Processes in Carbon Cycling

1. Processes in Carbon Cycling Burning fossil fuels • Carbon cycles between the living (biotic) and non-living (abiotic) environments. • Gaseous carbon is fixed in the process of photosynthesis and returned to the atmosphere in respiration. • Carbon may remain locked up in biotic or abiotic systems for long periods of time, e.g. in the wood of trees or in fossil fuels such as coal or oil. • Humans have disturbed the balance of the carbon cycle through activities such as combustion and deforestation. Petroleum

2. The Carbon Cycle

3. Nitrogen in the Environment • Nitrogen cycles between the biotic and abiotic environments. Bacteria play an important role in this transfer. • Nitrogen-fixing bacteria are able to fix atmospheric nitrogen. • Nitrifying bacteria convert ammonia to nitrite, and nitrite to nitrate. • Denitrifying bacteria return fixed nitrogen to the atmosphere. • Atmospheric fixation also occurs as a result of lightning discharges. • Humans intervene in the nitrogen cycle by producing and applying nitrogen fertilizers.

4. Nitrogen Transformations • The ability of some bacterial species to fix atmospheric nitrogen or convert it between states is important to agriculture. • Nitrogen-fixing species include Rhizobium, which lives in a root symbiosis with leguminous plants. Legumes, such as clover, beans, and peas, are commonly planted as part of crop rotation to restore soil nitrogen. • Nitrifying bacteria include Nitrosomonas and Nitrobacter. These bacteria convert ammonia to forms of nitrogen available to plants. Root nodules in Acacia Nodule close-up NH3NO2- NO3- Nitrosomonas Nitrobacter

5. Nitrogen Cycle

6. Water Transformations • The hydrological (water) cycle, collects, purifies, and distributes the Earth’s water. • Over the oceans, evaporation exceeds precipitation. This results in a net movement of water vapor over the land. • On land,precipitation exceeds evaporation. Some precipitation becomes locked up in snow and ice for varying lengths of time. • Most water forms surface and groundwater systems that flow back to the sea. Precipitation Rivers and streams

7. Precipitation (rain, sleet, hail, snow, fog) Transport overland: net movement of water vapor by wind Surface runoff (rapid) Rain clouds Rivers Water locked up in snow and ice Evaporation from the land Evaporation from inland lakes and rivers Precipitation to land Infiltration: movement of water into soil Precipitation Evaporation Precipitation over the ocean Aquifers: groundwater storage areas Percolation: downward flow of water Evaporation from the ocean Groundwater movement (slow) Transpiration Transpiration from plants The Water Cycle Condensationconversion of gaseous water vapor into liquid water Lakes Ocean storage 97% of total water