滇池浮游植物碳氮同位素时空分布特征及其影响因子分析

Spatio-temporal distribution and influencing factors of stable carbon and nitrogen isotopes of phytoplankton in Dianchi Lake

通过对旱季、旱雨季过渡期和雨季3个不同时期滇池浮游植物δ^(13)C、δ^(15)N的研究发现,滇池浮游植物δ^(13)C、δ^(15)N存在显著的时空分布特征.从旱季、过渡期到雨季,浮游植物δ^(13)C值分别为-20.44‰±0.72‰、-17.32‰±1.09‰和-15.92‰±1.74‰,呈逐渐升高趋势;而浮游植物δ^(15)N值的季节变化模式则相反,雨季(13.55‰±0.85‰)显著低于旱季(15.33‰±0.31‰)和过渡期(15.02‰±1.12‰).空间分布上,浮游植物δ^(13)C值呈现南高北低的变化特征,极差为13.17‰,δ^(15)N值则中部湖区高,南北部湖区低,极差为11.37‰.统计分析表明,浮游植物δ^(13)C值与水温、降水量、电导率和pH值等多因素相关,反映了生物生长速率和无机碳源的影响显著;浮游植物δ^(15)N值季节变化受降水量、总氮(TN)、总磷(TP)的影响,其空间变化与滇池流域内土地利用的空间分布格局一致.上述结果显示,城市生活污水仍然是滇池重要的污染来源,而农业化肥等面源污染对δ^(15)N值的时空变化起到显著的调控作用.因此,滇池流域土地利用与营养盐来源的空间差异以及西南季风区降水的季节变化是影响湖泊生态系统碳氮循环与同位素生物示踪信号的重要因子.

A comparative study of δ^(13)C and δ^(15)N values of phytoplankton in Dianchi during the dry,transitional and rainy seasons showed that the δ^(13)C and δ^(15)N levels of phytoplankton were characterized by significant spatial and temporal fluctuations.During the dry,transitional and rainy seasons,the δ^(13)C of phytoplankton were respectively at-20.44‰±0.72‰,-17.32‰±1.09‰and-15.92‰±1.74‰,showing a gradually increasing trend.However,the opposite trend was recorded for the seasonal variation of δ^(15)N levels in phytoplankton,because in rainy season the level was significantly lower(13.55‰±0.85‰)than in the transitional period(15.02‰±1.12‰),and in the dry season(15.02‰±1.12‰).The average of the spatial distribution of the δ^(13)C levels in phytoplankton is 13.17‰,with an upper level in the south basin and a lower level in the north basin.For the δ^(15)N levels of spatial distribution in phytoplankton,the average was 11.37‰,with a high value n the central basin and lower values in the southern and northern basins of the lake.About the level influencing factors,the statistical analyses showed that theδ^(13)C value of phytoplankton in Dianchi was strongly related to multiple factors such as water temperature,precipitation,electrical conductivity and pH value,indicating thatδ^(13)C level of phytoplankton was significantly affected by cell growth rate and inorganic carbon sources.The seasonal variation in theδ^(15)N values of phytoplankton in the lakes was mainly related to precipitation,and to the total nitrogen,and total phosphorus levels in the waters.The spatial variation in theδ^(15)N was consistent with the spatial pattern of catchment land uses in Dianchi.This indicated that urban domestic sewage still remains an important pollution source of Dianchi,while agricultural fertilizer and other non-point source pollution played an important role in modulating both spatial and temporal variation of the phytoplanktonδ^(15)N levels.Therefore,spatial patterns of land use and seasonal variations in precipitation,were importantly affecting the ecosystem nutrient cycling and isotopic levels in the biota of the Dianchi lake.