Lecture #5 Biogeochemical Cycles

Unit 1: Ecology

Biogeochemical Cycles

A biogeochemical cycle is the cyclic movement of a substance (for example, water, carbon, nitrogen, or phosphate) through the biotic (living) and abiotic (non-living) environments.

Biogeochemical cycles are a key component of ecosystems ecology.

Nature reuseseverything. All ofthe matterthat cycles throughliving organisms

areimportant inmaintaining thehealth of theecosystem.

–Biogeochemical cycles of matter involve biological processes, geological processes, and chemical processes.

– As matter moves through these cycles, it is never created or destroyed—just changed.

* In almost all biochemical cycles, there is much less of the substance in the living reservoir than the nonliving reservoir.

 

We’re in the Driver’s Seat - Human Activities greatly impact Many

Biogeochemical Cycles

1. The Water (hydrologic) Cycle1. The Water (hydrologic) Cycle

Plants absorb water from the soilWater may percolate down through

the soil and eventually collect in pools (groundwater)

Transpiration (release of water through leaves due to the sun) and respiration return water to the atmosphere

Precipitation (rain, snow, etc) returns water to the soil

Plants absorb water from the soilWater may percolate down through

the soil and eventually collect in pools (groundwater)

Transpiration (release of water through leaves due to the sun) and respiration return water to the atmosphere

Precipitation (rain, snow, etc) returns water to the soil

The Water Cycle

Only about 40% of precipitation on land comes from water evaporated over oceans; roughly 60% comes from transpiration of water through plants.

Freshwater Is a Precious and Often Scarce Resource

The Percentage of Available Global Freshwater is Very Small

Human Impact on the Water Cycle

• Withdraw large quantities of fresh water – water diversion, groundwater depletion, wetland drainage

• Clearing vegetation from land– Increases runoff, reduces infiltration,

increases flooding, increases soil erosion

• Modify water quality-adding nutrients (phosphates, nitrates)

2. The Carbon Cycle2. The Carbon Cycle

• Carbon is fixed by plants Carbon is fixed by plants – 6 CCO2 + 6 H2O CC6H12O6 + 6 O2

• Carbon is given off by consumersCarbon is given off by consumers– CC6H12O6 + 6 O2 6 CCO2 + 6 H2O

• Organisms containing carbon form fossil Organisms containing carbon form fossil fuelsfuels

• Burning fossil fuels releases carbonBurning fossil fuels releases carbon– 2 CC8H18 + 25 O2 16 CCO2 + 18 H2O

• Carbon is fixed by plants Carbon is fixed by plants – 6 CCO2 + 6 H2O CC6H12O6 + 6 O2

• Carbon is given off by consumersCarbon is given off by consumers– CC6H12O6 + 6 O2 6 CCO2 + 6 H2O

• Organisms containing carbon form fossil Organisms containing carbon form fossil fuelsfuels

• Burning fossil fuels releases carbonBurning fossil fuels releases carbon– 2 CC8H18 + 25 O2 16 CCO2 + 18 H2O

Photosynthesis and Cell Respiration cycle carbon and oxygen through the environment

The Carbon Cycle

Carbon Cycle

Human Impact on the Carbon Cycle

• Burning of fossil fuels & biomass (wood) generates huge amounts of carbon dioxide that cannot be taken up fast enough by the carbon sinks (oceans, forests).

• This excess carbon dioxide contributes to global warming, which may lead to loss of biodiversity globally, rising sea levels, more violent storms, and changes in precipitation patterns.

    

Human Impact on Carbon Cycle

• Removal of vegetation – decreases primary production (decreases carbon fixation) and subsequently, biodiversity

3. The Nitrogen cycle

Atmospheric nitrogen (N2) makes up nearly 78%-80% of air.

Organisms cannot use it in that form.

Lightning and some species of bacteria convert nitrogen into usable forms.

Nitrogen-fixing bacteria-

Bacteria that live in a symbiotic relationship with plants of the legume family (e.g., soybeans, clover, peanuts).

Nitrogen fixation-convert atmospheric nitrogen (N2) into ammonium (NH4

+) which can be used to make organic compounds like amino acids.

N2 NH4+

Only in certain types of bacteria and industrial technologies can fix nitrogen.

Ammonia is further changed by othertypes of soil bacteria (nitrification)into nitrate, which is taken up byplants and passed on to animals asthey consume the plants.

Eventually this is returned to thenonliving reservoir when the

organismdies and decays.

The Nitrogen Cycle

Humans Play a Major Role in the Nitrogen Cycle

Aerial fertilization (with nitrogen) of sugar beets.

Human Impact on the Nitrogen Cycle

• Use of synthetic nitrogen fertilizers may stimulate algal blooms (due to agricultural runoff), which depletes oxygen and decreases biodiversity.

A ‘dead zone’ forms seasonally near the area where the Mississippi river dumps into the Gulf of Mexico.

Virtually all marine life is killed due to the lack of oxygen available.

VIDEO CLIP ON THE DEAD ZONE

http://oceantoday.noaa.gov/happnowdeadzone/

Human impact on the Nitrogen Cycle Continued…. • Land management: Nitrogen-fixing

crops (legumes) add more useable nitrogen to the soil. (Example of crop rotation: corn, soybeans, corn, soybeans)

–On the other hand, overplanting of crops depletes nitrogen from soil.

Human Impact on the Nitrogen Cycle Cont.

• Burning fossil fuels- forms nitrogen dioxide (NO2) in atmosphere, which can react with water to form nitric acid (HNO3) & causes acid rain

The Phosphorous Cycle

Phosphorus - usually found in soil androcks in the form of calcium phosphate.  • Calcium phosphate dissolves in water

and forms phosphate ions. We can’t use this inorganic form of phosphorous.

** Phosphorous is an important component of DNA, bones and teeth

• Plants take up inorganic phosphate via their roots. It is then used to build organic phosphate .

• Consumers get organic phosphate

from plants.

• Decomposers return phosphate to soil

• Phosphate leaches into water supply–May form new phosphate containing rock

How is this cycle unique from the others?

Answer: There is NO atmospheric phase

in the phosphorous cycle!

Phosphorous Cycle

Human Impact on the Phosphorous Cycle

• Mining of large quantities of phosphate rock-used for organic fertilizers and detergents

• Runoff of wastes and fertilizers causes accumulation in lakes and ponds killing aquatic organisms

– leads to excessive algal growth, depletion of oxygen, & decrease in biodiversity; eutrophication ("over nourishment")

Take 2 minutes to summarize how matter cycles through the biosphere, how human activity impacts these cycles and the effect these impacts have on global biodiversity.