| As the major primary producers, submerged plant is an important part of the lake ecosystem.Because of their unique growth properties and functions in ecology and landscape, submerged plant play an important role in material circulation, energy flowing, purifying water quality and ecological restoration.During the period of "11th five-year special project", national science and technology major projects of water pollution control and management, the aquatic plant community recovery demonstration project was conducted in west area of the west lake by Hangzhou west lake water special project. Submerged plants in west area of the west lake was preliminary recovered. However, there still exist some problems at present:the clear water type system preliminary established is unstable, spatial niche is relatively single, the algae abnormal proliferation. Regard to above problems, so in the "twelfth five-year" national water special project, Hangzhou west lake project-- technology study and engineering demonstration of improvement for water environment of urban landscape lake, engineering construction of submerged plant patches mosaic pattern was timely followed-up to optimize the structure of submerged plant, hoping for one evolution that relying on the self-adjustment ability and self-organization ability of ecosystem, which make it to the direction of the orderly and virtuous cycle. In the west lake, there exist big difference for sediment and water level in different lake area and sites, and residue flocculants(Al salt as the main ingredient) are brought in through water diversion engineering. These factors naturally exert serious influence on the submerged plant. Before the conduction of the project, submerged plant patches mosaic pilot practice was built and monitored in Maojia port which last one whole year from May, 2014 to April, 2015. While in the meantime, outdoor simulation experiment was conducted, combined with the lake’s situ experiment, inwhich the effects of environmental factors, namely, sediment type, water depth, the flocculant were studied on the submerged plant Vallisneria natans and Hydrilla verticillata asexual reproduction, growth and physiological indicators and influence on reducing the nutrient, hoping for providing scientific support for the "twelfth five-year" demonstration project. The main results showed as follows:1. Conclusion of the impact of sediment type on growth morphological characteristics and physiological indexes of Vallisneria natans, Hydrilla verticillata.(1) Aquarium tank simulation sediment type exert significantly influence on Vallisneria natans stolons diffusion rate and tillering plant morphological characteristics and productivity(P < 0.05).Vallisneria natans presents biggest asexual reproduction ability in the lake mud sediment, followed by lake mud+sandy. Vallisneria natans chlorophyll content, G P and R C is very significantly different among different sediment types(P < 0.01). The water quality are improved obviously. Also, sediment type have a significant impact on biomass accumulation, tiller number and other forms of Hydrilla verticillata.Chlorophyll content and other physiological indexes in the L is the largest, and there were significant differences among the different sediemnts.(2) Conclusion of the situ experiment in Mao Jia port: Resisting-graze(NM) area sediment and patch mosaic pilot(BK) area sediment have remarkable effect on the growth morphological characteristics and physiology indexes of Vallisneria natans and Hydrilla verticillata. BK pilot sediment was more suitable for the growth of Vallisneria natans and it growed better in NM pilot area generally than BK pilot.Effect of situ sediment on plant’s physiological indexes chlorophyll content, protein content, SOD activity and malondialdehyde content exist significantly differences between the two species(P < 0.05). Hydrilla verticillata growed better in NM area wholely than in BK area, with the Hydrilla verticillata biomass, tiller number, plant height in NM area being superior to that in BK area. The NM pilot sediment is more suitablefor Hydrilla verticillata growth.2. Conclusion of the influence of Mao Jia port BK situ water depth on growth morphological characteristics and physiological indexes of Vallisneria natans, Hydrilla verticillata.With water level deeper, Vallisneria natans biomass and tiller number, stolon number and diameter, root weight all showed a trend of decrease, which concluded that the deep place( > 1.8m) wasn’t conducive to the growth of Vallisneria natans, and a certain degree of water depth( > 1.2m) will stimulate its stolons and root growth to assign more biomass to underground part. Water depth has significant effect on SOD activity and malondialdehyde, but not on chlorophyll and protein content. With water deepening SOD activity decreased, malondialdehyde content increased. Water depth has a great influence on morphological features of Hydrilla verticillata, but no obvious regularity. Hydrilla verticillata grow best in moderate water level(0.8 ~ 1.0 m), with the maximum biomass, plant number, plant height, internode length value in three water levels. Deep water level drive Hydrilla verticillata allocate relatively more biomass in underground in order to survive. Chlorophyll content decreases with the depth of the water, the bigest SOD activity and protein content located in the moderate water level, and malondialdehyde content increases with water level deepening.3. Conclusion of the influence of Al-flocculant on Vallisneria natans, Hydrilla verticillata growth morphological characteristics and physiological indexes:(1) In Wugui pond situ experiment Al-flocculant exert significant influence on the Vallisneria natans, Hydrilla verticillata growth morphology(P < 0.05). Overall, the Vallisneria natans and Hydrilla verticillata cultured in the site which located in downstream of the inlet(2# site) grow better than that in the site which beside the inlet 15m(1# site), with biomass, tiller number, plant height, stolons, root weight indexes being superior to that in 1#, infering that the water and sediment environment of 2# site were moreadvantageous to Vallisneria natans, Hydrilla verticillata growth and rudimental flocculants in water have inhibition effects on the growth morphology. Lake water flocculant drive the chlorophyll content, SOD activity and protein content of two kinds of submerged plants decrease, but stimulate malondialdehyde content increase.(2) However, the results of outdoor tanks simulation experiment differ from that lake-situ experiment, Vallisneria natans and Hydrilla verticillata biomass of treated group increased and tiller number, plant height, root weight, stolons indexes was bigger than that in the control group. But there was no significant difference(P > 0.05). Flocculating agent did not exert significant inhibition to Vallisneria natans, Hydrilla verticillata growth. Inversely, increasing water transparency as a result of improving the plants productivity. Flocculant had different degree influence on physiology index of Vallisneria natans and Hydrilla verticillata, overall showing a trend of upward after decline first. TN, TP and water chlorophyll-a concentration in general was on the decline, but the content of Al increased rising.4. Submerged plant patches mosaic community were optimized in Maojia port lakeIn May, 2014, Vallisneria natans, Myriophyllum verticillatum, Hydrilla verticillata,Ceratophyllum demersum, Potamogeton maackianus and Potamogeton pectinatus were planted in the patches mosaic pilot area. Up to October 2014, the total average coverage of submerged plant reached36.8%, with Vallisneria natans, Ceratophyllum demersum, Myriophyllum verticillatum becoming the dominant species through growing and diffusion, the respective average coverage being 56%, 66% and71%, the respective average biomass being 1320.8 g/m2, 955.1 g/m2 and 877.4 g/m2. While Hydrilla verticillata, Potamogeton pectinatus and Potamogeton maackianus has gradually disappeared. But Hydrilla verticillata can certainly grow well in NM pilot area where under the circumerstance of slightly harder sediment, shallow water depth( < 1.2 m) and controlling fish grazing. Submerged plant communityeventually reached a steady state with the total coverage of about 40% in April, 2015, with Vallisneria natans, Ceratophyllum demersum, Myriophyllum verticillatum and Potamogeton crispus being sampled,among which Potamogeton crispus was not planted in this project. On the whole, water quality was improved preliminary. TN, NO3--N presented downward trend during the experiment, and the TP concentration of experimental area was always lower than the control area, and chlorophyll content changed largely. Phytoplankton diversity index of experimental area in most months was greater than the control area.Suitable submerged macrophytes species for the growth in West Lake can preferably be Vallisneria natans, Ceratophyllum demersum, Myriophyllum verticillatum. Reconstruction and recovery of submerged plant should better be pushed from shallow water area to deeper gradually and the tightly harder sediment(if permitted, sediment can be modified accordingly) would be more conducive to submerged plant reconstruction. If possible, try to avoid the boat fairway to protect submerged plant against shock wave disturbance. Set barricade(as closed as possible) to control grazeing by fish, etc. |
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