How do biogeochemical cycles move nitrogen, phosphorus, and carbon through inland waters?

In inland water ecosystems, biogeochemical cycles facilitate the continuous movement of essential elements like nitrogen, phosphorus, and carbon between abiotic (nonliving) and biotic (living) components. These cycles are fundamental to ecosystem function, ensuring that nutrients are recycled to support biological productivity.123

Mechanisms of Nutrient Movement

• Carbon: As a gaseous cycle, carbon moves rapidly through the ecosystem. It is present as dissolved carbon dioxide in the water column, where it is taken up by primary producers (algae and macrophytes) during photosynthesis to form organic biomass. It is returned to the environment through the respiration of organisms and the decomposition of organic matter by bacteria, fungi, and other decomposers.123
• Phosphorus: Unlike carbon, phosphorus is a sedimentary nutrient and lacks a volatile gaseous state. It enters inland waters primarily through the weathering of rocks and runoff from the surrounding catchment. Once in the water, it is utilized by plants and algae, passed through the food chain to consumers, and returned to the water or sediments upon the death and decay of organisms. In streams, phosphorus may undergo "nutrient spiraling," where it is cycled while being transported downstream.453
• Nitrogen: Nitrogen also follows a gaseous cycle. It exists in inland waters in forms such as nitrates, which are essential plant nutrients. Like other elements, it is assimilated by biota and released back into the environment through decomposition.123

Ecosystem Impact

The availability of these nutrients, particularly phosphorus and nitrogen, is a primary determinant of biological productivity. Excessive input of these nutrients—often from agricultural or urban runoff—can lead to eutrophication, causing explosive growth of algae that may deplete oxygen and harm aquatic life.264