Study On Impact Factor And Technique Of Vegetation Restoration For Flood Beaches Wetlands On Along Yangtzi River

This paper studied the physiological and ecological responses of wetland plants on flood beaches along Yangtse River to environmental factors such as water depth, soil water content and sediment pollution level. These plants are sweet flag (Acorus tatarinowii), reed (Phragmites communis), Vallisneria spiralis, Hydrilla verticillata and Potamogeton crispus. The major restrict factors in the growth of these wetland plant were revealed. We discussed the wetland plants degradation mechanism on the basis of experiment. A few technologies on restoration and reconstruction of wetland vegetation were proposed. We constructed the artificial wetland using these techniques. Study of the suspended sediment removing and contaminant decontamination of artificial wetland was also conducted. The results were as follows:(1) Germination ratio and biomss are sensitive parameters on water depth at the growth of sweet flag. Different water depths had different effects on germination and seedlings growth of Sweet Flag. Germination ratio and average seedling height in complete flooding condition were just one third of those in water depth of 20cm condition. The optimum water depth is 40cm at the process of sweet flag, and when water depth is 141.8cm, sweet flag cannot live. Height and width of seedlings leaves, leaf area and diameter of rhizome were reduced while quantity of leaf and leaf water content increased with increase of water depth. Biomass of root, rhizome and leaf and total biomass of every treatment were reduced in different measures compared with water depth of 20cm on the 27th, 54th and 86th days. As time passes by, biomass varies under different water depths. Biomass of rhizome increased most, leaf lay the second place and root increased least under different water depths. The cell membrane lipid peroxidation and permeability of the seedlings leaves increased in the adversity of water depth from 100 to 120cm. Chlorophyll a, chlorophyll b and carotenoid of seedlings leaves reduced with increase of water depth. As water depth increased, Fv/Fm and qP decreased. Under the condition of long-term (54～58d) complete flooding (100～120cm), PSII of the seedlings had been significantly affected. ETR was affected. The portion of light energy absorbed by antenna pigment which was used for actinic chemistry electron transfer decreased. Electron taken part in CO₂ fixation decreased. qN increased in different measures on the 54th and 86th days. PSII of Sweet Flag leaf didn't be destroyed. The water depth of reed germination cannot be above 20cm. The water depth cannot be above 80cm at the process of reed seedlings growth.(2) Water content had significant effects on germination and seedlings growth of Sweet Flag and weed. The germination of Sweet Flag and weed were inhibited when soil water content was under 30 % VOL. Germination ratio and average seedlings height under continuous drought condition were just one third of that under normal growth condition; seedling height, leaf width, rhizome diameter, leaf number and leaf area were reduced with the decreasing soil water content, but no obvious difference of leaf water content was observed; In comparison with CK, the biomass of root, rhizome and leaf and total biomass of every treatment reduced to different extent on the 20^th, 40^th and 60^th days. As time passes by, the biomass differences among the soils with different water contents were increased. Ratio of biomass among leaf, rhizome and root was 1: 1.59: 0.82 on average, indicating that biomass increase of rhizome is the largest, while that of root is the least.; Chl a, chl b and carotenoid of seedlings leaf were reduced, but chlorophyll a/chlorophyll b ratio increased with decrease of soil water content; Fv/Fm and qP decreased with the increase of soil water content. Severe drought (soil water content under 10% VOL.) had obvious effects not only on Fm but also on qN which decreased to different extent on day 45 and 60, indicating that the photosystem apparatus—PSII was destroyed to different degrees. Furthermore, drought stress had dramatic effects on light curve of Sweet Flag and led to decreasing of maximum ETR.(3) V. spiralis can grow regularly in clean water under every water depth (60～170 cms). The maximal average height of V. spiralis growth was at the water depth of 130¹40cm. The chlorophyll content increased and then decreased with water depth increased. The maximal chlorophyll-a contents of V. spiralis was at the water depth of 150cm. The average height of V. spiralis growing at turbidity water (turbidity: 38.4NTU; transparency:35cm) decreased with increasing of water depth. At the 60d, the V. spiralis growing at the water depth of 150～170cm are all dead. The V. spiralis chlorophyll contents in turbidity water are higher than clean water body. The chlorophyll contents increased with water and light intensity decreased. PSII of the V. spiralis had been significantly affected in turbid water. At water depth of 120～170cm, the portion of light energy absorbed by antenna pigment which was used for actinic chemistry electron transfer decreased. Electron taken part in CO₂ fixation decreased. qN decreased in different measures. PSII of V. spiralis leaf were destroyed to varying degrees.(4) H. verticillata can grow regularly in the clean water body under every water depth condition (60～170 cms). The average height and chlorophyll contents increased with water depth. At the 60d, the H. verticillata growing at the water depth of 120～170cm are dead. The maximal chlorophyll-a contents of H. verticillata was at the water depth of 100～110cm. The H. verticillata chlorophyll contents in turbid water are lower than clean water, and they decreased as water depth increassed.(5) P. crispus can grow regularly in clean water under every water depth condition (50～160 cms). The average height of P. crispus increase as water depth increase. The average height and growth rate are related to water depths. The leave number and biomass are related to water depth: Y_{leave number} =10.805Ln(x)-18.674,Y_biomass= 0.1885e^0.0245x.(6) The TOC 0.35% of deposit fit to the growth of Vallisneria spiralis, Hydrilla verticillata and Myriophyllum spicatum. The TOC 0.66% of deposit affectd the growth of three plants. The effect is mainly to restrain plant height and the growth rate, but the effect is not seen at plant survival. Sediment deposition delay the germinating time of Potamogeton crispus. The delay time increased with the increase of sediment deposition thickness. The length, width and area of leave decreased with the increase of sediment deposition thickness.(7) A serial connected system of emerging plants, floating-leaved plants and submerged plants based on spatial distribution of natural wayer body were constructed by the aquatic marcrophytes, such as Cyperus alternifolius, Acorus tatarinowii, Trapa japonica, Ceratophyllum demersum, Hydrilla verticillata and Vallisneria spiralis. Sandy water flow across emerging plants, floating-leaved plants and submerged plants in order. The removal rates of SS were 73.68%. The aquatic marcrophytes not only removed the SS but also greatly improved the transparency of the water. The removal rates of TN and TP are 34.8% and 25.0%.(8) The out door demonstration research region of emerging plants, floating-leaved plants and submerged plants based on spatial distribution of natural layer body was constructed and the area was 2.66hm². We simulate the law of the tide of the Yangtse River: transfer 4320m3 water of the Yangtse River flow into the experiment region every day. The experiment lasted 100 hours. The input water quantity was 18000m³. The average hydraulic loading was 0.4775m/d. The wetland plants play an important role in improving and keeping the water transparency. Although there is intense disturbances in surroundings, water transparency will improve quickly as long as it doesn't endanger the survival of the wetland plants. The wetland plants are able to purify the N, P of the Yangtse River water. The removal rates of TN and TP are 57.48% and 36.97%. The wetland plants can decrease the SS content and increase the SS deposition. The removal rates of SS were 75%.The results of the demonstration research prove the effects of the concatenated wetland system which is made up of emerging plants, floating-leaved plants and submerged plants on suspended sediment interception. Thus it is practical to the silt control of the Yangtse River and the improvement of water quality. It is one of the best measures in the silt control of the Yangtse River and improvement of water quality.