望虞河表层沉积物中氮的分布与形态变化特征

为了揭示望虞河沉积物中氮的分布与形态变化特征及环境影响因素,于2011年5月、8月、11月和12月采集沿线10个监测断面的表层沉积物。利用逐级分离浸取法(BCR)测定沉积物中各形态氮的含量,并观测其主要理化指标。结果表明,(1)沉积物中总氮(TN)含量为347.85~2 733.56 mg/kg并沿程上升,其中排水期8月TN含量最高且沿程变化较大,调水期TN分布与变化趋势相近。以沉积物中TN含量为污染评价标准,沉积物在5月和12月较清洁,在11月为轻度污染,而在8月为重度污染状态。(2)望虞河上河段和贡湖湾表层沉积物中TN及各形态氮的含量较低,氮在5月、8月和11月以非转化态氮(NEF-N)为主,而在12月以可转化态氮(TF-N)为主,其中离子交换态氮(IEF-N)和有机态与硫化物结合态(OSF-N)受水环境变化影响较大。(3)在调水期,IEF-N和OSF-N含量较大且沿程变化较大,CF-N和IMOF-N显示出明显季节差异性;在排水期8月,IEF-N和OSF-N含量较低且变化平缓。(4)望虞河表层沉积物中氮的含量分布与形态变化主要受到总有机碳(TOC)含量、温度、氧化还原电位(ORP)和粒度的影响。

Characteristics of distribution and variation of nitrogen species in surface sediments of Wangyu River

In order to study the characteristics of distribution and variation of nitrogen species in the surface sediments of Wangyu River, as well as the influencing factors, 4 samplings (May, August, November and December) were carried out at 10 monitoring sections in 2011. Sequential extraction methods (BCR) were used to determine the nitrogen species and observations on their physicochemical parameters were performed. Results indicated that: (1) TN in 4 samplings ranged in 347.85~2 733.56 mg/kg and increased along Wangyu River. It peaked in August with large fluctuations and similar distribution patterns were observed in the other 3 samplings. By using TN content as the evaluation criterion, the sediments in May and December were clean, while they were slightly polluted in November and seriously polluted in August. (2) Low contents of N were observed in the upper reach of Wangyu River and Gonghu Bay. When TF-N was the major fraction in December, the nitrogen species in the 3 other samplings were mainly consisted of NEF-N. IEF-N and OSF-N were susceptible to the alteration of aquatic environmental conditions. (3) In the transfer period, higher contents and large variations were observed for IEF-N and OSF-N, CF-N and IMOF-N were observed with significant seasonal patterns. While in the drainage period, the contents and variations of IEF-N and OSF-N were small. (4) The distributions and variations of nitrogen species in the surface sediments in Wangyu River were mainly influenced by total organic carbon (TOC) content, temperature, ORP and the grain size.