Gu Xiao-zhi, Zhang Lei, Bo Xiang, Fan Cheng-xin
State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China.
Huan Jing Ke Xue. 2010 Apr;31(4):939-45.
In order to investigate the influence of sediment physical and chemical characteristics on the vertical distribution of NH4+, PO4(3-) and NO3(-) 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 NH4+ and NO3(-) 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 NH4+ and PO4(3-) 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 NH4+ and PO4(3-) 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 NH4+ diffusive flux, and the NH4+ diffusive flux, the maximum flux 3.57-4.48 mg/(m2 x d) in reed field, was nearly three times greater than the minimum flux 0.90-1.24 mg/(m2 x d) in seldom vegetation. However, there was a narrow PO4(3-) flux range from 0.02 to 0.04 mg/(m2 x d) in three fields while NO3(-) 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.
为了研究沉积物理化特性对NH4+、PO4(3-)和NO3(-)垂直分布及其在沉积物-水界面扩散通量的影响，采用孔隙水采集器（Peeper）获取了南四湖湿地芦苇和香蒲沉积物的多个孔隙水剖面。结果表明，种植芦苇和香蒲的区域沉积物性质，即含水量、孔隙率、KCl可提取的NH4+和NO3(-)，总体上大于植被稀少区域，2-5 cm深度的表层沉积物孔隙率分别增加了57.5%、34.6%。沉积物-水界面处NH4+和PO4(3-)的营养物质剖面随深度增加呈近似指数增长，在8 cm深度处浓度达到最大值，此时NH4+和PO4(3-)浓度出现峰值。沉积物-水界面的扩散通量（Jx）可根据菲克第一定律计算。通量计算表明，芦苇能有效降低NH4+扩散通量，芦苇地的NH4+扩散通量最大为3.57-4.48 mg/(m2·d)，几乎是植被稀少区域最小通量0.90-1.24 mg/(m2·d)的三倍。然而，三个区域的PO4(3-)通量范围较窄，为0.02至0.04 mg/(m2·d)，而NO3(-)浓度梯度呈现相反模式，扩散通量从上层底水向沉积物孔隙水单向发生。相关结果表明，沉积物中可提取营养物质含量与孔隙水含量相关，因此，控制可提取营养物质含量似乎是避免湿地中营养物质重新污染上层水体的可行措施。
