太湖北部藻类生长旺盛期大气氮、磷沉降特征

Atmospheric nitrogen and phosphorus deposition during optimal algal growth period in northern Lake Taihu

按照《大气降水样品的采集与保存标准》(GB/T 153580.2—92)收集大气N、P沉降物和降水量,并测定了2007年5～11月太湖北部梅梁湾藻类生长旺盛期间大气TN、TP的干、湿沉降通量。结果表明,太湖北部梅梁湾大气TN月湿沉降通量和月总沉降通量的变化趋势均呈双峰型特征,与当地梅雨和台风侵袭时的降水量呈明显正相关,并且TN的月湿沉降通量高于月干沉降通量,但降水量最少的11月则相反;大气TP月干、月湿沉降通量呈相互交替的变化趋势。大气N沉降物中主要以溶解性氮(TDN)为主,平均约占91.4%;而P沉降物中溶解性磷(TDP)占的比例相对较低,平均约为65.1%。经测定,2007年太湖北部梅梁湾TN和TP的年沉降通量分别为2976、84.0kg/km2,相比2002年7月至2003年6月分别下降34.4%和78.7%;2007年太湖北部梅梁湾大气TN的年沉降量高达6958t,远超过太湖湖泊生态系统理论允许的TN年沉降量。

Since the ＂Standard-emission＂ project took place in the Lake Taihu basin, atmospheric nitrogen （N） and phosphorus （P） deposition has played a more important role in algal bloom formation. To characterize atmospheric nitrogen and phosphorus deposition, bulk deposition and rain water were collected to measure the bulk atmospheric deposition rate （R1）, wet deposition rate （Rw） and dry deposition rate （Rd） for total nitrogen （TN）, all species of N, total phosphorus （TP）, and all species of P in northern Lake Taihu from May to November 2007, the period of optimal algal growth. The patterns of the bulk atmospheric deposition rate for TN and the wet deposition rate for TN exhibited double peaks during the observation period due to the effects of plum rains and typhoons. The monthly bulk atmospheric deposition rates for TP remained stable except for July, showing little effect of local weather condition. In bulk deposition samples, the average percent of total dissolved N （TDN） accounting for TN was 91.4% and changed little with time; however, the average percent of total dissolved P （TDP） accounting for TP was 65.1% and was much more time dependent. The estimated annual bulk atmospheric deposition rates of TN and TP during 2007 in Lake Taihu were 2 976 and 84.0 kg/km^2 , respectively, about 34.4% and 78.7% lower than the respective quantities of 07/2002-06/2003. The estimated safe annual bulk deposition load of TN for Lake Taihu was 6 958 t/a in 2007, including 4 642 t of wet deposition; both are lower than the respective quantities of 07/2002-06/2003 due to measures taken to conserve energy and emission control regulations in the Yangtze River Delta. High atmospheric N deposition loads in June, July, and September as well as elevated TP loads in July contributed to the cyanobacterial blooms in northern Lake Taihu during favorable summer and autumn algal growth periods.