Effects of Flood on Phytoplankton Diversity and Community Structure in Floodplain Lakes Connected to the Yangtze River

Although the Mississippi-Atchafalaya River system exports large amounts of nutrients to the Northern Gulf of Mexico annually, nutrient limitation of primary productivity still occurs offshore, acting as one of the major factors controlling local phytoplankton biomass and community structure. Bioassays were conducted for 48 hrs at two stations adjacent to the river plumes in April and August 2012. High Performance of Liquid Chromatography (HPLC) combined with ChemTax and a Fluorescence Induction and Relaxation (FIRe) system were combined to observe changes in the phytoplankton community structure and photosynthetic activity. Major fluorescence parameters (Fo, Fv/Fm) performed well to reveal the stimulating effect of the treatments with nitrogen (N-nitrate) and with nitrogen plus phosphate (+NPi). HPLC/ChemTax results showed that phytoplankton community structure shifted with nitrate addition: we observed an increase in the proportion of diatoms and prasinophytes and a decrease in cyanobacteria and prymnesiophytes. These findings are consistent with predictions from trait-based analysis which predict that phytoplankton groups with high maximum growth rates (μmax) and high nutrient uptake rates (Vmax) readily take advantage of the addition of limiting nutrients. Changes in phytoplankton community structure, if persistent, could trigger changes of particular organic matter fluxes and alter the micro-food web cycles and bottom oxygen consumption.

Phytoplankton abundance, community structure and diversity in the eutrophicated Orbetello lagoon (Tuscany) from 1995 to 2001

BackgroundEutrophication of freshwater systems can result in blooms of phytoplankton, in many cases cyanobacteria. This can lead to shifts in structure and functions of phytoplankton communities adversely affecting the quality of drinking water sources, which in turn impairs public health. Relationships between structures of phytoplankton communities and concentrations of the toxicant, microcystin–leucine–arginine (MC-LR), have not been well examined in large shallow lakes. The present study investigated phytoplankton communities at seven locations from January to December of 2015 in Tai Lake, and relationships between structures and diversities of phytoplankton communities and water quality parameters, including concentrations of MC-LR and metals, were analyzed.ResultsA total of 124 taxa of phytoplankton were observed, and the predominant taxa were Microcystis sp. and Dolichospermum flos-aquae of Cyanophyta and Planctonema sp. of Chlorophyta. The greatest diversities of phytoplankton communities, as indicated by species richness, Simpson, Shannon–Wiener, the Berger and Parker, and the Pielou evenness indices, were observed in spring. Furthermore, productivity of phytoplankton was significantly and negatively correlated with diversities. These results demonstrated that Simpson, Shannon–Wiener, the Berger and Parker, and the Pielou evenness indices of phytoplankton communities were significantly related to trophic status and overall primary productivity in Tai Lake. In addition, temperature of surface water, pH, permanganate index, biochemical oxygen demand, total phosphorus, arsenic, total nitrogen/total phosphorous ratio, and MC-LR were the main factors associated with structures of phytoplankton communities in Tai Lake.ConclusionThe present study provided helpful information on phytoplankton community structure and diversity in Tai Lake from January to December of 2015. Our findings demonstrated that Simpson, Shannon–Wiener, the Berger and Parker, and the Pielou evenness indices could be used to assess and monitor for status and trends in water quality of Tai Lake. In addition, MC-LR was one of the main factors associated with structures of phytoplankton communities in Tai Lake. The findings may help to address important ecological questions about the impact of a changing environment on biodiversity of lake ecosystems and the control of algae bloom. Further studies are needed to explore the relationship between MC-LR and phytoplankton communities in the laboratory.

This study investigates the dynamics of phytoplankton communities and nitrogen uptake in the Indian sector of the Southern Ocean during spring and summer. The study area is oligotrophic (Chl a stocks <50 mg m−2); nevertheless, a large spatial variation of phytoplankton biomass and community structure was observed. During both seasons the phytoplankton community in the seasonal ice zone showed higher biomasses and was mainly composed of large diatom cells. However, in the permanently open ocean zone the community had low biomass and was chiefly composed of nano- and picoflagellates. In the polar front zone, although biomass was higher, the community structure was similar to the open ocean zone. The results suggest that the variation in phytoplankton community structure on a larger scale resonates with gradients in water column stability and nutrient distribution. However, significant changes in biomass and nutrient stocks but little change in community structure were observed. Absolute nitrogen uptake rates were generally low, but their seasonal variations were highly significant. During spring the communities displayed high specific nitrate uptake (mean rate = 0.0048 h−1), and diatoms (in the seasonal ice zone) as well as nano- and picoflagellates (in the permanently open ocean zone and polar front zone) were mainly based on new production (mean ƒ-ratio = 0.69). The transition to summer was accompanied by a significant reduction in nitrate uptake rate (0.0048 h−1 → 0.0011 h−1) and a shift from predominantly new to regenerated production (ƒ-ratio 0.69 → 0.39). Ammonium played a major role in the seasonal dynamics of phytoplankton nutrition. The results emphasize that, despite a large contrast in community structure, the seasonal dynamics of the nitrogen uptake regime and phytoplankton community structure in all three subsystems were similar. Additionally, this study supports our previous conclusion that the seasonal shift in nitrogen uptake regime can occur with, as well as without, marked changes in community structure.

Dimethyl sulfide (DMS), primarily produced by marine organisms, contributes significantly to sulfate aerosol loading over the ocean after being oxidized in the atmosphere. In addition to exerting a direct radiative effect, the resulting aerosol particles act as cloud condensation nuclei, modulating cloud properties and extent, with impacts on atmospheric radiative transfer and climate. Thus, changes in pelagic ecosystems, such as phytoplankton physiology and community structure, may influence organosulfur production, and subsequently affect climate via the sulfur cycle. A fully coupled Earth system model, including explicit marine ecosystems and the sulfur cycle, is used here to investigate the impacts of changes associated with individual phytoplankton groups on DMS emissions and climate. Simulations show that changes in phytoplankton community structure, DMS production efficiency, and interactions of multielement biogeochemical cycles can all lead to significant differences in DMS transfer to the atmosphere. Subsequent changes in sulfate aerosol burden, cloud condensation nuclei number, and radiative effect are examined. We find the global annual mean cloud radiative effect shifts up to 0.21 W/m2, and the mean surface temperature increases up to 0.1 °C due to DMS production changes associated with individual phytoplankton group in simulations with radiative effects at the 2,100 levels under an 8.5 scenario. However, changes in DMS emissions, radiative effect, and surface temperature are more intensive on regional scales. Hence, we speculate that major uncertainties associated with future marine sulfur cycling will involve strong region‐to‐region climate shifts. Further understanding of marine ecosystems and the relevant phytoplankton‐aerosol‐climate linkage are needed for improving climate projections.

Inter-annual variability in the phytoplankton abundance and community structure of a tropical monsoonal estuary in response to variable monsoonal patterns

Temperature driving vertical stratification regulates phytoplankton community structure in the Bohai Sea and Yellow Sea

Phytoplankton communities play a significant role in the oceanic biological pump by forming the base of the trophic structure. Increase in nutrients loading affects spatial and temporal distribution of phytoplankton. This study examined the phytoplankton community structure and ecological indices in relation to nutrients dynamics in both estuarine and oceanic areas of Ramisi-Vanga systems along the Kenyan coast. Surface water samples were collected and analysed for nutrients (PO 4 3- -P, NO 3 - -N and NH 4 + -N) and phytoplankton abundance and community structure. This study reported very diverse phytoplankton community structure consisting of 88 taxa that were dominated by Chaetoceros sp., Coscinodiscus sp., Nitzschia sp., Pseudo-nitzschia sp., Alexandrium sp., Protoperidium sp. and Prorocentrum sp that are among the potentially harmful algae. Diatoms were the most abundant taxa in Ramisi-Vanga system. Phytoplankton abundance was found to be higher in the estuarine systems (1182.06±149.14 cells/L) as compared to the oceanic systems (551.99±166.70 cells/L) with high abundance observed in May for oceanic and estuarine systems. Shannon Weiner's species diversity index was greater than 2 in both oceanic and estuarine systems. Phytoplankton species' abundance, composition and diversity were found to be influenced by the availability of NH 4 + -N, NO 3 - -N and PO 4 3- -P. Phytoplankton cell density was below 4000 cells/ L, thus, this study has classified Ramisi-Vanga system as an oligotrophic system implying that the current level of land based activities are not having significant impacts on the phytoplankton communities.

The aquatic ecosystem is the ultimate sink for consumer and industrial waste discharge that contains nanometals such as titanium dioxide nanoparticle (n-TiO2). In this environment, nutrient availability and nanometals influence phytoplankton community structure and function. In a mesocosm experiment, we evaluated the interactive effect of n-TiO2 (48 mg L−1) and two nitrogen (N) levels (limited, LN; and replete, HN) on the phytoplankton community structure (biomass, species diversity and richness, algal species divisions), biochemical composition (carbohydrates, proteins, and lipids), and antioxidant response (peroxidase activity, POD). n-TiO2 decreased total phytoplankton biomass, and its combination with HN led to the highest decrease. Species diversity was not affected by N level, n-TiO2, and their interaction, while species richness decreased in combined n-TiO2 and HN treatment. All these recorded effects of n-TiO2 on the phytoplankton community structure were enhanced by increasing temperature over time. LN initially reduced phytoplankton carbohydrate content but increased by the presence of n-TiO2 and its interaction with N levels. Total protein and lipid content were not affected by n-TiO2 or its interaction with N levels. POD activity was increased by the interaction between n-TiO2 and the N levels tested. Our results indicate that the influence of n-TiO2 on the phytoplankton community was dependent on the concentration of N. Also, phytoplankton carbohydrate content and community structure varied with increasing water temperature. A few species thrived concerning biomass during exposure to the LN + n-TiO2 (Scenedesmus quadricauda, Coelastrum reticulum, and Microcystis sp.) and HN + n-TiO2 (Microcystis sp.) treatments. Members of the Chlorophyta were generally susceptible to the presence of n-TiO2 regardless of the N level. Thus, the presence of n-TiO2 in aquatic ecosystems can alter phytoplankton community structure and dynamics.

Freshwater phytoplankton communities are currently experiencing multiple global change stressors, including increasing frequency and intensity of storms. An important mechanism by which storms affect lake and reservoir phytoplankton is by altering the water column's thermal structure (e.g., changes to thermocline depth). However, little is known about the effects of intermittent thermocline deepening on phytoplankton community vertical distribution and composition or the consistency of phytoplankton responses to varying frequency of these disturbances over multiple years. We conducted whole‐ecosystem thermocline deepening manipulations in a small reservoir. We used an epilimnetic mixing system to experimentally deepen the thermocline via five short (24–72 hr) mixing events across two summers, inducing potential responses to storms. For comparison, we did not manipulate thermocline depth in two succeeding summers. We collected weekly depth profiles of water temperature, light, nutrients, and phytoplankton biomass as well as bottle samples to assess phytoplankton community composition. We then used time‐series analysis and multivariate ordination to assess the effects of intermittent thermocline deepening due to both our experimental manipulations and naturally occurring storms on phytoplankton community structure. We observed inter‐annual and intra‐annual variability in phytoplankton community response to thermocline deepening. We found that peak phytoplankton biomass was significantly deeper in years with a higher frequency of thermocline deepening events (i.e., years with both manipulations and natural storms) due to altered thermal stratification and more variable depth distributions of soluble reactive phosphorus. Furthermore, we found that the depth of peak phytoplankton biomass was linked to phytoplankton community composition, with certain taxa being associated with deep or shallow biomass peaks, often according to functional traits such as optimal growth temperature, mixotrophy, and low‐light tolerance. For example, Cryptomonas taxa, which are low‐light tolerant and mixotrophic, were associated with deep peaks, while the cyanobacterial taxon Dolichospermum was associated with shallow peaks. Our results demonstrate that abrupt thermocline deepening due to water column mixing affects both phytoplankton depth distribution and community structure via alteration of physical and chemical gradients. In addition, our work supports previous research that phytoplankton depth distributions are related to phytoplankton community composition at inter‐annual and intra‐annual timescales. Variability in the inter‐annual and intra‐annual responses of phytoplankton to abrupt thermocline deepening indicates that antecedent conditions and the seasonal timing of surface water mixing may mediate these responses. Our findings emphasise that phytoplankton depth distributions are sensitive to global change stressors and effects on depth distributions should be taken into account when predicting phytoplankton responses to increased storms under global change.

Nitrogen uptake regime and phytoplankton community structure in the Atlantic and Indian sectors of the Southern Ocean

The spatial distribution of environmental factors, chlorophyll a (Chla), phytoplankton abundance, and community structure in the Laizhou Bay were investigated in August 2018 (wet season after pollution control) to clarify the effects of the pollution control of the Xiaoqing River, which is a major source of pollution, on environmental factors and phytoplankton community structure in this area. The results showed that the environmental factors changed significantly after pollution control of the Xiaoqing River. The concentrations of dissolved inorganic nitrogen (DIN), dissolved inorganic silicon (DSi), NO3-, and NO2- decreased significantly, with values only 40.1% to 60.4% of those from the same period of in 2017 (the nearest year before the pollution control), whereas dissolved inorganic phosphorus (DIP) and NH4 increased by 2.5 and 1.4 times that of their concentrations in 2017. The spatial distribution of environmental factors changed significantly, with the nutrient concentrations around the Xiaoqing River estuary noticeably decreasing. The abundance of phytoplankton cells was 21.5×106 cell·m-3, which was close to the results of a previous study, whereas the ρ(Chla) was 2.43 μg·L-1, which decreased obviously. Both microscopic analysis and pigment taxonomy suggested that phytoplankton community structure in the Laizhou Bay changed clearly, with the dominant community shifting from diatoms alone to the co-dominance of diatoms and cyanobacteria. Chaetoceros curvisetus, Skeletonema costatum, and Cerataulina pelagica, which were commonly observed in the Laizhou Bay before pollution control of the Xiaoqing River, decreased in 2018, whereas the abundance of common dominant freshwater species (e.g., Merismopedia sp. and Synedra spp.) increased significantly. Redundancy analysis (RDA) showed that the phytoplankton community was significantly related to nitrogen, phosphate (negative correlation), and salinity (negative correlation) after pollution control of the Xiaoqing River, indicating that the variation in nutrient concentration and the structure of river runoff input may be the main factors affecting phytoplankton community and dominant species structure.

松花江哈尔滨段浮游植物群落格局及其与环境因子的相关性

Phytoplankton community structure is influenced by seabird guano enrichment in the Southern Ocean

Short-term variability of the phytoplankton community in coastal ecosystem in response to physical and chemical conditions' changes