Using diatom life-forms and ecological guilds to assess organic pollution and trophic level in rivers: a case study of rivers in south-eastern France

The European Union’s Water Framework Directive has set a target of achieving good ecological status for all aquatic environments in Europe by 2015. In order to determine the quality of aquatic environments, biological indicators such as diatoms are often used. However, biotic diatom indices can be difficult and time consuming to use because of complexity of species determination. We investigated whether the biological traits of diatoms in rivers (life-forms, size classes and ecological guilds) could be used to assess organic pollution and trophic level. We worked on a data set comprising 315 diatom species, determined at 328 river stations of south-east France and a variety of parameters. The abundances of some biological traits differed significantly between the different organic pollution and trophic levels, particularly stalked diatoms, and the motile and low-profile guilds.     

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

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

Downstream changes in phytoplankton composition and biomass in a lowland river–lake system (Warnow River, Germany)

To determine longitudinal changes in phytoplankton composition and biomass in the Warnow River (Germany), single water parcels were followed during their downstream transport in August and October 1996 and April 1997. In summer, the phytoplankton assemblage was dominated by centric diatom and cyanobacteria species. Stephanodiscus hantzschii, Pseudanabaena limnetica, Planktothrix agardhii and Aulacoseira granulata var. angustissima were the most frequent species. In autumn, small centric diatoms dominated the whole river course. Irrespective of the season, in the fluvial lakes of the upper river, a substantial increase of phytoplankton biomass was observed. Shallow upstream river stretches were associated with large biomass losses. In the deep, slow flowing lower regions, total biomass remained constant. Longitudinal changes in biomass reflected downstream variations in flow velocity and river morphology. Cyanobacteria, cryptophytes and diatom species were subjected to large biomass losses along fast flowing, shallow river sections, whereas chlorophytes were favoured. Diatoms and cryptophytes benefited from low flow velocity and increased water depth in the downstream river. Changes in water depth and flow velocity have been found as key factors that cause the longitudinal differences in phytoplankton composition and biomass in small rivers.     

Origin and succession of phytoplankton in a river-lake system (Spree,Germany)

The River Spree (Germany) flows through an impoundment and several shallow lakes in its middle and lower course. In this river-lake system, the seasonal and longitudinal dynamics of dominant phytoplankton populations were studied in relation to retention time of water, mixing conditions and nutrient supply from 1988–92. Some phytoplankton species populated the same river section for weeks or months each year at their season. Such stable populations have to origin from river zones functioning like mixed reactors. In the Spree system, centric diatoms originated from an impoundment and filamentous cyanobacteria from a flushed lake with longer retention time of water. Downstream, biomass and composition of phytoplankton altered nearly simultaneously along the system.The fate of planktonic organisms washed from mixed reactors into the flow depended on the conditions at the zones of origin. During spring, populations dominating phytoplankton communities of the well-mixed lakes grew further under river conditions. However the biomass of summer species, adapted to intermittent stratification, was halved along the river course. These seasonal differences were probably caused by lower maximum growth rates of summer species and enhanced losses (photorespiration, sedimentation or grazing of benthic filter feeders, but not of zooplankton) of algal populations under river conditions in summer.Phytoplankton assimilation, settlement of diatoms, or denitrification caused declining (probably growth limiting) concentrations of dissolved inorganic phosphorus (spring), silicon (early summer) or nitrogen (summer) along the river course, respectively. The minimum content of DRP was often followed by a clear-water phase. Reduced DSi supply selected against diatoms and additional DIN shortage favoured N₂-fixing cyanobacteria in the last lake of the system.R-strategists (sensu Reynolds) were selected in both the flushed, shallow lakes and the lowland river. In general, the biomass of cyanobacteria increased within the lakes and declined along the river course. Some diatom populations grew in the river, but were grazed or settled down in the lakes. Beside this general picture, different populations from the same phylogenetic group did not necessarily perform in similar ways.     

Assessing the current related heterogeneity and diversity patterns of benthic diatom communities in a turbid and a clear water river

Benthic diatoms were sampled in two rapids, in a turbid South-Finnish river (R. Keravanjoki, 22 FTU) and a clear water river in eastern Finland (R. Vaikkojoki, 4 FTU), to evaluate the diversity and spatial distribution patterns of diatom communities and especially their relationships to current velocity. In both rapids, epilithic diatoms were sampled in 15 sampling squares within three current velocity classes (10 cm s^–1, 40 cm s^–1 and 100 cm s^–1). The sampling squares had significantly different diatom communities in the three current velocity classes at both sampling sites, however, separation of the communities was much more pronounced in the clear water river (p < 0.001) than in the turbid river (p < 0.05). In the clear water river, communities at the highest velocity were highly different from those at the lower velocities. On the other hand, in the turbid river, communities were more similar at all velocities. Significant (p < 0.05) indicators for highest current velocity in the clear water R. Vaikkojoki were Fragilaria capucina var. gracilis Hustedt, F. capucina var. rumpens Lange-Bertalot and Meridion circulare Agardh. There were no significant indicators for high current velocity in the turbid R. Keravanjoki. Cocconeis placentula Ehr., Cymbella sinuata Gregory and Navicula lanceolata (Agardh) Ehr. were the three most abundant species in the highest velocity. This study showed that diatom community was highly specialized but low in diversity at the highest velocity in the clear water river. This pattern was not seen in the turbid R. Keravanjoki, indicating that the diatom community could withstand at the higher current velocities. In addition, the results show the importance of sampling in a variety of current regimes, particularly in clear water rivers, in order to properly assess the diatom diversity and community of a river section.     

Assessing the current related heterogeneity and diversity patterns of benthic diatom communities in a turbid and a clear water river

Benthic diatoms were sampled in two rapids, in a turbid South-Finnish river (R. Keravanjoki, 22 FTU) and a clear water river in eastern Finland (R. Vaikkojoki, 4 FTU), to evaluate the diversity and spatial distribution patterns of diatom communities and especially their relationships to current velocity. In both rapids, epilithic diatoms were sampled in 15 sampling squares within three current velocity classes (10 cm s^–1, 40 cm s^–1 and 100 cm s^–1). The sampling squares had significantly different diatom communities in the three current velocity classes at both sampling sites, however, separation of the communities was much more pronounced in the clear water river (p < 0.001) than in the turbid river (p < 0.05). In the clear water river, communities at the highest velocity were highly different from those at the lower velocities. On the other hand, in the turbid river, communities were more similar at all velocities. Significant (p < 0.05) indicators for highest current velocity in the clear water R. Vaikkojoki were Fragilaria capucina var. gracilis Hustedt, F. capucina var. rumpens Lange-Bertalot and Meridion circulare Agardh. There were no significant indicators for high current velocity in the turbid R. Keravanjoki. Cocconeis placentula Ehr., Cymbella sinuata Gregory and Navicula lanceolata (Agardh) Ehr. were the three most abundant species in the highest velocity. This study showed that diatom community was highly specialized but low in diversity at the highest velocity in the clear water river. This pattern was not seen in the turbid R. Keravanjoki, indicating that the diatom community could withstand at the higher current velocities. In addition, the results show the importance of sampling in a variety of current regimes, particularly in clear water rivers, in order to properly assess the diatom diversity and community of a river section.     

A diatom functional-based approach to assess changing environmental conditions in temporary depressional wetlands

Functional-based assessments to identify the effects of human-induced disturbances on diatom communities are increasingly used. However, information on the response of functional groups to natural disturbances in temporary depressional wetlands is limited although important for the development of temporary wetland biological assessments. We assessed how diatom life-form and ecological guilds responded to a seasonal hydrological and hydrochemical gradient in three least human-disturbed, temporary depressional wetlands. We assigned species to their respective life-form and ecological guild groups and compared metric composition along the gradient. Overall, temporal variability in alkalinity and ionic composition, essentially Na⁺, as well as hydrological factors, wetland depth and total relative evapotranspiration (ETo), were good predictors of diatom species and functional group composition. Low profile guilds dominated by pioneer life-forms showed the strongest relationship with higher disturbance levels (i.e. increasing Na⁺, alkalinity with a decrease in depth). Similarly, the planktonic guild and tube-living, rosette and adnate life-forms dominated at higher disturbance levels whereas the high profile diatoms displayed the reverse trend. Our study shows the effectiveness of functional-based assessments beyond traditional species-based approaches for understanding and predicting community responses to temporal changes in environmental conditions. We also highlight the benefit of using both life-forms and ecological guilds where a broad set of metrics can enhance our understanding of the mechanisms relating diatom composition to environmental stressors and provide signs of underlying ecological processes.     

Using fish guilds to assess community responses to temperature and flow regimes in unregulated and regulated Canadian rivers

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The use of periphytic diatoms as a means of assessing impacts of point source inorganic nutrient pollution in south-eastern Australia

1. Periphytic diatoms are used as indicators of water quality because their ecological tolerances or preferences to environmental variables are thought to be predictable. However, much of the present autecological information for periphytic diatoms has been derived from studies conducted in the northern hemisphere. In this present study we used periphytic diatoms to determine the impacts of inorganic nutrient pollution in a tidal river system in the temperate latitudes of south‐east Australia. In so doing, we assess the suitability of the use of the ‘northern hemisphere’ ecological tolerance/preference data for periphytic diatoms. 2. Artificial substrates were used to collect periphytic diatoms at 35 sites, which were positioned along the riverbanks and the middle of the river at various distances upstream and downstream of the sewage outfall. The sampling design took into account tidal excursions and the observed sewage plume dynamics. Periphytic diatoms were collected during the austral winter month of August and the austral spring months of September and October. We deployed the artificial substrates for 4 weeks to allow the periphytic diatoms to recruit and colonise, before identifying and enumerating the assemblages. 3. Data analysis included two approaches: multivariate visualisations of combinations of environmental and biological data to investigate shifts in species structure of the periphytic diatom assemblage and multimetric indices based on ecological tolerance/preference data. 4. We found that the spatial patterns inferred from multivariate and multimetric analyses were consistent. Temporal variation in the composition of the periphytic diatom assemblage was greater than the spatial variation along horizontal sections of the river (in any one deployment) due mainly to shifts between winter and spring species. 5. Outfall effects were most apparent in winter, possibly because subsequent deployments were swamped by growth of spring periphytic diatoms. The outfall effects included a shift towards pollutant tolerant species and a reduction in the variability of the periphytic diatom assemblage across the river. 6. We conclude that the use of periphytic diatoms and associated ecological tolerance/preference data as a means of assessing impacts of point source inorganic nutrient pollution is effective. An understanding of river and sewage flow patterns is essential to the design of appropriate monitoring programmes and to the interpretation of results, especially as periphytic diatoms are sensitive to many environmental variables.     

Changes in diatom-dominated biofilms during simulated improvements in water quality: implications for diatom-based monitoring in rivers

Although benthic diatoms are used to assess river water quality, there are few data on the rate at which diatom assemblages react to changes in water quality. The aim of this study was to assess the reaction time of diatoms and to discuss the changes occurring during water quality improvement on the basis of their autecological characteristics. In order to simulate this improvement, diatom-dominated biofilms grown on artificial sandstone substrata were transferred from several polluted rivers to an unpolluted river. They were sampled three times: before transfer and 1 and 2 months after transfer. The ecology and growth-forms of the taxa explained most of the changes in species composition observed during the experiment. Adnate diatoms gradually replaced motile and stalked taxa. Gomphonema parvulum, a stalked diatom positioned vertically in the biofilm, is adapted for light and space competition in high-density algal biofilms. When transferred to an unpolluted site, this growth-form is less competitive and does not tolerate the high grazing pressure. Fistulifera saprophila is a single celled motile diatom, living in organic matrices. When the artificial substrata were transferred to the unpolluted site, this particular ecological niche disappeared quickly. On the other hand, Achnanthidium minutissimum, which is considered to be cosmopolitan and an early colonizer, increased during the first month of transfer and then decreased. It was gradually replaced by A. biasolettianum, which was the taxon best suited to this pristine stream. The changes observed differed between treatments depending on the species composition and architecture of the biofilms. In particular, biofilms dominated by stalked and motile diatoms were more quickly modified than those dominated by small motile diatoms. The diatom index reflects these changes, and its values showed that about 60 days following a water quality improvement were necessary for transferred diatom assemblages to reach diatom index values similar as those at the unpolluted river.     

Diatoms shape the biogeography of heterotrophic prokaryotes in early spring in the Southern Ocean

The interplay among microorganisms profoundly impacts biogeochemical cycles in the ocean. Culture-based work has illustrated the diversity of diatom–prokaryote interactions, but the question of whether these associations can affect the spatial distribution of microbial communities is open. Here, we investigated the relationship between assemblages of diatoms and of heterotrophic prokaryotes in surface waters of the Indian sector of the Southern Ocean in early spring. The community composition of diatoms and that of total and active prokaryotes were different among the major ocean zones investigated. We found significant relationships between compositional changes of diatoms and of prokaryotes. In contrast, spatial changes in the prokaryotic community composition were not related to geographic distance and to environmental parameters when the effect of diatoms was accounted for. Diatoms explained 30% of the variance in both the total and the active prokaryotic community composition in early spring in the Southern Ocean. Using co-occurrence analyses, we identified a large number of highly significant correlations between abundant diatom species and prokaryotic taxa. Our results show that key diatom species of the Southern Ocean are each associated with a distinct prokaryotic community, suggesting that diatom assemblages contribute to shaping the habitat type for heterotrophic prokaryotes.     

Primary productivity and spatial structure of phytolithic growth in streams in the Great Smoky Mountains National Park,Tennessee

The purpose of this study was to examine the primary production rates of phytolithic communities found in the major different habitats of streams and determine the effects of physical and chemical parameters associated with each habitat on periphyton community spatial structure. The project was designed to study natural, intact communities within stream systems.A comparative analysis was made of phytolithic communities found in Camel Hump and Husky Branch streams in the Great Smoky Mountains National Park. Camel Hump flows through virgin forest area and Husky Branch flows through an area logged approximately 60 y ago. The effects of logging on Husky Branch stream and the surrounding watershed are discussed.Seasonal data were collected from July, 1981 through May, 1982 from fast flow, slow flow and pool areas within each stream. An incubation chamber designed for use in lotic systems was used for in situ measurements of ¹⁴C uptake. Rock samples collected at each site were used as substrates for community structure observations utilizing a scanning electron microscope.The algal communities of Camel Hump and Husky Branch streams were found to be predominantly composed of diatoms. The dominant genera in the fast, slow and pool areas included Achnanthes, Eunotia, Meridion, Navicula and Gomphonema. Fast flow areas were dominated by diatom species growing in a prostrate position. Slow flow areas were more densely populated by diatoms than the fast flow areas. Diatoms in the slow flow areas appeared mainly in prostrate position with a few stalked forms present. Pool area communities were less densely packed than slow flow areas and contained stalked and chain formations of diatoms.Results indicate that the physical and chemical parameters associated with each habitat affect the primary production rates and community structure found at the experimental sites. Measurements of carbon assimilation and chlorophyll a concentration were significantly greater in habitats of higher current velocity and light availability. Cell densities tend to increase with a decrease in current velocity. Habitats of high density showed a decrease in diversity and evenness. Correlations between productivity in the various habitats of each stream and other parameters measured in the study are discussed.     

How does water scarcity affect spatial and temporal patterns of diatom community assemblages in Mediterranean streams?

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Stream epilithic, epipelic and epiphytic diatoms: habitat fidelity and use in biomonitoring

We compared the use of epilithic, epiphytic, and epipelic diatom communities in stream biomonitoring by investigating species composition and relationships with measured water quality variables in two tributaries of the Grand River, Ontario, Canada. Although ordination showed some separation of the epilithon from other habitats, clear habitat preferences and seasonality were not identified. Canonical correspondence analysis showed that measured water quality variables explained the major gradients in the diatom data for all three habitats. The diatoms from each habitat were strongly related to alkalinity, suspended solids, biological oxygen demand and conductivity, and in addition, epipelic and epiphytic diatoms showed significant relationships with total phosphorus. It was concluded that although some species were more abundant in one habitat than the others, the community structure of the epilithic, epiphytic and epipelic habitats from these streams was not consistently different. The results indicate no apparent benefit to sampling discrete habitats for water quality monitoring using diatoms, however, the best relationship are obtained using the sum of the diatom data from all three habitats.     

Ecological niche breadth and microhabitat guild structure in temperate Australian reptiles: Implications for natural resource management in endangered grassy woodland ecosystems

Ecological theory predicts that species with narrow niche requirements (habitat specialists) are more vulnerable to anthropocentric disturbances than those with broad niche requirements (habitat generalists). Hence, understanding a species ecological niche and guild membership would serve as a valuable management tool for providing a priori assessments of a species extinction risk. It also would help to forecast a species capacity to respond to land use change, as what might be expected to occur under financial incentive schemes to improve threatened ecological vegetation communities. However, basic natural history information is lacking for many terrestrial species, particularly reptiles in temperate regions of the world. To overcome this limitation, we collated 3527 reptile observations from 52 species across an endangered woodland ecoregion in south‐eastern Australia and examined ecological niche breadth and microhabitat guild structure. We found 30% of species had low ecological niche values and were classified as habitat specialists associated with large eucalypt trees, woody debris, surface rock or rocky outcrops. Cluster analysis separated species into six broad guilds based on microhabitat similarity. Approximately 80% of species belonged to guilds associated with old growth vegetation attributes or non‐renewable litho‐resources such as surface rock or rocky outcrops. Our results suggest that agri‐environment schemes that focus purely on grazing management are unlikely to provide immediate benefits to broad suites of reptiles associated with old growth vegetation and litho‐resources. Our classification scheme will be useful for identifying reptile species that are potentially vulnerable to anthropocentric disturbances and may require alternative strategies for improving habitat suitability and reptile conservation outcomes in grassy woodland ecosystems.     

Macroinvertebrate and diatom communities as indicators for the biological assessment of river Picentino (Campania,Italy)

Pollution of rivers is an increasing problem that affects biological diversity and structure of natural ecosystem. The present study reported the results of the preliminary analysis of diatom and macroinvertebrate communities of river Picentino (Italy, Campania) in respect of the WFD/60/2000/EC. Because of the sensitive to a variety of environmental factors the two categories of organism are used as excellent indicators of changes taking place in water ecosystems, especially eutrophication. Sampling of benthic diatoms and macroinvertebrates has been carried out in five stations along the river during April–May 2014 in order to apply the ICMi and the STAR_ICMi and assess river quality. The data showed a diversification in diatomic and macroinvertebrate communities in relation to environmental stresses and level of pollution, with the disappearance of species higher sensitive to eutrophication and organic load in the upper course of the river. River water quality was found to deteriorate from the upperstream to the downstream because of the increasing of human impact and the intensive agriculture activity along the river.We conclude that the monitoring of diatomic and macroinvertebrate communities could give detailed information about the ecological status of rivers. However it is necessary to increase the achieved data by monitoring other biological communities in order to define adequated strategies to save and preserve the rivers habitat.     

Influence of ionic strength and conductivity on benthic diatom communities in a tropical river (Monjolinho), S?o Carlos-SP, Brazil

Benthic diatoms are important indicators of ecological conditions in lotic systems. The objective of this study was to elucidate the confounding effects of eutrophication, organic pollution and ionic strength and conductivity on benthic diatom communities. Benthic diatoms and water quality sampling was done at 10 sites during summer base flow period (2008 and 2009). Detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) were used to determine environmental gradients along which species vary with respect to ionic strength and conductivity and other environmental variables. Using variance partitioning, we assessed the individual importance of a set of environmental variables (eutrophication and organic pollution) versus ionic strength and conductivity on diatom community structure. The effects of ionic strength and conductivity and organic pollution, eutrophication and other environmental variables were integrated into overall resultant benthic diatom communities. Through partial CCA, we partitioned the variance in diatom data between two sets of exploratory variables, i.e. ionic strength and conductivity (26.9%); other variables, particularly eutrophication and organic pollution (23.0%); shared variance (11.3%) and unexplained variance (38.8%). Due to the interaction of the effects of ionic strength and conductivity and other variables in this study, laboratory experiments must be performed to confirm the observed effects of ionic strength and conductivity.     

Evaluation of Gangetic dolphin habitat suitability under hydroclimatic changes using a coupled hydrological-hydrodynamic approach

The aquatic ecosystems are an integral part of the global environment and play a critical role in hydrogeological processes in the rivers. In recent decades, the external stressors on the aquatic species have significantly increased due to hydrologic alterations, human activities, and anthropogenic changes to their natural habitat. Global climate change has led to rivers' hydrological flow regime shifts, leading to unsuitable habitat conditions. It is, therefore, crucial to assess the potential implications of climate change on habitat suitability to ensure the long-term sustainability of freshwater species. In this direction, we investigated the association between endangered Gangetic dolphin populations and climate-driven hydrologic flow regime alterations in the Kulsi river, India. We developed a coupled eco-hydraulic framework comprising hydrological and hydrodynamic modeling to study the impact of past and projected climate change scenarios on the habitat suitability of target species. The framework was tested on a 15-km stretch of the Kulsi River, where the dolphin population has significantly declined in recent years. The temporal changes in the Weighted Usable Area (WUA) were analyzed using flow parameters and habitat suitability curves. Our findings suggest that the dolphin population decline coincided with a decrease in WUA, indicating a strong association between flow regimes and habitat suitability. Under climate change scenarios, multi-model climate projections and hydrological-hydrodynamic simulations show a rising trend in precipitation and streamflow in the basin, with substantial uncertainty. Higher flow depth and velocity would enhance WUA (habitat suitability). Still, the proposed river development projects in upstream regions could pose a serious threat to fragile dolphin communities by changing the seasonal flow patterns. The findings of this study can be included in conservation action plans and flow regulations strategies in upstream projects to ensure the long-term survival of endangered species.     

Can season interfere with diatom ecological quality assessment?

To understand whether seasons influence the ecological quality assessment of streams on the basis of diatoms, a study was undertaken in two lowland water courses located in northwest Portugal, between autumn 2008 and summer 2009. Temporal variation in the chemical pollution of these streams was small as revealed by a number of physical and chemical parameters analyzed. PERMANOVA global test revealed significant variation in water temperature among seasons. The diatom communities also showed a temporal variation although not all the seasons were statistically different. The multidimensional scaling analysis showed that the main differences in the diatom communities were between two groups of seasons: autumn/winter and spring/summer. Species such as Cocconeis pseudolineata, Gomphonema parvulum var. exilissimum, Fragilaria vaucheriae, Encyonema minutum, and Nitzschia recta were more abundant in spring/summer, while species such as Mayamaea atomus and Nitzschia pusilla were more abundant in autumn/winter. The BIOENV routine confirmed that the biological and temperature patterns are highly correlated. Despite the effects observed on diatom communities, these differences were buffered by the EQR (IPS) values which do not reflect seasonal differences. Therefore, the use of the index IPS seems to allow the monitoring of the streams’ ecological quality throughout the year without the interference of the natural temporal variability of diatom communities.