【作者】 卢光远；

【导师】 宋秀贤； 俞志明；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 海洋化学， 2014， 博士

【摘要】 随着人类活动增多、气候变化等因素影响，近年近岸有害藻华的暴发频率和规模不断增加，其引起的海洋生态问题日益凸显。改性粘土治理有害藻华是国际上推荐的野外应急治理方法之一。本论文通过室内实验，开展改性粘土治理不同藻华生物的长期环境化学效应的研究，针对有害甲藻藻华、硅藻藻华自然消亡过程中营养盐循环特性及改性粘土絮凝后所引起水质营养环境的差异特征以及改性粘土治理有毒藻华过程中对水和沉积物环境因子、藻毒素的影响研究，结合分析大量粘土絮凝有害藻华机理、元素生物地球化学循环、粘土材料结构特性等研究文献，获得以下几方面的阶段性成果：(1)改性粘土治理方法能够高效絮凝去除高密度有害藻华生物P. micans、P.donghaiense、S. costatum、A. tamarense，由于硅藻细胞外壳含有大量硅元素，与粘土中铝元素易发生离子置换，外加硅藻细胞的自沉降特性，所以改性粘土对硅藻去除效率更为显著，改性粘土通过“互荫”效应、改变营养结构和胶体缓冲体系等方式影响有害藻华生物的微生境，显著影响其细胞代谢合成不同的荧光物质，单位藻细胞有机氮和磷短期内显著升高，改性粘土治理方法有效抑制了有害藻华生物二次增殖。(2)自然消亡过程中藻源有机物在降解过程中会释放大量营养物质，这些营养物质可为二次藻华暴发提供物质基础，改性粘土治理方法在除藻的同时有效地改善了水质环境，水体中TN、TP大幅降低，且未出现二次释放。实验末期海洋原甲藻P. micans改性粘土絮凝后TP约去除39.28%~42.47%，TN约去除26.22%~29.93%；东海原甲藻P. donghaiense改性粘土絮凝后TP约去除51.39%，TN约去除17.24%；中肋骨条藻S. costatum改性粘土絮凝后TP约去除93.36%%~93.60%，TN约去除53.75%~71.95%；塔玛亚历山大藻A. tamarense改性粘土絮凝后TP约去除42.86%~56.30%，TN约去除20.72%~35.53%。(3)改性粘土改变了水体中营养元素的浓度、形态比例以及元素循环过程，磷酸盐和硅酸盐以直接吸附影响为主，而溶解态无机氮以时间累加的间接效应为主，有效地降低了水体营养程度，由于不同营养元素的去除机理和速率有所不同（无机营养元素转化速率依次为v(NO3--N)<v(DIP)<v(NO2--N)<v(NH4+-N)），造成营养结构发生改变，改性粘土促进了藻华生物对无机态营养物质的吸收，同时加快了颗粒态营养物质的沉降速率，水体中TDN/TDP比值显著增加（>100），形成极度磷限制环境从而破坏了藻细胞二次增殖所需的适宜营养条件。(4)改性土治理方法形成的藻土有机粘土复合体聚合富集沉降大量有机氮和有机磷物质进入沉积物表层，通过沉积物颗粒、改性粘土颗粒与上覆水环境的离子交换作用、金属有机物螯合作用、沉积物压实作用等机制促使营养物质在月尺度上无法快速解吸或释放，同时改性粘土具有一定的抗微生物活性特征，减缓了有机氮、磷的降解，在月尺度上无机营养盐浓度未发生改变，使得这部分有机物如化石埋赋一样保存于沉积物中；另一方面，粘土颗粒表面为某些有机物质的聚合反应提供反应位置和催化中心，改性粘土自身的表面富集和选择催化特性促使叶绿素a和藻毒素PSTs等活性有机物质转化加速，沉积物中高毒性GTX1和GTX4向较低毒性GTX2和dcGTX3转化，尤其是沉积物-海水环境中，pH值和氧化环境在PSTs降解转化过程中起重要作用，毒素由高毒性向低毒性甚至无毒物质转化速率显著加快。改性粘土治理方法形成的絮体与“海洋雪”具有一定的相似性，但絮体来源、组成、形成状态有所不同。由于改性粘土添加是人为突发过程，对于自然水体而言这一过程如海底火山喷发般能突然改变区域微生物活性和元素地球化学循环过程。所以，针对特定水体条件和藻种，在筛选改性粘土用量和去除时应深入研究生态效应信息，在大规模施行前需要进行长时间尺度生态效应研究以保证安全使用这一治理方法。尽管本课题组针对改性粘土治理方法野外应用积累了大量经验，但是我们依然建议应该对其造成的环境影响需要慎重评估。研究改性粘土治理有害藻华后期营养元素的生物地球化学规律，对于正确认识海洋中的有害藻华消亡及有害藻华治理的后期生态效应都有重要意义。更多还原

【Abstract】 Harmful algal blooms (HABs) are one of the most serious and complex globalphenomena affecting aquatic environmental systems. The outbreak of HABs has beenaccelerating in frequency, scale, and duration over the past several decades. WhenHABs occur, they negatively affect not only water qualities and the habitats of marineorganisms but also aquaculture industries and local tourism, mostly because of thehigh biomass of cells. Among various options of mitigation strategies for harmfulalgal blooms (HABs), flocculation of algal cells by modified clay (MC) has beenproven to be an effective, low-cost, and environmentally benign method and is theonly technique that has been widely applied in the field, particularly in Japan, Korea,North America and China. Because of the enormous amounts of clay that may beapplied for a single event of HABs, however, it is of critical importance to examinethe long-term environmental effects of this treatment on sensitive aquatic systems.The study report here the investigation on the major nutrient variations and waterquality changes by comparing the natural decaying of different harmful algae withbloom levels of cell density to the flocculation of algae by modified clay application.The thesis concluded all results to summarize the following points.(1) The low dosage of modified clay could efficiently remove and control the algalcells of Prorocentrum micans (60%~89.5%removal), Prorocentrum donghaiense(>56%), Skeletonema costatum (>90%), and Alexandrium tamarense (>95%)with high cell density, particularly in diatom control. Modified clay particlesimpact the metabolism of harmful algae and inhibit the re-blooming of HABsthrough the combining effects of the “shading” effects of suspended particles,changing the chemical stoichiometry and buffer capacity in seawater. No cells were found to escape from the algae-clay aggregates and release into seawaterduring the one-month incubation period.(2) Modified clay particles also effectively eliminated the nutrients from seawaterand adsorbed both inorganic and organic phosphorus with39.28%~42.47%of TPand26.22%~29.93%of TN removal in Prorocentrum micans,51.39%of TP and17.24%of TN removal in Prorocentrum donghaiense,93.36%%~93.60%of TPand53.75%~71.95%of TN removal in Skeletonema costatum,42.86%~56.30%of TP and20.72%~35.53%of TN removal in Alexandrium tamarense.(3) The concentration, proportion and cycling of nutrient were alternated by modifiedclay flocculation. Phosphate and silicate were mainly removed by the direct effectof physical adsorption of modified clay. Dissolved inorganic nitrogen was mainlyeliminated by the indirect effect of chemical adsorption and time cumulativeeffects from modified clay suspended. The conversion rates of dissolvedinorganic macronutrients exhibited that v(NO3--N)<v(DIP)<v(NO2--N)<v(NH4+-N). Thus, the nutrient structure was changed to an unfavorableenvironment (TDN/TDP was up to>100in seawater), which was significantlydeviated from the required nutritional stoichiometry for HABs re-blooming.(4) The mechanisms underlying the effects elicited by MC on algal organicnitrogen/phosphorus are also discussed in the study. This study demonstrated thatMC particles could accumulate the algal matters to coagulate the polymericalgae-organic clay complexes settling into the surface sediment. The complexesblocked the nutrients and delayed the degradation and decomposition of algalorganic matter by preserving the recycling velocity of inorganic nutrients withoutsecondary pollution, exerting an antimicrobial activity effect of PACl in MC,organometallic chelation, and consolidation of particles, particularly within thewater-sediment environment, as the result, this part of the organic materials asfossil stored in burial sediments. On the other hand, the surface catalyticproperties of the modified clay particles provided reaction sites for the conversionof chlorophyll-a and algal toxins (PSTs) or other active organic matters.Moreover, the higher toxicity (GTX1and GTX4) changed into the low toxicity (GTX2and dcGTX3). The oxidation potential and high pH in seawater playedthe most important role in the degradation process of PSTs.The process of MC treatment forms aggregates, similar to the “marine snow” butdifferent sources, formation states and composition of aggregates. The integration andassociation of the whole interactions must be considered as well as the acute impact ofthe artificial addition process. Innovative synthesis studies investigating the long-termenvironmental effects of MC treatment should be conducted prior to the large-scaleapplication of the MC method. Although our group has had extensive experience inHABs on the Chinese coasts (in the Changjiang Estuary of Shanghai City, SouthChina Sea coast of Shenzhen City, Yellow Sea coast of Qingdao City, and the BohaiBay coast of Qinhuangdao City, among other locations), our findings suggest that areevaluation is necessary to determine the way in which algal detritus is representedin ocean biogeochemical models, and new field applications and observations arerequired to further clarify these processes. Further studies will be related to differentalgal scales, species, nutrient biogeochemical cycles, and how PSTs re-enter the foodchain to ensure the temporal environmental safety of the MC strategy.更多还原