【作者】 唐洪杰；

【导师】 王修林；

【作者基本信息】 中国海洋大学 ， 海洋化学， 2009， 博士

【摘要】 长江口及邻近海域海水富营养化及由此引起的各种海洋生态效应受到普遍关注。虽然关于该海域海水富营养化与赤潮发生关系的研究屡见报道,但对长江口及邻近海域海水富营养化趋势特别是其与赤潮发生之间关系尚缺乏了解。针对这一问题,本文在汇总20世纪50年代特别是80年代以来长江口及邻近海域海水中DIN、PO4-P和COD等年均浓度变化趋势的基础上,采用富营养化指数分析了长江口及邻近海域海水富营养化的变化趋势。同时,结合2002~2005年10个航次的调查数据,应用以线性相关性为主、以季节变化之间关系为辅研究的方法,研究了长江口及邻近海域20世纪80年代以来富营养化指数(EI及EI修正)与赤潮发生规模、频率的关系,进而分析了浮游植物生物量、COD和DO之间的线性相关性。并首次估算了东海31盐度线海域内DIN、PO4-P及COD的海洋环境容量。本文主要工作及结论如下:1.近50年来,长江口及邻近海域海水DIN、PO4-P、COD分别的年均浓度分别呈现出波动性上升、基本维持不变(年代间有波动)和波动性下降的变化趋势;海水中DIN、PO4-P呈现秋中及冬末(春初)高、夏中最低的“双峰”形月季变化趋势,与DIN和PO4-P不同,COD表现为丰水期高、枯水期低的季节变化特点;此外,DIN、PO4-P、COD总体上具有近岸高、外海低的特点。据此,研究海域海水的富营养化指数EI表现出了持续上升的年变化趋势,并且呈现出春、秋季节高,夏季最低的“双峰形”的季节变化特征,同时平面分布上呈近岸高、外海低的趋势。2.赤潮的发生主要受海水中DIN及PO4-P浓度的共同控制。本文从赤潮发生规模/频率、发生期及发生区域等方面研究了长江口及邻近海域海水中DIN、PO4-P、COD与赤潮发生的关系,结果表明,自20世纪80年代以来,海水中DIN及PO4-P年均浓度与赤潮发生年规模/频率之间存在显著线性相关性,而COD未表现出明显的相关性;赤潮主要发生在DIN和PO4-P冬末(春初)高峰之后的5~6月,与COD高值期基本吻合,甚至还略有提前。由此可见,赤潮的发生与COD之间的相关性不强。据此去除EI计算公式中COD项,简化得到了EI修正,采用同DIN、PO4-P、COD类似的方法,分析比较了海水富营养化指数EI及EI修正与赤潮发生之间关系的紧密程度,研究结果提示EI修正与赤潮发生的关联性更好,且强于DIN或PO4-P的影响,这样,研究海域赤潮的发生主要受到DIN、PO4-P的共同控制。3. COD的异常升高是赤潮爆发的结果,但非生源因素仍是研究海域COD的主要来源,致使EI修正与COD关系较弱。此外,EI修正的升高可以引起底层缺氧程度的加剧。现场调查结果显示,赤潮发生时,在赤潮区,伴随浮游植物生长产生的有机质贡献了49~71%的COD数值,成为COD主要来源。但在非赤潮区及整个调查海域,浮游植物生长对COD的贡献仅为13~17%和18~27%,说明非生物因素是COD的主要来源。另外,浮游植物对COD增长的贡献存在季节性差异,表现为夏>秋>春>冬,并且即使在夏季,其贡献率也仅为24%,说明对COD年均浓度来讲,陆源等非生源要素仍是其主要来源,而弱化了赤潮产生的影响。这是导致20世纪80年代以来EI修正年均值与COD年均浓度之间关系很弱的重要原因。此外,20世纪80年代起至今,EI修正的升高可以引起底层缺氧程度的恶化,表现为底层缺氧面积随EI修正的增大而增大,而溶解氧极小值随EI修正的增大而降低。从缺氧区形成时间上看,长江口外缺氧区的形成时间基本上同海水COD的高值期同步,也基本上与该海域赤潮爆发的主要时期相符,滞后于EI修正冬末春初峰值约1~2个月。4.国家一类海水水质标准下,东海DIN、PO4-P及COD的海洋环境容量分别为1.7×106 t·a-1、8.2×104 t·a-1和9.7×107 t·a-1。在当前的排海通量下,DIN和PO4-P分别减排1.7×106 t·a-1和6.0×104 t·a-1,相当于各自目前排海通量的60%和80%,将有助于减少长江口及邻近海域赤潮的发生。更多还原

【Abstract】 Eutrophication and its ecological effects in Changjiang Estuary and its adjacent area have been widely interested. Although the eutrophication-HABs ( harmful algal blooms) relationship has been reported in a lot of papers, there were still gaps to learn the long term trends of eutrophication and eutrophication-HABs relationship in Changjing River Estuary and its adjacent area. To fill the gaps, the data of concentrations of DIN, PO4-P and COD since 1950s especially of 1980s was collected, and the eutrophication index ( EI ) was used to analyze the eutrophication status in Changjing River Estuary and its adjacent area . Based on those data and the data of field surveys during the period of 2002 to 2005, considering the seasonal changes, the linear regression analysis of annual mean value as the chief method was used to explain the relationships between EI or EI’ and the occurrence scale and times of HABs. Similarly, the relationships among biomass, COD and DO were analyzed too. At last, the marine environmental capacity of DIN, PO4-P and COD in the area within 31 salinity range of East China Sea was estimated for the first time. The main conclusions are as follows:1. In the Changjiang Estuary and its adjacent area, the annually mean value of DIN concentration showed an undulatory increase, and PO4-P’s remained practically unchanged, but COD’s appeared a fluctuant downtrend in the last 50 years. And the monthly concentration of DIN and PO4-P exhibited a bimodal curve of which peaks were in the mid autumn and the end of winter (or early spring), the bottom was in the mid-summer. As for COD, its monthly concentration increased during high-water periods while decreased during low-water periods. The horizontal distribution of DIN, PO4-P and COD generally took on a clear pattern of decreaseing from inshore to offshore area. Thus, the temporal and spatial changing trend of EI was summarized. EI’s value has been increasing annually. Its monthly change suggested a bimodal distribution of which peaks were showed in autumn and spring and the bottom in summer, and its horizontal distribution showed a trend of higher inshore and lower offshore clearly. 2. The occurrence of HABs was controlled by DIN coordinated with PO4-P.The relationships between the three factors (eg. DIN, PO4-P and COD )and the characters of HABs including occurrence scales , frequency, outbreak time and area were studied in the Changjiang Estuary and its adjacent area. An appreciable liner relationship was observed between the annual mean concentration of DIN and PO4-P with the frequency or scales of HABs, while the pertinency for COD is not quite noticeable. The HABs mainly appeared in May and June, lagging behind the peaks of DIN and PO4-P in late winter or early spring, but coinciding with the high value period of COD or even taking place ahead of time a bit. Obviously, the occurrence of HABs and COD concentration didn’t associate tightly. Thus, the effect of COD should not be taken into account in the calculation of EI. According to this principle, a new computational formula of EI (EI’) was generated. By comparing the linear coefficient of the four factors (such as EI, EI’, DIN and PO4-P) with the occurrence scale or times of HABs annually, EI’ showed the tightest correlativity with the HABs. So, the occurrences of HABs in the researched area is controlled by DIN and PO4-P synergistically.3. The eruption of HABs brought exceptional rise of COD’s concentration, but abiotic factor was still the main source of COD that led to the uncertain relationship between EI’ and COD. Furthermore, the rise of EI’ could ultimately worsen the depletion of oxygen in the bottom waters.Based on field surveys, when HABs occurred, the organic matter produced by phytoplankton accounted for 49~68% of COD, becoming the leading source of COD in the HABs area. While in the non-red-tide area and the whole investigated area, the organic matter produced by phytoplankton accounted for only 13~17% and 21~27% of COD respectively. The results indicated that abiotic factor was the main source of COD. Additionally, seasonal variation existed when it came to the contribution of phytoplankton to the COD concentration. Generally, phytoplankton produced the most large portion of COD in summer, less in autumn, much less in spring, and least in winter. Even in summer, COD produced by phytoplankton accounted for only 24 percentage of the total amount. It is suggested that the annual mean concentration of COD was mainly attributed by the abiotic source such as terrigenous, which led to the obscure correlativity between the annual mean value of EI’ and COD since 1980s. Furthermore, the rise of EI’ would increase the hypoxia area and depress the minimal value of dissolved oxygen. The formation time of Changjiang Estuary hypoxic zone basically coincided with the high value period of COD and the peak outbreak period of HABs, but lagged behind the peak period of EI’ for one or two months.4. Under the First Grade Standard of National Sea Water Quality Requirement, the environmental capacity of DIN,PO4-P and COD was 1.7×106 t·a-1 , 8.2×104 t·a-1 and 9.7×107 t·a-1 respectively. Thus, 1.7×106 t·a-1 of DIN and 6.0×104 t·a-1 of PO4-P, amounts to 60% and 80% of present total discharge fluxes respectively, must be reduced to decrease the occurrence of HABs.更多还原