Effect of the molecular weight of DOM on the indirect photodegradation of fluoroquinolone antibiotics.

Dissolved organic matter (DOM) is ubiquitous and widespread in natural water and influences the transformation and removal of antibiotics. Nevertheless, the influence of DOM molecular weight (MW) on the indirect photodegradation of antibiotics has rarely been reported. This study attempted to explore the influence of the molecular weight of DOM on the indirect photodegradation of two fluoroquinolone antibiotics (FQs), ofloxacin (OFL) and norfloxacin (NOR), by using UV-vis absorption and fluorescence spectroscopy. The results showed that indirect photodegradation was considered the main photodegradation pathway of FQs in DOM fractions. Triplet-state excited organic matter (3DOM*) and singlet oxygen (1O2) were the main reactive intermediates (RIs) that affected the indirect photodegradation of FQs. The indirect photodegradation rate of FQs was significantly promoted in DOM fractions, especially in the low molecular weight DOM fractions (L-MW DOM, MW < 10 kDa). The results of excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC) showed that terrestrial humic-like substances had a higher humification degree and fluorophore content in L- MW DOM fractions, which could produce more 3DOM* and 1O2 to promote the indirect photodegradation of FQs. This study provided new insight into the effects of DOM at the molecular weight level on the indirect photodegradation of antibiotics in natural water.

Absorption and Fluorescence Properties of Chromophoric Dissolved Organic Matter Produced by Algae.

Four kinds of diatom (Chaetoceros curvisetus, Phaeodactylum tricornutum, Nitzschia closterium f. minutissima and Navicula halophile) and two kinds of dinoflagellates (Prorocentrum donghaiense and Gymnodinium) were cultured under laboratory conditions. Variations of optical properties of chromophoric dissolved organic matter (CDOM) were studied with absorption and fluorescence excitation-emission matrix spectroscopy(EEM) during growth of marine microalgae in incubation experiment. Absorption spectrum revealed absorption coefficient a(355) (CDOM absorption coefficients at 355 nm) of 6 kinds of marine microalgae above increased by 64.8%, 242.3%, 535.1%, 903.2%, 836% and 196.4%, respectively. Simultaneously, the absorption spectral slope (Sg), determined between 270 and 350 nm, representing the size of molecular weight of CDOM and humic-like composition, decreased by 8.7%, 34.6%, 39.4%, 53.1%, 46.7%, and 35.7%, respectively. Applying parallel factor analysis (PARAFAC) together with EEM got four components of CDOM: C1(Ex/Em=350(260) nm/450 nm), C2 (Ex/Em=260(430) nm/525 nm), C3 (Ex/Em=325 nm/400 nm) and C4(Ex/Em=275 nm/325 nm), which were relative to three humic-like and one protein-like fluorescent components of Nitzschia closterium f. minutissima and Navicula halophile. In incubation experiment, fluorescence intensity of these four components during growth of Nitzschia closterium f. minutissima increased by, respectively, 8.68, 24.9, 7.19 and 39.8 times, and those of Navicula halophile increased by 2.64, 0.07, 4.39 and 12.4 times, respectively. Significant relationships were found between the fluorescence intensity of four components of CDOM, a(355) and Sg. All results demonstrated that both content and molecular weight of CDOM produced by diatom and dinoflagellate studied in incubation experiment increased, but these two parameters changed more obviously of the diatom than those of dinoflagellate; the proportion of humic-like components in the composition of CDOM also increased clearly with the growth of marine microalgae, but protein-like fluorescent component had only a slow growth. Furthermore, the absorption spectrum of CDOM produced by different species of algae changed obviously and the relative composition fluorescence intensity of CDOM produced by different microalgae were found to vary among different composition from EEM, which suggested CDOM produced by different microalgae make quite different contributions to CDOM in natural seawater.

Antifouling potential of the marine microalga Dunaliella salina.

Marine organisms have usually been viewed as sources of environmentally friendly compounds with antifouling activity. We performed a series of operations to investigate the antifouling potential of the marine microalga Dunaliella salina. For the ethyl acetate crude extract, the antialgal activity was significant, and the EC50 value against Skeletonema costatum was 58.9 µg ml(-1). The isolated purified extract was tested for antifouling activity, the EC 50 value against S. costatum was 21.2 µg ml(-1), and the LC50 against Balanus amphitrite larvae was 18.8 µg ml(-1). Subsequently, both UHR-TOF-MS and GC-MS were used for the structural elucidation of the compounds, and a series of unsaturated and saturated 16- and 18-carbon fatty acids were detected. The data suggested that the fatty acid extracts from D. salina possess high antifouling activity, and could be used as substitutes for potent, toxic antifouling compounds.

Bioaerosols in the coastal region of Qingdao: Community diversity, impact factors and synergistic effect.

Atmospheric bioaerosols are influenced by multiple factors, including physical, chemical, and biotic interactions, and pose a significant threat to the public health and the environment. The nonnegligible truth however is that the primary driver of the changes in bioaerosol community diversity remains unknown. In this study, putative biological association (PBA) was obtained by constructing an ecological network. The relationship between meteorological conditions, atmospheric pollutants, water-soluble inorganic ions, PBA and bioaerosol community diversity was analyzed using random forest regression (RFR)-An ensemble learning algorithm based on a decision tree that performs regression tasks by constructing multiple decision trees and integrating the predicted results, and the contribution of different rich species to PBA was predicted. The species richness, evenness and diversity varied significantly in different seasons, with the highest in summer, followed by autumn and spring, and was lowest in winter. The RFR suggested that the explanation rate of alpha diversity increased significantly from 73.74 % to 85.21 % after accounting for the response of the PBA to diversity. The PBA, temperature, air pollution, and marine source air masses were the most crucial factors driving community diversity. PBA, particularly putative positive association (PPA), had the highest significance in diversity. We found that under changing external conditions, abundant taxa tend to cooperate to resist external pressure, thereby promoting PPA. In contrast, rare taxa were more responsive to the putative negative association because of their sensitivity to environmental changes. The results of this research provided scientific advance in the understanding of the dynamic and temporal changes in bioaerosols, as well as support for the prevention and control of microbial contamination of the atmosphere.

[Research on using 3-D fluorescence spectroscopy-wavelet transform-PSO for rapid discrimination of compositions of phytoplankton population].

Three-dimensional fluorescence of 17 red tide algae species that belong to 13 genera of five divisions was measured by fluorescence excitation-emission matrix spectroscopy. And 2-D wavelet db7 was selected to decompose the spectra at different levels to choose the alternative characteristic spectra. Based on the norm reference spectra constructed by cluster analysis, the linear regression model was solved by particle swarm optimization (PSO) algorithm and the discrimination method was established at the division and genus level. Some samples were tested: for single algal samples, and the correct discrimination ratios (CDRs) were 96.1% and 73.6%, respectively; For simulative mixed algal samples, when the dominance were 60%, 75%, 80% and 90% of the total biomass, the CDRs of the dominant algae were 86.7%, 96.9%, 98.7% and 99.4% with the average relative contents of 62.6%, 72.7%, 76.0% and 81.6%, respectively at the division level. And the CDRs were 51.0%, 68.9%, 72.0%, and 78.8% at the genus level, respectively. For 364 actual mixture samples, the CDRs of the dominant species (75%) were 99.4% at the division level and 75.9% at the genus level . For the particular field samples from mesocosm experiment and corrected from Jiaozhou Bay, results showed that the method can be used to realize the identification of red tide algae population and estimate the relative abundance of different classes, especially between diatoms and dinoflagellates.

Indirect photodegradation of sulfisoxazole: Effects of environmental factors (CDOM, pH, salinity, HCO3-, metal ions, halogen ions and NO3-).

It's a new perspective to explore the influences of chromophoric dissolved organic matter (CDOM) components and environmental factors on the removal of sulfisoxazole (SIX) from the water matrix. Reactive intermediates (RIs) trapping experiments demonstrated that excited triplet-state CDOM (3CDOM⁎) played a dominant promoting role (54.11%) in the CDOM-mediated SIX indirect photodegradation. Additionally, terrestrial humic-like (C1, C3 and C4) and marine humic-like (C2) fluorescent components were identified by parallel factor (PARAFAC) analysis of CDOM excitation-emission matrix spectroscopy (EEMs). C1 and C4 were significantly correlated (R2 > 0.91) with the SIX degradation rate owing to their higher productivity of RIs and a greater contribution to the production of 3CDOM⁎ compared to others. Salinity, pH and HCO3- were conducive to the SIX indirect photodegradation, while metal ions (Fe3+ and Cu2+), halogen ions (Cl- and Br-) and NO3- were opposite. These findings are essential for understanding the environmental fate of SIX in coastal waters.

Spatiotemporal patterns and influencing factors of dissolved heavy metals off the Yangtze River Estuary, East China Sea.

Dissolved heavy metal pollution in the ocean is becoming an environmental concern. Their distribution patterns are complex and influenced by multiple factors in the coastal ocean. Therefore, more investigations are needed to understand their behavior in the seawater. This study systematically investigated the distribution of Cu, Pb, Cd, As, Zn and seawater properties in the surface and bottom water off the Yangtze River Estuary, East China Sea in spring, summer and autumn, 2019. The results showed significant spatiotemporal distribution that three-zone-pattern of estuary, nearshore, and offshore can be divided. While sources, hydrodynamics, biological uptake and sediment resuspension affected the overall distribution, dissolved oxygen and pH dominantly influenced the estuary and offshore respectively, with more complex factors in the nearshore. Low ecological risks were assessed during the study, but global warming, ocean acidification and hypoxia are essential concerns to understand the biogeochemistry of dissolved heavy metals in the ocean.

Effects of organic nitrogen components from terrestrial input on the phytoplankton community in Jiaozhou Bay.

Dissolved organic nitrogen (DON) from terrestrial input exacerbates eutrophication and induces harmful algal blooms. We investigated the effects of hydrophilic (Hic) and low molecular weight (LMW) DON on the phytoplankton community in Jiaozhou Bay during autumn (October 2017) and spring (May 2018). Our results showed DON additions significantly increased algal growth while decreasing community biodiversity and provide a competitive advantage for Skeletonema costatum. These situations were further intensified by increasing temperature in autumn. Additionally, Hic DON had a higher bioavailability than LMW DON. Based on emission-excitation matrix spectra, we identified protein-like components as the main components of Hic DON whereas humus-like components were the principal components of LMW. Correlation analysis confirmed a positive correlation between DON bioavailability and protein-like components. Therefore, our results indicate DON from terrestrial input disrupts the structural stability of the phytoplankton community and increases the risk of harmful algal blooms, which in turn threaten coastal ecosystems.

No detected toxic concentrations in in situ algal growth inhibition tests--a convenient approach to aquatic ecotoxicology.

A newly proposed three-dimensional model for the effects of heavy metals on the growth of batch cultures of algae that allows the estimation of the no detected toxic effect concentration (NDEC) is presented. Two batch assays with exposure to copper were investigated in situ. As an endpoint in the in situ studies of ecotoxicology, the carrying capacity, a parameter of the logistic growth model, possesses higher sensitivity and reliability than the routine ecotoxicological endpoints in terms of the analysis based on the theoretical arguments and experimental results. Using the carrying capacity (B(f)) as the ecotoxicological endpoint, the NDEC from the proposed model is compared to the NOEC and EC(05) on the basis of field derived data. The results indicate that the NDEC is a promising possible alternative parameter to the NOEC.

[Research on the 3D discrete fluorescence spectrum technique for differentiation of phytoplankton population].

The present research was targeted to develop a fluorescence analyser for phytoplankton population which uses a series of LEDs as the light source. So the 3D discrete fluorescence spectra with 12 excitation wavelengths (400, 430, 450, 460,470, 490, 500, 510, 525, 550, 570 and 590 nm) were determined by fluorescence spectrophotometer for 43 phytoplankton species. Then, the wavelet, Daubechies-7 (Db7), and Bayes Classifier were applied to extract the characteristics for each classes from the 3D discrete fluorescence spectra. Lastly, the fluorescence differentiation method for phytoplankton populations was established by multivariate linear regression and non-negative least squares, which could differentiate phytoplankton populations at the levels of both divisions and genus. This method was tested: for simulatively mixed samples(the dominant species accounted for 70%, 80%, 90% and 100% of the gross biomass, respectively) from 32 red tide algal species, and the correct discrimination rates at the level of genus were 67.5%, 75.8%, 81.4% and 79.4%, respectively. For simulatively mixed samples (the dominant divisions algae accounted for 50%, 75% and 100% of the gross biomass, respectively) from 43 algal species, the discrimination rates at the level of division were 95.2%, 99.7% and 91.9% with average relative content of 38.1%, 63.2% and 90.5%, respectively.

Indirect photodegradation of sulfathiazole and sulfamerazine: Influence of the CDOM components and seawater factors (salinity, pH, nitrate and bicarbonate).

Sulfonamides (SAs) are ubiquitous antibiotics that are increasingly detected in the aquatic environment, and may cause potential harm to the environment and humans. Indirect photodegradation has been considered to be a promising natural degradation process for antibiotics in the environment. Chromophoric dissolved organic matter (CDOM) is an important participant in the indirect photodegradation of antibiotics. Indirect photodegradation of sulfathiazole (ST) and sulfamerazine (SM) were studied in the presence of CDOM and marine factors (salinity, pH, nitrate (NO3-) and bicarbonate (HCO3-)) to simulate photodegradation of these compounds in the coastal seawater environment. The main findings are as follows. First, the indirect photodegradation rates of ST and SM in the presence of CDOM were significantly increased and followed the pseudofirst order kinetics. Second, 1O2 played a critical role in the indirect photodegradation of ST and its contribution rate was 54.2%; 3CDOM⁎ performed similarly in the case of SM with a 58.0% contribution rate. Third, CDOM was divided into four fluorescent components by excitation-emission matrix spectroscopy and parallel factor analysis (EEMs-PARAFAC), including three exogenous components and an autochthonous component. The exogenous components with high molecular weight and higher number of aromatic groups played a decisive role in the indirect photodegradation of ST and SM due to their ability to generate higher levels of reactive intermediates (RIs). Finally, seawater factors (salinity, pH, NO3- and HCO3-) influenced the indirect photodegradation of ST and SM by influencing the steady-state concentrations of RIs. This report is the first study of indirect photodegradation of ST and SM from the perspective of the CDOM components and simulated coastal waters.

Indirect photodegradation of sulfadiazine in the presence of DOM: Effects of DOM components and main seawater constituents.

The presence of pharmaceuticals and personal care products in coastal waters has caused concern over the past decade. Sulfadiazine (SD) is a very common antibiotic widely used as human and fishery medicine, and dissolved organic matter (DOM) plays a significant role in the indirect photodegradation of SD; however, the influence of DOM compositions on SD indirect photodegradation is poorly understood. The roles of reactive intermediates (RIs) in the indirect photolysis of SD were assessed in this study. The reactive triplet states of DOM (3DOM∗) played a major role, whereas HO· and 1O2 played insignificant roles. DOM was divided into four components using excitation-emission matrix spectroscopy combined with parallel factor analysis. The components included three allochthonous humic-like components and one autochthonous humic-like component. The allochthonous humic-like components contributed more to RIs generation and SD indirect photolysis than the autochthonous humic-like component. A significant relationship between the indirect photodegradation of SD and the decay of DOM fluorescent components was found (correlation coefficient, 0.99), and the different indirect photodegradation of SD in various DOM solutions might be ascribed to the different components of DOM. The indirect photolysis rate of SD first increased and then decreased with increasing pH. SD photolysis was enhanced by low salinity but remained stable at high salinity. The increased carbonate concentration inhibited SD photolysis, whereas nitrate showed almost no effect in this study.

Influences of the hydrophilic components of two anthropogenic dissolved organic nitrogen groups on phytoplankton growth in Jiaozhou Bay, China.

Increasing human activities have caused the accumulation of dissolved organic nitrogen (DON) in the ocean, which can alter dominant coastal phytoplankton species. However, insights into DON's effects on marine phytoplankton growth are insufficient compared with those of dissolved inorganic nitrogen (DIN), especially regarding the role of specific DON components. Therefore, in this study, the effects of the hydrophilic (Hic) and low molecular weight (LMW) components of two anthropogenic DON sources on the growth and bioavailable nitrogen uptake of phytoplankton were studied using in situ cultural experiments conducted in Jiaozhou Bay, China. Animal-derived DON from domestic and livestock breeding showed a higher bioavailability compared with that of vegetal DON derived from agricultural sources, with bioavailable component proportions of 76% ± 4% and 66% ± 3%, respectively. Both forms of DON could be absorbed by Skeletonema costatum, stimulating it to become the dominant species in the mesocosm ecosystem; the hydrophilic components of DON contributed approximately 75% of the uptake of DON by S. costatum. The bioavailability of LMW DON was significantly (p < 0.05) lower than that of the Hic DON. The high bioavailability of the Hic DON was mainly associated with its protein-like T1 and T2 components, identified using parallel factor analysis on the excitation-emission-matrix spectra, while the low bioavailability of LMW DON was mainly associated with the humus-like A component. The protein-like T2 components may be directly absorbed by algae, while T1 may be transformed through mineralization and algal absorption. Understanding the impacts of anthropogenic DON and its components on phytoplankton will help improve coastal environmental management. More knowledge of the effect of anthropogenic DON on the phytoplankton community structure in coastal waters should be accumulated in the future.

Nutrient-rich submarine groundwater discharge fuels the largest green tide in the world.

One of the largest "green tide" (Ulva prolifera) outbreaks in the world has occurred every year from 2007 to present in the Southern Yellow Sea, China. Currently, the coastal area around Jiangsu Province (Subei Shoal region) is thought to be the origination point of these giant green tide blooms. The combination of high nutrient demand but low river discharge and other inputs suggests that there is a significant flux of submarine groundwater discharge (SGD) in this area. By using a radium mass balance model, we estimated the SGD flux in the area to be (0.7-1.4) × 109 m3 d-1 (6.1-12 cm d-1), at the high end of SGD fluxes worldwide. Geographically, Subei Shoal is less than 5% of the entire Southern Yellow Sea area, while our calculated SGD flux just for the shoal area is ~3 times larger than previously documented for the whole Southern Yellow Sea. Therefore, Subei Shoal may be considered a SGD hotspot that plays an important role in SGD associated material fluxes. Compared to inputs from local rivers, atmospheric deposition, and anthropogenic activities, SGD-derived nutrients are the main source term that can support the growth of macroalgae. We specifically highlight that this type of areas that are shallow, intensively mixed, anthropogenically polluted, sandy or muddy with heavy bio-irrigation, may have a higher risk of suffering harmful ecological problems, even with limited terrestrial runoff.

[Research on the 3D fluorescence spectra differentiation of phytoplankton by coiflet2 wavelet].

In the present paper, the authors utilize the wavelet base function coiflet2 (coif2) to analyze the 3D fluorescence spectra of 37 phytoplankton species belonging to 30 genera of 7 divisions, and these phytoplankton species include common species frequently causing harmful algal blooms and most predominant algal species in the inshore area of China Sea. After the Rayleigh and Raman scattering peaks were removed by the Delaunay triangulation interpolation, the fluorescence spectra of those phytoplankton species were transformed with the coiflet2 wavelet, and the scale vectors and the wavelet vectors were candidate for the feature spectra. Based on the testing results by Bayesian analysis, the 3rd scale vectors were the best feature segments at the division level and picked out as the fluorescence division feature spectra of those phytoplankton species, and the group of the 3rd scale vectors, the 2nd and 3rd wavelet vectors were the best feature segments at the genus level and chosen as the fluorescent genus feature spectra of those phytoplankton species. The reference spectra of those phytoplankton species at the division level and that at the genus level were obtained from these feature spectra by cluster analysis, respectively. The reference spectra base for 37 phytoplankton species was composed of 107 reference spectra at the division level and 155 ones at the genus level. Based on this reference spectra base, a fluorometric discriminating method for phytoplankton populations was established by multiple linear regression resolved by the nonnegative least squares. For 1 776 samples of single phytoplankton species, a correct discriminating rate of 97.0% at genus level and 98.1% at division level can be obtained; The correct discriminating rates are more than 92.7% at the genus level and more than 94.8% at the division level for 384 mixed samples from two phytoplankton species.

Extraction and identification of toxic organic substances from decaying green alga Ulva prolifera.

In this study, the extraction, identification, and antialgal activity of toxic organic substances from decaying green alga Ulva prolifera, a disaster-causing alga on green tides in the Yellow Sea, were investigated. The toxic organic substances of U. prolifera were isolated by a sequence of procedures, namely, liquid-liquid extraction (LLE), silica gel chromatography column separation (SGCC), C18 solid phase extraction (C18 SPE), and acid-alkali separation (AAS) and their antialgal activities were tested against diatom Skeletonema costatum. The results showed that the 96h-EC50 value in each procedure was 57.00 mg•L-1, 12.14 mg•L-1, 11.70 mg•L-1, and 6.31 mg•L-1 in turn. Additionally, the initial (ethyl acetate extract in LLE) and final (Organic phase A in AAS) yield of toxic organics were 318 mg•kg-1 and 9 mg•kg-1 (the wet weight of U. prolifera). The final active fractions were preliminary identified as five 16- and 18-carbon fatty acids and four enols using GC-MS. The study may further evaluate the effect of bioactive substances on marine life after U. prolifera green tides bloom.

Characterization of the development stages and roles of nutrients and other environmental factors in green tides in the Southern Yellow Sea, China.

Large-scale floating green tides in the Southern Yellow Sea (SYS) caused by the macroalgal species Ulva prolifera have been recurring for 13 years and have become one of the greatest marine ecological disasters in the world. In this study, we attempt to explore the development pattern of green tides and find its key environmental influencing factors. The satellite remote sensing data of the development process of green tides fit the logistic growth curve (R2 = 0.93, P < 0.01) well, showing three distinct growth phases (lag, exponential growth, and short plateau phases). Correspondingly, the green tide-drifting area from the coast of Jiangsu to the nearshore waters of the Shandong Peninsula was divided into three sections: the lag phase zone (A), the exponential growth phase zone (B), and the plateau phase zone (C). Zone A in the south of Jiangsu coastal waters had abundant inorganic nutrients that were indispensable to the green tide initiation. Zone B was mainly located out of Haizhou Bay, south of 34.5° N and north of 35.5° N, where approximately 80% of the green tide biomass was generated. The rich bioavailable nutrient sources, suitable temperature, and irradiance in this area were the main promotion factors for the rapid growth and scale expansion of green tides. Wet precipitation in zone B in May and June also played an important role in the final scale of green tides. Zone C had poor nutrients, increasing temperature, and irradiance (high transparency), which limited the continued expansion of green tides, and organic nutrients might be an important support to green tides development in this region. The study based on the growth phases of green tides could help us further understand the eutrophication mechanism in the green tide outbreaks in SYS.

Role of nutrients in the development of floating green tides in the Southern Yellow Sea, China, in 2017.

The largest-scale green tides in the world caused by Ulva prolifera have been recurring annually in the Southern Yellow Sea since 2007. In this study, spatio-temporal variations of green tides and nutrients were investigated in the spring and summer of 2017, and the roles of different nutrients in the development of green tides are discussed. The results showed that the development of green tides could be divided into two parts according to the distinct growth phases of green tides: (1) the development area (DA), which was located south of 35°N and characterised by the quick expansion of green tide and high-content nutrient; (2) the accumulation area (AA), which was located north of 35°N and characterised by high U. prolifera coverage area and low-content inorganic nutrients. Through calculation of nutrient reductions, we found that DA provided 96% of nitrogen and 87% of phosphorus for the development of green tides in 2017, and the dominant nutrient species were dissolved inorganic nitrogen and dissolved organic phosphorus. Regarding AA, the dominant nitrogen component was dissolved organic nitrogen. Thus, we conclude that reducing the level of nutrient input in order to alleviate the eutrophication of seawater in the Jiangsu coastal area may be an important measure for reducing the scale of green tides.

An anomalous bi-macroalgal bloom caused by Ulva and Sargassum seaweeds during spring to summer of 2017 in the western Yellow Sea, China.

An unprecedented bi-macroalgal bloom caused by Ulva prolifera and Sargassum horneri occurred from spring to summer of 2017 in the western Yellow Sea (YS) of China, where annual large-scale green tides have prevailed for a decade. The distinct genesis and blooming dynamics of the two seaweed species were detected and described. Unlike the consistent raft-origin of the floating Ulva biomass, the massive pelagic S. horneri was derived from multiple sources (residual seaweeds from the previous winter bloom and those drifting from offshore water in the south). The scale of the green tide in 2017 was found smaller than the previous four years. We then discussed a number of hypotheses attributing to this reduction, including reduced epiphytic green algae from aquaculture rafts and the influences of the massive pelagic S. horneri. However, further research is needed to identify the origin of the pelagic S. horneri in the western YS and any affiliations with the benthic populations, and to elucidate the interactions of this species with the annual green tides and the ensuing consequences.

Composition variations and spatiotemporal dynamics of dissolved organic matters during the occurrence of green tide (Ulva prolifera blooms) in the Southern Yellow Sea, China.

Seawater samples were collected from April 6 to September 6, 2017 in the Southern Yellow Sea, China where green tides often occurred, and analyzed for nutrients, dissolved organic carbon (DOC), and fluorescent dissolved organic matter (FDOM). The DOC concentrations increased significantly in the green tide areas by approximately 1.2 times compared to those in the non-green tide areas. From the large-scale outbreak to the complete dissipation of the green tide, the fluorescence intensities of the four FDOM fluorescent components identified in the green tide areas were significantly higher than those in the non-green tide areas. During the extinction period, the fluorescence intensities of the three humus-like components and one protein-like component were approximately 1.8 and 1.3 times higher than those in the non-green tide areas, respectively. These findings suggested that the outbreak of green tide could release DOM into water and affect the biogeochemical cycle in green tide regions.