巢湖水华暴发期水-沉积物界面溶解性氮形态的变化

2008年4~10月,连续对巢湖8个样点进行采样,分析了上覆水和表层沉积物间隙水中溶解性氮形态在水华暴发过程中的变化,估算了水-沉积物界面无机氮的扩散通量.结果表明,上覆水中NH4+-N含量随水华暴发强度的增加而减小,溶解性总氮(DTN)含量在水华暴发后明显升高,而NO3--N含量只在水华暴发严重时才明显减少.在大规模水华暴发前(4~5月)上覆水中DTN的主要组成部分是NO3--N和NH4+-N,在水华暴发后则是溶解性有机氮(DON).间隙水中PDTN以NH4+-N为主,其浓度随温度的增加而升高; DON在水华暴发过程中呈先下降后上升的趋势.通量计算结果表明,沉积物作为NH4+-N的“源”一直由间隙水向上覆水释放,西半湖扩散通量在13.06~32.94mg/(m2·d)之间,东半湖扩散通量在4.54~17.41mg/(m2·d)之间.沉积物-水界面交换是湖泊营养盐重要的补充途径,为水华持续暴发提供营养来源.

Dissolvable nitrogen variation at water-sediment interface during alga blooming process in Chaohu Lake

In order to recognize the concentrations changes during the alga bloom and estimate the diffuse flux of inorganic nitrogen at the sediment -water interface, dissoluble nitrogen forms in the overlying water and surface sediment pore water from eight sites of Chaohu Lake were investigated and analysized from April to October in 2008. Concentrations of NH_4~+-N decreased as alga bloom intensity increasing, and concentrations of NO_3~--N decreased obviously only during the period of serious alga bloom, while concentrations of dissoluble total nitrogen (DTN) increased obviously after alga bloom. NO_3~--N and NH_4~+-N were the major dissoluble nitrogen forms in the overlying water before the big-size alga bloom during the period of April and May, however, the dissoluble organic nitrogen (DON) was the major nitrogen form after the alga bloom. NH_4~+-N was the major nitrogen form in the pore water, which concentrations increased with the temperature increase. Concentrations of DTN decreased firstly and then increased during the alga bloom process. According to the diffuse flux calculation, NH_4~+-N always released from pore water to overlying water, the diffuse flux in the western and eastern lake regions ranged from 13.06 to 32.94 mg/(m~2·d) and 4.54 to 17.41 mg/(m~2·d), respectively. Nutrient exchanges at the sediment-water interface are the most important nutrient supplement way for the sustainable algal bloom.