In Situ Enclosure Experiment For Recovery And Purification Ability Of The Submerged Plants In Yunlonghu Reservoir

In situ enclosures were set up in Yunlonghu R eservoir and 4 native species of submerged plants, Potamogeton malaianus Miq, Vallisneria spiralis L., Ceratophyllum demersum L and Myriophyllum spicatum L were transplanted to study the potential of revegetation and its influences on the physical, chemical and biological index of water. The trial site was chosen to be about 10m off the south bank of the west part of the Yunlonghu Reservoir and the water depth is about lm. This research includes three parts. 1. Surveys on the growth performances of the four species of submerged plants after transplantation. 2. Assessment of the effects of the four species of submerged plants on the physical and chemical index, such as water clarity, dissolved oxygen, TN, TP; in water and the TN, TP in sediment. 3. Analysis of the effects of the four species of submerged plants on the phytoplankton community structure and biomass. The main results are as follows:1. The four species of submerged plants grew very well in the enclosure. Among them, the biomass of the Ceratophyllum demersum L. increased fastest, it achieved the largest value (6.22kg/m~2) at the harvest time in August, 29.8 times the initial biomass. The Vallisneria spiralis L. grew most slowly, its biomass is just 1.58kg/m~2 at the harvest time in August. The recovery effects were differentiated by the kind, the morphology, the physiology of the four species of submerged plants.2, After transplanting the submerged plants, the water clarity improved effectively, and the dissolved oxygen increased, the TN, TP, COD and BOD in water decreased obviously. The purification abilities, however, were different among the four different submerged plants. Myriophyllum spicatum L., improved water clarity most effectively. Ceratophyllum demersum L., made the dissolved oxygen condition much better. Vallisneria spiralis L. was the most effective in absorption of the total nitrogen. The de-phosphorus effect of the Myriophyllum spicatum L. was the best. Myriophyllum spicatum L. and the Ceratophyllum demersum L. were much better for deleting organics. Vallisneria spiralis L. had highest fixation capabilities for TN and TP in the sediments.3, The development of the submerged plants could reduce the density and biomass of the phytoplankton significantly. In the enclosures with transplanted submerged plants, the succession of phytoplankton community was mainly from green algae to diatom. In contrast, the phytoplankton community succession of the control and the open reservoir without submerged plants were changed from the type of "green algae and diatom" to the type of "green algae and blue-green algae".4, The combination of submerged plants had a synergistic effect. The water purification ability of the enclosure W4 with the three species, Potamogeton malaianus Miq, Vallisneria spiralis L. and Myriophyllum spicatum L. was better than the ones with only one species of submerged plant and the biomass was much higher as well.