稻田排水在沟塘湿地净化中总氮浓度的周期性特征

基于高邮灌区水稻全生育期排水沟塘湿地水体中总氮质量浓度日变化资料,采用复Morlet小波函数,对沟塘湿地水体总氮质量浓度变化周期进行了分析.结果表明,沟塘湿地水体总氮质量浓度变化存在5个时间尺度的周期震荡,以23 d为主周期,每6~7 d质量浓度高低交替一次.因此,在满足稻田排水调控要求的前提下,TN质量浓度较高的稻田排水入沟塘后,净化周期以7~13 d或19~25 d为宜,经此段时间净化,水中TN质量浓度平均降低30%~58%和28%~66%,最大消减率分别达79%和93%;TN质量浓度较低时,沟塘湿地净化时间以13~19 d为佳,TN质量浓度平均降低14%~72%,最高降幅87%.选择在该净化周期内对沟塘湿地进行排水,水中TN质量浓度处于较低水平,排水对下游水体造成的污染最轻.

Periodic variation of total Nitrogen concentration during decontamination course of paddy field drainage in ponds

Based on the daily data of the total Nitrogen (TN) concentration in pond water in Gaoyou Irrigation District during the child-bearing period of rice, the periodic variation of the TN concentration was analyzed by use of the compound Morlet wavelet function. The results show that there are obvious periodic variations with five time scales. Under the dominant period of 23 d, the TN concentration alternates every 6～7 d between high and low concentrations. Thereby, under the perquisite of satisfying the control requirements of paddy field drainage, after the paddy field drainage with high TN concentration enters into the ponds, the decontamination period of the ponds should be 7～13 d or 19～25d.) Under this retention, the TN concentration is decreased by 30%～58% or 28%～66% on average, with the maximum decrease of 79% or 93%, respectively. When the paddy field drainage with low TN concentration enters into the ponds, the decontamination period of the ponds should be 13～19 d. The TN concentration is decreased by 14%～72% on average, with the maximum decrease of 87%. During this retention period, the drainage water from pond is probably in a low state of TN concentration. Accordingly, the lightest nitrogen pollution to the downstream rivers will be attained.