Studies On Growth Characteristics Of Vallisneria Natans And Bioremediation Technology In Muddy Waters

In this paper, grwoth characteristics of the submergedplantsVallisneria natans and bioremediation technology in turbid waterswere studied. Firestly, the ecological investigation and the characteristics ofgrowth and distribution of V. natans in natural waters were carried out, thenthe lab experiments were designed for finding out the optimum grwothconditions for V. natans. And the growth and degenerate state of V. natansin lower illumination at lab and field were compared to find the suspendedsediment limiting contents and floating algae limiting concentration for V.natans surviving. By the river bioremediation engineering and technologywith aquatic plants, the community of V. natans was successfullyestablished in the limited muddy waters. The studies would providescientific theoretical absis and technological supporting for thebioremediation and restoration and water enviroment improvement withaquatic plants.(1) Investigating the resources of V. natans in Xinjiang River(Shangrao section). The resources of V. natans in Xinjiang River (Shangraosection), Jiangxi province is very rich, and the V. natans presents some regularity in both horizontal and vertical distribution. The distribution areaof V. natans is about6.1%in whole investigation area, and the averageminimum and maximum water depth for V. natans growth are0.67m and2.09m, respectively. The biomass of V. natans presents first increases andlate decreases with increasing water depth. At100~150cm in depth, thebiomass of V. natans is the largest, about4.47kg/m2, and at30~50cm indepth, the biomass of V. natan is the smallest, about4.47kg/m2.(2) Studing the optimum conditions for the grwoth of V. natans. Withdesigned experiment for the grwoth of V. natans in different temperature,light and sediment type, the result showed that the optimum grownconditions for V. natans were temperature25℃, light intenstiy100μmol/(m2·s), and substrate with mud-sand mixed sediment type.(3) Carring out the critical depth and light intensity for V. natans inriver. As for muddy Litang river, the largest biomass of V. natans was foundat the depth of60~90cm. The critical depth for V. natans surviving wasabout90~120cm in depth, and where the average light intensity was about45~70μmol/(m2·s) in whole year. We found that V. natans density wasnegatively correlated with water depth, while the average leaf length of V.natans was positively correlated with the water depth. Throughout theinvestigation, there was plenty plants of V. natans in riverside area, whilethere was no plants of V. natans in river center area. Further lab experiments showed that plant biomass, tiller number, average root lengthand photosynthetic oxygen evolution rate per plant of V. natans decreasedwith the light intenstiy decrease (P<0.01). The critical light intensity of V.natans would be about10μmol/(m2·s), and the photosynthetic oxygenevolution rate was about10.52μmol/(g (FW)·h). Below the critical lightintensity, the V. natans began negative growth.(4) Researching the effecion of suspended sedimen and floating algaewith lower light intensity on the V. natans growth. Scenedesmus obliquusgrew with "S"-type. The time for reaching stable was positively correlatedwith the suspended sediment contents but negatively correlated with theconcentration of algal cells added. At0.1g/L suspended sediment contentsand algal cell density108cell/L, the algae chlorophyll a concentrationincreased faster than that in other groups, and reached up to253.75μg/L in15days. The curves of light intensity under waters in all groups presentedthe trends with first rising and later decreasing. The light intensity in thegroup with1.0g/L suspended sediment content and108cell/L algae celldensity decreased to lowest in15days, about42.41μmol/(m2·s). With thetime delay and suspended sediment content increase, the V. natansphotosynthetic oxygen evolution rate presented a decrease trend. Thephotosynthetic oxygen evolution rate at the group with1.0g/L suspendedsediment content and108cell/L algae cell density decreased to the lowest in 15days, about10.88μmol/(g (FW)·h).(5) With submerged plants bioremediation engineering and technology,the V. natans vegetation community was successfully restored in muddyriver. The initial submerged plants V. natans (47%) and cabomba (35%) asdominant species were implanted to the artificial lake in June. While in July,August, September, Hydrilla and V. natans become the dominant specieswith35%,55%,50%and40%,40%,45%; respectively. Finaly, V. natanstook an absolute advantage in November, December and Juanary with80%,95%and95%, respectively. Thus, in the limiting muddy river with lowerlight intensity, V. natans plants had a dominant position in the community,not only effectively reducing turbidity and increase the transparency ofriver water, but also absorbing and decreasing the nutrient content in riverwater, and showing a strong reproductive capacity for communityestablishing.