Methodological aspects of moss sample preparation. Effects of freezing and duration of washing on the cellular distribution of elements in Fontinalis squamosa Hedw.

Aquatic bryophytes are widely used in biomonitoring studies, mainly because of their capacity to act as bioaccumulators. As different methods can be used to preserve and process moss samples, the results of elemental analyses may also vary, particularly if the contents of different cellular compartments are analyzed separately. In the present study, we compared the total concentrations of some elements and the concentrations of these in different cellular locations in frozen-thawed and fresh samples of the aquatic moss Fontinalis squamosa that were also washed for different lengths of time before analysis. We used the sequential elution technique (SET) to extract the different fractions, and we determined the concentrations of K, Mg, Ca, Cd, Co, Cu, Al and Zn in the extracts. The results varied depending on the element, cellular location and moss sampling site. In the moss samples processed after freezing, the greatest differences were in the intracellular concentrations of K, Mg and Cd, which were lower than in the fresh samples. Minor differences were found in the concentrations of elements in other cellular locations and in the total concentrations of elements. The increase in the duration of the initial washing step, carried out to remove soluble and particulate intercellular elements, may also cause the release of elements (e.g. K and Mg) bound to extracellular exchange sites. The concentrations in the other cellular fractions and the total concentrations were less affected by the washing duration. Neither freezing nor the use of long washing times are recommended for processing moss samples prior to extraction of elements by the SET. Further studies are needed to confirm and clarify the observations.     

Illumina sequencing of bacterial 16S rDNA and 16S rRNA reveals seasonal and species-specific variation in bacterial communities in four moss species

In order to better understand the factors that influence bacterial diversity and community composition in moss-associated bacteria, a study of bacterial communities in four moss species collected in three seasons was carried out via high-throughput sequencing of 16S rDNA and 16S rRNA. Moss species included Cratoneuron filicinum, Pylaisiella polyantha, Campyliadelphus polygamum, and Grimmia pilifera, with samples collected in May, July, and October 2015 from rocks at Beijing Songshan National Nature Reserve. In total, the bacterial richness and diversity were high regardless of moss species, sampling season, or data source (DNA vs. RNA). Bacterial sequences were assigned to a total of 558 OTUs and 279 genera in 16 phyla. Proteobacteria and Actinobacteria were the two most abundant phyla, and Cellvibrio, Lapillicoccus, Jatrophihabitans, Friedmanniella, Oligoflexus, and Bosea the most common genera in the samples. A clustering algorithm and principal coordinate analysis revealed that C. filicinum and C. polygamum had similar bacterial communities, as did P. polyantha and G. pilifera. Metabolically active bacteria showed the same pattern in addition to seasonal variation: bacterial communities were most similar in summer and autumn, looking at each moss species separately. In contrast, DNA profiles lacked obvious seasonal dynamics. A partial least squares discriminant analysis identified three groups of samples that correlated with differences in moss species resources. Although bacterial community composition did vary with the sampling season and data source, these were not the most important factors influencing bacterial communities. Previous reports exhibited that mosses have been widely used in biomonitoring of air pollution by enriching some substances or elements in the moss-tag technique and the abundant moss associated bacteria might also be important components involved in the related biological processes. Thus, this survey not only enhanced our understanding of the factors which influence microbial communities in mosses but also would be helpful for better use and development of the moss-tag technique in the environmental biomonitoring.     

Early morning photosynthesis of the moss Tortula ruralis following summer dew fall in a Hungarian temperate dry sandy grassland

Air temperature and humidity, moss surface temperature, moss water content, and photosynthetically active radiation were measured through a clear dry night and early morning in July 1998; CO₂ gas exchange of the moss was measured by infra-red gas analysis. The measurements showed progressive absorption of water by the moss through much of the night. The moss reached sufficient water content for about 1.5 h of positive net CO₂ uptake immediately after dawn. The cumulative net carbon balance on this occasion was negative, but mornings with heavier dew could give a positive daily carbon balance, and short, early morning periods of photosynthesis during prolonged dry weather may mitigate long-term desiccation damage and allow for regular molecular repair.     

Assessment of the uncertainty of trace metal and nitrogen concentrations in mosses due to sampling,sample preparation and chemical analysis based on the French contribution to ICP-Vegetation

Moss bio-monitoring is a convenient tool for establishing specific or large-scale exposure to atmospheric trace metals and nitrogen pollution. However, the uncertainty associated with sampling, sample preparation and chemical analysis of bio-monitors has been poorly documented, with the exception of one study dealing with lichens; thus, the uncertainty associated with moss bio-monitoring has never been assessed. Here, we propose following the Eurachem guidelines to determine the uncertainties associated with the concentrations of elements measured in mosses during the sampling survey across France in 2011. In addition, we assess the analytical method used in four surveys from 1996 to 2011. Uncertainties were expressed as linear functions of the element concentrations, with minimum and maximum slopes of 14 and 61%, corresponding to nitrogen and chromium, and a median of 32%. Although the data reveal that some steps of the protocol should be performed carefully, they also indicate that the protocol was executed properly and is reproducible. The chemical analyses contribute to a small proportion of the uncertainty associated with the protocol, except for the analysis of chromium. The sampling period, and intra-site variability largely contribute to this uncertainty. The moss species did not introduce additional uncertainty. This integrative assessment of measurement uncertainty will help improve the protocol for future surveys. Such studies could be useful for developing a standard operating procedure and could be used to improve comparisons between countries and to identify temporal trends across Europe.     

Among-habitat and Temporal Variability of Selected Macroinvertebrate Based Metrics in a Mediterranean Shallow Lake (NW Spain)

According to the European Water Framework Directive, waterbodies have to be classified on the basis of their ecological status using biological quality elements, such as macroinvertebrates. This needs to take into consideration the influence of natural variation (both spatial and temporal) of reference biological communities as this may obscure the effects caused by anthropogenic disturbance. We studied the influence of among-habitat and temporal (seasonal and interannual) changes on the macroinvertebrate communities of an Iberian shallow lake and the variability of 21 measures potentially useful for bioindication purposes. Two series of data were examined: (a) macroinvertebrate samples taken on four occasions over an annual cycle were used to assess the effects of seasonality and among-habitat variability; (b) macroinvertebrate samples collected in three consecutive summers were used to assess interannual variability. Coefficients of variation, expressed as percentage, were used to quantify the effect of among-habitat and temporal variability on the selected metrics. According to our results, % Insecta, Shannon–Wiener diversity index and the qualitative taxonomic metrics (measures based on number of taxa) were robust in terms of temporal (seasonal and interannual) and among-habitat variability. Abundance ratio and some metrics based on functional feeding groups were highly variable. Therefore, qualitative taxonomic metrics may be promising tools in biomonitoring programs of Mediterranean shallow lakes due to their comparatively low variability.     

Experimental separation of resource quantity from temporal variability: seedling responses to water pulses

We tested the hypothesis that higher temporal variability in water supply will promote higher species richness of germinating and surviving seedlings using assemblages of 70 species of herbaceous plants from limestone pavement habitats. In a two-factor greenhouse experiment, doubling the total volume of water added led to greater germination (measured as number of germinated seeds and species) and establishment (survival and biomass) but the effects of temporal variability depended on the response variable considered. Low pulse frequencies of water addition with total volume added held constant resulted in greater temporal variability in soil moisture concentration that in turn promoted higher density and richness of germinated seedlings. Low pulse frequencies caused an eight-fold greater mortality in the low total volume treatment and biomass production to decline by one-third in the high total volume treatment. The effects of increasing temporal variability in water supply during recruitment stages can thus be opposite on different components of plant fitness and may also depend on total resource quantity. While greater species richness in more temporally variable soil moisture conditions was attributable to sampling effects rather than species-specific responses to the water treatments, species relative abundances did vary significantly with temporal variability. Changes in the amplitude or frequency of resource fluctuations may alter recruitment patterns, and could have severe and relatively rapid effects on community structure in unproductive ecosystems.Electronic Supplementary Material The French version of this article is available in the form of electronic supplementary material at.     

Evaluation of the efficacy of the sequential elution technique,by use of electron microscopy methods

Abstract

In the present study, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS) was used in conjunction with the sequential elution technique (SET) to evaluate the efficacy of extraction of Zn from the moss Pseudoscleropodium purum (Hedw.) M. Fleisch. Moss samples were collected from two areas, a contaminated area (with high concentrations of Zn) in the surroundings of a steel works, and an uncontaminated area. Some samples from the uncontaminated area were used as controls, and others were incubated in a solution of ZnCl₂ for subsequent analysis of uptake and location of Zn. The concentrations of Zn in the different cell compartments of the moss were determined by use of the SET, and different points on the surface of the moss and in deposited particles were analysed by SEM–EDS. The results showed that the extracellular fraction obtained by SET includes the Zn bound to cation exchange sites in the moss and Zn bound to particles on the moss surface, which leads to overestimation of extracellular Zn. After extracellular extraction, Zn was not detected on the surface of the moss or in the particles. To avoid problems associated with the presence of particles on the moss surface, a washing procedure should be used to remove such particles before application of the SET. Another possibility is to use the intracellular concentration, as this is not affected by the metal load in the particles and better reflects those contaminants that affect the moss metabolism.     

Environmental variability drives phytoplankton assemblage persistence in a subtropical reservoir

Temporal changes of assemblages may result from environmental variability and reflect seasonal dynamics of their ecosystem. In the subtropics, the hydrological regime is usually characterized by well‐defined wet and dry seasons, regulating discharge and influencing a series of environmental variables that affect phytoplankton persistence. Therefore, we may expect that dry seasons are environmentally more stable than wet seasons. We analysed interannual phytoplankton assemblage variability (or, inversely, persistence) in a subtropical reservoir sampled every austral summer and winter during 5 years. We tested (i) if phytoplankton assemblage structure differed between the dry (summer) and wet (winter) seasons; (ii) if assemblage persistence differed between the seasons; (iii) if assemblage persistence was related to environmental stability; and (iv) if assemblage dissimilarity increased over time. Phytoplankton assemblages differed between the summer and winter seasons. Winter indicator species were mostly Bacillariophyceae or Cryptophyceae, whereas Cyanophyceae and Chlorophyceae taxa were more frequent and abundant in summer. Assemblages in the dry season were more persistent among years than those occurring during rainy periods. Similarly, environmental variability tended to be lower among dry than among rainy seasons. The relation between the phytoplankton temporal cycle and the temporal patterns of environmental variability supports our prediction that high environmental stability results in more persistent assemblages. Assemblage dissimilarity increased as sampling years were farther apart, for both seasons. Additionally, assemblages in the rainy periods showed a more pronounced increase in dissimilarity, as their changes among years were less predictable. We found a clear temporal pattern and an increased dissimilarity over time in the phytoplankton assemblage structure. Unravelling these temporal patterns may improve our understanding of phytoplankton temporal dynamics, and may have implications for management and monitoring programs. High dissimilarity of assemblages among years, particularly among rainy periods, can obscure human impacts, and monitoring programs should take this into account.     

Long-term population and community patterns of benthic macroinvertebrates and fishes in Northern California Mediterranean-climate streams

Long-term studies can document temporal patterns in freshwater ecosystems, and this is particularly important in mediterranean-climate (med-climate) regions because of strong interannual variation in precipitation amounts and consequently stream flow. We review long-term studies of populations and communities of benthic macroinvertebrate and fishes from sites throughout the med-climate region of California and develop generalities that may apply broadly to med-climate streams worldwide. Severe drought may result in community shifts, and alter age-structure in both macroinvertebrates and fishes. Within-year seasonal patterns in macroinvertebrate communities can be influenced by annual variability in flow regimes. Macroinvertebrate biological-monitoring metrics with consistently low intra-annual variability may be especially applicable in med-climate streams, as is the use of different temporal windows to describe reference periods to reduce influence of interannual variability on impact detection. Long-term data can be used to develop macroinvertebrate-based metrics that can either show or be independent of climate-change effects. Most macroinvertebrate species are temporally rare in their annual occurrence. Multiple components of natural flow regimes can favor native over invasive fishes. Long-term, quantitative information from med-climate streams is generally lacking, which is a hindrance to both management practices and development of appropriate ecological constructs.     

Phantom hitch-hikers mislead estimates of genetic variation in Antarctic mosses

Previous studies of Antarctic mosses employing RAPDs have reported extraordinarily high levels of genetic variation, even within a single clump of moss. This is unexpected given their extreme isolation in Antarctica and lack of sexual reproduction. We offer an alternative explanation: that unusually elevated levels of genetic variability are artefacts from contamination of a number of biota known to be naturally associated with Antarctic mosses. We utilized sequence variation of nrITS and RAPDs to further investigate the effect of naturally occurring contaminants on estimates of genetic variation of mosses. Our results indicate that these ``phantom hitch-hiker' contaminants hinder attempts to accurately and reliably estimate levels of genetic variation by non-specific PCR-based approaches. Furthermore, screening samples via amplification of nrITS failed to identify all contaminated samples, hence we caution against relying solely on ``quick' screening methods and suggest that suspect samples be carefully examined for contamination.     

Factors influencing the distribution of aquatic plant communities in Irish canals

Terrestrial tardigrades are often found in the lichens and mosses growing on trees and rocks. The assertion that tardigrades in these habitats are very patchy in their distribution has rarely been backed by quantitative sampling. This study assesses spatial variability in tardigrade populations inhabiting small patches (0.1 cm² to over 5 cm²) of moss and lichen on trees and rocks at three sites in the United States of America. Tardigrades were collected from four replicate rocks in the Ouachita Mountains of Arkansas, with 30 lichen patches collected on two adjacent boulders and 20 moss patches on a second pair of boulders. In Fort Myers and in Citrus Springs, Florida, 30 lichen patches per tree were collected from two pairs of trees. The tardigrades in each sample were extracted, mounted, identified, and counted. The variation in tardigrade abundance among lichen or moss patches within rocks or trees was very high; the only consistent pattern was that very small patches usually lacked tardigrades. Tardigrade diversity and abundance also varied greatly within sites when lichens and mosses of the same species from different rocks and trees were compared (in the most extreme case one tree had numerous individuals of two tardigrade species present while the other had almost no tardigrades). The results of this quantitative sampling support the assertion that tardigrades are very patchy in distribution. Given the considerable time investment required for the quantitative processing of tardigrade samples, this high spatial variability in tardigrade diversity and abundance requires that researches testing ecological hypotheses about tardigrade abundance check variability before deciding how many samples to take.     

Age-specific fitness components and their temporal variation in the barn owl

Theory predicts that temporal variability plays an important role in the evolution of life histories, but empirical studies evaluating this prediction are rare. In constant environments, fitness can be measured by the population growth rate lambda, and the sensitivity of lambda to changes in fitness components estimates selection on these traits. In variable environments, fitness is measured by the stochastic growth rate lambda(S), and stochastic sensitivities estimate selection pressure. Here we examine age-specific schedules for reproduction and survival in a barn owl population (Tyto alba). We estimated how temporal variability affected fitness and selection, accounting for sampling variance. Despite large sample sizes of old individuals, we found no strong evidence for senescence. The most variable fitness components were associated with reproduction. Survival was less variable. Stochastic simulations showed that the observed variation decreased fitness by about 30%, but the sensitivities of lambda and lambda(S) to changes in all fitness components were almost equal, suggesting that temporal variation had negligible effects on selection. We obtained these results despite high observed variability in the fitness components and relatively short generation time of the study organism, a situation in which temporal variability should be particularly important for natural selection and early senescence is expected.     

Reorganisation of a long-term monitoring network using moss as biomonitor for atmospheric deposition in Germany

The determination of atmospheric deposition in forests can be accomplished using technical sampling devices (bulk samplers, wet only samplers), biomonitors or modelling. In Europe, since 1990 moss sampled every five years at up to 7300 places in up to 35 countries was used as biomonitor. In the moss specimens, heavy metals (HM), nitrogen (N, since 2005) and persistent organic pollutants (POPs, since 2010) were determined. Germany participated in all surveys with the exception of that in 2010. For the moss survey 2015, the biomonitoring network applied in the 2005 campaign should be reorganized. To this end, a complex statistically based methodology including a decision support system was developed and implemented. Its application yielded a network with a reduction of sample points from 726 to 402. By use of the data collected in 2005 the performance of the reorganized network did not reveal significant loss of statistical validity.     

Towards the development of a macroinvertebrate sampling technique for palustrine wetlands in South Africa: a pilot investigation in the KwaZuluNatal midlands

A study was undertaken in November 2003 to derive a suitable sampling technique for collecting a representative sample of aquatic macroinvertebrates from a selected emergent vegetation biotope in a palustrine wetland, Melmoth Vlei, KwaZulu-Natal, South Africa. The aim was to undertake a preliminary investigation on the development and testing of a macroinvertebrate sampling technique for use in emergent sedge-dominated palustrine wetlands (sensu Cowardin et al. 1979), which could contribute to the development of a South African wetland health biomonitoring programme. Sweep nets and activity traps were evaluated for their effectiveness in terms of macroinvertebrate collection. Sweep net sampling was tested over a range of sweep intensities to determine the minimum number of sweeps required to collect a representative sample. Sampling efficiency of activity traps placed at four depths was tested, and taxon diversity and composition of sweep net and activity trap samples were compared to determine whether activity traps are required to supplement sweep net data. A total of 32 taxa (identified mainly to family level) were identified in the samples collected. Taxon diversity and composition did not differ in the activity traps placed at the four depth locations. Taxon diversity did not differ significantly between different sweep intensities. This may be a result of high variability of macroinvertebrate distribution within a wetland. There is evidence, however, to suggest that this result is due to an inadequate sample size. There was a significant difference in taxon composition between the different sweep intensities (P < 0.05) and between activity trap and sweep net samples (P < 0.05). Sixty-eight percent of taxa appeared more frequently in sweep net sampling than in activity trap sampling. Two taxa were found exclusively in activity traps, although the numbers of these taxa collected were not significant, and they do not represent any unique trophic group. Based on these findings, it was concluded that activity traps are not required to supplement sweep net data, and a technique using a sweep net with a sweep intensity of five would be suitable for collecting a representative sample of macroinvertebrates from a palustrine wetland.     

Spatial versus Day-To-Day Within-Lake Variability in Tropical Floodplain Lake CH4 Emissions – Developing Optimized Approaches to Representative Flux Measurements

Inland waters (lakes, rivers and reservoirs) are now understood to contribute large amounts of methane (CH₄) to the atmosphere. However, fluxes are poorly constrained and there is a need for improved knowledge on spatiotemporal variability and on ways of optimizing sampling efforts to yield representative emission estimates for different types of aquatic ecosystems. Low-latitude floodplain lakes and wetlands are among the most high-emitting environments, and here we provide a detailed investigation of spatial and day-to-day variability in a shallow floodplain lake in the Pantanal in Brazil over a five-day period. CH₄ flux was dominated by frequent and ubiquitous ebullition. A strong but predictable spatial variability (decreasing flux with increasing distance to the shore or to littoral vegetation) was found, and this pattern can be addressed by sampling along transects from the shore to the center. Although no distinct day-to-day variability were found, a significant increase in flux was identified from measurement day 1 to measurement day 5, which was likely attributable to a simultaneous increase in temperature. Our study demonstrates that representative emission assessments requires consideration of spatial variability, but also that spatial variability patterns are predictable for lakes of this type and may therefore be addressed through limited sampling efforts if designed properly (e.g., fewer chambers may be used if organized along transects). Such optimized assessments of spatial variability are beneficial by allowing more of the available sampling resources to focus on assessing temporal variability, thereby improving overall flux assessments.     

Spatial and temporal distribution patterns of drifting pupal exuviae of Chironomidae (Diptera) in streams of tropical northern Australia

1. Periodic collecting of floating cast pupal cuticles of chironomids (exuviae) in two tropical northern Australian streams demonstrates (i) spatial heterogeneity in species composition across a wide stream, (ii) temporal heterogeneity in the maximum abundance of each species, and that (iii) species accumulate as a function of sample size and duration of sampling, 2. Spatial heterogeneity is ascribed to variation in larval microhabitat across the wide stream, combined with short exuvial drift duration and restricted upstream mixing. 3. Temporal heterogeneity is ascribed to diel periodicity in adult emergence and, as with spatial heterogeneity, to the short floating life. 4. The consequences of spatial and temporal variation for the sampling of exuvial drift are discussed in relation to the objectives of particular programmes. Thus, if the objective is assessment of chironomid species composition for inventory purposes such as faunistics or conservation, the large sample sizes attained by 24-h sampling are necessary and appropriate. However, for rapid assessment that requires comparable samples at different sites, species numbers may be optimized by temporally and spatially restricted sampling of the maximal emergence period, which in this study is at dusk, or by subsampling from a 24-h sample.     

Identifying the scales of variability in stream macroinvertebrate abundance, functional composition and assemblage structure

1. Many natural ecosystems are heterogeneous at scales ranging from microhabitats to landscapes. Running waters are no exception in this regard, and their environmental heterogeneity is reflected in the distribution and abundance of stream organisms across multiple spatial scales. 2. We studied patchiness in benthic macroinvertebrate abundance and functional feeding group (FFG) composition at three spatial scales in a boreal river system. Our sampling design incorporated a set of fully nested scales, with three tributaries, two stream sections (orders) within each tributary, three riffles within each section and ten benthic samples in each riffle. 3. According to nested anova s, most of the variation in total macroinvertebrate abundance, abundances of FFGs, and number of taxa was accounted for by the among‐riffle and among‐sample scales. Such small‐scale variability reflected similar patterns of variation in in‐stream variables (moss cover, particle size, current velocity and depth). Scraper abundance, however, varied most at the scale of stream sections, probably mirroring variation in canopy cover. 4. Tributaries and stream sections within tributaries differed significantly in the structure and FFG composition of the macroinvertebrate assemblages. Furthermore, riffles in headwater (second order) sections were more variable than those in higher order (third order) sections. 5. Stream biomonitoring programs should consider this kind of scale‐dependent variability in assemblage characteristics because: (i) small‐scale variability in abundance suggests that a few replicate samples are not enough to capture macroinvertebrate assemblage variability present at a site, and (ii) riffles from the same stream may support widely differing benthic assemblages.     

A comparison of manual and automated systems for soil CO2 flux measurements: trade-offs between spatial and temporal resolution

Soil respiration is affected by distributions of roots and soil carbon substrates and by temperature and soil water content, all of which vary spatially and temporally. The objective of this paper was to compare a manual system for measuring soil respiration in a temperate forest, which had a greater spatial distribution of measurements (n=12), but poorer temporal resolution (once per week), with an automated system which had poorer spatial distribution (n=3) but superior temporal frequency of measurements (hourly). Soil respiration was measured between 18 June and 21 August, 2002, at the Harvard Forest in central Massachusetts, USA. The fluxes measured within 1 h of each other by these systems were not significantly different. However, extrapolations of the mid-morning manual measurements to daily flux values were consistently lower (averaging 13% lower) than the daily estimates obtained from summing the 24 hourly measurements of the automated system. On the other hand, seasonal flux estimates obtained by interpolating between weekly manual sampling dates or by summing the hourly automated measurements were nearly identical. Underestimates by interpolated weekly manual measurements during some periods were cancelled by overestimates during other periods. Hence, a weekly sampling schedule may be sufficient to capture the most important variation of seasonal efflux of CO(2) from the soil. The larger number of chambers that could be measured with the manual system (larger n) resulted in a smaller 95% confidence interval for characterizing spatial variability within the study area on most dates. However, the greater sampling frequency of the automated system revealed rapid responses of soil respiration to wetting events, which permitted better empirical modelling of the effects of soil temperature and moisture on soil respiration than could have been achieved with the manual sampling system. Most of the positive residuals of a function that predicts soil respiration based on temperature were from fluxes measured within 12 h of a rain event, and the residuals were positively correlated with water content of the O horizon. The automated system also demonstrated that Q(10) values calculated for diel variation in soil temperature over a few days were not significantly different than Q(10) values for the entire 3 month summer sampling period. In summary, a manual system of numerous, spatially well-distributed flux chambers measured on a weekly basis may be adequate for measuring seasonal fluxes and may maximize confidence in the characterization of spatial variance. The high temporal frequency of measurements afforded by automation greatly improves the ability to measure and model the effects of rapidly varying water content and temperature. When the two approaches can be combined, the temporal representativeness of the manual measurements can be tested with the automated measurements and the spatial representativeness of the automated measurements can be tested by the manual measurements.     

Modeling the effects of varying data quality on trend detection in environmental monitoring

Detection of changes in ecosystem characteristics is a principal tool for identifying and understanding the effects of anthropogenic activities on the condition and functioning of ecosystems. It is widely known that temporal trends can be blurred by the imprecision of the data. Research program managers are aware of the difficulties surrounding representative sampling and therefore enforce strict sampling protocols. Standardized sampling can be so effective that the initially much smaller uncertainty in the instrumental analysis becomes substantial. However, until now the effect of the quality of the instrumental analysis on the time required for trend detection has only rarely been quantified. In this paper, we present a novel technique and theoretical computations for the detection of trends in single and combined indices. The theory is clarified with examples from the International Co-operative Programme on Assessment and Monitoring of Air Pollution on Forests (ICP Forests). Moreover, the theoretical computations were made for normalized or scaled distributions and are therefore equally valid outside the field of environmental monitoring. The results show that, when sampling protocols largely reduce the variability of representative sampling, poor quality of the instrumental analysis blurs the data such that environmental monitoring or long-term ecological research programs can lose the ability to detect trends by causing up to three decades-long delay in detecting changes. We can thus conclude that high quality of the instrumental analysis is a prerequisite for a sensitive monitoring program.     

Longitudinal and seasonal variation of the benthic macroinvertebrate community and biotic indices in an undisturbed Pyrenean river

The present work aims to analyze the spatio-temporal variability in benthic macroinvertebrate assemblages and biotic indices in an undisturbed and unpolluted Pyrenean river. Samples were collected seasonally over 2 year-cycles (2001–2002) at fifteen sampling sites along the Erro River (Ebro River Basin, Spain) during a exhaustive biomonitoring program following the IBMWP–IASPT scoring system protocol routinely applied in Iberia. Despite absolute values of the biotic indices showed high spatio-temporal variation, the IBMWP–IASPT scoring system proved useful because water quality classes were consistent throughout seasons and years as well as along-river. The original macroinvertebrate families’ presence/absence data matrix was reduced in a number of ways to conduct different statistical procedures in order to detect and separate the underlying near-natural spatial and temporal gradients of the assemblage composition in the Erro River. Along-river, spatial variation of the macroinvertebrate community composition was well assessed by similarity analysis, which clearly detected physical features on the river (drought-affected reach, gorge, towns and flow gauging weirs). Categorical principal component analysis (CATPCA) synthesized and jointly ordered macroinvertebrate samples in a spatio-temporal gradient in the factorial map defined by the first two principal components providing a parsimonious way to assess the assemblages’ variation. These two variation gradients throughout the macroinvertebrate families’ occurrence data were subsequently confirmed separately by several correspondence analyses and revealed additional information, as the representative families for each sampling site group and season could be identified. Furthermore, these spatio-temporal gradients were discussed and put in relation with changes in the aquatic habitat (water temperature, conductivity, total dissolved solids, water velocity, channel width, canopy cover, etc.). The near-natural functioning of the Erro River promoted us to emphasize that conservation efforts should aim to maintain the free-flowing as a permanent source of variability.