geo 200: physical geography biogeochemical cycles

GEO 200: Physical Geography

Biogeochemical Cycles

Rev. 15 April 2006 Biogeochemical Cycles 2

Environmental spheres

• Earth’s surface is a complex interface where four spheres meet, overlap, and interact. These spheres provide important organizing concepts for the systematic study of Earth’s physical geography:– Lithosphere (the solid, inorganic portion)

– Atmosphere (the gaseous envelope that surrounds Earth)

– Hydrosphere (water in all its forms)

– Biosphere (life and the places where it can exist)


Life on the landscape, part 1

• Biosphere boundaries tough to pin down because biosphere impinges spatially on other three.– Both plants and animals interact with other components of

natural landscape and may be important influence on development and evolution of soil, landforms, water, and more.

• Consists of all organisms that live on Earth.


Life on the landscape, part 2

• Vegetation used to cover most of land surface, but no more because of humans.– Humans have altered and modified much of remaining

vegetation in world.


Geography of life

• Because of complexity of organisms, a geographer can only focus on certain aspects rather than the whole.– Seek generalizations and patterns (in distributions and

relationships) and assess their overall significance.


Biogeochemical cycles, part 1

• Scientists believe that the composition of the Earth’s atmosphere and hydrosphere has changed little over the last billion years or so.– This suggests grand cycles that kept everything in steady-

state condition:• Flow of energy through photosynthesis

• Hydrologic cycle

• Carbon cycle

• Oxygen cycle

• Nitrogen cycle

• Other mineral cycles



• Human impact is having a deleterious effect on every one of these cycles.

• The flow of energy– Photosynthesis is the basic process whereby plants convert

solar energy produce stored chemical energy from water and carbon dioxide and which is activated by sunlight.



• Flow of energy (continued)– How solar energy ignites life processes in biosphere:

• Solar energy becomes fixed in biosphere via photosynthesis by green plants.

– In presence of sunlight, green plant takes carbon dioxide from air, combines with water, and creates carbohydrate compounds, a form of chemical energy.

» This chemical energy then flows through biosphere when animals eat the plants or eat other animals that had eaten plants.

– Two main components are Hydrogen Cycle and Carbon Cycle.

» CO2 + H2O (via sunlight) —> carbohydrates + O2



• The hydrologic cycle is also called water cycle; it is imperative to life.

• The carbon cycle follows the change from carbon dioxide to living matter and back to carbon dioxide.– Atmospheric carbon dioxide is converted by photosynthesis

into carbohydrate compounds.

– Some of the carbon dioxide is consumed directly by plant respiration.



• Carbon cycle (continued)– Plant growth is dependent on a surplus of carbohydrate

production.

– Net photosynthesis is the difference between the amount of carbohydrate produced in plant photosynthesis and lost via plant respiration.

– Net primary productivity is the amount of net photosynthesis of a plant community over a period of a year or a measure of the biomass of that community.



• Carbon cycle (continued)– Net primary productivity varies geographically with the

greatest productivity in the tropics and decreasing amounts toward the poles.

– Humans have interfered with delicate balance in carbon cycle that had been fixed by photosynthesis.

• Through burning of fossil fuels, humans rapidly accelerating the rate at which carbon is freed from reservoirs and converted into carbon dioxide.



• The oxygen cycle follows the movement of oxygen by various processes through the environment.– An extremely complicated process because oxygen occurs

in many chemical forms and is released into the atmosphere in a variety of ways.

• Oxygen now in atmosphere is largely a byproduct of vegetable life.



• Nitrogen cycle follows an endless series of processes in which nitrogen moves through the environment.– Nitrogen comprises 78% of atmosphere, but only certain

species of soil bacteria and blue-green algae can use it in this gaseous form; need nitrogen cycle so other life forms can assimilate it.

– Nitrogen fixation is the conversion of gaseous nitrogen into forms that can be used by plant life.



• Nitrogen cycle (continued)– Denitrification is the conversion of nitrates into free

nitrogen in the air.

– Humans significantly altering balance of natural nitrogen cycle through agriculture processes and crop choices.

• Excess nitrogen runoff affects lakes and streams by depleting their oxygen supply.



• Other mineral cycles– Specific trace minerals, notably phosphorus, sulfur, and

calcium, play important roles as nutrients for life.• Like carbon, oxygen, and nitrogen, they move over and over

through cycles.– Cycles are variable from place to place.

– The amounts of biotic nutrients are finite.

– Human interference is either damaging or modifying some of these cycles.



• Other mineral cycles (continued)– Principal chemical components of biosphere:

• Carbon

• Oxygen

• Nitrogen


Food chains, part 1

• A food chain is sequential consumption in which organisms feed upon one another, with organisms at one level providing food for organisms at the next level, etc. Energy is thus transferred through the ecosystem.– Chain is misleading because there is no orderly linkage of

equivalent units, as a chain implies.

• Plants are the fundamental unit in any food chain.– They trap solar energy through photosynthesis.


Food chains, part 2

• A food pyramid is another conceptualization of energy transfer through the ecosystem from large numbers of “lower” forms of life through increasingly smaller numbers of “higher” forms, as the organisms at one level are eaten by the organisms at the next higher level.


Food chains, part 3

• There is increasing concern that some chemical pollutants can become concentrated in food chains.– Some stable substances (those resistant to degradation)

such as DDT and heavy metals such as mercury and lead become concentrated at higher levels of a food chain.

– These can result in harmful effects and even death of consumers at the top of the food chain.


Classification schemes, part 1

• Systematic study of plants and animals is domain of biologists.

• The Linnaean system is the most significant and widely used biological classification.– Focuses on the morphology of the organisms and groups

them on the basis of structural similarity.



• The Linnaean system (continued)– The principal disadvantage for geographic use is that it is

based entirely on anatomic similarities.• Geographers are more interested in distribution patterns and habitat

preferences.– Can’t come up with anything better.

– Widespread agreement on a scheme very unlikely.



• Seeking pertinent patterns– Perhaps 600,000 plant species and more than twice as

many animal species.• Biota are the total complex of plant and animal life.

• Fauna are the animals.

• Flora are the plants.

– Terrestrial biota is much more diverse than its oceanic counterpart.


Ecosystems and biomes, part 1

• Two organizing principles are ecosystem and biome.• Ecosystem: a concept for all scales

– An ecosystem includes the totality of interactions among organisms and the environment in the area of consideration.

• Ecosystems encompass both the living and nonliving portion and how energy flows among them.

• Weakness of the ecosystem concept is that there is an almost infinite variety in the magnitude of ecosystems that can be studied:

– The range includes whole Earth itself to drop of water.


Ecosystems and biomes, part 2

• Biome: a scale for all biogeographers– A biome is a large, recognizable assemblage of plants and

animals in functional interaction with its environment.• The biome is the most appropriate scale for understanding world

distribution patterns.

• There are eleven major types.

• Often significant and even predictable relationships exist between the biota (particularly the flora) of a biome and the associated climate and soil types.

• An ecotone is the transition zone between biotic communities in which the typical species of one community intermingle or interdigitate with those of another.


Relationships, part 1

• A generalization that is true on one scale may be invalid at another.– Whatever the scale, there are nearly always exceptions to

the generalizations.

– The smaller the scale, the more numerous the exceptions. • Small-scale shows a relatively large portion of Earth’s surface.



• Generalization and scale (continued)– In environmental relationships, two types of competition at

work:• Intraspecific competition is among members of the same species.

• Interspecific competition is among members of different species.

– Limiting is the most important variable determining the survival of an organism.



• The influence of climate– Various climatic factors exert the most prominent

environmental constraints:• Light

• Moisture

• Temperature

• Wind

– Photoperiodism is the response of an organism to the length of exposure to light in a 24-hour period.



• Influence of climate (continued)– Availability of moisture governs broad distribution patterns

of the biota more significantly than any other climatic feature.

– Wind is not as influential as other climatic factors, except where winds are persistent.

• Wind may influences temperature and moisture.



• Edaphic influences– Edaphic factors are soil characteristics.

• Influence biotic distributions:– Directly affecting flora;

– Usually indirectly affecting fauna.

• Topographic influences– On a global scale, topographic influences are the most

important factor affecting distribution.



• Wildfire– Wildfire is the most important of the abrupt and

catastrophic events that affect the distribution of plants and animals.

• Has a widespread influence, affecting all portions of the continents except for always-wet regions and always-dry regions where there is not enough combustible vegetation.


Yellowstone fires, part 1

• National Park Service policy is to let natural fires burn unless they threatened human life, private property, or significant natural resources.– Followed theory that ecosystem in parks should be allowed

to function naturally, so shouldn’t interfere with natural processes.

• Horrendous weather conditions made Yellowstone ripe for conflagration.



• Suppression often caused more harm than benefit, with bulldozer scars lasting 10 times as long as any scars from fire.

• The number of animals killed by the fires was relatively close to the average number killed by cars in an average summer.



• The positive results of fires the far outweighed the negative ones.– The fires created a healthier, more diverse ecosystem.

• The fires resulted in a mosaic of vegetation rather than prevalence of lodgepole pine.

– Fires promote seed germination for some species, especially coniferous trees, thus the fires promoted a massive amount of regeneration in the region’s forests.



• Positive results (continued)– The fires promoted recycling of bound-up nutrients.

• Increased nutrient availability allowed for vigorous growth of grasses, herbs, and shrubs.

– New vegetative growth supports large populations of arthropods and rodents, which invigorate food webs.

• A long-range viewpoint is imperative in policy decisions.



• Predictive correlations– Climate influences vegetation distributions more than any

other environmental factor.

– Also influences faunal distribution, not as much as vegetation patterns do.

geo 200: physical geography biogeochemical cycles

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