In aquatic ecosystems, how is carbon primarily inputted?

In aquatic ecosystems, carbon primarily enters through the process of photosynthesis. In this context, aquatic plants, including phytoplankton, algae, and submerged macrophytes, use sunlight to convert carbon dioxide (CO2) dissolved in the water into organic matter, primarily sugars. This process not only generates energy for the plants themselves but also forms the basis of the food web, feeding herbivores and subsequently higher trophic levels.

Photosynthesis serves as a critical mechanism by which carbon is captured from the atmosphere (via diffusion into the water) and transformed into organic compounds, contributing to the carbon cycle. This input of carbon supports the growth and productivity of aquatic ecosystems, thereby influencing the overall health and functioning of these environments.

While fertilizer runoff, decomposition, and groundwater filtration can also contribute to carbon dynamics in aquatic environments, they do not primarily serve as the main input of carbon. Fertilizer runoff can lead to nutrient loading and algal blooms, decomposition releases carbon back into the water, and groundwater filtration can alter water chemistry, but these processes are secondary in importance to the direct fixation of carbon through photosynthesis.