Biogeochemical Cycles

• What is a Biogeochemical Cycle?– Only so much matter on earth because it is acts

as a closed system.• Energy enters as sunlight, but no matter usually

exits or enters.

– These cycles act as a way to recycle matter within the biosphere from one form to another.

Energy Vs. Matter

• Energy is TRANSFERRED– One-way flow of energy through food-chains and food

webs.• Energy from sun goes to plants, which then goes to

consumers. – Each trophic level loses ~90% of energy as heat.– Only 10% of energy is used for life processes.

• Matter is TRANSFORMED– This is why we have biogeochemical cycles.– Only have a given amount of matter because Earth is a

closed ecosystem.

Nutrient Cycles

• Carbon - key ingredient in living tissue– “Carbon-based” life forms

• Nitrogen - required for amino acids used in protein synthesis

• Phosphorus - required for DNA and RNA

Water Cycle

• Water is required by all living things on Earth, including us.

• Cycles through atmosphere, ocean, and land

Water Cycle

• Major processes that bring water into the atmosphere– Evapotranspiration

• Evaporation - water heats up, forming water vapor, which then moves into atmosphere.

• Transpiration - water from plant leaves evaporates.– Condensation

• Cloud formation as water vapor in atmosphere cools, condensing into the small droplets that form clouds.

Water Cycle

• Major process that brings water out of the atmosphere:– Precipitation

• Droplets that formed clouds become to large and are released as snow, sleet, hail, or rain.

Water Cycle

• Processes on land:– Runoff

• Precipitation “runs” along land until it reaches a body of water, such as a lake, river, or ocean.

– Seepage (aka infiltration)• Precipitation “seeps” (moves into) soil to form

ground water below the soil’s surface.– Root uptake

• Plants absorb ground water from soil via their roots.

Carbon Cycle

• How is carbon taken up and released?– Photosynthesis, respiration, decomposition– Erosion, volcanic activity, and other geological

activity– Fossil fuel formation (deposition)– Human activity

• All these activities transfer carbon dioxide.

Carbon Facts

• 71% of world’s carbon is in the oceans.• 22% exists as fossils.• 3% contained in dead organic matter and

phytoplankton.• 3% held in terrestrial ecosystems.• Only 1% within the atmosphere as carbon dioxide.

Phosphorus Cycle

• Where is a majority of phosphorus located?– On land in rock and soil minerals.– In the ocean as sediment.– Small amount in living organisms, bound

within organic molecules such as DNA and RNA as well as in skeletons of animals.

– Unlike other nutrients, it DOES NOT enter the atmosphere.

Phosphorus Cycle

• What is the major form that phosphorus is found in?– Phosphate compounds (PO4

3-)

Nitrogen Cycle

• What form does most nitrogen exist in?– Nitrogen gas in the atmosphere (N2)

Nitrogen Cycle

• How do we get to a usable form?– Bacterial nitrogen fixation– Atmospheric nitrogen fixation– Decomposition and excretion

• What are these usable forms?– Ammonia (NH3), Nitrate (NO3

-) and nitrite (NO2

-).

Nitrogen Cycle

• What can “fix” nitrogen to a usable form?– Bacteria

• On root nodules of legumes such as beans; convert nitrogen gas to ammonia.

• In soils, convert ammonia to nitrates and nitrites

– Enzyme necessary for this requires that no oxygen be present.

Nitrogen Cycle

• What process removes usable nitrogen?– Denitrification

• Bacteria convert nitrates back into nitrogen gas

How Nutrients Effect an Ecosystem

• Nutrient limitation– Similar to when a person has a deficiency in a

vitamin or necessary nutritional component (like iron or calcium), ecosystems can have a deficiency in a given nutrient.

– This nutrient is called the limiting nutrient, because it limits the primary productivity of an ecosystem.

How Nutrients Effect an Ecosystem

• What is primary productivity?– The rate at which organic material is created by

producers, such as plants on land or phytoplankton in the ocean.

• What happens when a limiting nutrient no longer becomes limiting?– In the ocean, this creates an algal bloom.

How Nutrients Effect an Ecosystem

Limiting Nutrients

• A limiting nutrient limits the amount of primary productivity an ecosystem is capable of…– In the ocean, nitrogen is limiting.– In freshwater, phosphorus is limiting.

• An increase in a limiting nutrient can lead to algal blooms…

Algal Blooms

• Increase in algae as a result of increased nutrient.– Step 1: Algae grow and reproduce rapidly.– Step 2: Algae die.– Step 3: Decomposers (bacteria) in the water take up

all the oxygen via respiration as they break down the dead algae.

– Step 4: Limited to no oxygen left for other animals in the water column.

– Step 5: Other animals such as fish, die due to lack of oxygen.