洞庭湖浮游植物增长的限制性营养元素研究

近20年水质监测资料表明，洞庭湖水体富营养化日趋严重。洞庭湖水体主要污染物为氮和磷，而营养盐赋存形态及其含量对浮游植物生长的影响在洞庭湖尚未见报道。2011年9月至2012年8月对洞庭湖浮游植物生物量及主要营养盐赋存形态与含量进行监测，同时利用藻类增长的生物学（NEB）评价方法对限制浮游植物增长的营养盐进行了研究，并分析了浮游植物生物量与各营养元素之间的相关性。结果表明：洞庭湖主要污染物总氮（TN）和总磷（TP）的年平均值分别为1.90 mg·L-1和0.093 mg·L-1，溶解态无机氮（DIN）平均占ρ（TN）比例为87%，溶解态总磷（DTP）平均占ρ（TP）比例为70%。洞庭湖水体中，DIN是TN的主要贡献者，且不同形态DIN的贡献大小依次为ρ（NO3--N）〉ρ（NH4＋-N）〉ρ（NO2--N）；磷形态组成中，TP主要以溶解反应性磷（SRP）存在。春季洞庭湖水体中ρ（TN）、ρ（TP）较高，这一结果可能源于春季面源污染。洞庭湖水体中ρ（Chla）与氮显著正相关，与磷显著负相关。NEB 实验结果表明氮对洞庭湖浮游植物生长有明显的促进作用，其幅度随氮浓度的增加而加强，而磷对浮游植物的生长影响不大，有时出现抑制作用，硝态氮与磷之间不存在交互作用。因此，氮可能是洞庭湖浮游植物增长的主要限制性营养因子，这一研究暗示在洞庭湖富营养化控制过程中应特别注重氮的控制。

Nutrient limiting phytoplankton growth in Dongting Lake

Water quality monitoring data in recent two decades in Dongting Lake showed that its eutrophication level had increased seriously. Nitrogen and Phosphorus were the major pollutants in the lake. However, the effects of composition and concentration of nutrients on phytoplankton growth in Dongting Lake has not been reported yet. The biomass of phytoplankton, forms of main nutrients and their concentrations in Dongting Lake were investigated from September, 2011 to August, 2012. Nutrient enrichment bioassay （NEB） and the correlation analysis between biomass of phytoplankton and nutrient concentration were used to detect its limiting nutrient. The results showed that the annual average concentrations of TN and TP in the lake were 1.90 mg·L-1 and 0.093 mg·L-1, respectively. Dissolved inorganic nitrogen （DIN） accounted for 87% of TN on average, while dissolved total phosphorus （DTP） accounted for 70%of TP on average. DIN was the major contributor to TN. In addition, the contribution of different forms of DIN to TN was sequenced asρ（NO3--N）〉ρ（NH4＋-N）〉ρ（NO2--N）. Soluble reactive phosphorus （SRP） was the major contributor to TP. Due to spring non-point source pollution, concentrations of TN and TP were higher in spring. In the water column, chlorophyll a （Chl a） concentration was positively related to nitrogen, and negatively related to phosphorus. The results of NEB experiment showed that addition of nitrogen could obviously boost phytoplankton biomass, and its effects increased with the continuous addition of nitrogen. While phosphorus addition did not affect phytoplankton growth. On the contrary, it sometimes inhibited growth of phytoplankton. There were no effects of interactions between nitrate and phosphorus. In summary, nitrogen was the nutrient limiting phytoplankton growth in Dongting Lake. More attention should be paid on nitrogen during the control of eutrophication in Dongting Lake.