Physicochemical and morphological characterization of two small polluted streams in southwest Germany

As a supporting component of the VALIMARproject, physicochemical investigations wereconducted monthly from 1995 to 1999 at theKrähenbach/Aich stream system (two samplingsites) and at the Körsch stream (sixsampling sites). Several physicochemicalparameters were analysed continuously bydataloggers during the entire sampling period.Moreover, a selection of the most importantmorphological parameters of the stream wererecorded in 1998.The results of these physicochemicalinvestigations demonstrated that theKrähenbach/Aich system could becharacterized as a natural rhithral submontanecarbonate stream system that is welloxygenated. Low temporal variations in pH,conductivity and chloride occurred at allsampling sites in the Krähenbach whichcoincided with the geological conditions atthis test stream. Because of relatively lowconcentrations of organic and inorganiccompounds during the entire study period thesites AB and AC in the Krähenbach/Aichsystem were classified as slightly polluted.The morphological assessment of the streamindicated a moderately affected status atboth of these streams.Physicochemical and morphologicalinvestigations along the Körsch streamsystem (KA to KE including the tributary streamSulzbach) indicated a highly affected rhithralsubmontane carbonate system characterized byhigh water velocity, flow rate and dissolvedoxygen. The Körsch, however, differssignificantly with respect to watertemperature, conductivity, pH, BOD₅,nutrients, and chloride concentrations from theKrähenbach. As a result of differentanthropogenic inputs (e.g. several sewageplants, agriculture activities and waste waterdumping) the Körsch sites KA to KD wereclassified as critically to heavilypolluted. The morphological assessmentindicated a clearly affected to damagedstatus. The upstream site KE could becharacterized as slightly polluted and itsmorphological structure as moderatelyaffected.     

Steroid analysis and xenosteroid potentials in two small streams in southwest Germany

The presence of estrogenic substances in thewater of the small streams Körsch (Kö)and Krähenbach (Kr), Southwest Germany, wasdetermined by chemical and biological analysis.Because a large proportion of the Kö waternear its mouth consists of sewage treatmentplant (STPs) effluents, the impact of STPs onlevels of estrogens in surface water is anenvironmental issue of concern. In July 1996,water samples were taken from Kr and Kö(four sites) and tested in the E-Screen assaywith human MCF-7 breast cancer cells. AllKö samples induced estrogen-dependent cellproliferation resulting in 17-estradiolequivalent concentrations (EEQ) between 3.3 and9.7 ng/L while the Kr water showed no effect.In 1998/99 eight samples from Kö (near itsmouth) and nine samples from Kr were collectedand tested in the E-Screen after solid phaseextraction. Some estrogenicity was detectablein three Kr samples but Kö samples had amedian EEQ of 3.1 ng/L (range: 1.2–42 ng/L).GC/MS analysis revealed differences in thelevels of 17-estradiol and estronebetween the two streams. 17-estradiolwas detectable in five Kö samples only (0.7–1.8 ng/L). Estrone was found in the Köfrom 2.5 to 38 ng/L (median: 7.6 ng/L) and inthe Kr between 0.8 and 22 ng/L (median: 1.7 ng/L). Analysis for nine phenolic xenoestrogensrevealed rather low levels for five compoundswhich occurred more frequently and in higherconcentrations in the Kö. After asemi-field exposure of adult male rainbow troutfor 4 weeks in Kö water, plasmavitellogenin levels were significantly highercompared to those levels detected in the sameanimals before exposure.     

Chemical analyses of water, sediment and biota in two small streams in southwest Germany

As a component of the VALIMAR project a comprehensive chemicalanalysis study was conducted in two small streams, the Körsch andthe Krähenbach, in southern Germany. The investigated pollutantswere heavy metals (HM), polycyclic aromatic hydrocarbons (PAHs),polychlorinated biphenyl's (PCBs) and a set of 33 pesticides.Samples from stream water, sewage treatment plant effluents,stream sediment and fish were analyzed. In the stream water, HMand PAHs showed slightly higher concentrations in the Körsch thanin the Krähenbach, whereas the pesticide concentrations (mainlyplant protective agents) were significantly higher in the Körschthan in the Krähenbach. Because of their similar occurrence andconcentrations in the Körsch water and in the sewage treatmentplant effluent, it appears that most of the pesticides wereintroduced into the river via the sewage treatment plant. Only inthe cases of terbuthylazine, triallate, chlorfenvinfos,metazachlor and mecoprop were the occurrence and concentrationsin the Körsch higher suggesting that run-off was the mostimportant route for these five compounds in this stream.The sediments of the two streams clearly differed in terms ofpollutant concentration. Polycyclic aromatic hydrocarbons, PCBsand HM were found in slightly higher concentrations in the Körschthan in the Krähenbach whereas pesticide concentrations weresignificantly higher in the Körsch. Results of each samplingdemonstrated extreme variations, due to frequent high-watersituations that led to high turnover and wash out of thesediment. In the sediment samples, most of the detected compoundswere more lipophilic than were those detected in water.Brown trout (Salmo trutta f. fario) and loach (Barbatulabarbatula) were sampled directly from the natural streams, from astream water fed bypass exposure system, and from a controlsystem in the laboratory. In the case of PAHs, PCBs andpesticides, concentrations were higher in fish exposed to theKörsch water than to the Krähenbach water. Heavy metals did notdifferentiate between the two streams. Polychlorinated biphenylsand pesticides showed higher concentrations in fish from thefield, which can be explained by longer exposure periods. Incontrast, PAHs showed the lowest concentrations under fieldconditions. Polycyclic aromatic hydrocarbons were possiblydisplaced by other compounds of high concentration. The pesticidepatterns in trout were quite similar in the different exposuretypes with primarily lindane, PCP and trifluraline contributingto these pattern changes. In loach, larger variations in allcontaminant concentrations were found but the same threecompounds also contributed most to the observed pattern changes.The analytical results were compared with various internationalobjective values for a good water quality as well as with valuesfrom other studies concerning the pollutant concentrations ofsediment and fish. All collected chemical data form a basis forthe biomarker investigations conducted by the other participantsof the VALIMAR project in order to find correlations betweenbiomarker responses and chemical pollution data of the twostreams.     

珠海市土石场空间分布特征与景观生态影响评价

人为水土流失是一种人类干扰下的典型景观退化现象．将人为侵蚀在空间上的表现称之为人为侵蚀景观．在遥感和GIS技术支持下,结合大量的实地调查资料,对珠海最主要的人为侵蚀景观类型——土石场开展空间分布分析和景观生态影响评价．调查范围内珠海土石场有235个,其中三灶、井岸两镇(区)分布最为集中,分别为28、29个．缓冲区分析表明,土石场的分布与距交通道路的远近呈对数线性相关,其中在距交通道路100～200m距离范围内分布最为集中．设计景观生态影响度评价指数,对面积大于5000m^2的152个土石场进行景观生态影响度评价结果表明,对周边景观生态环境影响极强的土石场有9个,属于强一级的有17个,应首先对这些土石场开展景观生态恢复．     

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     

次生林概念与生态干扰度

近一个世纪强烈的人为干扰使世界范围内的原始林面积锐减,次生林已成为中国乃至世界森林资源的主体.虽然在文献与现实中"次生林（Secondary forest）"被广泛使用,但次生林的概念在各个国家,甚至同一国家或地区以及各种不同文献中存在相互矛盾的情况,这给次生林研究与经营实践带来诸多不便;而不准确的次生林定义也为与各个层次的决策制定者及公众之间的交流带来了障碍.本文在查阅大量国内外关于次生林概念文献的基础上,结合近年来关于次生林生态与经营研究实践,综合分析了次生林概念的不确定性,同意以往次生林定义中的基本内涵,并认为：次生林是由于人为破坏性干扰或异常自然干扰使原始林固有的林分结构、物种组成或基本功能发生了显著变化,经过天然更新或人工诱导天然更新恢复形成的林分.但该定义中仍存在着很多不确定性, 如:怎样的干扰为"人为破坏性干扰"和"异常自然干扰";"林分结构、物种组成或基本功能"发生了怎样的变化为"显著变化";"人工诱导天然更新"中"人工"参与的成分比例如何等.次生林概念是在20世纪初由植物演替学家提出,当时未考虑干扰的持续性;而实际上,无论是次生林还是原始林,均是森林生态系统演替过程中的某一状态,在现代森林生态系统研究中,应重新规范"次生林"的概念.考虑到"次生林"定义的不确定性或困难性,建议使用"森林自然度"或"森林生态系统成熟度"或"森林干扰度"来表达现实森林所处的状态,但该方面的研究与实践尚需加强.     

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.     

Benthic diatom communities in boreal streams: community structure in relation to environmental and spatial gradients

An important goal for community ecology is the characterization and prediction of changes in community patterns along environmental gradients. We aimed to identify the major environmental correlates of diatom distribution patterns in boreal running waters. We classified 197 stream sites based on their diatom flora. Direct ordination methods were then used to identify the key environmental determinants of this diatom-based stream typology. Finally, we tested whether a regional classification scheme based on terrestrial landscapes (ecoregions) provides a reasonable framework for a regional grouping of streams based on their diatom flora. Two-way indicator species analysis produced 13 site groups, which were primarily separated by chemical variables, mainly conductivity, total P and water colour. In partial CCA, the environmental and spatial factors accounted for 38% and 24%, respectively, of explained variation in community composition. A high proportion (almost 40%) of variation explained by the combined effect (spatially-structured environmental) indicated that diatom communities of boreal streams incorporate a strong spatial component. At the level of subecoregions, classification strength was almost equally strong for all sites as for near-pristine reference sites only. Procrustes analysis indicated that spatial factors and patterns in diatom community structure were strongly concordant. Our data support the argument that diatom communities are strongly spatially structured, with distinctly different communities in different parts of the country. Because of the strong spatial patterns of community composition, bioassessment programs utilising lotic diatoms would clearly benefit from regional stratification. A combination of regional stratification and the prediction of assemblage structure from local environmental features might provide the most robust framework for diatom-based assessment of the biological integrity of boreal streams.     

Health status of Pomatoschistus microps populations in relation to pollution and natural stressors: implications for ecological risk assessment

Effects induced on wild populations by recurrent environmental contamination may difficult the ecological risk assessment of punctual pollution events such as oil spills. Here, the issue was addressed by comparing the health status of Pomatoschistus microps populations from four NW Iberian estuaries, using an integrated chemical–biological monitoring. Despite high seasonal variability, the parameters measured discriminated estuaries with different contamination levels and associated biological effects with chemical and abiotic stress. The decreased health status of fish from polluted sites strengthens the need of considering pollution-induced background effects and seasonal variability when assessing impacts and risks of oil and other chemical spills.     

Health status of Pomatoschistus microps populations in relation to pollution and natural stressors: implications for ecological risk assessment

Effects induced on wild populations by recurrent environmental contamination may difficult the ecological risk assessment of punctual pollution events such as oil spills. Here, the issue was addressed by comparing the health status of Pomatoschistus microps populations from four NW Iberian estuaries, using an integrated chemical-biological monitoring. Despite high seasonal variability, the parameters measured discriminated estuaries with different contamination levels and associated biological effects with chemical and abiotic stress. The decreased health status of fish from polluted sites strengthens the need of considering pollution-induced background effects and seasonal variability when assessing impacts and risks of oil and other chemical spills.     

Comparing the sensitivity of diverse macroinvertebrate metrics to a multiple stressor gradient in Mediterranean streams and its influence on the assessment of ecological status

Biological indicators are increasingly being used as integrative measures of the ecosystem health in streams, particularly those using macroinvertebrate assemblage composition. Monitoring biological quality of rivers has not a long tradition in some Mediterranean European countries like Spain. Several macroinvertebrate metrics have been recently proposed to assess ecological status in Mediterranean streams, so it is necessary to compare the use of proposed biological quality metrics to select the most appropriate ones.In the present work, two classic richness metrics (total number of families and number of the Ephemeroptera, Plecoptera and Trichoptera families), three indices (IBMWP, IASPT and t-BMWQ) and two multimetric indices, recently proposed to be used in Mediterranean streams (ICM-9 and ICM-11a or IMMi-L), were compared by the analysis of the sensitivity of these metrics to a multiple stressor gradient which reflected the main pressures present in the study area. For this purpose, data from 193 sites sampled in spring (95 reference sites and 98 disturbed sites) belonging to five different Mediterranean stream types present in 35 basins were studied.The results showed that the adjusted regression coefficients (r²) for all seven metrics in the exponential regression models were higher than linear ones, thus indicating an exponential relationship between metrics and the environmental alteration. The two studied multimetric indices presented higher regression coefficients (r² = 0.590–0.669) than the three indices (r² = 0.524–0.574) and the two metrics (r² = 0.471–0.525), therefore showing a better response to a stressor gradient in Mediterranean streams. Within the multimetric indices group, ICM-11a showed the highest regression coefficients. Based on the results obtained, we suggest using the ICM-11a, apart from the IBMWP, to assess ecological status in Mediterranean streams.     

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.     

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.     

Length of human C-bands in relation to the degree of chromosome condensation

Summary The C-band length of human chromosome 1 in prophase and prematurely condensed interphase chromosomes is relatively shorter than in metaphase chromosomes. However, even in chromosomes with the same degree of contraction the absolute length of the C-band varies considerably. This allocyclic behaviour of human constitutive heterochromatin has to be kept in mind if C-bands of different individuals are compared.Sponsored by the Deutsche Forschungsgemeinschaft (Sp 144)     

Evaluating the ecological status of rivers using an index of ecological distance: An application to diatom communities

Community structure changes with pollution or stress. In the Water Framework Directive, high ecological status through biological parameters is defined as a slight or minor deviation from the reference community, while the good status is defined as a small deviation.To assess the importance of this deviation, and then to measure the degradation of ecological status along a river, an index based on the concept of “ecological distance” between species was created and called ecological distance index (EDI). It was tested on diatom data from a pilot watershed (the Garonne river basin, South-West France).The results show a good correlation between the EDI and the IPS (Indice de Pollusensibilité Spécifique – specific pollusensitivity index – a diatom-based biotic index) ecological ratios, which means first that the EDI is a valuable indicator of ecological status, and that it can account for ecoregional specificities. This index can be applied to any communities (macro-invertebrates, fish, etc.), since: (i) typical reference communities are found for each river type; (ii) species are characterised then ranked by pollution sensitivity values.     

Longitudinal extent of acidification effects of plantation forest on benthic macroinvertebrate communities in soft water streams: evidence for localised impact and temporal ecological recovery

Plantation conifer forest can increase the risk of acidification in acid-sensitive catchments with consequences for macroinvertebrates and ecosystem functioning. This study compared headwater streams in forested and non-forested catchments to appraise the distance required for the acid effect on macroinvertebrates to diminish downstream. Strict criteria were followed in the selection of paired streams, including similarities in elevation, aspect, stream order, geographical proximity, geology and soil type, with no inflowing tributaries in the first 2.5 km and no major land-use other than plantation forest and moorland. Consequently two headwater streams (one forested, one non-forested) drained Ordovician sedimentary geology and two headwater streams (one forested, one non-forested) drained Old Red Sandstone (ORS) were selected. All streams drained peaty soils. Up to six sites at 500 m intervals were sampled in triplicate by multihabitat kick sampling. Ecological impact and recovery from acid effects involved the entire macroinvertebrate community, but varied between seasons. Acid-sensitive Ephemeroptera revealed marked effects of episodic acidification, with Baetis rhodani and Rhithrogena semicolorata found to be transient between seasons. The increase in acid-sensitive ephemeropteran species with increasing distance downstream indicates the finite effects of forest mediated acidification on soft water streams in Ireland. Ecological impact appears, therefore, to be localised within the catchment, with ecological recovery occurring a short distance downstream. This is the first study to have reported such results.     

Evaluating effects of weed cutting on water level and ecological status in Danish lowland streams

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Human impact on the ecological performance of Potamogeton species in northwestern Germany

The changes in habitat quality of lowland rivers in Lower Saxony (Germany) during the past 40 years are outlined. Almost all chemical, physical, and morphological parameters have changed, resulting in most cases in an enhanced potential productivity, accompanied by a complex disturbance regime. Historical reconstruction of the change in river vegetation is presented to compare the frequency of macrophyte species 40 years ago with the situation of today. For a total of 289 sampling sites, the floristic change was exactly reconstructed. Nearly all species show a decline in frequency. This trend is also recognizable in Potamogeton, with the exception of two narrow-leaved species.An attempt is made to explain both decline and maintenance in terms of life history characters (vital attributes) allowing the species to react to the changing habitat conditions. The successful species are characterized by certain life history characteristics which enable them to survive under the current disturbance regime. Most important aspects of life history are the ability to reproduce by means of turions and other fragments, a long-lived, deep-rooting rhizome system, phenotypic plasticity of above-ground parts, synchronous shoot polymorphism, and the potential to regenerate quickly from remaining buds after disturbance. The decline of formerly frequent species can be attributed mainly to the lack of certain key characters; however, physiological characters also may be important. The extirpation of some rare species could also be caused by random fluctuations in small populations. The general importance of population ecological research, particularly demography, life history theory, and the modelling of clonal populations in conservation ecology is stressed.     

Benthic diatom assemblages in mountain streams: community structure in relation to environmental and human pressures

The objective of this study was to determine the environmental factors that best explain the distribution and community composition of benthic diatoms in undisturbed mountain streams in the Eastern Highlands of Zimbabwe. Benthic diatoms were sampled during the dry season from 21 sampling sites established along altitudinal gradient of the study rivers. A total of 119 diatom species belonging to 38 genera and twelve families were recorded for all the 21 sites sampled. No significant differences were observed in species diversity and equitability amongst the three river systems. However, species richness, diversity and equitability decreased significantly along the longitudinal gradient of the rivers, with the highest richness, diversity and evenness being recorded in the upper reaches. Temperature, velocity, NO₃^? and Ca²⁺ levels were strongly associated with changes in diatom communities in the three rivers. Inventory of diatom communities has applications in many fields of biological research including conservation and biological monitoring of ecosystem changes.