Macrophyte Assemblages Research Articles

Macrophyte assemblages in relation to environmental, temporal and spatial variations in lakes of a subtropical floodplain-river system, Argentina

This work analyses the variation in the structure of macrophyte assemblages in relation to environmental (lake morphometry and water physico-chemistry), temporal and spatial variables, in seven floodplain lakes placed in the surrounding of the Salado and the Paraná Rivers confluence in the Paraná floodplain-river system. We recorded the variations in cover of thirteen of the most important macrophyte species among rooted and free-floating life forms. A discriminant analysis of the main coordinates showed significant differences among floodplain lakes (spatial variation), as well as among the 13 months studied (temporal variation). Redundancy analysis indicated that electrical conductivity, maximum depth, shoreline development index, lake area and water temperature had significant influence on macrophyte assemblages. In a partial RDA, environmental and temporal variables accounted for a similar percentage of total explained variation (∼50%), whereas spatial variables, including distance to main channel, accounted for 30.6%. Results show that the environmental variables of lakes, temporal descriptors, and the spatial position of lakes along the floodplain can explain a significant fraction of variation of macrophyte assemblages. These results allow us to understand the dynamic of macrophyte assemblages along temporal and spatial scales and their association with flooding regime, considering local (physico-chemical and morphometric) and landscape (spatial) characteristics of the floodplain environments.

Macrophytes assemblages in mountain lakes of Alerce Andino National Park (41° S, Lakes Region, Chile).

The lakes studied (Chapo, Sargazo, Chaiquenes and Triángulo) are located in the Alerce Andino National Park (41°30'S, 71°32'W), Chile. An inventory of the aquatic and riparian species was performed between December 2010 and January 2011. A null model analysis was done to determine the existence of regulatory factors of species associations, and the Jaccard index was applied to determine floristic similarities. It identidied 23 species, the high number was reported (14) and the most introduced species number (4) were reported at Sargazo lake, whereas the low species number was observed in Triángulo lake with three species. The analysis of the null model revealed the presence of regulatory factors in one of the three simulations. However, in the other two simulations, the species associations appeared to be random, presumably because many species were repeated at the study sites. According to the Jaccard index, Triángulo Lake is noticeably different from the other lakes, probably due to its marked oligotrophy.

Fragmentation and groundwater supply as major drivers of algal and plant diversity and relative cover dynamics along a highly modified lowland river

Algae and aquatic vascular plants were investigated along a highly modified medium-sized lowland river (Oglio River, northern Italy). We focused on the role of fragmentation and groundwater supply in driving macrophyte assemblages, paying particular attention to soft-bodied benthic algae. Four different a priori stretch types (dammed, groundwater-dependent, potamal and rhithral) were identified along the river longitudinal gradient as proxies of river hydrology and relative human-induced flow alterations. Over three years (2009–2011), taxa diversity, cover data, spatial and temporal dynamics and indicator and detector species were compared with physical, chemical and hydrological variables at 30 different river sites. Data was explored by indicator species analysis, nonmetric multidimensional scaling, and PROTEST. A total of 88 taxa, of which 36 were algae (equal to 40.9% of the total diversity), 3 bryophytes (3.4%) and 49 vascular plants (55.7%), were recorded. Taxa diversity peaked at the groundwater-dependent sites for both algae and vascular plants (with a mean of 12.8±2.7 and 12.7±4.8 taxa per site, respectively). Algae cover values were one order of magnitude higher than those of vascular plants (with an overall mean of 37.0±24.2% per site). The vascular plants counterbalanced the algae coverage values exclusively at the dammed sites (27.6±23.2% vs 28.2±13.9%, respectively). A clear zonation of communities emerged from the multivariate analysis, which revealed taxa rearrangements that largely overlapped the river stretch types. Inter-annual comparisons confirmed the strong stability of the primary producer communities in the short term (three years). Our work substantiates the pivotal role played by fragmentation and hydrology, in addition to groundwater, in structuring riverine macrophyte communities. Further investigations are needed to resolve the uncertainty surrounding the non-linear responses of macrophytes to the physical and chemical conditions of rivers.

Environmental drivers of aquatic macrophyte assemblages in ponds along an altitudinal gradient

The aim of this study was to explore the environmental drivers of the aquatic macrophyte assemblage in a large, heterogeneous Spanish region covering a wide altitudinal range. We hypothesized that physicochemical variables affecting assemblages would differ depending on altitude. The study was conducted in 46 plateau ponds and 21 mountain ponds. Our results revealed a shift in hydrophyte assemblage composition and structure along an altitude and water chemistry gradient. However, altitude was not a good predictor of species richness. Conductivity and nutrient concentrations were higher in plateau ponds than in mountain ponds and binary logistic regression showed that conductivity was the best variable for differentiating between both pond types. Canonical correspondence analysis indicated that conductivity was the main factor responsible for the species distribution in both pond types. Generalized linear models showed that in plateau ponds, total phosphorus and mean depth were the strongest predictors of submerged macrophyte coverage, and no model could be created for richness. In the mountain ponds, conductivity and pond area explained coverage of submerged plants, while richness was related to pond area. Our results corroborated the hypothesis to be tested, and the conclusions obtained may be of relevance for making decisions on conservation and restoration.

Native submerged macrophyte distribution in seasonally-flowing, south-western Australian streams in relation to stream condition

Submerged macrophytes are important structural and biological components of many lowland streams with potential to support ecosystem processes in degraded streams, provided that growth is not excessive. In a low-gradient agricultural landscape, a survey was used to explore associations between submerged macrophyte growth, biodiversity and variables assessing stream condition in seasonally-flowing streams. These variables were sampled across fifty-three reaches on seven adjacent streams in the mediterranean climate region of south-western Australia. Native submerged macrophytes were present in 43 % of sampled reaches, forming two distinct macrophyte assemblages dominated either by Potamogeton spp. together with Otteliaovalifolia, or by Cycnogeton spp. The Potamogeton/Ottelia assemblage was present in degraded reaches with higher light availability and deposition of fine sediments, but did not show excessive growth, even under nutrient-enriched conditions. Conversely, Cycnogeton spp. were associated with shaded conditions and greater flow. Reaches with macrophytes present had significantly higher macroinvertebrate abundance and family richness than those without, although rarefied family richness was similar among reaches with and without submerged macrophytes. The more structurally complex Potamogeton/Ottelia assemblage supported a greater abundance of grazers, shredders and predators than the simpler Cycnogeton spp. In degraded agricultural streams, remnant and colonising populations of submerged macrophytes may compensate for loss of riparian-derived habitat and resources for macroinvertebrates, and thus the food supply for predatory species.

The relationship between macrophyte assemblages and environmental variables in drainage and irrigation canals in Slovakia

AbstractOur study provides new knowledge about macrophyte assemblages and environmental variables of Slovak drainage and irrigation canals. The canal system, comprising ca. 15% of all flows in Slovakia, is one of the oldest in Central Europe. This information represents a first step toward exploitation of macrophytes as an obligatory biological quality element for the assessment of ecological potential according to the requirements of the Water Framework Directive. Among 61 canals studied, a total of 85 aquatic plant species (35 hydrophytes, 16 amphiphytes and 34 helophytes) were recorded during the years 2012–2014, including three neophytes and 18 threatened species. Physico-chemical variables explained the highest proportion of species variability, whilst hydromorphological variables and landscape variables were much less significant. Chemical oxygen demand, ammonium nitrogen, electrical conductivity, water pH, flow velocity and water depth were identified as most important drivers of species composition of aquatic macrophytes and explained 21.1% of the variability. The CCA results revealed differences in species composition of canals reflecting the geographical origin and environmental conditions as well, relating to South-Eastern and South-Western Slovakia. In conclusion, macrophytes in drainage and irrigation canals are able to reflect several environmental variables and might provide valuable information for bioindication in assessing the ecological potential.

Macrophyte assemblages in the aquatic-terrestrial transitional zone of oxbow lakes in the Danube floodplain (Austria)

The Lobau wetland and oxbow ensemble is part of the large Danube River floodplain area between Vienna (Austria) and Bratislava (Slovakia). The Danube River regulation scheme implemented in the late 19th century considerably affected the Lobau area, which is part of the Danube National Park today. Terrestrialization processes in the floodplain started with the river regulation and pose an increasing threat to the aquatic and wetland vegetation of this ecosystem. Former vegetation studies were either directed toward phytosociological description of associations or to a general vegetation inventory and mapping, where transitions between vegetation types are not accounted for. Our purpose is to provide a detailed insight into the vegetation zonation pattern along the aquatic-terrestrial inundation gradient in the Lobau floodplain area. We sampled a total of 49 belt transects. Samples in each transect were classified into groups using two-way indicator species analysis (TWINSPAN). Resulting groups of all transects were subjected to fuzzy c-mean clustering (FCM), defining ‘community types’ by means of indicator species analysis (ISA). We found 36 significant indicator species typifying 14 community types. Nine types belong to the shoreline vegetation and five types characterize the aquatic habitats. In addition to these community types, two transitional zones were found, one defined as open water/wetland transition and one as wetland/upland transition. Along the aquatic-terrestrial environmental gradient, different floristic and quantitative relations of community types and transition zones were identified. Finally, the importance of such a fine-scale description of zonation patterns along the inundation gradient is discussed in relation to long-term monitoring programmes as the basis for rehabilitation or wetland conservation measures.

Dynamics of recruitment and establishment of the invasive seaweed Codium fragile within an eelgrass habitat.

Knowledge of the potential distribution (i.e. abundance and spatial extent) of an invasive species is important to estimating its potential impacts on recipient communities. Most previous studies have focused on the potential spatial extent of invasive species populations at regional scales, but little is known on how species successfully recruit and establish at more local scales. In this study, we examined how recruitment of the green alga Codium fragile ssp. fragile (hereafter Codium) can vary spatially and the environmental factors associated with Codium establishment in eelgrass (Zostera marina) beds. Standardized recruitment blocks (65 blocks in a 720 × 240 m2 grid) were used to monitor the number of Codium recruits, juveniles and adults over 2 years. Environmental factors (depth, relative water flow, light and temperature) and attributes of the surrounding macrophyte assemblage (eelgrass density, eelgrass length, Codium biomass) were also measured. Recruitment occurred on all blocks or nearby artificial structures (i.e. buoys) and mainly originated from button stages (i.e. female gametes or utricles). Contrary to other studies, the abundance of Codium (recruits, juveniles and adults) was best predicted by the density of the native canopy-forming species, Z. marina, which highlights a positive interaction between native and non-native canopy-forming species. Seasonal variation in recruitment was observed; it was lower during the summer. Recruitment did not show any distinct spatial pattern (e.g. gradient or patch), but the same spatial pattern of recruitment was observed every sampling date, suggesting that there are “hotspots” for recruitment. In general, the total number of Codium fronds observed on a block at the end of the experiment was positively correlated with the cumulative number of recruits. However, recruitment occurred on some blocks but recruits never grew, suggesting that some environmental factors limit Codium distribution and abundance in eelgrass beds. Overall, the assessment of Codium recruitment over 2 years showed that the colonization of suitable locations by Codium within seagrass beds may take several years and that some factors may not only limit, but also inhibit Codium expansion within eelgrass beds.

Macrophytes in boreal streams: Characterizing and predicting native occurrence and abundance to assess human impact

Macrophytes are a structurally and functionally essential element of stream ecosystems and therefore indispensable in assessment, protection and restoration of streams. Modelling based on continuous environmental gradients offers a potential approach to predict natural variability of communities and thereby improve detection of anthropogenic community change. Using data from minimally disturbed streams, we described natural macrophyte assemblages in pool and riffle habitats separately and in combination, and explored their variation across large scale environmental gradients. Specifically, we developed RIVPACS-type models to predict the presence and abundance of macrophyte taxa at stream sites in the absence of human influence and, used data from impacted streams to explore the responses of three biotic indices to anthropogenic stress. The indices used, taxonomic completeness (O/E-taxa), a measure of compositional dissimilarity (BC-index) and an index taking into account the abundance of species (AB-index), are based on predicted and observed macrophyte communities. We found that size of the catchment area, altitude, latitude and percentage of lakes in the catchment were the large scale environmental variables that best predicted the natural variation of assemblages. The RIVPACS approach substantially improved both the precision and accuracy to predict the natural communities and the sensitivity to human disturbance. O/E-taxa performed best in relation to the null model decreasing the variation by 20% in pools, 29% in riffles and 32% in combined data. In general, models based on the riffle assemblages performed better than models based on pool assemblages, but including both habitats and predicting abundances instead of only presence/absence yielded the greatest accuracy and sensitivity. Our results support the use of multivariate modelling techniques in predicting reference condition to assess status of stream macrophyte communities.

The ecological condition of geographically isolated wetlands in the southeastern United States: The relationship between landscape level assessments and macrophyte assemblages

Geographically isolated wetlands (GIWs) are common features of the Dougherty Plain physiographic region in southwestern Georgia. Due to lack of protection at the state and federal levels, these wetlands are threatened by intensive agricultural and silvicultural land uses common in the region. Recently, the ecological condition of such GIWs was assessed for the southeastern United States using the Landscape Development Intensity Index (LDI), a practical assessment tool that relies on remotely sensed land use and land cover (LULC) data surrounding isolated wetlands to rapidly predict wetland condition. However, no assessments have been attempted for GIWs in the Dougherty Plain specifically. Our goal was to develop a framework to guide and refine remote assessment of wetland condition within this agriculturally intense region of the southeastern USA. In this study, we characterized human disturbances associated with isolated wetlands in the Dougherty Plain, and paired the rapid assessment of GIWs using LDI with an intensive assessment of wetland plant communities. Specifically, we: (1) examined how macrophyte assemblages and vegetation metrics vary across a human disturbance gradient in the Dougherty Plain; (2) compared multiple condition assessment outcomes using variations of the LDI method that differed in spatial extent and resolution of LULC categories; and (3) determined the predicted condition of GIWs in the Dougherty Plain as indexed by LDI and compared with region-wide assessments of GIWs of the southeastern USA. Generally, the relationship between wetland plant communities and surrounding land use supported the assumptions of the LDI index in that wetlands surrounded by agricultural land use classes featured distinct plant communities relative to those surrounded by forested land use classes. Our results indicated that finer spatial resolution of LULC data improved the predictive ability of LDI. However, based on incongruence between wetland vegetation composition and LDI scores in some forested landscapes, this study identified limitations of the LDI assessment method, particularly when applied in regions in which prescribed fire is an important ecological driver of vegetation and habitat. Thus, we conclude that LDI may be biased toward an overestimation of reference condition GIWs, even though the habitat may be functionally degraded by the absence of natural processes such as fire. Regardless, relative to the assessment of the entire southeastern US, a greater proportion of total GIWs of the Dougherty Plain were identified as impaired due to the intensity of irrigated agricultural land use.

Partitioning beta diversity of aquatic macrophyte assemblages in a large subtropical reservoir: prevalence of turnover or nestedness?

The identification of factors promoting biodiversity and, more specifically, the causes that contribute to beta diversity is a central and growing issue in ecology. In this study, we used long-term data (1999–2007, including a pronounced drawdown in 2000) to assess the beta diversity partitioning of aquatic macrophyte assemblages in five arms of the Itaipu reservoir. We partitioned beta diversity (βsor) into two components: nestedness (βnes) and species turnover (βsim). To check whether environmental variables (electrical conductivity, water transparency, and fetch) were correlated with the components of beta diversity, we used a permutational multivariate analysis of variance. Over the study period (1999–2007), we observed high values of beta diversity and prevalence of spatial turnover of the species. They were correlated with all environmental factors studied, which demonstrated significant interactions. Dendritic-shaped arms, high shore development, local physical and chemical conditions of the water, and biotic interactions could be determining factors for the prevalence of spatial turnover of aquatic macrophyte assemblages. The drawdown promoted an enormous quantity of dead macrophyte biomass, specifically submerged species that preferentially colonized shallow margins of the reservoir. On the other hand, large open areas were available for colonization of ruderal species and seed bank germination. This dynamic led to an increase of beta diversity and turnover values in the year of the drawdown compared to the 1999 and 2001. This pattern remained until the end of the study, characterizing the aquatic macrophytes of the Itaipu reservoir as an assemblage with high beta diversity and prevalence of species turnover over nestedness, among and within arms.

The growth of the non-nativeCrassula helmsii(Crassulaceae) increases the rarity scores of aquatic macrophyte assemblages in south-eastern England

The impact of invasive species on native species is often overlooked. Anecdotal and unmeasured evidence often gains more notice as more empirical research is not available. This study examined the impact of the aquatic invasive species Crassula helmsii across a range of waterbody and landscape types in south east England. Plant species lists were compiled for both invaded and uninvaded sites. Scoring systems using both national and county level indices were used to give a measurement of species rarity. The results showed how invasion has not caused species diversity reductions. Examination of the results has shown how species assemblages have been altered, but often favouring rarer species. Explanations for these findings are discussed. Limitations of the findings including translation to other species and to other geographical areas are also discussed.

Space and seasonality effects on the aquatic macrophyte community of temporary Neotropical upland lakes

Temporal and spatial scales are key factors that affect species distribution. Temporary lakes may be intensely affected by both scales, and the aquatic macrophyte community can rapidly respond to such environmental changes. Here, we investigate 26 Neotropical temporary upland lakes and describe the species richness and composition as well as the species richness within functional groups and the functional composition of aquatic macrophytes to better understand the effect of spatial and temporal scales on these attributes. Additionally, we highlight the scenarios where we found rare and endemic species during sampling. Our findings mainly suggest that spatial and temporal scales do not affect the total species richness or species richness within the functional groups. However, the temporal scale affects the species composition and functional-group composition. The species composition changes between dry and rainy seasons (beta-diversity), and such change was less dramatic six years after the first sampling. The identical pattern was found for the functional-group composition (functional beta-diversity). We also found small or few endemic species populations that co-occurred with potentially invasive species, which could threaten endemic species and lead to global extinctions. Finally, we suggest that the temporal dynamics of temporary lakes are fundamental in maintaining regional biodiversity. However, this dynamic may change over time by moving towards a future with a more homogeneous aquatic macrophyte assemblage, what may create a scenario with more functionally redundant species. Subsequently, applied ecological studies in such environments to better understand the temporal dynamics of the aquatic macrophyte community may help to improve future proposals of biodiversity management and protection.

Diversity patterns of Pampean stream vegetation at different spatial scales

We examined diversity patterns at different spatial scales by observing the changes in the slopes of Species–Area relationships (SAR) and Local–Regional (L–R) relationships. Stream vegetation was sampled at four scales (reach (N=50), stream (N=25), watershed (N=9), and ecoregion (N=2)) in the Pampa Region (Buenos Aires, Argentina). The slopes of the SARs fitted to the logarithmic model increased significantly with scale from reach to ecoregion. For the L–R relationships, the slopes were significantly different from zero when analyzing stream richness in relation to reach richness, and undistinguishable from zero when analyzing watershed richness in relation to stream richness. The differences found in the slopes of the SAR mean that the scales proposed a priori are indeed different diversity scales. On the other hand, the linear relationship between reach and stream richness suggests that macrophyte assemblages in streams function as metacommunities, whose dynamics could be explained by the dispersal process. Thus, we propose that the metacommunities in streams and the assemblages in watersheds and ecoregions can be considered as the three diversity scales most relevant when attempting to understand macrophyte dynamics in Pampean streams. The increase in the species accumulation rate across all scales indicates that any actions for the conservation of macrophyte diversity in Pampean streams should be taken at the largest scale, that is, the ecoregion scale; on the other hand, the loss of species in the headwaters not only implies a decrease in local diversity, but also a loss of species downstream, that is why particular attention should be paid to the headwaters.

Harnessing the potential of the multi‐indicator palaeoecological approach: an assessment of the nature and causes of ecological change in a eutrophic shallow lake

Summary Multi‐indicator palaeoecological studies have become increasingly popular over the last decade as the need for a more complete understanding of lake ecological histories has increased. However, the true potential of the full biological record for assessing the potential drivers of observed ecological shifts in lake sediment records has rarely been demonstrated. Here, we examine the remains of a range of food‐web components including algae (diatoms), macrophytes (plant macrofossils), zooplankton (chitinous and ephippial Cladocera remains), invertebrates (including chironomids, bryozoans, Mollusca) and fish (fish scales and fish leech egg cocoons) in multiple sediment cores from Groby Pool, an enriched English shallow lake, to assess whole‐ecosystem response to eutrophication over the last two centuries. We focus on three striking changes in the palaeorecord, namely the post‐1900 increase in Daphnia spp., the post‐1840 decline in Cristatella mucedo and the post‐1940 increase in Cocconeis placentula, and utilise the multi‐indicator palaeoecological data to evaluate possible explanations for these patterns. Principal curves analysis revealed marked and broadly simultaneous changes in the plant macrofossils, cladocerans, diatoms and chironomids (as well as in other animal remains such as bryozoans and Mollusca), indicating an early period of enrichment most likely associated with land‐use change in the late 18th century, followed by a more recent eutrophication phase coincident with the discharge of sewage effluent to the lake from 1935. Ecological change, resulting from eutrophication, was shown to have progressed slowly and steadily and to have occurred at all trophic levels with a shift from a relatively diverse ‘mesotrophic’ macrophyte assemblage, dominance by benthic diatoms and plant‐associated Chydoridae and chironomids towards a relatively species‐poor, ‘eutrophic’ macrophyte community with dominance by planktonic algae (e.g. Cyclostephanoid diatom taxa), planktonic Cladocera (Bosmina, Daphnia) and a chironomid fauna dominated by mud‐associated taxa. The inferred shift in the macrophyte community from charophyte to fine‐leaved pondweed and Callitriche truncata suggests a reduction in the seasonal duration of plant dominance. The multi‐indicator analysis indicates that a combination of increased phytoplankton biomass and low zooplanktivorous fish predation is likely to explain the recent increases in Daphnia spp., while loss of plant habitat and increased competition for food appear to be the most likely causes of the observed decline in C. mucedo, and resistance to increased grazing pressure from invertebrates is the most probable driver of the C. placentula increase. Our study illustrates the potential of using the full array of fossil groups preserved in lake sediment cores to infer ecosystem dynamics over centennial timescales and to contribute to our understanding of the mechanisms that may link biological assemblages to a range of forcing factors. Further, this paper provides methodological guidance by demonstrating the ability of amalgamated records from three cores to reveal a strong sequence of events and coherent patterns.

Abundance, biomass, and macrophyte consumption by rudd in Buffalo Harbor and the Niagara River, and potential herbivory by grass carp

Abstract The invasive rudd and grass carp consume aquatic macrophytes, thereby altering important habitat, creating novel trophic pathways, and adversely affecting indigenous species. We estimated the abundance and biomass of rudd and their consumption of macrophytes in Buffalo Harbor (northeastern Lake Erie) and the upper Niagara River during 2012–2013. We also estimated consumption of macrophytes by hypothetical populations of grass carp equal in biomass to rudd populations. Using mark-recapture methods, we estimated that 2571 (95% CI: 2362–2821) rudd were present in Buffalo Harbor and 142,957 (95% CI: 135,127–151,751) were present in the upper Niagara River. Biomass of rudd was estimated at 1.89 mt (95% CI: 1.73–2.07) in Buffalo Harbor and 100.21 mt (95% CI: 94.72–106.38) in the upper Niagara River. Using observed water temperatures and published consumption rates, we estimated that (1) rudd could have consumed 98 mt of macrophytes in Buffalo Harbor and 5210 mt in the upper Niagara River, and (2) hypothetical populations of grass carp equal in biomass to rudd could consume 96 mt of macrophytes in Buffalo Harbor and 4941 mt in the upper Niagara River. Rudd abundance and biomass are substantial in these two waters, and consumption of aquatic macrophytes by rudd may threaten existing aquatic habitat and restoration projects. Annual standardized surveys of fish and macrophyte assemblages would provide data necessary to monitor rudd populations, detect invasion and reproduction by grass carp, and assess habitat changes resulting from herbivory by these two invasive fishes.

Environmental Factors Influencing Macrophytes Assemblages in a Middle-Sized Mediterranean Stream

The occurrence of aquatic plants was analysed in a medium-sized river in Greece. There were three objectives. The first was to examine the macrophyte assemblage structure along the river. The identification and hierarchical structure of aquatic plant assemblages were analyzed using Bray–Curtis analysis. Taxa primarily responsible for the differences among the assemblages were identified using similarity percentage analysis. The second objective was to investigate whether habitat features have greater impact on aquatic plant assemblages than chemical parameters. Partial canonical correspondence analysis was used for partitioning the total variation of the biological response. The third objective was to further explore the relationships between hydrophytes (water-supported plants) richness and water quality using linear regression model. The results showed that from the 86 macrophyte taxa recorded, the 25 were found to be primarily responsible for the differences among the macrophytic assemblages. Both geomorphological and physicochemical variables proved to be significant in the Monte Carlo permutation test. The 14 out of 19 geomorphological variables were statistically significant (p<0.004) and included in the final canonical correspondence analysis model. From physicochemical variables, temperature, conductivity and water velocity were significant predictors of species distribution. Total macrophyte variation was divided into portions: (i) explained exclusively by geomorphological variables (34%); (ii) explained exclusively by physicochemical variables (3%); (iii) explained by both variables (52%); and (iv) unexplained (4%). Partitioning clearly revealed that macrophyte assemblage structure was strongly associated with geomorphological features. Τhe results indicated that hardness, DO and chl-a play a more prominent role in hydrophyte species richness at community level. Copyright © 2015 John Wiley & Sons, Ltd.

Macrophyte species richness and composition are correlated with canopy openness and water depth in tropical floodplain lakes

Aquatic macrophytes colonize a variety of environments, and they play important roles in ecosystem function and in community structure. One key challenge for aquatic ecologists is to investigate the environmental factors that drive the richness and distribution of these plants. In this study, we assessed the importance of selected morphometric variables and of the canopy openness of the riparian vegetation to explain macrophyte species richness and composition. We sampled macrophytes along gradients of depth, littoral slope, distance from the connection with the river, and canopy openness in floodplain lakes connected with the Upper Parana River. We used quadrats to survey a total of 40 sites in 11 lakes. We recorded 31 macrophyte species and found that macrophyte richness was best and positively correlated with canopy openness. This correlation suggests that canopy openness plays an important role as an environmental filter, regulating the amount of light availability for macrophytes. Macrophyte species composition was best correlated with depth, indicating that zonation of macrophyte species also occurs in these shallow lakes. These findings emphasize the importance of morphometric variables and canopy openness for structuring macrophyte assemblages. In addition, our results suggest that canopy openness and depth may be considered in management strategies aiming to recover macrophyte diversity and the processes mediated by aquatic macrophytes in small and shallow floodplain lakes.

Explanatory variables associated with diversity and composition of aquatic macrophytes in a large subtropical river floodplain

The structure of aquatic macrophyte assemblages can be affected by myriad factors, including physical, chemical and morphometric characteristics. We describe the patterns of plant species diversity and composition and vegetation height in aquatic ecosystems and their potential determinants at a regional scale in the Middle Paraná River floodplain. Sampling was conducted in twenty-three water bodies, including secondary channels, connected lakes and disconnected lakes. We compared the macrophyte species richness, composition and vegetation height in water bodies with different degrees of connectivity with the river and assessed the most important abiotic explanatory variables (morphometric, physical and chemical) associated with these assemblage attributes. Species accumulation curves showed that species richness did not differ between water bodies with different degrees of connectivity, although it tended to be lowest in secondary channels. Species richness was specifically associated with depth, conductivity, percent of solar radiation reaching the bottom and nitrate. Macrophyte assemblage composition was related primarily to the degree of connectivity, as rare species mostly occurred in disconnected lakes. Composition was also related to the degree of wind exposure (fetch), distance to shoreline and depth. Finally, vegetation height (a surrogate for biomass) was associated with the ammonium and sediment organic matter. Thus, a combination of morphometric and abiotic factors explained species richness, while degree of connectivity and morphometry explained assemblage composition. Vegetation height was explained by nutrients. These results suggest that a single set of variables is not sufficient to explain different aspects of macrophyte assemblages.

Influene of aquatic macrophytes on the interactions among aquatic organisms in shallow wetlands (Upo Wetland, South Korea)

Seasonal monitoring was implemented to understand the influence of macrophyte bed structure on the composition and trophic interaction of aquatic organisms (algae, zooplankton, macro-invertebrate, and fish) in a shallow wetland (Upo Wetland, South Korea). Distinct division of the plant assemblage (reed zone and mixed plant zone) was observed. The reed zone was composed solely of Phragmites communis, whereas the mixed plant zone comprised a diverse macrophyte assemblage (Salvinia natans, Spirodela polyrhiza, Trapa japonica, Ceratophyllum demersum, and Hydrilla verticillata). Most of the aquatic organisms were more abundant in the mixed plant zone than in the reed zone, and this was positively associated with the seasonal development of macrophyte cover. Stable isotope analysis showed seasonal interactions among aquatic organisms. The majority of aquatic animal (zooplankton, Odonata, and Ephemeroptera) were dependent on epiphytic particulate organic matter (EPOM), and the dependence on EPOM gradually increased toward autumn. Interestingly, Lepomis macrochirus consumed Ephemeroptera and zooplankton in both macrophyte zones, but Micropterus salmoides depended on different food items in the reed zone and the mixed plant zone. Although, M. salmoides in the reed zone showed food utilization similar to L. macrochirus, it consumed Odonata or small L. macrochirus in the mixed plant zone. Based on these results, it appears that differences in the structure of the two macrophyte zones support different assemblages of aquatic organisms, strongly influencing the trophic interactions between the aquatic organisms.