强水动力湖泊夏季分层期氮的生物地球化学循环初步研究:以贵州红枫湖南湖为例

Nitrogen biogeochemical cycles in lakes with strong hydraulic power during summer stratification:A case study of Hongfeng Lake in Guizhou Province,Southwest China

湖泊在夏季由于藻类生长而消耗大量硝酸盐,水体硝酸盐含量一般要低于春季。而红枫湖南湖水体硝酸盐含量却高于春季(比平均含量高0.83mg/L),说明尚有其他重要的硝酸盐来源。据估算,南湖水体硝酸盐含量升高0.83mg/L约需要1.66×105kg硝酸盐,另外有约10.1×105kg硝酸盐随下泻水输出南湖,再加上夏季藻类生长(生产的chla量约为640kg)所消耗的硝酸盐3.52×105kg,共消耗硝酸盐15.28×105kg。扣除河流输入的4.42×105kg硝酸盐,南湖尚存在约10.86×105kg硝酸盐的亏空。利用氮稳定同位素示踪技术,结合硝酸盐及叶绿素a(chla)含量、溶解氧(DO)等的变化,认为这部分硝酸盐来自湖泊中下部(斜温层)有机质的大量矿化(硝化),是水动力驱动高DO的上部水体下沉从而引起下部有机质(硝化)的结果。南湖这种强水动力湖泊整个夏季分层期氮的生物地球化学循环是斜温层有机质矿化(硝化)释放硝酸盐和变温层藻类生长同化硝酸盐为有机质同时发生的特殊类型。

Nitrogen stable isotopic technique,combined with the concentration ch anges of nitrate,chlorophyll a (chla)and dissolved oxygen(DO),is used to study nitrogen biogeochemistry cycles during summer stratif ication in Hongfeng Lake.In general,nitrate concentrations in lakes are lower i n summer than in spring because algae consume nitrate in summer.However,nitrate concentrations in South Lak e of Hongfeng Lake increase by 0.83mg /L.This indicates that there are o ther important sources of nitrate to the lake in summer.It is calculated t hat the net yield of chla is about 640kg,a nd 3.52×10 5 kg nitrates is assimilated.The increase of 0.83mg /L in the lake waters also needs about 1.66×10 5 kg nitrates.And about 10.1×10 5 kg nitrates are discharged into North Lake of Hongfeng Lake.Apart fr om the import of 4.42×10 5 kg nitrates from inflow steams,there is a margin of 10.86×10 5 kg nitrates.It is suggested that they come from the thermocline of the lak e due to mineralization(and nitrification)of organic matters.With the help of hydraulic power,waters with high DO f rom inflow steams and from the epilimnio n of the lake sink at the inlet of the la ke.Mineralization(and nitrification)is the result of the hydraulic pattern.The nitrogen biogeochemistry cycles in the lakes with strong hydrauli c power,such as the South Lake,is a special type,with the concurrence of mi neralization(and nitrification)of organic matters in thermocline and u ptake of nitrate by algae in epilimni on.