洱海上覆水不同形态氮时空分布特征

为研究洱海上覆水各形态氮时空变化特征及其环境效应,收集了1992~2009年洱海上覆水总氮数据,逐月调查了2010年上覆水各形态氮含量.结果表明,1992~2010年洱海上覆水TN含量在0.20~0.67mg/L之间,总体呈上升趋势.2010年上覆水TN年均值为0.57mg/L,DTN为0.41mg/L,NH4+-N为0.17 mg/L,NO3--N为0.086 mg/L,DON为0.15mg/L,颗粒态氮(PN)为0.16mg/L,满足Ⅲ类水体要求;TN、DTN和DON北部最高,NH4+-N和NO3--N中部最高、PN南部最高;上覆水各形态氮年内呈先升后降趋势,TN、DON和PN在7月份达到最高值,DTN和NO3--N在9月份达到最高值,NH4+-N在6月份达到最高值;上覆水TN、DTN、DON和PN垂向分布底层最高,表层次之,温跃层12m处出现峰值.上覆水氮形态时空分布主要受外源氮输入影响,内源氮释放以DON和PN形态为主,NH4+-N和NO3--N分布受水生植物分布影响较大,TN是影响藻类季节性变化的主要因子.洱海营养水平受上覆水氮浓度影响较大,应以控制外源氮输入为重点,特别是雨季之初6、7月份,北部“三江”流域是重点控制区域.

Space-time evolution trends of water nitrogen in Lake Erhai

Characteristics of temporal and spatial distribution and the environmental effect of different nitrogen forms in overlying water of Lake Erhai was analyzed by collecting the history data of total nitrogen (TN) content from 1992 to 2009 and investigating the different nitrogen forms in overlying water in 2010 month by month. The results indicated that the contents of TN ranged from 0.20 mg/L to 0.67 mg/L, and showed a rise tendency as a whole in the overlying water of Lake Erhai from 1992 to 2009. For the overlying water of Lake Erhai in 2010, the average annual content of TN DTN, NH4+-N, NO3--N, DON and PN was 0.57,0.41,0.17,0.086,0.15, 0.17 mg/L, which met Class III water body requirements. The contents of TN, DTN and DON were highest in the northern, that of NH4+-N and NO3--N were highest in the middle, and that of PN were highest in the southern. The tendency of nitrogen content in overlying water of Lake Erhai was ascend in first and descend at last within a year. The contents of TN, DON and PN reached the highest in July, DTN and NO3--N peaked in September, and NH4+-N peaked in June. For the vertical distribution, contents of TN, DTN, DON and PN were in order of bottom layer > surface layer > the thermocline, and the peak appeared at 12 cm of the thermocline in the overlying water of Lake Erhai. The temporal and spatial distribution of different nitrogen forms in the overlying water of Lake Erhai was mainly affected by exogenous nitrogen input. The endogenous nitrogen was mainly released in the form of DON and PN and greatly impacted by water body perturbation. The distribution of NH4+-N and NO3--N was greatly affected by hydrophyte. The contents of TN were one of the main factors affected the seasonal change of the algae. The nitrogen contents of the overlying water had a greater effect on the eutrophication of Lake Erhai and the exogenous nitrogen input should be controlled mainly, especially at the beginning of the rainy season in June and July, and then the “north three rivers” basin was the key control area.