蠡湖水体氮、磷时空变化及差异性分析

蠡湖是一个典型处于从浊水藻型向清水草型转换过渡时期的浅水湖泊.根据2012~2013年周年的现场调查资料和历史监测资料,分析了水体氮、磷的空间分布、变化规律及主要影响因素,并探讨了水体氮、磷形态的时空差异及其相应的控制对策.结果表明,蠡湖仍然没有从根本上解决水体的富营养化问题,水体中氮、磷浓度仍处于一种不稳定的状态,各采样点总氮(TN)浓度在0.74~4.93mg/L之间,平均值为1.35mg/L;总磷(TP)浓度在0.03~0.31mg/L之间,平均值为0.073mg/L.空间上,TN和TP浓度自东向西依次递减,呈现东蠡湖高于西蠡湖,沿岸区高于湖心区的趋势;季节上,TN、TP浓度呈现夏季、秋季较高,而冬季、春季低的特点;水体中氮主要以溶解态为主,DTN占TN的比例在35%~99%之间,平均为77.98%;而磷主要是以颗粒态的形态占优势,颗粒态磷占TP的比例在11%~90%之间,平均值为59%.多元统计表明,TN与DTN和总悬浮物(TSS)之间呈正相关关系,但与TSS的相关性系数较小,而TP与DTP和TSS都呈显著正相关.因此,要降低水体中氮磷浓度,可以从减少通过干湿沉降进入湖泊水体的氮磷或者降低沉积物再悬浮、抑制底泥氮磷释放两个方面入手.

Spatial-temporal dynamic changes of nitrogen and phosphorus and difference analysis in water body of Lihu Lake

Lihu Lake is a typical shallow lake in the transitional period from unshiftable state of algae-dominated turbid water to unshiftable state of macrophytes-dominated clear water. The distribution characteristics, change rule and key impacting factors of nitrogen and phosphorus in overlying water were discussed by the field survey data investigation from 2012-2013 and the historical monitoring date collection. And the spatial-temporal difference of nitrogen and phosphorus forms in overlying water and the corresponding control measures were also studied on focus. The eutrophication of Lihu Lake was still not fundamentally solved, and the concentration of nitrogen and phosphorus in overlying was still in an unstable state. The concentration of nitrogen and phosphorus was in the range of 0.74~4.93mg/L and 0.03~0.31mg/L, with the mean value of 1.35 and 0.073mg/L, in respectively. Concentrations of total nitrogen (TN) and total phosphorus (TP) decreased from the east district of Lihu Lake to the west, and lakeside areas was higher than lake center. Concentrations of TN and TP were higher in summer and autumn, but lower in winter and spring. Dissolved nitrogen was the main nitrogen state in water, accounting for 35%~99% of TN, with the mean value of 77.98%.While phosphorus mainly existed in particulate state, and particulate phosphorus accounted for 11%~90% of TP, and the mean value was 59%. Results of multivariate statistics analysis showed that TN was positively correlated with DTN and TSS, but with smaller correlation coefficient with TSS. However, TP was significantly positive with both DTP and TSS. Therefore, two methods should be used to reduce the concentration of nitrogen and phosphorus in water body, one is cutting down the dry and wet deposition into lake, and the other is reducing sediment resuspension and restraining the release of nitrogen and phosphorus from sediments.