桑沟湾贝类养殖水域沉积物再悬浮的动力机制及其对水体中营养盐的影响

Dynamic mechanism of sediment resuspension with its effects on content of nutrients in water in the shellfish culture area of Sanggou Bay

基于海流、波浪、水环境和沉积环境指标的实测资料,探讨了桑沟湾贝类养殖水域沉积物再悬浮的动力机制,并估算了一次大的动力过程作用下桑沟湾沉积物中氮、磷营养盐的释放量。结果表明,(1)在小风速(≤5.0m/s)条件下,波浪在海水-沉积物界面产生的切应力量值与底流切应力大致相当;在较大风速(5.0～11.8m/s)条件下,波浪切应力比底流切应力高出一个量级;(2)当风浪较小(风速≤3.6m/s)时,随底层流速的周期性变化,底层水体浊度变化并未呈现出明显的规律性,二者相关系数值仅为0.22,这说明底流作用只会引起沉积物的水平输运,对沉积物再悬浮的贡献相对较小,沉积物再悬浮的动力主要来自波浪扰动;(3)据估计,桑沟湾贝类养殖水域沉积物再悬浮的临界波浪切应力在0.04N/m2左右,对应的风速约为8m/s;(4)据估算,一次大的动力过程作用下桑沟湾沉积物中无机氮和活性磷酸盐的最大释放量,春季分别为10.24t和1.71t,这相当于全湾水体中无机氮平均含量增加9.54μg/L,活性磷酸盐平均含量增加1.59μg/L;夏季分别为11.04t和0.95t,相当于全湾水体中无机氮平均含量增加10.28μg/L,活性磷酸盐平均含量增加0.88μg/L;(5)贝类养殖使桑沟湾生物沉积作用加强,而沉积物再悬浮造成的内源释放,又对桑沟湾的水产养殖产生反馈作用。

On the basis of survey data on sea current, wave and water environmental parameters, dynamic mechanism of sediment resuspension in the shellfish culture area of Sanggou Bay was investigated, and the maximum release amount of dissolved inorganic nitrogen（DIN） and phosphate （DIP）caused by sediment resuspension was also estimated. The results were as follows. （1） As the wind speed was≤5.0 m/s, the shear stress produced by wave was roughly equivalent to that produced by bottom current. As the wind speed was 5.0-11.8 m/s, the wave stress was much larger than current stress. （2）The bottom current may just cause horizontal transport of sediment; the major dynamic causing sediment resuspension was from wave dis-turbance. （3）It was estimated that the critical wave stress value causing sediment resuspension was about 0.04N/m^2 in the shellfish culture area of Sanggou Bay, the corresponding wind speed being 8.0 m/s. （4） Owing to sediment resuspension during a big dynamic process, about 10.24 t of DIN and 1.71 t of DIP could be released into the bay in spring, which would result in the situation that the average concentrations of DIN and DIP increased by 9.54μg/L and 1.59μg/ L, respectively. Similarly, about 11.04 t of DIN and 0.95 t DIP could be released into water of the bay in summer, making the average concentrations of DIN and DIP increased by 10.28μg/ L and 0.88μg/L, respectively. （5） Shellfish culture in Sanggou Bay intensified the bio-deposition, whereas the nutrient release caused by sediment resuspension would produce feedback action on aquculture.