洱海沉积物中不同形态氮的时空分布特征

为揭示沉积物中氮形态变化的影响因素及其生态效应,对洱海表层沉积物中不同形态氮的空间分布和季节性变化特征进行了研究. 结果表明:洱海表层沉积物中w(TN)在2354～6174mg/kg之间,空间分布呈湖区北部＞南部＞中部的趋势；w(TTN) (TTN为可交换态氮)在1158～2921mg/kg之间,占w(TN)的43%,其分布趋势与w(TN)相同；各形态TTN表现为SOEF-N(强氧化剂可提取态氮,w为974～2515mg/kg)＞WAEF-N(弱酸可提取态氮,w为91～210mg/kg)＞SAEF-N(强碱可提取态氮,w为38～198mg/kg)＞IEF-N(离子交换态氮,w为66～130mg/kg),w(WAEF-N)和w(IEF-N)的分布趋势与w(TTN)相同,w(SAEF-N)中部较高,w(SOEF-N)南部较高. 沉积物中w(TN)和w(NTN)(NTN为非转化态氮)7月较高,TTN及其各形态氮质量分数1月较高. 不同形态氮质量分数随沉积物深度的增加均呈下降趋势,NTN的富集速率高于TN. 洱海沉积物中w(TN)高于长江中下游湖泊,表层TN富集明显. 沉积物氮释放风险较大,但其w(TTN)和w(IEF-N)占w(TN)的比例低于长江中下游湖泊,即洱海沉积物氮释放量小于长江中下游湖泊；洱海沉积物中各形态氮质量分数与w(TOM)均呈显著正相关,与水深呈负相关,显示有机态氮与有机质同步沉积且受外源输入影响较大,w(IEF-N)分布同时受水生植物等影响. 

Characteristics of Temporal and Spatial Distribution of the Nitrogen Forms in the Sediments of Erhai Lake

The affected factors and ecological effects of the nitrogen form changes in sediments from Erhai Lake were discussed by studying their characteristics of spatial distribution and seasonal variations. The results indicated that the contents of the total nitrogen (TN) were between 2354and 6174mg/kg, and the spatial distribution showed the whole downward trends in the northern, the southern and the middle regions. The contents of the transferable total nitrogen (TTN) were between 1158and 2921mg/kg and contributed 43% to the TN, and its spatial distribution trends were the same as that of their TN. The decreasing order of the content of different forms of TTN was:SOEF-N (974-2515mg/kg)＞WAEF-N (91-210mg/kg) ＞SAEF-N(38-198mg/kg) ＞IEF-N (66-130mg/kg). The spatial distribution trends of WAEF-N and IEF-N were the same as that of their TN with higher densities in the middle region for SAEF-N and in the south region for SOEF-N. The seasonal variations of the TN and NTN contents were the highest in the summer (July) and that of TTN and their different forms were the highest in the spring (January). The content of different nitrogen forms showed a decreasing trend with the sediment depth increased. The enrichment rate of NTN was higher than that of TN in the surface sediment. The content of TN in the sediments of Erhai Lake was higher than that in the lakes of the middle and the lower regions of the Yangtze. Meanwhile, the surface enrichment of TN was great. The percentage of TTN and IEF-N in the total nitrogen was relatively low, although the releasing risk of nitrogen was high. This,indicated that there was a small amount of the nitrogen released in the sediment of Erhai Lake. The content of different forms of nitrogen showed a significant positive correlation with TOM and a negative correlation with the water depths for the sediments. Moreover, the nitrogen and the organic matter were synchronously precipitated. The exogenous inputs had strong influences on the nitrogen contents, and the distribution of TTN was greatly affected by the activities of aquatic species such as aquatic plants.