胶州湾生物-物理耦合模型参数灵敏度分析

Parameter sensitivity analysis of a coupled biological-physical model in Jiaozhou Bay

参数灵敏度分析旨在评价模型中各参数对模拟结果的影响程度,是参数优化和模型校正的基础步骤,也是认识模型行为的重要工具。所建的胶州湾生物-物理耦合模型包括浮游植物、浮游动物、营养盐、碎屑和溶解氧5类状态变量,对其涉及的50个参数进行灵敏度分析,得到3个非常灵敏性参数、2个灵敏性参数、11个比较灵敏性参数和34个不太灵敏性参数。非常灵敏及灵敏性参数包括浮游植物生长速率(μPRPC)、暗反应修正因子(FAC)、光饱和强度(α)、浮游植物死亡率(μDEPC)和水体消光系数(bla),主要影响浮游植物生长和死亡过程,反映了浮游植物在生态系统中的基础性和重要性作用。这5个参数显著地影响碳和营养盐循环,是整个胶州湾生态系统最主要的影响参数,应优先进行优化。比较灵敏性参数的影响主要表现在营养盐对浮游植物生长或死亡的限制以及温度对光饱和量的限制,浮游动物生长、牧食和死亡过程以及浮游植物生物量对牧食的限制,叶绿素a的生产,缺氧条件下沉积物释放磷以及浮游植物对磷的摄取等过程,这些参数对于各状态变量的灵敏性存在不同程度的差异,从而表征不同的特点。与不太灵敏性参数相关的过程主要为叶绿素a和碎屑消光作用,温度对浮游植物生长、浮游动物牧食、碎屑和沉积物矿化的限制,碎屑和沉积物矿化与沉降,与无机氮相关的大部分过程,溶解氧浓度变化等,这些过程除了受模型内部参数影响外,还在很大程度上受水深、海水温度和陆源污染等外部因素影响。比较灵敏及不太灵敏性参数影响模型局部过程,是模型校正的重要依据,除了非常灵敏及灵敏性参数以外,叶绿素a、浮游动物、碎屑和无机磷四种状态变量可分别根据叶绿素a最大生产系数(K CHmax)、浮游动物一级死亡率(μDEZC1)、有机碎屑矿化率(μREDC)和浮游植物磷摄取的半饱和常数(h UPPP)进行校正。与营养盐相关参数的灵敏度分析表明,胶州湾浮游植物处于磷限制,无机氮主要受陆源排污影响。因此,对无机氮的校正主要通过合理设置沿岸河流径流量或陆源污染物浓度与比例以及无机氮初始场。溶解氧对各参数均不太灵敏。

The marine ecological models have been widely applied. The key factor limiting application of ecological models is the uncertainty of these models, primarily due to the uncertainty of the parameters used. The purpose for sensitivity analysis of parameters for ecological models was to assess influential degrees of various parameters on simulating outcomes with a particular model, which are the essential procedures for parameter optimization and model calibration and the important tools for understanding the behaviors of the model. In this study, we conducted sensitivity analysis on 50parameters for five state variables i.e. phytoplankton, zooplankton, nutrient, detritus and dissolved oxygen included in the coupled biological-physical model for Jiaozhou Bay. We found that among 50 parameters, three were highly sensitive, two were sensitive, 11 were moderately sensitive and 34 were less sensitive. The highly sensitive and sensitive parameters included phytoplankton growth rate （upapc）, factors for dark reaction correction （FAC）, light saturation intensity , phytoplankton death rate （uDEPC） and light extinction coefficient of water （bla）. They have major impacts on plant growth and death, reflecting the essentialness and importance of phytoplankton in ecosystem. The plant growth process has the most important impacts on the stimulating results. The key factor limiting plant growth is light whereas light extinction of water is the most important factor limiting light intensity. These five parameters have significant impacts on carbon and nutrient cycles, and are the most important parameters in Jiaozhou Bay ecosystem. Thus, they should be optimized with the first priority. The impacts of moderately sensitive parameters are mediated mainly via the influence of nutrient on phytoplankton growth and death, temperature influence on light saturation intensity and the influence on zooplankton growth, grazing and death as well as the impacts of phytoplankton biomass on grazing, chlorophyll a generation, phosphorus release from disposed substances under hypoxia condition and phosphorus absorption by plants. There are different degrees of variations in sensitivity of the state variables and thus, they have different characteristics. The less sensitive parameters-related processes are mainly light extinction of chlorophyll a and detritus, temperature limitation to zooplankton growth, zooplankton grazing, and mineralization of detritus and sediment, mineralization/deposition of detritus and sediment, the inorganic nitrogen-related processes and changes in dissolved oxygen concentration. These processes are influenced not only by model＇ s internal parameters but also by external factors such as water depth, sea water temperature and pollutions from land-based sources. Moderately and less sensitive parameters affect model＇s local processes, and thus are the important basis for model calibration. Additionally, four state variables i.e. chlorophyll a, zooplankton, detritus and inorganic phosphorus, are calibrated according to the maximal production constant of chlorophyll a （gcHm） , first-order zooplankton death rate （/XDEZC1 ）, mineralization rate of organic detritus （uREDC） and half-saturation constant of phosphorus absorption by zooplankton （ hurpp ）. The sensitivity analysis of nutrient-related parameters has shown that phytoplankton in Jiaozhou Bay is limited by phosphorus and however inorganic nitrogen is principally effected by pollutions from land-based sources. Dissolved oxygen is less sensitive on each parameter.