Proliferation Of Phytoplankton Research Articles

Phytoplankton morphological traits and biomass outline community dynamics in a coastal ecosystem (Gulf of Trieste, Adriatic Sea)

AbstractTrait-based ecology has recently gained increasing importance in phytoplankton research. In particular, the taxonomic and morphological traits, such as size and shape of phytoplankton cells, can help to unveil the ecological processes and their drivers in the pelagic domain. Our study aims to shed light on the trophodynamics of phytoplankton communities in a coastal ecosystem in the northern Adriatic Sea (Gulf of Trieste) using data on individual traits such as biomass, size and shape of phytoplankton taxa during a one-year study. The phytoplankton parameters were investigated at the levels of the whole community, groups, and individual cells, analysing also the probability distributions of biomass and size of the latter level. The results showed good agreement between abundance and biomass data, as well as individual size and biomass with differences partly explained by cell shapes. We have emphasized the role of the local freshwater source in bottom-up control, alternating with top-down control of phytoplankton dynamics through taxonomic and morphological diversity. The predominant bimodal and non-power law distribution, especially during and around the biomass peaks, confirmed the importance of nano- and microphytoplankton size classes and the role of blooms in destabilizing the trophic webs. We suggest that the analyses of distribution types of individual cell size and biomass can be appropriate to spot ecological processes driving to unconstrained phytoplankton proliferation or to periods of trophic web stability.

Phosphorus inactivation mitigates the effect of warm winters in a temperate shallow lake (Mielenko Lake, Poland)

Direct and indirect anthropopressure on water ecosystems is the serious problem throughout the world.. In the Northern Hemisphere, an increase in average air temperatures is observed, which implies the occurrence of a shorter period of snow and ice cover during the winter season. The winter 2019/2020 was unusual, because that was the first time in the record, that a complete lack of permanent ice cover was observed on numerous lakes in Poland. Such unusual conditions could influence lake functioning. Hence we analyzed the chemistry of the water–sediment interface (near-bottom and interstitial water and sediment) in the shallow, eutrophic Mielenko Lake (area 7.9 ha, max depth 1.9 m) in 2013 and 2019–2022 period to assess the influence of prolonged water circulation on the bottom zone. Mielenko Lake was subjected to a phosphorus inactivation procedure using Al and Fe salts (PAX 18, PIX 111) in 2020 and 2021. Our research revealed that unusually prolonged winter circulation caused a significant decrease in organic matter content in bottom sediment in 2020, as well as a decrease in NaOH-nrP fraction and TP amounts. That effect was short-term and it did not significantly influence the NaOH-rP fraction amounts. The released P was probably built in macrophytes biomass during vegetation season, because P inactivation has been limiting phytoplankton proliferation, and it favored shifting to a clearwater state with macrophytes domination. This was confirmed by decreasing in phytoplankton biomass, and a massive expansion of the macrophytes range noted in the second year of restoration. Our study shows, that P inactivation could mitigate the negative effects of warm winters in shallow lakes.

Response of chlorophyll-a to rainfall event in the basin of the South China sea: Statistical analysis

Chlorophyll-a (Chl-a) is an essential ecological indicator, and affected by processes such as typhoons, mesoscale eddies, and Rossby waves. However, the impact of more frequent and widespread precipitation events on Chl-a seems to be overlooked. This study utilized remote sensing data and reanalysis data to investigate the response of Chl-a to 240 precipitation events in the central South China Sea from 2005 to 2019. The results indicate that precipitation events have a significant impact on Chl-a concentration. Following a precipitation event in 2019, the Chl-a concentration in the affected area increased by approximately 0.22 mg m−³ from the 3rd to the 7th day. The reasons for the increase in Chl-a concentration were the vertical mixing induced by wind stirring and the upwelling caused by wind stress curl, which transported nutrients to the euphotic zone, lowering the sea surface temperature and triggering a proliferation of phytoplankton. Additionally, dissolved nutrients in precipitation provided a nutrient source for Chl-a growth. The contributions of nutrient supply, wind speed, and wind stress curl to the increase in Chl-a concentration during precipitation events were 18%, 37%, and 45%, respectively. Precipitation events enhanced marine primary productivity, playing a crucial role in deepening our understanding of ocean-atmosphere interactions and their impact on marine ecosystem.

Qualitative Model of the Causal Interactions between Phytoplankton, Zooplankton, and Environmental Factors in the Romanian Black Sea

In order to analyze how environmental factors affect planktonic organisms along the Romanian Black Sea coast, this study created semi-quantitative models of the causal relationships between phytoplankton, zooplankton, and physicochemical parameters by utilizing user-friendly modeling tools. Eleven years of time-series data (March–September 2008–2018) were used to investigate the relationships between phytoplankton, zooplankton, and environmental factors (such as temperature, salinity, and nutrients). Variables such as marine reporting units and phytoplankton species and classes were used to identify developmental patterns, utilizing the Mental Modeler platform to consider interactions between the physicochemical parameters and phytoplankton, phytoplankton and zooplankton, and zooplankton and physicochemical parameters. Although the increase in the overall number of elements and linkages was uncertain in waters with variable salinity compared to marine ones, the semi-quantitative models created for the three marine reporting units along the Romanian Black Sea coast were comparable in terms of complexity. Across the typical and examined types of phytoplankton proliferation (normal, abundant, and blooms), the number of components and connections in the case of phytoplankton blooms substantially decreased as species- and growth-promoting variables increased.

Impacts of Harmful Algal Blooms (HABs) on Agriculture: A Short Communication

agriculture, which requires clean water, healthy soil, and adequate nutrients, is crucial to meet the growing demand for food and fiber. Over application of nutrients to meet demand has degraded surface water quality, leading to accelerated eutrophication. Cultural eutrophication is a process by which aquatic ecosystems such as ponds, lakes, and estuaries become so enriched with nutrients—primarily nitrogen and phosphorus—as to become unusable for safe consumption and ecological purposes. Eutrophication has intensified due to climate change. Increased temperatures, intense storms, and drought can drive the formation of eutrophic and hypereutrophic conditions. Hypereutrophication results in the rapid proliferation of algae and phytoplankton, resulting in algal blooms. Harmful algal blooms (HABs), including the proliferation of cyanobacteria, which can produce cyanotoxins such as microcystins and cylindrospermopsin, can also grow in hypereutrophic conditions. These toxins can detrimentally impact humans, wildlife, and agricultural systems (e.g., fish, livestock, and crops). Fish that ingest algal toxins may suffer from liver damage and oxidative stress, with varying effects depending on the type of fish, the amount of exposure, and the duration of exposure to toxins. Additionally, a few studies report livestock death after drinking water contaminated with byproducts of HABs such as microcystin, nodularin, cylindrospermopsin, anatoxin-a, guanitoxin, and saxitoxin. The available research on the effects of microcystin on crops, vegetables, and fruits consistently demonstrates their negative impact. This short communication article summarizes the literature published between 2012 and 2022 documenting the impact of microcystins on agricultural commodities, particularly livestock and various crops. Although awareness has increased, few publications have discussed microcystin-related livestock deaths in recent years. However, numerous global studies have highlighted the harmful effects of microcystins on crops, fruits, and vegetables. The researchers suggest that in cases where the levels of microcystin exceed the standards established by the World Health Organization, careful monitoring is needed. Human exposure to microcystin may occur through the consumption of livestock, crops, and vegetables contaminated by microcystins through drinking or irrigation. More research is needed to understand the fate and transport mechanisms of microcystins in various agricultural settings, including controlled, simulated, and field experiments.

Modeling Dynamic Processes in the Black Sea Pelagic Habitat—Causal Connections between Abiotic and Biotic Factors in Two Climate Change Scenarios

The paper contributes to the Sustainable Development Goals (SDGs) targeting Life Below Water by introducing user-friendly modeling approaches. It delves into the impact of abiotic factors on the first two trophic levels within the marine ecosystem, both naturally and due to human influence. Specifically, the study examines the connections between environmental parameters (e.g., temperature, salinity, nutrients) and plankton along the Romanian Black Sea coast during the warm season over a decade. The research develops models to forecast zooplankton proliferation using machine learning (ML) algorithms and gathered data. Water temperature significantly affects copepods and “other groups” of zooplankton densities during the warm season. Conversely, no discernible impact is observed on dinoflagellate Noctiluca scintillans blooms. Salinity fluctuations notably influence typical phytoplankton proliferation, with phosphate concentrations primarily driving widespread blooms. The study explores two scenarios for forecasting zooplankton growth: Business as Usual, predicting modest increases in temperature, salinity, and constant nutrient levels, and the Mild scenario, projecting substantial temperature and salinity increases alongside significant nutrient decrease by 2042. The findings underscore high densities of Noctiluca scintillans under both scenarios, particularly pronounced in the second scenario, surpassing the first by around 70%. These findings, indicative of a eutrophic ecosystem, underscore the potential implications of altered abiotic factors on ecosystem health, aligning with SDGs focused on Life Below Water.

Monitoring of chlorophyll-a and suspended sediment concentrations in optically complex inland rivers using multisource remote sensing measurements

In recent decades, phytoplankton proliferation and sediment input to rivers (especially urban rivers) have become more dramatic under the compound pressure of climate change and human activities. Given the generally narrow width of rivers and current high spatial resolution satellites, which are limited by band settings, bandwidth, and the signal-to-noise ratio, UAVs with their exceptional spatiotemporal resolution can be used as a useful tool for river environmental monitoring and inversion uncertainty assessment. In this study, UAV-based hyperspectral (X20P) and multispectral (P4M) images, along with Sentinel-2 MultiSpectral Instrument (MSI), Landsat-8 Operational Land Imager (OLI) and Landsat-9 OLI2 data, were used to assess the uncertainty in retrieving chlorophyll-a (Chla) and suspended sediment (SS) concentrations in rivers. Chla and SS models based on UAV and satellite data were constructed using stepwise multiple regression and typical Chla and SS retrieval algorithms, respectively, and the performance of the models was the focus of our research. The results demonstrated that in the Chla concentration inversion, each sensor performed as follows: X20P > P4M > Landsat9 OLI2 > Sentinel-2 MSI > Landsat8 OLI, and the performance in the SS concentration inversion was as follows: X20P > Sentinel-2 MSI > P4M > Landsat9 OLI2 > Landsat8 OLI. In addition, the uncertainty of high spatial resolution satellite retrievals was analyzed with the assistance of the UAV-based model. Results showed that narrow bandwidths and finely tuned band settings are more essential for the Chla inversion. The typical Chla retrieval algorithm, NDCI, is only effective in certain bands (band 1 from 684 to 724 nm and band 2 from 660 to 680 nm). It is also noted that Landsat8 and Landsat9 lack some key band settings (e.g., the red-edge band of 700–710 nm), severely limiting practical application in relation to Chla. However, specific variances in different sensor bands have a relatively small impact on SS inversion, for example, the correlation between SS and the R/B (a typical SS retrieval algorithm) constructed by each sensor ranged from 0.68 to 0.77. Chla monitoring, on the other hand, necessitates a higher spatial resolution than SS monitoring. The accuracy decreased markedly when UAV images were resampled to 10 m and 30 m spatial resolution. However, it is not as crucial for the SS inversion, images with the original spatial resolution (RMSE<30cm = 6.28 mg/L) were resampled to 10 m resolution (RMSE10m = 5.85 mg/L) and 30 m resolution (RMSE30m = 4.08 mg/L) while using P4M for SS inversion, and the accuracy increased. Our results demonstrated and highlighted various options for future monitoring of Chla and SS, while exploiting the synergy between UAVs and satellites to achieve more precise observations at greater spatial and temporal scales, which will benefit aquatic environment management and protection.

Vertical distribution rules and factors influencing phytoplankton in front of a drinking water reservoir outlet

The phenomenon of algal blooms caused by the excessive proliferation of phytoplankton in drinking water reservoirs is becoming increasingly frequent, seriously endangering water quality, ecosystems, water safety, and people's health. Thus, there is urgent need to conduct research on the distribution rules and factors influencing phytoplankton in drinking water reservoirs. Given that the outflows from reservoirs usually come from the middle and lower layers of the water column and the current studies on phytoplankton in drinking water reservoirs are usually carried out on the surface, an 8-month monitoring of vertical phytoplankton and the corresponding influencing factors in front of the outlet in a drinking water reservoir was conducted. Based on the monitoring results, the distribution rules of phytoplankton and the associated factors were analyzed. The results showed that phytoplankton biomass significantly decreased with increasing water depth, but the biomass near the outlet (40 m depth) still reached the WHO level 2 warning threshold for algal blooms multiple times. During the monitoring period, Cyanophyta, Chlorophyta and Bacillariophyta dominated. The selected multisource environmental factors explained 60.5 % of the spatiotemporal changes in phytoplankton, with thermal intensity (water temperature and thermal stratification intensity) being the driving factor. Meanwhile, excessive TN and TP provided necessary conditions for the growth of phytoplankton. Based on influencing factors, reducing upstream nutrient inflows and thermal stratification intensity are recommended as measures to prevent and control algal blooms. This study provides insights into the vertical distribution rules and factors influencing phytoplankton in a drinking water reservoir, which can provide a reference for the management of drinking water reservoirs and the prevention and control of algal blooms.

Remotely sensed-based analysis about climatic and landscape change effects on phytoplankton bloom in Barra Bonita Reservoir (São Paulo State, Brazil)

The constant land use and land cover (LULC) changes combined with climatic factors are frequently assigned to anthropogenic eutrophication, one of the main ecological imbalances in aquatic systems characterized by dense phytoplankton proliferation. Beyond the degradation of freshwater ecosystems, some cyanobacterial and algae species produce toxins harmful to living beings. Distinct studies in the literature, usually supported by in situ data, have discussed the influence of LULC and climatic changes on phytoplankton bloom events. In this context, motivated by the importance of understanding the environmental mechanisms assigned to phytoplankton bloom events and considering the difficulties imposed by field data collection, our study focuses on analyzing the mentioned issue only using remotely sensed time series data. For this purpose, we performed a temporal analysis between 1985 and 2018 over a portion of the Barra Bonita Hydroelectric Reservoir, Brazil. Initially, we obtained the landscape occupation, precipitation, and temperature information from the MapBiomas, FLDAS, and CHIRPS projects, respectively. A fully automatic algorithm fed by Landsat image series and supported by Google Earth Engine functions was developed and employed to identify and quantify phytoplankton bloom events. Then, the obtained data were inspected by distinct statistical procedures, including correlation and trend analysis. Although there was an absence of a relationship between the climatic components and the emergence of phytoplankton blooms, it was identified using linear regression models (R2 ≥ 78 % ) an intensification of blooms after the increase in nonnatural forestry areas, reduction of pastures, and advance of agricultural areas. Furthermore, machine learning methods were employed to obtain nonlinear regression models (R2 ≥ 73 % ), making evident that the landscape changes are mainly responsible for the phytoplankton insurgences in the analyzed region. This result agrees with other studies found in the literature and highlights the possibility of investigating anthropogenic eutrophication only using remotely sensed data and automatic algorithms.

Composition of dissolved organic matter (DOM) in lakes responds to the trophic state and phytoplankton community succession

Dissolved organic matter (DOM), a heterogeneous mixture of diverse compounds with different molecular weights, is crucial for the lake carbon cycle. The properties and concentration of DOM in lakes are closely related to anthropogenic activities, terrigenous input, and phytoplankton growth. Thus, the lake's trophic state, along with the above factors, has an important effect on DOM. We determined the DOM sources and molecular composition in six lakes along a trophic gradient during and after phytoplankton bloom by combining optical techniques and the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). CDOM pools in eutrophic lakes may be more biologically refractory than in oligotrophic and mesotrophic lakes. Molecular formulas of DOM were positively correlated with the TSI (trophic state index) value (R2 = 0.73), with the nitrogen-containing compounds (CHON) being the most abundant formulas in all studied lakes. Eutrophication modified the molecular formulas of DOM to have less CHO% and more heteroatom S-containing compounds (CHOS% and CHNOS%), and this was the synactic result of the anthropogenic perturbation and phytoplankton proliferation. In eutrophic lakes, summer DOM showed higher molecular lability than in autumn, which was related to the seasonal phytoplankton community succession. Although the phytoplankton-derived DOM is highly bioavailable, we detected a simpler and more fragile phytoplankton community ecosystem in autumn, which may be accompanied by a lower phytoplankton production and metabolic activity. Therefore, we concluded that the lake eutrophication increased the allochthonous DOM accumulation along with sewage and nutrient input, and subsequently increased its release with phytoplankton bloom. Eutrophication and phytoplankton growth are accompanied by more highly unsaturated compounds, O3S+O5S compounds, and carboxylic-rich alicyclic compounds (CRAMs), which are the biotransformation product of phytoplankton-derived DOM. Eutrophication may be a potential source of refractory DOM compounds for biodegradation and photodegradation. Our results can clarify the potential role of water organic matter in the future global carbon cycle processes, considering the increasing worldwide eutrophication of inland waters.

Metabolic plasticity of mixotrophic algae is key for their persistence in browning environments

Light availability is the main regulator of primary production, shaping photosynthetic communities and their production of ecologically important biomolecules. In freshwater ecosystems, increasing dissolved organic carbon (DOC) concentrations, commonly known as browning, leads to lower light availability and the proliferation of mixotrophic phytoplankton. Here, a mixotrophic algal species (Cryptomonas sp.) was grown under five increasing DOC concentrations to uncover the plastic responses behind the success of mixotrophs in browning environments and their effect in the availability of nutritionally important biomolecules. In addition to the browning treatments, phototrophic, heterotrophic and mixotrophic growth conditions were used as controls. Despite reduced light availability, browning did not impair algal growth compared to phototrophic conditions. Comparative transcriptomics showed that genes related to photosynthesis were down‐regulated, whereas phagotrophy gene categories (phagosome, lysosome and endocytosis) were up‐regulated along the browning gradient. Stable isotope analysis of phospholipid fractions validated these results, highlighting that the studied mixotroph increases its reliance on heterotrophic processes with browning. Metabolic pathway reconstruction using transcriptomic data suggests that organic carbon is acquired through phagotrophy and used to provide energy in conjunction with photosynthesis. Although metabolic responses to browning were observed, essential fatty acid content was similar between treatments while sterol content was slightly higher upon browning. Together, our results provide a mechanistic model of how a mixotrophic alga responds to browning and how such responses affect the availability of nutritionally essential biomolecules for higher trophic levels.

Nutrient overload promotes the transition from top-down to bottom-up control and triggers dystrophic crises in a Mediterranean coastal lagoon

The excess input of nutrients that triggers eutrophication processes is one of the main destabilizing factors of coastal ecosystems, being coastal lagoons prone to suffer these effects and present dystrophic crises. This process is aggravated by the current trend of rising temperatures and more frequent torrential rains due to climate change. We observed that the Mar Menor lagoon had a great capacity for self-regulation of its trophic web and resistance to the eutrophication process, but after 30 years of nutrient input due to the change in the agricultural regime in its drainage basin in the 1990s, the lagoon ecosystem has suffered several of these events. In this work, we characterize the seasonal dynamic of the pelagic system during the last dystrophic crises. Phosphorus and nitrogen alternate as the limiting nutrient for phytoplankton proliferation. The entrance of phosphorus is mainly related to vacation periods, while nitrogen inputs, both superficial and sub-superficial, are more related to chronic high nitrates concentration in the water table after the agricultural activities carried out in the area changed. Our analysis reveals that the summer season is prone to suffer periodical hypoxia events when the N/P ratio decreases, and the temperature rises. In the Mar Menor, the ecological balance has been maintained in recent decades thanks to, among other mechanisms, the spatial and temporal segregation of top-down control over phytoplankton exerted by three species of jellyfish. However, the deep reduction in the abundance of the summer jellyfish species and the excessive proliferation of phytoplankton has meant the loss of this control. Moreover, we have registered a decline in the abundance of all the other zooplanktonic groups during the dystrophic crises. We suggest that management actions should address the input sources of water and nutrients, and an integrated management of the activities carried out throughout the watershed.

Particulate and dissolved fluorescent organic matter fractionation and composition: Abiotic and ecological controls in the Southern Ocean

Phytoplankton-derived organic matter sustains heterotrophic marine life in regions away from terrestrial inputs such as the Southern Ocean. Fluorescence spectroscopy has long been used to characterize the fluorescent organic matter (FOM) pool. However, most studies focus only in the dissolved FOM fraction (FDOM) disregarding the contribution of particles. In order to assess the dynamics and drivers of the dissolved and particulate fractions of FOM, we used a Lagrangian approach to follow the time evolution of phytoplankton proliferations at four different sites in the Southern Ocean and compared the FOM in filtered and unfiltered seawater aliquots. We found that filtration had little effects on FOM visible spectrum fluorescence intensities, implying that most of this signal was due to dissolved fluorophores. On the other hand, protein-like fluorescence was strongly supressed by filtration, with fluorescence of particles accounting for up to 90 % of the total protein-like FOM. Photobleaching was identified as the main driver of visible FDOM composition, which was better described by indices of phytoplankton photoacclimation than by measurements of the incident solar radiation dose. In contrast, protein-like FOM intensity and fractionation were primarily related to abundance, composition and physiological state of phytoplankton proliferations. The chlorophyll a concentration from non-diatom phytoplankton explained 91 % of the particulate protein-like FOM variability. The proportion of protein-like fluorescence found in the dissolved phase was predicted by the combination of potential viral and grazing pressures, which accounted for 51 and 29 % of its variability, respectively. Our results show that comparing FOM measurements from filtered and unfiltered seawater provides relevant information on the taxonomic composition and cell integrity of phytoplankton communities. A better understanding of the commonly overlooked FOM fractionation process is essential for the implementation of in situ fluorescence sensors and will also help us better understand the processes that govern OM cycling in marine systems.

Water quality changes and shift in mechanisms controlling hypoxia in response to pollutant load reductions: A case study for Shiziyang Bay, Southern China

Shiziyang Bay, located in the upstream of the Pearl River Estuary, has frequently suffered from hypoxia since 2000, which has persisted in recent years despite effective controls on anthropogenic pollutant loads. To explore the underlying causes, changes in dissolved oxygen (DO), nutrients, chemical oxygen demand (COD), and chlorophyll a (Chl a) along the bay in response to altered pollutant inputs were investigated using observations collected in summers of 2015–2019 and historical data during 2000–2008. In addition, DO sources and sinks were calculated based on data from August 2020 and laboratory incubations for water column respiration (WCR) and sediment oxygen uptake, and were compared with their equivalents in August 2008 to elucidate changes in primary processes controlling hypoxia. The results showed that ammonia has decreased significantly with pollutant control, while other parameters responded in different trends, especially for Chl a (with a substantial increase over time). The intensified eutrophication contributed to high COD levels, leading to a strong WCR (as dominant oxygen depletion) close to that in the 2000s and thereby maintaining low-oxygen conditions despite reduced effluent discharges. The shifted primary oxygen-consuming substances from allochthonous inputs to in-situ phytoplankton production were also evidenced by significant correlation between oxygen consumption rate and Chl a in recent data. Simultaneously, the enhanced algal blooms could also modulate oxygen supply, resulting in higher photosynthetic oxygen production and lower air-sea reaeration compared with the past. Furthermore, the impact of major environmental changes on exacerbated eutrophication was explored and it was speculated that notable declined sediment loads would be important by improving light conditions to promote phytoplankton proliferation in the bay. Collectively, substantial control on eutrophication as well as tracking DO source-to-sink processes is of great importance to mitigate hypoxia in Shiziyang bay.

A Roomba for Rivers

Presents a photograph of Interactive Autonomous Dynamic Systems' (IADYS) new product called the Jellyfishbot. The machine, which can run autonomously or at the direction of a remote operator, goes around collecting the junk and gunk (like plastic bottles, oil spills, and algae) that float on the water, as well as detritus located up to 10 meters below the surface. The Jellyfishbot is studded with sensors that allow it to navigate autonomously. The sensors also measure the quality of the water in terms of salinity, temperature, turbidity, and the proliferation of organisms, including cyanobacteria and phytoplankton.

Off-Flavors in Aquacultured Fish: Origins and Implications for Consumers

Off-flavors in fish and water are considered a worldwide problem. Several factors, such as the presence of phosphorus, micronutrients, and organic matter, contribute to phytoplankton proliferation and the production of off-flavors. Geosmin and 2-methylisoborneol are the most common off-flavors that confer the smell of earth or mold to water and fish. These metabolites are not considered toxic, but they can be easily transferred from water to living organisms and accumulate in the biota, up the trophic levels and to consumers, including fish species. Numerous processes have been studied to eliminate or reduce the presence of off-flavors in recirculating aquaculture systems. Managing off-flavors must be eco-friendly and consumer-friendly. Strategies against off-flavors must be efficient and low-cost. However, these solutions may be different for each fish production system. We review herein the main compounds produced by cyanobacteria that can accumulate in fish used in aquaculture that can affect the quality of food, as well as production costs and consumer preference.

The spatiotemporal characteristics of water quality and phytoplankton community in a shallow eutrophic lake: Implications for submerged vegetation restoration

One of the most serious consequences of eutrophication in shallow lakes is deterioration of water quality, proliferation of phytoplankton and disappearance of submerged macrophytes. After removing herbivorous and plankti-benthivorous fish, submerged macrophyte restoration was utilized at the entire lake (82.7 km2) to combat eutrophication and improve water quality in the shallow subtropical aquaculture of Lake Datong. We conducted two years of monitoring, from March 2018 to February 2020. During the first year of restoration, 80% of the area of Lake Datong (approximately 60 km2) was successfully recovered by submerged vegetation, and the water quality was improved. For example, the phosphorous (P) content (including total P (TP), dissolved reactive P (DRP) and total dissolved P (TDP)) and turbidity decreased, and the Secchi depth (SD) increased. However, the submerged vegetation disappeared from autumn 2019 in the intermittent recovery area (MN), while the continuous recovery area (DX) continued to recover with an abundance of submerged vegetation. During the second year, the water quality continued to improve significantly in the DX area, with high biomass and coverage of submerged vegetation. In the MN area, although turbidity and ammonia nitrogen (NH4+-N) increased significantly and SD decreased significantly, the P content (TP, TDP, and DRP) still continued to decrease. The restoration of submerged macrophytes could significantly decrease the density of phytoplankton. Over time, there was a regime shift in Lake Datong. The structural equation model (SEM) results illustrated that the water level and submerged plant coverage were the primary drivers that triggered changes in the state of the lake ecosystem. Our results highlight the potential of restoring submerged vegetation to control water eutrophication at the whole-lake scale. However, the water level in spring was the primary driver that triggered changes in the state of the lake ecosystem. Water level management should be emphasized during the early stages of recovery of submerged plants.

Proliferation of phytoplankton along a 500 km transect of the St. Lawrence River from its outflow at Lake Ontario

Observation of phytoplankton and water chemistry along the main channel of the St. Lawrence River was made at a high spatial resolution (every 12 km) in order to infer the factors that influence development of this phytoplankton community. The phytoplankton community in the main channel was collected over a 10-d period (mid July 2018) from the headwaters to near the beginning of the St. Lawrence River estuary. Total phosphorus concentration in river water increased with distance downstream (154–2,750 nM) and phytoplankton biomass (1.4–10.5 µg chl-a/L) was strongly correlated (r = 0.84, 46 d.f.) to the concentration of total phosphorus. Diatoms, chrysophytes and dinoflagellates dominated the phytoplankton community at the outlet of Lake Ontario and total chlorophyll-a concentrations increased three-fold with 500 km transit downstream from Lake Ontario; phycocyanin-rich Cyanobacteria showed the greatest proportional increase (227%). Total P concentrations observed in 1997 along this transect were identical to those observed in 2018; however, chl-a concentrations were much lower in 1997, a finding attributed to a greater filter feeding benthic organism impact on the standing crop of phytoplankton. Observations support the hypothesis that the phytoplankton community composition in this large river is strongly influenced by the headwater characteristics (Lake Ontario) and gradually influenced by entrainment of nutrient-rich tributary waters.

Phytoplankton community and driving environmental factors in Lake Dongping after 3 years implementation of the east route of South-to-North Water Diversion Project

为掌握东平湖浮游植物在南水北调东线工程运行后的群落结构变化特征及探究其环境驱动因子，于通水运行3周年后的2017年分4个季节对东平湖的18个样点进行采样调查，同步开展水环境调查.结果显示：共检出浮游植物191种属（包括变种），其中硅藻门、绿藻门、裸藻门、蓝藻门、金藻门、黄藻门、甲藻门和隐藻门分别为64、57、28、22、8、5、4和3种属；优势种属包括蓝藻门的漂浮泽丝藻（Limnothrix planctonica）和色球藻（Chroococcus sp.），绿藻门的小球藻（Chlorella vulgaris）以及硅藻门的小环藻（Cyclotella sp.）、舟形藻（Nauicula sp.）和针杆藻（Synedra sp.）等（优势度Y>0.02）；全年密度和生物量分别为6.74×10⁶ cells/L和5.71 mg/L，并呈现显著季节与空间差异.浮游植物密度季节变化为夏季 > 秋季 > 冬季 > 春季，生物量季节变化为夏季 > 冬季> > 秋季 > 春季；春、夏、秋、冬季物种数分别为71、78、53和125种，Shannon-Wiener多样性指数（H'）均值分别为1.90、1.84、1.76和2.52，Margalef丰富度指数（D）均值为3.07、3.98、2.79和4.75；冗余分析与Pearson相关性分析结果显示，水体综合营养状态指数、高锰酸盐指数、氨氮和水温是影响东平湖浮游植物群落结构的关键驱动因子.对比南水北调东线工程实施之前及通水初期的结果，东平湖浮游植物优势种群无明显变化，密度则较通水初期稍有升高.本研究分析了东平湖浮游植物群落的时空分布特征，发现调水工程可能通过物质带入影响水质，进而引起浮游植物量增加，湖区养殖的退出及增殖放流的实施降低了富营养化风险，但仍存在浮游植物生物量特别是蓝藻生物量升高的风险，建议在调水管理中加强水域生态监测及生境调控技术研究，保障调水水质安全.;In order to investigate the community characteristics of phytoplankton and the determining factors in Lake Dongping after implementation of the east route of South-to-North Water Diversion Project, seasonal samples of phytoplankton and aquatic environment from 18 sampling sites were collected in 2017. A total of 191 taxa of phytoplankton (genera or species) were identified with 64 taxa of Bacillariophyta, 57 taxa of Chlorophyta, 28 taxa of Euglenophyta, 22 taxa of Cyanophyta, 8 taxa of Chrysophyta, 5 taxa of Xanthophyta, 4 taxa of Pyrrophyta and 3 taxa of Cryptophyta. The dominant taxa were Limnothrix planctonica and Chroococcus sp. of Cyanophyta, Chlorella vulgaris of Chlorophyta and Cyclotella sp., Nauicula sp. and Synedra sp. of Bacillariophyta, etc (Y>0.02). The phytoplankton density and biomass were 6.74×10⁶ cells/L and 5.71 mg/L with the seasonal variation of density being summer > autumn > winter > spring and that of biomass being summer > winter > autumn > spring, respectively. About the phytoplankton diversity in four quarters, the number of species was 71, 78, 53 and 125, while the averages of the Shannon-Wiener index were 1.90, 1.84, 1.76 and 2.52 and Margalef diversity index were 3.07, 3.98, 2.79 and 4.75, respectively. Meanwhile, the results of redundancy analysis and Pearson analysis for the relationship between phytoplankton and aquatic environment showed that the factors such as comprehensive nutrition state index, permanganate index, ammonia nitrogen concentration, and water temperature played a key role in affecting the structure and dynamics of the phytoplankton community in Lake Dongping. Compared with before implementation of the east route of South-to-North Water Diversion Project and the initial stage of it, although the density of phytoplankton showed a rise, there was no obvious response in their dominant genera. This study preliminarily verified the spatiotemporal distribution characteristics of the phytoplankton community in Lake Dongping. Total phytoplankton density was found to have increased with the change of water quality caused by the east route of South-to-North Water Diversion Project. The withdrawal of aquaculture and implementation of fishery enhancement and releasing had reduced the risk of eutrophication, but the proliferation of phytoplankton probably increased the risk of algal-bloom in Lake Dongping. Given the changes of phytoplankton community and water quality after water diversion, it is necessary to strengthen the ecological monitoring and controlling in the management of water quality safety and stability.

Monitoring air quality can help for lakes excessive proliferation of phytoplankton control

Previous studies assessing excessive proliferation of phytoplankton (EPP) in lakes are generally based on single investigation and focused on limited environmental factors; meanwhile, less attention has been paid to lakes susceptibility to EPP. Here, we identify the priority of lakes for EPP control in a basin by assessing EPP in multiple lakes and identify the key factors related to lakes’ vulnerability to EPP. Field measurements, as well as multi-source survey data acquisition were conducted for 63 shallow lakes in the middle-lower Yangtze River basin. Resource-use efficiency by phytoplankton (RUE) was then used to represent lake susceptibility to EPP. Generalized linear models were used to assess the relative importance of environmental factors for RUE. We found that most lakes (76.19 %) were not suitable for recreation, due to health concern attributed to irritative or allergenic risk caused by EPP. Phosphorus was the primary limiting nutrient for EPP (74.60 % of lakes) which should be limited to < 0.09 mg/L. The linear model that included latitude, particulate matter 10, and precipitation explained 27.60 % of the variation of RUETP among lakes. In contrast, the linear model that included ozone, Secchi depth, and wind speed explained 19.41 % of the variation of RUETN among lakes. The key factor related to RUETP and RUETN was particulate matter 10 and ozone, respectively, both of which potentially increase RUE or reflect it. Our results suggest that integrating multiple survey datasets is critical for lakes EPP assessment in a basin, while lakes impacted by air pollution are a high priority for EPP control.