What combination of actions can promote nutrient uptake by littoral macrophytes to improve water quality in eutrophic lakes?

• A. Increasing nutrient inputs
• B. Restoring macrophyte beds and reducing external nutrient inputs
• C. Removing all macrophytes
• D. Increasing light limitation

Answer: (B)

The main idea here is to boost the ability of the littoral zone to take up and store nutrients by macrophytes, while limiting the nutrients coming in from outside. Restoring native macrophyte beds increases the total biomass and surface area for nutrient uptake, so more nitrogen and phosphorus can be removed from the water and sediments. This growth also helps stabilize sediments, which reduces internal recycling of nutrients back into the water, and the plant roots can oxygenate the rhizosphere, supporting processes that trap and immobilize nutrients.

At the same time, reducing external nutrient inputs lowers the overall supply of nutrients entering the lake. With fewer nutrients available, the macrophyte community can more effectively compete for what remains, enabling their uptake to have a stronger positive impact on water quality and clarity. The combination—reestablishing macrophyte beds and cutting external nutrient inputs—creates conditions that maximize nutrient removal by the littoral macrophytes and minimizes ongoing nutrient loading, leading to cleaner water in eutrophic lakes.

Introducing more nutrients, removing macrophytes, or increasing light limitation would not promote this process and would generally worsen water quality.