chapter 4 biogeochemical cycles organisms environment
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Chapter 4
Biogeochemical Cycles
Organisms
Environment
Nutrient Cycles
• Compartment – represents a defined space in nature
• Pool – amount of nutrients in a compartment
• Flux rate – the quantity of nutrient passing from one pool to another per unit time.
Major Nutrient Cycle Pathways
Pool
Flux rate
Biogeochemical Cycles
• Gaseous Type – a large portion of a given element exists in a gaseous form in the atmosphere.
• Sedimentary Type – An element does not have a gaseous phase, or its gaseous compounds do not make up a significant portion of its supply.
Energy Flows in one direction, but nutrients are more or less cycled within ecosystems
Nutrient Turnover Time is Temperature Related
Mean turnover time (yr)
Forest Region #Organic matter
N K Ca Mg P
Boreal coniferous 3 353 230.0 94.0 149.0 455.0 324.0
Boreal deciduous 1 26 27.1 10.0 13.8 14.2 15.2
Temperate coniferous 13 17 17.9 2.2 5.9 12.9 15.3
Temperate deciduous 14 4 5.5 1.3 3.0 3.4 5.8
Mediterranean 1 3 3.6 0.2 3.8 2.2 0.9
All Stands 32 12 34.1 13.0 21.8 61.4 46.0
Turnover time – the time an average atom will remain in the soil before it is recycled into the trees or shrubs
Nitrogen Cycle
• Nitrogen is used to make essential organic compounds such as proteins (amino acids), DNA, and RNA.
• Nitrogen is the atmosphere’s most abundant element (global gaseous cycle).• 78% of the volume is chemically un-reactive
nitrogen gas N2.
• Takes a lot of energy to break the triple covalent bonds holding N N
• Microbes mostly responsible for N cycle
Have You Hugged Your Microbes Today? Besides making beer, they are responsible for:
• Nitrogen fixation –conversion of gaseous nitrogen to ammonia (N2 + 3H2 2NH3) which can be used by plants.
– Biotic: Rhizobium, Azotobacter, cyanobacteria, Rhodospirillium (a purple bacteria), and some Pseudomonas
– Abiotic: Lightning
• Nitrification - Two-step process in which ammonia is oxidized first to NO2
- (by Nitrosomonas) and then to NO3- (by
Nitrobacter).
• Denitrification – conversion of nitrate ions (by some Pseudomonas or other anaerobic bacteria in waterlogged soil or in the bottom sediments of a water body) into nitrogen gas (N2) and nitrous oxide gas (N2O)
• Ammonification – the conversion (by decomposer heterotrophic bacteria) of nitrogen-rich organic compounds, wastes, cast-off particles, and dead bodies into available ammonia (which can be used by plants).
Gaseous N2
Nitrogen Fixation
Ammonia: NH3, NH4+
Food Web
1. Nitrification
Nitrite: NO2-
2. Nitrification
Nitrate: NO3-
Denitrification
Nitrogenous Waste
Ammonification
Ecosystem Nitrogen Cycle
Loss by Leaching
Cycling of Nitrogen
assimilation
Provides Energy
Nitrate
Proteins
Requires Energy
Energy and the Nitrogen Cycle
Phosphorous Cycle• The phopsphorous cycle is slow, and on a human
time scale most phosphorous flows from the land to the sea.– Circulates through the earth’s crust, water, and living
organisms as phosphate (PO4)– Bacteria are less important here than in the nitrogen
cycle
• Guano (bird poop), mined sediments, and ‘uphill’ movement of wastewater are the main ways phosphorous is cycled in our lifetime
• Geologic process (mountain formations / uplifting of ocean sediments) cycle phosphorus in geologic time
Phosphorous is Important
• Most soils contain very little phosphorous; therefore, it is often the limiting factor for plant growth on land unless added as fertilizer.
• Phosphorous also limits primary producer growth in freshwater aquatic ecosystems.
• ATP
Food web
Soil
River Flow
Ocean Water
Food web
Sediments
Guano
Mining
Phosphorous Cycle
Geologic Uplifting
Sulfur Cycle
• The sulfur cycle is a gaseous cycle.– Sulfate (SO4) is the principal biological form
– Essential for some amino acids– Usually not limiting, but the formation of iron
sulfides converts the insoluble form of phosphorous to a soluble form
• Sulfur enters the atmosphere from several natural sources.– Hydrogen sulfide (H2S) is released by volcanic
activity and by the breakdown of organic matter in swamps, bogs, and tidal flats (This answers Matt’s question about who farted in the salt marsh).
Sulfur Cycle
Food Web
Organic Matter H2SHeterotrophic
microorganisms
SO4
Anaerobic Sulfur-reducers
Aerobic Sulfide-oxidizers
S
ExcretionSulfur bacteria
Sulfur bacteria
FeS
+Fe3
FeS2
OH SH
Soluble Phosphorous
Black Anaerobic Mud
Very Slow Flux Rate
Rap
id C
ycli
ng
Volcanoes, Sea spray
Carbon Cycle• Carbon is the basic building block of organic
compounds necessary for life.• The carbon cycle is a global gaseous cycle
– Carbon dioxide makes up 0.036% of the troposphere and is also dissolved in water
• Key component of nature’s thermostat– Too much taken out of the atmosphere, temp’s
decrease– Too much added to atmosphere, temp’s increase
CO2 Uptake and Release
• Terrestrial producers remove CO2 from the atmosphere and aquatic producers remove CO2 from water via photosynthesis.
• The cells in oxygen-consuming producers, consumers, and decomposers break down the organic compounds and release CO2 back to the atmosphere or water.
• The link between photosynthesis and respiration is a major part of the global carbon cycle
Primary Productivity
CO2
C6H12O6
Photosynthesis Respiration
Solar Energy
Heat Energy
Biomass (g/m2/yr)
O2
Available to Consumers
Chemical Energy (ATP)
NP
P
GP
P
Other Links of the Carbon Cycle
• Fossil Fuels – large stores of carbon which are not released as CO2 unless extracted and burned.
– In only a few hundred years, we have extracted and burned fossil fuels that took millions of years to form.
• Limestone (CaCO3) – largest storage for the earth’s carbon is in sedimentary rocks such as limestone.– Carbon reenters the cycle as some of the rock
releases dissolved CO2 back to the atmosphere.
– Geologic processes can bring sediments to the surface and expose carbonate rock to the atmosphere.
Atmospheric / Aquatic CO2
Food Web
Photosynthesis RespirationCombustion of wood / fossil
fuels
Limestone Rocks
Carbon Cycle
SedimentationWeathering
Volcanic Action
~216.9 Tg returned to atmosphere
~212.9 Tg taken from atmosphere
~4 Tg added to atmosphere per year
About 1.3 ppm per year
Each point = monthly average
Average Mean Temperature
Hydrologic Cycle• Collects, purifies, and distributes the
Earth’s fixed supply of water – powered by the sun.
• Distribution of Earth’s Water Supply:– Salt water (oceans) = 97.4%
– Freshwater = 2.6%• 80% in glaciers and ice caps• 20% in groundwater• 0.4% in lakes and rivers (0.01% of all water!)
– Anytime of year, the atmosphere holds only 0.0001% of water on the planet.
• Although large quantities are evaporated and precipitated each year
• About 84% of water vapor comes from the ocean
1. Evaporation – conversion of water into water vapor
2. Transpiration – evaporation from leaves of water extracted from soil by roots
3. Condensation – conversion of water vapor into droplets of liquid water
4. Precipitation – rain, sleet, hail, and snow
5. Infiltration – movement of water into soil
6. Percolation – downward flow of water through soil and permeable rock formations to groundwater storage areas called aquifers
7. Runoff – downslope surface movement back to the sea to resume cycle
Main Processes of the Hydrologic Cycle
• More water evaporates from the oceans than return to it as precipitation and vice versa for the land
• Approximately 90% of the rain in the Mississippi valley originates from the sea
• Human activity tends to increase runoff rate, thus reducing the recharge rate of aquifers– Pavement, ditches,
river channelization, deforestation
• Groundwater is the source of about half our drinking water, most irrigation, some significant industrial use– Some significant aquifers may run dry if we don’t let them
recharge
• Increase in global temperature has led to increase in sea level rise.– Glacier melt– Thermal expansion
• River Continuum Concept models how biotic communities adjust to changes in the ‘downhill’ part of the hydrologic cycle.
The Flood Pulse
1959-2005 Atchafalaya River Stage at Butte La Rose USACE Gage ID = 03120
0
1
2
3
4
5
6
7
8
9
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Avg
. M
on
thly
Riv
er S
tag
e (m
)
= Average Stage
= 2005 Stage
September
December
February
April
AprilJuneAugust
September
Floodplain Zones
From Larson et al. 1981; Hall and Lambou 1990
I II III IV V VI
Aquatic Ecosystem
Active Floodplain
Floodplain Upland Transition
Terrestrial Or Upland Ecosystem
Bottomland Hardwood Ecosystem
Floodplain System
Watershed Biogeochemistry
• Watershed – The entire terrestrial and aquatic area that drains into a waterbody.
• Loss of nutrients from ecosystems is usually by runoff
Calcium flow in a forested watershed
Deforestation increases the rate of nutrient loss due to runoff.
Note Scale Change
Stream Nitrite Concentration
Other stream nutrient increase two years after the deforestation:
Calcium 417%, Magnesium 408%, Potassium 1,558%, Sodium 177%
Standing Biomass
• Standing Biomass - all the plant matter in a given area.
• Nutrients are either found in the soil or in the standing biomass.
• In a temperate forest system, recycling is slow.– Consequently, at any given time, a large
proportion of nutrients are in the soil.– So when the land is cleared, it is fertile and
can support many years of agriculture
The Tropics: A Closed System
• The speed of nutrient cycling in the humid tropics promotes high productivity, even when soils are poor in nutrients.– Nutrients are cycled so quickly there is little
opportunity for them to leak from the system– Waters in local streams and rivers can have as
few nutrients as rain water
• Because there is virtually no loss of nutrients, many tropical forests have virtually closed nutrient cycles.– The opposite would be an open system, in
which nutrients are washed out rapidly
Rapid Cycling in the Tropics
• Reasons for rapid cycling in the tropics:– Warm climate– No winter to retard decomposition– An army of decomposers– Abundant mycorrhizal fungi on shallow roots
• Fungi that grow symbiotically with plant roots
• Facilitate water and nutrient uptake
Tropical Rain Forest Paradox
• Most tropical rain forests are poor in nutrients – especially oxisol.– as little as 10% of the total nutrients are in an
oxisol soil at any given time.
• When the forests are cleared for farmland, the land can only support three or four harvests.
• Well, how can they support the amount of primary production we find in a tropical rain forest?
Tropical Soils
• When the logging trucks take the trees in the tropics, they are carrying the majority of the nutrients!
Cycling of Nonessential Elements
• Bioaccumulation - The storage of chemicals in an organism in higher concentrations than are normally found in the environment.
• Fat soluble compounds move across cell membranes and dissolve in fats (lipids).– Tend to stay in the organism and thus accumulate
– If they were soluble in water, then they would flush out
Bioaccumulation of Tributylin (TBT)
• TBT is a chemical found in nautical paint that was found in oysters along the coast of California in the late 1980s’.– Probably caused shell thickening and chamber
malformations
• Some oysters had TBT concentrations 30,000 times higher than in the water.
Biomagnification
• Biomagnification – the accumulation of chemicals in organisms in increasingly higher concentrations at successive trophic levels.
• Consumers at higher trophic levels ingest a significant number of individuals, along with the fat-soluble pollutants stored in their tissue.
• Top carnivores may accumulate poisons in concentrations high enough to prevent their eggs from hatching, cause deformities, or even death.– Concentrations in predators can be a million times
higher in predators than the concentration in the soil or the water
Terrestrial Biomagnification• DDT used to control elm bark beetle
(Dutch elm disease).
Aquatic Biomagnification
• PCB’s dumped into the Great Lakes and move through the food chain
One of the reasons the Brown Pelican became endangered.
Brown Pelican Recovery• The Brown pelican was abundant in LA in 1950. • Texas populations significantly declined between
1957 and 1961. LA’s population was eliminated.– Listed as endangered in the US on October 13,
1970• Primary cause of decline was pesticides: DDT
compounds (DDE and DDD), and PCB’s (dieldrin and endrin).– These chemicals were moved through the food chain– Impaired reproductive success (egg shells became very
thin and would often collapse)
• Populations have since recovered– DDT banned in 1972– Egg shells have shown increasing thickness
Environmental Mercury
• Usually implicated in fish consumption advisories: 1.0 ppm methyl mercury warrants fish consumption advisories in the US.
• Natural Sources:– Volcanoes, soil, under sea vents, mercury-rich
geologic zones, freshwater, oceans, plants, forest fires etc.
• Anthropogenic Sources– Mining and industrial applications, waste
incineration, coal-fired plants, paint, thermometers, etc.
Mercury Chemistry
• Elememental mercury (Hg0) – Most common form of environmental mercury – High vapor pressure, low solubility, does not
combine with inorganic or organic ligands, not available for methylation
• Mercurous Ion (Hg+)– Combines with inorganic compounds only– Can not be methylated
• Mercuric Ion (Hg++)– Combines with inorganic and organic
compounds– Can be methylated
Methylation
• Basically a biological process by microorganisms in both sediment and water
• Influenced by environmental variables that affect both the availability of mercuric ions for methylation and the growth of the methylating microbial populations.– Rates are higher in anoxic environments,
freshwater, and low pH
– Presence of organic matter can stimulate growth of microbial populations, thus enhancing the formation of methylmercury (sounds like a swamp to me!)
Methylmercury Bioaccumulation
• Mercury is accumulated by fish, invertebrates, mammals, and aquatic plants.
• Inorganic mercury is the dominate environmental form of mercury, it is depurated about as fast as it is taken up so it does not accumulate.
• Methylmercury can accumulate quickly but depurates slowly, so it accumulates– Also biomagnifies
• Percentage of methylmercury increases with organism’s age.
Environmental mercury has increased due to anthropogenic causes
http://water.usgs.gov/wid/FS_216-95/FS_216-95.html
Percent of sites in Louisiana that have mercury advisories that include each group of fish. Total sites listed = 16.
Species % Sites
Largemouth Bass 75
Bowfin 69
Crappie 56
FW Drum 50
Catfish 25
Buffalo 19
Sunfish 19
Top predators tend to be listed more often.
How Much Mercury Do You Have?
Dr. Ed Chesney at LUMCON is part of a larger study:
https://webapps.sph.harvard.edu/eer/LRAS/
http://www.louisianasportsman.com/details.php?id=191
http://www.lumcon.edu/
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