What is one of the main disadvantages of using bottom covers in aquatic weed control?

Using bottom covers in aquatic weed control has a significant disadvantage as they can float to the surface due to gas accumulation. When organic matter decomposes beneath the covers, it can produce gases like methane and carbon dioxide. This buildup can create enough buoyancy to lift the covers, leading to their ineffective placement and the potential for uncontrolled weed growth above the surface. The floatation can also disrupt the intended ecological balance and require additional management efforts to maintain control over the aquatic environment.

In contrast, although other choices might seem appealing at first glance, they do not represent inherent disadvantages of using bottom covers. For instance, being inexpensive, easy to install, or even suggesting enhanced plant growth generally points to benefits rather than drawbacks in the context of aquatic weed management. Therefore, the correct answer highlights a critical limitation that affects the efficacy of bottom covers as a control strategy.