洞庭湖氮磷时空分布及形态组成特征

为探究洞庭湖水体营养盐形态结构与时空分布特征,分别于2014年8月(丰水期)和2015年1月(枯水期)在入湖河流、湖体、出湖口设置16个代表性断面采集水样,分析了氮、磷营养盐的特征指标。结果表明:1洞庭湖水体中,总氮(TN)含量为1.60~3.65 mg/L,平均值2.25 mg/L,总磷(TP)含量为0.060~0.359 mg/L,平均值0.138 mg/L;颗粒态总氮(TPN)含量为0.07~1.39 mg/L,平均值0.25 mg/L,颗粒态总磷(TPP)含量为0.003~0.172 mg/L,平均值0.05 mg/L;2时空分布上,水体中氮、磷含量整体表现为丰水期高于枯水期,出湖口最高,东洞庭湖高于西、南洞庭湖,入湖河流差异大的特征,颗粒态氮磷呈现自西向东呈逐渐增加趋势,与悬浮物(SS)的空间分布一致;3形态组成上,洞庭湖水体中氮磷以溶解态为主(TDN/TN为88.0%、TDP/TP为66.7%),三峡工程2003年蓄水前后,洞庭湖磷营养盐形态组成发生了大的变化,由以颗粒态磷为主(TDP/TP 20.0%~35.6%)转变为以溶解态为主,而氮营养盐形态组成基本未变;4营养结构上,洞庭湖大多数断面TN/TP在10~22,且氮、磷浓度远高于水体富营养的限制阈值,比较适宜藻类生长。相关分析显示,洞庭湖TN、TP、TDN、TDP均与Chl-a相关性不显著,因此认为洞庭湖氮、磷营养盐对藻类生长的限制作用不明显。

Temporal-spatial Distribution and Speciation of Nitrogen and Phosphorus in Dongting Lake

Nitrogen and phosphorus are the primary pollutants and main indicators of eutrophication in Dongting Lake. In this study, the spatial-temporal distribution of nitrogen and phosphorus in Dongting Lake were investigated and the relationships between nitrogen and phosphorus levels and phytoplankton growth were analyzed. The study was carried out in August 2014 (wet season) and January 2015 (dry season) at 16 sampling stations that covered inflowing rivers, Dongting Lake and outflowing rivers. Physiochemical parameters were determined both in situ and by laboratory analysis of water samples; SD, WT, Chl-a, CODMn, TP, TN, TDP and TDN. Results show:(1) The concentration of TN ranged from 1.60 to 3.65 mg/L (average, 2.25 mg/L), and the concentration of TP ranged from 0.060to 0.359 mg/L (average, 0.138 mg/L).The concentration of total particulate nitrogen (TPN) varied from 0.07-1.39mg/L (average, 0.25 mg/L),and total particulate phosphorus (TPP) varied from 0.003-0.172mg/L (average, 0.05 mg/L).(2) Temporally, the concentrations of nitrogen and phosphorus were higher in wet season than dry season. Spatially, the highest concentrations of nitrogen and phosphorus occurred at the outlets of Dongting Lake, followed by the eastern lake area and then the western and southern lake areas. Obvious differences of nutrient concentration were observed among the four inflowing rivers. Particulate nitrogen and phosphorus increased gradually from west to east, consistent with the spatial distribution of SS.(3) Total dissolved nitrogen (TDN) and total dissolved phosphorus(TDP)were the primary species in Dongting Lake (88.0% TN and 66.7% TP). After Three Gorges Reservoir was first impounded in 2003, TDP increased from 20.0% to35.6%of TP, but nitrogen speciation remained nearly the same. (4)With regard to the nutrient structure, TN/TP ratios at most sampling sites ranged from10-22.Correlationsbetween nutrient levels (TN, TP, TDN and TDP) and Chl-a were not significant, indicating that algal growth is not limited by nitrogen or phosphorus in Dongting Lake. Concentrations of nitrogen and phosphorus in Dongting Lake are far higher than the threshold value for eutrophication and promote algae growth.