Nitrogen fixation is the chemical processes by which nitrogen is made available to plants for growth; denitrification is the process by which nitrogen is removed from the water environment and released to the atmosphere. In streams and lakes, nitrogen fixation occurs primarily on macrophytes, which are aquatic plants (above). In wetlands, nitrogen fixation occurs primarily in sediment. In all three habitats, denitrification occurred exclusively in sediments. Understanding these processes better in these areas will help us protect large waterbodies such as lakes and rivers.