太湖草型湖区沉积物再悬浮对水体营养盐的影响

再悬浮过程中沉积物对水体营养盐的内源贡献是湖泊,特别是浅水湖泊富营养化研究中的重要问题.采用原位沉积物柱样和原状上覆水的Y型扰动装置,被用来研究常规风情下太湖草型湖区沉积物的再悬浮和沉降过程对水体营养盐负荷的影响.结果表明,小风和中风的再悬浮过程导致水体氨氮和磷酸根磷含量显著下降,单位面积水柱含量最大变化量分别为-0.140 g·m-2和-1.59 mg·m-2;大风条件下,水体氨氮含量下降幅度很小,磷酸盐则出现明显增加趋势,最大增量为0.81mg·m-2.再悬浮过程之后的沉降过程中,中、小风条件的水体氨氮含量变小,大风条件的含量没有明显变化.磷酸根磷含量在中、小风条件下与风浪前差别较小,大风条件的含量则明显增大,最大增量为1.36 mg·m-2.因此,沉积物的再悬浮过程和沉降过程对上覆水体的营养盐动态负荷都产生重要影响.与太湖无植被湖区的研究结果对比说明,水生植物的存在对风浪作用下沉积物与上覆水的物质交换有一定的抑制作用.

Effects of Sediment Resuspension on Aqueous Nutrient Loading in Grass Type Zone of Lake Taihu

Internal nutrient loading caused by sediment resuspension is becoming a key issue in studying water eutrophication of shallow lakes. A Y-shape apparatus was used to simulate sediment resuspension and sedimentation process under hydrodynamic conditions in situ in grass type zone of Lake Taihu, and effects on aqueous nutrient loading were investigated. The results indicated that, in the light and moderate wind processes, content of ammonia nitrogen and phosphate had remarkably reduced with the increase of the amount of suspended sediments in water column, with the maximal change of -0.140 g x m(-2) and -1.59 mg x m(-2) at the sediment-water interface for the two nutrients respectively, and in the strong wind process, concentration of aqueous phosphate had a significant increase, with the maximal flux of 0.81 mg x m(-2) at the sediment-water interface, while concentration of aqueous ammonia nitrogen showed a small decrease. And in the later sedimentation process after wind, content of aqueous ammonia nitrogen was lower than that before the light and moderate wind processes, but approximated to that before the strong wind process. Content of aqueous phosphate was close to that before the light and moderate wind processes, but had a marked increase compared to that before the strong wind condition, with the maximal increment of 1.36 mg x m(-2). Consequently, sediment resuspension and sedimentation processes impact nutrients loading of overlaying water evidently. Comparison of the results with those from non-grass type zone in Lake Taihu illustrates that the presence of aquatic macrophytes played some roles in reducing the release of nutrients during the sediment resuspension process.