Rainfall-induced changes in aquatic microbial communities and stability of dissolved organic matter: Insight from a Fen river analysis.

Microbial communities are pivotal in aquatic ecosystems, as they affect water quality, energy dynamics, nutrient cycling, and hydrological stability. This study explored the effects of rainfall on hydrological and photosynthetic parameters, microbial composition, and functional gene profiles in the Fen River. Our results demonstrated that rainfall-induced decreases in stream temperature, dissolved oxygen, pH, total phosphorus, chemical oxygen demand, and dissolved organic carbon concentrations. In contrast, rainfall increased total dissolved solids, salinity, and ammonia-nitrogen concentrations. A detailed microbial community structure analysis revealed that Cyanobacteria was the dominant microbial taxon in the Fen River, accounting for approximately 75% and 25% of the microalgal and bacterial communities, respectively. The abundance of Chlorophyta and Bacillariophyta increased by 47.66% and 29.92%, respectively, whereas the relative abundance of Bacteroidetes decreased by 37.55% under rainfall conditions. Stochastic processes predominantly affected the assembly of the bacterial community on rainy days. Functional gene analysis revealed variations in bacterial functions between sunny (Sun) and rainy (Rain) conditions, particularly in genes associated with the carbon cycle. The 3-oxoacyl-[acyl-carrier-protein] reductase gene was more abundant in the Fen River bacterial community. Particular genes involved in metabolism and environmental information processing, including the acetyl-CoA C-acetyltransferase (atoB), enoyl-CoA hydratase (paaF), and branched-chain amino acid transport system gene (livK), which are integral to environmental information processing, were more abundant in Sun than the Rain conditions. In contrast, the phosphate transport system gene, the galactose metabolic gene, and the pyruvate metabolic gene were more abundant in Rain. The excitation-emission matrix analysis with parallel factor analysis identified four fluorescence components (C1-C4) in the river, which were predominantly protein- (C1) and humic-like (C2-C4) substances. Rainfall affected organic matter production and transport, leading to changes in the degradation and stability of dissolved organic matter. Overall, this study offers insight into how rainfall affects aquatic ecosystems.

Effects of polystyrene nanoplastics on the physiological and biochemical characteristics of microalga Scenedesmusquadricauda.

The contamination of the aquatic environment with microplastics has become a global environmental concern. Microplastic particles can be shredded to form smaller nanoplastics, and knowledge on their impacts on phytoplankton, especially freshwater microalgae, is still limited. To investigate this issue, the microalga Scenedesmus quadricauda was exposed to polystyrene nanoplastics (PS-NPs) of five concentrations (10, 25, 50, 100, and 200 mg/L). The growth; the contents of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD); the chlorophyll content; and concentrations of soluble protein and soluble polysaccharide were accordingly measured. The results showed that the microalgal density increased with the increase of the polystyrene nanoplastic concentrations, and the physiological features of alga were enhanced after the stimulation of nanoplastics. Furthermore, a high concentration (200 mg/L) of nanoplastics increased the contents of chlorophyll, soluble protein, and polysaccharide (P < 0.05). The antioxidant enzyme activities of Scenedesmus quadricauda were significantly activated by nanoplastics. Lastly, we propose three possible algal recovery mechanisms in response to nanoplastics in which Scenedesmus quadricauda was tolerant with PS-NPs by cell wall thickening, internalization, and aggregation. The results of this study contribute to understanding of the ecological risks of nanoplastics on freshwater microalgae.

Association between the Classification of the Genus of Batrachospermaceae (Rhodophyta) and the Environmental Factors Based on Machine Learning.

Batrachospermaceae is the largest family of freshwater red algae, widely distributed around the world, and plays an important role in maintaining the balance of spring and creek ecosystems. The deterioration of the current global ecological environment has also destroyed the habitat of Batrachospermaceae. The research on the environmental factors of Batrachospermaceae and the accurate classification of the genus is necessary for the protection, restoration, excavation, and utilization of Batrachospermaceae resources. In this paper, the database of geographical distribution and environmental factors of Batrachospermaceae was sorted out, and the relationship between the classification of genus and environmental factors in Batrachospermaceae was analyzed based on two machine learning methods, random forest and XGBoost. The result shows: (1) The models constructed by the two machine learning methods can effectively distinguish the genus of Batrachospermaceae based on environmental factors; (2) The overall AUC score of the random forest model for the classification and prediction of the genus of Batrachospermaceae reached 90.41%, and the overall AUC score of the taxonomic prediction of each genus of Batrachospermaceae reached 85.85%; (3) Combining the two methods, it is believed that the environmental factors that affect the distinction of the genus of Batrachospermaceae are mainly altitude, average relative humidity, average temperature, and minimum temperature, among which altitude has the greatest influence. The results can further clarify the taxonomy of the genus in Batrachospermaceae and enrich the research on the differences in environmental factors of Batrachospermaceae.

Thoreabaiyunensis sp. nov. (Thoreales, Rhodophyta) and T.okadae, a new record from China.

The freshwater red algal order Thoreales has a triphasic life history, of which the "Chantransia" phase is a small filamentous sporophyte. The "Chantransia" stage is difficult to distinguish from species in the genus Audouinella by its morphological characteristics. In this study, five "Chantransia" isolates (GX41, GX81, GD224, GD225, GD228) were collected from Guangxi Zhuang Autonomous Region and Guangdong Province in China. Based on morphological data, all five isolates were similar to A.pygmaea, whereas sequence data from the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) gene and the 5' region of the mitochondrial cytochrome oxidase I gene (COI-5P) determined that these specimens represented the "Chantransia" stage of two species in the genus Thorea rather than Audouinella. Phylogenetic analyses of the concatenated genes supported the proposal of a new species, T.baiyunensis, and a new geographic record of T.okadae, a species previously described only in Japan. Therefore, combined with previous records, four species of this genus are now recognized in China, including T.hispida, T.violacea, T.baiyunensis and T.okadae.

Transcriptome Analysis Reveals the Mechanisms of Tolerance to High Concentrations of Calcium Chloride Stress in Parachlorella kessleri.

Salt stress is one of the abiotic stress factors that affect the normal growth and development of higher plants and algae. However, few research studies have focused on calcium stress, especially in algae. In this study, the mechanism of tolerance to high calcium stress of a Parachlorella kessleri strain was explored by the method of transcriptomics combined with physiological and morphological analysis. Concentrations of CaCl2 100 times (3.6 g/L) and 1000 times (36 g/L) greater than the standard culture were set up as stresses. The results revealed the algae could cope with high calcium stress mainly by strengthening photosynthesis, regulating osmotic pressure, and inducing antioxidant defense. Under the stress of 3.6 g/L CaCl2, the algae grew well with normal cell morphology. Although the chlorophyll content was significantly reduced, the photosynthetic efficiency was well maintained by up-regulating the expression of some photosynthesis-related genes. The cells reduced oxidative damage by inducing superoxide dismutase (SOD) activities and selenoprotein synthesis. A large number of free amino acids were produced to regulate the osmotic potential. When in higher CaCl2 stress of 36 g/L, the growth and chlorophyll content of algae were significantly inhibited. However, the algae still slowly grew and maintained the same photosynthetic efficiency, which resulted from significant up-regulation of massive photosynthesis genes. Antioxidant enzymes and glycerol were found to resist oxidative damage and osmotic stress, respectively. This study supplied algal research on CaCl2 stress and provided supporting data for further explaining the mechanism of plant salt tolerance.

A Parachlorella kessleri (Trebouxiophyceae, Chlorophyta) strain tolerant to high concentration of calcium chloride.

Members of coccoid green algae have been documented in various extreme environments. In this article, a unicellular green alga was found to slowly grow in high concentration (3.6 g/L) and pure calcium chloride solution in the laboratory. It was successfully cultured and a taxonomic study combined approaches of morphological and molecular methods was conducted to determine its classification attribution, which was followed by a preliminary physiology research to explore its unique tolerance characteristics against calcium chloride stress. The strain was identified as Parachlorella kessleri by very similar morphology and the same phylogenetic position. The morphological differences among the three species in genus Parachlorella were then discussed and the characteristic traits of absent or thin mucilaginous envelop and mantel-shaped chloroplast for P. kessleri were supported. In addition, the almost strictly spherical shape of adult cells could further distinguish the P. kessleri from the other two species. The tolerant characteristics to CaCl2  stress for this strain were confirmed and the limit concentration was revealed as between 2000 and 4000 times than the standard BG11 culture concentration. Therefore, this P. kessleri strain is expected to be a good material to explore the mechanism of resistance to calcium ions stress for eukaryotic microbiology.

Comparative morphological, physiological, biochemical and genomic studies reveal novel genes of Dunaliella bioculata and D. quartolecta in response to salt stress.

BACKGROUND: Salinity is an essential abiotic stress in plants. Dunaliella is a genus of high-salt-tolerant microalgae. The present study aimed to compare the characterizations of D. bioculata and D. quartolecta at different levels and investigate novel genes response to salt stress. METHODS AND RESULTS: High chlorophyll contents were detected in D. bioculata on the 35th d of salt stress, while high lipid and carotenoid contents were detected in D. quartolecta via morphological and biochemical analyses. Physiological analysis showed that D. quartolecta cells had a smaller increase in osmotic potential, a smaller decrease in the Na+/K+ ratio and photochemical efficiency (Fv/Fm), and a lower relative conductivity than D. bioculata cells. The genomic lengths of D. quartolecta and D. bioculata were 396,013,629 bp (scaffold N50 = 1954 bp) and 427,667,563 bp (scaffold N50 = 3093 bp) via high-throughput sequencing and de novo assembly, respectively. Altogether, 25,751 and 26,620 genes were predicted in their genomes by annotation analysis with various biodatabases. The D. bioculata genome showed more segmental duplication events via collinearity analysis. More single nucleotide polymorphisms and insertion-deletion variants were detected in the D. bioculata genome. Both algae, which showed a close phylogenetic relationship, may undergo positive selection via bioinformatics analysis. A total of 382 and 85 novel genes were screened in D. bioculata and D. quartolecta, with 138 and 51 enriched KEGG pathways, respectively. Unlike the novel genes adh1, hprA and serA, the relative expression of livF and phbB in D. bioculata was markedly downregulated as salinity increased, as determined by qPCR analysis. The relative expression of leuB, asd, pstC and proA in D. quartolecta was markedly upregulated with the same salinity increase. CONCLUSION: Dunaliella quartolecta is more halophilic than D. bioculata, with more effective responses to high salt stress based on the multiphase comparative data.

Seasonal and spatial patterns of eukaryotic phytoplankton communities in an urban river based on marker gene.

The seasonal and spatial eukaryotic phytoplankton composition in the Fenhe River was investigated based on the 18S rDNA V4 region. The relationship between phytoplankton functional groups and environmental factors was explored to effectively capture the responses of these taxa to environmental gradients and their effects on ecosystem function. Our results indicated that the Chlorophyta and Bacillariophyta had higher relative abundance than other taxa, and their diversity and richness indices in spring were higher than those in other seasons. The linear discriminant analysis effect size (LEfSe) analyses detected that the potential seasonal biomarkers included Desmodesmus, Cyclotella, Pseudoschroederia, Discostella, Scenedesmus, Monoraphidium, and Nannochloropsis; the spatial biomarkers included Amphora, Neochloris, Hindakia, Pseudomuriella, Coccomyxa, Chloroidium, Scherffelia, Chromochloris, and Scotinosphaera. The systemic evolution and distribution characteristics of the first 50 representative sequences showed that the dominant genus included Desmodesmus in spring, Pseudopediastrum in summer, Mychonastes in autumn, and Monoraphidium in winter. Main seasonal variation of phytoplankton functional groups was as follows: spring (J + F + C + X1) → summer (J + F + X1 + X2) → autumn (J + F + X1 + C) → winter (X1 + J + B + X2). Pearson correlation, redundancy analysis, and variance partitioning analysis showed temperature and phosphate were the determining factors causing the changes of phytoplankton functional groups and community composition in the Fenhe River.

Discovery of Conserved and Novel MicroRNAs in Galdieria sulphuraria.

BACKGROUND: As a thermoacidophilic microalga, Galdieria sulphuraria has a unique biological function. MicroRNA (miRNA) plays an important regulating role in plant various stress responses. OBJECTIVE: In this study, we identified lots of conserved and novel miRNAs in G. sulphuraria (gsu-miRNAs), and predicted their putative targets for the first time. MATERIALS AND METHODS: Conserved and novel gsu-miRNAs were predicted via deep sequencing on the Illumina HiSeq 4000 platform combined with bioinformatics analysis with a series of filtration criteria. Characterization of gsu-miRNAs and their targets were searched by different bioinformatics software. Some gsu-miRNAs were validated by Northern blot and RT-PCR analysis. MiRNA target gene function was predicted via GO and KEGG analysis. The interrelationship between gsu-miRNAs and target genes was constructed via Cytoscape networks analysis. RESULTS: A total of 134 gsu-miRNAs belonging to 124 MIRNA families were identified. Characterization analysis and experimental validation revealed that most of them were credible. A few miRNAs showed conservatism between G. sulphuraria and 20 representative plants. 1,589 putative miRNA targets were predicted. GO analysis revealed that the genes targeted by gsu-miRNAs involved in some important physiological processes of this alga, such as the ETC, and KEGG pathway analysis revealed that RNA transport and the PPP were predicted to be the two most enriched pathways. Cytoscape networks between miRNAs and target genes indicated their various interactions. CONCLUSIONS: Research on gsu-miRNAs, which act as key regulators during gene expression in G. sulphuraria will open a new avenue for further developing this thermoacidophilic alga at the post-transcriptional level.

The complete mitochondrial genome of an oil-rich microalga Parachlorella kessleri TY (Chlorophyta).

Parachlorella kessleri TY isolated from the lawn soil belongs to Trebouxiophyceae, Chlorophyta. The complete mitogenome of P. kessleri sequenced and described. It is a circular duplex molecule 64,744 bp in length consisting of 28 protein-coding genes, 23 transfer RNA (tRNA) genes, four ribosomal RNA (rRNA) genes, and one putative open reading frames (ORFs). Phylogenetic analysis places P. kessleri mitogenome in a branch sister to Picochlorum sp., Lobosphaera incisa, and Chloroparvula sp., clade in which Picochlorum as P. kessleri also reported as oil-rich green microalgae.

Molecular Mechanism of Lipid Accumulation and Metabolism of Oleaginous Chlorococcum sphacosum GD from Soil under Salt Stress.

The oleaginous microalgae species Chlorococcum sphacosum GD is a promising feedstock for biodiesel production from soil. However, its metabolic mechanism of lipid production remains unclear. In this study, the lipid accumulation and metabolism mechanisms of Chlorococcum sphacosum GD were analyzed under salt stress based on transcriptome sequencing. The biomass and lipid content of the alga strain were determined under different NaCl concentrations, and total RNA from fresh cells were isolated and sequenced by HiSeq 2000 high throughput sequencing technology. As the salt concentration increased in culture medium, the algal lipid content increased but the biomass decreased. Following transcriptome sequencing by assembly and splicing, 24,128 unigenes were annotated, with read lengths mostly distributed in the 200-300 bp interval. Statistically significant differentially expressed unigenes were observed in different experimental groups, with 2051 up-regulated genes and 1835 down-regulated genes. The lipid metabolism pathway analysis showed that, under salt stress, gene-related fatty acid biosynthesis (ACCase, KASII, KAR, HAD, FATA) was significantly up-regulated, but some gene-related fatty acid degradation was significantly down-regulated. The comprehensive results showed that salt concentration can affect the lipid accumulation and metabolism of C. sphacosum GD, and the lipid accumulation is closely related to the fatty acid synthesis pathway.

Characterization and Comparative Analysis of MicroRNAs in 3 Representative Red Algae.

Background: MicroRNA (miRNA) is a key regulator at the gene posttranscriptional regulation level. We have previously identified miRNAs and their putative targets in 3 representative red algae, Chondrus crispus, Galdieria sulphurariais and Porphyridium purpureum. Objectives: In this study, unique molecular and evolutionary characterization of miRNAs were revealed in the 3 red algae based on the comparative miRNAs profiling. Materials and Methods: Genome locations of small RNAs (sRNAs), miRNAs and MIRNAs (MIRs) in the 3 red algae were shown by collinearity analysis. Characterization of miRNAs and MIRs were profiled via bioinformatics analysis. Taken MIR156s and miR156s for examples, red algae miRNAs evolutionary features were demonstrated via phylogenetic and evolutionary information analysis. MiRNA targets main inhibition type was validated via performing data statistics and RLM-RACE PCR. Key target genes and their function were predicted by the common Gene Ontolgoy (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. Results: Quantity, nucleotide bias and common sequences of miRNAs were analyzed in the 3 red algae. Four typical precursor structures and primary molecular features of red algae miRNAs were profiled. Genome-wide collinearity analysis of sRNAs, miRNAs and MIRs in the 3 red algae was performed to show their distribution and interrelation based on the deep sequencing data. Taken red algae MIR156s for example, their family members and sequences divergence were demonstrated. The whole evolutionary processes of miR156s and pre-miR156s in red algae were steady with negative selected pressure though diverse phylogenetic relationships and evolutionary parameters showed. Through 3 red algae miR156 targets validation, cleavage was validated as their main miRNA targets inhibition type. The common target genes (GO:0009536) enriched significantly for plastid formation will provide important insights for red algal biopigment research. The common KEGG pathways (ko01100) enriched significantly were predicted without a detailed reference metabolic map. Conclusions: MiRNA plays an essential role in gene expression regulation involved in diverse biological processes of red algae. Comprehensive molecular and evolutionary features of miRNAs in the 3 red algae will provide insights for further utilizing the algae resources at the molecular level.

Relationship between ß-Carotene Accumulation and Geranylgeranyl Pyrophosphate Synthase in Different Species of Dunaliella.

To study the relationship between ß-carotene synthesis and geranylgeranyl pyrophosphate synthase (GGPS) activity, 15 species of Dunaliella were used to determine the changes in photosynthetic pigment contents, chlorophyll fluorescence parameters, ß-carotene content, and GGPS activity. By observing the morphology and size of 15 species of Dunaliella, D8 has the largest individual algal cell and D9 has the smallest individual. Growth was relatively slow during days one through seven. After about eight days, the cells entered the logarithmic growth period and grew rapidly to a high density. After about 45 days, they entered a mature period, and growth slowed down. The contents of chlorophyll, carotenoids, and ß-carotene increased during growth. D1 has the highest accumulation of ß-carotene, and GGPS enzyme activity has a positive linear relationship with the ß-carotene synthesis content. Phylogenetic analysis showed that the GGPS proteins of the 15 species were highly homologous, and the GGPS protein was not part of the membrane.

Phylogenetic and Morphological Evolution of Green Euglenophytes Based on 18S rRNA.

Green euglenophytes are a group of eukaryotes with ancient origin. In order to understand the evolution of the group, it is interesting to know which characteristics are more primitive. Here, a phylogenetic tree of green euglenophytes based on the 18S rRNA gene was constructed, and ancestral states were reconstructed based on eight morphological characters. This research clarifies the phylogenetic relationships of green euglenophytes and provides a basis for the study of the origin of these plants. The phylogenetic tree, which was constructed by Bayesian inference, revealed that: Eutreptia and Eutreptiella were sister groups and that Lepocinclis, Phacus, and Discoplastis were close relatives; Euglena, Cryptoglena, Monomorphina, and Colacium were closely related in addition to Trachelomonas and Strombomonas; and Euglena was not monophyletic. An ancestral reconstruction based on morphological characters revealed seven primitive character states: ductile surface, spirally striated, slightly narrowing or sharp elongated cauda, absence of a lorica, chloroplast lamellar, shield or large discoid, pyrenoid with sheath, and with many small paramylon grains. However, the ancestral state of the length of the flagellum could not be inferred. Euglena and Euglenaria, which both possessed all of the ancestral character states, might represent the most ancient lineages of green euglenophytes.

Analysis of Adaptive Evolution and Coevolution of rbcL Gene in the Genus Galdieria (Rhodophyta).

To research the adaptive evolution and coevolution of the rbcL gene in the genus Galdieria, 36 sequences were selected. The bioinformatics of proteins encoded by rbcL genes of Galdieria were analyzed, and phylogenetic trees were constructed by the maximum-likelihood method. Then, adaptive evolution and coevolution were analyzed. The phylogenetic tree showed that the inner groups were clustered into four branches, in which the sequences of Galdieria maxima were divided into two small branches, and the posterior probability of each branch is above 94.9%. Eleven reliable positive selection sites were detected in the branched-site model, indicating that the rbcL protein-coding gene of Galdieria underwent adaptive evolution to adapt to extreme environments. Site 269 F is located in the loop 6 domain, while sites 272 D and 273 W are located in the 6-helix structure. Many coevolution pairs were detected, which were closely related to the hydrophobic and molecular weight correlation values of amino acids. The results are helpful to research the evolution process of freshwater red algae, to explore the changes of its essential genes and protein functions to adapt to different environmental pressures, and to understand the close relationship between amino acids in proteins and the molecular mechanism of evolution.

Harvesting biomass of an oil-rich microalga Parachlorella kessleri TY02 by ferric chloride: Effects on harvesting efficiency, lipid production and municipal wastewater treatment.

Inorganic coagulants have been widely used to harvest microalgal biomass. A great deal of attention has been mainly focused on the response of harvesting efficiency, lipid production and feasibility of the reuse of medium to inorganic coagulants. The physiological state of harvested cells and feasibility of wastewater treatment remain unclear. In this context, the effect of ferric chloride as a conventional inorganic coagulant on the harvesting efficiency, physiological state and lipid content of an oil-rich microalga Parachlorella kessleri TY02 was evaluated. Moreover, the performance of harvested cells for municipal wastewater treatment was also evaluated. When the dosage of iron ions was 0.077 mg/mg dry biomass and the sedimentation time was 5 min, the microalga had good harvesting efficiency and cell viability. As the dosage of iron ions was up to 0.15 mg/mg dry biomass, cell viability notably decreased. Cells harvested by 0.077 and 0.15 mg/mg dry biomass of iron ions showed good wastewater treatment efficiency. It was also found that long sedimentation time (40 min) not only did not promote harvesting efficiency, but also reduced cell viability. Iron ions had no notable effect on lipid content of the microalga. Through comprehensive evaluation of harvesting efficiency, lipid production, physiological state and wastewater treatment efficiency, it indicated that 0.077 mg/mg dry biomass of iron ions could be used to harvest biomass of the microalga.

Comparison of the transcriptomes of different life history stages of the freshwater Rhodophyte Thorea hispida.

Thorea hispida exclusively inhabits freshwater environments and is characterized by a triphasic life history. In this study, the organelle genomes and transcriptomes of different life history stages of T. hispida were examined using next generation sequencing. The chloroplast and mitochondrial genomes of the chantransia stage were 175,747 and 25,411 bp in length, respectively. The chantransia stage was highly similar to the gametophyte stage based on comparisons of organelle genomes and phylogenetic reconstruction. Transcriptomic comparisons of two stages found that ribosome-related genes were the most up-regulated in the gametophyte stage of T. hispida. Seven meiosis-specific genes, including SPO11 initiator of meiotic double-stranded breaks(spo11), meiotic nuclear divisions 1(mnd1), RAD51 recombinase(rad51), mutS homolog 4(msh4), mutS homolog 5(msh5), REC8 meiotic recombination protein(rec8), and DNA helicase Mer3(mer3), were differentially regulated between the two life history stages. The organelle genomes and transcriptomes from T. hispida provided in this study will be valuable for future studies of freshwater red algae.

Spatio-temporal variation and risk assessment of hydrochemical indices in a large diversion project of the Yellow River, northern China, from 2008 to 2017.

Large-scale, inter-basin water diversion projects have been developed to relieve water scarcity crisis and water pollution problems. Environmental status and ecosystem impacts are largely unknown for the Wanjiazhai Yellow River Diversion Project (YRDP-WJZ), a water body critical in northern China. In the current study, twelve hydrochemical indices (including Mn, Cu, Zn, Hg, Pb, NH3-N, COD-Mn, DO, BOD5, COD, TP, and TN) were collected from 2008 to 2017 based on multiple analytical approaches to understand environmental status and ecological risks. Human health risk and threats to aquatic organisms from heavy metals were assessed. Heavy metals have no regular spatial distribution. Biochemical parameters and nutrients pollute seriously in midstream and downstream, respectively. Hydrochemical indices suggested high levels of pollution in the midstream section. Water quality improved downstream of the Fenhe Reservoir, but total nitrogen and total phosphorus in the downstream section increased in recent years. The Canadian Council of Ministers of the Environment Water Quality Index (CWQI) suggested midstream water quality was poor in general, and 80% of annual calculations had a marginal grade. For aquatic organisms, ecological risks of Cu and Zn were high. For local residents, drinking water was generally safe, but continued monitoring is critical due to ongoing threats to water quality in these areas.

Effects of Different Environmental Factors on the Growth and Bioactive Substance Accumulation of Porphyridium purpureum.

Genus Porphyridium is a primitive single-celled red algae widely distributed in seawater, freshwater, and moist soil. It can synthesize bioactive substances such as phycoerythrin, extracellular polysaccharides and polyunsaturated fatty acids during the growth process. In this paper, the culture and bioactive substance yield of Porphyridium purpureum were studied by setting salinity, nitrogen-to-phosphorus ratio, and pH at different gradient levels. The results showed that the optimal conditions for the growth of P. purpureum were salinity 34 ppt, nitrogen-to-phosphorus ratio 169:1, and pH 8; the optimal conditions for obtaining the polysaccharides were salinity 17 ppt, nitrogen-to-phosphorus ratio 14:1, and pH 8; the optimal conditions for obtaining phycoerythrin were salinity 17 ppt, nitrogen-to-phosphorus ratio 68:1, and pH 8; the optimal conditions for obtaining the lipids were salinity 34 ppt, nitrogen-to-phosphorus ratio 1:1, and pH 8. In actual production applications, culture conditions should be set according to different product accumulation purposes in order to achieve the optimal production efficiency.

The spatiotemporal contribution of the phytoplankton community and environmental variables to the carbon sequestration potential in an urban river.

The phytoplankton (internal driving forces) and environmental variables that affect complex biochemical reactions (external driving forces) play an important role in regulating photosynthetic carbon fixation. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) exists in various phytoplankton species and is an important enzyme in the photosynthetic process. To investigate the phytoplankton composition (internal driving forces), we selected the functional gene of the Rubisco large subunit (rbcL) as the target gene for this study. Phytoplankton gross primary productivity was measured using light and dark biological oxygen demand bottles to assess the carbon sequestration potential. The fundamental environmental indicators were determined to analyze the mechanisms that drive the carbon fixation process. The correlation results indicated that green algae were only controlled by nitrate, and that diatoms were positively correlated with phosphate. The cluster analysis results demonstrated that nitrite was the major driver controlling phytoplankton primary productivity. During the wet seasons (spring and summer), the contribution of the planktonic community respiration to the carbon sequestration potential was higher than net primary productivity (NPP), followed by dissolved organic carbon and nitrate. During the dry season (autumn), NPP, total nitrogen, and nitrite ranked highest in terms of carbon sequestration potential. The contributions of green algae and diatoms to the carbon sequestration potential were temporally higher than those of cyanobacteria. The maximum carbon sequestration potential occurred during autumn because of diatom production and the function of phosphate, whereas the minimum carbon sequestration potential occurred in summer. Spatially, the upstream carbon sequestration potential was higher compared with downstream because of the effect (contribution) of cyanobacteria (Phormidium), diatoms (Surirella solea and Thalassiosira pseudonana), and environmental variable (nitrite). These findings provide a better understanding of the underlying mechanisms of phytoplankton productivity and the influences of environmental variables on carbon sequestration in urban river ecosystems.