东洞庭湖秋季氮磷营养盐结构及水华风险分析

Nitrogen and phosphorus nutrient structure characteristic and risk analysis of cyanobacterial bloom in East Dongting lake in autumn

以东洞庭湖区小型入湖河流、主洪道、主湖体为研究区域,于2016年9月分别设置12个代表断面进行氮、磷营养盐等环境因子及浮游植物调查。通过对氮磷营养盐形态结构、浮游植物群落结构及环境因子与浮游植物的RDA典范对应分析,探讨了秋季东洞庭湖蓝藻水华发生的风险水平。结果表明:(1)东洞庭湖ρ_(TN)为0.96~1.86 mg/L,平均1.58 mg/L,ρ_(TP)为0.065~0.137 mg/L,平均0.101 mg/L,其中入湖河流的ρ_(TN)、ρ_(TP)最低。水体氮磷以溶解态为主,ρ_(DTN)/ρ_(TN)为88.5%,ρ_(DTP)/ρ_(TP)为56.0%,其中ρ_(DIN)/ρ_(DTN)为75.4%,ρ_(PO34--P)/ρ_(DTP)为80.5%,ρ_(TN)/ρ_(TP)为16.9;其中东洞庭湖藻密度为9×10~4~325.2×10~4个/L,平均72.6×10~4个/L。(2)空间分布上,主湖体藻密度高于主洪道,主洪道及主湖体大部分水域优势属种为硅藻门的直链藻(Melosira sp.),其中主湖体北部尾部水域大小西湖发生了蓝藻水华,其优势属种为蓝藻门的颤藻(Oscillatoria sp.)、鱼腥藻(Anabeana sp.)。(3)RDA分析表明TP与流速是影响东洞庭湖水体蓝藻生长的主要环境因子,其它环境因子也有一定的影响。(4)主洪道、主湖体已轻度富营养,秋季藕池河断流时段,主湖体发生蓝藻水华的风险较大,尤其大小西湖水域爆发蓝藻水华的风险极大,主洪道由于水体较为浑浊,流速较大,对藻类生长有抑制作用,发生蓝藻水华的风险较小。

The environmental factors,such as nitrogen and phosphorus nutrient,and phytoplankton were investigated by setting up 12 representative sampling points in the small rivers entering the lake,the main flood way and the main body of East Dongting lake in September 2016. Cyanobacterial bloom risk were explored based on the analysis of nitrogen and phosphorus nutrient morphological structure,the phytoplankton community structure and RDA analysis between environmental factors and phytoplankton. The results showed that:① ρTN was 0. 96 ~ 1. 86 mg/L with an average of 1. 58 mg/L,ρTP was 0. 065 ~ 0. 137 mg/L with an average of 0. 101 mg/L in East Dongting lake,ρTN and ρTP were the lowest in the rivers entering the lake. DTN and DTP dominated in N,P composition,ρDTN/ρTN was 88. 5%,ρDTP/ρTP was 56. 0%,ρDIN/ρDTN was 75. 4%,ρPO43--P/ρDTP was80. 5%,and ρTN /ρTP was 16. 9.② The algal density was 9 × 10^4~ 325. 2 × 10^4 cells/L with an average of 72. 6 × 10^4 cells/L in the whole lake. In terms of spatial distribution,algal density in the main lake was higher than that in the main flood way,Melosira sp. of Bacillariophyta was the dominant species in the main flood way and most of the lake. Cyanobacterial bloom happened in Daxiaoxihu water body in the northern tail of the main lake body,Oscillatoria sp. and Anabaena sp. of Cyanophyta were the dominant species.③ RDA analysis showed TP and flow velocity were the main environmental factors affecting algae growth in the East Dongting lake,and other environmental factors also had certain effects.④ The main flood way and the main lake body had been in light eutrophication,the main lake body faced larger risk of algae bloom in autumn when Ouchi river( a distributary river from Changjiang river to Dongting lake) breaks,especially for Daxiaoxihu. The main flood way has lower risk of algae bloom due to the turbid water and larger velocity.