| Water hyacinth (Eichhornia crassipes (Mart.) Solms.) , which originated from South America and was first introduced into China in 1900's, has become one of the most invasive aquatic weeds in the world. It is now widely spreading in many Chinese provinces, like Fujian, Guangdong, Yunnan, Jiangsu, Zhejiang and Henan. Water hyacinth growes mainly in rivers, lakes and ponds to form a monotonous dominant population, which suppressed the growth of other aquatic plants and has caused serious social, economic and environmental losses with its fast extending distribution and development. In places infested with the weed, waterways are often blocked and thus water transportation for industry and tourism affected. At present, mechanical control (e.g. hand-pulling and use of draglines), chemical control, and biological control (introducing natural enemies, pathogens and plant allelopathy) have been used to control water hyacinth in most countries affected by the infestation of the weed. However, these control measures have each their own disadvantages or setbacks to put them into practice. To develop a more sustainable and effective control strategy of water hyacinth, further research will be needed on both the methods now available and the methods with potentials. There is no report about controlling water hyacinth using ecological measures and exploiting the relationship between water hyacinth and its environment in China. Therefore, this paper mainly analysed the relationship between the predominant water quality, environmental factors, and the growth status of water hyacinth. The effects of different nutrient levels, such as, N, P and pH, on water hyacinth were measured, thus providing a solid and scientific base for developing an integrated control system of water hyacinth in Fujian Province.The results were as follows:1. Distribution and severe damage of water hyacinth in FujianAcross the Fujian province, water hyacinth had caused severe damage in Nanping, Fuzhou and Zhangzhou. It's also widely distributed along the Min River and Wu Long River. Water hyacinth mainly grows in ponds, lakes and in some inland rivers that inhibited the aquiculture life and the function of waterpower station to a certain extent in Sanming, Longyan , Quanzhou and Putian. There was also a slight damage caused by the infestation of water hyacinth in Ningde and Xiamen.2. Relationship between water quality and growth status of water hyacinth Research of the relationship showed that in places infested with the weed, water quality was lower due to higher total nitrogen and total phosphorus as well as lower dissolved oxygen. Eutrophication of water provided superior and ideal condition for the growth of water hyacinth. All of these surveys indicated that water hyacinth growed well with a higher total nitrogen and phosphorus under different water qualities in Fujian province. Nitrogen was the most important factors that restricted the development of water hyacinth. The weed was not so sensitive to phosphorus. Otherwise, the total phosphorus greatly influenced the number of stolons and petioles. Total nitrogen played a significant part in the upward growth of water hyacinth.3. Effects of three kinds of water quality on the growth status of water hyacinth: In the solution, concentration of total nitrogen in treatment Md (Total N: 13.8 mg·L-1, Total P: 0.614 mg·L-1) was much higher than that of the CK (Total N: 1.17 mg·L-1, Total P: 0.014 mg·L-1) and Ro (Total N: 0.156 mg·L-1, Total P: <0.005 mg·L-1), but total phosphorus was only lowered by 0.1 mg.L-1 in each of the three treatments. After 60 days, the growth was inhibited under treatment Ro without nitrogen and phosphorus. The measured biomass of water hyacinth also had slow development under the same condition. The difference between Ro and Md (cultured with nitrogen and without phosphorus) reached the highest level after 60 days of treatment. The result indicated that nitrogen concentration was the most important factor in limiting the growth of water hyacinth, while it acquired little growth from the phosphorus.4. The impact of the water hyacinth growth and development for different water nutritional conditions (1) Growth characteristics The growth performance of water hyacinth was the best in the water of which the N concentration was in the range of 25-30 mg.L-1, P concentration was in the range of 5.7～7 mg.L-1 or the pH was in the range 7～9. The growth of water hyacinth was subject to varying degrees of restrictions if the related index of water were higher or lower than this range.(2) BiomassThe biomass of water hyacinth increased the most in the water in which the N concentration was 30 mg.L-1, P was 6.33 mg.L-1, or the pH was in7～9. The increase of the biomass was subject to varying degrees of restrictions if the related index of water were higher or lower than this range.(3) Chlorophyll contentThe chlorophyll content had different levels of drop in the nutrition conditions, in which, the chlorophyll content dropped when the N or P had a high concentration and was processed higher than when the N or P was processed in low concentration. The decreased value of water hyacinth chlorophyll content was low in the water whose N was in the range of 20～30 mg.L-1, or the P was in the range of 4～5 mg.L-1, the decreasing speed of treated dissolved oxygen concentration where the pH was 3 and 5 was faster than the others. The decreased value of water hyacinth chlorophyll content was low in the water where pH was in the range of 7～9.(4) Coverage rateD-value of the coverage, before and after the experiment reached the maximum in the water where N was 25 mg.L-1, P 7 mg.L-1 or the pH 7.(5) Dissolved oxygen concentrationAt the time of that the different nutritional conditions changed the growth and development of water hyacinth, the growth of water hyacinth had resulted in the drop of the concentration of dissolved oxygen. The decreasing range of dissolved oxygen concentration in high nitrogen concentration with N6 (30 mg.L-1) and N7 (35 mg.L-1) were faster than that in N1(5 mg.L-1) and N2(10 mg.L-1). It also showed that in treatments P2 (5 mg.L-1) and P5 (8 mg.L-1), with a pH 3 and 5 respectively, the decreasing range of dissolved oxygen concentration was little faster than other relative treatments.
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