What are the harms of water hyacinth? A detailed guide to integrated control methods

Scientific name of water hyacinth: Eichhornia crassipes, also called water lettuce. The stems and leaves of water hyacinth hang above the water, and the tillering branches creep along the water surface. The flowers are multi-angled and trumpet-shaped, with bright and beautiful colors. The leaves are emerald green and rather dark. The leaf margins are entire, smooth and textured. The fibrous roots are well developed, tillering and reproduction are fast, and management is extensive. It is a good plant for beautifying the environment and purifying water quality. In areas suitable for its growth, it often spreads excessively, seizes the water surface, affects shipping, suffocates fish, and harms health; it is difficult to destroy and difficult to eradicate at the root. It is an organism with two sides, and is not suitable for large-scale planting.

Water hyacinth greatly likes fertilizer, especially nitrogen fertilizer. When the nutrient content of the water layer is high, the plants are tall, the root system is relatively short, there are few flowers, and reproduction is fast with high yield; when nutrients are low, the plants are small, the root system is long, the leaf color is yellow, the inflated petiole is purple, it tends to flower, and the yield is relatively low. Water hyacinth likes warmth and can grow within the range of 0 to 40 °C. It begins to reproduce above 13 °C, growth accelerates above 20 °C, grows fastest at 25 to 32 °C, slows above 35 °C, and gradually dies above 43 °C.

The root system of water hyacinth has strong absorption capacity and can enrich nutrients in water. Fresh grass contains 0.24% nitrogen, 0.07% phosphoric acid, 0.11% potassium oxide, 1.2% crude protein, 0.2% crude fat, 1.1% crude fiber, 2.3% nitrogen-free extract, 1.3% ash, and water accounts for 93.90%. Besides being used as pig feed and for making compost, because it is sensitive to arsenic, it can also be used as an indicator plant for monitoring the degree of arsenic pollution in water bodies. When the water body contains 0.06 ppm arsenic, water-soaked chlorotic spots appear at the leaf tips, then the lesions expand, and the leaves lose water, turn yellow, and curl over. Because it has the function of enriching heavy metals such as zinc, lead, mercury, nickel, and cadmium in water and removing suspended matter from water bodies, it can be used to purify domestic sewage and industrial wastewater, but the secondary pollution caused by the decay of plant residues must be properly addressed. It can also be used as an ornamental plant. But when it grows too vigorously, it often blocks river channels and becomes a harmful weed.

The harms of water hyacinth and integrated control

Water hyacinth is also called water lettuce, Eichhornia crassipes, water lotus, and so on. It is a perennial aquatic weed, usually floating freely on the water surface. The leaves are clustered, and the petioles form a sponge-like inflated body. It has both sexual and asexual reproduction methods, and usually mainly reproduces asexually through stolons. Under suitable conditions, it can reproduce a new plant every 5 days. It can also flower, set seed, and carry out sexual reproduction. The spike inflorescence ranges from light purple to green. One inflorescence produces about 300 seeds, and the seeds fall into the water after maturity. Seeds can survive in water for 5-20 years, and under suitable conditions they germinate and grow along the fluctuation line of the riverbank water surface. The suitable temperature for water hyacinth growth is 28-30 °C. One mu of water surface has about 130,000 water hyacinth plants, with a total weight of 18-25 tons. Fifty years ago, China, which had an extreme shortage of grain, introduced water hyacinth from South America and widely stocked it in rural rivers and ponds in the south as pig feed. In the past 10 years, farmers who have bid farewell to grain shortages no longer salvage water hyacinth. At the same time, industrialization has worsened the water quality of rivers and lakes and increased the degree of eutrophication. As a result, water hyacinth spread rapidly and became a disaster, even "charging" from rural inland rivers and lakes into major rivers. Too much water hyacinth covers the water surface. If not removed in time, it can also hinder drainage and irrigation and block water flow during the flood season. Dense water hyacinth also reduces the ability of light to penetrate the water body, affects the growth of underwater organisms, increases the concentration of carbon dioxide in the water, reduces aquatic product yields, increases water evaporation, and provides suitable breeding places for mosquitoes. Some scholars list it as one of the "world's ten major harmful weeds." At present, the methods for controlling water hyacinth mainly include chemical control, biological control, manual and mechanical salvage, and integrated control. Chemical control methods are simple and rapid in effect. Commonly used herbicides such as paraquat and glyphosate are used for control. However, herbicides are highly destructive to the water body ecosystem, pollute the environment, and cannot remove water hyacinth seeds, so the effect cannot last. Biological control uses the theory of ecological balance between plants and natural enemies, introducing their natural enemies from the place of origin of water hyacinth, establishing populations, and achieving long-term control of water hyacinth. Biological control is environmentally safe, low in cost, and long-lasting in effect, and is valued at home and abroad, but its disadvantage is that it takes effect slowly. From releasing natural enemies to obtaining significant control effects generally takes 3-5 years or even longer. Manual and mechanical control methods use manual or mechanical salvage treatment of water hyacinth and take effect quickly, but when the affected area is large, the labor intensity is high. Like chemical control, manual and mechanical control also makes it difficult to remove seeds in the water, and the control effect cannot last. Integrated control methods use the above control measures in a targeted way, making up for each other's shortcomings, and keep the water hyacinth population at a low level for a long time. Experts believe that if the runaway growth of water hyacinth is to be effectively stopped at present, the key is to purify water quality and eliminate the environment suitable for its growth; at the same time, water hyacinth also has a certain function of purifying water and blocking water. Under suitable conditions, one hectare of water hyacinth can absorb the nitrogen and phosphorus elements discharged by 800 people in one day. Water hyacinth can also remove heavy metal elements such as cadmium, lead, mercury, thallium, silver, cobalt, and strontium from sewage, thereby "turning waste into treasure." According to the principle of seeking benefits and avoiding harms, experts have developed three channels for the comprehensive utilization of water hyacinth: through fermentation and conversion, increase the protein content of water hyacinth to make feed; use the characteristic that water hyacinth contains large amounts of nitrogen, phosphorus, and potassium to make organic and inorganic compound fertilizer; extract nutrients from it and process and refine food, health products, medicines, and feed additives. Using water hyacinth to purify sewage is a simple and feasible method with low cost, energy savings, and relatively high benefits. Experts say that in the future, the model of using water hyacinth to treat sewage will be promoted, making both sewage and water hyacinth valuable resources.