Classification trees (CTs) were used to study habitat preferences of the roach (Rutilus rutilus) in the Flemish stream basins (Belgium). The presence/absence of the roach was modeled based on a set of physicochemical and structural variables. The predictive performances of the CTs models were assessed based on the Cohen’s kappa statistics and percentage of correctly classified instances. An optimizer, genetic search algorithm (GAs), was combined with CTs to select the most important predictors for the fish habitat preferences. GAs improved the predictive performances of CTs and resulted in an easy interpretation of the models by making a selection of the variables that were used as input of CTs models. The models allowed to identifying the most important variables affecting habitat requirements of roach in streams. Based on the outcomes of models, the habitat preferences of roach in streams are mainly influenced by the habitat variables rather than water quality variables. It is proposed that CTs in combination with GAs can have high potential when applied for decision-making in the context of stream restoration and conservation management programs.     

Assessment of the effectiveness of best management practices for streams draining agricultural landscapes using diatoms and macroinvertebrates

In this study, a bioassessment was conducted to determine the effectiveness of best management practices (BMPs) implemented in farms in the Upper Delaware River watershed, NY (USA). Diatom and macroinvertebrate communities were analyzed across 17 low-order streams, designated as reference, BMP, or non-BMP. Streams lacking improvements (non-BMP) had significantly greater specific conductance, pH, TDP, NH₄ ⁺-N, and NO₃ ⁻-N than did reference streams. Diatom model affinity (DMA) values were significantly greater in reference and BMP streams than in non-BMP streams; non-BMP streams bordered on a “severely impacted” rating. The Trophic Diatom Index (TDI) varied two-fold among stream classes, with non-BMP > BMP > reference. TDI and DMA values were highly correlated, and both varied significantly with conductance, TDP, NH₄ ⁺-N, and NO₃ ⁻-N. Macroinvertebrate taxa, EPT richness, and Simpson’s diversity did not differ significantly among stream classes. Macroinvertebrate metrics (HBI, Bioassessment Profile, Percent Model Affinity) varied by stream class, but none indicated greater water quality in BMP sites. Nonetheless, each correlated significantly with conductance and TDP in the directions predicted by each model. Our data suggest that diatoms are more sensitive to moderate increases in nutrients, conductivity, and pH in high-gradient agricultural streams, and may be more useful in assessing stream management practices.     

The influence of stream habitat and water quality on macroinvertebrate communities in degraded streams of northwest Mississippi

Streams in the loess hills of northwest Mississippi have undergone dramatic physical changes since European settlement and both physical and water quality processes may play a role in influencing biotic communities of these stream systems. The objectives of this study were to identify the response of macroinvertebrate taxa to water quality and habitat parameters in streams of northwest Mississippi, examine the efficacy of an a priori classification system of stream channel evolution and condition class using macroinvertebrate communities, and examine short-term (<2 yr) temporal variation of macroinvertebrate communities. Separation of sites based on four condition classifications was not distinct. However, best attainable sites did plot together in an ordination analysis suggesting similarity in macroinvertebrate communities for least disturbed sites. Similarly, for stage of channel evolution, sites characterized by lack of bank failure and sinuous fluvial processes had relatively similar macroinvertebrate communities. Ordination analysis also indicated high temporal variation of macroinvertebrate communities. Reference sites (best attainable and stable sites) had more similar communities between years than unstable and impacted sites. Results of this study: (1) suggest total solids, total phosphorus concentration, percent substrate as sand, ammonia concentration, and conductivity were important variables for structuring stream macroinvertebrate communities in northwest Mississippi, (2) identify potential indicator taxa for assessing such streams based on water quality and physical habitat, (3) provide support for current a priori site classifications at the best attainable (least impacted) category relative to the macroinvertebrate communities, and (4) demonstrate that between-year variation is an important factor when assessing streams of north Mississippi and this variability may be related to the degree of stream degradation.     

Comparison of mayfly (Ephemeroptera) taxocenes of permanent and intermittent Central European small streams via species traits

The recurrent drying out of small streams in past decades has shown an urgent need to pay attention to the impact of global climate change. The objectives of this study were to describe the effect of drying out on the composition of the mayfly taxocene and evaluate the relevance of individual species traits for survival of mayflies to drying out. The mayfly taxocenes of two model localities, one at an intermittent and one at a permanent brook, were investigated in 2002, 2003 and 2005. Compared with the permanent stream, the taxocene of the intermittent stream was short of nine species, foremost rheobionts and high oxygen demand species. To explain further differences between both stream types in survival and recolonisation ability, 15 species traits were evaluated. These included so-called “ecological traits” (e.g., habitat and substrate range, density, distribution, current velocity adaptation) and “biological traits” connected with life cycle and larval/adult adaptations. Species showing the highest number of advantageous traits (with only exception of Electrogena sp. cf. ujhelyii — species of taxonomically unclear status) were able to successfully survive under the unfavourable conditions of the intermittent brook. Biological traits considered more important in many respects seem to be good predictors for assessing sensitivity to extreme temperature changes, hydrological regime fluctuations and the survival/recolonisation ability of species in exposed habitats.     

Local stream habitat variables predicted from catchment scale characteristics are useful for predicting fish distribution

South-east Queensland (Australia) streams were described by 21 local habitat variables that were chosen because of their potential association with fish distribution. An Assessment by a Nearest Neighbour Analysis (ANNA) model used large-scale variables that are robust to human influence to predict what the values of each of the 21 local habitat variables at each site would be without modification from human activity. The ANNA model used elevation, stream order, distance from source and longitude to predict the local habitat variables; other candidate predictor variables (mean rainfall, latitude and catchment area) were not found to be useful. The ANNA model was able to predict five of the 21 local habitat variables (average width, sand (%), cobble (%), rocks (%) and large woody debris) with an R ² of at least 0.2. The observed values of these five local habitat variables were used to model the distributions of individual fish species. The species distribution models were developed using logistic regression based on a subset of the data (some of the data were withheld for model validation) and a forward stepwise model selection procedure. There was no difference in predictive performance of fish distribution models for model predictions based on observed values and model predictions based on ANNA predicted values of local habitat variables in the withheld data (p-value = 0.85). Therefore, it is possible to predict the suitability of sites as habitat for given fish species using estimated (estimates based on large-scale variables) natural values of local habitat variables.     

Competitive reversals inside ecological reserves: the role of external habitat degradation

 Habitat degradation is the slow – and often subtle – deterioration in habitat quality that accompanies human activities through increases in road density, pesticide use, hunting pressure, etc. Such degradation is of particular concern in fragmented habitats where economic or jurisdictional boundaries rather than ecological ones determine the level of exploitation adjoining habitat patches endure. To examine the consequences habitat degradation might have on species interactions, we posited a patch of pristine habitat surrounded by “matrix” habitat whose degradation level was variable. Using a coupled pair of diffusive Lotka–Volterra competition equations with Robin (mixed) boundary conditions, we modeled the dynamics of two competing species inhabiting the pristine patch and incorporated matrix degradation through a tunable “hostility” parameter representing species’ mortality rates in the matrix. We found that the numerical range of competition coefficients over which one species is the competitive dominant and the other inferior may grow or shrink as matrix quality deteriorates. In some cases, degradation of the exterior habitat would bring about a complete competitive reversal inside the preserve. This result, wherein a formerly inferior species supplants a formerly dominant one – even inside the “protected” remnant patch itself – has policy implications for both nature reserve design and management of human activities outside park boundaries. Received: 30 April 1997