2010年洱海全湖氮负荷时空分布特征

Characteristics of Temporal and Spatial Distribution of Nitrogen Loading in Erhai Lake in 2010

为探讨不同来源的氮负荷对洱海水体富营养化的贡献,对洱海入湖河流、干湿沉降和沉积物内源等来源的氮的负荷、形态及其时空变化特征进行了研究.结果表明:与2008年相比,2010年洱海入湖TN负荷下降了28%.入湖河流是TN负荷的主要来源,占总入湖负荷的37%;入湖河流TN负荷与ρ(TN)、ρ(Chla)呈极显著正相关;入湖河流TN负荷以NO3--N为主,占39%.入湖河流氮负荷季节性变化明显,7月最高;区域性差异较大,北部3条河流是主要来源,其中弥苴河入湖TN负荷占入湖河流TN负荷的57%.沉积物内源TN负荷占总入湖负荷的29%,NH4+-N负荷占内源TN负荷的98%,并且与水体ρ(Chla)呈显著正相关.沉积物中TN和NO3--N扩散通量北部湖区最高,NH4+-N扩散通量南部湖区最高;TN扩散通量9月最高、12月最低.干湿沉降入湖TN负荷以NH4+-N为主,季节性变化明显,6月最高.控制洱海外源入湖氮负荷,应以雨季之初为关键时期,以弥苴河及其流域为重点区域,兼顾坝区农业种植结构调控,同时应加强湖泊水体生态修复,控制内源释放.

The contribution of different sources of nitrogen loading in the Erhai Lake eutrophication was studied by analyzing the morphology and characteristics of temporal and spatial variation of nitrogen loading.The sources included the rivers flowing into Erhai Lake,dry and wet deposition,and sediment release.In 2010,the TN loading of Erhai Lake decreased 28% than that in 2008,and the rivers flowing into Erhai Lake was the main TN loading source by contributing 37% with a significant positive correlation with its contents of TN and Chla.The main morphology of rivers TN loading was the NO3--N,which contributed 39% to the total entering nitrogen loading.The nitrogen loading of rivers into the lake significantly varied with seasonal changes reaching the peak value in July and showing largely spatial differences.The three rivers in the north region was the main source,and the Miju River provided the greatest contributions of 57% to the total river entering TN loading.The endogenous TN loading from the sediment releasing was about 29% of the TN loading and this showed a significant positive correlation with the content of Chla.Its morphology was mainly NH4＋-N and contributed 98% to the total fluxes of nitrogen.The highest value of the diffusion flux of TN and NO3--N in the sediment was in the northern region,and that of NH4＋-N was in the southern.The maximum value occurred in September and the minimum value occurred in December.The nitrogen loading by the dry and wet depositions changed significantly with seasons,and its morphology was mainly in the form of NH4＋-N.Its maximum value occurred in June.The critical period should be the beginning of the rainy season to control of external nitrogen loading into Erhai Lake,and Miju River and its watershed was the key area.Consequently,the agricultural planting structure in this area should be taken into account and the ecological restoration would be applied to control the endogenous sediment release.