Macro-floral assemblages in upland Welsh streams in relation to acidity, and their importance to invertebrates

SUMMARY 1. Macro-flora (angiosperms. bryophytes and macroscopic algae) and macroinvertebrates were sampled in 1984 at eighty-eight sites on soft-water streams in upland Wales. Assemblage patterns were related to stream chemistry using TWINSPAN, DECORANA and multiple discriminant analysis.
2. Floral assemblages could be related most strongly to pH and aluminium concentration, with Scapania undulata, Nardia compressa and filamentous chlorophytes characterizing streams of mean pH5.2–5.8, whilst Fontinalis squamosa occurred mostly at pH 5.6–6.2 and Lemanea at pH 5.8–7.0. We propose an indicator system based on thesetaxa.
3. Assemblages of invertebrates and flora concorded highly significantly, sites with Scapania and Nardia holding impoverished faunas. Because some acid sensitive invertebrates (e.g. Ecdyonurus and Ancylus ) can feed from acid tolerant plants (e.g. Scapania ), we hypothesize that they are restricted physiologically from acid streams.     

The influences of habitat and seasonal sampling regimes on the ordination and classification of macroinvertebrate assemblages in the catchment of the River Wye,Wales

Assemblages of benthic macroinvertebrates were assessed in relation to environmental variables at 45 sites in the catchment of the Welsh River Wye in 1982.Samples were collected from three habitats (margins, riffles, flats) and in two seasons (Spring and Autumn), separated and combined data sets being ordinated by DECORANA and classified by TWINSPAN. Correlations between primary ordinations were high (p < 0.001) and always strongly related to total hardness or pH; secondary ordinations were also intercorrelated and were related to stream slope.In each instance, total hardness and slope were the strongest discriminants between site groupings produced by TWINSPAN. It is concluded that relationships between faunal assemblages, stream chemistry and stream physiography would be effectively detected in the Wye catchment in either Spring or Autumn and in each of the habitats sampled. However, the most precise categorization of assemblage type required a sampling strategy which combined habitat and seasonal data.     

The ordination and classification of macroinvertebrate assemblages in the catchment of the River Wye in relation to environmental factors

SUMMARY. 1. Macroinvertebrates were sampled from three habitats at forty-five sites in the catchment of the Welsh River Wye. Species assemblages were ordinated by DECORANA. classified by TWIN-SPAN and related to physico-chemical factors using correlation and multiple discriminant analysis respectively.
2. DECORANA axis 1 was correlated with pH or total hardness, whilst axis 2 correlated with slope or distance from source. TWINSPAN groupings were also related to hardness and, to a lesser extent, slope. Assemblages at soft-water sites (<15gm⁻³ CaCO₃) were composed mostly of Plecoptera but at hard-water sites, even at high slope (>10 m km⁻¹), the fauna was dominated numerically by Ephemerop-tera, net-spinning Trichoptera, Mollusca and Crustacea.
3. We suggest that our data do not support the River Continuum Concept unless there are modifications to allow for multiple gradients.     

长白山高山冻原植物群落的数量分类和排序

本文用目前在国际上比较先进的双向指示种分析(TWINSPAN)多元等级分划分类方法和无趋势对应分析(DCA)排序方法对长自山高山冻原植物群落进行了研究。研究结果表明:DCA的第2轴与长白山高山冻原59个植物群落类型的土壤水分梯度紧密相关, TWINSPAN将长白山高山冻原59个植物群落分为12组。此外, 本文还对长白山高山冻原植物群落的TWINSPAN和DCA分类结果与经典分类方法对其分类的结果进行了比较。     

Using Diatom Assemblages to Assess Urban Stream Conditions

We characterized changes in diatom assemblages along an urban-to-rural gradient to assess impacts of urbanization on stream conditions. Diatoms, water chemistry, and physical variables of riffles at 19 urban and 28 rural stream sites were sampled and assessed during the summer base flow period. Near stream land use was characterized using GIS. In addition, one urban and one rural site were sampled monthly throughout a year to assess temporal variation of diatom assemblages between the urban and rural stream sites. Canonical correspondence analysis (CCA) showed that the 1st ordination axis distinctly separated rural and urban sites. This axis was correlated with conductivity (r = 0.75) and % near-stream commercial/industrial land use (r = 0.55). TWINSPAN classified all sites into four groups based on diatom assemblages. These diatom-based site groups were significantly different in water chemistry (e.g., conductivity, dissolved nutrients), physical habitat (e.g., % stream substrate as fines), and near-stream land use. CCA on the temporal diatom data set showed that diatom assemblages had high seasonal variation along the 2nd axis in both urban and rural sites, however, rural and urban sites were well separated along the 1st ordination axis. Our results suggest that changes in diatom assemblages respond to urban impacts on stream conditions.     

Lebensgemeinschaften koexistierender Arten der Wasserkäfergattung Hydroporus aus zwei norddeutschen Untersuchungsgebieten (Coleoptera; Dytiscidae)

The community structure of 15 species of the genus Hydroporus was investigated in various pools with the multivariate software DECORANA, TWINSPAN and CANOCO. Abiotic values measured at 22 bog pools were correlated to DECORANA-data. Typical communities in the Ohemoor (near Hamburg) are related to the factors shaddow, absorption, calcium, and sodium. Data of coexisting Hydroporus species (including other small Dytiscidae, Haliplidae, Noteridae) from 93 pools (near Seedorf/Schleswig-Holstein) could be devided into 4 typical communities (bog, wood, sand-pit, agricultural areas).     

LOTIC ALGAL COMMUNITIES IN THE MT. ST. HELENS REGION SIX YEARS FOLLOWING THE ERUPTION1

A survey of 21 lotic habitats from the Mt. St. Helens region, Washington, was conducted during late summer 1986, six years after the eruption. A total of 152 taxa was observed (94 diatoms, 36 chlorophytes, 19 cyanophytes, 2 xanthophytes, and I rhodophyte). Sampling sites were classified by TWINSPAN (two-way indicator species analysis) and ordinated by DECORANA (detrended correspondence analysis). In general, both techniques corresponded well with each other and grouped sites according to the intensity of disturbance that they experienced. Species richness and diversity values tended to be lowest at the most heavily disturbed sites. Chlorophyll a values ranged over two orders of magnitude and tended to be higher at sites sampled from small, low-discharge tributaries. Loowit Creek, a thermally influenced stream that begins within the volcanic crater, was dominated by thick mats of the cyanophyte Mastigocladus laminosus. A general comparison of the present study with one conducted just after Mt. St. Helens erupted suggests that successional processes are operating in these lotic algal communities.     

Macroinvertebrate communities in streams in the Himalaya, Nepal

• 1 Macroinvertebrates were sampled in the riffles of fifty-eight streams from three regions of the Himalaya (Anapurna, Langtang and Everest) in Nepal. A semi-quantitative method with identification to family level was used to describe communities on-site.
• 2 Stream physicochemistry was assessed and the community structure of macroinvertebrates was related to chemistry, physiography (substratum composition, altitude and size), geographical location and the dominant land use in each catchment (terraced agriculture, forest or scrub). Community data were analysed by ordination (DECORANA) and classification (TWINSPAN).
• 3 The concentration of cations in stream water decreased significantly with altitude. Chemistry also differed between regions; sites from Anapurna had a higher pH and conductivity than those in the other two areas.
• 4 Communities were dominated by aquatic insect larvae, with Ephemeroptera, in particular the Baetidae, most numerous across sites.
• 5 There were, nevertheless, differences in community structure between sites, which were related closely to stream physicochemistry. Ordination scores were strongly correlated with altitude, magnesium concentration and substratum composition. Classification was also linked to altitude and chemistry, differentiating high-altitude sites with low silica concentrations from others. Sites from the Anapurna and Everest regions, with their contrasting chemistry, were also separated.
• 6 Community structure was also related to land use: streams draining catchments dominated by terraced agriculture had different communities from those in scrub or forest. This result was confounded, however, by the strong relationship between land use, altitude and chemistry; sites in terracing were at lower altitude, had higher concentrations of silica and a higher proportion of fine sediments than those in the other land-use types.
• 7 Overall, our data indicate that natural features of the relief and geology in the Himalaya create strong gradients in their invertebrate faunas, but that activities of man may have an effect on stream structure and ecology through catchment management.

     

Measuring Tailing's 'element of chance in pond populations'

SUMMARY. 1. A series of small seasonal pools on a freshwater marsh was used to estimate the element of chance in animal community patterns.
2. The pools were artificially created in 1963. They were all the same age, size, shape, depth and had the same substrate. Other physico-chemical parameters, and the faunas, were sampled. Community assemblages were analysed using multivariate classification and ordination (TWINSPAN and DECORANA). and related to physico-chemical characteristics. Communities correlated with distance of pools from permanent water and annual drying/flooding regimes.
3. TWINSPAN analysis in 1987 was used to identify co-occurring groups of animals and the sets of ponds with which each group was associated. The presence or absence of a taxon from a pool within a set in which it otherwise commonly occurred was used as a measure of the element of chance.
4. The mean occurrence of taxa in pools in which they were expected was 79.6.16.2%. The mean occurrence in pools in which they were not expected was 10.9.10.5% ( n =80).     

Macroinvertebrate communities of streams in western Nepal: effects of altitude and land use

1. The influence of altitude and land-use changes on macroinvertebrate assemblages from riffles in forty-three streams in the Dolpo region of western Nepal were examined. Sampling sites ranged in altitude from 850 to 4250m, and land-use patterns fell into five categories: alpine, forest, grassland, pasture and agricultural land. 2. TWTNSPAN classification of physicochemical data separated streams into groups on the basis of climatic and physical factors. Streams from high, cold, alpine areas were separated from those in warmer, lower, agricultural areas. 3. In all, 138 macroinvertebrate taxa were collected from fifty-three insect families. Ephemeroptera were most common, especially Baetidae. 4. Taxonomic richness declined with increasing altitude. Ten insect families were significantly more abundant in lowland streams, and five were more common in alpine streams. 5. TWINSPAN and DECORANA revealed distinct invertebrate groupings of the forty-three streams surveyed. A high percentage of the variance (79.3%) in ordination space was explained by DECORANA axes 1 and 2. Altitude, temperature, stream width and land use were implicated in structuring invertebrate communities.     

Distribution of benthic invertebrates in acid,brown water streams in the South Island of New Zealand

Acid, brown water streams are common on the west coast of the South Island, New Zealand. Acid precipitation is not a significant problem in this region where stream water acidity is brought about by high concentrations of humic substances. The interrelationships between pH, alkalinity, conductivity, DOC and total reactive aluminium were investigated at 45 running water sites. pH (range 3.5–8.1) was strongly correlated with alkalinity (range 0–49 g·m⁻³ CaCO₃) and less strongly with conductivity (range 2.0–9.7 mS·m⁻¹). A strong positive correlation was found between DOC and total reactive aluminium concentration both of which were correlated negatively with pH. In all brown water streams, most aluminium was probably in the non-toxic, organically complexed form. Benthic invertebrate assemblages were examined at 34 sites. Taxonomic richness was not correlated with pH and similar numbers of ephemeropteran, plecopteran and trichopteran taxa were taken from acidobiontic (pH ⩽ 5.5), acidophilic (pH 5.6–6.9) and moderately alkaline (pH ⩾ 7.0) groups of streams. Many species occurred over a wide pH range and had a lower limit of about pH 4.5. The mayfly, Deleatidium occurred at 33 sites and was amongst the five most abundant taxa at 32 of them. The stoneflies, Zelandobius confusus, Austroperla cyrene and Stenoperla maclellani, an elmid, Hydora sp. and a caddisfly, Psilochorema sp. also occurred in over half the streams and frequently were abundant. Few habitat specialists were found. Benthic assemblages were not associated strongly with measured physicochemical factors but streams in close proximity tended to have similar faunas. This suggests that the availability of suitable colonizers sets the limits to species richness and is important in determining the composition of benthic assemblages at a particular locality.     

锦屏水电站植被数量分类与排序

以锦屏梯级水电站大河湾段植被为研究对象,以河流流向为基础布置样方,将50个样方物种重要值及其环境因子进行TWINSPAN数量分类和DCA排序,结果显示:(1)由TWINSPAN数量分类将植被划分为7种类型,雅致雾水葛(Pouzolzia elegans)灌草群落为该区域的主要群落.(2)以TWINSPAN数量分类为基础的DCA二维排序图将样方分为6个生态类型,DCA 二维排序图横轴从左至右海拔高度逐渐降低;排序纵轴由下至上坡度逐渐升高.(3)以TWINSPAN数量分类在DCA排序图中有明确的分布范围和界限,DCA排序与TWINSPAN数量分类结合使用,能很好反映群落与环境因子间的生态关系.     

Diatoms as indicators of water quality in some English urban lakes

SUMMARY. 1. The paper describes diatom communities from a series of linked urban lakes in relation to water chemistry and uses multivariate statistical techniques to show how indicator groups can he defined.
2. Diatoms are classified into ecological groups using two-way species indicator analysis (TWINSPAN). Each ecological group is associated with a specific range of water-quality conditions. The headwater stream environments are differentiated from the lake habitats at level 1. At level 2 of TWINSPAN. the sampling sites are grouped into five ecological groups, according to their water chemistry and irrespective of the time of year.
3. Detrended correspondence analysis (DCA) and principal components analysis (PCA) provide two statistically independent methods of assessing the environmental gradients along which the ecological groups are distributed. The most important physico-chemical parameters are total hardness, specific conductance and pH, followed by phosphates and nitrates.
4. Ecological groups I-V correspond to an environmental gradient ranging from the forested headwaters, which are acidic, of low specific conductance, total hardness and nutrient content, through the urban lakes, which are alkaline and of relatively high total hardness, specific conductance and nutrient content.
5. Twelve site groups are identified at level 3 of TWINSPAN, each of which corresponds to a narrower range of water-quality conditions within the ecological groupings. A specific diatom assemblage is associated with each site group.
6. Benthic diatoms form an integral part of the diatom assemblages found in the water column and this is identified as a topic for further study.     

Classification of the Tatra Mountain lakes (Slovakia) using chironomids (Diptera,Chironomidae)

Chironomid assemblages in thirty-three mountain lakes situated above tree line in the Slovakian part of the Tatra Mountains were studied during 2000–2002. Chironomid species/taxa, collected as pupal exuviae, were correlated with physical, chemical, and lake morphometry variables of 22 lakes. Two-way indicator species analysis (TWINSPAN) was used to classify the lakes into four distinct groups: higher situated alpine lakes, lower situated alpine lakes, subalpine lakes and acidified lakes. Presence/absence of eight taxa was identified as indicative for this classification. In discriminant function analysis, pH, dissolved organic carbon, altitude and lake area were the most significant variables reflecting differences among groups of lakes. This model of four variables allowed 77% success in the prediction of group membership. A multiple regression model with lake area, concentration of magnesium and total phosphorus accounted for 37% of the variance in taxa richness. Lakes with greater area contained more chironomid taxa than smaller ones. Lakes with higher alkalinity and higher trophic status tend to support more taxa. Canonical correspondence analysis (CCA) indicated that most variation in the composition of chironomid assemblages was related to pH and to altitude. The results can be used as reference data for long-term monitoring of the Tatra lakes, especially in connection with a recovery from acidification and global climatic change.     

模糊C－均值聚类和TWINSPAN分类的比较研究

以英国威尔士北部Ｓｎｏｗｄｏｎｉａ山地Ａｂｅｒ山谷植被为例,对模糊ｃ－均值聚类和ＴＷＩＮＳＰＡＮ分类进行了应用和比较研究。两种方法的结果一致。模糊ｃ－均值聚类结果给出样地和植被类型间的隶属程度,在一定程度上优于ＴＷＩＮＳＰＡＮ。     

Short-term experimental acidification of a Welsh stream: comparing the biological effects of hydrogen ions and aluminium

SUMMARY. 1. A soft-water stream iti upland Wales was dosed with sulphuric acid and aluminiutn sulphate at two successive points to create sitnultaneous episodes of low pH, and low pH with increased aluminiutn. Chemical atid biological responses were measured before, during and after the episode and were compared with a reference zone. 2. The pH fell frotn ～7.0 to 4.28 (±0.18 SD) and 5.02 (±0.10) respectively in the acid and aluminium zones. Corresponding aluminium concentrations during the episode were 0.052 g Al m^?3 (±0.008) and 0.347 g Al nr³ (±0.047), the former not differing significantly from the reference zone. The concentration of cadmium rose to 0.002- 0.011 g Cd m^?3in both treated areas, but the concentrations of other metals were unchanged. 3. In situ toxicity tests were performed with macroinvertebrates and fish. Chironomus riparius. Hydropsyche angustipennis and Dinocras cephalotes suffered no mortality. Ecdyonurus venosus, Baetis rhodani and Gammarus pulex showed up to 25% mortality in both treatment zones and further mortalities occurred after the episode. Brown trout Salmo trutta and salmon Valmo salar s howed 7–10% mortality in the acid zone, but 50–87% in the aluminium zone, where salmon had a significantly shorter LT₅₀than trout. 4. The drift of Simuliidae increased during treatment in both acid and aluminium zones. Drift densities of Dixa puherula, Protonemura meyeri, Ephemeralla ignita and Dicranota sp. increased in the aluminium zone. The most pronounced response was by Baetis rhodani in the aluminium zone where drift density increased by ×8.4 during the episode. 5. Baetis rhodani was the only taxon to show a significant decline in benthic density during the treatment, and then only in the aluminium zone. Drift could account for most of the losses. 6. The depth distribution of invertebrates in the substratum differed between zones following treatment. More individuals were present at the surface of the reference zone (1287 m^?2±747) than at the surface of the other zones (<400 m^?2); however, densities at greater depths were similar. These patterns probably reflected differences prior to the treatments.     

Urban plant ecology patterns and processes: a case study of the flora of the City of Plymouth, Devon, U. K.

Aim Using a large database that has been created over the past 5 years with the RECORDER package, presence/absence data for 829 species of vascular plants in the 103 1-km² squares that cover the city of Plymouth (pop. 243,373) have been analysed by two-way indicator species analysis (TWINSPAN ) and canonical correspondence analysis (CCA) to establish the major species assemblages and to examine their spatial distribution across the city in relation to variation in land use. Location The City of Plymouth. Methods Nine groupings of squares emerged and their distribution was mapped across the city. Interpretation of those groups and their variation in relation to the land use ordination axes showed that TWINSPAN groups lying along the first axis of variation correlated floristic variation with the process of urban development and the historical evolution of urban structure. The second axis appeared to be related to particular remnant semi-natural habitats within the city that could be regarded as ‘hot-spots’ for survival of many plant species. Species were categorized into four types on the basis of their recency and mode of arrival in the city and by using the historical flora of Plymouth produced by T. R. Archer-Briggs in 1880. Variations in the sources of species in relation to the TWINSPAN classification groups were then examined. A second ordination was also computed; this time with geological, altitudinal and distance variables. TWINSPAN groups were then superimposed on the ordinations using polygons to assist with biogeographical interpretation. Results and conclusions The results of both the multivariate analyses and distribution of species by source are then discussed in the context of previous research into urban plant ecology, particularly in Central Europe. The problems of inferring process from pattern in this meso-scale study are reviewed and suggestions are made for further research into urban ecology and biogeography in the city.     

The influence of chemistry and habitat features on the microcrustacea of some upland Welsh streams

SUMMARY. 1. Microcrustaceans were sampled during September 1990 from three microhabitats (margins, stony riffles and gravel) at thirteen stream sites in mid-Wales.
2. Patterns in the distribution, abundance and community structure of microcrustacean taxa were related to stream chemistry, physiography, substratum composition and marginal habitat structure. Patterns of distribution between microhabitats were also assessed.
3. Chemical variables were the strongest correlates with microcrustacean parameters. Total numbers of microcrustaceans and harpacticoid copepods were reduced at sites with high aluminium concentrations, and ostracods were scarce or absent at the most acidic sites. In contrast, cyclopoid copepods were more abundant and species rich at low pH.
4. Microcrustacean communities were most species rich at sites with a high percentage cover of macrophytes on the substratum. Cladoceran species richness and abundance, and the abundance of several microcrustacean species, were also positively correlated with percentage macrophyte cover.
5. Three site groupings produced by TWINSPAN classification were primarily related to percentage macrophyte cover and marginal habitat structure, with chemistry and land use also of importance.
6. Total microcrustacean abundance was highest in margins, but of all the species, only the harpacticoid Bryocamptus cuspidatus showed a strong microhabitat preference.     

Relationships between bathymetry, water quality and diatoms in some Hebridean lochs

SUMMARY 1. Computer methods for mapping and calculating morphometric characteristics are described and applied to seventeen previously unsurveyed South Uist lochs.
2. Deposited sea salt is shown to have a major effect on water quality and the effect varies according to distance from the west coast. Calcium concentrations appear to be determined by dissolution of locally abundant shell debris. Sulphate and particularly nitrate concentrations are influenced significantly by catchment sources.
3. Surface sediment diatom assemblages from all seventeen sites are analysed using multi-variate methods (Hill, 1979). Assemblages are shown to be clearly distributed along DECORANA axis 1 and are clustered into five groups by TWINSPAN.
4. Correlation analysis of water quality, morphometric characteristics, and DECORANA axes scores indicates that conductivity has the strongest influence on surface sediment diatom assemblage composition whereas morphometric characteristics have no demonstrable effect.