固氮作用对黑潮上游区域生态系统影响的模拟研究

Modeling the impact of N_2-fixation on the ecosystem dynamics in the upstream Kuroshio

为了研究固氮作用对黑潮上游区域生态系统的影响, 建立了一个包含固氮生物在内的NPZD（nutrient,phytoplankton, zooplankton, detritus）生物模型, 初步模拟结果与观测结果相吻合.通过比较模型中有固氮生物和无固氮生物两种情况下, 黑潮上游区域生态系统各参量以及各级生产力的差异, 揭示了该区域固氮生物的季节性分布特征,阐明了固氮作用对海洋生态系统动力过程的重要影响.结果表明, 固氮生物由于水文和化学因素的影响, 主要出现在夏、秋季.固氮产生的新氮源使黑潮上游区域硝酸盐、铵盐、浮游动植物和大小碎屑的量都有明显增加.浮游植物的平均生长速率提高了大约64%, 初级生产力、再生生产力和新生产力分别增加了30%左右.在夏季50m 以浅水体, 固氮作用支持了50%-80%的新生产力, 是新生产力的主要贡献者; 而在50-200m 水体, 固氮作用支持了10%-50%的新生产力, 深层水的垂直混合带来的氮营养盐成为新生产力的主要贡献者.

An NPZD(nutrient,phytoplankton,zooplankton,detritus) model with incorporation of a diazotroph function group was used to simulate the temporal change of ecosystem in the upstream Kuroshio Current. The modeled nutrients,chlorophyll-a,and productivity showed good agreements with the observations. The impacts of N_2-fixation on nutrient concentrations,plankton biomass,and detritus were assessed by comparisons of the modeled simulations with and without diazotrophs. Our results suggested that diazotrophs were most abundant in summer and fall when other phytoplankton were nitrogen limited. The mean growth of phytoplankton could increase by 64% with the input of new nitrogen from N_2-fixation,leading to 30% increase of primary production,regenerated production,and new production,respectively. In summer,N_2-fixation supported 50%~80% of the new production in the upper 50 m,but only 10%~50% in the depths of 50~200 m. This finding suggested that N_2-fixation was an important source of new nitrogen for phytoplankton production above 50 m in the upstream Kuroshio,but new production below 50 m was largely contributed by the vertical nutrient fluxes from below.