Lecture #3 Biogeochemical Cycles

Material Cycles• Hydrologic Cycle - path of water through the environment

– Solar energy continually evaporates water stored in the oceans and land, and distributes water vapor around the globe.

• Condenses over land surfaces, supporting all terrestrial systems

–Responsible for cellular metabolism, nutrient flow in ecosystems, and global distribution of heat and energy

Hydrologic CycleMain Processes:– Evaporation-conversion of water into water vapor– Transpiration-evaporation from leaves– Condensation-conversion of water vapor into droplets

of liquid water– Precipitation-rain, sleet, snow, hail– Infiltration-movement of water into soil– Percolation-downward flow of water through soil and

permeable rock– Runoff-surface flow down slope to ocean

Hydrologic Cycle

Human Impacts on 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)

Types of Nutrients

• Nutrient – Any atom, ion, or molecule an organism needs to

live grow or reproduce– Ex: carbon, oxygen, hydrogen, nitrogen… etc

• Macronutrient – nutrient that organisms need in large amount– Ex: phosphorus, sulfur, calcium, iron … etc

• Micronutrient – nutrient that organism need in small amount– Ex: zinc, sodium, copper… etc

Nutrient Cycles

• Nutrient cycles (= biogeochemical cycles): natural processes that involve the flow of nutrients from the nonliving environment to living organisms & back again.

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Carbon Cycle• Carbon is one of the building blocks of organic molecules-

(carbohydrates, fats, lipids, nucleic acids)-essential to life

• Short Cycle: Photosynthesis & Cell RespirationBegins with intake of CO2 during photosynthesis. Carbon atoms are incorporated into sugar (C6H12O6), and is eventually released by cellular respiration either in the plant or in organisms that consumed it.

• Long Cycle: Sometimes the carbon is not recycled for a long time. Coal and oil are the remains of organisms that lived millions of years ago. The carbon in these is released when we burn them. Some carbon is also locked in calcium carbonate (shells, limestone).

Carbon Cycle

• The parts of the cycle that remove carbon dioxide from the atmosphere (vegetation) are called carbon sinks.

• The parts of the cycle that release carbon dioxide are called carbon sources.

Human Impact on the Carbon Cycle

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

• This excess carbon dioxide contributes to global warming.

Ocean Acidification: http://latimesblogs.latimes.com/greenspace/2010/04/manmade-carbon-dioxide-making-oceans-more-acidic-study-finds.html

• Removal of vegetation – decreases primary production (decreases carbon fixation)

Carbon Cycle

Nitrogen Cycle• Nitrogen is needed to make essential organic molecules

including proteins and nucleic acids such as DNA .

• Nitrogen is the most abundant element in the atmosphere, however the nitrogen must be “fixed” so plants can use it.

• Plants take up inorganic nitrogen from the environment and build protein molecules which are later eaten by consumers.

• Members of the bean family (legumes) have nitrogen-fixing bacteria living in their root tissue. Blue green algae can also fix nitrogen.

Major processes of the Nitrogen CycleNitrogen Fixation (2 parts) 1)Ammonification: Nitrogen-fixing bacteria (or lightning)

change nitrogen to a more useful form by combining it with hydrogen to make ammonia

2) Nitrification: Other bacteria convert ammonia NH4+ to nitrites and nitrates NO3- which can be taken up by plants to make proteins and other nitrogen containing organic compounds, and passed along through whatever food chains exist.

–Ways that Nitrogen re-enters the environment:• Death of organisms• Excrement and urinary wastes

–Nitrogen re-enters atmosphere when denitrifying bacteria break down nitrates into N2 and nitrous oxide (N2O) gases (Denitrification)

Human Impact on the Nitrogen Cycle

Use of synthetic fertilizers. Agricultural runoff adds nitrogen to aquatic ecosystems-stimulates algal blooms, depletes oxygen, & decreases biodiversity

• Land management: Nitrogen-fixing crops add more useable nitrogen to the soil. On the other hand, overplanting of crops depletes nitrogen from soil.

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

• Burning grasslands & cutting forests-remove N from soil– leads to decreased N in soils

Nitrogen Cycle

Phosphorus Cycle

Why is Phosphorous important?

Answer: It is used to build nucleic acids such as DNA, RNA, and ATP.

The natural reservoir of Phosphorous is in the soil.

This is the only biogeochemical cycle WITHOUT a gas phase!

Main processes of the P cycle• Weathering: Phosphorus slowly released from rock or

soil minerals as inorganic phosphate which dissolves in H20

• Uptake: by plants to form organic phosphates• This form can move through food webs: used to build

nucleic acids (DNA, RNA and ATP), certain fats in cell membranes, bones/teeth/shells

• Break down of organic forms to phosphate by decomposers

• Cycle takes a long time as deep ocean sediments are significant sinks

Phosphorus Cycle

Human Impacts on Phosphorous Cycle

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

• Clear cutting tropical areas decreases available phosphorous

• 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")

Sulfur Cycle

• Most sulfur is tied up in underground rocks and minerals.

• Inorganic sulfur is released into air by weathering and volcanic eruptions.

– Cycle is complicated by large number of oxidation states the element can assume.

Human Impacts on Sulfur Cycle

Human activities release large amounts of sulfur,primarily by burning fossil fuels.

• Sulfur compounds are an important determinant in rainfall acidity

• The following contributes about 1/3 of atmospheric sulfur emissions:

– Burning sulfur containing coal and oil to produce electric power

– Petroleum refining– Other industrial processes

Sulfur Cycle