Algal Communities Research Articles

Response of periphytic algae community structure characteristics to hydrodynamic conditions in an open channel

Response of periphytic algae community structure characteristics to hydrodynamic conditions in an open channel

Peculiarities of the Formation of Benthic Algae Communities in the Kyiv Reservoir (Ukraine)

Peculiarities of the Formation of Benthic Algae Communities in the Kyiv Reservoir (Ukraine)

Ecological and statistical models to configure flow regime for environment benefit in highly engineered rivers: a case study in the MacKenzie River, Southeast Australia.

Ecological and statistical models were developed using freshwater algal assemblages to assess water quality and ecological health of a regulated river. These models were used to inform configuration of flows to maintain or improve environmental conditions of the waterway whilst meeting consumptive water supply commitments. The flow regime of the MacKenzie River, western Victoria, Australia, has been substantially modified since the construction of a water supply reservoir on its upper reach in 1887. Water is withdrawn at several locations downstream of the reservoir, creating a substantially modified flow regime, impacting key environmental values of the river. To assess the impact of the different flow regimes on river health and ecosystem function, ten sites were repeatedly sampled along the river between February 2012 and April 2014. Physical and chemical characteristics of water, including pH, temperature, turbidity, electrical conductivity, dissolved oxygen, total nitrogen, total phosphorous, cations, and anions, were measured. Biological properties of the algal periphyton communities, including dry mass, ash-free dry mass, chlorophyll-a concentration, and species composition, were also measured. Exploration of the algal assemblage and water chemistry data using the computationally unconstrained ordination technique such as principal component analysis principal component analysis (PCA), correspondence analysis (CA), detrended correspondence analysis (DCA), and canonical correspondence analysis (CCA) indicated two strong gradients in the data sets. Furthermore, the quantitative ecosystem response models have been developed as the prototype tool to assist in the future configuration of flows in this river. The empirical data and models showed the lower reaches of the river to be in poor condition under low flows, but this condition improved under flows of 35 ML/day, as indicated by the reduction in green algae and cyanobacteria and improvement. Finally, the results are presented to tailor discharge and duration of water volume by amalgamation of consumptive and environmental flows to improve the condition of the stream thereby supplementing the flows dedicated to environmental outcomes.

Alien Algae Species Invasions in Humic Rivers within Weakly Human Impact Basin.

Increasing anthropogenic influence and climate change are leading to significant transformations in living conditions for indigenous representatives of aquatic communities. The problem of alien species invasions is actively discussed in the example of large rivers and water reservoirs, but medium and small rivers with weak anthropogenic influence have been insufficiently studied in this aspect. With the help of analysis of literary data and the results of our own long-term observations of phytoplankton using morphological and molecular genetic methods in some left-bank Volga tributaries, we identified six invasive species of different taxonomic groups of algae, with a predominance of diatoms. The relevance of using both traditional and modern approaches to identifying invasive algae species is revealed. Such invasive species as Thalassiosira incerta, T. faurii, Skeletonema subsalsum, Unruhdinium kevei, and Gonyostomum semen were part of planktonic communities; the benthic species Plagiotropis lepidoptera var. proboscidea sometimes reached a significant level of development (up 6 to 44% from total biomass) in plankton. It was demonstrated that some algae species have firmly taken the position of dominants and subdominants in planktonic algae communities. The expansion of alien representatives of microphytobenthos was noted in the Volga River basin for the first time. For Gonyostomum semen, its European origin was revealed, for plankton and benthic diatom-Ponto-Caspian. Our study showed that the processes of invasion and subsequent development of alien species take place in habitats with weak anthropogenic influence, which is likely determined by the hydrological, hydrochemical, and climatic changes in river basins and the high adaptive capabilities of invasive species.

Variations in growth, photosynthesis, oxidative stress and microcystin production in Microcystis aeruginosa caused by acute exposure to Benzalkonium Chloride and Benzalkonium Bromide

Due to the COVID-19 pandemic, the use of quaternary ammonium salts (QACs) and their release into the aquatic environment increased dramatically. The ecological risks of QACs still need to be explored. Two extensively used QACs, Benzalkonium Chloride (BAC) and Benzalkonium Bromine (BAB), were selected to explore their acute toxic effects on a common bloom-forming cyanobacterium M. aeruginosa. Both QACs had the same 96 h-EC50 concentration on M. aeruginosa, which was 0.97 mg L-1. Nevertheless, BAC was able to inhibit the growth of M. aeruginosa at real environmental concentrations. Under the EC50 concentration, the inhibition of photosynthesis was more intense induced by BAC than BAB. The ROS levels under BAC and BAB stress were 5.88 and 4.31 times of the control, demonstrating that the oxidative stress caused by BAC was stronger. Notably, the increase of antioxidant substances such as SOD, CAT and GSH and the significant upregulation of genes such as sod2 proved that oxidation defense mechanisms were activated in response to the stressors. Both QACs significantly promoted the synthesis and release of microcystin-LR but the mechanism was different. The effects of QACs on microbial and algal communities and on microcystins synthesis should be paid special attention in future environmental management work.

Living Algal Community Voucher and Taxonomy in Dickinson County Iowa: A Case for Collection-Based Research

Integrative taxonomy is necessary for advancing the field of phycology and understanding regional algal diversity. Collection-based studies for the purposes of providing descriptive voucher flora of living algal communities inform future long-term monitoring and genetic barcoding studies. In this study, littoral composite samples were taken from eight sites (Center Lake, Emerson Bay, Freda Haffner Kettlehole State Preserve, Millers Bay, East Okoboji Lake, West Okoboji Lake, Big Spirit Lake, Upper Gar Lake) in Dickinson County, Iowa, for the purposes of fine level taxonomy. This region has a history of eutrophication, and algal blooms have caused Iowa water resource issues in the past. Micrography for these voucher floras was conducted for taxa representing at least 10% or more of the total estimated algal biomass of evaluated slides. Our voucher floras comprise micrographs of living cells across nine different algal groups and 54 unique taxonomic entities. Unique taxa from these sites include Glaucocystis nostochinearum Itzigsohn, Draparnaldia acuta (C.Agardh) Kützing, and Chaetophoropsis elegans (Roth) B. Wen Liu, Qian Xiong, X.Dong Liu, Z. Yu Hu & G. Xiang Liu. We also document species belonging to toxin-producing Cyanobacteria genera Mycrocystis and Dolichospermum.

Characteristics of sublittoral vegetation in the northwestern Okhotsk Sea based on the concept of adaptive zone

Sublittoral vegetation in the northwestern Okhotsk Sea is described on the data of diving survey in 2020 and some additional data obtained from 2003 to 2022. Five macroalgae associations (Saccharinetum latissimae, Pseudolessonietum laminarioidae, Alarietum esculentae, Sargassetum miyabeae, and Zosteretum marinae) and one group of red algae communities are identified and classified into 5 alliances, 3 orders and 3 classes. All these associations occur over entire area (from 56º to 59º N), within almost whole range of the surveyed depths (2–11 m), and occupy a total of 88 % of the vegetation cover, with statistically uniform distribution. Coenofloras of the associations are poor: up to 5–6 species or multispecies groups have been noted in every association. The concept of an adaptive zone is proposed as an optimal methodological basis for describing marine sublittoral plant communities in the temperate zone. The sublittoral associations in the study area are considered as elementary Petersen-type communities with on average ¾ of the bottom cover and biomass formed by the main dominant species. These associations and higher syntaxa can be built into the most common floristic system of syntaxonomic classification. The adaptive zone concept allows to solve the problem of subjectivism in selection of syntaxa, so the syntaxonomy becomes closer to natural classification with ecological meaning. Successful applicability of the adaptive zone concept for the algae resources assessment is proven; the stock in the surveyed area of 64 km2 is evaluated as 200 . 103 t.

Nutrient metrics to compare algal photosynthetic responses to point and non-point sources of nitrogen pollution

Point- and non-point source nutrients are likely to have different ecological impacts in receiving waters, due to differences in the concentration and proportions of nutrient fractions. However, the direct comparison of their ecological impacts in receiving waters has barely been quantified. We undertook algal bioassays with algal communities from river sites and showed that there was a photosynthetic yield (Fv/Fm) response to nutrient enrichment when river nutrient concentrations were relatively low, but not at higher nutrient concentrations. To combat this variability in the photosynthetic state of algae, we developed a standardized algal bioassay (3-day), using a cultured species of algae which was starved of nitrogen, to compare the photosynthetic response to three nitrogen sources: treated wastewater, aquaculture farm discharges, and soil erosion-derived nutrient sources. This study showed that the nutrient parameter that had the highest correlation with algal photosynthetic response was total dissolved nitrogen (TDN), i.e., the sum of dissolved inorganic and organic nitrogen, rather than dissolved inorganic nitrogen alone. This was true across all three nutrient sources (R2 = 0.58–0.78). Additionally, the same concentrations of TDN from soil erosion-derived and aquaculture samples resulted in a significantly higher algal photosynthetic response, compared to the treated wastewater. This indicates that TDN from soils and aquaculture farms was significantly more bioavailable to the cultured algae than treated wastewater. When a range of parameters were correlated with algal responses, organic and inorganic nutrients, and organic carbon were the parameters that had the highest explanatory power for soil erosion-derived and aquaculture samples (R2 = 0.75–0.87). The importance of organic compounds in these equations points to the potential of microbial transformation of organic nutrients into more bioavailable forms during the 3-day bioassay. This highlights the need to understand the relationship between algal and microbial communities in natural systems for nutrient source impact assessment. This study provides an improved understanding and metrics for comparing the algal growth response to different nutrient sources.

Algal and Cyanobacteria Community Composition within Sarracenia purpurea Phytotelmata across the Eastern Seaboard of the United States

Algal and Cyanobacteria Community Composition within Sarracenia purpurea Phytotelmata across the Eastern Seaboard of the United States

Present-day characteristics of phytoplankton, microphytobenthos and phytoepiphyton of the Kaniv Reservoir

The paper studies quantitative diversity and dominant complexes of phytoplankton, microphytobenthos and phytoepiphyton in lotic and lentic biotopes within the Kaniv Reservoir in summer seasons of 2017–2022, considers their association with some abiotic variables, assesses the trophic state, information diversity according to Shannon’s index and water quality. The cell count of planktonic algae varied within 2780–124155 thous. cells · dm–3, biomass – 0.631–11.636 mg · dm–3, benthic algae – 390–13874 thous. cells · 10 cm–2 and 0.162–2.651 mg mg · 10 cm–2, epiphytic algae – 50–680 thous. cells mg · 10 cm–2 and 0.050–1.679 mg · 10 cm–2 respectively. In lotic biotopes the phytoplankton cell count was higher than in lentic biotopes due to algal inflow from the Kyiv Reservoir and tributaries. The structural organization of phytoplankton and microphytobenthos is represented by oligodominant complexes of Cyanobacteria – Bacillariophyta and Bacillariophyta – Cyanobacteria respectively, and phytoepiphyton – by monodominant complex of Bacillariophyta. The necessity to distinguish dominant complexes according to cell count and biomass has been proven. The dominant complexes of algal communities clearly divide into three clusters (for plankton, benthos and epiphyton), and each of them – into two clusters (for lotic and lentic biotopes). The Sorensen similarity between phytoplankton and microphytobenthos was higher than between phytoplankton and phytoepiphyton, which can be explained by sedimentation of planktonic forms on the bottom under different ecological conditions. High cell count and biomass, diverse dominant complex of algal communities depend upon some abiotic variables (solar radiation, photic layer thickness, water temperature in summer, nutrient content). According to phytoplankton the trophic state of the Kaniv Reservoir is assessed as eutrophic–polytrophic, and according to contour algal communities – as oligo-mesotrophic–mesotrophic. This difference complies with the “alternative stable states” theory. That is, in summer the water reservoir is in “turbid state”, when planktonic Cyanobacteria grow intensively, screen the water surface and suppress the photosynthesis of benthic and epiphytic algal communities. The water quality of the Kaniv Reservoir is within the 1st–3rd classes (clean–satisfactory clean waters), there are no point of diffuse sources of water pollution, which mainly coincides with retrospective data.

Assessing ecological responses to exposure to the antibiotic sulfamethoxazole in freshwater mesocosms

Antibiotics are a contaminant class of worldwide concern as they are frequently detected in aquatic ecosystems. To better understand the impacts of antibiotics on aquatic ecosystems, we conducted an outdoor mesocosm experiment in which aquatic communities were exposed to different concentrations of the antibiotic sulfamethoxazole (0, 0.15, 1.5, 15 and 150 μg/L). These concentrations include mean (0.15 μg/L) and maximum detected concentrations (15 and 150 μg/L) in aquatic ecosystems worldwide. Sulfamethoxazole was applied once a week for eight consecutive weeks to 1530 L outdoor mesocosms in the Netherlands, followed by an eight-week recovery period. We evaluated phytoplankton-, bacterial- and invertebrate responses during and after sulfamethoxazole exposure and assessed impacts on organic matter decomposition. Contrary to our expectations, consistent treatment-related effects on algal and bacterial communities could not be demonstrated. In addition, sulfamethoxazole did not significantly affect zooplankton and macroinvertebrate communities. However, some effects on specific taxa were observed, with an increase in Mesostoma flatworm abundance (NOEC of <0.15 μg/L). In addition, eDNA analyses indicated negative impacts on the insects Odonata at a sulfamethoxazole concentration of 15 μg/L. Overall, environmentally relevant sulfamethoxazole concentration did not result in direct or indirect impairment of entire aquatic communities and ecological processes in our mesocosms. However, several specific macroinvertebrate taxa demonstrated significant (in)direct effects from sulfamethoxazole. Comparison of the results with the literature showed inconsistent results between studies using comparable, environmentally relevant, concentrations. Therefore, our study highlights the importance of testing the ecological impacts of pharmaceuticals (such as sulfamethoxazole) across multiple trophic levels spanning multiple aquatic communities, to fully understand its potential ecological threats.

Photophysiological responses of bottom sea-ice algae to fjord dynamics and rapid freshening

Sea ice algae have a broad salinity tolerance but can experience stress during rapid decreases in salinity that occur with seasonal ice melt and during ice sample melt. This study investigated the impact of salinity on the photophysiological responses of bottom-ice algal communities from two Svalbard fjords (Tempelfjorden and Van Mijenfjorden). To further investigate the impact of salinity alone, and particularly to rapid freshening, the responses of a lab-cultured ice algal community from Van Mijenfjorden were assessed. Photophysiological responses were mainly determined via 14C-based incubations which provided photosynthesis-irradiance curves. Main findings showed that i) the bottom-ice algal community in Tempelfjorden was characterized by lower photosynthetic efficiency and chlorophyll a biomass than the Van Mijenfjorden communities, and ii) a lab-cultured ice algal community from Van Mijenfjorden dominated by pennate diatoms had significantly lower photosynthetic efficiency, maximum photosynthesis and photoacclimation index after a decrease in salinity from 33 to 10. The lower photosynthetic efficiency and chlorophyll a biomass at Tempelfjorden may be attributed to the almost two-fold lower bulk-ice salinity in Tempelfjorden compared to Van Mijenfjorden, which was likely associated with freshwater inputs from the tidewater glacier Tunabreen during sea ice formation. Other factors such as under-ice light intensities, brine volume fraction and brine nutrient concentrations likely also contributed to variability in ice algal response. Furthermore, experimental results indicated that the cultured Van Mijenfjorden community was negatively impacted by a rapid (within 4 to 24 h) reduction in salinity from 33 to 10. We further documented a significant start of recovery of these algae after 168 h. From this work, we surmise that decreases in surface water salinity, for example arising from the intensifying freshening of fjord waters, may only cause temporary changes in ice algal photoacclimation state and thus in chlorophyll a biomass. Further, this study also supports the need for salinity buffered melt of sea ice samples to reduce artificial bias in biological measurements.

Neolithic human activity caused eutrophication in small central European lakes

Human activities during the Early Neolithic have had major influences on central European terrestrial ecosystems through deforestation, burning, animal husbandry and agriculture. However, much less is known about how these landscape-scale changes affected aquatic ecosystems. In this study, we examined diatom assemblages preserved in radiocarbon dated and intermittently laminated sediment cores collected at Burgäschisee and Moossee, two small lakes on the Swiss Plateau, and compared the results with archaeological evidence for Neolithic lakeshore settlements and palaeobotanical records indicating distinct catchment scale phases of changing land use. The new diatom records were used to reconstruct changes to the lake ecosystem and of lake water nutrient concentrations from 6600 to 3800 calibrated radiocarbon years BP (cal yr BP). Blooms of small sized Stephanodiscus spp. together with algal remains (Cyanobacteria, Chlorophyta) indicate distinct phases of lake nutrient enrichment particularly during a land use and settlement phase associated with the Cortaillod culture (5800–5500 cal yr BP). In contrast, other land use phases were not associated with clear indications of water quality changes. Diatom response to human impact in the catchment was more pronounced at Burgäschisee relative to Moossee, notably for the phase corresponding to the Cortaillod culture.The new results agree with previous studies that provided evidence of Neolithic human impact on lake ecosystems in central Europe. For small lakes, such as Moossee and Burgäschisee, the establishment of Neolithic lakeside settlements and land uses did not only lead to pronounced terrestrial ecosystem changes in the catchment but apparently influenced the lake ecosystems themselves. The different response of the diatom assemblages in the two lakes also suggests that the impact of land use on nutrient concentrations and algal communities varied between lakes during the Neolithic, presumably due to different intensities of human impact at different sites, but likely also due to differences in geographical and hydrological settings of the lakes (basin morphologies, stratification, and mixing regimes).

Insights into the ecological impact of trout introduction in an oligotrophic lake using sedimentary environmental DNA

Introduced trout can induce trophic cascades, however, a lack of pre-introduction data limits knowledge on their impact in many lakes. Traditional paleolimnological approaches have been used to study historic species changes, but until recently these have been restricted to taxa with preservable body-parts. To explore the ecosystem effects of Salmo trutta (brown trout) introduction on an oligotrophic lake in Aotearoa-New Zealand, we used a multi-marker sedimentary environmental DNA (sedDNA) approach coupled with pigments to detect changes across multiple trophic levels. DNA was extracted from core depths capturing approximately 100 years before and after the expected arrival of S. trutta, and metabarcoding was undertaken with four primer sets targeting the 12S rRNA (fish), 18S rRNA (eukaryotes) and cytochrome c oxidase (COI; eukaryotes) genes. The earliest detection of S. trutta eDNA was 1906 (1892–1919 CE with 95% high probability density function) suggesting their introduction was shortly before this. Native fish diversity (12S and 18S rRNA) decreased after the detection of S. trutta, albeit the data was patchy. A shift in overall eukaryotic and algal communities (18S rRNA and COI) was observed around 1856 (1841–1871 CE) to 1891 (1877–1904 CE), which aligns with the expected S. trutta introduction. However, taxonomy could not be assigned to many of the 18S rRNA and COI sequences. Pigment concentrations did not change markedly after S. trutta introduction. SedDNA provides a new tool for understanding the impact of disturbances such as the introduction of non-native species; however, there are still several methodological challenges to overcome.

Methylphosphonate Is Utilized by Commensal Microbiota of Macroalgae in the Oligotrophic Sargasso Sea

AbstractThe essential nutrient phosphorus is biologically scarce in the Sargasso Sea, yet the pelagic macroalgae Sargassum, for which this area of the North Atlantic Ocean is named, thrives. We tested the hypothesis that Sargassum holobionts utilize methylphosphonate (MPn) as an alternative source of phosphorus, finding lysis liberated phosphonate‐derived methane. The observed activity occurred at concentrations as low as 35 nM MPn and was inhibited by antibiotics, implicating bacterial epibionts of the holobiont capable of MPn lysis at realistic environmental concentrations. Dark incubations resulted in diminished methane production, consistent with commensalism between microbe and host. A survey of macroalgal species inhabiting the Sargasso Sea found ubiquitous capacity for MPn lysis; such capacity was absent in species inhabiting phosphorus‐replete waters of the California Current, pointing to phosphorous limitation as a selective pressure. These results suggest that bacterial epibionts of algal communities acquire phosphorus from phosphonates while simultaneously serving as a source of atmospheric methane.

Impacts of flue gas desulfurization (FGD) gypsum on water quality and the algal community in catfish aquaculture ponds

Catfish aquaculture ponds are at high risk of experiencing excessive algal growth, especially cyanobacteria, that can lead to negative water quality issues due to their consistent input through regular feedings and internal cycling of nutrients. Conventional algaecides used in aquaculture, such as copper sulfate, may be effective in the short-term but can potentially lead to developed resistance in phytoplankton over time or harmful effects on non-target species. An alternative nutrient management strategy, which has traditionally been used in land-based agriculture, is via flue gas desulfurization (FGD) gypsum, a form of calcium sulfate that is created as a by-product of carbon-based energy sources. A six-month field experiment was conducted on active catfish aquaculture ponds at a farm in west Alabama to test the effects of FGD gypsum on water quality, including its ability to manage excessive algal blooms throughout the growing season. In stark contrast to previous results from FGD gypsum application in eutrophic waters, it was discovered that FGD gypsum-treated ponds experienced a large increase in soluble reactive phosphorus (SRP) that led to a spike in phytoplankton abundance, specifically cyanobacteria. Supplementary microcosm experiments aided in determining that FGD gypsum could extract legacy phosphorus out of the nutrient-rich flocculant sediment found in aquaculture ponds. While these results were unexpected and ultimately undesired, we did discover that the use of FGD gypsum at the 500 mg/L concentration does not produce any trace metal contamination in the water column or in the fish tissue. Overall, this experiment discovered new results that FGD gypsum could produce when used in hypereutrophic waters with nutrient-rich sediments and provides the foundation for future research directions to determine the specific mechanisms behind the interaction of FGD gypsum with the sediment.

Size matters: Microherbivores make a big impact in coral aquaculture

Reef restoration activities and the ornamental trade are increasing the demand for sexually propagated corals. One challenge faced in scaling up the aquaculture production of corals is high mortality as a result of fouling organisms overgrowing coral spat, with manual removal of algae and other fouling organisms being costly and time consuming. Here we test the use of microherbivore grazers as a potential biocontrol method for fouling in coral aquaculture and compare their effectiveness to manual cleaning by an aquarist. Recruits of six coral species (Acropora millepora, Acropora kenti, Goniastrea retiformis, Porites lobata, Dipsastraea speciosa and Lobophyllia corymbosa) were reared for 112 days with aquarist cleaning, or co-cultured with gastropods (Calthalotia strigata or Turbo haynesi), sea urchins (Tripneustes gratilla or Echinomentra mathaei), the hermit crab Clibanarius cf. taeniatus or under a control treatment with no grazers. Corals grown in the aquarist cleaning treatment displayed high survival and growth, though similar responses were observed for most coral species grown with C. strigata or T. gratilla, likely due to minimal damage via overgrazing and the promotion of relatively short turf algal communities in these treatments. However, effort required, measured as average cleaning time, was 2–3 times greater in the aquarist treatment compared to C. strigata or T. gratilla treatments. Survival of coral recruits housed with C. cf. taeniatus, E. mathaei or T. haynesi were variable, likely due to the dominance of long, filamentous turf algae in tanks with E. mathaei, and physical disturbance to recruits by C. cf. taeniatus and T. haynesi. Our results demonstrate microherbivores have potential for application in aquaculture to promote production, while also reducing labour costs.

Effects of antidepressant exposure on aquatic communities assessed by a combination of morphological identification, functional measurements, environmental DNA metabarcoding and bioassays

The antidepressant fluoxetine is frequently detected in aquatic ecosystems, yet the effects on aquatic communities and ecosystems are still largely unknown. Therefore the aim of this study is to assess the effects of the long-term application of fluoxetine on key components of aquatic ecosystems including macroinvertebrate-, zooplankton-, phytoplankton- and microbial communities and organic matter decomposition by using traditional and non-traditional assessment methods. For this, we exposed 18 outdoor mesocosms (water volume of 1530 L and 10 cm of sediment) to five different concentrations of fluoxetine (0.2, 2, 20 and 200 μg/L) for eight weeks, followed by an eight-week recovery period. We quantified population and community effects by morphological identification, environmental DNA metabarcoding, in vitro and in vivo bioassays and measured organic matter decomposition as a measure of ecosystem functioning. We found effects of fluoxetine on bacterial, algal, zooplankton and macroinvertebrate communities and decomposition rates, mainly for the highest (200 μg/L) treatment. Treatment-related decreases in abundances were found for damselfly larvae (NOEC of 0.2 μg/L) and Sphaeriidae bivalves (NOEC of 20 μg/L), whereas Asellus aquaticus increased in abundance (NOEC <0.2 μg/L). Fluoxetine decreased photosynthetic activity and primary production of the suspended algae community. eDNA assessment provided additional insights by revealing that the algae belonging to the class Cryptophyceae and certain cyanobacteria taxa were the most negatively responding taxa to fluoxetine. Our results, together with results of others, suggest that fluoxetine can alter community structure and ecosystem functioning and that some impacts of fluoxetine on certain taxa can already be observed at environmentally realistic concentrations.

First insight in cyanobacterial and algal communities from cave stream (Stopić Cave, Serbia)

First insight in cyanobacterial and algal communities from cave stream (Stopić Cave, Serbia)

Long-term changes of phytoplankton productivity in freshwater ecosystems of the Pearl River Delta as recorded by organic geochemical proxies in sediment cores

Phytoplankton productivity (PP) is expected to be impacted by climate change and anthropogenic activity in freshwater ecosystems, but the effects and interactions of these environmental stressors are often complex and not clearly understood. In this research, we investigated the influences of climate change and human activity on changes in PP recorded by sedimentary organic geochemical proxies (including bulk properties, Rock-Eval parameters, n-alkanols, and sterols) in the Pearl River Delta of southern China over the past few decades. Multiple proxies suggested that PP has increased in the mesotrophic Lian'an reservoir (LA) and the eutrophic Liuhuahu lake (LHH) since the 1960s. Phytoplankton sterols revealed that the dominant algal community consisted of dinoflagellates, cyanobacteria, and green algae in LA, while cyanobacteria and green algae were the primary algae groups in LHH. Phytoplankton proxies exhibited significant positive correlation with rising temperature (r > 0.57, p < 0.05) and nutrient loadings (r > 0.80, p < 0.01), suggesting that climate warming and nutrient input have contributed to the variations in PP. Climate change has caused a rise in temperature and changes in precipitation, along with human activity such as agriculture, dam construction, and sewage input, have collectively impacted aquatic environments. The generalized additive model (GAM) was used to quantitatively analyze the impacts of climate change and anthropogenic activity on aquatic ecosystems. Results demonstrated the cumulative and synergistic effects of climate change and anthropogenic activity, and higher climatic influences observed after the 1990s. The synergistic effects led to algal blooms and restricted the growth of aquatic macrophytes, particularly in the eutrophic LHH. This has worsened eutrophication and resulted in an imbalance in aquatic ecosystems. In summary, this research emphasizes the interactions between climate change and anthropogenic activity, and PP variations in aquatic ecosystems and underscores the importance of studying these factors to comprehend the influence of environmental stressors.