What is copper primarily used for in aquatic systems?

Copper is primarily used for the control of algae in aquatic systems. It acts as an algaecide, helping to manage and reduce the growth of unwanted algal blooms, which can deplete oxygen levels in the water and harm aquatic life. The effectiveness of copper in controlling algae is due to its ability to disrupt cellular processes within the algae, leading to cell death and a reduction in population.

In aquatic environments, excessive algae can lead to issues such as eutrophication, which causes water quality to deteriorate and can result in the death of fish and other aquatic organisms. By applying copper in a controlled manner, aquatic managers can help maintain a balanced ecosystem, promote healthier water conditions, and prevent the adverse effects associated with algae overgrowth.

The other options do not reflect the primary use of copper. For instance, while there's a relationship between certain nutrients and fish growth, copper isn't a fertilizer for weeds or a direct enhancer of fish growth. Similarly, copper doesn’t directly work to increase water clarity, although controlling algae can indirectly improve clarity by reducing algal populations that contribute to murkiness.