Biogeochemical Cycles Nutrients exist in pools of chemical elements - 3 main compartments where these nutrients exist are: 1) atmosphere - carbon in carbon dioxide, nitrogen in atmospheric nitrogen 2) lithosphere - the rocks - phosphates, calcium in calcium carbonate, potassium in feldspar 3) hydrosphere - the water of oceans, lakes, streams and soil - nitrogen in dissolved nitrate, carbon in carbonic acid
Atmosphere LithosphereHydrosphere Living Organisms
Nutrients are input to ecosystems via: 1) from atmosphere - direct uptake such as carbon dioxide (photosynthesis) and nitrogen (taken up and fixed by bacteria and blue-green algae); Wetfall (rain, snow, fog) carrying the nutrients and washing them out of the atmosphere; Dryfall - particles directly settle out of the air; 2) from lithosphere - from weathering of rocks - some due to mechanical weathering by freezing and thawing and erosion, most due to chemical weathering by water running over the rocks; 3) from hydrosphere - streamflow carries nutrients into new areas
Living Organisms and Nutrient Cycles Living organisms are a compartment in which carbon exists in carbohydrates (mainly cellulose) and fats, nitrogen in protein, and phosphorus in ATP
Nutrient Fluxes For some nutrients in some ecosystems, nutrient fluxes may be in balance so that inputs = outputs But for other ecosystems and nutrients, the cycle may be out of balance from too much input so that input > output storage or too much output output > input loss
General Scheme for Biogeochemical Cycles Consumers Producers Nutrients available to producers Abiotic reservoir Geologic processes Decomposers
Evaporation determines the flux of water through the cycle because it is in evaporation that energy is input The atmosphere holds about 2.5 cm of water spread evenly over the earth's surface at any one time 65 cm of rain falls across the earth each year - water cycles through atmosphere 25 times a year, each transit takes about 2 weeks Most of the evaporation on land is due to losses by plants during respiration - 55 x 10 18 g while total for land is 59 x 10 18
Some Carbon Cycle Numbers World's terrestrial biota respires about 120 x 10 9 metric tonnes of carbon per year Human activities release about 5.1 to 5.9 x 10 9 metric tonnes per year The observed increase in atmospheric CO 2 is due to about 2.9 x 10 9 tonnes per year - which is 39 - 57% of human input The rest is probably dissolved in the oceans though some is absorbed by terrestrial plants and put into extra biomass. 1750 atmospheric CO 2 was 280 ppm, 400 ppm in May 2013 Current estimate is that by 2050 atmospheric CO 2 will reach 660 ppm
Increase in Atmospheric CO 2 and Global Temperature
Nitrogen Cycle To become a part of an organism, nitrogen must first be fixed or combined with oxygen or hydrogen. Nitrogen cycle is mainly an atmospheric cycle – Nitrogen fixation mainly occurs by atmospheric N being fixed by microbes in soil; 3 - 4% of annual influx is fixed by lightning and brought to earth by wetfall. When plants and animals eventually die, their nitrogen compounds are broken down giving ammonia (ammonification). Some of the ammonia is taken up by the plants; some is dissolved in water or held in the soil where bacteria convert it to nitrates (nitrification). It may also be converted to free nitrogen (denitrification) and returned to the atmosphere – especially in low oxygen environments.
The global Phosphorus budget: Pools of available phosphorus, in 10 12 grams P Sediment 4 x10 9 Soils 200,000 Sea 90,000 Mineable rock 10,000 Terrestrial 3,000 Fluxes (x10 12 g P/yr) Terrestrial cycle 60 Mining extraction 12 Transport airborne dust 1 Transport rivers 21 Marine cycle 1000 Burial 2
Cultural Eutrophication Eutrophication means well fed and in natural situation is okay Cultural eutrophication – human sources introduce nutrients, especially phosphorus or nitrogen, to a body of water leading to very high concentrations of the nutrient causing increased growth of algae.
Eutrophication Timeline Late 1800’s – Seattle starts to grow to city size – raw sewage dumped into Lake Washington 1926 – Seattle builds sewage treatment plant – sewage sent to Puget Sound 1940’s – area grows – suburbs build 10 treatment plants that dump treated sewage in Lake Washington between 1941-1954 1955 – Oscillatoria found growing in lake Action taken to clean lake – 1963 sewage diverted to Puget Sound, 1964 water quality improves, 1968 no sewage dumped into lake; 1975 – back to pre-pollution state
Lake Washington – Reduction in Phosphorus followed by reduction in growth of cyanobacteria measured as amount of chlorophyll in the water