【作者】 史洁；

【导师】 魏皓；

【作者基本信息】 中国海洋大学 ， 物理海洋学， 2009， 博士

【摘要】 桑沟湾是我国黄海沿岸重要的水产增养殖水域,近年来,随着对水产品需求的不断提高,人们在扩大养殖面积的同时,也提高养殖密度,而随之带来的结果是养殖设施和养殖生物对桑沟湾的水动力结构产生很大影响,使该湾的潮流结构改变,潮流流速明显减小,海水交换周期延长等等,进而营养盐的补充受到限制,反过来影响养殖生物的生长和产出。首先,为了了解养殖活动对桑沟湾水动力场的影响,于2006年4月和7月在桑沟湾进行了潮流特征综合观测。由于高密度筏式养殖,养殖设施和养殖生物占据了上层水体,阻碍了海水流动,形成了潮流上边界层,潮流垂直结构与一般非养殖海区明显不同,同一位置,最大流速出现在中下层,表层海水先涨先落;从湾口到湾顶,潮流流速显著衰减,相距仅5.2 km的两站,表层平均流速衰减达63%,湾顶站比湾口站潮流相位提前1 h,可见养殖活动对海水流动的阻碍作用不容忽视。基于观测得到的桑沟湾潮流结构特征,对养殖设施和主要养殖生物(海带)带来的阻力分别进行参数化,加入POM水动力模型中,对桑沟湾的水动力场进行模拟。进而,用此水动力模型驱动保守物质输运模型模拟该湾半交换时间的分布,并与不考虑养殖阻力的模拟结果进行比较。加入养殖阻力的水动力模型能够模拟出桑沟湾更加真实的潮流流速大小和特有的垂直结构,即高密度筏式养殖活动带来的潮流上边界层的存在;由于养殖活动的影响,桑沟湾的水动力场与开展大规模养殖前相比,平均流速减小40%,平均半交换时间延长71%。其次,将加入养殖阻力的POM水动力模型与桑沟湾生态模型和海带个体生长模型耦合得到桑沟湾养殖模型,模拟无机氮营养盐和浮游植物的季节变化和大面分布,无机氮营养盐收支情况和海带养殖产量。无机氮与浮游植物存在明显的季节变化,养殖活动的季节性增大了无机氮和浮游植物季节变化幅度,二者的大面分布受大面积海带和贝类养殖的影响;海带生长期间,外海补充是无机氮的最重要的源;模拟得到海带的总产量为7.01万吨干重,最终产量分布受外海对营养盐补充的控制,靠近湾口的养殖区产量大,湾内营养盐补充不足的区域,产量较小。应用桑沟湾养殖模型进行数值实验,研究各个过程的改变对海带养殖产量的影响。结果表明:(1)如果不采用贝藻间养,由于缺少贝类排泄对无机氮的补充,最终海带总产量减小0.3万吨,减产4.3%,海带-贝类混养区减产更为明显,达19.6%。(2)如果海带养殖期内多大风事件,搅动底沉积物,使得底沉积释放无机氮增大一倍,海带的总产量增加0.29万吨,增产4.1%,贝藻混养区增产明显,达19.6%。(3)温度对产量影响不大。(4)在无机氮缺乏的海带养殖后期,对营养盐补充不足海带-贝类混养区集中施肥,肥料利用率最高,得到的海带产量提高最大。(5)在不考虑养殖设施和养殖生物的水动力场的驱动下,海带生长期内,高估外海对桑沟湾内无机氮营养盐补充81.5%,进而高估海带产量38.5%。最后,改变养殖密度,研究水动力场的变化,随之带来的无机氮营养盐补充的变化,及最终海带养殖产量的变化,探讨最适养殖密度和最大养殖产出。养殖密度越大,对海水流动的阻碍作用越强,海带生长期间由外海输送到湾内的无机氮营养盐就越少,因此,提高养殖密度,最终的海带产量不一定得到相应的增加。不同养殖密度下,海带产量的模拟结果表明,养殖密度为现有养殖密度的0.9倍时,海带的产量最大,即由本模型计算得到,0.9倍于现有养殖密度为最适养殖密度,对应的最大海带养殖产出为7.21万吨干重。更多还原

【Abstract】 Sungo Bay is among the largest aquaculture production site in China. With the increasing need of the aquaculture products, the culture area has been enlarged and the culture density has been raised. Consequently, the aquaculture establishment and spices have great influence on the tidal dynamic features, such as forming an unique vertical structure of tidal current, decreasing the current velocity, prolonging the water exchange cycle and so on. As a result, the production that based on the supply of nutrients will be inhibited.In order to study the influences of the aquaculture activities on the dynamic structures, two cruises were carried out during spring and summer of 2006. Many interesting phenomena were observed comparing with normal coastal water of China. The current profile has the maximum value the middle or lower layer and phase lag propagate from upper to lower depth caused by the long kelp in water. The maximum speed decrease by 63% at these two sites which 5.2 km apart. There forms another boundary at the surface due to the frames and buoys which may have stronger friction than the seabed.Based on the observation, Princeton Ocean Model (POM) has been improved to simulating the dynamic structure of the Sungo Bay, by adding the parameterization of the frictional effects of both the establishments and kelp. Results of model output indicate that suspended aquaculture results a 40% reduction in the average current speed and a 71% prolonger in the average half-life time.Then, a three-dimensional coupled physical-ecosystem-kelp model, called Sungo Bay Culture Model, is established to simulate the annual cycle and seasonal distribution of DIN (dissolved inorganic nitrogen) and phytoplankton, the sink and source of nutrient, and the production of kelp. The seasonal aquaculture activities make the seasonal variations of DIN and phytoplankton biomass more obvious. The distributions of DIN and phytoplankton biomass are mainly influenced by the aquaculture scenarios. During the period of kelp culture, DIN from the open sea due to the exchange of water is an important source of nutrient supporting the growth of kelp. Model result indicates that the final production of kelp is 7.01*104 t dry weights, and the distribution of kelp production is mainly controlled by the supply of nutrient from the open sea. The production near the mouth of the bay is much larger than the inner part where DIN is deficient due to the poor water exchange ability.Using the Sungo Bay Culture Model, a series of numerical experiments are implemented to study the influences of different processes on the kelp production. Polyculture of kelp and bivalve is a scientific aquaculture scenario for the growth of kelp. If only the monoculture of kelp is implemented, the final kelp production will decrease by 0.3*104 t (4.3%), because of the lack of 278.46 t N from the excretion of the bivalve. Strong wind events in winter make a positive contribution to the kelp production by increase the benthic release of DIN. The variation of water temperature has no significant influence on the kelp production. Fertilizing in polyculrure area of kelp and bivalve, where there is less DIN supply from the open sea, during the latter stages (from February) when DIN gradually becomes deficient is the most efficient way of fertilization and increase kelp production most. Disregard of physical barriers associated with culture results in a serious overestimation of the DIN supply by 81.5% and thus an overestimation of kelp production by 38.5%.When increasing the density of kelp culture, the frictions caused by the culture activities increase at the same time, which inhibit the supply of DIN from the open sea. As a consequence, there is no definite increase in the kelp production when increasing the culture density. Model results under different culture density indicate that when the culture density is 0.9 times of present culture density, the kelp production reaches to the peak, and the value is 7.21*104 t. So, 0.9 times of present density is the optimum culture density according to this Sungo Bay Culture Model.更多还原