Biogeochemical Cycles Tracking Materials
Through Ecosystems
Diversity in
Nature
In general, higher biodiversity in ecosystems confers “stability”,
i.e., increased homeostasis
Threats to biodiversity include a variety of human activities
(logging, mining, manufacturing activities, hunting, over-population,
cultural mores, habitat loss or damage to forests and wetlands) Global Threats
Invasion into wilderness areas
Rainforests of Brazil and Ecuador
Mountains of Tibet
Yangtze River Valley in China
Coltran mining in Republic of Congo (preserved areas for the Mountain
Gorilla)
Expansion of manufacturing worldwide
Waste Disposal (electronics in Asia)
Pulp and paper mills in Ecuador Interconnectedness
Loss of Habitat
Reduces ecological resiliency
Affects biodiversity
Alters trophic relationships (e.g., oil pollution)
Reduced Ecosystem Quality
Results in instability and vulnerability (e.g., coral reefs)
Materials that enter a pathway move somewhere else in the ecosphere
Biomagnification (DDT, radionuclides, mercury)
Long-distance transport (sulfur dioxide and nitrogen oxides lead to
acid deposition)
Air pollutants enter the rain cycle (e.g., mercury, sulfur dioxide) Complexity
of Food Webs
Most ecosystems are characterized by complex, interactive food webs
Trophic dynamics may include predation, parasitism, and other
interdependent relationships
Feeding behaviors may be elaborate and adaptive (e.g., attack and
avoidance strategies such as armor or camouflage) Biogeochemical
Cycles
Chemicals move through biotic communities in recurring cycles
Reservoirs may be sedimentary (earth’s surface), or gaseous
(atmospheric)
Pollutants can move through the same pathways (e.g., DDT or mercury
following the carbon cycle) Hydrologic Cycle
Water vapor formation via evaporation is highest in tropical regions
Water vapor moves from equator to the poles, then cools and falls back
to earth as precipitation
Sea salt provides precipitation nuclei
Land runoff carries chemicals and sediments into oceans Carbon Cycle
Follows food web dynamics
CO2 generated through cell respiration is raw material for
photosynthesis
Dissolved carbon dioxide forms bicarbonate ions (acts as "buffer" in
ocean water)
CO2 + H2O = H2CO3 = H+
+ HCO3-
Calcium carbonate occurs in marine shells
Calcium carbonate from shells can accumulate to form limestone
Marine sediments from the past helped to form deposits of fossil fuels
(e.g., petroleum, natural gas)
Oxidation of fossil fuels releases heat, CO2
Sulfur dioxide, nitrogen oxides released
Carbon Cycle (see textbook) Nitrogen Cycle
Producers commonly utilize ammonia (NH3), nitrite (NO2), or nitrate
(NO3)
Conversion to amino acids (precursors of proteins)
Animals excrete nitrogen as ammonia, urea, or uric acid
Bacterial degradation of animal wastes Nitrogen
Compounds
Nitrogen gas
Nitrates
Amino Acids
Urea (ammonia)
Nitrites
Nitrates
Nitrogen gas Bacteria
Nitrogen-fixing bacteria
Plant uptake
Digestion/Assimilation
Ammonifying bacteria
Nitrite bacteria
Nitrate bacteria
Denitrying bacteria
Atmospheric reservoir of nitrogen (~79% of air at surface)
Sources of nitrates
Electrical discharges during thunderstorms
Nitrogen fixation by microorganisms such as cyanobacteria in oceans
Runoff from land (agricultural, residential) may contain nitrogen
compounds Phosphorus Cycle
Producers commonly utilize soluble phosphates (PO4)
Conversion in living organisms to calcium apatite (teeth, bones),
adenosine triphosphate, or ATP (used in photosynthesis and cell
respiration),
and in nucleic acids (DNA, RNA) for transfer of genetic information
Sedimentary reservoir of phosphorus (rocks, ocean sediments)
Sources of phosphates
Weathering of rocks
Microbial conversion of dead organisms
Phosphatizing Bacteria
Runoff from land (agricultural, residential) may contain phosphorus
compounds
Loss of phosphorus in marine systems
Sinking from the photic zone into the sediments
Off the coasts of California and Peru, large quantities of
nutrient-laden materials sink
Upwelling currents bring nutrients back to surface (e.g., 50% of
world’s commercial fish catch – 0.1% of ocean’s surface) Mercury Cycle
Mercury often released into marine ecosystems as an industrial
byproduct (e.g., wastes from coal-fired facilities)
Bacterial methylation (attaching CH3 to the mercury) produces
methylmercury in sediments
Bioaccumulation (or biomagnification) of mercury through the food chain
Methyl
mercury can accumulate in the tissues of pilot whales (long-distance
migration patterns)
Pilot whales may be consumed by humans (e.g., Faroe Islands off the
Danish coast)
Cause damage to neurological system