城市溪流中径流式低坝对底栖动物群落结构的影响

调查了浙江省安吉县内具径流式低坝的城市溪流(6个样点)和参照溪流(3个样点)的底栖动物群落,目的是了解城市溪流底栖动物群落结构退化规律和径流式低坝(2—3 m)对城市溪流底栖动物群落组成与结构的影响。结果表明,参照样点的底质组成以大石块(35.92%)和卵石(33.66%)为主,城市溪流以砾石为主(57.97%)。城市溪流水温和电导率显著高于参照溪流,TN和TP高于参照溪流。底栖动物总分类单元数和EPT分类单元数显著低于参照溪流。城市溪流河道内水坝上下游之间的流速(P=0.273)和宽深比(P=3.92)无显著差异。坝下游水体中的TP高于坝上游,电导率、溶解氧、pH值和水温在坝上下游之间几乎一致。除BI指数坝下游高于坝上游外,坝上下游间底栖动物总分类单元数、EPT分类单元数以及多样性指数、优势度和均匀度指数没有显著差异。但坝下游的耐污类群比例显著高于坝上游,敏感类群比例则显著低于坝上游。与坝上游相比,坝下游捕食者比例上升和集食者比例下降。NMDS结果进一步表明,城市溪流内水坝的建设导致坝上下游底栖动物群落物种组成明显改变。     

Effects of episodic acidification on macroinvertebrate assemblages in Swiss Alpine streams

1. Despite long‐standing ecotoxicological evidence that episodes of acidification in streams are important biologically, there is still uncertainty about their effects on invertebrate communities. We surveyed 20 streams in an acid sensitive Alpine area (Canton Ticino, Switzerland), where episodes are driven by snowmelt in spring and by rainstorms at other times of the year. Samples of water and macroinvertebrates were collected in pre‐event conditions (winter and summer) and during periods of high flow (spring and autumn). 2. Using pH, [Ca²⁺] and [Alⁿ⁺], streams were clustered into six acid–base groups that were either well buffered (groups 4–6), soft‐water with stable pH (group 3), or poorly buffered with low pH at high flow (groups 1 and 2). 3. Severe episodes occurred during snowmelt, when the group 1 streams became acidic with pH down to 5.0 and [Alⁿ⁺] up to 140 μg L^?1. pH declined to 6.2 in streams of group 2, but remained > 6.6 in groups 3–6. 4. Detrended canonical correspondence analysis showed that the streams sensitive to episodes (groups 1 and 2) had different invertebrate assemblages from well‐buffered sites (groups 4 and 5) or soft‐water stable streams (group 3), with faunal differences largest following spring snowmelt. Empididae, Isoperla rivulorum, Rhithrogena spp. and Baetis spp. were scarce in streams sensitive to episodes (groups 1 and 2). By contrast, Amphinemura sulcicollis was scarcer in hard‐water streams (groups 4–6). Taxonomic richness was lower in the episodic streams of group 1 than in other streams. 5. Together, these results indicate clear biological differences between acid‐sensitive streams with similar low‐flow chemistry but contrasting episode chemistry. Severe episodes of acidification appear to affect macroinvertebrate assemblages in streams in the southern Swiss Alps.     

河流微生境异质性与大型底栖动物空间分布的关系

大型底栖动物是河流生态系统较好的指示类群,越来越广泛地应用于河流生态状况评价.识别大型底栖动物空间分布的影响因素可以分为宏观尺度因子、中观尺度因子和微观尺度因子.前人的研究较多集中于中观尺度.本研究基于10 m河段微生境因子与大型底栖动物调查,采用地统计学方法,在微观尺度上分析了大型底栖动物空间分布特征及其与微生境的关系.结果表明:不同生境类型中底栖动物指标存在差异性,激流、深潭和急流的Shannon指数平均值分别为2、1.9、1.78;大型底栖动物密度、生物量、丰富度指数及Shannon指数具有空间自相关性,存在一定的扩散效应;微生境因子与大型底栖动物指标及物种的空间关系存在差异性,其中,水深和流速与大型底栖动物关系的拟合度较弱,底质组成与大型底栖动物的拟合关系相对较好,底栖动物密度与粒径<4 mm底质体积百分比呈现正空间自相关,生物量、丰富度指数、Shannon指数与粒径>32 mm底质体积百分比呈现正空间自相关.本研究结果可为底栖动物扩散机制研究、调查样方设置、物理生境修复等提供参考.     

钱塘江中游流域不同空间尺度环境因子对底栖动物群落的影响

溪流底栖动物群落结构受不同空间尺度环境因子的共同作用。基于2010年钱塘江中游流域60个样点的大型底栖无脊椎动物和环境变量数据,寻找与研究流域底栖动物群落结构变化密切相关的关键环境变量,解析流域尺度和河段尺度的环境因子对底栖动物群落的相对影响。PCA分析表明该区域的主要环境梯度是流域内的土地利用类型及其引起的溪流物理生境退化程度和水体营养状态。CCA分析发现影响底栖动物群落的流域尺度的关键环境变量是纬度、海拔、样点所在流域大小、森林用地百分比,河段尺度是总氮、总磷、钙浓度、二氧化硅浓度和平均底质得分。偏CCA分析得到两种尺度环境因子对底栖动物变异的总解释量为26.4%,流域尺度和河段尺度变量分别为总解释量的50%和31%;方差分解结果表明研究区域大型底栖无脊椎动物受到两种尺度环境因子的综合影响,且流域尺度环境因子较河段尺度环境因子更为重要,体现了其在溪流生态系统保护、恢复、监测和评价中的重要参考价值。     

Salinity effects on macroinvertebrate assemblages and waterbird food webs in shallow lakes of the Wyoming High Plains

We determined the biomass and community structure of macroinvertebrates (>500 µm) associated with macrophytes, sediments, and unvegetated open water in three oligosaline (0.8 to 8.0 mS cm^–1) and three mesosaline (8.0 to 30.0 mS cm^–1) lakes in the Wyoming High Plains, USA. Total biomass of epiphytic and benthic invertebrates did not change with salinity, but biomass of macroinvertebrate zooplankton in open water was significantly higher in mesosaline lakes. Community composition of invertebrates differed between the two salinity categories: large grazer/detritivores (gastropods and amphipods) were dominant in oligosaline lakes, whereas small planktivores and their insect predators were more prevalent in mesosaline lakes. Both direct physiological effects of salinity, as well as a shift in the form of primary production from macrophytes to phytoplankton, probably explain these changes in community composition. Salinity effects on invertebrate communities appear to be less important to top avian consumers than are costs of osmoregulation.     

The influence of different spatial‐scale variables on caddisfly assemblages in Flemish lowland streams

1. Patterns in species assemblages are the result of the combined influence of processes acting on different spatial scales. Various studies describe the distribution of macroinvertebrate communities and their relationship with environmental factors at different geographical scales, but only a few of these studies concentrate on Western European lowlands. 2. Using Flanders as representative for the densely populated Western‐European lowlands, the specific aims of this study are: (i) to identify the different trichopteran species assemblages and to characterise them biologically using indicator species; (ii) to determine which environmental gradients most influence the observed species assemblages; and (iii) to analyse the relative importance of different spatial scale variables in constraining the Trichoptera distributions. 3. Assessment of the main environmental gradients suggested that the absence of Trichoptera from certain locations was mainly due to elevated nutrient concentrations and lower oxygen contents, confirming their sensitivity to anthropogenic disturbance. 4. Five Trichoptera species assemblages were distinguished based on Bray–Curtis dissimilarity coefficients. These assemblages did not differ significantly in species richness, but a shift in stream zonation preference was observed. In the ordination analysis 11 variables that were selected using a stepwise model building function manifested themselves as upstream–downstream and size‐related gradients. The Trichoptera assemblages in lowland streams thus appear to follow a longitudinal succession pattern that corresponds with the species‐specific preferences. 5. Partitioning the variance over the different spatial scales indicated that the reach‐scale variables were far more important in explaining the variation in species composition. The study design, which limited the minimum–maximum range of catchment‐scale characteristics, however, may have led to an overestimation of the impact of the local‐scale variables.     

Spatial variability in macroinvertebrate assemblages along and among neighbouring equatorial glacier‐fed streams

1. During the past two decades, understanding of the structure and function of glacier‐fed stream ecosystems at temperate latitudes has increased substantially. In contrast, information on their tropical counterparts is very limited. We studied three neighbouring glacier‐fed streams in the tropical Andes of Ecuador. Our main goals were (i) to determine overall longitudinal patterns in density, taxon richness and the composition of macroinvertebrate assemblages and driving factors in equatorial glacial streams and (ii) to examine variability among replicate streams in faunal metrics and assemblages, and stream‐specific effects of supposed environmental key factors. 2. We measured four geographical and 17 environmental factors and collected five Surber samples (500 cm²) of macroinvertebrates at each of nine sites, three sites along three streams. The streams were located 1–5 km apart. In each stream, the three sites were placed at comparable distances from the glacier and were grouped as ‘upper’ (50–200 m), ‘middle’ (1.5 km) and ‘lower’ sites (3.5–5.6 km). 3. In total, 2200 individuals (64% chironomids) were collected and 47 taxa (30 dipterans, 18 of these Chironomidae) identified. Density ranged from 176 to 372 ind. m^?2, and the number of taxa ranged from 2 to 6 at the upper sites and 868–3044 ind. m^?2 and 21–27 taxa at the lower sites. Density, number of taxa, rarefied richness and axis‐1 coordinates from a MDS ordination increased logarithmically with distance from the glacier. These faunal metrics were equally related to altitude and glacier per cent of catchment and correlated with maximum conductivity, mean temperature, mean daily maximum temperature and a channel stability index. As expected, the mean difference in distance decay in similarity was higher at the upper (47% km^?1) than at the lower reaches (20% km^?1) of the streams. 4. The number of taxa varied among sites within the upper and middle groups, but not among the lower sites. In contrast, but in accordance with our expectation, assemblage composition did not differ among upper sites but did so at middle and lower sites, following a supposed decrease in environmental harshness along the streams. Relationships between faunal metrics and the four environmental variables mean temperature, the stability index, chlorophyll a and coarse particulate organic matter also varied among the three streams. Generalised linear model analyses revealed that temperature interacted with stream on macroinvertebrate density, while chlorophyll a had a significant effect on the number of taxa in interaction with stream and stability. 5. The basic predictions of the Milner et al. (2001a) , model regarding longitudinal faunal patterns and temperature and stability as main driving factors were met by our three replicate equatorial glacial streams. Qualitative departures from the model were mainly because of zoogeographical differences. We demonstrated that variability in assemblages between comparable sites in closely situated streams was considerable, and the effect of key environmental factors varied among streams and interacted with other factors. Quantifying spatial variation in benthic assemblages may help us foresee possible consequences for biodiversity as a result of glacial retreat.     

Longitudinal changes in macroinvertebrate assemblages along a glacial river system in central Iceland

1. Macroinvertebrate assemblages were studied in the glacial river West-Jökulsá, originating from the Hofsjökull Ice Cap in central Iceland at an altitude of 860 m. Sampling sites were distributed from the source to 45 km downstream at 160 m a.s.l. Comparative studies were carried out on non-glacial rivers and tributaries in the area, at similar altitudes and distances from the glacial source.
2. Detrended correspondence analysis (DCA) demonstrated that species composition of benthic macroinvertebrates was related to the distance from the glacier. Assemblages at sampling sites furthest from the glacier were similar in species composition to sites in non-glacial rivers. Temporal variation was small compared with longitudinal zonation.
3. Based on canonical correspondence analysis (CCA) of data from the main glacial river, distance from the glacier, altitude, bryophyte biomass and the Pfankuch Index of channel stability were the measured explanatory variables having a significant effect on the structure of macroinvertebrate assemblages, accounting for 31% of the total variation in the data set. When data from all the rivers were analysed, altitude, bryophyte biomass, channel slope, suspended sediment concentration and maximum water temperature explained 21% of the variance.
4. Macroinvertebrate communities were in general agreement with the predictions of the conceptual model of Milner & Petts (1994) for the upstream reaches. The assemblages consisted mainly of Orthocladiinae and Diamesinae (Chironomidae), although other taxa such as Simuliidae, Plecoptera and Trichoptera were also found in low numbers. Shredders were lacking from the benthic communities, apparently because of continued glacial influence in the river even 45 km downstream from the glacier and lack of allochthononus inputs from riparian vegetation.     

Spatio-temporal variation in macroinvertebrate assemblages of glacial streams in the Swiss Alps

1. Changes in water chemistry, benthic organic matter (BOM), and macroinvertebrates were examined in four different glacial streams over an annual cycle. The streams experienced strong seasonal changes in water chemistry that reflected temporal changes in the influence from the source glacier, especially in water turbidity, particulate phosphorus and conductivity.
2. Nitrogen concentrations were high (nitrate-N values were 130–274 μg L^–1), especially during spring snowmelt runoff. Benthic organic matter attained >600 g m^–2 dry mass at certain times, peaks being associated with seasonal blooms of the alga Hydrurus foetidus .
3. Macroinvertebrate taxon richness was two to three times higher (also numbers and biomass) in winter than summer suggesting winter may be a more favourable period for these animals. Benthic densities averaged 1140–3820 ind. m^–2, although peaking as high as 9000 ind. m^–2. Average annual biomass ranged from 102 to 721 mg m^–2, and reached >2000 mg m^–2 at one site in autumn.
4. Taxa common to all sites included the dipterans Diamesa spp. and Rhypholophus sp., the plecopterans Leuctra spp. and Rhabdiopteryx alpina , and the ephemeropterans Baetis alpinus and Rhithrogena spp. Principal components analysis clearly separated winter assemblages from those found in summer.     

The response of stream macroinvertebrates to substrate size and heterogeneity

Manipulations of substrate size and components of heterogeneity were designed to test their independent effects and interactions on the abundance and species richness of stream macroinvertebrates. Two components of substrate heterogeneity, variation in size class proportions and number of size classes, had no independent effect on abundance or richness; and in general did not interact with median particle size. Median particle size, stream current, and detritus accounted for most of the significant variation in macroinvertebrates colonizing the experimental substrates. Rocks with high surface heterogeneity (roughness) were colonized by more individuals (but not taxa) than rocks with low surface heterogeneity.     

科尔沁沙质草地植物群落高度空间异质性对不同放牧方式的响应

放牧是影响草地植被空间异质性的重要生物驱动因素。大型草食动物会通过采食、践踏和排泄粪便等方式影响草地植被空间异质性。同时,植物群落高度是重要的草地结构参数,但目前关于不同放牧方式对草地植物群落高度空间异质性的研究较少。该研究基于传统及地统计学方法,设置未放牧(NG)、牛单牧(CG)、羊单牧(SG)、牛羊混牧(MG) 4种处理,探究科尔沁沙质草地植物群落高度空间异质性对不同放牧方式的响应。结果表明:研究样地内植物群落平均高度为SG (38.86 cm)> NG(21.01 cm)> MG (17.29 cm)> CG (13.36 cm)。各处理下变异系数的结果均为中等变异,且变异范围在37.82%–66.97%之间,依次为NG> MG> CG> SG。通过对半方差函数参数进行最适模型拟合, NG、MG、CG、SG 4种处理分别对应球状模型、指数模型、线性模型、线性模型,且结构比大小为MG (82.7%)> NG (80.3%)> SG (40.2%)> CG (39.1%)。此外,采用Kriging插值法和分形维数对研究样地内植物群...     

梯级水坝运行对漫湾库区底栖动物群落结构及分布格局的影响

底栖动物是对水生态系统退化和生境条件改变最为敏感的生物类群之一,同时也是开展梯级水坝水生态系统变化和演替研究的指示生物.本研究以国际生物多样性保护及水电梯级开发生态影响研究的热点地区澜沧江中下游为例,以澜沧江干流兴建的第一座水坝漫湾库区为研究区域,分别于2011和2016年开展底栖动物定点采样,并结合其蓄水前(自然河段,1996年)和单级水坝蓄水初期(1997年)的历史调研数据,全面分析了梯级水坝运行前后漫湾库区底栖动物群落的结构、分布格局及演变趋势.结果表明: 漫湾库区底栖动物群落的优势种组成逐渐由寡毛纲和昆虫纲种类演变为软体动物门类占绝对优势;沿库区生境的纵向梯度变化,底栖动物密度和生物量均表现为升高的趋势,而静水区增加更为显著;对底栖动物功能摄食群的分析表明,静水区由掠食者和收集者占优势演变为滤食者类占绝对优势;梯级水坝运行后,采用生物指数评价结果表明,2016年库区综合水质指标明显优于2011年.漫湾库区底栖动物群落的演变与上游梯级小湾水坝的调度运行及库区的水文状况和泥沙淤积情况密切相关,并随着梯级水坝的运行处于动态变化之中.     

Riparian ecotones and spatial variation of fish assemblages in Portuguese lowland streams

The first results of a long-term study on the role of riparian ecotones on the population and community dynamics of Iberian stream fish are presented and discussed. Riparian and macrophyte cover, bank slope and depth were among the most important variables affecting fish distribution. In general small fish favoured shallow areas with high macrophyte cover, whereas large fish dominated in deep areas with a high riparian cover. Slight spatial changes in terrestrial prey use were found suggesting a minor role for this resource during autumn. Finally, no significant spatial differences were found for linear growth, although some differences were obtained for the condition factor.     

Assessing streamflow characteristics as limiting factors on benthic invertebrate assemblages in streams across the western United States

1. Human use of land and water resources modifies many streamflow characteristics, which can have significant ecological consequences. Streamflow and invertebrate data collected at 111 sites in the western U.S.A. were analysed to identify streamflow characteristics (magnitude, frequency, duration, timing and variation) that are probably to limit characteristics of benthic invertebrate assemblages (abundance, richness, diversity and evenness, functional feeding groups and individual taxa) and, thus, would be important for freshwater conservation and restoration. Our analysis investigated multiple metrics for each biological and hydrological characteristic, but focuses on 14 invertebrate metrics and 13 streamflow metrics representing the key associations between streamflow and invertebrates. 2. Streamflow is only one of many environmental and biotic factors that influence the characteristics of invertebrate assemblages. Although the central tendency of invertebrate assemblage characteristics may not respond to any one factor across a large region like the western U.S.A., we postulate that streamflow may limit some invertebrates. To assess streamflow characteristics as limiting factors on invertebrate assemblages, we developed a nonparametric screening procedure to identify upper (ceilings) or lower (floors) limits on invertebrate metrics associated with streamflow metrics. Ceilings and floors for selected metrics were then quantified using quantile regression. 3. Invertebrate assemblages had limits associated with all streamflow characteristics that we analysed. Metrics of streamflow variation at daily to inter‐annual scales were among the most common characteristics associated with limits on invertebrate assemblages. Baseflow recession, daily variation and monthly variation, in streamflow were associated with the largest number of invertebrate metrics. Since changes in streamflow variation are often a consequence of hydrologic alteration, they may serve as useful indicators of ecologically significant changes in streamflow and as benchmarks for managing streamflow for ecological objectives. 4. Relative abundance of Plecoptera, richness of non‐insect taxa and relative abundance of intolerant taxa were associated with multiple streamflow metrics. Metrics of sensitive taxa (Ephemeroptera, Plecoptera and Trichoptera), and intolerant taxa generally had ceilings associated with flow metrics while metrics of tolerant taxa, non‐insects, dominance and chironomids generally had floors. Broader characteristics of invertebrate assemblages such as abundance and richness had fewer limits, but these limits were nonetheless associated with a broad range of streamflow characteristics.     

Regional and local drivers of macroinvertebrate assemblages in boreal springs

Aim To identify the most important environmental drivers of benthic macroinvertebrate assemblages in boreal springs at different spatial scales, and to assess how well benthic assemblages correspond to terrestrially derived ecoregions. Location Finland. Methods Benthic invertebrates were sampled from 153 springs across four boreal ecoregions of Finland, and these data were used to analyse patterns in assemblage variation in relation to environmental factors. Species data were classified using hierarchical divisive clustering (twinspan ) and ordinated using non‐metric multidimensional scaling. The prediction success of the species and environmental data into a priori (ecoregions) and a posteriori (twinspan ) groups was compared using discriminant function analysis. Indicator species analysis was used to identify indicator taxa for both a priori and a posteriori assemblage types. Results The main patterns in assemblage clusters were related to large‐scale geographical variation in temperature. A secondary gradient in species data reflected variation in local habitat structure, particularly abundance of minerogenic spring brooks. Water chemistry variables were only weakly related to assemblage variation. Several indicator species representing southern faunistic elements in boreal springs were identified. Discriminant function analysis showed poorer success in classifying sites into ecoregions based on environmental than on species data. Similarly, when classifying springs into the twinspan groups, classification based on species data vastly outperformed that based on environmental data. Main conclusions A latitudinal zonation pattern of spring assemblages driven by regional thermal conditions is documented, closely paralleling corresponding latitudinal patterns in both terrestrial and freshwater assemblages in Fennoscandia. The importance of local‐scale environmental variables increased with decreasing spatial extent. Ecoregions provide an initial stratification scheme for the bioassessment of benthic macroinvertebrates of North European springs. Our results imply that climate warming, landscape disturbance and degradation of spring habitat pose serious threats to spring biodiversity in northern Europe, especially to its already threatened southern faunistic elements.     

Climatic changes and 13-year trends in stream macroinvertebrate assemblages in New South Wales, Australia

Over the period from 1994 to 2007, air and water temperatures in the Australian state of New South Wales (NSW) increased while rainfall and river flows declined. Data on the occurrence of stream macroinvertebrate families in bioassessment samples collected in NSW during this period were examined to see whether a biological response to these climatic and hydrological trends could be discerned. Multiple logistic regression was used to test for long-term trends in the probability of detection of individual macroinvertebrate families within the samples, taking account of the latitude, longitude, altitude, hydraulic habitat, time of year and subsampling method associated with each sample. Of the 124 families and family groups tested, 33 had statistically significant increasing trends, 37 had significantly declining trends and 54 had no significant trend; however, many of the last group were seldom collected and their trend estimates had wide confidence limits. Significant relationships were found between the thermophily and rheophily of the families and the estimated strength and direction of their long-term trends, with families that favour colder waters and faster-flowing habitats more likely to have declined. Although many families showed trends of increasing detection within samples, such trends do not necessarily equate to increasing prevalence in the environment because the extent of wetted habitat has probably declined, especially flowing habitat. In addition, because of likely intrafamilial trait diversity, increasing or apparently increasing families may include species in decline. Many freshwater macroinvertebrate species in NSW may be threatened by anthropogenic climate change, exacerbated by water withdrawals. The thermal tolerances, rheophily and other pertinent traits of individual species need to be determined to identify those most at risk.     

Seasonal dynamics of macroinvertebrate assemblages in the benthos and associated with detritus packs in two low-order streams with different riparian vegetation

• 1 The seasonal dynamics of the benthic macroinvertebrate assemblage, and the subset of this assemblage colonising naturally formed detritus accumulations, was investigated in two streams in south‐west Ireland, one draining a conifer plantation (Streamhill West) and the other with deciduous riparian vegetation (Glenfinish). The streams differed in the quantity, quality and diversity of allochthonous detritus and in hydrochemistry, the conifer stream being more acid at high discharge. We expected the macroinvertebrate assemblage colonising detritus to differ in the two streams, due to differences in the diversity and quantity of detrital inputs.
• 2 Benthic density and taxon richness did not differ between the two streams, but the density of shredders was greater in the conifer stream, where there was a greater mass of benthic detritus. There was a significant positive correlation between shredder density and detritus biomass in both streams over the study period.
• 3 Detritus packs in the deciduous stream were colonised by a greater number of macroinvertebrates and taxa than in the conifer stream, but packs in both streams had a similar abundance of shredders. The relative abundance of taxa colonising detritus packs was almost always significantly different to that found in the source pool of the benthos.
• 4 Correspondence analysis illustrated that there were distinct faunal differences between the two streams overall and seasonally within each stream. Differences between the streams were related to species tolerances to acid episodes in the conifer stream. Canonical correspondence analysis demonstrated a distinct seasonal pattern in the detrital composition of the packs and a corresponding seasonal pattern in the structure of the detritus pack macroinvertebrate assemblage.
• 5 Within‐stream seasonal variation both in benthic and detritus pack assemblages and in detrital inputs was of similar magnitude to the between‐stream variation. The conifer stream received less and poorer quality detritus than the deciduous stream, yet it retained more detritus and had more shredders in the benthos. This apparent contradiction may be explained by the influence of hydrochemistry (during spate events) on the shredder assemblage, by differences in riparian vegetation between the two streams, and possibly by the ability of some taxa to exhibit more generalist feeding habits and thus supplement their diets in the absence of high quality detritus.

     

Concordance between ecotypes and macroinvertebrate assemblages in Mediterranean streams

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

Spatial and temporal changes of benthic macroinvertebrate assemblages in acidified streams in the Bohemian Forest (Czech Republic)

Outflows from two atmospherically acidified lakes in the Bohemian Forest were studied in 2005 and 2007. While Lake ?ertovo has been strongly acidified (～pH 4.6), Lake Laka was only slightly acidified in the past and is recovering now (～pH 5.2). The water chemistry and macrozoobenthos composition were analysed along longitudinal gradients of both lake outflows to determine the present status of their streams. A certain progression in stream chemistry to more neutral conditions was observed along the longitudinal gradients of both streams. However, a possible recovery of macrozoobenthos was evident only in the Lake Laka outflow, mainly via an increasing number of Ephemeroptera and Trichoptera taxa, and an increasing number of Gammarus fossarum, both along the longitudinal gradient and during the period of study. In contrast, no considerable changes were observed in the macrozoobenthos composition of the Lake ?ertovo outflow, presumably because its chemistry was harmful for acidosensitive taxa such as Ephemeroptera and Trichoptera. Plecoptera and Chironomidae were the most numerous groups in this stream. The biological recovery of both streams will depend on further chemical improvement in their catchments as well as on the dispersal ability of benthic organisms.