Search Results (9)

The increasing amount of plastic debris in water ecosystems provides a new substrate (epiplastic microhabitats) for aquatic organisms. The majority of research about epiplastic communities has focused on seawater environments, while research is still quite limited and scattered concerning freshwater systems. In this study, we analyze the first stages of colonization on different types of plastic by a periphytic algae community (its composition and dominant species complex) in freshwater bodies located in a nature reserve (within the Middle Volga Basin). A four-week-long incubation experiment on common plastic polymers (PET, LDPE, PP, and PS), both floating and dipped (~1 m), was conducted in two hydrologically connected karst water bodies in July 2023. The composition of periphytic algae was more diverse (due to the presence of planktonic, benthic, and periphytic species) than the phytoplankton composition found in the water column, being weakly similar to it (less than 30%). Significant taxonomic diversity and the dominant role of periphytic algae were noted for diatoms (up to 60% of the total composition), cyanobacteria (up to 35%), and green (including Charophyta) algae (up to 25%). The composition and structure of periphytic algae communities were distinct between habitats (biotope specificity) but not between the types of plastic, determined primarily by a local combination of factors. Statistically significant higher values of abundance and biomass were demonstrated for some species, particularly for Oedogonium on PP and Nitzschia on LDPE (p-value ≤ 0.05). As colonization progressed, the number of species, abundance, and dominance of individual taxa increased. In hydrologically connected habitats, different starts of colonization are possible, as well as different types of primary succession (initiated by potentially toxic planktonic cyanobacteria or benthic cyanobacteria and mobile raphid diatoms). Within the transparency zone, colonization was more active on the surface (for example, in relation to green algae on PP (p-value ≤ 0.05)). These results indicate a tendency for microalgae communities to colonize actively submerged plastic materials in freshwater, and they may be useful in assessing the ecological status of these aquatic ecosystems. Full article

Human activities have resulted in the eutrophication of rivers, leading to heightened concerns regarding the occurrence of filamentous algal blooms. With the increasing utilization of rivers by humans, the occurrence of these nuisance filamentous algae is expected to increase in frequency in the future. Blooms primarily occur due to energy congestion at the trophic level of primary producers, resulting from inefficient energy flow in both the bottom-up and top-down pathways. To investigate the mechanism underlying the outbreak of filamentous algae, two streams in the southern Taihang catchment with different nutrient conditions were selected for this study. The objective of this study was to understand the effects of nutrient levels and other potential factors on the distribution and succession of filamentous algae. Our findings revealed a positive correlation between nutrient conditions and the biomass of filamentous algae. Cladophora and Spirogyra were identified as the dominant species among filamentous algae, each exhibiting unique distribution patterns in the two streams. Spirogyra thrived predominantly in the Baligou stream, where lower nutrient levels and warmer temperatures prevailed. In contrast, Cladophora flourished in the nutrient-rich Nanping stream at colder temperatures. Results from the generalized linear model indicated that the biomass of Cladophora was influenced by nutrient concentration, water depth, water temperature, and macrobenthic biomass. The biomass of Spirogyra, on the other hand, was primarily determined by water temperature, nutrient concentrations, water depth, and velocity. The positive correlation between Cladophora and macrobenthos revealed a possible mutually beneficial relationship, suggesting that macrobenthos may promote the growth of Cladophora by inhibiting periphytic diatoms. In return, the macrobenthos benefit from a secure refuge and an environment conducive to foraging and reproduction. This study suggested that to alleviate energy flow congestion in the benthic food chain, it is advisable to address this issue by either reducing nutrient loadings in rivers or enhancing the presence of benthivorous fishes in streams. Full article

In Lake Ladoga (northwestern Russia), we found a diatom, putatively Fragilaria sublanceolata-baikali, an endemic species from Lake Baikal (southeastern Siberia, Russia). To determine whether this population matches a previously recognized species from Lake Baikal and assess how it differs from other similar Fragilaria taxa, we studied the valve morphology of three morphologically similar Fragilaria populations (the putative F. sublanceolata-baikali, F. pectinalis and F. perminuta) sampled in Lake Ladoga, along with a population of F. sublanceolata-baikali sampled in Lake Baikal. We used light and scanning electron microscopy with a combination of traditional and geometric morphometric methods. To analyze covariation between the valve shape and size (i.e., allometry), we examined differences in the ontogenetic–allometric trajectories at both the interspecific and intraspecific levels. In addition, the effect of size correction of the valve shape on species differentiation was tested. Traditional morphometrics revealed that F. sublanceolata-baikali is distinguished from F. pectinalis and F. perminuta by valve length, while F. pectinalis and F. perminuta are distinguished by striae density. All three species of Fragilaria showed separate and parallel allometric trajectories. In contrast, the two populations of F. sublanceolata-baikali were on a common allometric trajectory, indicating the conspecificity between these populations. Prior to allometric correction, geometric morphometrics was not able fully discriminate between the three Fragilaria species. After allometric correction, the three Fragilaria species were clearly separated in a size-corrected morphospace, whereas the two populations of F. sublanceolata-baikali formed a tightly overlapping group. Thus, we conclude that geometric morphometrics can reliably distinguish between these morphologically similar species of Fragilaria, but only after accounting for allometric shape variation. Our study confirmed morphological similarity between the two geographically distant populations of F. sublanceolata-baikali, which indicates that this taxon can be considered as invasive in Lake Ladoga. Full article

Outbreaks of periphytic algae, including filamentous algae, have been observed after submerged macrophyte restoration and are common in early stages. Dynamic changes in the periphytic algae community on Vallisneria natans and artificial V. natans were investigated in situ, and their characteristics were compared on the two substrates. The results showed that more periphytic algae species occurred on V. natans (77 taxa) than on artificial V. natans (66 taxa) (F = 2.089, p = 0.047). The cell density and chlorophyll a (Chl. a) content of periphytic algae were 3.42–202.62-fold and 2.07–15.50-fold higher on the artificial substrate than on V. natans, respectively. Except for Lyngbya perelagans (i.e., the only common dominant periphytic algae species on the two substrates), the dominant species on V. natans were Cocconeis placentula and Ulothrix tenerrima, while those on the artificial substrate were Stigeoclonium aestrivale, Oscillatoria tenuis and Achnanthes minutissima. The cell density of periphytic algae was significantly affected by the total phosphorus (TP) and NO₃⁻-N and electric conductivity on V. natans, and by TP and NH₄⁺-N on artificial V. natans. The malondialdehyde content of V. natans was significantly correlated with the periphytic algae biomass. V. natans was more affected by periphytic algae during its slow-growing period, and the contribution order of stress to V. natans was diatoms > cyanobacteria > green algae. Our findings might contribute to the understanding the effect of substrate specificity on periphytic algae communities, and have important implications for the restoration of submerged plants in eutrophic lakes. Full article

Despite the reported allelopathic nature of the Eucalyptus genus, eucalypt leachates have unknown effects on the trophic base of stream green food webs. Eucalypt plantations have increased worldwide, including riparian ecosystems. We aimed to test whether short-term eucalypt leachates might alter water chemistry, periphytic algal biomass and diatoms, and herbivorous invertebrates’ (i.e., scrapers). We studied two oligotrophic and well-preserved headwaters from NW Spain. The experiment followed a before-after control-impact paired (BACIp) design, with weekly sampling before and after eucalypt leaves addition to streams. In the stream with lower discharge, the eucalypt treatments seemed to affect increases in biomass accrual (Chl-a) and diatom assemblages, disfavouring sensitive species (e.g., Eunotia minor and Achnanthidium pyrenaicum). Therefore, the ecological status was reduced from high to good. In the stream with higher discharge, invertebrate assemblages changed with scrapers having their abundances modified in comparison with the control (e.g., Habrophlebia sp. and Elmidae). Results suggest that eucalypt leaves leachates exert toxic effects on periphyton and on diatom and invertebrate assemblages, and this effect might be mediated by discharge. Alterations at the base of stream food webs may compromise their good ecological status. Further studies are necessary to identify whether this toxicity is due to allelopathic processes. Full article

Associating anthropogenic effects with variations in biodiversity is key to understanding how anthropogenic impacts are extrapolated in public supply micro-watersheds. The structure and dynamics of metacommunities in aquatic environments depend not only on the river network itself, but on a multitude of factors. Therefore, we associate the density and species richness of diatoms, assessed in a micro-watershed, with the following driver factors: local environmental variables, spatial variables, landscape characteristics, and the historical community, comparing their possible dispersal routes. Variance partitioning was performed using partial RDA models, with prior selection of predictor variables, to estimate the relative role of each predictor in the diatom community. The small scale of the micro-watershed resulted in a small spatial gradient, reflecting in the low variation in community richness across sampling stations. However, temporal heterogeneity associated with fluctuating precipitation throughout the year may cause temporal variation in the relative abundance of species. This pattern is a result of the supply of resources that increases biodiversity over time, as it allows the coexistence of species that alternate between dominance and persistence. Thus, even on a small scale and during one year of sampling, we demonstrated that predictors of different natures act together to explain diatom communities in micro-watersheds. Full article

Periphytic diatoms play important functional roles in aquatic ecosystems. Their community compositions are widely used in water quality monitoring due to their wide distribution, short reproductive cycles, and sensitivity to environmental changes. In this study, 116 samples of periphytic diatom samples were collected from lakes in the lower reaches of the Yangtze River. The weighted average without tolerance down-weighting regression method was used to develop total phosphorus (r² = 0.661), total nitrogen (r² = 0.699), and chemical oxygen demand (r² = 0.423) models, and the optimal and tolerance values of 78 periphytic species were calculated. Then, a new index, the comprehensive diatom index (CDI), was established on the basis of the optima and tolerances of these 78 species concerning the three environmental variables (TP, TN, and COD) to assess the water trophic status of the lakes in this region. According to the CDI, the trophic statuses of 8, 17, 23, 30, 22, and 14 sample sites were oligotrophic, mesotrophic, light eutrophication, moderate eutrophication, heavy eutrophication, and ultra-eutrophication, respectively. The CDI was more strongly correlated with the conductivity, pH, TP, TN, COD, and TDS than other diatom indices. These results demonstrate that the CDI is a useful metric for assessing the water trophic status of the lakes in the lower reaches of the Yangtze River. Full article

Predicted climate-induced changes in the Great Lakes include increased variability in water levels, which may shift periphyton habitat. Our goal was to determine the impacts of water level changes in Lake Superior on the periphyton community assemblages in the Keweenaw Peninsula with different surface geology. At three sites, we identified periphyton assemblages as a function of depth, determined surface area of periphyton habitat using high resolution bathymetry, and estimated the impact of water level changes in Lake Superior on periphyton habitat. Our results suggest that substrate geology influences periphyton community assemblages in the Keweenaw Peninsula. Using predicted changes in water levels, we found that a decrease in levels of 0.63 m resulted in a loss of available surface area for periphyton habitat by 600 to 3000 m² per 100 m of shoreline with slopes ranging 2 to 9°. If water levels rise, the surface area of substrate will increase by 150 to 370 m² per 100 m of shoreline, as the slopes above the lake levels are steeper (8–20°). Since periphyton communities vary per site, changes in the surface area of the substrate will likely result in a shift in species composition, which could alter the structure of aquatic food webs and ecological processes. Full article

The rising concern about the potential toxicity of synthetic gold nanoparticles (AuNPs) in aquatic environments requires a rigorous estimation of physico-chemical parameters of reactions between AuNPs and major freshwater microorganisms. This study addresses the interaction of 10-nm size, positively charged AuNPs with periphytic freshwater diatoms (Eolimna minima). The adsorption experiments on viable cells were performed in 10 mM NaCl and 5 mM NaCl + 5 mM NaHCO₃ solution at a variable pH (3–10), at an AuNPs concentration from 1 µg/L to 10,000 µg/L, and an exposure time from a few minutes to 55 days. Three types of experiments, adsorption as a function of time (kinetics), pH-dependent adsorption edge, and constant-pH “Langmuirian” type isotherms, were conducted. In addition, long-term interactions (days to weeks) of live diatoms (under light and in the darkness) were performed. The adsorption was maximal at a pH from 3 to 6 and sizably decreased at a pH of 6 to 10. Results of adsorption experiments were modeled using a second order kinetic model, a Linear Programming Model, Freundlich isotherm, and a ligand binding equation for one site competition. The adsorption of AuNPs(+) most likely occurred on negatively-charged surface sites of diatom cell walls such as carboxylates or phosphorylates, similar to previously studied metal cations. Under light exposure, the AuNPs were stabilized in aqueous solution in the presence of live cells, probably due to the production of exometabolites by diatoms. The adsorbed amount of AuNPs decreased after several days of reaction, suggesting some AuNPs desorption. In the darkness, the adsorption and assimilation were stronger than under light. Overall, the behavior of positively charged AuNPs at the diatom–aqueous solution interface is similar to that of metal cations, but the affinity of aqueous AuNPs to cell exometabolites is higher, which leads to the stabilization of nanoparticles in solution in the presence of diatoms and their exudates. During photosynthetic activity and the pH rising above 9 in the vicinity of diatom cells, the adsorption of AuNPs strongly decreases, which indicates a decreasing potential toxicity of AuNPs for photosynthesizing cells. The present study demonstrates the efficiency of a thermodynamic and kinetic approach for understanding gold nanoparticles interaction with aquatic freshwater peryphytic microorganisms. Full article