黄、东海低营养层生态系统对自然环境变化响应的模拟与分析

Exploring the response of regional ocean environment to climate change has recently been a hotspot in ocean research. The Yellow Sea and East China Sea are experiencing changes in water temperature and circulation due to influences of global warming and weakening of monsoon; the inputs of nutrients also undergo inter-annual variations due to changes in Kuroshio intrusion onto the shelf of East China Sea. These natural factors combine with human induced influences to cause changes in the ecosystems of the Yellow Sea and East China Sea. The study of the variation and mechanism of marine ecosystem can provide the scientific basis for the protection of eco-environment security, and also support the sustainable development of human and nature. In this study we propose to analyze the seasonal and interannual variations of temperature, salinity, nutrients, oxygen and chlorophyll a in the Yellow Sea and East China Sea, through combining field observation and historical data collection. A three-dimensional model, including online coupling of physical-biochemical and suspended particulate matter, will be used to study the variations of the physical environment and low trophic level ecosystem in the Yellow Sea and East China Sea in the recent 20 years. Model results will be analyzed to assess to what extent, and by what mechanisms, the nutrients concentration and structure, as well as the phytoplankton biomass and species group, are affected by the interannual variations of physical processes, e.g. temperature, stratification, solar radiation, monsoon and Kuroshio. The effect of the transportation and distribution of suspended matter on the nutrients cycle and budget will be examined by the coupled model. The extent to which the oceanic and riverine nutrients input affect the distribution of nutrients and phytoplankton in the Yellow Sea and East China Sea will be quantified and explained. All these studies will improve the understanding of the variation of marine ecosystem, and help the establishment of corresponding strategy to improve marine environment.

陆架海生态环境对全球气候变化的响应是当前国际研究的热点问题之一，气候变暖、季风减弱造成海域水温和环流结构变化，东海陆架黑潮入侵带来营养盐外源输入的年际变化，这些自然环境变化与人类活动同样都会引起黄、东海生态系统的动荡。认识近海生态系统对自然变化的响应规律，有助于区分自然和人文活动强迫的作用。本课题拟收集历史资料，建立三维物理-生物地球化学-悬浮物耦合的低营养层生态系统动力学模型，模拟和分析黄、东海温度、盐度、营养盐、溶解氧和叶绿素等理化因子的季节和年际变化规律；设计敏感性实验，探讨黄、东海营养盐浓度和结构、浮游植物生物量和种群结构对温度、层化、光照、季风、黑潮等物理过程长期变化的响应，甄别关键影响因子；分析悬浮物分布和输运对生物初级生产过程及营养盐循环和收支的影响；认识陆源输入和外海输入营养盐长期变化在黄、东海低营养层生态系统变异中的作用。为制定海洋生态环境变化应对策略提供科学依据。

认识黄、东海低营养层生态系统对人类活动和自然变化的响应，有益于深入了解我国近海生态系统的变化规律及其控制机制，可为保障我国海洋生态环境安全提供必需和可靠的科学依据。在历史数据和现场调查基础上，建立了黄、东海高分辨率物理-生化耦合生态动力学模型，模式中包括了大洋、河流、大气干湿沉降和水-沉积物界面对营养盐的输入。光照、温度、水体稳定度和营养盐共同控制浮游植物的生长，冬末春初，光照，温度和水体稳定度对于浮游植物生长起关键作用，而春末夏初，除了近河口区，则是营养盐水平限制了浮游植物的生长。黄、东海叶绿素季节变化的幅度比年际变化大得多，季节变化主要发生在近岸海域，年际变化主要发生在长江口、黄海西南部海域以及浙闽沿岸海域。外洋输入是黄、东海生态系统的重要的营养盐来源之一，黑潮营养盐输入增加后，东海叶绿素的增加春夏季节发生在次表层，秋冬季节发生在表层，高磷黑潮水输入有利于长江口外硝酸盐的吸收。黑潮和台湾海峡营养盐变化对叶绿素的影响，冬半年体现在东海外陆架和黑潮主流区，夏季台湾海峡影响主要表现在东海的中陆架，而黑潮主要影响黑潮主流区和长江口外海域。长江输入的是高氮水，长江营养盐输入变化，引起叶绿素的变化主要发生在夏半年，空间上主要集中在长江口外浊度锋面以外海域，春秋季可以影响到浙江外海。对营养盐的影响，长江影响主要发生在表层，黑潮影响更多发生在底层，台湾海峡影响介于两者之间，空间上看长江主要影响长江外海域，台湾海峡影响中陆架，黑潮影响外陆架，并且沿着底层能影响到长江口外海域。以RCP4.5未来气候变化情景，结合两种极端河流营养盐载荷特征，对未来黄、东海营养盐进行了情景预测。两种河流排放情景下，河口邻近海区和苏北浅滩无机氮、无机磷营养盐浓度将显著增加，硅酸盐浓度在黄海有所增加，海区富营养化加剧。