The impact of eutrophication on aquaticmacrophyte diversity in weakly mineralized streams in the Northern Vosges mountains(NE France)

The relationships between water chemistry and aquatic macrophyte species were studied in an attempt to evaluate the impact of eutrophication on aquatic macrophyte diversity in weakly mineralized streams in the Northern Vosges mountains (NE France). The macrophyte specific richness and abundance increased along an upstream to downstream zonation, which was characterized by an increase in mineralization and nutrient levels. A comparison of aquatic macrophyte diversity of two streams has shown the impact of human-induced perturbations (fish-farms, domestic sewage) in such weakly mineralized and poorly buffered waters. Disturbed sites with very high nutrient loading were characterized by a low vascular plant richness and by the presence of filamentous algae. In order to preserve the floristic diversity of weakly mineralized streams, water quality should be improved, the riverbanks restored and discharges reduced.     

Characterisation of the potamal Danube River and the Delta: connectivity determines indicative macrophyte assemblages

The complexity of water bodies in the eu-potamal river corridor and the main delta channels of the Romanian Danube is exemplified by the macrophyte vegetation. Two hypotheses provided the background for our study: (a) is the macrophyte vegetation of large, permanently connected branches significantly separated from that of the main river channel; (b) is the macrophyte composition of the Danube main stem significantly altered when the river divides into the three large navigable Delta channels. Water bodies considered were two contiguous sections of the main river channel, two large branches remaining from the historical floodplain, and the three main Delta channels. We quantified macrophyte diversity and floristic variation. Our data set was prepared from the MIDCC-project data base, in which macrophyte occurrence, abundance and habitat parameters are stored for contiguous survey units of the whole Danube river corridor. Field survey method followed that of Kohler and the European Standard EN14184. Results confirmed our first hypothesis: permanently connected side branches still support significantly different macrophyte assemblages, making them important indicators of floodplain connectivity. The diversion of the Danube into its three large navigable delta channels significantly alters the macrophyte vegetation from the c. 300 km of main stem up-river, substantially supporting our second hypothesis. Our results largely enhance the knowledge on aquatic plant biodiversity in the eu-potamal Danube, forming a solid base for long-term studies. We also discuss the relevance of our results regarding the ecological, as well as the conservational, quality of rivers and their floodplains.     

Comparison of different biological indices for the assessment of river quality: application to the upper river Moselle (France)

The aim of our study was to assess the water quality of the upper Moselle river by using biological indices. Simultaneous physico-chemical surveys were also undertaken from May 1999 to April 2000. Twelve sampling sites were selected in order to provide a wide range of potential pollution. Chemical analysis did not reveal any major problem of pollution. However a lower water quality resulting from domestic pollution was established for some sampling sites. A biological monitoring combining both macroinvertebrates and macrophytes was performed. Biological indices based on plant community structure and macrophyte composition were not pertinent tools, whereas simple indices based on taxonomic richness of particular groups of macroinvertebrates were strongly correlated with several chemical parameters, showing that such simple biological variables should represent powerful indicators of ecosystem degradation.     

汉江中下游水生植物群落及演替

水生植物是河流生态系统的重要组成部分, 研究河流水生植物群落组成及演替对于河流生态系统健康诊断具有重要意义。该研究采用野外生态学研究方法, 于2013年9月和2014年6月2次对汉江中下游12个典型代表性江段的水生植物群落的组成、分布和生物量等进行调查。调查结果表明, 现阶段汉江中下游的主要水生植物共有69种, 隶属28科49属, 其中优势种主要是穿叶眼子菜(Potamogeton perfoliatus)、竹叶眼子菜(P. malaianus)、芦苇(Phragmites australis)、南荻(Triarrhena lutarioriparia)和喜旱莲子草(Alternanthera philoxeroides)等。结合早期的研究表明, 汉江中游江段沉水植物优势群落变化明显; 下游则呈现出由沉水植物群落向挺水植物群落演替的格局。挖沙和污染等人类干扰以及水位波动、河流底质和植物繁殖策略等自然因素可能是导致汉江中下游水生植物优势种变化和群落演替的主要因素。该研究结果可为汉江中下游的水生植物多样性保护和生态修复提供科学依据。     

An application of canonical correspondence analysis for developing ecological quality assessment metrics for river macrophytes

1. Aquatic macrophyte composition and abundance is required by the European Union's Water Framework Directive for determining ecological status. Five metrics were produced that can be combined to determine the deviation of aquatic macrophytes from reference conditions in Northern Ireland's rivers. 2. Species optima and niche breadths along silt, nitrate, pH, conductivity and dissolved oxygen gradients were generated from aquatic macrophyte and water quality surveys conducted at 273 sites throughout Northern Ireland using Canonical Correspondence Analysis (CCA). Five metric scores based on these environmental gradients were determined at new monitoring sites using the mean optima of the species occurring at the site, weighted by percentage cover and niche breadth of each species. 3. A preliminary reference network of 32 sites of high physico‐chemical and hydromorphological quality, and representative of the range of river types in Northern Ireland, enabled reference metric scores to be produced for each river type. Five unimpacted and twenty impacted sites were used for testing the performance of the metrics. By subtracting reference metric scores from metric scores at a monitoring site measures of ecological impact could be determined along five different impact gradients. Metrics were also combined to give a measure of total ecological change. 4. The metrics system distinguished unimpacted from impacted sites and correctly identified 77% of the known impacts. The metrics distinguished different types of impact, e.g. silt and nitrate. 5. Aquatic macrophyte occurrence and abundance has high natural variability at a site, both temporally and spatially. This method was designed to be sensitive to ecological change whilst reducing noise caused by natural variation.     

Macrozoobenthos response to environmental degradation in a heavily modified stream: Case study the Upper Elbe River,Czech Republic

Benthic macroinvertebrates are an important indicator of river health. However, their response upon water quality development downstream the pollution outlets considerably depends on the environmental habitat characteristics. Three successive stretches, each of them providing three different mesohabitats in stillwater (S), torrential (T) and riparian (R) zones were selected for evaluation of the impact of altered metapotamal river bed morphology (channelization) and chemical determinants of water quality on the Upper Elbe River. In downstream direction, the stretches are separated by weirs and characterized as a low polluted low modified natural stream (N), a low polluted channelized stream (C) and a channelized polluted stream (CP). Altogether, 111 benthic macroinvertebrate taxa were recorded in the Pardubice hotspot between Němčice and Přelouč. Despite different levels of stream bed and water quality degradation, micro- and mesohabitat characteristics appeared to be the most important factors determining the diversity of macrozoobenthos in riffle (substrate size structure) and in shoreline (macrophyte community composition and structure) mesohabitats. The diversity of macroinvertebrate communities was highest in riparian mesohabitats compared to stillwater and torrential ones. Saprobic indices increased in downstream direction, thus indicating the decline of water quality.     

Environmental drivers of freshwater macrophyte diversity and community composition in calcareous warm‐water rivers of America and Africa

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Predicting diversity versus community composition of aquatic plants at the river scale

We tested the relative importance of physical versus chemical factors in explaining aquatic plant species diversity and community composition within a temperate lowland river. A total of 38 macrophyte species were identified at 33 sites along the 104 km length of the Rideau River, a National Heritage River of Canada. Species richness ranged from 0 to 15 species per site, and Shannon diversity from 0 to 2.98. Macrophyte species richness and Shannon diversity were significantly related to the physical characteristics of sites. For Shannon diversity, 77% of the increase was explained by an increase in sediment organic content and a decrease in water velocity. For species richness, 70% of the increase was explained by the latter factors in addition to an increase in the littoral zone (0–2 m depth contour) width and planktonic chlorophyll concentrations. River water chemistry did not explain any observed variation in either Shannon diversity or species richness in this moderately enriched system. In contrast to species richness, the physical and chemical variables measured failed to explain variation in community composition. Cluster analysis did not reveal any grouping of species into distinct communities. Canonical correlation analysis showed that environmental variables had minimal effect on the distribution of most species, with only floating-leaved species responding to water velocity. We conclude that physical factors can predict species diversity at the within river scale but not the species composition at a given site, underlying the need to preserve the geomorphological diversity of rivers to maintain plant diversity.     

Effects of land use on aquatic macrophyte diversity and water quality of ponds

1. Aquatic macrophyte diversity and water quality of 55 ponds in western Japan were related to land use and morphometric variables to identify the environmental factors that sustain biodiversity and the spatial extent at which these factors operate. 2. The relevant spatial extent for floating‐leaved macrophyte richness (500 m from pond edge) was larger than that for submerged macrophyte occurrence (10, 75 and 100 m), whereas emergent macrophyte richness was best explained at much larger extents (1000 m). Total macrophyte richness was explained at the extent of 500, 750 and 1000 m. The extents relevant for explaining the physicochemical condition of pond water (100 and 250 m) were similar to those for submerged and floating‐leaved macrophytes, suggesting that these two growth forms are more sensitive to water quality compared to emergent macrophytes. 3. Diversity of all three growth forms and that of total macrophytes collectively were inversely related to turbidity and nutrient concentration; among the three growth forms, submerged macrophytes were most affected by water quality. 4. Negative relationships were found between the proportion of urban area and the diversity of the three growth forms and that of total macrophytes and water quality. Species richness of emergent, floating‐leaved and total macrophytes decreased with depth and increased with surface area up to about 5000 m², above which it declined. 5. Urbanisation and enlargement of ponds were the two main factors that decreased aquatic macrophyte diversity in irrigation ponds. To alleviate the adverse effects of urban areas on aquatic macrophyte diversity, our results suggest that management efforts should focus on the creation of buffer zones within the relevant spatial extent from the pond edge.     

No biotic homogenisation across decades but consistent effects of landscape position and pH on macrophyte communities in boreal lakes

It has been predicted that spatial beta diversity shows a decreasing trend in the Anthropocene due to increasing human impact, causing biotic homogenisation. We aimed to discover if vascular aquatic macrophyte communities show different spatial patterns in beta diversity in relation to land use and environmental characteristics in different decades from 1940s to 2010s. We aimed to discover if spatial structures differ between species-, phylogeny- and functional-based beta diversity. We used presence–absence data of aquatic macrophytes from five decades from small boreal lakes. We utilized generalised dissimilarity modelling to analyse spatial patterns in beta diversity in relation to environmental gradients. We found that lake elevation and pH were the most important variables in each decade, while land use was not particularly important in shaping beta diversity patterns. We did not find signs of a decreasing trend in spatial beta diversity in our study area during the past 70 yr. We did not find signs of either biotic homogenisation or biotic differentiation (taxonomic, phylogenetic or functional). Vascular aquatic macrophyte communities showed only slightly different beta diversity patterns in relation to human impact across decades. The patterns of different facets of beta diversity diverged only slightly from each other. Lake position in the landscape, reflecting both natural connectivity and lake characteristics, explained the patterns found in beta diversity, probably because our study area has faced only modest changes in land use from 1940s to 2010s when compared globally. Our study highlights the fact that biotic homogenisation is not an unambiguous process acting similarly at all spatial and temporal scales or in different environments and different organism groups.     

Seasonal zooplankton dynamics in main channel and backwater habitats of the Upper Mississippi River

This study used stratified random sampling to examine the spatial and temporal distribution of zooplankton communities in a large floodplain river (Mississippi River, USA). Potential mechanisms controlling zooplankton abundance and community structure were considered. Main channel and backwater habitats included in this study differed between a turbid upper pool reach where aquatic macrophytes were sparse and a lower pool reach which was considerably less turbid and had extensive aquatic macrophyte coverage. Samples were collected monthly during the summer over a 2-year period and multivariate analysis was used to examine the spatial and temporal distribution of zooplankton. Significant differences were found in zooplankton density and community composition among habitats and reaches within the pool. Rotifers were the dominant taxa and seasonality was pronounced, with peak densities often occurring in late-spring. Community structure varied by habitat and reach, which suggests that water quality, physical habitat characteristics, presence of aquatic macrophytes, and zooplankton sources can all influence the zooplankton communities of the Upper Mississippi River. Characterization of the zooplankton communities provides a basis for understanding changes in the river ecosystem and examination of zooplankton communities among habitats provides insight into the mechanisms affecting zooplankton dynamics.     

湖泊底质与水生植物相互作用综述

简要阐述了湖泊生态系统中底质和水生植物的概念及重要性,综述了底质理化性质对水生植物生长的影响,以及水生植物对底质营养盐的释放和底质再悬浮的作用。通过大量的研究综述回顾论述了不同的湖泊底质类型在一定程度上决定了水生植物的生长状态,适合的底质营养盐范围能促进水生植物生长,不同水生植物对底质营养盐的耐受性有差异。水生植物能促进底质沉降并减少再悬浮,水生植物的存在对沉积物中磷的活性有显著的影响。污染底泥的修复能为水生植物的立地与生长提供了良好的底质条件,有利于富营养化湖泊水生植被的恢复与重建。     

Effects of stream restoration and management on plant communities in lowland streams

1. We evaluated restoration success on macrophyte species diversity and composition in lowland streams using communities in 30 naturally meandering stream reaches in the western part of Jutland, Denmark, as reference target communities. Fuzzy set clustering was used to examine the floristic and environmental similarity among reaches, whereas fuzzy set ordination was used to relate floristic patterns to environmental variables. 2. Two major groups of streams were identified based on their floristic composition. One group consisted of reference and restored reaches and the other of the majority of channelised reaches. We found that management exerted a strong influence on the macrophyte communities and that the identified groups were related to differences in management intensity. 3. Our results also indicate that bank morphology and bed level affected macrophyte communities in the streams, particularly the richness and abundance of terrestrial species. The analyses performed suggest that shallow and wide banks allow for a larger migration of species from the stream banks into the streams, thereby enhancing species diversity within the stream channel. 4. The results of this study suggest that macrophyte communities in channelised lowland streams can recover following restorative interventions given that stream management (i.e. weed cutting and dredging) is minimised and that stream banks are reprofiled to improve the lateral connectivity between the stream and its valley.     

新疆开都河流域水生植物多样性及其影响因素

河流是一个连续的、流动的、独特而完整的系统,研究河流生态系统中水生植物的多样性分布格局及其影响因素对河流生态学研究具有重要意义。本文通过野外调查,研究了新疆开都河流域水生植物多样性、主要水生植物群落特征及与环境因子之间的关系,并利用水分-能量动态假说和栖息地异质性假说对该流域水生植物物种多样性的地理格局进行解释。结果表明: 开都河流域共有水生植物71种,隶属于24科39属;聚类分析可将开都河流域水生植物群落划分为10个主要群落类型,其中芦苇群落物种丰富度最高,狭叶香蒲群落和金鱼藻群落物种丰富度最低;流域水生植物群落Shannon指数与pH呈显著负相关,Simpson指数与pH、经度呈显著负相关,与海拔呈显著正相关;流域水生植物群落类型主要受海拔、水深及水温的影响;流域水生植物物种多样性随经纬度无明显变化规律。水分-能量动态假说和栖息地异质性假说共解释开都河流域水生植物多样性格局变量的31.4%,表明这两个假说对于该流域水生植物多样性格局的解释力并不高。     

Aquatic macrophytes in the large, sub-tropical Itaipu Reservoir, Brazil

In the last three decades, rapid assessment surveys have become an important approach for measuring aquatic ecosystem biodiversity. These methods can be used to detect anthropogenic impacts and recognize local or global species extinctions. We present a floristic survey of the aquatic macrophytes along the Brazilian margin of the Itaipu Reservoir conducted in 2008 and compare this with a floristic survey conducted ten years earlier. We used ordination analysis to determine whether assemblage composition differed among reservoir arms. Macrophyte species were sampled in each of the 235 sampling stations using a boat, which was positioned inside three places of each macrophyte stand to record species and search for small plants. We also collected submerged plants using a rake with the boat moving at constant velocity for ten minutes. We assigned individual macrophyte species to life form and identified representative species for each life form. A total of 87 macrophyte taxa were identified. The "emergent" life forms contained the highest number of species, followed by "rooted submerged" life forms. The extensive survey of macrophytes undertaken in September 2008 recorded more species than a survey conducted between 1995 and 1998. This could be due to changes in water physico-chemistry, disturbances due to water drawdown and the long period between surveys, which may have allowed natural colonization by other species. Additionally, differences in the classification systems and taxonomic resolution used in the surveys may account for differences in the number of species recorded. Assemblage composition varied among the arms and was affected by underwater radiation (as measured using a Secchi disk) and fetch. Five non-native species were found. Two of these non-native species (Urochloa subquadripara and Hydrilla verticillata) are of special concern because they have a high frequency of occurrence and occupy large marginal areas of the reservoir. Future surveys should be conducted to determine the habitat most frequently colonized by these species. This would allow management strategies to be developed to protect native aquatic biota and prevent interference with the recreational and commercial uses of the Itaipu Reservoir.     

Effects of deferring grazing on the floristic diversity of Stipa tenacissima Loefl. ex L. rangelands in central Algerian steppe

The present work aims to study the effect of deferring grazing on the floristic diversity of Stipa tenacissima Loefl. ex L. rangelands in the central Algerian steppe in two different bioclimatic stages, namely semi‐arid and arid. This work is part of a perspective to know the floristic characteristics of an area excluded from grazing and an unrestricted rangeland, in two different environments in order to highlight the factors that are conceivably responsible for the diversification of flora in the steppe ecosystems. In the present study, a number of 96 floristic surveys were performed during the spring season of the years 2014, 2015 and 2016. The methodology adopted is a subjective sampling. The minimum area retained is 100 m² defined by the method of Braun Blanquet and de Bolos (1957, Annales Estacion Experimental de Aula Dei, 5, 266). This method has been used to study the floristic diversity represented by the floristic richness, Shannon index, the equitability, the biological and the phytochoric type. The climatic correction according to the altitudinal gradient was applied to determine the bioclimatic stage. The results from the surveys indicate that the rangelands at the studied sites contain 109 species, 27 families and 63 genera out of which 79 species and 22 families are in the semi‐arid bioclimatic stage. A two‐way analysis of variance was employed to examine the effect of the bioclimatic stage and the pasture land put at rest. Variance analysis of the diversity indices showed that the bioclimatic stage has a significant impact on the floristic richness and flora diversity of the S. tenacissima steppe (p ≤ 0.01) with a 5% threshold; on the other hand, the protection of these ecosystems does not have a remarkable influence on the floristic diversity (p > 0.05). In recent years, climatic disturbances have resulted in changes in vegetation, even in rested areas located between the study localities.     

Detecting river environmental quality through plant and macroinvertebrate bioindicators in the Aniene River (Central Italy)

From the source to the mouth of the Aniene River, a tributary of the Tiber near Rome, there is a multifactorial gradient of increasing disturbance and water pollution. We first investigated the variation of riverine and aquatic vegetation along the Aniene, analysing the floristic composition by means of transects comprising both water and shore. We then compared vascular plants and macroinvertebrates to establish which was the more reliable bioindicator of water pollution and disturbance in river habitats. The floristic dataset can be ordered according to the two axes of NMMDS. Axis I showed a high correlation with the Extended Biotic Index (EBI) (Spearman’s rho = 0.89) and Hemeroby indicator of disturbance in plants (Spearman’s rho = −0.70), and Axis II with Shannon diversity of plants (Spearman’s rho = −0.67). These results have been summarised in two GIS maps, for EBI and Hemeroby, and allow to distinguish two sectors of the Aniene: upper and low-middle, correlated with geomorphology, density, type of settlement and degree of pollution. EBI and Hemeroby indicators collect information about environmental quality along different scales.     

Aquatic macrophytes diversity in lagoons of a tropical floodplain: The role of connectivity and water level

Abstract The goal of this research is to evaluate how the assemblages of aquatic macrophytes in marginal floodplain habitats, with different degrees of connectivity to the main river, respond to water level fluctuations. Samples were carried out quarterly (May 2000 to March 2002) in seven lagoons of the Upper Paraná River floodplain (22°30′ and 22°45′‐S and 53°15′ and 53°30′‐W) with different degrees of connectivity (connected and disconnected to the main river). In each lagoon, a shore‐pelagic zone transect was marked and at every 2 m the depth and the cover of each aquatic macrophyte species were recorded (Domin‐Krajina scale) in a quadrat of 0.25 m². A total of 29 aquatic macrophyte species and an unusual decrease in water level were recorded in August 2001. Drawdown had a negative impact on species richness, only in connected lagoons, which was shown by a positive relationship between depth and species number (r‐Spearman = 0.86; P < 0.01). Depth affected Beta diversity positively (r‐Spearman = 0.79; P < 0.05). Drawdown affected the connected and disconnected lagoons differently, which can be attributed to their different morphometry. In this period, ‘habitat contraction’ was higher on connected lagoons. Positive correlation between mean species number and depth, and between beta diversity and depth, are factors that support this affirmation. Indicator species analysis showed that for disconnected lagoons, Oxycaryum cubense (Cyperaceae), Polygonum meissnerianum (Polygonaceae) and P. ferrugineum, with indicator values (IndVal) of 53, 30 and 25%, respectively, were indicator species. Salvinia spp. (Salvinaceae) (62%), P. acuminatum (44%) and the Ricciaceae Ricciocarpus natans (0%) were the indicator species of the connected lagoons.     

Ecomorphological analysis as a complementary tool to detect changes in fish communities following major perturbations in two South African estuarine systems

Ecomorphological changes as a result of natural perturbations in estuarine fish communities were investigated in two South African estuaries (Swartvlei and East Kleinemonde), both before and after the loss of aquatic macrophyte beds in these systems. The fish communities were analysed using an ecomorphological diversity index (EMI) and the results compared to a traditional index, the Shannon-Wiener diversity index. The EMI revealed that the major changes in fish community composition recorded in both estuaries were associated with quantitative variations at the species level. Both estuaries essentially lost their macrophyte beds and ended up with the same type of bottom habitat (bare sediment). In both cases the fish morphological variability decreased immediately after aquatic macrophyte loss and then increased to end above the initial value. The ecomorphological analysis appeared to be sensitive to major ecological disturbances that occurred during the study period and this was confirmed by the morphospace configuration. The results indicate that the ecomorphology of the fish community responds to habitat changes and that this change corresponds to alterations in the representation of the different feeding types. These findings therefore contribute to the measurement of morphological changes in estuarine fish assemblages as a result of habitat changes within the ecosystem and we propose that ecomorphological analyses add another dimension to the information provided by existing diversity indices in studying changing fish communities.     

Effects of an exotic invasive macrophyte (tropical signalgrass) on native plant community composition,species richness and functional diversity

1. The issue of freshwater species being threatened by invasion has become central in conservation biology because inland waters exhibit the highest species richness per unit area, but apparently have the highest extinctions rates on the planet. 2. In this article, we evaluated the effects of an exotic, invasive aquatic grass (Urochloa subquadripara– tropical signalgrass) on the diversity and assemblage composition of native macrophytes in four Neotropical water bodies (two reservoirs and two lakes). Species cover was assessed in quadrats, and plant biomass was measured in further quadrats, located in sites where tropical signalgrass dominated (D quadrats) and sites where it was not dominant or entirely absent (ND quadrats). The effects of tropical signalgrass on macrophyte species richness, Shannon diversity and number of macrophyte life forms (a surrogate of functional richness) were assessed through regressions, and composition was assessed with a DCA. The effects of tropical signalgrass biomass on the likelihood of occurrence of specific macrophyte life forms were assessed through logistic regression. 3. Tropical signalgrass had a negative effect on macrophyte richness and Shannon and functional diversity, and also influenced assemblage composition. Emergent, rooted with floating stems and rooted submersed species were negatively affected by tropical signalgrass, while the occurrence of free‐floating species was positively affected. 4. Our results suggest that competition with emergent species and reduction of underwater radiation, which reduces the number of submersed species, counteract facilitation of free‐floating species, contributing to a decrease in plant diversity. In addition, homogenisation of plant assemblages shows that tropical signalgrass reduces the beta diversity in the macrophyte community. 5. Although our results were obtained at fine spatial scales, they are cause for concern because macrophytes are an important part of freshwater diversity.