Spatiotemporal dynamics of phytoplankton biomass and community succession for driving factors in a meso-eutrophic lake

Different responses of phytoplankton taxa to water N and P inputs in a freshwater wetland: A mesocosm study

The intensification of human activities has led to a large amount of nitrogen (N) and phosphorus (P) inputs into water, resulting in an increase in nutrient load and an imbalance of N and P stoichiometric ratio in wetlands. However, whether and how water eutrophication influences phytoplankton diversity, community composition, and biomass remain largely unclear. As part of a two-year (2022-2023) field experiment, this study was conducted to examine the effects of N and P inputs on phytoplankton community in a freshwater wetland in the North China Plain. The results showed that N and P inputs did not change the Shannon-Wiener or Evenness indices of phytoplankton community, but increased phytoplankton biomass by 30 % and 62 %, respectively. In addition, N input enhanced the biomass of non-dominant taxa (e.g., Cryptomonas, Chrysophyta, Dinoflagellates, and Euglena) by two-fold, likely due to the inhibited growth of submerged macrophytes and thus the increased water temperature. In contrast, P input increased the biomass of dominant taxa (e.g., Cyanobacteria, Bacillariophyta, and Chlorophyta) by 116 %, which was primarily attributed to the elevated water pH and reduced light intensity. Moreover, the enhanced phytoplankton biomass under water eutrophication positively contributed to the water-air interface methane (CH4) emissions in this study, suggesting an important role of phytoplankton in regulating wetland C cycling. Our findings indicate the differentially regulatory mechanisms of N and P inputs on the structure and biomass of phytoplankton community, and can provide more insights for protecting and managing wetland ecosystems under water eutrophication.

Bacterially mediated phosphorus cycling favors resource use efficiency of phytoplankton communities in a eutrophic plateau lake

Resource use efficiency has garnered much attention globally owing to its linkage with phytoplankton growth and extinction. However, little is known about how microbially mediated phosphorus (P) cycling affects phytoplankton P resource use efficiency (RUEP), especially in eutrophic plateau lakes. Here, we studied the vertical relationship between bacterial communities and phytoplankton RUEP in water profiles from Hongfeng Lake, a eutrophic lake located in the Guizhou Plateau, and further revealed the influence of bacterially mediated endogenous P release on phytoplankton RUEP. Generally, phytoplankton RUEP increased slightly and then decreased toward deep water layers. Compared to dormancy and recovery periods, outbreak period showed higher RUEP in water profiles and bottom waters. The importance of phytoplankton RUEP in the co-occurrence networks progressively increased from dormancy to outbreak periods. Rhodococcus may affect phytoplankton RUEP in water profiles by dissolving Ca-P or polymerizing excess phosphate. Functional composition of P-related genes was largely affected by NH4Cl-Po, BD-TP and BD-Pi in recovery period, and by NaOH-Po in outbreak period. During phytoplankton growth, bacterial P functional genes promote phytoplankton RUEP mainly by regulating Pi solubilization and Po mineralization in surface sediments. Note that ppk could regulate the formation of polyphosphates and thus reduce phytoplankton RUEP. Taken together, our study revealed the relationship between bacterially mediated P cycling and phytoplankton RUEP, which can effectively monitor the potential risk of phytoplankton blooms and improve eutrophication management.

Changing Patterns and Driving Factors of Plankton Coupling Relationships in Lakes around the Yangtze River, China

In recent decades, cyanobacterial blooms have intensified in many lakes in China. Algal blooms are closely linked to the predation pressure on phytoplankton, but the changes in the relationship between phytoplankton and their primary predators, zooplankton, remain unclear. To investigate the changing patterns and driving factors of the relationship between plankton, the historical data of plankton from 14 typical freshwater lakes around the Yangtze River were collected from multiple databases. By comparing the structure of plankton communities in typical lakes between the 1990s and the 2010s, it was found that the phytoplankton density was elevated in 79% of all the lakes; on average, it had increased to 3156 times higher than it had been. In contrast, the zooplankton density was elevated in only 57% of these lakes, and this value was only two times higher than it had been. In 11 out of the 14 lakes, the zooplankton density growth rate was lower than that of the phytoplankton. The percentage of cyanobacteria in these lakes increased from 53% to 62%, and the changes in cyanobacteria were significantly negatively correlated with the changes in zooplankton. Eutrophication caused this significant increase in phytoplankton, especially cyanobacteria. Cyanobacterialization, changes in fish community structures, biological invasion, and river-lake relationships impede zooplankton survival. This combination of factors hinders plankton coupling in many lakes. This study attempts to provide new insights for lake ecological management.

Marine coastal chemistry related to inland inputs in San Jorge gulf and the adjacent north coast

Coastal regions are sectors where human activities impact the marine ecosystem, and if necessary control measures are not taken, they can generate negative consequences for health and ecosystem services. Within the framework of the Pampa Azul initiative and under the One Health paradigm, the interconnection between the terrestrial and marine environments of the San Jorge Gulf and the adjacent north coast has been studied. In November, 2022, a campaign was carried out aboard the R/V "Mar Argentino" at thirty-four stations near the coast. There, for the first time, simultaneously with in-situ measurements of physical variables, macronutrients (NO3-, PO4-3, Si(OH)4 and NH4+), particulate silica (BSi and LSi), trace metals in the particulate material (Cd, Cu, Cr, Fe and Pb) and the phytoplankton community were analyzed. The results showed a high nutrient dynamic, with a significant influence of natural stratification and anthropogenic condition due to the discharge of effluents off the cities of Comodoro Rivadavia and Caleta Olivia. Under natural conditions, NO3- and Si(OH)4 limited the surface primary production by 47 % and 41 %, respectively. Additionally, due to the anthropogenic contribution, NH4+ concentration reached 3 μM, increasing the proliferation of nanophytoplankton, among other consequences. As a result of nutrient dynamics, the uptake of Si(OH)4, the growth rate of diatoms and their production of BSi were decoupled. Furthermore, a significant correlation between LSi and Fe in particulate matter was evidenced, opening new lines of research that relate dust storms to primary productivity in this marine environment. The measured concentrations of trace metals do not appear to be a biological risk; however, contamination by Cd (37.6 μg g- 1 d.w.) and Cu (214.97 μg g- 1 d.w.) off Camarones poses a significant concern that must be addressed in the immediate future.

Dependence of evolution of Cyanobacteria superiority on temperature and nutrient use efficiency in a meso-eutrophic plateau lake

Algal blooms in lakes have been a challenging environmental issue globally under the dual influence of human activity and climate change. Considerable progress has been made in the study of phytoplankton dynamics in lakes; The long-term in situ evolution of dominant bloom-forming cyanobacteria in meso-eutrophic plateau lakes, however, lacks systematic research. Here, the monthly parameters from 12 sampling sites during the period of 1997-2022 were utilized to investigate the underlying mechanisms driving the superiority of bloom-forming cyanobacteria in Erhai, a representative meso-eutrophic plateau lake. The findings indicate that global warming will intensify the risk of cynaobacteria blooms, prolong Microcystis blooms in autumn to winter or even into the following year, and increase the superiority of filamentous Planktothrix and Cylindrospermum in summer and autumn. High RUETN (1.52 Biomass/TN, 0.95-3.04 times higher than other species) under N limitation (TN < 0.5 mg/L, TN/TP < 22.6) in the meso-eutrophic Lake Erhai facilitates the superiority of Dolichospermum. High RUETP (43.8 Biomass/TP, 2.1-10.2 times higher than others) in TP of 0.03-0.05 mg/L promotes the superiority of Planktothrix and Cylindrospermum. We provided a novel insight into the formation of Planktothrix and Cylindrospermum superiority in meso-eutrophic plateau lake with low TP (0.005-0.07 mg/L), which is mainly influenced by warming, high RUETP and their vertical migration characteristics. Therefore, we posit that although the obvious improvement of lake water quality is not directly proportional to the control efficacy of cyanobacterial blooms, the evolutionary shift in cyanobacteria population structure from Microcystis, which thrives under high nitrogen and phosphorus conditions, to filamentous cyanobacteria adapted to low nitrogen and phosphorus levels may serve as a significant indicator of water quality amelioration. Therefore, we suggest that the risk of filamentous cyanobacteria blooms in the meso-eutrophic plateau lake should be given attention, particularly in light of improving water quality and global warming, to ensure drinking water safety.

The dynamic changes in phytoplankton and environmental factors within Dongping Lake (China) before and after the South-to-North Water Diversion Project

Dongping Lake is one of the most important regulation and storage lakes along the eastern route of the South-to-North Water Diversion Project in China, the water quality condition of which directly influences the safety of water diverting, because it serves as a Yangtze River water redistribution control point. However, the changes in algae, and in environmental factors affecting their community structures, before and after the water diversion project are rarely reported. In this study, the temporal variations of phytoplankton abundance were examined based on monthly samples collected at three stations from May 2010 to April 2022. The total abundance of algae greatly decreased after the water diversion project was implemented, with a relatively stable biodiversity and evenness before and after the water translocation. Multiple statistical methods were used together with the water quality indices (WQIs) and the nutrient status index (TSIM) to evaluate overall water condition and analyse relationships among environmental factors. The WQIs demonstrated a general "Good" water quality with a seasonal differentiation, and that water conditions during water transfer periods were better than during non-water transfer periods, which may be ascribed to the improved hydraulic conditions and purified water environment during water transfer periods. Redundancy analysis showed that water temperature, ammonia nitrogen, water transparency, and total phosphorus were the most important environmental factors, with relatively decreased contribution rates towards phytoplankton communities after the water translocation. Importantly, some dominant phytoplankton genera of Chlorophyta, Bacillariophyceae, and Cyanophyceae were similarly affected by water transparency, and nitrogen and phosphorus nutrients in summer after the water translocation. These research findings helped us gain a comprehensive understanding of the changing patterns of water quality and microalgae and their relationships before and after the water diversion project, providing a guidance for future lake management in regulating hydraulic conditions and improving water quality of Dongping Lake.

Spatial and temporal patterns of phytoplankton community succession and characteristics of realized niches in Lake Taihu, China

Understanding the dynamics and succession of phytoplankton in large lakes can help inform future lake management. The study analyzed phytoplankton community variations in Lake Taihu over a 21-year period, focusing on realized niches and their impact on succession. The study developed a niche periodic table with 32 niches, revealing responses to environmental factors and the optimal number of niches. Results showed that the phytoplankton in Lake Taihu showed significant spatial and temporal heterogeneity, with biomass decreasing as one moved from the northwest to the southeast and expanding towards central lake area, and towards autumn and winter. Different phytoplankton groups in Lake Taihu occupied realized niches shaped by temperature, nitrate, and phosphate. To predict the response of eutrophic freshwater lake ecosystems to human activities and climate change, it is critical to interpret the law of phytoplankton bloom and niche succession.