Which method can be used to reduce light penetration in ponds to control submerged aquatic plants?

Using pond dyes is an effective method for reducing light penetration in ponds, which can help control submerged aquatic plants. Pond dyes work by imparting color to the water, often blue or black, which limits the amount of sunlight that can penetrate to the lower layers of the water column. This reduction in light can inhibit photosynthesis for submerged plants, ultimately reducing their growth and spread.

In contrast to the other methods mentioned, pond dyes specifically target the light availability aspect of aquatic plant growth. While water aeration can improve water quality by increasing oxygen levels and promoting beneficial microbial activity, it does not directly address light penetration issues. Increased fish stocking, while it can help in managing vegetation through herbivory, may not significantly affect light levels as fish do not block light. Herbicide applications are intended for direct management of aquatic plants but do not necessarily reduce light penetration as effectively or as long-term as the application of dyes can.