Physical factors and dissolved reactive silica affect phytoplankton community structure and dynamics in a lowland eutrophic river (Po river,Italy)

We tested the hypothesis that species composition and persistence of phytoplankton communities in nutrient rich lowland rivers depends mainly on physical factors. The study aimed to analyse the effects of water discharge, temperature and chemistry on phytoplankton dynamic and species composition in the lowland reach of the eutrophic Po river (Italy). Both taxonomical and morpho-functional methods were used. True planktonic and tychoplanktic (i.e. detached taxa of benthic origin that remain in suspension) species were found, among which only a few taxa and functional groups prevailed. Diatoms were the most abundant, with a clear dominance of species either sensitive to the onset of water stratification or well adapted to turbid waters. Phytoplankton abundance, biomass and chlorophyll-a followed similar trends, attaining the highest values in summer, at low discharge rates. Correlation and multivariate analysis revealed that the development of a stable phytoplankton community was mainly controlled by water discharge rates. Namely, changes in water flow rates induced major variations in the community structure. The seasonal succession of phytoplankton assemblages was also related to water temperature and dissolved reactive silica availability to some extent overlapping flow effects.     

Downstream variations of phytoplankton in the St.Lawrence River (Québec, Canada)

Longitudinal variations of phytoplankton biomass and composition were assessed in a 250 km-long section of the St.Lawrence River, which alternately runs through narrow (< 2 km) river cross sections and wide (up to 10 km) fluvial lakes. In the main river stem, concentrations of suspended matter and total phosphorus increased with distance downstream, whereas light penetration decreased. Seasonal changes in plankton composition and biomass were more important than those resulting from differences in water mass (tributary) of origin. Sampling at three cross river sections and in two fluvial lakes showed a progressive downstream decrease in phytoplankton biomass and changes in size structure and taxonomic composition. River plankton was primarily composed of small (< 10 µm equivalent spherical diameter), truly planktonic cells belonging to Cryptophyceae and diatoms, with Chlorophyceae in summer. Plankton sampled in summer among rooted macrophytes in fluvial lakes exhibited a higher biomass of resuspended periphytic algae than in the main river stem, which contributed slightly to downstream phytoplankton biomass.Successive river cross sections always shared about 50% of their taxa, indicating a rapid downstream transport of algae within the main water mass. However, the proportion of species common to all cross sections was highest during the spring freshet, and lowest during summer low discharge, likely resulting from the development of a distinct flora in fluvial lakes during summer. Conversely, about 30% of the identified taxa were exclusive to a cross section and were replaced by others occurring downstream. Overall, phytoplankton composition along the St.Lawrence River is primarily controlled by advective forces, which result in a homogeneous flora in the main river stem, with a local contribution of resuspended periphyton from fluvial lakes.     

Functional diversity of phytoplankton highlights long‐term gradual regime shift in the middle section of the Danube River due to global warming,human impacts and oligotrophication

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The hydro-morphological index of diversity: a tool for describing habitat heterogeneity in river engineering projects

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Hydromorphological restoration of running waters: effects on benthic invertebrate assemblages

1. River restoration has received considerable attention, with much recent focus on restoring river hydromorphology to improve impoverished aquatic communities. However, we still lack a clear understanding of the response of aquatic biota to river restoration. 2. We studied the effects of hydromorphological restoration on benthic invertebrate assemblages in 25 river sites in Germany using standardised methods. Restoration efforts were primarily aimed to restore habitat heterogeneity; correspondingly, habitat diversity increased at most sites. 3. Similarity of benthic invertebrate assemblages between restored and unrestored river sections was low (mean similarity was 0.32 for Jaccard and 0.46 for Sørensen). Community‐based metrics, such as the percentage of Ephemeroptera, Plecoptera and Trichoptera taxa, also differed between restored and unrestored sections. 4. Only three of the 25 restored sections were classified as having ‘good ecological quality’ class according to the European Water Framework Directive criteria; hence, poor water quality is probably one factor impeding recolonisation. 5. Our results show that isolated restoration measures do not necessarily result in positive effects on aquatic biota and that better understanding of the interconnectedness within a catchment is required before we can adequately predict biotic responses to structural river restoration.     

A pilot macroinvertebrate-based multimetric index (MMI-CS) for assessing the ecological status of the Chishui River basin,China

As the only undammed river in the Yangtze River basin and an important rare fish reserve, the Chishui River has attracted the world's attention. It was recently selected as a reference river for a pilot biomonitoring assessment within the European Union-China River Basin Management Programme. As the outcome of the project, a pilot multimetric index (MMI-CS) was developed for future assessment of the ecological status of the Chishui River basin. In this study, eight core metrics were selected and used to build the multimetric system. These metrics included the total number of taxa (TotalTax), the number of taxa of sprawlers (SprwlTax), the number of intolerant taxa (IntolTax), the Hilsenhoff biotic index (HBI), the percentage of Ephemeroptera, Trichoptera and Plecoptera (EPTPct), the number of Ephemeroptera taxa (EphemTax), the percentage of collectors (CllctPct) and the average score per taxon (ASPT). Five ecological status ratings (“Excellent”, “Good”, “Fair”, “Poor” and “Very Poor”) were established. The results of the evaluation showed that the index was reasonable and effective. The results of the assessment showed that sites with higher ecological status were distributed mainly in the upper and middle reaches of the region and that sites with lower ecological status were centrally distributed in the lower reaches. Moreover, the index should be refined and validated using additional datasets obtained in different seasons in the future for routine bioassessment within the framework of sustainable management.     

Riverine transport and nutrient inputs affect phytoplankton communities in a coastal embayment

1. Rivers often transport phytoplankton to coastal embayments and introduce nutrients that can enrich coastal plankton communities. We investigated the effects of the Nottawasaga River on the nearshore (i.e. within 500 μm of shore) phytoplankton composition along a 10-km transect of Nottawasaga Bay, Lake Huron in 2015 and 2016. Imaging flow cytometry was used to identify and enumerate algal taxa, which were resolved at sizes larger than small nanoplankton (i.e. >5 μm). Multivariate analysis (perMANOVA and redundancy analysis) and a dilution model were used to examine how nutrients and the transport of algal taxa affected community composition in the bay.
2. Sampling stations with different percentages of river water had significantly different phytoplankton communities. Phytoplankton community composition was also strongly associated with nutrients, including total phosphorus, which also varied with the percentage of river water. The majority of the 51 phytoplankton taxa identified in 2016 had numerical abundances in the bay that could be explained simply by the dilution of incoming river water.
3. Phytoplankton transported from the river had a higher proportion of edible-sized cells (<30 μm), particularly in summer when colonial cyanobacteria were numerically dominant in the bay. Six taxa were more abundant than expected from the dilution of river water and included some cyanobacteria with late summer maxima. Five of the taxa that were transported from the river were less abundant than expected in the bay.
4. Whereas impacts of fertilisation due to the characteristically higher nutrient concentration in the river are to be expected, the strong and highly correlated effects of transport within the narrow coastal band of this study largely concealed any distinct fertilisation effects.
5. Riverine inputs may strongly influence the nearshore assemblage of phytoplankton in oligotrophic embayments in large lakes, creating hotspots for productivity, species turnover, and trophic dynamics.

     

Structures of benthic insect communities in two southeastern Wyoming (USA) streams: similarities and differences among spatial units at different local scales

Four sites on each of two southeastern Wyoming streams, Medicine Bow River (MBR) and Rock Creek (RC), were investigated during the summer and autumn of 2001 and 2002. This investigation resulted in inventories of benthic insect communities being obtained from these two streams. It also resulted in twelve metrics being calculated from benthic insect communities, and these metrics were compared between two spatial units at different local scales. Of the metrics used, five indicated taxa richness, four indicated relative abundance, two indicated diversity, and one involved a biotic index for organic pollution. More specifically, we used each metric to compare the montane with the plains sub-basin, as well as to compare two distinctly different types of substrates within each of the sub-basins. Also, metrics were compared between the two streams. Results indicated that few differences were observed between naturally-occurring substrates within sub-basins. In addition, few differences were observed between the two streams. In contrast, however, several differences were observed between the montane and plains sub-basins. Such differences were caused from naturally-occurring variations in hydraulic and ecological conditions. These findings suggest that the spatial scale should be carefully considered when selecting metrics for use in monitoring programs that are designed to detect anthropogenic disturbances in lotic systems. Handling editor: K. Martens     

The role of phytoplankton diversity metrics in shallow lake and river quality assessment

Ecological water quality problems are frequently connected to increment of phytoplankton productivity and overdominance of some phytoplankton species. Metrics that show monotonously increasing or decreasing tendencies along stressor gradients is recommended for ecological state assessment. Diversity metrics are influenced by various physical disturbances and show high within-year variability; thus, there is no agreement on the usefulness of these metrics as state indicators.To test the usefulness of phytoplankton diversity in ecological state assessment we investigated the productivity–diversity relationships for lakes and rivers in the Carpathian Basin (Hungary). We demonstrated that the shape of productivity–diversity relationship depends on the investigated water body type. Regarding lakes, hump-shaped relationship was found for all computed metrics. Parallel with the increase in phytoplankton productivity values, diversity metrics showed monotonously increasing tendencies in rhithral and decreasing tendencies in large potamal rivers. We found no systematic relationship in the case of small lowland rivers.Changes of diversity metrics calculated for species and functional groups showed similar tendencies within the types, only the slopes of regression lines differ each other.The use of diversity metrics as ecological state indicators should be restricted to water body types where diversity decreases or increases monotonously with phytoplankton biomass. Regarding the lakes the use of diversity metrics is not recommended for ecological state assessment. In rhithral and large potamal river assessment, application of diversity metrics should be strongly considered. We demonstrated that diversity metrics can be useful components of multimetric indices proposed to use by the Water Framework Directive.     

Phytoplankton dynamics in relation to connectivity,flow dynamics and resource availability—the case of a large,lowland river,the Hungarian Tisza

Large lowland rivers with sufficient hydrological storage capacity are capable of supporting primary production, but the dynamics of the advecting phytoplankton is poorly understood. Our study aimed at exploring how longitudinal versus lateral connectivity, flow dynamics versus resource availability and continuous versus discontinuous environmental gradients shaped the species composition of phytoplankton. Samples were taken from February to October 2000 along the Hungarian Tisza River (HTR) and in its main tributaries. Longitudinal and seasonal patterns were related to resources (light and nutrients) availability and flow dynamics derived from a 1D hydrodynamic model. The HTR was autotrophic during the study period, but tributary input considerably exceeded net autochtonous production. The Szamos River was the major source of both phytoplankton and nutrients in the HTR. Chryso- and euglenophytes were flushed into the main river from floodplain oxbows during high discharge. Imported algae experienced discontinuity in environmental gradients when entering the main river. The merged impact areas of two dams (IAD) that separate the two large meandering patches of the HTR disrupted the longitudinal profiles of both physico-chemical variables and attributes of algal assemblages (biomass, species composition, richness, similarity between adjacent sampling sites). Hydraulic storage along the IAD selectively favoured the recruitment of cryptophytes that, however, could not compensate for the enhanced sedimentation of diatoms in terms of biomass. Although the meandering patches presented several small-scale differences in major environmental gradients, both patches supported the growth of planktonic diatoms. Changes in algal biomass were decoupled from nutrient availability. We conclude that various measures must be applied in various lowland rivers within the same catchment to control their trophic status as a component of the ‘good ecological status’ defined in the Water Framework Directive.     

Interim Responses of Littoral River Channel Vegetation to Reestablished Flow after Phase I of the Kissimmee River Restoration Project

Measurements of littoral vegetation stands and species‐level surveys of associated plant communities were made in channels of the Kissimmee River from 1998 through 2008, a period that spanned channelized, non‐flowing conditions through 7 years of near‐continuous reestablished flow. Dissected by flood control canal C‐38 in 1971, the river was virtually without flow until early 2001, when Phase I of the Kissimmee River Restoration Project (KRRP) reestablished flow to a central section of river channel. This study evaluated the effects of reestablished flow on littoral vegetation in river channels as an indicator of system status and progress toward the project goal of ecological integrity. Predictions of vegetation response to reestablished flow included reduction in the width of vegetation stands, and changes in the growth‐form composition of littoral stands from near‐equal dominance by floating and emergent species to overwhelming dominance by emergent growth forms. Variables included plant cover by species and growth‐form, width of vegetation stands, and vegetated percentage of channel. Under the currently incomplete (interim) status of the KRRP, results for littoral vegetation stands indicate trends in the predicted directions of change, and three of four predicted changes have occurred. Vegetation stand widths decreased substantially and littoral plant communities became heavily dominated by emergent species; BACIPS (before‐after‐control‐impact‐paired series) analyses indicated significant restoration effects for most littoral stand metrics.     

Flood pulse influence on phytoplankton communities of the south Pantanal floodplain, Brazil

Four sites situated on the Pantanal floodplain (Paraguay River and floodplain) were sampled throughout the annual cycle, mainly during the rising water period, with the aim of evaluating the effects of the flood pulse on the composition and population densities of the phytoplanktonic communities. Comprehensive water chemistry data were collected. Eighty-two taxa were found, numerically dominated by Chlorophyceae (23 taxa). Cryptophyceae (principally Cryptomonas brasiliensis) occurred in all samples, and were responsible for 47–58% of the phytoplankton abundance in the studied area. Highest phytoplanktonic population density was at the rising water period, when the limnological changes are most marked as the river water first enters into contact with the floodplain. During this period, when intense decomposition occurs, the Cryptophyceae decreased and the Euglenophyceae increased, except at site 1 (Castelo Lake), where this group were more stable during the year, representing 35–56% of the phytoplankton. In the falling water period (September and October), the phytoplankton was also represented by Bacillariophyceae and Cyanophyceae. In the Pantanal, the great abundance and sometimes dominance of Cryptophyceae, may be due largely to adverse conditions for the development of other groups; the former are adapted to low availability of dissolved nutrients, and high water transparency, such conditions prevailing during the high water period.