A new biological indicator to assess the ecological status of Mediterranean trout type streams

Fuelled by the generalized degradation of freshwater ecosystems, the development of tools to assess their ecological status has been the focus of intensive research in the last decades. Although fish are one of the key biological quality elements used to describe the ecological status of rivers, fish metrics that accurately respond to disturbances in Mediterranean trout type streams are still lacking. In these systems, multimetric indices are not optimal indicators because of their low species richness and abundances, thus alternative approaches are needed. Since carrying capacity defines the potential maximum abundance of fish that can be sustained by a river, its relationship with actual density (D/K ratio) could be an accurate indicator of population conservation status and consequently of the ecological status of the river. Based on this rationale, we modeled carrying capacity dynamics for 37 brown trout populations during a 12-year study period. We analyzed the response of the D/K ratio to a gradient of increasing environmental harshness and degradation in order to assess its suitability to accurately measure brown trout conservation status. Our results showed that the D/K ratio was highly sensitive to temporal and spatial variations in environmental conditions and the levels of human-induced environmental degradation. Variations in the environmental and human degradation factors included in the best explaining regression models developed for the whole population and by age classes accounted for between 58 and 81% of the variation in the D/K ratio. Likewise, the D/K ratio was sensitive to both general and life stage specific disturbance factors. Further analyses helped identify the factors limiting population abundance. Therefore, the D/K ratio could be an interesting indicator to consider when defining objective management plans and corrective actions in degraded rivers and streams subject to Mediterranean climatic conditions.     

Using algal metrics and biomass to evaluate multiple ways of defining concentration-based nutrient criteria in streams and their ecological relevance

We examined the utility of nutrient criteria derived solely from total phosphorus (TP) concentrations in streams (regression models and percentile distributions) and evaluated their ecological relevance to diatom and algal biomass responses. We used a variety of statistics to characterize ecological responses and to develop concentration-based nutrient criteria (derived from ecological effects) for streams in Connecticut, USA, where urbanization is the primary cause of watershed alteration. Mean background TP concentration in the absence of anthropogenic land cover was predicted to be 0.017 mg/l, which was similar to the 25th percentile of all study sites. Increased TP concentrations were significantly correlated with altered diatom community structure, decreased percent low P diatoms and diatoms sensitive to impervious cover, and increased percent high P diatoms, diatoms that increase with greater impervious cover, and chlorophyll a (P < 0.01). Variance partitioning models showed that shared effects of anthropogenic land cover and chemistry (i.e., chemistry affected by land cover) represented the majority of explained variation in diatom metrics and chlorophyll a. Bootstrapped regression trees, threshold indicator taxa analysis, and boosted regression trees identified TP concentrations at which strong responses of diatom metrics and communities occurred, but these values varied among analyses. When considering ecological responses, scientifically defensible and ecologically relevant TP criteria were identified at (1) 0.020 mg/l for designating highest quality streams and restoration targets, above which sensitive taxa steeply declined, tolerant taxa increased, and community structure changed, (2) 0.040 mg/l, at which community level change points began to occur and sensitive diatoms were greatly reduced, (3) 0.065 mg/l, above which most sensitive diatoms were lost and tolerant diatoms steeply increased to their maxima, and (4) 0.082 mg/l, which appeared to be a saturated threshold, beyond which substantially altered community structure was sustained. These criteria can inform anti-degradation policies for high quality streams, discharge permit decisions, and future strategies for watershed development and managment. Our results indicated that management practices and decisions at the watershed scale will likely be important for improving degraded streams and conserving high quality streams. Results also emphasized the importance of incorporating ecological responses and considering the body of evidence from multiple conceptual approaches and statistical analyses for developing nutrient criteria, because solely relying on one approach could lead to misdirected decisions and resources.     

Critical influence of seasonal sampling on the ecological quality assessment of small headwater streams

Variability in the ecological quality assessment of reference sites was tested on small headwater streams in Ireland. Although headwater streams constitute a large portion of the river channel network, they are not routinely monitored for water quality. Various metrics were used including the Irish Q-value and the newly developed Small Streams Risk Score (SSRS), and metrics applied elsewhere in the Atlantic biogeographic region in Europe, including the Biological Monitoring Working Party score (BMWP), the Average Score per Taxon (ASPT), the Ephemeroptera, Plecoptera and Trichoptera taxa (EPT), the Belgium Biotic Index (BBI) and the Danish Stream Fauna Index (DSFI). The AQEM (version 2.5a) assessment software was used to apply some of these metrics. The spring and summer datasets are used to test the performance of biotic metrics with respect to season, and the applicability of their use to assess the ecological quality of wadeable streams. The quality status of most sites assigned by the various metrics was high using the spring invertebrate data, and an apparent considerable deviation in quality status occurred when the summer data was applied. Seasonal differences were noted using all the biotic indices and are attributed to the absence of pollution-sensitive groups in summer. Seasonal variability in the water quality status was particularly evident in acidic streams draining non-calcareous geologies with peaty soils that had relatively lower numbers of taxa. Some indices applied reflect a greater seasonal difference in the quality category assigned. The least amount of variability between seasons was obtained using the ASPT and the SSRS risk assessment system. Results suggest that reference status is reliably reflected in spring when more pollution-sensitive taxa were present, and that a new ecological quality assessment tool is required for application in summer when impacts may be most severe. This highly heterogeneous freshwater habitat seems to have too few taxa present in the summer to reliably determine the ecological quality of the stream using the available indices. Handling editor: R. Bailey     

Factors influencing macrophyte metrics in Estonian coastal lakes in the light of ecological status assessment

Macrophytes and factors affecting their distribution were studied in 19 coastal lakes of Estonia. The aim of the study was to determine the factors influencing the distribution of macrophytes in coastal lakes and to assess the suitability of valid macrophyte metrics. Our hypothesis was that in coastal lakes most of the macrophyte distribution patterns are caused by lake-specific variables. Morphological, physico-chemical and catchment area characteristics of the lakes varied greatly. Lakes were in different development stages—lakes nearest to the Baltic Sea were younger and more influenced by brackish water and the furthest lakes were older with more freshwater. All that variability was reflected in macrophyte parameters. Factor analysis of environmental indices divided them into three groups—catchment area, morphometric and water chemistry factors. The first factor may be considered as a pressure and the other two as lake-type-specific factors. Lake catchment area parameters had an influence on Bolboschoenus maritimus, Chara tomentosa and Typha latifolia abundance. Morphometric parameters had an influence on the depth distribution of macrophytes and water chemistry factors on the abundance of helophytes. Current indicator species showed more variability associated with lake-specific factors than with changes in status or the influence of pressures.     

Influence of groundwater exploitation on the ecological status of streams in a Mediterranean system (Selva Basin,NE Spain)

The ecological status of streams depends on an equilibrium between hydrological processes and biological dynamics. Water discharge is the main requisite for a wealthy riparian habitat. Nevertheless, human practices severely affect water availability through stream water derivation and groundwater withdrawal. In this sense, impacts upon aquifer water storage and its effects on base flow generation have a significant effect on stream biology. Consequently, biological indicators will point out poor conditions resulting from such human impacts. In this paper, the effects of groundwater exploitation on stream discharge and surface water quality are evaluated and compared to biological indicators in a Mediterranean catchment.The stream–aquifer relationship is investigated by considering the hydrological context of each river reach, including human pressures, and the hydraulic head in the contiguous alluvial aquifer, where it exists. These data allow us to differentiate distinct types of reaches that are defined according to a “Stream–Aquifer relationship and chemical Pressure” (SAP) classification, which is used later on to standardize the different hydrochemical and biological features of the sampling points.Stream water and groundwater hydrochemistry are compared to depict the hydraulic behavior of the sampled watercourses during wet and dry periods. Specific elements are used as tracers of groundwater inputs, wastewater influence, or even stagnant conditions during the dry season. This dataset defines a framework to interpret the biological status of each reach based on the Iberian biological monitoring working party indicator (IBMWP). Affinities between hydrological and hydrochemical conditions with biological indicator values allow the causal effects of groundwater exploitation on stream ecology to be defined.The use of multivariate principal component analysis shows that the dataset variance is distributed according to the SAP classification, and that variable grouping is in agreement with the observed hydrological processes and their effects on biological indicator values.This work provides evidence of the importance of groundwater dynamics on biological indicators in a human-modified environment. When using the SAP classification, biological indicators acquire a broader meaning as they reveal the status of biological processes and the causal references. Such information is relevant for water management assessment within the context of the European Water Framework Directive, as it emphasizes the control of groundwater exploitation as a key parameter in the preservation of stream ecological status and the achievement of the objectives of the directive.     

Long-term recovery of macroinvertebrate biota in grossly polluted streams: Re-colonisation as a constraint to ecological quality

To meet targets imposed by the European Water Framework Directive (2000/60/EC) it is vital that measures to improve the status of rivers are both effective and economically viable. Achievement of such aims needs robust understanding of biological responses to changes in water quality vis-à-vis mechanisms of and constraints to the colonization of previously polluted sites. This study therefore examined the long-term chemical and biological changes in historically polluted rivers to elucidate the responses of macroinvertebrate biota to improvements in chemical water quality. For three historically polluted sites in the English Midlands, data from surveys over a period of ca. 50 years were analysed. Ammonia (NH₃) and 5-day biochemical oxygen demand (BOD₅) were used as chemical water quality indicators. Variations in the ecological recovery of the study sites were assessed using an average pollution sensitivity score (Average Score Per Taxon) and the number of taxa present (usually to family level) present in hand-net samples. Ecological recovery varied widely and was influenced by the intensity and spatial extent of the pollution and the proximity of available sources of potential colonisers. At the site most isolated from potential sources of colonizing taxa, no clean-water macroinvertebrate taxa were recorded 30 years after the major sources of pollution ceased. Where clean-water colonisers were more readily available, significant improvements in ecological quality followed within 2–5 years of the improvements in chemical quality. Macroinvertebrate communities and hence monitoring data may thus be indicative of long past conditions or of biological isolation rather than contemporaneous chemical conditions. Combined chemical and biological data were used to explore a generic model for predicting recovery rates and success. Neither BOD₅ nor NH₃ were found to provide a consistent and meaningful prediction of either average pollution tolerance of macroinvertebrate taxa or of the number of taxa present. Long-term relationships between macroinvertebrate variables and chemical water quality variables, however, were non-linear, suggesting that water quality thresholds may have to be exceeded before biological recovery can occur. Even when chemical water quality has been improved substantially, the apparent ecological status of macroinvertebrate communities may not reflect reduced pollution levels attained until adequate time to allow for re-colonisation (possibly decades) has elapsed.     

Development of a macroinvertebrate multimetric index for the assessment of low-land streams in the neotropics

The water and habitat quality in Panamanian streams and rivers are being degraded by agriculture, urbanization, industrial activities, mining, and other forms of development. Thus, the need for standards, especially those examining the biological attributes of lotic systems, are urgently required. We describe the development of a multimetric index based on macroinvertebrates collected in low-land streams in the Panama Canal Watershed (PCW), which differed in their levels of human impacts. The index was developed using 12 streams and validated using a further three, all of which were sampled on four occasions, in the dry and wet seasons of 2007 and 2008. We examined 42 metrics related to macroinvertebrate community structure, composition, and function. Based on their ability to distinguish reference from moderately or severely impacted streams, and on their independence, we selected seven metrics (Margalef's index (taxa), Shannon's evenness index (taxa), number of EPT (taxa), % of Trichoptera, ratio of Chironomidae/Diptera individuals, % of scrapers, and % of shredders). These metrics were then standardized and developed into the Neotropical Low-land Stream Multimetric Index (NLSMI). Overall, the NLSMI distinguished well among the different levels of impairment (Reference, Moderate impact, and Severe impact) and showed a strong, significant correlation with principal component analysis (PCA) axis one values, with the PCA based on a set of physico-chemical variables indicative of stream quality. The wet season generally resulted in lower NLSMI values, leading us to suggest that sampling for biomonitoring be carried out in the dry season. Overall, this preliminary macroinvertebrate NLSMI shows promise for developing a biomonitoring programme to assess the ecological integrity of streams, to aid with management, restoration, and conservation, and to serve as a basis to develop a more geographically extensive multimetric index.     

Effects of natural hydrological variability on fish assemblages in small Mediterranean streams: Implications for ecological assessment

Small Mediterranean streams are shaped by predictable seasonal events of flooding and drying over an annual cycle, and present a strong inter and intra-annual variation in flow regime. Native fish assemblages in these streams are adapted to this natural environmental variability. The distinction of human-induced disturbances from the natural ones is thus a crucial step before assessing the ecological status of these streams. In this aim, the present study evaluates the effects of natural hydrological variability on fish assemblages from disturbed and least disturbed sites in small intermittent streams of south Portugal. Data were collected over the last two decades (1996–2011) in 14 sites located in the Guadiana and Sado river basins. High variability of fish assemblages was strongly dependent on human-induced disturbances, particularly nutrient/organic load and sediment load, and on natural hydrological variability. Natural hydrological variability can act jointly with anthropogenic disturbances, producing changes on fish assemblages structure of small intermittent streams. In least disturbed sites, despite the natural disturbances caused by inter-annual rainfall variations (including drought and flood events), fish assemblages maintained a long-term stability and revealed a high resilience. On the contrary, disturbed sites presented significantly higher variability on fish assemblages and a short and long-term instability, reflecting a decrease on the resistance and resilience of fish assemblages. Under these conditions, fish fauna integrity is particularly vulnerable and the ecological assessment may be influenced by natural hydrological variations. High hydrological variability (especially if it entails high frequency of dryer years and meaningful cumulative water deficit) may affect the impact of the human pressures with significant and consistent consequences on fish assemblage composition and integrity. In this study, fish metrics that maximize the detection of human degradation and minimize the response to natural variability were based on the relative abundance of native species (insectivorous species, eurytopic species, water column species, native lithophilic species), relative abundance of species with intermediate tolerance and relative number of exotic species. Results highlight the importance of assessing temporal variability on stream biomonitoring programs and emphasize the need to improve the assessment tools, accounting for long-term changes in fish assemblages, namely by selecting the most appropriate fish metrics that respond to anthropogenic disturbances but exhibit low natural temporal variability, essential both in the characterization of the biological reference conditions and in the development of fish indexes in intermittent streams.     

An assessment of macrophyte community metrics in the determination of the ecological condition and total phosphorus concentration of Mediterranean ponds

The macrophyte vegetation of 51 ponds situated in the Duero river basin on the Northern Iberian Plateau was studied with the aim of selecting metrics that responded clearly to perturbation and that should be included in a multimetric index for assessing the ecological condition (expression of the quality of the structure and functioning of aquatic ecosystems associated with surface waters) of Mediterranean ponds. Furthermore, the specific response of metrics to the total phosphorus (TP) concentration was also investigated because of agricultural activities, which usually increase the concentration of nutrients in aquatic systems, are one of the principal types of impairment affecting ponds in the Duero basin.A total of 19 metrics representing several aspects of the structure of macrophyte communities (cover, richness, diversity) were selected as potential metrics.The strong overlap which was observed for macrophyte metrics between classes of ecological conditions (bad, poor, moderate, good, best available) and TP concentrations (>600, 600-300, 300-100, 100-50, <50 μg L⁻¹ TP) constitutes a major problem in defining and separating these classes. For this reason, Mann-Whitney U-test and discrimination efficiency were carried out to determine which of the measures best discriminated between slightly impaired sites (ponds in good or best available condition) and perturbed ponds (ponds in moderate, poor or bad condition). Most of the metrics showed significant differences (p < 0.05) between slightly impaired and perturbed ponds. However, only total cover and hydrophyte richness, which had the highest discrimination efficiency (>78%), showed no inter-quartile overlap (25th-75th percentile) between the two ecological classes. For these reasons, both total cover and hydrophyte richness were selected for the implementation of a multimetric index able to discriminate between slightly impaired and degraded Mediterranean flatland ponds.Currently, eutrophication is considered the main pressure on lakes. However, macrophyte metrics were far less sensitive to TP concentration than to ecological condition changes. This shows that other pressures are also of considerable importance. Thus, the definition of the ecological condition of lakes using macrophytes should not be based only on responses to eutrophication pressure, as has been done in some European countries.     

Coastal and estuarine ecological risk assessment: the need for a more formal approach to stressor identification

Application of ecological risk assessment to coastal and estuarine systems is accelerating although it initially lagged behind applications to land and freshwaters. Broader spatial and temporal scales, and multiple stressor integration are appropriately being considered more frequently in all risk assessment activities. This expansion and integration is essential for coastal risk assessment. Because coastal assessments must deal with co-occurrence of several candidate stressors manifesting within broad spatial and temporal scales, wider use of formal methods for assessing causal linkages is needed. Simple Bayesian inference techniques are discussed here to demonstrate their utility in quantifying the belief warranted by available information. The applicability of Bayesian techniques is illustrated with two examples, possible causes of fish kills on the Mid-Atlantic US coast and possible causes of hepatic lesions in fish of Puget Sound (Washington, US).     

Environmental factors accounting for benthic macroinvertebrate assemblage structure at the sample scale in streams subjected to a gradient of cattle grazing

Macroinvertebrate assemblages were related to environmental factors that were quantified at the sample scale in streams subjected to a gradient of cattle grazing. Environmental factors and macroinvertebrates were concurrently collected so assemblage structure could be directly related to environmental factors and the relative importance of stressors associated with cattle grazing in structuring assemblages could be assessed. Based on multivariate and inferential statistics, measures of physical habitat (% fines and substrate homogeneity) had the strongest relationships with macroinvertebrate assemblage structure. Detrital food variables (coarse benthic and fine benthic organic matter) were also associated with assemblage structure, but the relationships were never as strong as those with physical habitat measures, while autochthonous food variables (chlorophyll a and epilithic biomass) appeared to have no association with assemblage structure. The amount of variation explained in taxa composition and macroinvertebrate metrics is within values reported from studies that have examined macroinvertebrate metric–sediment relationships. The % Coleoptera and % crawlers had consistent relationships with % fines during this study, which suggests they may be useful metrics when sediment is a suspected stressor to macroinvertebrate assemblages in Blue Ridge streams. Findings from this study also demonstrate the importance of quantitative sampling through time when research goals are to identify relationships between macroinvertebrates and environmental factors.     

Periphyton biomass and ecological stoichiometry in streams within an urban to rural land-use gradient

This study examined the effects land use on biomass and ecological stoichiometry of periphyton in 36 streams in southeastern New York State (USA). We quantified in-stream and land-use variables along a N–S land-use gradient at varying distances from New York City (NYC). Streams draining different landscapes had fundamentally different physical, chemical, and biological properties. Human population density significantly decreased (r = −0.739; P < 0.00001), while % agricultural land significantly increased (r = 0.347; P = 0.0379) with northing. Turbidity, temperature, conductivity, and dissolved Mg, Ca, SRP, pH, DOC, and Si significantly increased in more urban locations, but NO₃ ⁻ and NH₄ ⁺ did vary not significantly along the gradient. Periphyton biomass (as AFDM and Chl-a) in rural streams averaged one-third to one-fifth that measured in urban locations. Periphyton biomass in urban streams averaged 18.8 ± 6.0 g/m² AFDM and 75.6 ± 28.5 mg/m² Chl-a. Urban Chl-a levels ranging between 100 and 200 mg/m², are comparable to quantities measured in polluted agricultural streams in other regions, but in our study area was not correlated with % agricultural land. Periphyton nutrient content also varied widely; algal C varied >20-fold (0.06–1.7 μmol/mm²) while N and P content varied >6-fold among sites. Algal C, N, and P correlated negatively with distance from NYC, suggesting that periphyton in urban streams may provide greater nutrition for benthic consumers. C:N ratios averaged 7.6 among streams, with 91% very close to 7.5, a value suggested as the optimum for algal growth. In contrast, periphyton C:P ratios ranged from 122 to >700 (mean = 248, twice Redfield). Algal-P concentrations were significantly greater in urban streams, but data suggest algal growth was P-limited in most streams regardless of degree of urbanization. GIS models indicate that land-use effects did not easily fit into strict categories, but varied continuously from rural to urban conditions. We propose that the gradient approach is the most effective method to characterize the influence of land use and urbanization on periphyton and stream function.     

The influence of riparian vegetation on macroinvertebrate community structure in four Hong Kong streams

The benthic macroinvertebrate communities of four Hong Kong streams with similar water chemistry but differing riparian conditions were investigated. Differences in chlorophylls and detritus standing stocks reflected the degree of shading by riparian vegetation; Tai Po Kau Forest Stream (TPKFS) and Bride's Pool (BP) had an allochthonous food base while autochthonous energy sources were relatively more important in Lam Tsuen River (LTR) and Pui O Stream (POS). The macrobenthos was dominated by aquatic insects and morphospecies richness (excluding Chironomidac) ranged from 70 (POS) to 94 (TPKFS). Differences in total macroinvertebrate abundance across sites were not related to chlorophylls or detritus.
Highly significant differences in the morphospecies comprising the most numerous taxa at each site were observed, and TPKS and BP were more similar to each other than to the LTR-POS pair with respect to top-ranked taxa. Intraspecific comparisons of the abundance of these taxa revealed significant differences for 23 out of 30 morphospecies. Multiple regression of the abundance of key morphospecies against independent variables (chlorophylls a , b and c , total chlorophyll and detritus) yielded significant best-fit models for all taxa showing intersite differences in abundance. These data can be interpreted as reflecting the influence of riparian vegetation on stream community structure via an effect on food supply. The results were discussed with reference to the applicability of the River Continuum Concept in the tropics.     

Spatial scale and ecological relationships between the macroinvertebrate communities of stony habitats of streams and lakes

1. Comparative studies of distinct, but not ecologically isolated, systems such as lakes and streams may improve our understanding of the importance of ecological linkages in aquatic ecosystems. 2. In this study we compared the macroinvertebrate benthos of stony habitats in Swedish lakes and streams. Community composition was used to evaluate zoogeographic patterns and functional feeding guilds were used to identify mechanisms potentially affecting such patterns. 3. Stream communities were generally more diverse and species‐rich and had a higher proportion of grazers, shredders and passive‐filter feeders than lakes. Lake communities had a higher proportion of predators and collector‐gatherers. Of the 10 most common taxa, only Leptophlebia mayflies, clams (Sphaeriidae) and the isopod Asellus aquaticus were recorded in both lakes and streams. 4. Among‐site variance in macroinvertebrate communities accounted for by regional‐scale variables was low (6.4% for lakes and 10.1% for streams), compared with that by local‐scale variables (21% for lakes and 37.6% for streams). For lakes, the among‐site variance in macroinvertebrate communities was best explained by habitat‐scale characteristics followed by ecosystem, riparian, catchment, geographic position and ecoregion. For streams, the variance in macroinvertebrate communities was best explained by ecosystem characteristics followed by habitat, catchment, riparian, ecoregion and geographic position. 5. Conspicuous differences in spatial pattern were revealed between lakes and streams. For lakes, the most unequivocal differences in community composition and function occurred at the transition zone between the mixed forests in the south and the boreal coniferous forests in the north. Surprisingly, streams did not respond as strongly to profound landscape‐level differences in climate and vegetation cover. 6. The spatial differences noted between macroinvertebrate communities of lakes and streams may be because of differences in retention of detrital matter. Our findings imply that detrital inputs are qualitatively similar, but that the retention and processing of coarse particulate organic matter was presumably higher in lake littoral regions than in stream riffle habitats. 7. Although our findings support the conjecture that species distribution is determined fundamentally by conditions prevailing at the local‐scale, regional factors such as land use/type and the role of history were important and seemingly act as strong determinants of large‐scale patterns in biodiversity.     

Macrozoobenthos communities and biocoenotic assessment of ecological status in relation to degree of human impact in small streams in southwest Germany

One of the major objectives of the VALIMAR project is to determine the ecological significance of various fish biomarker studies as indicators of chronic pollution in small streams in southwest Germany. Results of these fish biomarker investigations were compared to information from complementary studies on the meiobenthos, macrobenthos, and fish community studies to assess the ecological significance of these biomarker investigations. The main objective of this study was to provide biological assessments of the biomarker sites on the basis of the macrozoobenthos communities. Since no validated framework for the assessment of the biological integrity existed in Germany, two multimetric approaches were adapted to the whole stream system by investigating benthos and fish communities of 46 sites of varying degrees of human disturbance. Assessment of the communities was conducted in accordance with the European Community Water Framework Directive. Species distribution of benthos depended upon stream type and pollution status of streams. Biological attributes and bioindices of benthos communities, however, did not correlate with typological parameters like stream size or dominant substrate but correlated better with pollution parameters like conductivity or chloride concentration. Using a set of 18 measures, such as portion of sessile individuals, Rheoindex, oxygen availability index, and portion of pool dwellers, the benthos communities were characterized and evaluated. The composition of the fish communities was mainly determined by stream type, pollution and migration barriers. The influence of chemical parameters could be assessed by developing a“fish chemistry index”, which calculatesthe similarity of the present fish community with the potential natural community, but excludes those species strongly effected by deficits in stream channel morphology. Both fish chemistry index and benthic indices strongly correlated with pollution index parameters, clearly distinguishing between the more polluted Körsch sites and the less pollutedKrähenbach and Aich sites. Most of the single bioindices as well as overall assessment by multimetric indices indicated a gradient of decreasing quality from the reference stream Krähenbach to theslightly polluted Aich and Körsch upstream site (KE, upstream of all sewage treatment plants) and finally to the most polluted Körsch site directlybelow the most upstream sewage treatment plant (KD). According to the Water Framework Directive, the classification of ecological status of the benthos communities ranges from “high” (best of 5 classes) forthe reference stream to “bad” (5th class) for KD. Assessment of the fish community tends to score somewhat worse than the benthos due to deficits in morphological quality of the stream reaches. The benthos assessment and the newlydeveloped “fish chemistry index” correlated well with chemical water quality and hence with biomarkers, whereas ecological status of fish and overall ecological status was also influenced by river morphology. In conclusion all tested assessment methods on biocoenotic level are reliable indicators for the degree of human disturbance on small streams, whereas biomarkers are more suited for risk assessment and the investigation ofcause-effect-relationships.     

Freshwater diatom and macroinvertebrate diversity of coastal permanent ponds along a gradient of human impact in a Mediterranean eco-region

Mediterranean coastal areas are characterised by heavily transformed landscapes and an ever-increasing number of ponds are subjected to strong alterations. Although benthic diatoms and macroinvertebrates are widely used as indicators in freshwater ecosystems, little is still known about the diatom communities of lowland freshwater ponds in the Mediterranean region, and, furthermore, there are few macroinvertebrate-based methods to assess their ecological quality, especially in Italy. This article undertakes an analysis of benthic diatom and macroinvertebrate communities of permanent freshwater ponds, selected along a gradient of anthropogenic pressures, to identify community indicators (taxa and/or metrics) useful to evaluate the effect of human impacts. A series of 21 ponds were sampled along Tyrrhenian coast in central Italy. Five of these ponds, in a good conservations status and surrounded by woodland were selected as ‘reference sites’ for macroinvertebrates and epipelic diatoms. The remaining sixteen ponds were located in an agricultural landscape subject to different levels of human impact. The total number of macroinvertebrate taxa found in each pond was significantly higher in reference sites than in both the intermediate and heavily degraded ones, whereas the diatom species richness did not result in a good community variable to evaluate the pond ecological quality. The analysis revealed a substantial difference among the compositions of diatom communities between reference ponds and degraded ponds. The former were characterised by the presence of several species belonging to genera, such as Pinnularia sp., Eunotia sp., Stauroneis sp., Neidium sp., all of which were mostly absent from degraded ponds. Furthermore, the taxonomic richnesses of some macroinvetebrate groups (Odonata, Ephemeroptera, Trichoptera, Coleoptera), and taxa composition attributes of macroinvertebrate communities (total abundance, percentages of top three dominant taxa, percentages of Pleidae, Ancylidae, Hirudinea, Hydracarina) significantly correlated with variables linked with anthropogenic pressures. The results of the investigation suggested that diatoms tended more to reflect water chemistry through changes in community structure, whereas invertebrates responded to physical habitat changes primarily through changes in taxonomic richness. The methodologies developed for the analysis of freshwater benthic diatom and macroinvertebrate communities may have a considerable potential as a tool for assessing the ecological status of this type of water body, complying with the European Union Water Framework Directive 2000/60/EC. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008     

An improved macroinvertebrate multimetric index for the assessment of wadeable streams in the neotropical savanna

Multimetric indices (MMIs) have been successfully used to assess ecological conditions in freshwater ecosystems worldwide, and provide an important management tool especially in countries where biological indicators are fostered by environmental regulations. Nonetheless, for the neotropics, the few published papers are limited to small local scales and lack standardized sampling protocols. To fill the gaps left by previous studies, we propose a stream MMI that reflects anthropogenic impacts by using macroinvertebrate assemblage metrics from a data set of 190 sites collected from four hydrologic units in the Paraná and São Francisco River Basins, southeastern Brazil. Sites were selected through use of a probabilistic survey design allowing us to infer ecological condition to the total of 9432 kilometers of wadeable streams in the target population in the four hydrologic units. We used a filtering process to determine the least- and most-disturbed sites based on their water quality, physical habitat structure, and land use. To develop the MMI, we followed a stepwise procedure to screen our initial set of biological metrics for influence of natural variation, responsiveness and discriminance to disturbances, sampling variability, and redundancy. The final MMI is the sum of 7 scaled assemblage metrics describing different aspects of macroinvertebrate assemblage characteristics: Ephemeroptera richness, % Gastropoda individuals, Shannon-Wiener diversity index, % sensitive taxa richness, % scraper individuals, temporarily attached taxa richness, and gill respiration taxa richness. The MMI clearly distinguished the least-disturbed sites from the most-disturbed sites and showed a significant negative response to anthropogenic stressors. Of the total length of wadeable streams in the study area, 38%, 35%, and 27% were classified by the MMI as being in good, fair, and poor condition, respectively. By reducing the subjectivity of site selection, rigorously selecting the set of reference sites, and following a standardized metric screening method, we developed a robust MMI to assess and monitor ecological condition in neotropical savanna streams. This improved MMI provides an effective ecological tool to guide decision makers and managers in developing and implementing improved, cost-effective environmental policies, regulations, and monitoring of those systems.