Bắt nguồn từ thực vật thủy sản kiểm soát với sỏi, cát, hoặc đất sét đã được chủ yếu là không thành công bởi vì hệ thống gốc vẫn còn để sản xuất măng mà thâm nhập bao gồm đất, và bởi vì nhiều loài thực vật thủy sản thiết lập lại thông qua các mảnh vỡ mang đến các trang web được xử lý từ các khu vực hồ khác, hoặc bằng hạt, turions , và thân rễ sống sót trong điều trị. Một lựa chọn khác là tấm tổng hợp và các vật liệu kiểm tra. Hiệu quả. | 1 5 Sediment Covers and Surface Shading for Macrophyte Control INTRODUCTION Rooted aquatic vegetation control with sand gravel or clay has been mostly unsuccessful because root systems remain to produce shoots that penetrate earthen covers and because many aquatic plants reestablish through fragments carried to the treated site from other lake areas or by seeds turions and rhizomes that survive the treatment. Another option is synthetic sheeting and screening materials. Their effectiveness is higher because shoots may be unable to penetrate them but they are expensive application is labor intensive effectiveness is correlated with application techniques and types of material and most materials manufactured for this purpose are not widely available. Some are no longer manufactured. Engel 1982 listed these advantages of sediment covers 1. Their use is confined to specific lake areas. 2. Screens are usually out of sight and thus create no disturbance on shore. 3. They can be installed in places where harvesters or sprayer boats cannot gain access. 4. No toxic substances are released. 5. They usually require no permit or license. 6. They are easy to install over small areas. 7. They can be removed. These are their disadvantages Engel 1982 1. They fail to correct the cause of the problem. 2. They are expensive. 3. They are difficult to apply over large areas or on sites with obstructions. 4. They may slip on steep grades or float to the surface after trapping gases beneath them. 5. They can be difficult to remove or relocate. 6. They may rip during application. 7. Some materials are degraded by sunlight. Reviews include Armour et al. 1979 Cooke 1980 Nichols and Shaw 1983 Perkins 1984 and Newroth and Truelson 1984 . COMPARISON OF SYNTHETIC SEDIMENT COVERS Polyethylene One of the earliest uses of sediment covers was the treatment of 10 ha of Marion Millpond Wisconsin with mm 4 ml impermeable black polyethylene sheeting Born et al. 1973 Peterson .
