氨氮和硝氮在太湖水华自维持中的不同作用

The different roles of ammonium and nitrate in the bloom self-maintenance of Lake Taihu

通过室内实验和野外监测相结合的方法,探讨了氨氮(NH4+-N)和硝氮(NO3--N)在太湖水华自维持中的不同作用.室内实验结果表明,水华微囊藻在以NH4+-N为氮源时比以NO3--N为氮源时具有更高的生长以及光合能力,当生长在不同的NH4+-N/NO3--N(浓度比)上时水华微囊藻均优先吸收NH4+-N,而当NH4+-N浓度大于2mg/L时,水华微囊藻的生长速率急剧下降;野外监测结果显示,在太湖藻型区,水体中的氮源以NO3--N为主,除了竺山湾,其余湖区全年NH4+-N/NO3--N基本在0.5以下,NH4+-N年平均浓度在2mg/L以下.结果表明,太湖中巨大的氨再生量使得浮游植物能以NH4+-N为主要氮源生长,而低浓度NH4+-N环境避免了浮游植物的生长受到抑制,两者共同保证了夏秋季太湖浮游植物的高生长以及光合能力,使得微囊藻生长旺盛、蓝藻水华维持在严重状态.

The different roles of ammonium （NH4＋-N） and nitrate （NO3＂-N） in the bloom self-maintenance of Lake Taihu were discussed through the combination of laboratory study and field monitoring. During laboratory study, Microcystis flos-aquae growing on NH4＋-N had higher ability of growth and photosynthesis than those growing on NO3-N and they always assimilated NH4＋-N preferentially when growing on different ratios of NH4＋-N/NO3--N, but when NH4＋-N concentration exceeded 2rag/L, their growth rate declined sharply. Field monitoring results showed that in algae-dominated regions of Lake Taihu, the dominated nitrogen source was NO3-N. Except in Zhushan Bay, the concentration ratios of NH4＋-N/NO3＂-N were mainly below 0.5 all over the year and the annual mean concentrations of NH4＋-N were below 2mg/L. These results indicate that the large quantity of regenerated NH4＋ enable the phytoplankton of Lake Taihu to rely mainly on NH4-N to grow, while low NH4＋-N concentration avoid inhibiting their growth, which ensure their high ability of growth and photosynthesis, leading the vigorous growth of Microcystis and maintenance of serious bloom of Lake Taihu.