Infl uence of sequential tropical cyclones on phytoplankton blooms in the northwestern South China Sea

Upper ocean responses to the passage of sequential tropical cyclones over the northwestern South China Sea(SCS)in 2011 were investigated using satellite remote sensing data,Argo reanalysis data,and an array of mooring data.We found that the sea surface low temperature region lasted for more than 38 days and two phytoplankton blooms occurred after the passage of sequential tropical cyclones.The upper ocean cooling reached 2–5°C with a right-side bias was observed along the typhoon track to about 200 km.The maintenance of low temperature region and the two phytoplankton blooms were mainly driven by upwelling and near-inertial turbulence mixing induced by the sequential tropical cyclones.The fi rst phytoplankton bloom appeared on the 7 th day after the passage of the three tropical cyclones,and the chlorophyll-a(chl-a)concentration increased by 226%,which may be mainly driven by typhoons induced upwelling.The second phytoplankton bloom occurred on the 30 th day,the chl-a concentration increased by 290%.Further analysis suggested that only the typhoons with similar characteristics as Nesat and Nalgae can induce strong near-inertial oscillation(NIO).Strong turbulent mixing associated with the near-inertial baroclinic shear instability lasted for 26 days.The measured mean eddy diff usivity in the upper ocean was above 10-4 m 2/s after typhoon Nesat.Enhancement of the turbulent mixing in the upper ocean helped to transport nutrient-rich cold waters from the deep layer to the euphotic layer,and is a major mechanism for the long-term maintenance of low temperature region as well as the second phytoplankton bloom.

Latitudinal and interannual variations of the spring phytoplankton bloom peak in the East Asian marginal seas

Combined studies of latitudinal and interannual variations of annual phytoplankton bloom peak in East Asian marginal seas(17°–58°N, including the northern South China Sea(SCS), Kuroshio waters, the Sea of Japan and the Okhotsk Sea) are rarely. Based on satellite-retrieved ten-year(2003–2012) median timing of the annual Chlorophyll a concentration(Chl a) climax, here we report that this annual spring bloom peak generally delays from the SCS in January to the Okhotsk Sea in June at a rate of(21.20±2.86) km/d(decadal median±SD). Spring bloom is dominant feature of the phytoplankton annual cycle over these regions, except for the SCS which features winter bloom. The fluctuation of the annual peak timing is mainly within ±48 d departured from the decadal median peak date, therefore this period(the decadal median peak date ±48 d) is defined as annual spring bloom period. As sea surface temperature rises, earlier spring bloom peak timing but decreasing averaged Chl a biomass in the spring bloom period due to insufficient light is evident in the Okhotsk Sea from 2003 to 2012. For the rest of three study domains, there are no significant interannual variance trend of the peak timing and the averaged Chl a biomass. Furthermore this change of spring phytoplankton bloom timing and magnitude in the Okhotsk Sea challenges previous prediction that ocean warming would enhance algal productivity at high latitudes.

Growth characteristics of algae during early stages of phytoplankton bloom in Lake Taihu,China

Three treatments, sediment plus lake water （S＋W）, sterilized sediment plus lake water （SS＋W）, and sediment plus filtered lake water （S＋FW）, were recruited to investigate the growth characteristics of algae during pre-bloom and the importance of algal inocula in the water column and sediment. The results showed that in the water column, biomass of all algae increased in all treatments when recruitment was initiated, whereas this tendency differed among treatments with further increment of temperature. The process of algal growth consisted of two stages： Stage I, the onset of recruitment and Stage II, the subsequent growth of algae. Compared with S＋W, in Stage I, SS＋W significantly increased the biomass of cyanophytes by 178.70%, and decreased the biomass of non-cyanophytes by 43.40%; In Stage II, SS＋W notably stimulated the growth of all algae, thus incurring the occurrence of phytoplankton bloom. Further analyses revealed that both metabolic activity and photochemical activity of algae were enhanced in SS＋W, which resulted from the releasing of nutrients from sediment. These results suggest that algal growth in Stage II and algal inocula in the water column can be important factors for the formation of phytoplankton bloom. In addition, possible mechanisms promoting algal recruitment and subsequent growth of algae were explored.

The biogeochemical behavior of dissolved aluminum in the southern Yellow Sea:Influence of the spring phytoplankton bloom

Many recent studies have investigated the nutrient-type profiles of dissolved aluminum(Al) in the ocean.Significant scavenging of dissolved Al can occur during phytoplankton blooms,but the mechanism remains unclear.The distribution of dissolved Al in the southern Yellow Sea(SYS) was investigated in winter and spring 2009.Following measurements at grid stations during the spring sampling cruise,two drifting anchor surveys of more than 100 h were conducted to trace the variation of dissolved Al concentration during the spring phytoplankton bloom(SPB).The concentration of dissolved Al in the SYS decreased from 40 nmol/L in February to 30 nmol/L in March and 10-20 nmol/L in April,while the concentration of Chl a increased from < 2 μg/L in March to > 4 μg/L in April.The concentration of dissolved Al in the SYS decreased significantly with the development of the phytoplankton bloom,which indicated biological scavenging of dissolved Al from water column.The proportion of dissolved Al scavenged from water column by different phytoplankton species differed at the two drifting stations,with greater removal efficiency demonstrated by diatoms than dinoflagellates.Phytoplankton samples collected from the Chl a maximum layer were washed with trace metal clean reagent(oxalate-EDTA-citrate,abbreviate as oxalate solution,Tovar-Sanchez et al.,2003) to enable the surface-scavenged(extracellular) and intracellular Al pools associated with phytoplankton to be differentiated.Thirty-nine to ninetysix percent of the total Al was found to be existed in the interior pools,which indicated that biological absorption was the important way to scavenge dissolved Al during phytoplankton blooms in the SYS.

Community Structures of Phytoplankton with Emphasis on Toxic Cyanobacteria in an Ohio Inland Lake during Bloom Season

The community structures of phytoplankton are important factors and indicators of lake water quality. Harmful algal blooms severely impact water supply, recreational activities and wildlife habitat. This study aimed to examine the phytoplankton composition and variations using microscopy, and identify harmful Cyanobacteria in weekly samples taken from four sites at Harsha Lake in southwest Ohio. Over the course of the summer in 2015, the phytoplankton of Harsha Lake consisted mainly of 13 taxa belonging to Bacillariophyta, Chlorophyta, Cryptophyta, Cyanobacteria, Dinophyta and Euglenophyta. Their significant successions started with Bacillariophyta and/or Chlorophyta, then bloomed with Cyanobacteria and ended with Chlorophyta and/or Dinophyta. Cyanobacteria members: Microcystis, Planktothrix, Dolichospermum, Aphanizomenon, Cylindrospermopsis, and Oscillatoria from the Cyanophyceae were identified to be dominant genera. These organisms varied spatially and temporally in similar patterns along with the variations of nutrients and formed the summer bloom with the total biomasses ranging from 0.01 to 114.89 mg L-1 with mean of 22.88 mg L-1. M. aeruginosa and P. rubescens were revealed as the microcystin producers, while A. circinalis and Aphanizomenon sp. were identified as a saxitoxin producer through cloning and sequencing PCR products of mcyA, mcyE and sxtA genes. The biomasses of phytoplankton, Cyanobacteria and Microcystis were positively correlated to nutrients, especially to total nitrogen. The total ELISA measurement for microcystin positively correlated with Cyanobacteria (R2 = 0.66, P Microcystis (R2 = 0.64, P 2 = 0.59, P < 0.0001). The basic information on the occurrence and biomasses of Cyanobacteria and total phytoplankton, and the analysis for toxic species, which were the first report for the inland water in Ohio, USA, will document the succession patterns of phytoplankton and toxin production over a season and provide data to predict risk occurrence to both human and ecological factors.

Relationship between bacteria and phytoplankton during the giant jellyfish Nemopilema nomurai bloom in an oligotrophic temperate marine ecosystem

Bacterial abundance, phytoplankton community structure and environmental parameters were investigated to study the relationships between bacteria and phytoplankton during giant jellyfish Nemopilema nomurai blooms in the central Yellow Sea during 2013. N. nomurai appeared in June, increased in August, reached a peak and began to degrade in September 2013. Results showed that phosphate was possible a key nutrient for both phytoplankton and bacteria in June, but it changed to nitrate in August and September. Phytoplankton composition significantly changed that pico-phytoplankton relative biomass significantly increased, whereas other size phytoplankton significantly decreased during jellyfish bloom. In June, a significantly positive correlation was observed between chlorophyll a concentration and bacterial abundance（r=0.67, P0.001, n=34）.During jellyfish outbreak in August, there was no significant correlation between phytoplankton and bacteria（r=0.11, P0.05, n=25）, but the relationship（r=0.71, P0.001, n=31） was rebuilt with jellyfish degradation in September. In August, small size phytoplankton occupied the mixed layer in offshore stations, while bacteria almost distributed evenly in vertical. Chlorophyll a concentration significantly increased from（0.42±0.056） μg/L in June to（0.74±0.174） μg/L in August, while bacterial abundance just slightly increased. Additionally, the negative net community production indicated that community respiration was not entirely determined by the local primary productivity in August. These results indicated that jellyfish blooms potentially affect coupling of phytoplankton and bacteria in marine ecosystems.

三峡水库小江回水区水华暴发期浮游植物群落结构及其与环境因子的关系

三峡水库蓄水以来,支流水华频发,尤以小江情况最为严重,给三峡库区的生态安全带来较大隐患。为探究支流水华暴发特征和主控因素,于20142021年小江水华暴发期间在小江高阳江段进行浮游植物及环境因子调查,并使用单因素方差分析、聚类分析、百分比相似性分析以及基于距离的线性模型等方法,对小江水华暴发期间浮游植物和环境因子在不同年份不同水层间的差异以及二者的关系进行研究。结果表明:小江水华暴发期内,浮游植物的种类数在43~70种之间,其中2015年蓝藻种类数明显减少,2018年以后硅藻种类数明显减少;采样期间浮游植物平均细胞密度在0.66×10^(6)~61.28×10^(6)cells/L之间,同期表层细胞密度明显高于中层和底层;各层水体间水华微囊藻、铜绿微囊藻、不定微囊藻等10种藻的密度存在明显差异,是主要差异种;显著影响表层、中层和底层浮游植物群落结构变动的环境因子是水位的日平均变幅;水位的日平均变幅与藻类优势种拟合关系显示,当日水位下降幅度在0.5 m以上时,浮游植物平均密度会呈指数级减少。研究结果可为三峡库区支流水华的防控提供数据支持。

Stocks and dynamics of particulate and dissolved organic matter in a large, shallow eutrophic lake(Taihu, China) with dense cyanobacterial blooms

Cyanobacterial blooms occur in eutrophic lakes worldwide, and greatly impair these ecosystems. To explore influences of cyanobacterial blooms on dynamics of both particulate organic matter(POM) and dissolved organic matter(DOM), which are at the base of the food chain, an investigation was conducted from December 2014 to November 2015 that included various stages of the seasonal cyanobacterial blooms(dominated by M icrocystis) in a large-shallow eutrophic Chinese lake(Taihu Lake). Data from eight sites of the lake are compiled into a representative seasonal cycle to assess general patterns of POM and DOM dynamics. Compared to December, 5-fold and 3.5-fold increases were observed in July for particulate organic carbon(POC, 3.05–15.37 mg/L) and dissolved organic carbon(DOC, 5.48–19.25 mg/L), respectively, with chlorophyll a(Chl a) concentrations varying from 8.2 to 97.7 μg/L. Approximately 40% to 76% of total organic carbon was partitioned into DOC. All C, N, and P in POM and DOC were significantly correlated with Chl a. POC:Chl a ratios were low, whereas proportions of the estimated phytoplankton-derived organic matter in total POM were high during bloom seasons. These results suggested that contributions of cyanobacterial blooms to POM and DOC varied seasonally. Seasonal average C:P ratios in POM and DOM varied from 79 to 187 and 299 to 2 175, respectively. Both peaked in July and then sharply decreased. Redundancy analysis revealed that Chl a explained most of the variations of C:N:P ratios in POM, whereas temperature was the most explanatory factor for DOM. These findings suggest that dense cyanobacterial blooms caused both C-rich POM and DOM, thereby providing clues for understanding their influence on ecosystems.

一类新的赤潮藻源——微塑料附生赤潮藻

全球海洋中持续增长的微塑料(microplastics,MPs)为微藻提供了新的栖息生境和传播载体,附生在MPs表面的微藻被称为微塑料附生微藻(epimicroplastic microalgae,EMP-MA)。有关EMP-MA的研究可以追溯到1971年,但直到2022年才正式提出EMP-MA的概念,并且由于MPs污染加剧,EMP-MA也逐渐受到了关注。硅藻、甲藻、蓝藻、绿藻等藻类均会在MPs表面附生,其中硅藻是最丰富和最多样的类群,常见的附生硅藻有曲壳藻属(Achnantes)、双眉藻属(Amphora)、卵形藻属(Cocconeis)、舟形藻属(Navicula)和菱形藻属(Nitzschia)等。值得注意的是,在EMP-MA群落中还发现了多种赤潮藻类,如卵形蛎甲藻(近似种)(Ostreopsis cf.ovata)、太平洋亚历山大藻(Alexandrium pacificum)、具刺膝沟藻(Gonyaulax spinifera)、东海原甲藻(Prorocentrum donghaiense)和尖刺伪菱形藻(Pseudo-nitzschia pungens)等。这些赤潮藻类可能随着MPs一起在风、海流等外力的驱动下向四处扩散,从而为赤潮的发生提供种源,增加赤潮的暴发和扩散风险,并且随着MPs污染加剧和全球气候变化,这种风险可能会随之增加。然而,目前尚未有直接证据证明MPs表面附生的赤潮藻类确实引发了赤潮或造成了赤潮扩散。为此,我们应当持续关注MPs附生赤潮藻类的时空动态并积极建立MPs附生赤潮藻类扩散风险评估体系,对其引发赤潮的可能性或诱发赤潮的关键环境因子开展深入研究,以期完善赤潮暴发和扩散机制,为海洋防灾减灾工作提供理论依据。

Specific oceanographic characteristics and phytoplankton responses influencing the primary production around the Ulleung Basin area in spring

The East Sea(Sea of Japan)is a marginal,semi-closed sea in the northwestern Pacific.The Ulleung Basin area,which is located near the subpolar front of the East Sea,is known to have high primary production and good fisheries in spring season.After episodic wind-driven events during the spring of 2017,horizontal and vertical profiles of physical chemical biological factors were investigated at 29 stations located in the Ulleung Basin area.In addition,growth responses of phytoplankton communities to nutrient additions were evaluated by bioassay experiments to understand the fluctuation of phytoplankton biomass.Because of strong northwestern wind,phytoplankton biomass was scattered and upwelling phenomenon might be suppressed in this season.The phytoplankton abundances in the coastal stations were significantly higher than offshore and island stations.In contrast,the nutrient and chlorophyll a(Chl a)concentrations and the phytoplankton biomass were quite low in all locations.Bacillariophyceae was dominated group(>75.1%for coastal,40.0%for offshore and 43.6%for island stations).In the algal bioassays,the phytoplankton production was stimulated by N availability.The in vivo Chl a values in the+N and+NP treatments were significantly higher than the values in the control and the+P treatments.Based on the field survey,the higher nutrients in coastal waters affected the growth of diatom assemblages,however,little prosperity of phytoplankton was observed in the offshore waters despite the injection of sufficient nutrients in bioassay experiments.The growth of phytoplankton depended on the initial cell density.All of results indicated that a dominant northwestern wind led to a limited nutrients condition at euphotic layers,and the low level of biomass supply from the coasts resulted in low primary production.Both supplying nutrients and introducing phytoplankton through the currents are critical to maintain the high productivity in the Ulleung Basin area of the East Sea.

The response of spring phytoplankton assemblage to diluted water and upwelling in the eutrophic Changjiang(Yangtze River) Estuary

A comprehensive study on the phytoplankton standing stocks, species composition and dominant species in the eutrophic Changjiang（Yangtze River） Estuary（CE） was conducted to reveal the response of phytoplankton assemblage to Changjiang Diluted Water（CDW） and upwelling in the spring. Phytoplankton presented peak standing stocks（13.03 μg/L of chlorophyll a, 984.5×103 cells/L of phytoplankton abundance） along the surface isohaline of 25. Sixty-six species in 41 genera of Bacillariophyta and 33 species in 19 genera of Pyrrophyta were identified, as well as 5 species in Chlorophyta and Chrysophyta. Karenia mikimotoi was the most dominant species, followed by Prorocentrum dentatum, Paralia sulcata, Pseudo-nitzschia delicatissima and Skeletonema costatum. A bloom of K. mikimotoi was observed in the stratified stations, where the water was characterized by low nitrate, low phosphate, low turbidity, and specific ranges of temperature（18–22 °C） and salinity（27–32）. K.mikimotoi and P. dentatum accumulated densely in the upper layers along the isohaline of 25. S. costatum was distributed in the west of the isohaline of 20. Benthonic P. sulcata presented high abundance near the bottom,while spread upward at upwelling stations. CDW resulted in overt gradients of salinity, turbidity and nutritional condition, determining the spatial distribution of phytoplankton species. The restricted upwelling resulted in the upward transport of P. sulcata and exclusion of S. costatum, K. mikimotoi and P. dentatum. The results suggested that CDW and upwelling were of importance in regulating the structure and distribution of phytoplankton assemblage in the CE and the East China Sea.

Silica supply and diatom blooms in the Jiaozhou Bay, China

The variations in nutrients（molar ratios） and chlorophyll a in the Jiaozhou Bay were examined before and after a diatom bloom in a period that lasted from November 2003 to March 2004. Negative relationships between nutrient concentrations, Si/P, Si/N ratios and chlorophyll a content were found during the bloom, which reflected the relationship between nutrient concentrations, phytoplankton biomass and growth. Large increase in nutrient concentrations, particularly SiO_3-Si after the late autumn, is one of major reasons inducing the diatom bloom in winter, and the bloom was finally controlled due to SiO_3-Si depletion by phytoplankton. The bloom was mainly controlled by SiO_3-Si. Before 1998, relatively low level of SiO_3-Si kept ecological balance of eutrophication waters in the Jiaozhou Bay. In recent years, however, human activities have increased SiO_3-Si concentration, which is likely one of the primary cause for the increased diatom blooms in the Jiaozhou Bay. Therefore, it is necessary to control SiO_3-Si concentration in the Jiaozhou Bay.

Distribution and controlling factors of phytoplankton assemblages associated with mariculture in an eutrophic enclosed bay in the East China Sea

The distribution of phytoplankton and its correlation with environmental factors were studied monthly during August 2012 to July 2013 in the Yantian Bay. A total of 147 taxa of phytoplankton were identified, and the average abundance was in the range of 0.57×10~4 to 7.73×10~4 cell/L. A total of 19 species dominated the phytoplankton assemblages, and several species that are widely reported to be responsible for microalgae blooms were the absolutely dominant species, such as Skeletonema costatum, Navicula sp., Thalassionema nitzschioides,Pleurosigma sp., and Licmophora abbreviata. The monthly variabilities in phytoplankton abundance could be explained by water temperature, dissolved oxygen, salinity, dissolved inorganic nitrogen（DIN）, and suspended solids. The results of a redundancy analysis showed that p H and nutrients, including DIN and silicate（SiO_4）, were the most important environmental factors controlling phytoplankton assemblages in specific months. It was found that nutrients and pH levels that were mainly influenced by mariculture played a vital role in influencing the variation of phytoplankton assemblages in the Yantian Bay. Thus, a reduction of mariculture activities would be an effective way to control microalgae blooms in an enclosed and intensively eutrophic bay.

Does reduced sediment load contribute to increased outbreaks of harmful algal blooms off the Changjiang Estuary?

Harmful algal blooms（HABs） have been increasingly frequent in coastal waters around the world over the last several decades. Accelerated coastal eutrophication, resulting from the increased anthropogenic loadings of nutrients, is commonly assumed to be the primary cause of this increase. However, although important,accelerated coastal eutrophication may not be the only explanation for the increasing blooms or toxic outbreaks in estuarine waters. Changes in riverine material fluxes other than nutrients, such as sediment load, may significantly affect biological activities and HAB incidence in estuarine and coastal waters. A case study off the Changjiang（Yangtze River） Estuary indicated that with the increasing riverine loadings of nutrients, the sediment load from the Changjiang River has been reduced by 70% over the past four decades. A comparison of long-term data revealed that the phytoplankton biomass maximum has expanded to a region of much lower salinity due to the drastic reduction in riverine sediment load and the subsequent improvement in light penetration in the Changjiang River plume. Furthermore, there was an apparent mirror-image relationship between the sediment load from the Changjiang River and the HAB incidence off the Changjiang Estuary over the past four decades, and the number of HAB incidents was significantly negatively correlated with the sediment load. Therefore, it is argued that the drastic decline in sediment load from the Changjiang River reduced turbidity in the Changjiang Estuary and thus contributed to the increased frequency of HABs in the buoyant discharge plumes.

A re-investigation of the bloom-forming unarmored dinoflagellate Karenia longicanalis(syn.Karenia umbella)from Chinese coastal waters

The dinoflagellate genus K arenia is known for recurrent harmful blooms worldwide. However, species diversity of the genus is generally overlooked owing to the difficulty of identifying small unarmored dinoflagellates. We have established four clonal cultures of K arenia longicanalis isolated from the type locality, Hong Kong harbor(strain HK01) and other three locations along the Chinese coasts(strains YB01, DT01, and NJ01). The morphology of the strain was studied by light and scanning electron microscopy(LM and SEM) and the pigment composition analyzed by high-performance liquid chromatography. We provide the first molecular data of K. longicanalis based on the large subunit(LSU) rRNA gene sequence and internal transcribed spacer(ITS). The four strains showed identical LSU rDNA sequences with a similarity of 99.4% to the holotype of K arenia umbella(strain KUTN05) from Australia. In the ITS phylogeny, the sequence of K. umbella branched between the Chinese strains of K. longicanalis. A careful comparison of the morphology of K. longicanalis and K. umbella reveals the similarity in the diagnostic characters. Diff erences may appear due to the sample treatment for SEM. We conclude that K. umbella is a junior synonym of K. longicanalis.

Spatio-temporal variability of phytoplankton assemblages and its controlling factors in spring and summer in the Subei Shoal of Yellow Sea, China

The Subei Shoal is a special coastal area with complex physical oceanographic properties in the Yellow Sea.In the present study,the distribution of phytoplankton and its correlation with environmental factors were studied during spring and summer of 2012 in the Subei Shoal of the Yellow Sea.Phytoplankton species composition and abundance data were accomplished by Utermohl method.Diatoms represented the greatest cellular abundance during the study period.In spring,the phytoplankton cell abundance ranged from 1.59×10^3 to 269.78×10^3 cell/L with an average of 41.80×10^3 cell/L,and Skeletonema sp.and Paralia sulcata was the most dominant species.In summer,the average phytoplankton cell abundance was 72.59×10^3 cell/L with the range of 1.78×10^3 to 574.96×10^3 cell/L,and the main dominant species was Pseudo-nitzschia pungens,Skeletonema sp.,Dactyliosolen fragilissima and Chaetoceros curvisetus.The results of a redundancy analysis(RDA)showed that turbidity,temperature,salinity,pH,dissolved oxygen(DO),the ratio of dissolved inorganic nitrogen to silicate and SiO4-Si(DIN/SiO4-Si)were the most important environmental factors controlling phytoplankton assemblages in spring or summer in the Subei Shoal of the Yellow Sea.

Assessment of the consecutive harmful dinoflagellate blooms during 2015 in the Izmit Bay(the Marmara Sea)

A series of red tides were observed during 2015 in the Izmit Bay（the Marmara Sea） which is located in the most industrialized and populated region of Turkey. Six samplings were carried out in this area following the red tides.Nitrite-N, nitrate-N, ammonia, silica and orthophosphate concentrations were analyzed spectrophotometrically.Physicochemical conditions were measured by CTD probe. Plankton quantification was performed using counting chambers under microscopes. Prorocentrum micans was the most abundant species, except on May 14,2015, when Noctiluca scintillans was dominant. The abundance of P. micans reached average 18×10~6 ind./L on May 3, 2015 in the Karamürsel station, simultaneously with elevated levels of NH_3 and o-PO_4^（3–）. The sample was also abundant in dead amphipods（（72±12） ind./L） that had been covered by mucilage aggregates produced by P.micans. The highest biomass（calculated by carbon） was recorded as（268±26.0） mg/L on May 14 in the Hereke station. Beside the anthropogenic wastewater discharges, unknown sources and resuspensions caused increases in nutrient levels. After long term northeaster gusts（35 km/h for 5 d） an upwelling occurred on November 6, 2015 after wind-induced sediment resuspension. Although nutrient discharges remarkably decreased over 30 years through established wastewater treatment plants, harmful phytoplankton blooms still occur. Comparing the present results with other studies in nearby Mediterranean seas reveals that the most intense harmful dinoflagellate bloom in recent years occurred in the Izmit Bay. Therefore, additional protection measures necessary for a cleaner Izmit Bay. These incidents also demonstrate that contaminants, accumulated in sediment,may have long-lasting effects on enclosed marine ecosystems.

武汉市后官湖藻类越冬及复苏过程

2021年10月—2022年4月通过现场调查开展了武汉市典型富营养化湖泊后官湖藻类越冬及复苏过程研究。结果表明:后官湖越冬期共检出浮游植物6门26属,其中以绿藻门(Chlorophyta)、硅藻门(Bacillariophyta)、蓝藻门(Cyanophyta)为主;从时间尺度上看,水体中藻类丰度于11月初(秋季)开始下降,12月份—次年2月份(冬季)处于较低水平,3—4月份(春季)呈上升趋势;底泥藻类丰度从10—11月份则呈现先上升后下降的趋势,并于1月末2月初降至最低,随后上升,该变化较水体而言有所延迟,可能与藻类垂向迁移有关。相关性分析表明:水体和底泥中的藻细胞密度对水温均有较强的响应(p<0.01),水体和底泥中藻细胞密度的变化分别主要取决于绿藻和蓝藻的变化,说明越冬期大量蓝藻细胞沉降至湖底;冬季(11月份—次年2月份)后官湖水体与底泥藻类丰度的比值相对较低,说明大多数藻细胞在冬季沉降在底泥中。研究揭示了武汉市后官湖藻类越冬及复苏过程,为揭示水华发生机理,开展水华防治提供理论支撑。

春末东海北部冷涡区环境特征及藻华成因探讨

基于2019年春末所获取的东海调查资料,通过分析温度、盐度、营养盐和叶绿素a(Chl-a)等理化参数的分布特征和空间格局,重点对东海北部冷涡区水文环境特征、营养盐动力过程及藻华发生机制进行了探讨.研究表明:济州岛西南海域的低温区清晰显示了春末东海北部冷涡的位置,且冷涡边缘锋面区冷水的抬升指示了上升流的存在.冷涡区的营养盐来源于冬季南下的黄海西部沿岸流的水平输运,冷涡边界锋区的上升流在一定程度上控制着营养盐的垂向输送.春末济州岛西南的Chl-a高值区(最高Chl-a含量为5.69μg/dm^(3))预示了藻华的发生,其与东海北部冷涡和营养盐高值区位置总体相吻合.较高的营养盐水平、良好的光照和增强的水体稳定度是春末东海北部冷涡区藻华形成的有利因素,同时该冷涡与南部高温、高盐水交汇形成的西北-东南向锋面对Chl-a高值区的空间格局与位置也具有重要影响.济州岛西南海域水体浊度较低,满足浮游植物生长所需光照条件所能达到的垂向深度较大,导致冷涡藻华区存在次表层Chl-a高值.该研究为进一步深入认识东海北部初级生产过程的调控机制和开展区域生态系统动力学研究等提供了重要科学依据.

2020年春季长江口连续低氧特征及其影响机制

自20世纪50年代发现长江口的低氧现象以来,众多学者对其展开了研究,但是对于该海域的长时间连续观测仍然较为缺乏,对低氧形成的动态过程难以有清楚的认知。利用大戢山西南海域的坐底观测站2020年1月至5月的底层溶解氧(Dissolved Oxygen,DO)数据,分析了该站点处溶解氧的变化特征,发现观测期间底层溶解氧出现了2次发展过程完全不同的低氧现象:第一次低氧形成过程较为缓慢,在2020年1月至4月,溶解氧缓慢降低,到4月出现并维持低氧;第二次低氧形成较为迅速,在5月中下旬,溶解氧在10 d内从接近饱和迅速降低到低氧状态。通过对2次低氧形成过程中不同环境要素的分析发现,1月至3月溶解氧降低主要原因是升温导致的氧溶解度下降以及沉积物耗氧,4月则是有机物分解导致的低氧,同时4月上中旬的弱风条件有利于形成层结,维持低氧,在5月初出现持续的强风混合海水,第一次低氧过程结束。而大风混合海水后也将底层营养盐输送到表层,使得海表浮游植物大量繁殖,出现赤潮,赤潮末期大量浮游植物死亡沉降到海底进行分解,再加上5月中下旬风混合较弱,使得5月末又迅速进入低氧状态。借助于连续的观测数据,对于2020年春季2次连续低氧的分析可以补充对长江口低氧季节变化的认知,为研究长江口的春季低氧变化特征及形成机制提供重要参考。