Occurrence Of Harmful Algal Blooms Research Articles

Spatiotemporal variation of paralytic shellfish toxins in the sea area adjacent to the Changjiang River estuary

The Changjiang (Yangtze River) River estuary (CRE) and its adjacent coastal waters is a notable region for nutrient pollution, which results in severe problems of coastal eutrophication and harmful algal blooms (HABs). The occurrence of HABs, particularly those of dinoflagellate Alexandrium spp. capable of producing paralytic shellfish toxins (PSTs), has an increasing risk of contaminating seafood and poisoning human-beings. The investigation of PSTs, however, is often hampered by the relatively low abundance of Alexandrium spp. present in seawater. In this study, a monitoring strategy of PSTs using net-concentrated phytoplankton from a large volume of seawater was employed to examine spatiotemporal variations of PSTs in the CRE and its adjacent waters every month from February to September in 2015. Toxins in concentrated phytoplankton samples were analyzed using high-performance liquid chromatography coupled with a fluorescence detector (HPLC-FLD). The results showed that PSTs could be detected in phytoplankton samples during the sampling stage in the CRE and its adjacent waters. Toxin content increased gradually from February to May, reached the peak in June, and then decreased rapidly from July to September. The maximum value of PST content was 215 nmol m−3 in June. Low-potency toxins N-sulfocarbamoyl toxins 1/2 (C1/2) were the most dominant components of PST in phytoplankton samples from February to June in 2015, while high-potency gonyautoxin 4 (GTX4) became the dominant component from July to September. Toxins were mainly detected from three regions, the sea area north to the CRE, the sea area east to the CRE, and sea area near Zhoushan Island south to the CRE. Based on the results of this study, it can be inferred that the three regions around the CRE in May and June is of high risk for PST contamination and seafood poisoning.

Algal blooms in the middle and lower Han River: Characteristics, early warning and prevention

Eutrophication with the sustained occurrence of harmful algal blooms (HABs) has been widely recognized since the 1990s as one of the largest drinking water quality issues in the middle and lower reaches of the Han River (MLHR, the largest tributary of Yangtze). Due to impoundment of the middle route of the South to North Water Diversion Project (SNWDP), the height of the Danjiangkou Reservoir Dam was raised in 2014, resulting in lower discharge (or flow rate) for the MLHR, and subsequently enhancing the potential occurrence probabilities of HABs. Here, the characteristics of HABs that took place during the 1992 to 2018 period were summarized based on the historical water quality and meteorological data. Then, some key factors governing the HABs were analyzed to explore the underlying mechanisms. The results showed that diatoms (Cyclotella sp.) were the dominant species of the HABs. The simultaneous increase of algal density and total phosphorus (TP) concentration during algal blooms revealed that phosphorus was the key limiting nutrient for algal growth. The algal density was significantly negatively correlated with water discharge (R2 = 0.764), or flow rate (R2 = 0.711), indicating that the increase of water discharge from Danjiangkou Reservoir could possibly mitigate the occurrence of HABs. The threshold level of water discharge for HAB prevention was estimated as 500 m3/s in Xiantao Gauging Station before the height of the Dam was raised in 2014, but it subsequently increased to 800 m3/s afterwards. Our study clearly revealed that the occurrence probabilities of HABs in the MLHR were higher than before because of the increase in the phosphorus concentration and the decrease in water discharge under the new engineering conditions of the SNWDP. Therefore, it is urgent to undertake strategies for the HABs prevention in the MLHR.

HARMFUL ALGAL BLOOMS MONITORING USING SENTINEL-2 SATELLITE IMAGES

Abstract. Over the last few decades in coastal areas, the occurrence of Harmful Algal Blooms (HAB) has increased. The phenomenon is harmful to the health of coastal residents as well as marine organisms and can cause damage to the economy of the region. In this article, considering the need of a method for detecting red tide phenomenon using high spatial resolution satellite images, we tried to test the capability of spectral features, which can be generated using Sentinel-2 satellite images, in detecting red tide phenomenon. For this purpose, we generated an algorithm for detecting spectral features, which the red tide phenomenon causes a noticeable change in their value compared with the non-blooming condition. The ability of the selected spectral features in detecting HABs has been evaluated using statistical methods such as type I and II error, overall accuracy, kappa coefficient, and ROC curves. The best case, for the spectral feature, is (R4−R8A)/(R4+R8A), 5% for type I and 6% for type II error were achieved where R4 stands for reflectance in band 4 and R8A is the reflectance in band 8A of a Sentinel-2 satellite image.

Warming Amplifies the Frequency of Harmful Algal Blooms with Eutrophication in Chinese Coastal Waters.

Widespread coastal eutrophication is known to increase the prevalence of harmful algal blooms (HABs). Increased HABs have also been linked to climate change, with ocean warming predicted to lead to increased prevalence and earlier timing of HABs. Testing the predictions of warming to HABs is difficult due to the lack of long-term observations across spatial scales. Here, we use a 45 year (1970-2015) record of the occurrence and duration of HABs along Chinese coast to show that the HAB frequency has increased at a rate of 40 ± 4% decade-1, with earlier timing by 5.50 ± 1.78 days decade-1. The increasing frequency of blooms varied with latitude and is significantly correlated with warming at an average rate of 0.17 ± 0.03 °C decade-1, with the positive relationship being strongest in more eutrophic provinces. HAB frequency increased with elevated dissolved inorganic nutrient concentration, but this increase was amplified further with warming. Warming and eutrophication showed additive roles in triggering HABs. Swift action to mitigate eutrophication is essential to avoid a sharp increase in the HABs in coastal waters with further warming.

Early Prediction of Margalefidinium polykrikoides Bloom Using a LSTM Neural Network Model in the South Sea of Korea

Shin, J.; Kim, S.M.; Son, Y.B.; Kim, K., Ryu, J.-H., 2019. Early prediction of Margalefidinium polykrikoides bloom using a LSTM neural network model in the South Sea of Korea. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 236-242. Coconut Creek (Florida), ISSN 0749-0208.Harmful algal blooms (HABs) have been occurring within the South Sea of Korea (SSK) for decades, causing significant ecological impacts and economic problems for many fish farms concentrated in coastal areas. The occurrence of HABs is related to various factors, including meteorological and physical factors, making it difficult to predict the timing of their occurrence. However, it is essential to make a preliminary forecast of HAB occurrence through analysis of such factors to minimize the damage. In this study, a deep neural network model of long short-term memory (LSTM) that can predict the occurrence time of Margalefidinium polykrikoides blooms is presented and evaluated. Satellite data were used to extract sea surface temperature (SST) and photosynthetically available radiation (PAR), which are environmental factors known to be related to HABs occurrence. M. polykrikoides blooms that have occurred in the past 21 years (1998–2018) have been shown to be initiated when SST reaches around 25 °C within the summer season. The prediction performance of LSTM-based neural network was evaluated using test data from 2017 and 2018, and the root-mean-squared-error (RMSE) and prediction accuracy were determined. Prediction for 2017 matched well with the test data; however, for 2018, the network predicted that a HAB would occur between July 19 and Sep. 03, with an RMSE of 0.233 and accuracy of 94.8 %, but the actual occurrence of HAB was between July 24 and Aug. 20. This study shows that the trained LSTM-based network would be useful for early prediction of the future red tide blooms in SSK.

A research note: Potential importance of N[formula omitted] fixers in the coastal northwestern East/Japan Sea

Biological nitrogen (N2) fixation, a fundamental step in aquatic and terrestrial N cycles, is an important process through which “new” reactive nitrogen (N) is produced. The role of N2 fixation in fueling the occurrence of harmful algal blooms (HABs) is one of the major concerns in the present scenario. Since N2 fixation occurs under highly specific environmental conditions, determining the suitability of various ecosystems for potential N2 fixation is important. The introduction of 15N2 bubble experiments in 1995 has led to significant N2 fixation rate estimates from various parts of the world oceans; however, Korean coastal waters, which are prone to HABs, remained unstudied. The present study aimed to construct a research note on N2 fixation in the Korean coastal waters on the basis of a preliminary data set of N2 fixation rates (range; 0.31–2.35 nmol N L−1 h−1) obtained from the coastal northwestern East/Japan Sea. The results indicate that N2 fixation is not currently a significant N source in the northwestern East/Japan Sea. However, the possibility of N2 fixers being a future significant N source and a fuel for HABs in the East/Japan Sea under favorable environmental conditions cannot be ruled out.

Harmful algal bloom and associated health risks among users of Lake Victoria freshwater: Ukerewe Island, Tanzania.

There is a global concern regarding the occurrences of harmful algal blooms (HABs) and their effects on human health. Lake Victoria (LV) has been reported to face eutrophication challenges, resulting in an increase of bloom-forming cyanobacteria. This study is aimed at understanding the association of HABs and health risks at Ukerewe Island. A cross-sectional study conducted on 432 study subjects and water samples for cyanobacteria species identification were collected at LV shores. The results reveal that concentrations of cyanobacteria cells are beyond (WHO) acceptable limits; species of Microcystis aeruginosa range from 90,361.63 to 3,032.031.65 cells/mL and Anabaena spp. range from 13,310.00 to 4,814,702 cells/mL. Water usage indicates that 31% use lake water, 53% well water and 16% treated supplied pipe water. Vomiting and throat irritation was highly reported by lake water users as compared to wells and pipe water (P < 0.001). Gastrointestinal illness (GI) was significantly elevated among lake water users as compared to pipe and well water users (P < 0.001). Visible blooms in lake water were associated with GI, skin irritation and vomiting as compared to water without visible blooms (P < 0.001). The concentration of cyanobacteria blooms poses greater risks when water is used without treatment.

Resource partitioning strategies during toxin production in Microcystis aeruginosa revealed by integrative omics analysis

Escalating rates of urbanization and climate change have led to increased occurrence of harmful algal blooms (HABs) in natural waters. HABs caused by Microcystis aeruginosa produce toxic secondary metabolites, such as microcystins (MCs). To understand resource partitioning strategies between cell growth and MC production in response to environmental triggers, we tested the effect of interactions between light and nitrogen on Microcystis aeruginosa PCC 7806. Statistical models revealed that both light and nitrogen affected the transcriptome and metabolome, however, light was the most important of these two factors driving changes at the transcriptome level. On the contrary, effects at metabolome level were less pronounced and were restricted to a few inter-related networks that share rate-limiting substrates and pathway intermediates. Through the integrative systems level approach, we found certain networks belonging to cellular growth, cellular scavenging and secondary metabolites that drive the overall resource partitioning strategy in Microcystis. Additionally, rate limiting metabolites (malonyl-CoA and metabolite couplet SAM; S-adenosyl methionine–SAH; S-S-Adenosyl-L-homocysteine) that occur at the crossroads of the light and nitrogen dependent pathways were identified, thus controlling the metabolic flux and resource allocation in Microcystis cultures. Through these observations, we provide a conceptual model for environmental responses of Microcystis. This model could be validated through controlled feeding experiments and specific genetic mutants to obtain further insights.

Formation of iodinated trihalomethanes and noniodinated disinfection byproducts during chloramination of algal organic matter extracted from Microcystis aeruginosa

The increasing occurrence of harmful algal blooms in surface waters may increase the input of algal organic matter (AOM) to the dissolved organic matter pool. The formation of iodinated trihalomethanes (I-THMs) and noniodinated disinfection byproducts (DBPs) in synthetic waters containing AOM extracted from Microcystis aeruginosa was investigated in chloramination (preformed and in-situ formed chloramine, NH2Cl and Cl2-NH2Cl, respectively) and chlorination (Cl2) processes. AOM is much more favorable for iodine incorporation than natural organic matter (NOM). For example, the formation of I-THM from AOM is much higher than NOM isolate extracted from treated water (e.g., 3.5 times higher in the NH2Cl process), and thus higher iodine utilization and substitution factors from AOM were observed. Short contact time (2 min) chlorination in Cl2-NH2Cl process leading to the formation of halogenated intermediates favored I-THM formation, compared with NH2Cl process. However, further increasing chlorine contact time from 5 min to 24 h facilitated the conversion from iodide to iodate and thus I-THM formation decreased. Meanwhile, the formation of noniodinated THM4, haloacetonitriles (HANs), and haloacetaldehydes (HALs) increased. Factors including concentrations of AOM and bromide, pH, and chlorine/nitrogen ratios influenced the formation of I-THMs and noniodinated DBPs. To evaluate the benefit of mitigating I-THM formation over the risk of noniodinated DBP formation, measured DBPs were weighed against their mammalian cell toxicity indexes. Increasing the chlorine exposure increased the calculated cytotoxicity based on concentrations of measured I-THMs and noniodinated DBPs since unregulated HANs and HALs were the controlling agents.

New method for algae comprehensive utilization: Algae-derived biochar enhances algae anaerobic fermentation for short-chain fatty acids production

Interest in the resource utilization of algae has gradually increased due to the frequent occurrence of harmful algal blooms. Here, biochar derived from algae was applied to algae anaerobic fermentation for short-chain fatty acids (SCFAs) production. In the presence of algae-derived biochar, the concentration of SCFAs within 4 d (4334 mg COD/L) was approximately doubled compared to the control (2016 mg COD/L), and the fermentation time for maximal SCFAs yield was shortened. Biochar improved the disruption of algae to release more intracellular macromolecular organics. Altering algae hydrolysis, the activity of hydrolase and the contents of functional gene were advantageous to SCFAs accumulation by providing more micromolecular organics in the presence of biochar. Additionally, the relative abundance and survival of acid-forming bacteria were enhanced significantly. Furthermore, biochar accelerated the electron transport and energy synthesis in the biological system, driving the biological reactions that allow microorganisms to function and life to flourish.

Biological pollution potential in the water of Bintan-Riau Islands Province, Indonesia: First appearance of harmful algal bloom species

The increased number of human population in coastal areas can be the common dominator of an event of harmful algal blooms (HABs), which might be of a negative impact on human activities. Generally, HABs occur due to the dynamics of some phytoplankton species. The objective of this study was to inventory the phytoplankton distribution in the water of Bintan-Riau Island in Indonesia. In the perspective of the pollution biology mitigation, phytoplankton samples were collected from 4 to 5 composited sub-samples of the seven sites around the Bintan water (Dompak, Kijang, Kampung Baru, Lobam, Trikora, Tanjung Unggat and Senggiling). The investigation revealed the presence of 41 phytoplankton taxa. Bacillariophyta was the dominant group of phytoplankton in the coastal waters of the Bintan Island. The highest abundance of phytoplankton is found in the Dompak and Senggiling waters with the number of phytoplankton per mL reached 1.846.667 and 2.050.667 cells/mL, respectively. Both stations had the highest number of phytoplankton species (26 species) compared to other stations. The harmful phytoplankton group found was dinophyceae (genus Ceratium), which was observed in almost all the coastal waters of Bintan Island. The highest abundance of dinophyceae was in the waters of Kampung Baru, Lagoi. In this study, HABs proliferation was associated with nitrate concentration, which recorded high values in all the observation sites. An eutrophication study is needed to understand the broader complexity of nutrient effects governing the occurrence of HABs in the coastal areas, which can help in the mitigation of problems caused by HABs, particularly in Dompak and Senggiling stations.

Remotely sensing harmful algal blooms in the Red Sea.

Harmful Algal Blooms (HABs) are of global concern, as their presence is often associated with socio-economic and environmental issues including impacts on public health, aquaculture and fisheries. Therefore, monitoring the occurrence and succession of HABs is fundamental for managing coastal regions around the world. Yet, due to the lack of adequate in situ measurements, the detection of HABs in coastal marine ecosystems remains challenging. Sensors on-board satellite platforms have sampled the Earth synoptically for decades, offering an alternative, cost-effective approach to routinely detect and monitor phytoplankton. The Red Sea, a large marine ecosystem characterised by extensive coral reefs, high levels of biodiversity and endemism, and a growing aquaculture industry, is one such region where knowledge of HABs is limited. Here, using high-resolution satellite remote sensing observations (1km, MODIS-Aqua) and a second-order derivative approach, in conjunction with available in situ datasets, we investigate for the first time the capability of a remote sensing model to detect and monitor HABs in the Red Sea. The model is able to successfully detect and generate maps of HABs associated with different phytoplankton functional types, matching concurrent in situ data remarkably well. We also acknowledge the limitations of using a remote-sensing based approach and show that regardless of a HAB’s spatial coverage, the model is only capable of detecting the presence of a HAB when the Chl-a concentrations exceed a minimum value of ~ 1 mg m-3. Despite the difficulties in detecting HABs at lower concentrations, and identifying species toxicity levels (only possible through in situ measurements), the proposed method has the potential to map the reported spatial distribution of several HAB species over the last two decades. Such information is essential for the regional economy (i.e., aquaculture, fisheries & tourism), and will support the management and sustainability of the Red Sea’s coastal economic zone.

Are pelagic seabirds exposed to amnesic shellfish poisoning toxins?

Marine birds have been hypothesized to be underreported victims of harmful algal blooms (HABs). Toxic blooms of Pseudo-nitzschia spp., the primary amnesic toxin producer microalgae, domoic acid (DA) are known to cause massive mortalities of coastal seabirds and marine mammals around the world. However, these fatalities are only detected when birds die nearby the coastline and little is known about possible outbreaks of pelagic seabirds in oceanic areas. Here we aim to understand whether pelagic seabirds are exposed to amnesic shellfish poisoning (ASP) toxins. For this purpose, we tracked pelagic seabirds feeding on small epipelagic fish and squid, reported to be vectors of DA, which are obtained in high productivity zones where intense Pseudo-nitzschia blooms regularly occur. In particular, we tracked Cory’s (Calonectris borealis) and Scopoli’s (C. diomedea) shearwaters breeding in Gran Canaria (Canary Is.) and in Menorca (Balearic Is.) and feeding on the Canary Current region and the Catalonian coast, respectively. We sampled birds for blood at the recovery of the GPS (Global Positioning System) and analyzed it for DA determination by Liquid Chromatography coupled with Tandem Mass Spectrometry (LC–MS/MS). Among the 61 samples analyzed from Gran Canaria, and 87 from Menorca, 31 (50.8%) and 28 (32.2%) from each location presented detectable levels of DA ranging 1.0–10.6 ng mL−1. This work reveals that DA can be detected at variable levels in the blood of ASP-asymptomatic shearwaters and suggests a chronic exposure of shearwaters to DA, highlighting the need for further studies on DA effects. These results are of high relevance due to the vulnerability of these marine birds, which populations are in continuous decline. Since global warming is expected to alter and increase the occurrence of HABs, marine toxins might become an additional stressor for seabirds and exacerbate the already precarious conservation status of many species.

Physical transport processes affect the origins of harmful algal blooms in estuaries

The effects of physical transport processes on the initiation of harmful algal blooms (HABs) in estuaries were investigated through both mathematical model analysis and numerical model experiments. This study highlights the influence of the flushing effect due to physical transport processes on the location of bloom initiation, which is comparable to or even more important than local processes. The theoretical analysis suggests that the differential flushing effect at different waterbodies due to complex geometry is one of the dominant factors causing inhomogeneous distribution of algal density during HAB initiation. The ratio of residence time to volume is one of the key variables that determine the differential timing of HAB occurrence in estuary-subestuary systems with multiple interconnected waterbodies. As a result, a HAB tends to be observed first in those locations with relatively long residence time and small waterbodies, such as tributaries or areas with large eddies. Multiple unconnected originating locations can co-exist within an estuary.Two three-dimensional model experiments with realistic forcings were conducted to demonstrate the flushing effect on annual Cochlodinium polykrikoides bloom in the lower James River. The results show that while the environmental conditions that affect local processes, such as salinity and temperature, are important in determining the originating locations of HABs, the differential flushing effect is the dominant factor driving the spatial difference in the density of C. polykrikoides in this region during the bloom initiation. This explains why the occurrence of the first bloom in this region is frequently observed in the Lafayette River, a relatively small waterbody with long residence time. Because of the relatively low growth rate of C. polykrikoides and because of the high water-exchange between the mainstem and tributaries of the James River, initial cyst distribution is suggested to have a relatively small impact on originating locations of the bloom compared to flushing effect and salinity, and the HAB originating locations do not have to be in the waterbody with abundant cysts.

Oceanography of Harmful Algal Blooms on the Ecuadorian Coast (1997–2017): Integrating Remote Sensing and Biological Data

Ocean climate drivers and phytoplankton life strategies interact in a complex dynamic to produce harmful algal blooms (HABs). This study aims to integrate historical biological data collected during “red tide” events along the Ecuadorian coast between 1997 and 2017 in relation to five ocean variables derived from satellite remote sensing data to explain the seasonal drivers of coastal processes associated with HABs dynamics. Seasonality of the occurrence of HABs was assessed in relation to oceanographic variables by applying multiple correspondence analysis (MCA) to the Ecuadorian central coast (Zone 1) and at the outer and inner Gulf of Guayaquil (Zone 2). Sixty-seven HABs events were registered between 1997 and 2017. From a total of 40 species of phytoplankton identified, 28 were identified as non-toxic and the remaining 12 are well known to produce toxins. Dinoflagellates were the taxonomic group most highly associated with potential HABs events along the entire Ecuadorian coast. HABs appear to be constrained by the Humboldt coastal upwelling, high precipitation, and associated coastal runoff, with higher biomass abundance in the Gulf of Guayaquil than in the central coast. Results from the MCA reveal that in the central Ecuadorian coast (oligotrophic system), toxic HABs occurred with low abundance of dinoflagellates, while in the Gulf of Guayaquil (eutrophic system), toxic HABs corresponded to a high abundance of dinoflagellates. In both cases, high values were found for sea surface temperature, precipitation, and irradiance—characteristic of wet seasons or El Nino years. Non-toxic HABs occurred with a high abundance of dinoflagellates, ciliates, and centric diatoms, corresponding to colder waters and low levels of precipitation and irradiance. These findings confirm that dinoflagellates display several strategies that enhance their productive capacity when ocean conditions are warmer, allowing them to produce toxins at high or at low concentrations. Considering that the Gulf of Guayaquil is essential to tourism, the shrimp industry, fisheries, and international shipping, these findings strongly suggest the need to establish an ecosystem health research program to monitor HABs and the development of a preventive policy for tourism and public health in Ecuador.

Nutrient conditions and the occurrence of a Karenia mikimotoi (Kareniaceae) bloom within East Johor Straits, Singapore

Harmful algal bloom occurrences have been an increasing problem in Southeast Asia, including Singapore. Triggers and consequences associated with such events are difficult to understand because of highly variable environmental conditions. This study provides a description of bloom patterns within the East Johor Straits (EJS) environment between Peninsular Malaysia to the north and Singapore to the south. There were two sampling periods during 1) Oct 2015–Feb 2016; and 2) Oct–Nov 2017. Sampling on Feb 2016 was increased to a five-day sampling following a bloom of the dinoflagellate Karenia mikimotoi (with high densities of >8,000 cells mL−1). The study examined taxa abundances, nutrient content, as well as salinity and chlorophyll-a profiles. During both sampling periods, elevated raphidophyte densities preceded reduced-diatom conditions which, in turn, coincided with more abundant dinoflagellate densities. Nutrient measurements indicated that the environment was often eutrophic, with high inputs particularly of nitrogen (N) sources. The inorganic-nitrogen (N) and phosphate (P) content was also close to the 16N:1P Redfield’s ratio, suggesting that the EJS could readily switch between N- or P-limitation. The EJS was frequently also silicate (Si)-limited, which could limit diatom productivity in the future. Moreover, salinity was markedly reduced on Jan 2016 (around 20–25 PSU), but was higher (around 27 PSU) at the other sampling times. These patterns present the case that EJS blooms may involve an “open-niche” condition requiring diatom densities to be decreased. This outcome may be driven by environmental or biotic factors, but further monitoring is needed to establish these conclusions.

The Incidence of Marine Toxins and the Associated Seafood Poisoning Episodes in the African Countries of the Indian Ocean and the Red Sea.

The occurrence of Harmful Algal Blooms (HABs) and bacteria can be one of the great threats to public health due to their ability to produce marine toxins (MTs). The most reported MTs include paralytic shellfish toxins (PSTs), amnesic shellfish toxins (ASTs), diarrheic shellfish toxins (DSTs), cyclic imines (CIs), ciguatoxins (CTXs), azaspiracids (AZTs), palytoxin (PlTXs), tetrodotoxins (TTXs) and their analogs, some of them leading to fatal outcomes. MTs have been reported in several marine organisms causing human poisoning incidents since these organisms constitute the food basis of coastal human populations. In African countries of the Indian Ocean and the Red Sea, to date, only South Africa has a specific monitoring program for MTs and some other countries count only with respect to centers of seafood poisoning control. Therefore, the aim of this review is to evaluate the occurrence of MTs and associated poisoning episodes as a contribution to public health and monitoring programs as an MT risk assessment tool for this geographic region.

Porewater-derived nutrient fluxes in a coastal aquifer (Shengsi Island, China) and its implication

As an important component of the hydrological and biogeochemical cycle, porewater discharge represents a significant pathway for releasing chemical solutes into coastal zones, particularly in highly permeable aquifers. In this study, a 222Rn advection-diffusion model was used to estimate the porewater discharge in a coastal aquifer (Shengsi Island, East China Sea) during November 2015. Porewater discharge was estimated to range from 7.4 to 25.8 (mean: 12.9 ± 5.8) cm d−1. Furthermore, the estimated porewater-derived nutrient fluxes (dissolved inorganic nitrogen (DIN), phosphorus (DIP) and silicon (DSi)) (mol m−2 d−1) were (1.7 ± 1.4) × 10−2, (2.1 ± 1.1) × 10−4 and (1.5 ± 1.3) × 10−2, respectively. The Si/N ratio of coastal seawater at Shengsi Island was ∼0.83, which is close to that of porewater along the coastal aquifers of Shengsi Island (∼0.92) but higher than that of the Yangtze River Estuary (∼0.68). Thus, porewater-derived Si flux with a higher Si/N ratio may mitigate the outbreak of non-siliceous algae (i.e., Prorocentrum dentatum) in adjacent waters of Shengsi Island. By comparing the SGD-derived nutrient fluxes worldwide, this study suggests that Si flux with a higher Si/N ratio through porewater discharge (or SGD) may strongly influence the Si budget and cycling because such porewater/SGD-derived Si can compensate for the dwindling Si flux from riverine sources due to human activity (i.e., dam construction, reservoirs). Our results are expected to increase our understanding of not only biogenic elements of cycling processes but also eco-environment processes such as the occurrences of harmful algal blooms alone river-influenced coasts.

Turn the potential greenhouse gases into biomass in harmful algal blooms waters: A microcosm study

Carbon sources are a critical requirement for the proliferation of algae and the occurrence of harmful algal blooms (HABs), but are often turned into methane (CH4) after the collapse of severe HABs. Here, we attempt to remove HABs, reduce algal-derived CH4 emissions, and repair the broken carbon biogeochemical cycle in aquatic systems using an integrated ecological approach including flocculation, capping, and submerged macrophyte induction, preliminary at a microcosm scale. This strategy sustainably reached 98% algal removal after 65 days of incubation and resulted in an aerobic microenvironment (ORP = +12 mv) at the sediment-water interface. The approach contributed to an approximate 60% decline in CH4 released from the aquatic environment into the atmosphere jointly through assimilation of mineralized organic carbon by submerged macrophytes, production of carbon dioxide (CO2) under aerobic conditions, and aerobic CH4 oxidation. Some of the CO2 produced in the aquatic phase contributed to inorganic carbon and formed the submerged macrophytes biomass. A combination of flocculation, capping, and submerged macrophyte incubation were significant contributors to altering the carbon budget and sealing nearly 99% of the carbon in the simulated ecosystem (the majority in sediment, followed by submerged macrophytes), providing a sustainable way to reuse algal-derived carbon and reduce CH4 emissions.

Is Submarine Groundwater Discharge (SGD) Important for the Historical Fish Kills and Harmful Algal Bloom Events of Mobile Bay?

Large-scale fish and crustacean kills, locally known as Jubilees, and harmful algal blooms (HABs) have been occurring in Mobile Bay (Alabama) for more than a century. In fact, the first record describing a Jubilee event in Mobile Bay during 1867 was the first ever-documented case of mass mortalities of marine animals caused by hypoxia. To evaluate the importance of submarine groundwater discharge (SGD) in the occurrence of Jubilees and HABs in Mobile Bay, a 3-year study was conducted using a multi-method approach. Significant spatial and temporal variations of SGD were revealed in the bay only by applying a combination of geochemical and shallow geophysical techniques. The development of seasonal hypoxia observed in bay waters in areas impacted by Jubilees was the result of anoxic SGD inputs, which magnitude and spatial distribution were controlled by shallow lithological heterogeneities created during the modern development of the bay. Although when compared to the river discharge SGD contributed between 0.2 (wet season) and 5% (dry season) of the total freshwater inputs to Mobile Bay, 80% of the total SGD in the bay occurred in areas ecologically impacted by hypoxia and Jubilees. In these areas, SGD comprised up to 37% of the total water inputs during the dry season, coinciding with the time of the year when Jubilees and HABs occur. In conclusion, while SGD might not be a significant source of fresh water to Mobile Bay or other estuaries worldwide, enhanced SGD caused by site-specific lithological heterogeneities can have a critical role in the development of hypoxia and ecological issues in nearshore waters.