Biogeochemical Cycles

Biogeochemical Cycles Chapter 3.5-3.6 AP Environmental Science

Overview • What is nutrient cycling? • Hydrological Cycle • Carbon Cycle • Nitrogen Cycle • Phosphorous Cycle • Sulfur Cycle

Nutrient Cycling • Driven directly or indirectly by solar energy and gravity. • Nutrients can accumulate in “resiviors” at different points along a nutrient cycle. • Nutrients on Earth and finite and must be continually recycled

Hydrological Cycle • Natural renewal of water • 90% atmospheric water comes from transpiration • 0.024% of Earth’s water is usable

Human Impacts • Withdrawal of large amounts of water from natural systems, sometimes higher than replacement rates • Clearing of vegetation around water sources • Decreased transpiration • Increased runoff • Increased flooding

Carbon Cycle • Based on atmospheric carbon dioxide • 0.038% of Earth’s atmosphere is CO2 • Photosynthesis and aerobic respiration play a very important role in this cycle

Human Impacts • Increasing amounts of carbon dioxide leads to increased greenhouse gases • Clear cutting of forests reduces CO2 absorption • Warming ocean waters can solubulize less CO2 • Fossil fuels are “out” of the cycle and we add them back into it

Nitrogen Cycle • Major reservoir is the atmosphere • N2 cannot be used by most organisms • Nitrification – bacteria convert N2 into NH3 • Denitrification – bacteria convert NH3 and NH3+ back in N2

Human Impacts • Nitric oxide (NO) is converted to nitric acid (HNO3) • Nitrous oxide (N2O) is a greenhouse gas • Release of nitrogen faster than normal through habitat destruction • Excess nitrates in the environment from runoff and sewage • Nitrogen removal from crap growing

Phosphorous Cycle • Does not have an atmospheric component • Based around phosphate (PO4-3) • Phosphate can leave the cycle for a long time once it enters the ocean and settles

Human Impacts • Phosphate is a major limiting factor in plant growth • We release lots of phosphate into the environment due to fertilizers and sewage runoff

Sulfur Cycle • Focuses on sulfates (SO4-2) and H2S • Sources include volcanoes, dust storms, sea spray, and bacteria byproducts • Some bacteria can use sulfur to power their metabolic activities

Human Impacts • Excess sulfur in the atmosphere can lead to sulfuric acid rain • Mining and extraction from the Earth input’s a large amount of sulfur into the cycle • Burning sulfur laced coal leads to acid rain

Methods for studying ecology • Study science directly • Study ecosystems in the laboratory • Use models to simulate ecosystems

Biogeochemical Cycles