大气氮沉降对南黄海初级生产过程影响的数值研究

Modelling the Effects of the Atmospheric Nitrogen Deposition on the Primary Production Process in the Southern Yellow Sea

本研究利用三维物理-生物耦合模型模拟了大气氮沉降对南黄海主要初级生产过程的影响,并通过数值实验区分了不同季节大气氮沉降的贡献。模拟结果显示,大气氮沉降明显增大了南黄海表层溶解无机氮的浓度,近岸海域增加量较大,可以达到3.0 mmol/m^3,且由近岸海域到黄海中部海域有明显的递减趋势,这主要是由于近岸海域无机氮来源众多,导致浓度较高,大气沉降的氮不会被浮游植物生长吸收,出现氮累积。大气氮沉降明显促进了黄海中部春季表层水华和夏季次表层叶绿素最大值两个重要初级生产过程,春季表层叶绿素增加量最大,可达0.20 mg/m^3,夏季次表层叶绿素浓度增加最显著,可达0.10 mg/m^3,分别约为峰值浓度的10%和6%。不同季节大气氮沉降对初级生产过程的贡献不同,冬季氮沉降可以存留下来影响春季水华过程,但作用小于春季氮沉降;夏季,由于水体层化较强,本季的氮沉降对次表层叶绿素最大值的促进作用并不明显,反而冬季氮沉降的影响大于春季和夏季的氮沉降。同时,大气氮沉降也促进了氮循环的各个过程,包括浮游植物生长吸收、呼吸释放和矿化过程。

In our study, a three-dimensional coupled biophysical model is carried out to estimate the influence of atmospheric nitrogen deposition(AND) on the primary production process in the Southern Yellow Sea, and the contribution of AND in different seasons has been distinguished through the numerical experiments. The results show that AND significantly increases the concentration of surface dissolved inorganic nitrogen(DIN) in the South Yellow Sea. The maximum value of DIN concentrations appears in offshore waters, which is 3.0 mmol/m^3. The concentration of DIN decreases obviously from offshore waters to the central Yellow Sea. The higher concentration of DIN due to many sources of it in the coastal waters will cause that the AND is not absorbed by phytoplankton and nitrogen accumulation will occur. The AND significantly promotes the blooms in the surface during spring and the chlorophyll maximum in the subsurface during summer. The chlorophyll increases obviously by 0.20 mg/m^3 in the surface during spring and 0.10 mg/m^3 in the subsurface during summer, which are about 10% and 6% of the peak concentration respectively. The contribution of AND in different seasons is different. The AND in winter can stay in the water to influence the spring blooms, but that is less important than the AND in spring. The influence of the AND in summer on the chlorophyll maximum in the subsurface during summer is not obvious due to the strong stratification of the water, however, the influence of the AND in winter is more important than that in spring and summer. The AND also contributes to the processes of the nitrogen cycle, including the absorption of nitrogen to the phytoplankton, the release of nitrogen due to breathing of phytoplankton and the mineralization.