acid_precipitation-2002.html: 54_22AcidPrecipitationMap.jpg
Average pH for precipitation in the contiguous United States in 2002.

acid_precipitation.html: 54_21AcidPrecipitationMap.jpg
Distribution of acid precipitation in North America and Europe, 1980.
The numbers identify the average pH of precipitation in the shaded areas.
Acidified soils damage plants by interfering with cation exchange .

biogeochemical.html: _FPX_18 54_18BiogeochemicalCycles.jpg

Review: Generalized scheme for biogeochemical cycles.

biomagnification.html: 54_23BiomagnificationPCB.jpg
Biological magnification of PCBs in a Great Lakes food web.

Polychlorinated Biphenyls (PCBs) are non-flammabe electrical insulaters whose chemical stability allow them to persist in tissue and become concentrated up trophic levels.

Toxic effects include cancer and effects on the immune, reproductive, nervous, and endocrine systems. Congress banned their production in 1977.

Another example of biological magnification in raptors is the pesticide DDT , which was banned by the EPA in 1971.

carbon-dioxide.html: 54_24CarbonDioxGlobalTemp.jpg
The increase in atmospheric carbon dioxide at Mauna Loa, Hawaii, and average global temperatures over land from 1958 to 2004.

Though average global land temperatures over this period fluctuate a great deal (red), there is a warming trend.

Excessive carbon levels in the atmosphere can lead to global warming dur to the greenhouse effect .

carbon_cycle.html: 54_17CarbonCycle.jpg
THE CARBON CYCLE
Biological importance: Carbon forms the framework for the organic molecules essential to all organisms.

Forms available to life: Photosynthetic organisms convert CO₂ to organic forms used by consumers.

Reservoirs: The major reservoirs include fossil fuels, soils, aquatic sediments, oceans (dissolved compounds), plant and animal biomass, and the atmosphere. The largest reservoir is sedimentary rocks such as limestone, though this pool turns over very slowly.

Key processes: Photosynthesis by plants and phytoplankton removes substantial amounts of CO₂ each year, balanced by CO₂ released through cellular respiration. The burning of fossil fuels is adding significant amounts of additional CO₂.

cfc.html: 54_27ChlorineOzone.jpg
How free chlorine in the atmosphere destroys ozone.

1. Chlorine from CFCs interacts with ozone (O₃), forming chlorine monoxide (ClO) and O₂.
   
2. Two ClO molecules react, forming chlorine peroxide (Cl₂O₂).
   
3. Sunlight causes Cl₂O₂ to break down into O₂ and free chlorine atoms.

The destruction of atmospheric ozone can lead to depletion of the ozone layer in the stratosphere.

cycling.html: 54_16NutrientCycling.jpg
A general model of nutrient cycling.

decomposing.html: 54_03DecomposingTree.jpg
Fungi decomposing a dead tree.

Detritivores such as bacteria and fungi recycle essential chemical elements by decomposing organic material and returning elements to inorganic reservoirs.

elements.html: ../ch41/41_02EssentialMinerals_T.jpg

energy-partitioning.html: 54_10EnergyPartitioning.jpg
Energy partitioning within a link of the food chain.

Less than 17% (1/6) of the caterpillar's food is actually used for secondary production (growth).

The efficiency of energy transfer between trophic levels usually ranges from 5% to 20%.

energy.html: ../ch01/01_04EcosysEnergyFlow_CL.jpg

energy_flow.html: 54_02EnergyNutrientFlow.jpg
Energy enters, flows through, and exits an ecosystem, whereas chemical nutrients cycle within it.

Energy (orange arrows) enters an ecosystem as solar radiation, moves as chemical energy transfers through the food web, and exits as heat radiated into space. Most transfers of nutrients (blue arrows) through the trophic levels lead eventually to detritus; the nutrientss then cycle back to the primary producers.

eutrophication.html: 54_07Eutrophication.jpg
The experimental eutrophication of a lake.

In 1974, the far basin of this lake was separated from the near basin by a plastic curtain and fertilized with inorganic sources of carbon, nitrogen, and phosphorus.

Within two months, the fertilized basin was covered with a cyanobacterial bloom, which appears white.

The near basin, which was treated with only carbon and nitrogen, remained unchanged.

In this case, phosphorus was the limiting nutrient, and its addition stimulated the explosive growth of cyanobacteria.

evapotranspiration.html: _FPX_18 54_08EvapotranspiratNPP.jpg

Actual evapotranspiration (temperature and moisture) related to terrestrial net primary production in selected ecosystems.

facts.html: 54_25CarbonDioxTreeGrow.jpg

Large-scale experiment on the effects of elevated CO₂. Rings of towers in the Duke University Experimental Forest emit enough carbon dioxide to raise and maintain CO₂ levels 200 ppm above present–day concentrations.

hubbard_brook.html: 54_19HubbardBrook.jpg
Research at the Hubbard Brook Experimental Forest shows that nitrate runoff is 60 times greater from the deforested watershed than in a control (unlogged) watershed.

limiting-iron.html: 54_06LimitingNutrientA.jpg

Which nutrient limits phytoplankton production along the coast of Long Island?

limiting-nitrogen.html: 54_06LimitingNutrientA.jpg

Which nutrient limits phytoplankton production along the coast of Long Island?

limiting.html: 54_09SaltMarShLimiting.jpg
 EXPERIMENT   Over the summer of 1980, researchers added phosphorus to some experimental plots in the salt marsh, nitrogen to other plots, and both phosphorus and nitrogen to others. Some plots were left unfertilized as controls.

 RESULTS  

 CONCLUSION   These nutrient enrichment experiments confirmed that nitrogen was the nutrient limiting plant growth in this salt marsh.

nitrogen_cycle.html: 54_17NitrogenCycle.jpg
THE NITROGEN CYCLE
Biological importance: Nitrogen is a component of amino acids and nucleic acids. Forms available to life: Producers can use inorganic ammonium (NH₄⁺) or nitrate (NO₃^-). Animals can only use organic nitrogen. Reservoirs: The main reservoir is the atmosphere, which is 80% nitrogen gas (N₂). The other reservoirs are bound in soils, aquatic sediments, dissolved in water, and in living biomass. Key processes: Nitrogen enters ecosystems by nitrogen fixation, the conversion of N₂ to NH₄⁺ or NO₃^-. Ammonification decomposes organic nitrogen to NH₄⁺. Nitrifying bacteria convert NH₄⁺ to NO₃^-, while denitrifying bacteria use NO₃^- instead of O₂ in their metabolism and releases N₂.

npp-regional.html: 54_05NetPrimaryProduction.jpg
Regional annual net primary production for Earth.
Lighter violet indicates regions of lowest net primary production, with increasing net primary production indicated by darker violet, light blue, dark green, light green, yellow, orange, and red in that order.

npp.html: 54_04NetPrimaryProduction.jpg
Net primary production of different ecosystems.
The geographic extent (a) and the net primary production per unit area (b) of different ecosystems determine their total contribution to worldwide net primary production (c). Algal beds and reefs constitute the most productive ecosystem per unit area, the coral reef.

ozone_hole.html: 54_28OzoneHole.jpg
Erosion of Earth’s ozone shield.
The ozone hole over Antarctica is visible as the blue patch in these images based on atmospheric data.

ozone_layer.html: 54_26AnarcticOzoneLayer.jpg
Thickness of the ozone layer over Antarctica in units called Dobsons.

phosphorus_cycle.html: 54_17PhosphorusCycle.jpg
THE PHOSPHORUS CYCLE
Biological importance: Phosphorus is a constituent of nucleic acids, including ATP, phospholipids, and is a a mineral component of bones and teeth.

Forms available to life: The only biologically important inorganic form of phosphorus is phosphate (PO₄^3-), which plants absorb and use to synthesize organic compounds.

Reservoirs: The largest accumulators of phosphorus are in sedimentary rocks. There are also quantities of phosphorus in soils, dissolved in oceans, and in biomass.

Key processes: Weathering of rocks adds phosphorus to soil; some leaches into groundwater and surface water and find its way to sea. Phosphate taken up by producers may be eaten by consumers and distributed through the food web. Phosphate is returned to soil or water through either decomposition of biomass or excretion by consumers.

pyramid-biomass-inverted.html: 54_12BiomassPyramidB.jpg
Inverted pyramid of biomass.
A rapid turnover of producers can allow a small standing crop of producers to support a larger consumer population.

pyramid-biomass.html: 54_12BiomassPyramidA.jpg
Pyramids of biomass (standing crop).
Numbers denote the dry weight (g/m²) for all organisms at a trophic level.

pyramid-numbers.html: 54_13PopSizePyramid.jpg

A pyramid of numbers.
In a bluegrass field in Michigan, only three top carnivores are supported in an ecosystem based on production by nearly 6 million plants.

pyramid-production.html: 54_11NetProductionPyramid.jpg
An idealized pyramid of net production.
This example is based on a trophic efficiency of 10% between trophic levels.
Primary producers convert only about 1% of solar energy into net primary production.

sargasso.html: 54_01NutrientEnrichExper_T.jpg
0 Sargasso_Sea Iron is the limiting nutrient for phytoplankton growing in the Sargasso Sea , where windblown dust from land containing iron particles cannot reach, and lack of currents prevent water circulation.

soil-nutrient.html: 54_20SoilNutrientLoss.jpg
Agricultural impact on soil nutrients.

Removal of harvested plant biomass for market removes mineral nutrients that would otherwise be cycled back to the local soil.

To replace the lost nutrients, farmers apply fertilizers enriched with nitrogen and phosphorus.

trophic-energy.html: 54_14TrophicLevelEnergy.jpg
Relative food energy available to the human population at different trophic levels.
A vegetarian diet is more efficient in supporting a consumer population like humans.

water_cycle.html: 54_17WaterCycle.jpg
THE WATER CYCLE
Biological importance: Water is essential to all organisms.

Forms available to life: Liquid water is the primary phase in which water is used, though some organisms can harvest water vapor.

Reservoirs: The oceans contain 97$ of the water in the biosphere. About 2$ is bound in glaciers and polar ice caps, and the remaining 1% is in lakes, rivers, and ground water.

Key processes: The main processes are evaporation of liquid water, condensation into clouds, and precipitation. Transpiration by plants also moves significant volumes of water. Surface and groundnwater flow can return water to the oceans.