Biogeochemical cycles

·        involve both biotic and abiotic processes and storage reservoirs

Fundamental macronutrient elements

·        Carbon – building block of organic compounds

·        Hydrogen

·        Oxygen – used in respiration; obviously, with H above, makes water

·        Nitrogen – with oxygen, makes proteins

o       fertilizer, made from atmospheric nitrogen

·        Phosphorus – important in energy cycle of cells (ATP, ADP)

o       fertilizer, from marine sediments produced in rich ancient upwelling zones (uncommon in geologic record)

o       often the limiting nutrient in lakes, streams, estuaries – thus increased input causes eutrophication

·        Sulfur – component of proteins


·        also Calcium (skeletal material), Sodium, Potassium (blood chemistry)


Micronutrient elements – many examples

·        often, too little = problem, too much = problem; threshold level for effect may exist

·        example: Zinc often in vitamin tablets, but too much (e.g. from mining smelter pollution) = heavy metal poisoning

·        Selenium (Se): narrow range of healthy concentration in humans, but

o       leached from dryland soils and concentrated in irrigation wastewater, California Central Valley

o       wastewater used to make Kesterson Wildlife Refuge, but high selenium in water toxic to waterfowl

o       irrigation caused change in biogeochemical cycle, decreased Se in soil reservoir, increased Se in surface water reservoir

·        food-chain concentration: (also called biomagnification): increased concentration of element or compound in an organism’s tissue above that of its food source because of metabolic processes.  Passed on at each step up food chain



·        many pollutant elements and compounds naturally occurring, concentrated by human activity

o       may be beneficial to humans, plants, animals within some range

o       harmful in too high of concentrations

o       e.g., mercury in industrial waste concentrated in food chain (Minamata Bay, Japan, p. 370-371 text)

o       e.g., copper concentrated in mine waste through ore processing

·        human-made pollutants

o       many organic compounds (e.g. PCBs, CFCs, organophosphate pesticides, etc.)

o       human-made radioactive isotopes of naturally occurring elements (e.g., cesium-137)

o       human-made elements formed in nuclear reactors (e.g. plutonium-239)

·        natural pollution? examples:

o       deadly hydrogen sulfide gas from volcanic eruptions

o       global acid rain from large meteorite impact in certain rock types

o       poison springs – water dissolves material in toxic concentrations from certain rock types


Carbon cycle (see Fig. 16.7, p. 373 text)

·        Reservoirs (mass of storage in billions of metric tons of carbon; 1 metric ton = 1000 kg):

o       atmosphere (720)

o       oceans (39,000)

o       soil (1500)

o       marine sediments and sedimentary rocks (100,000,000)

·        by far the largest reservoir, but slow flux in and out

o       biomass (560) – mostly plants

o       fossil fuels (4000)

·        Transfer processes  (mass flow in billions of metric tons of carbon per year)

o       volcanism (0.1/yr to atmosphere)

o       land photosynthesis-respiration (120/yr in and out of plants)

o       ocean (phytoplankton) photosynthesis-respiration (107/yr in and out of phytoplankton)

o       marine sediment deposition (?)

o       rock weathering and erosion (0.6/yr to oceans)

·        CO2 dissolved in water during weathering reactions is carried to oceans

o       land-use changes (1.6/yr to atmosphere)

o       fossil fuel burning (5.4/yr to atmosphere) – large flux


Atmospheric CO2 increase from 270 ppm (pre-Industrial Revolution) to present 370 ppm

·        measurement on top of Mauna Loa, island of Hawaii since 1958 shows increase at increasing rate (Fig. 20-16 text, p. 479)

·        largely fossil fuel burning

·        annual “global biosphere breathing” cycles also clearly shown in Fig. 20-16

o       winter increase in CO2 (more global respiration)

o       summer decrease in CO2 (more global photosynthesis)