BIOGEOCHEMICAL CYCLES (NUTRIENT CYCLES) - Continuation

Davis, M. L. and Masten, S.J. (2004). Principles of Environmental Engineering and Science. NY: McGraw Hill (Chapter 4)

http://www.starsandseas.com/SAS%20Ecology/SAS%20chemcycles/ecolcycle.htm

SULFUR CYCLE Just as plants cannot convert N2 into something useful in the nitrogen cycle, neither can plants use elemental sulfur 2S.

Again, plants are depended upon bacteria, in this case chemoautotrophic bacteria, which oxidizes elemental sulfur to sulfates, as in the following formula

2S + H2O + 3O2 ---> 2H2SO4. Once in the form of sulfate (2H2SO4), plants can then incorporate the sulfur into proteins.

Proteins are not only made from carbon and nitrogen, but many important proteins also contain sulfur.

Sulfur is also an important component of coenzyme A, which is used to produce energy in cellular respiration.

So the availability of sulfur is essential to maintaining life.

Sulfur shares other characteristics to the nitrogen cycle. 2H2SO4 can be converted into hydrogen sulfide (H2S) by sulfur bacteria, as can proteins when broken down by decomposers.

PHOSPHORUS CYCLE The keystone of getting phosphorus into trophic systems are plants.

Plants absorb phosphorous from water and soil into their tissues, tying them to organic molecules.

Once taken up by plants, phosphorus is available for animals when they consume the plants.

When plants and animals die, bacteria decomposes their bodies, releasing some of the phosphorus back into the soil.

Once in the soil, phosphorous can be moved 100s to 1,000s of miles from were they were released by riding through streams and rivers.

So the water cycle plays a key role of moving phosphorus from ecosystem to ecosystem.

Phosphorous in unpolluted waters is imported through dust in precipitation or via weathering of rocks.

Phosphorus is normally present in watersheds in extremely small amounts as inorganic orthophosphate, suspended as organic colloids, absorbed onto particulate organic and inorganic sediments

In polluted waters, the major source of phosphorus is from human activities

The decomposition of algae releases phosphorus which is transferred to sediments and to undecomposed organic matter

In some cases, phosphorous will travel to a lake, and settle on the bottom.

There, it may turn into sedimentary rocks, limestone, to be released millions of years later.

So sedimentary rocks store or conserve much of the phosphorus for future eons.

http://www.starsandseas.com/SAS%20Ecology/SAS%20chemcycles/cycle_phosphorus.htm

Additional Notes

CARBON CYCLE Photosynthesis - plants take up CO2 and convert it into organic matter

Organic compounds in fossil fuels also come from photosynthesis (plants)

CO2 is released from fossil fuels by combustion process

Terrestrial (plants and geologic formation) – reservoir of carbon

Ocean- the major carbon sink (reservoir), contains dissolved CO2 , carbonate and bicarbonate ions

Cycling of carbon involves release of CO2 by animal respiration, fires, diffusion from oceans, weathering of rocks, and precipitation of carbonate minerals

NITROGEN CYCLE Proteins, nucleic acids, and other organic chemicals contain nitrogen, so nitrogen is a very important atom in biological organisms.

Nitrogen makes up 79% of Earth's atmosphere, but most organisms can not use nitrogen gas (N2).

N2 enters the trophic system through a process called nitrogen fixation. Bacteria found on the roots of some plants can fix N2 to organic molecules, making proteins. Again, animals get their nitrogen by eating plants

Animals releases nitrogen in their urine. Fish releases NH3, but NH3 when concentrated, is poisonous to living organisms. So organisms must dilute NH3 with a lot of water.

Living in water, fish have no problem with this requirements, but terrestrial animals have problems.

Animals convert NH3 into urine, or another chemical that is not as poisonous as NH3. The process of NH3 release is called ammonification.

Because NH3 is poisonous, most of the NH3 which is released is untouchable. But soil bacteria have the ability to assimilate NH3 into proteins. These bacteria effectively eats the NH3, and make proteins from it. This process is called assimilation.

Some soil bacteria do not convert NH3 into proteins, but they make nitrate NO3- instead. This process is called nitrification.

Some plants can use NO3-, consuming nitrate and making proteins. Some soil bacteria, however, takes NO3-, and converts it into N2, returning nitrogen gas back into the atmosphere. This last process is called denitrification, because it breaks nitrate apart.

Human Influences on the Ecosystem Ecosystems change naturally but human activity can speed up natural processes by several magnitudes in terms of time

Examples: Large scale agricultural operations (for food supply) can result in the release of pesticides, fertilizers and carbon dioxide and other greenhouse gases to the environment

Dam construction for hydroelectric power (a clean, renewable energy source) can have detrimental effects on river ecosystems

Human activity can also change ecosystems through destruction of species , where the loss of habitat can threaten the existence of individual species (forests) Localized destruction of the milkweed plant

deprives the butterfly of its nesting environment

Excessive hunting causes the extinction of species e.g., the manatee whose habitat is the Everglades is threatened by poaching, also the rhinoceros is threatened by poaching for its horns

Introduction of nonnative (exotic) species into the ecosystems can threaten species e.g., the introduction of rabbits into Norfolk island resulted in the loss of 13 species of vascular plants

The release of toxic chemicals can threaten wildlife e.g., DDT which threatened the existence of the American bald eagle; DDT uptake from contaminated prey results in failure to reproduce