Macrophyte Assemblages Research Articles

The role of an invader in its native range: could differential grazing by apple snails structure the submersed macrophytes assemblages in Southern Pampas (Argentina)?

The role of an invader in its native range: could differential grazing by apple snails structure the submersed macrophytes assemblages in Southern Pampas (Argentina)?

Eutrophication homogenizes shallow lake macrophyte assemblages over space and time

AbstractEutrophication is commonly implicated in the reduction in macrophyte species richness in shallow lakes. However, the extent to which other more nuanced measures of macrophyte diversity, such as assemblage heterogeneity, are impacted concurrently by eutrophication over space and time and the joint influences of other factors (e.g., species invasions and connectivity) remains relatively poorly documented. Using a combination of contemporary and paleoecological data, we examine how eutrophication influences macrophyte assemblage heterogeneity and how nutrient enrichment interacts with watercourse connectivity, lake surface area, and relative zebra mussel abundance over space (within and among lakes) and time (decades to centuries) at the landscape scale. The study system is the Upper Lough Erne, Northern Ireland, UK, which is composed of a large main lake and several smaller satellite lakes that vary in their hydrological connectivity to the main lake. By applying homogeneity analysis of multivariate dispersions and partial redundancy analysis, we demonstrate that contemporary lake macrophyte heterogeneity and species richness are reduced in lakes with intensified eutrophication but are increased in lakes with greater zebra mussel abundance and lake surface area. Watercourse connectivity positively influenced assemblage heterogeneity and explained larger proportions of the variation in assemblage heterogeneity than local environmental factors, whereas variation in species richness was better related to local abiotic factors. Macrophyte fossil data revealed within‐ and among‐lake assemblage homogenization post‐1960, with the main lake and connected sites showing the highest rates of homogenization due to progressive eutrophication. The long‐term and contemporary data collectively indicate that eutrophication reduces assemblage heterogeneity over time by overriding the importance of regional processes (e.g., connectivity) and exerts stronger pressure on isolated lakes. Our results suggest further that in connected lake systems, assemblage heterogeneity may be impacted more rapidly by eutrophication than species richness. This means that early effects of eutrophication in many systems may be underestimated by monitoring that focuses solely on species richness and is not performed at adequate landscape scales.

Macrophyte assessment in European lakes: Diverse approaches but convergent views of ‘good’ ecological status

The European Water Framework Directive has been adopted by Member States to assess and manage the ecological integrity of surface waters. Specific challenges include harmonizing diverse assessment systems across Europe, linking ecological assessment to restoration measures and reaching a common view on ‘good’ ecological status.In this study, nine national macrophyte-based approaches for assessing ecological status were compared and harmonized, using a large dataset of 539 European lakes. A macrophyte common metric, representing the average standardized view of each lake by all countries, was used to compare national methods. This was also shown to reflect the total phosphorus (r2 = 0.32), total nitrogen (r2 = 0.22) as well as chlorophyll-a (r2 = 0.35–0.38) gradients, providing a link between ecological data, stressors and management decisions. Despite differing assessment approaches and initial differences in classification, a consensus was reached on how type-specific macrophyte assemblages change across the ecological status gradient and where ecological status boundaries should lie.A marked decline in submerged vegetation, especially Charophyta (characterizing ‘good’ status), and an increase in abundance of free-floating plants (characterizing ‘less than good’ status) were the most significant changes along the ecological status gradient. Macrophyte communities of ‘good’ status lakes were diverse with many charophytes and several Potamogeton species. A large number of taxa occurred across the entire gradient, but only a minority dominated at ‘less than good’ status, including filamentous algae, lemnids, nymphaeids, and several elodeids (e.g., Zannichellia palustris and Elodea nuttallii). Our findings establish a ‘guiding image’ of the macrophyte community at ‘good’ ecological status in hard-water lakes of the Central-Baltic region of Europe.

Indirect effects of extreme precipitation on the growth of Vallisneria denseserrulata Makino

Submerged macrophytes are important for maintaining a clear water state in shallow lakes but are now threatened by the ongoing climate changes involving more extreme weather events. We explored the effects of extreme precipitation (higher water level, higher loading of nutrients (phosphorus and nitrogen)) on the growth of the submerged macrophyte Vallisneria denseserrulata Makino in a 10-month long mesocosm experiment. We used three macrophyte communities (one, three and six species) and four simulated scenarios of water level and nutrient loading (constant 75 cm, no nutrient loading; gradual water level increase from 75 cm to 150 cm over three months; extreme water level increase to 150 cm within one day at the same nutrient loading as in the gradual increase; constant 75 cm and the same nutrient loading as in the two former treatments). Leaf chlorophyll fluorescence, biomass, morphology of macrophytes and periphyton biomass were recorded. In the treatment with an extreme increase in water level, macrophyte biomass declined, whereas plant height and leaf number remained unchanged compared with the treatments where only nutrient but not water levels were increased. The combined effect of increased water level and enhanced nutrient loading (gradual and extreme change) did not differ significantly from the constant 75cm treatment without additional nutrient loading. No significant differences were found in epiphyton biomass among the water level treatments, while epipelon biomass was marginally higher and plant volume inhabited lower in the two treatments with a water level increase. Changes in macrophyte assemblages only had limited effects on maximum leaf width and the relative electron transport rate of V. denseserrulata. In conclusion, V. denseserrulata was overall resilient to the major simulated changes in precipitation, except when the water level increased suddenly, and only marginally influenced (leaf chlorophyll fluorescence parameter) by the composition of the macrophyte assemblage.

Functional and Taxonomic Differentiation of Macrophyte Assemblages Across the Yangtze River Floodplain Under Human Impacts.

Human activities and the consequent extirpations of species have been changing the composition of species assemblages worldwide. These anthropogenic impacts alter not only the richness of assemblages but also the biological dissimilarity among them. One of the main gaps in the assessment of biodiversity change in freshwater ecosystems is our limited understanding regarding how taxonomic and functional facets of macrophyte assemblages respond to human impacts on regional scales. Here, we assess the temporal (before 1970s against after 2000s) changes in taxonomic and functional richness and compositional dissimilarities, partitioned into its turnover and nestedness components, of freshwater macrophyte assemblages across the floodplain lakes of the Yangtze River in China. We found that functional and taxonomic assemblage differentiation occurred simultaneously under increasing human impact, concomitant to a general decrease in functional and taxonomic richness. However, this effect weakened when the historical level of taxonomic dissimilarity among assemblages was high. Macrophyte species with large dispersal range and submersed life form were significantly more susceptible to extirpation. The impact of human activities on differentiation was complex but habitat loss and fishery intensity were consistently the main drivers of assemblage change in these lakes, whereas water quality (i.e., light pollution and nutrient enrichment) had weaker effects. Further, macrophyte taxonomic and functional differentiation was mainly driven by the nestedness component of dissimilarity, accounting for changes in assemblage composition related to changes in species richness independent of species replacement. This result, markedly different from previous studies on freshwater fish assemblages conducted in these lakes, represents a novel contribution toward achieving a more holistic understanding of how human impacts contribute to shape community assemblages in natural ecosystems.

Associations between Macrophyte Life Forms and Environmental and Morphometric Factors in a Large Sub-tropical Floodplain.

Macrophyte assemblages are composed of species with different life forms and various ecological functions. Our aim was to investigate the potential environmental determinants of changes in the biomass of individual life forms and of the composition of the macrophyte assemblage in terms of life forms diversity. We sampled 23 waterbodies at low and high water levels in the Middle Paraná River floodplain. Macrophyte biomass samples were collected and classified in terms of life forms. We performed a redundancy analysis using the biomass of the various life forms to assess the importance of environmental variables to the composition of macrophyte life forms. Linear regressions were applied to investigate the environmental determinants of the biomasses of individual life forms. The degree of connectivity and the combination of depth, hydrology and nitrate were the main determinants of the composition in terms of life forms. The biomass of each individual life form was explained by different combinations of environmental variables, but the connectivity was the most important one. Our study shows that groups of species with similar life forms respond to environmental factors in particular ways, which might alter the biomass composition of life forms. Given that the ecosystem functioning depends on the functional characteristics of local communities, our findings about the relation between environmental changes and the community composition in terms of life forms (or functional composition) can be a helpful tool for predicting changes on ecosystem processes (such as nutrient cycling) against possible future scenarios.

Environmental Variability and Macrophyte Assemblages in Coastal Lagoon Types of Western Greece (Mediterranean Sea)

Coastal lagoon types of Western Greece were allocated to a spectrum of meso to polyhaline chocked lagoons; poly to euhaline restricted lagoons; and euhaline restricted lagoons along the Ionian Sea coast. This diversity comprises wide ranges of physical, chemical and environmental parameters in a seasonal and annual scale, which explains the variability in the distribution of benthic macrophytes. Four different macrophyte assemblages were distinguished, characterized by annual or perennial species. Extensive statistical analysis showed that salinity and nitrate concentrations had a great impact on the composition and distribution of macrophyte assemblages into lagoon types that also changed their abundance on a seasonal and annual scale. During the monitoring period, an important salinity shift in a chocked lagoon might cause the gradual loss of Zostera noltii and its replacement by Ruppia cirrhosa. Restricted lagoons were characterized by higher species diversity, while the other three identified macrophyte assemblages were dominated by the angiosperms Ruppia cirrhosa and Cymodocea nodosa. This integrated study of coastal lagoons is likely to be broadly applicable, since it was based on important parameters affecting such ecosystems, and the provided links between macrophyte assemblages and abiotic factors are of critical importance to improve management and environmental policies.

Changes in climate, land use and local conditions drive macrophyte assemblages in a Mediterranean shallow lake

espanolLas lagunas mediterraneas sufren procesos de deterioro derivados de la eutrofizacion, los cambios en los usos del suelo de su cuenca de drenaje y el cambio climatico. Es esperable que las plantas acuaticas respondan a los cambios ecologicos al encontrarse en estrecho contacto con los factores ambientales. En este estudio se evalua la influencia del clima, los usos del suelo y las caracteristicas locales en los cambios experimentados por la comunidad de macrofitos de la laguna Sentiz, un medio lenitico y de caracter estepario situado en el noroeste de Espana. Para ello, se han utilizado datos de las caracteristicas locales, imagenes de satelite, ortofotografias y series climaticas. El estudio revelo la existencia de importantes cambios en los factores ecologicos determinantes de las comunidades de macrofitos, destacando los cambios sufridos en la profundidad media, la superficie del medio palustre, la vegetacion higrofila, la temperatura media anual y la cobertura de pastizal. Asimismo, se ha encontrado que la evolucion temporal de la cobertura de los hidrofitos sumergidos y con hojas flotantes estuvo determinada por las caracteristicas locales, mientras que la cobertura de los grandes y pequenos helofitos estuvo definida por los cambios en los usos del suelo y en las condiciones climaticas, respectivamente. Nuestro estudio sugiere que las estrategias de conservacion de las comunidades de macrofitos en lagunas someras mediterraneas deben enfocarse no solamente en la gestion de las caracteristicas locales de cada laguna, sino tambien en la gestion de sus cuencas de drenaje y teniendo en cuenta la evolucion climatica. En este sentido, nuestros resultados mejoran el conocimiento de los factores ambientales de las comunidades de macrofitos de lagunas someras mediterraneas, incorporando series historicas tanto de las caracteristicas fisico-qui- micas del ecosistema como de sus comunidades biologicas. Finalmente, se pretende aportar informacion relevante de los factores determinantes de las comunidades de macrofitos a la hora de implementar estrategias de gestion y conservacion de estos y de otros ecosistemas leniticos similares. EnglishMediterranean shallow lakes are affected by many deterioration processes like eutrophication, land-use changes along its drainage basin and climate change. Aquatic plants are expected to reflect the ecological changes of shallow lakes since they are in close contact with the environmental factors. We assessed the influence of climate, land use and local conditions on macrophyte community changes in Sentiz Lake, a steppe water body located in the northwest of Spain, using long term data of local conditions, satellite imagery, orthophotography and climatic series. We found important changes in the environmental drivers of aquatic macrophyte assemblages (e.g. mean depth, water surface area, shore vegetation, mean annual temperature and grassland coverage). Similarly, we found that aquatic macrophyte growth forms responded to different environmental controlling factors: submerged and floating-leaved hydrophytes responded to local conditions, while big helophytes and small helophytes responded to land use and climate, respectively. Overall, our study suggests that management efforts aimed at preserving aquatic macrophyte assemblages of shallow Mediterranean lakes should focus not only on local conditions of each lake but also on their watersheds and climate. Therefore, this study improves the knowledge of the environmental drivers of aquatic macrophyte assemblages of shallow Mediterranean lakes, incorporating long term data of both physical and biological parameters and providing a basic framework for applying management and conservation strategies in these and other similar ecosystems

Relationships between contemporary and subfossil macrophyte assemblages in Mediterranean ponds

Mediterranean ponds have been historically far less studied than temperate lakes of northern Europe and, for this reason, the availability of historical data is limited for these endangered ecosystems. In the absence of such data, macrofossils from surface sediment may provide highly relevant information concerning modern and past assemblages. Herein we explore the correspondence between contemporary macrophyte assemblages and their sedimentary remains from surface sediment in 35 ponds located in the North Iberian Plateau. The results show that plant macrofossils reflect both the contemporary communities from which they are derived and the environmental forces controlling their assemblage composition (primarily total phosphorous and chlorophyll-a). Overall, macrofossils may represent a useful tool for reconstructing the historical evolution of macrophyte communities, as well as the driving environmental variables, in the poorly investigated Mediterranean ponds. However, the absence of some littoral and helophytic remains in the surface sediment samples may indicate that caution should be exercised to avoid potential biases when reconstructing past macrophyte communities. Hence, we suggest that addressing the effects of coring location and the complex patterns of production and distribution of subfossils in relation to their source vegetation may provide intriguing insights for future research in Mediterranean paleolimnology.

Anthropogenic water bodies as drought refuge for aquatic macroinvertebrates and macrophytes

Ecological research associated with the importance of refuges has tended to focus on natural rather than anthropogenic water bodies. The frequency of disturbances, including drought events, is predicted to increase in many regions worldwide due to human-induced climate change. More frequent disturbance will affect freshwater ecosystems by altering hydrologic regimes, water chemistry, available habitat and assemblage structure. Under this scenario, many aquatic biota are likely to rely on permanent water bodies as refuge, including anthropogenic water bodies. Here, macroinvertebrate and macrophyte assemblages from waste-water treatment and raw-water storages (i.e. untreated potable water) were compared with nearby natural water bodies during autumn and winter 2013. We expected macroinvertebrate and macrophyte assemblages in raw-water storages to be representative of natural water bodies, while waste-water treatment storages would not, due to degraded water quality. However, water quality in natural water bodies differed from raw-water storages but was similar to waste-water treatment storages. Macroinvertebrate patterns matched those of water quality, with no differences occurring between natural water bodies and waste-water treatment storages, but assemblages in raw-water storages differed from the other two water bodies. Unexpectedly, differences associated with raw-water storages were attributable to low abundances of several taxa. Macrophyte assemblages in raw-water storages were representative of natural water bodies, but were less diverse and abundant in, or absent from, waste-water treatment storages. No clear correlations existed between any habitat variables and macroinvertebrate assemblages but a significant correlation between macrophyte assemblages and habitat characteristics existed. Thus, there were similarities in both water quality and macroinvertebrate assemblages between natural water bodies and waste-water treatment storages, and similarities in macrophyte assemblages between raw-water storages and natural water bodies. These similarities illustrate that anthropogenic water storages support representative populations of some aquatic biota across the landscape, and thus, may provide important refuge following disturbance where dispersal capabilities allow.

Comparison of aquatic macrophyte community structure between natural wetlands and rice fields with different cultivation ages.

Recent studies indicate that rice fields contribute to the conservation of aquatic plants, however, repeated cultivation can reduce the species diversity harbored by rice fields. Repeated tillage, agrochemical application and environmental homogeneity can reduce plant diversity and select for species more tolerant to disturbance. Our hypotheses were: 1) macrophyte richness and biomass decrease with increased rice crop age; and 2) macrophyte species of rice fields are a subsample of natural wetlands and species loss will increase with crop age. We investigated three rice fields of each different ages (old, intermediate and new ones) and three natural intermittent wetlands for this study. Each area was sampled four times throughout the rice cultivation cycle (off-season, initial growth, final growth and post-harvest). Our results showed that the mean macrophyte richness and biomass were similar between rice fields of different ages and lower than that of natural wetlands. Although species composition in the different-aged rice fields was not markedly different, there was nestedness in the rice fields as age increased. In this study, we verified that macrophyte richness and biomass in rice fields was lower than natural wetlands and the species composition was different among wetland types (rice fields and natural wetlands), however our hypothesis that species richness and biomass will decrease with crop age was not confirmed. All rice crops had similar macrophyte assemblage structure (richness, biomass and species composition). However, the another hypothesis tested was confirmed, macrophyte assemblage of rice fields is a subset of natural wetlands and as, the age of a rice field increases, the species that occur in older rice field are subsets of species that occur in younger ones.

TAXONOMIC LEVEL NEEDED TO DETECT SIGNIFICANT CHANGES IN POLYCHAETE COMMUNITIES OVER DIFFERENT MACROPHYTE ASSEMBLAGES ON ROCKY INTERTIDAL SHORES

Environmental degradation has more significant impacts on rocky intertidal communities after global changes increase progressively. Thus, ecological monitoring should be conducted properly to analyse potential drivers and their impacts. However, most of the ecological monitoring in rocky intertidal shores is more interested in macroalgae. Polychaetes associated with macrophyte assemblages should be also involved in the monitoring because they are important in determining coastal health and productivity. A successful ecological monitoring should consider three factors: taxonomic level, statistical power, and sample size. In this study, those factors were analysed in the relationships between polychaetes and macrophytes. Four taxonomic levels of polychaetes (i.e. order, family, genus, species) were tested based on 25 samples collected from rocky intertidal shores of Gunung Kidul, Yogyakarta, Indonesia. Relationships between each of taxonomic richness of polychaetes and each of macrophytes variables (i.e. species richness, biomass, species composition) were analysed using a Generalised Linear Models fitted by Poisson Distribution and log link. The statistical power of those relationships and the sample size needed to obtain a strong statistical power (>0.8) were also recorded. Relationships between each of taxonomic composition of polychaetes and each of macrophyte variables were analysed using a distance-based Redundancy Analysis based on Bray-Curtis dissimilarity on log(x+1) transformed abundance data with 999 permutations. Results showed that family-based data analysis was sufficient to detect significant relationships between polychaetes and macrophytes. However, the statistical power of most relationships was relatively weak (<0.8). Hence, the family-based data analysis should select a 44-sample size to gain significant relationships with a strong statistical power.

Enhanced effects of biotic interactions on predicting multispecies spatial distribution of submerged macrophytes after eutrophication.

Water eutrophication creates unfavorable environmental conditions for submerged macrophytes. In these situations, biotic interactions may be particularly important for explaining and predicting the submerged macrophytes occurrence. Here, we evaluate the roles of biotic interactions in predicting spatial occurrence of submerged macrophytes in 1959 and 2009 for Dianshan Lake in eastern China, which became eutrophic since the 1980s. For the four common species occurred in 1959 and 2009, null species distribution models based on abiotic variables and full models based on both abiotic and biotic variables were developed using generalized linear model (GLM) and boosted regression trees (BRT) to determine whether the biotic variables improved the model performance. Hierarchical Bayesian‐based joint species distribution models capable of detecting paired biotic interactions were established for each species in both periods to evaluate the changes in the biotic interactions. In most of the GLM and BRT models, the full models showed better performance than the null models in predicting the species presence/absence, and the relative importance of the biotic variables in the full models increased from less than 50% in 1959 to more than 50% in 2009 for each species. Moreover, co‐occurrence correlation of each paired species interaction was higher in 2009 than that in 1959. The findings suggest biotic interactions that tend to be positive play more important roles in the spatial distribution of multispecies assemblages of macrophytes and should be included in prediction models to improve prediction accuracy when forecasting macrophytes’ distribution under eutrophication stress.

Environmental effects on macrophyte assemblages of small and medium-sized rivers in two bioregions of Central Europe

Effect of environmental variables on macrophyte assemblages were studied in 97 small and medium-sized rivers in two bioregions (Pannonian and Carpathian) in Slovakia during three years (2013–2016). In total, 153 species were determined (100 vascular plants, 36 bryophytes and 17 macro-algal growths); 106 taxa and 113 taxa in the Pannonian and the Carpathian bioregion, respectively. The floristic composition of the studied bioregions varies and is influenced by several sets of environmental variables. Macrophyte vegetation in the Pannonian bioregion is influenced by altitude, width of the river bed, flow velocity and water reaction (explaining 16.3% of variability), whilst mesolithal, depth of water, shading by trees, concentration of total phosphorus in water and altitude (21.9%) drive species composition in the Carpathians. Similarly to overall species composition, the distribution pattern of alien and endangered species differs between bioregions. In the Carpathian bioregion, endangered species are concentrated in two groups (vascular vs. non-vascular plants) according to the width of the river bed and flow velocity. In contrast, all evaluated species groups (endangered, alien and other species) have scattered distribution in the Pannonian bioregion. Two endangered species, Butomus umbellatus and Berula erecta, exceed the frequency of 20% only in the Pannonian bioregion. On the other hand, the frequency of 10% is exceeded by two alien species, Elodea canadensis in the Pannonian bioregion and Impatiens glandulifera in the Carpathian bioregion. In conclusion, monitoring of aquatic macrophytes, including endangered and alien species, provides valuable information usable in ecological assessment.

Macrophyte assemblage composition as a simple tool to assess global change in coastal areas. Freshwater impacts and climatic changes

Macrophyte assemblages are one of the most sensitive biological communities to assess anthropogenic impacts and climate changes. Community composition responds very quickly to environmental changes driving towards a predictable composition. The increase or decrease of the trophic status (i.e. nutrient concentrations, suspended particulate matter, Chlorophyll-a) and temperature are the most important factors responsible for the replacement of taxa of high ecological value (sensitive taxa) with opportunistic species. A qualitative and quantitative study of macrophytes in 4 areas along the coasts of the Northern Adriatic Sea, from Venice (Italy) to Savudrija (Croatia) and the analysis of river outflows in this region during one year (May 2012–April 2013) provided information about their spatial variability. The coasts of the Veneto Region and Friuli-Venezia Giulia, which are affected by significant freshwater inputs, showed a strong biodiversity reduction or a dominance of thionitrophilic taxa. No seagrasses colonized these areas. On the other hand, the coasts of Croatia had negligible fresh water inputs and macrophyte communities were dominated by sensitive taxa such as the seagrass Cymodocea nodosa and some species belonging to genus Cystoseira.

Refining the palaeoecology of lacustrine testate amoebae: insights from a plant macrofossil record from a eutrophic Scottish lake

Arcellinida (lobose testate amoebae) preserve well in lake sediments and have shown great potential as palaeolimnological indicators, but a limited understanding of their ecology prevents more in-depth interpretations of both contemporary and fossil assemblages. Loch Leven, Scotland, has a well-documented history of nutrient-enrichment and associated lake biological change, creating a temporal gradient along which testate amoeba ecology can be investigated. Plant macrofossil data from a dated sediment core (LEVE14) indicate that a transition from oligo-mesotrophic to eutrophic conditions occurred over at least the last 200 years, enabling direct comparisons to be drawn with fossil testate amoeba assemblages from the same core. Cluster analysis and principal components analysis show that testate amoebae and macrophytes responded synchronously to an early phase of nutrient-enrichment after ca. AD 1200, and to anthropogenic water-level lowering and further enrichment after ca. AD 1830. The results of indicator species analysis (IndVal) support the suggestion inferred previously that Cucurbitella tricuspis is an indicator of nutrient-enrichment, while the association of some less abundant taxa, specifically Difflugia amphora and Mediolus corona, with eutrophic environments is also corroborated. Overall, the testate amoeba assemblage response appears to reflect a complex interaction of factors which were ultimately driven by eutrophication. These include variations in microhabitat associated with changing plant structure and sedimentary conditions influenced by macrophyte community succession. In particular, a shift from an oligo-mesotrophic macrophyte assemblage composed of isoetid plants to one dominated by Potamogeton spp. and dense stands of Characeae is suggested to influence the relative proportions of sediment dwelling and plant-associated testate amoebae. The results highlight the utility of testate amoebae as benthic indicators of lake nutrient-enrichment and demonstrate the value of using multi-proxy palaeolimnological data to refine the ecology of lesser-studied palaeoecological groups.

Eutrophication erodes inter-basin variation in macrophytes and co-occurring invertebrates in a shallow lake: combining ecology and palaeoecology

Aquatic biodiversity is commonly linked with environmental variation in lake networks, but less is known about how local factors may influence within-lake biological heterogeneity. Using a combined ecological and multi-proxy palaeoecological approach we investigated long-term changes in the pathways and processes that underlie eutrophication and water depth effects on lake macrophyte and invertebrate communities across three basins in a shallow lake—Castle Lough, Northern Ireland, UK. Contemporary data allow us to assess how macrophyte assemblages vary in composition and heterogeneity according to basin-specific factors (e.g. variation in water depth), while palaeoecological data (macrophytes and co-occurring invertebrates) enable us to infer basin-specific impacts and susceptibilities to nutrient-enrichment. Results indicate that variability in water depth promotes assemblage variation amongst the lake basins, stimulating within-lake macrophyte assemblage heterogeneity and hence higher lake biodiversity. The palaeo-data indicate that eutrophication has acted as a strong homogenising agent of macrophyte and invertebrate diversities and abundances over time at the whole-lake scale. This novel finding strongly suggests that, as eutrophication advances, the influence of water depth on community heterogeneity is gradually eroded and that ultimately a limited set of eutrophication-tolerant species will become homogeneously distributed across the entire lake.

Role of environmental factors in affecting macrophyte dominance in transitional environments: The Italian Lagoons as a study case

AbstractOne of the main challenges to facilitate the classification of water bodies is to identify direct relationships between anthropogenic pressures and the behavior of biological organisms such as macrophytes in different environments including transitional areas. The investigation of many lagoons and ponds described here shows that macrophyte variables and the community composition have strong and univocal relationships with ecological parameters that are a measure of anthropogenic pressure on the ecological status of water bodies. The areas surveyed represent about 78% of the Italian transitional waters (169 sites sampled both in spring and fall). Anthropogenic impacts affect the availability of nutrients in the water column and surface sediments, causing changes in water transparency and phytoplankton concentration (as chlorophyll‐a [Chl‐a]) that act as the main drivers of variation for macrophyte assemblages, changing species dominance and the conditions that govern their presence or absence. The response of macrophytes to anthropogenic pressure is quite similar in all the examined transitional environments, even when the basin morphology, species richness and composition are different. Some taxa and species assemblages are so sensitive to environmental changes that monitoring them can be considered the most suitable and rapid method for assessing the quality of the environment they inhabit.

The relationship between habitat factors and aquatic macrophyte assemblages in the Danube river in Serbia

Our objectives were to offer insight into the characteristics of the physical environment in the River Danube in Serbia; and to show the relationship between selected environmental factors and the composition and abundance of macrophyte species. The macrophyte survey method followed the European Standard EN 14184, applying Kohler?s five-level descriptive scale. Principal component analysis was carried out to examine the variation in aquatic vegetation, and to analyze the effect of environmental variables on the aquatic vegetation, redundancy analysis was used. To build a simpler model with fewer explanatory variables, yet sufficiently explaining species variability, forward selection of environmental variables was done. Our results confirmed that physical environmental factors significantly influence the establishment and structure of macrophyte vegetation, with the level of hydrological connectivity to the main river channel being the most important, followed by the transparency of the water column, sediment texture and water-flow velocity. In order to inspect the individual relation between best-fitted plant species and each of selected environmental variables, Spearman?s rank correlation coefficients were calculated. We have distinguished plant species with preferences to specific combinations of analyzed factors. Our results provide a background for future, more specific studies on the macrophyte/habitat relationship.

<b>Diaspore bank of aquatic macrophytes maintaining species diversity in a Neotropical pond

The diaspore bank is an important component of biological diversity acting mainly as storage and source of diaspores, which also indicate dynamics and patterns of maintenance of plant diversity. We tested the hypothesis that the diaspore bank would be the responsible factor for the maintenance of the aquatic plant species, used two techniques to evaluate the diaspore bank: seedling emergence and direct counting of field samples. Density and richness of the diaspore bank were correlated with plant cover of the aquatic macrophyte communities and also with the euphotic zone radiation in different phases of the hydrological cycle. The diaspore bank is a key factor in maintenance of aquatic macrophyte assemblages in this pond. Nymphaea amazonum was one of the dominant species in the pond and presented temporally peaks of plant cover. Furthermore, depth allowed induction of germination of stored diaspores. Therefore, the diaspore bank may predict which species colonizes a site when environmental characteristics are favorable and allows inferring which processes are linked to changes in structure of aquatic macrophyte assemblages. These mechanisms are the means for recovery of macrophyte species under natural disturbances, represented by water level oscillations in floodplains.