利用薄膜扩散平衡技术分析沉积物间隙水溶解态反应性磷

Determination of soluble reactive phosphorus in porewaters of sediments using the technique of diffusive equilibration in thin films

沉积物间隙水溶解态反应性磷(SRP)是反映沉积物磷地球化学特征的敏感指标,对其高分辨率获取一直是难点.基于薄膜扩散平衡(DET)原理,以琼脂糖为原料制备薄膜,通过平衡、切片、提取、测定等步骤,获得溶解态反应性磷的含量信息.实验确定薄膜在磷溶液中的平衡时间为24h,通过0.25mol/L硝酸提取16h可将薄膜萃取的磷提取完全.利用DET技术对不同沉积物间隙水SRP进行了分析,与实际浓度的差异在±5%以内;对沉积物剖面的分析结果与Rhizon、微型Peeper等采样技术基本一致,垂直分辨率可达到3mm左右.利用DET技术对太湖草型和藻型湖区沉积物间隙水SRP进行了分析,发现草型湖区间隙水剖面SRP呈峰形分布,且横向空间分异明显;藻型湖区间隙水SRP随沉积深度的增加呈升高趋势,扩散梯度随水温升高而增强.

Distribution of soluble reactive phosphate （SRP） in pore waters is a sensitive indicator showing geochemical properties of phosphorus in sediments. Concentration of SRP in synthetic solutions was obtained based on the principle of diffusive equilibration in thin films （DET）. Analytical procedure generally includes equilibration of the gels in solutions or pore waters, section of the gels after retrieval, back elution of phosphorus in the gels, and analysis of SRP in the eluents. Equilibrium and extraction times were determined at 24h and 16h, respectively, with 0.25mol/L HNO3 used as an extractant. Concentrations of SRP in pore waters of different sediments measured by using the established DET technique agree well with its actual values, and the variations are generally within ±5%. Analytical results for sediment profiles with this technique, which has a vertical resolution at about 3mm, also show comparison with those using sampling techniques of Rhizon and Mini-Peeper. The established DET technique was used to measure SRP profiles in sediments of macrophyte- and algal-dominated regions in Lake Taihu. Peak-shape distribution and horizontal heterogeneity of SRP were observed in macrophyte-dominated region, while an upward and increasing movement of SRP was observed in algal-dominated region with an increase in water temperature.