Nutrient Cycles in Ecosystems

What are Nutrients? Nutrients are chemicals required for growth and other life processes. Nutrients move through the biosphere in nutrient cycles or exchanges.

Nutrient Cycle AKA Biogeochemical Cycle The flow of a nutrient from the environment to living organisms and back to the environment Main reservoir for the nutrient is in the environment

geochemical cycle Fig. 47-14, p.852 Main nutrient reservoirs in the environment geochemical cycle fraction of nutrient available to ecosystem herbivores, carnivores, parasites primary producers detritivores, decomposers Fig. 47-14, p.852

Three Categories Hydrologic cycle Atmospheric cycles Water Atmospheric cycles Nitrogen and carbon Sedimentary cycles Phosphorus and sulfur

Carbon Cycle Carbon moves through the atmosphere and food webs on its way to and from the ocean, sediments, soil and rocks Sediments and rocks are the main reservoir (AKA carbon stores or sinks)

Carbon in the Oceans Most carbon in the ocean is dissolved carbonate or decaying organic matter. Ocean currents carry dissolved carbon It becomes layers of shells deposited on the ocean floor or carbonate rocks such as limestone

Carbon in Atmosphere Atmospheric carbon is mainly carbon dioxide Carbon dioxide is added to atmosphere cellular respiration, volcanic action, burning fossil fuels Removed by photosynthesis

Human Effects CO2 levels have risen by more than 30% since the start of the Industrial Revolution due to burning of fossil fuels CO2 is a Greenhouse gas which absorbs heat in the atmosphere and contributes to global climate change. Clearing land for agriculture and urban development reduces plants that can absorb and convert CO2.

Clearing Land for Burning Fossil Fuels Urban Expansion Agriculture

Nitrogen Cycle Nitrogen is used in making proteins in the body and DNA Main reservoir is nitrogen gas in the atmosphere

Nitrogen Fixation and Uptake Plants cannot use nitrogen gas Nitrogen-fixing bacteria convert nitrogen gas into ammonium (NH4+) Ammonium can be taken up by some plants

Nitrification and Uptake Nitrifying bacteria convert ammonium to nitrites (NO2–), and then to nitrates (NO3-) which are taken up by plants

Nitrogen Loss Nitrogen is often a limiting factor in ecosystems Nitrogen is lost from soils via leaching and runoff Denitrifying bacteria convert nitrates and nitrites back to nitrogen gas

Human Effects Humans increase rate of nitrogen loss in soil by clearing forests and grasslands Humans increase nitrogen in water by using fertilizers which cause algae blooms (eutrophication) that use up O2 in the water and block sunlight

Human Effects Humans increase nitrogen in the air by burning fossil fuels which leads to acid precipitation. Too much or too little nitrogen can compromise plant health

Phosphorus Cycle Phosphorus is essential for life processes in plants and animals Main reservoir is Earth’s crust; no gaseous phase

Phosphorus Cycle Weathering releases these phosphates from rocks. - chemical weathering, via acid precipitation or lichens - physical weathering, including wind, water and freezing Phosphates are then absorbed by plants, which are then eaten by animals.

Phosphorus Cycle Figure 47-27, Page 862

Human Effects In tropical countries, clearing lands for agriculture may deplete phosphorus-poor soils In developed countries, phosphorus runoff is causing eutrophication of waterways