PURIFICATION EFFECTS AND MECHANISMS OF NATURAL PONDS ON SUMMER RAINFALL RUNOFF POLLUTION

摘要

Four natural ponds, a non-plant pond, a submerged plant pond, an emerging plant pond, and an emerging-submerged complex plant pond, in Lingang New city of Shanghai were chosen to study the purification effects and mechanisms on summer rainfall runoff pollution. A total of 3343.9 g TN, 169.5 g TP and 338891.6 g COD_(Cr) were intercepted by these four different types of natural ponds during the three selected representative rainfall runoff events. The results showed that the emerging plant pond exhibited the highest purification efficiency, and the emerging-submerged complex plant pond exhibited the lowest. The emerging plant pond and the emerging-submerged complex plant pond performed a relative high removal rate of TP, which was 57.6% and 57.4%, respectively. Additionally, the emerging plant pond exhibited a relative high total removal rate of TN and COD_(Cr), which was 46.4% and 47.3%, respectively. At the same time, planktonic algae density of most samples had decreased over time, which indicated a purification effect by different natural ponds in the experimental period. Besides, it was found that substrate sludge absorption and plant assimilation of rainfall runoff pollutions might be the two important mechanisms in purifying rainfall runoff pollutants using natural ponds.