南四湖湿地沉积物及孔隙水基本特性研究

Characteristics of Sediments and Pore Water in Lake Nansi Wetland

利用平衡式孔隙水采样技术Pore Water Equilibrators(Peeper)来获得沉积物的孔隙水剖面,研究了南四湖湿地芦苇、香蒲沉积物的理化性质对孔隙水营养盐的垂向分布特征及其扩散通量的影响.结果表明,通过种植芦苇和香蒲,沉积含水量、孔隙度及交换态的氨氮、硝态氮含量均较无植物的对照区有明显提高.在2～5cm亚表层,芦苇区和香蒲区孔隙度分别提高了57.5%和34.6%.在沉积物-水界面附近,孔隙水中氨氮和可溶性磷酸盐浓度随剖面深度的增加呈指数关系增长,在沉积物6～8cm左右达到最大值.运用Fick第一定律对孔隙水营养盐的扩散通量进行估算,发现芦苇较香蒲更能有效地抑制孔隙水中氨氮的再次释放,从对照区的最高值3.57～4.48mg/(m2.d)降低0.90～1.24mg/(m2.d);磷酸根扩散通量3个区域的数值相差不大,在0.02～0.04mg/(m2.d)间波动;硝态氮3个区域均表现为上覆水向间隙水中扩散.相关分析结果表明,沉积物中交换态营养盐含量与孔隙水中含量呈显著正相关关系,因此控制营养盐的可交换态含量可能是防止湿地沉积物营养盐二次污染的有效途径之一.

In order to investigate the influence of sediment physical and chemical characteristics on the vertical distribution of NH 4＋ ,PO43 -and NO 3-and their diffusive fluxes at sediment-water surface,pore water equilibrators（Peeper） were employed to obtain multiple pore water profiles from reed and bulrush sediments in Lake Nansihu wetland. The results showed that sediment properties in the planted reed and bulrush fields,i. e. water content,porosity,KCl-extractable NH 4＋ and NO 3-were generally greater than those in seldom vegetation,and the porosity in 2-5 cm depth subsurface sediments increased by 57. 5% ,34. 6% ,respectively. Nutrient profiles of NH 4＋ and PO34 -at sediment-water interface exhibited a nearly exponential increase with increasing depth including a concentration maximum at a 8 cm depth,where there was a spike in the NH 4＋ and PO43 -concentration. The diffusive flux （Jx） across the sediment-water interface could be calculated from Fick＇s first law. The flux calculations showed reed could effectively decreased NH 4＋ diffusive flux,and the NH 4＋ diffusive flux,the maximum flux 3. 57-4. 48 mg /（ m^2·d） in reed field,was nearly three times greater than the minimum flux 0. 90-1. 24 mg /（m2.d） in seldom vegetation. However,there was a narrow PO43 -flux range from 0. 02 to 0. 04 mg /（m2.d） in three fields while NO 3-concentration gradient showed an opposite pattern and diffusive flux occurred in one direction from the overlying bottom water to the sediment pore water. The correlative results suggested that extractable nutrient contents in sediments correlated with pore water content,therefore,controlling extractable nutrient contents appeared to a viable measure to avoid nutrient recontamination to overlying water in wetlands.