How do watersheds play a role in the nitrogen cycle, carbon cycle, and water cycle?

Answer 1

Wetlands play a critical role in regulating the movement of water within watersheds as well as in the global water cycle Wetlands, by definition, are characterized by water saturation in the root zone, at, or above the soil surface, for a certain amount of time during the year. This fluctuation of the water table (hydroperiod) above the soil surface is unique to each wetland type.

Nitrogen- The biological and chemical process of nitrification/denitrification in the nitrogen cycle transforms the majority of nitrogen entering wetlands, causing between 70% and 90% to be removed aerobic substrates, organic nitrogen may mineralize to ammonium, which plants and microbes can utilize, adsorb to negatively charged particles (e.g., clay), or diffuse to the surface. As ammonia diffuses to the surface, the bacteria Nitrosomonas can oxidize it to nitrite. The bacteria Nitrobacter oxidizes nitrite to nitrate. This process is called nitrification. Plants or microorganisms can assimilate nitrate, or anaerobic bacteria may reduce nitrate (denitrification) to gaseous nitrogen (N2) when nitrate diffuses into anoxic (oxygen depleted) water. The gaseous nitrogen volatilizes and the nitrogen is eliminated as a water pollutant. Thus, the alternating reduced and oxidized conditions of wetlands complete the needs of the nitrogen cycle and maximize denitrification rates

Carbon- Wetlands store carbon within peat and soil. Storing carbon is an important function within the carbon cycle, particularly given observations of increasing levels of carbon dioxide in the atmosphere and concerns about global warming. When wetlands are drained, the oxidizing conditions increase organic matter decomposition, thus increasing the release of carbon dioxide. When wetlands are preserved or restored, the wetlands act as a sink for carbon since organic matter decomposition is stable or slowed.

watersheds also play an important role in the water cycle. The water cycle is the flow of water through rain, groundwater (water underground), rivers and oceans (and other bodies of water), and through evaporation into the atmosphere. Once the evaporated water is in the atmosphere it is collected back into rain again. The cycle constantly repeats itself.

http://www.epa.gov/safewater/kids/flash/flash_watercycle.html
illustration of the water cycle

Answer 2

Are you asking about watersheds or wetlands?
Watersheds define which areas communicate hydrologically both above and below ground. The only impact watersheds have on the C and N cycles is to where and how quickly a drainage basin will transport contaminants and nutrients.

Consider two trees growing 50 meters apart residing in different watersheds. At both locations the climate, soil, sunshine, and insects are identical. The only difference is where the rainwater that drips of the tree's leaves will go.

"watersheds also play an important role in the water cycle"
This is probably the biggest understatement I've ever seen on Yahoo!Answers. LOL