Which component is NOT involved in the output of carbon in aquatic ecosystems?

In aquatic ecosystems, output of carbon typically occurs through several processes, including decomposition, diffusion, and respiration. Decomposition involves the breakdown of organic matter, releasing carbon back into the environment. Respiration by aquatic organisms also returns carbon dioxide to the water and atmosphere, as organisms convert organic substances into energy, producing carbon dioxide as a byproduct.

Diffusion plays a crucial role in the movement of carbon dioxide into and out of water bodies. It allows carbon dioxide, dissolved in water, to move to the atmosphere and vice versa, contributing to the overall carbon cycle.

Photosynthesis, while it uses carbon dioxide to produce oxygen and organic compounds, represents a carbon input into the ecosystem rather than an output. During photosynthesis, aquatic plants and phytoplankton convert carbon dioxide into organic matter using sunlight, effectively sequestering carbon rather than releasing it.

Therefore, the process of photosynthesis is not involved in the output of carbon in aquatic ecosystems, making it the correct answer in this context.