Transcript Chapter 1

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
Flux rate
Pool
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).
Ecosystem Nitrogen Cycle
Gaseous N2
Nitrogen Fixation
Ammonification
Ammonia: NH3, NH4+
1. Nitrification
Nitrite: NO2-
Food Web
2. Nitrification
Nitrate: NO3Loss by
Leaching
Denitrification
Nitrogenous
Waste
Cycling of Nitrogen
assimilation
Energy and the Nitrogen Cycle
Proteins
Provides
Energy
Requires
Energy
Nitrate
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
Phosphorous Cycle
Guano
Food web
Soil
Ocean Water
Food web
Mining
Sediments
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
Volcanoes, Sea spray
Rapid Cycling
Excretion
Sulfur bacteria
Food Web
SO4
Aerobic Sulfideoxidizers
Organic Matter
Anaerobic Sulfurreducers
H2S
Heterotrophic
microorganisms
S
Sulfur bacteria
+Fe3
Very Slow
Flux Rate
OH
SH
FeS
FeS2
Black Anaerobic Mud
Soluble
Phosphorous
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
Heat
Energy
Primary Productivity
Solar Energy
CO2
Chemical
Energy (ATP)
Respiration
GPP
Photosynthesis
C6H12O6
NPP
O2
Biomass (g/m2/yr)
Available to
Consumers
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.
Carbon Cycle
Atmospheric /
Aquatic CO2
Photosynthesis
Respiration
Combustion of
wood / fossil
fuels
Food Web
Weathering
Volcanic
Action
Sedimentation
Limestone Rocks
~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
Main Processes of the Hydrologic Cycle
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
• 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
9
= Average Stage
= 2005 Stage
Avg. Monthly River Stage (m)
8
7
6
5
4
3
2
1
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
1959-2005 Atchafalaya River Stage at Butte La Rose USACE Gage ID = 03120
April
February
December
September
April
June
August
September
Floodplain Zones
I
II
III
IV
Active Floodplain
Aquatic
Ecosystem
Bottomland Hardwood Ecosystem
Floodplain System
From Larson et al. 1981; Hall and Lambou 1990
V
VI
Floodplain
Upland
Transition
Terrestrial Or
Upland
Ecosystem
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.
Stream Nitrite Concentration
Note Scale Change
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/