Nutrient
Cycling
Lake Victoria
 Incredible
diversity
of cichlid fishes.

More than half of
the 500 species
now endangered.
 Nile
perch
 Increased
phytoplankton

Cyanobacteria
Lake Victoria
 Algal
bloom causes and increasing rate
of decomposition as algae die off.
 Bacteria use oxygen during
decomposition – lower DO.
 Lower oxygen results in increased death
for fishes.
Lake Victoria
 Changes
including increased
phytoplankton can result from a change
in the lake chemistry.
 Ecology includes the study of the
interaction between organisms and the
physical environment.

Study how nutrients cycle within an
ecosystem.
What is a Nutrient?
 Nutrients
are chemical elements and
compounds that are essential to the
health and survival of an organism.

proteins, carbohydrates, cellulose, nucleic
acids, and other compounds that provide
an organism's structure and physiology.
 The
concentrations of nutrients within
an ecosystem determine which species
can live there and in what abundance.
Nutrients
 Macronutrients
large amounts.

C, N, P, S, O, H
 Micronutrients
quantities.

are required in relative
are required in smaller
Zinc, Iodine, Potassium, Iron
Nutrients
 Nutrient
availability, species-specific
nutrient requirements, and effectiveness
of each plant's nutrient-capturing strategy
all affect survival and competitive vigor.
 Focus on Nitrogen, Phosphorous, Carbon
Lac Bleu and Lac Clair
 The
change in the ecosystem seen in the
demo Lac Clair may have resulted in a
change in lake chemistry.

Change in concentration of limiting
nutrients.
 Nitrogen
 Phosphorous
The Chemistry
of Lake
Victoria
 The
concentrations
of Nitrogen and
Phosphorous tripled
between 1960 &
1990.
 Algal biomass
increased.
 Water clarity
declined.
The Chemistry of Lake Victoria
 The
increased nutrients in Lake Victoria
resulted from a change in the use of
surrounding land.



Deforestation (increased runoff)
Increased agriculture (fertilizer use)
Nile perch introduction may have also
contributed.
Flux


Trees take up nitrogen
through their roots and
use it to construct
proteins and other
organic compounds
they need to grow.
Ecologists often
describe this
movement of material
as a flux, measured as
mass per unit time.
Pools
 If
the magnitude of the input is greater
than zero, the tree takes up nitrogen,
causing the amount stored in the tree's
nitrogen pool to increase.
 Simply stated: as the tree grows, it
accumulates nitrogen.
Outputs
 Whenever
a tree
sheds leaves or drops
branches, it exports
nitrogen.
 Collectively, these
outputs can be
considered a single
flux represented by an
arrow pointing away
from the tree.

Δ Storage = Inputs - Outputs
Closed System
 Nitrogen
cycles
between the tree
pool and the soil
pool.


Tree takes up N from
soil for growth.
Decaying leaves
return N to the soil.
Open System
 Ecosystems
receive and lose nutrients
from and to a variety of external sources
and sinks.
 One of the largest potential sources of
nitrogen is the atmosphere.
Open System


Through a process
called nitrogen
fixation, nitrogen from
the atmosphere is
added to the soil
nitrogen pool; thus,
fixation is an input.
Conversely,
denitrification is an
important output that
removes nitrogen
from the soil pool and
returns it to the
atmosphere.
Nutrient Cycling
 The
processes involved in these transfers
are collectively known as nutrient cycling,
so called because the same nutrients are
constantly reused within the biosphere.
Nutrient Cycling
 By
physically altering the landscape
and/or changing biological
communities, disturbances such as fire,
floods, and crop harvesting can affect
the relative sizes of various fluxes and
therefore how tightly nutrients cycle.
 As a result, ecosystems often gain or lose
nutrients in the period following a
disturbance.
Water Cycling in Terrestrial
Biomes


Water plays a major role in the movement of
nutrients within ecosystems.
The largest pools of nitrogen and phosphorus
(N2 in the atmosphere and calcium
phosphate minerals in sedimentary rock,
respectively) are relatively unavailable to
biota.

Soluble forms of both nitrogen (e.g., nitrite and
nitrate) and phosphorus (phosphate) are readily
taken up by plants and microbes.
Hydrologic Cycle
 Because
water is such an important
vector for the movement of nutrients, it is
crucial to understand the hydrologic
cycle.
 The average residence time of water in
the atmosphere is only 9.3 days, whereas
its residence time in oceans is nearly 3,100
years!
Inputs & Outputs
 Most
essential macronutrients enter
terrestrial systems from the atmosphere.

Gaseous exchange acts as a nutrient
output as well as an input.
 Physical
weathering of rock and soil is
another significant nutrient input in
terrestrial ecosystems.
Inputs and Outputs
 Wetfall
and dryfall act as nutrient inputs in
both terrestrial and aquatic ecosystems.
 Animals moving between ecosystems can
act as both nutrient input and output
agents.
 Surface water, leaching, and
groundwater flow carry nutrients out of
terrestrial ecosystems.
Energy Flows While Nutrients
Cycle




When nutrients move in, around, and out of
ecosystems, energy also moves.
Green plants and algae and other primary
producers capture solar energy during
photosynthesis.
This energy is converted into chemical energy
stored in the bonds that hold molecules
together.
As chemicals move around an ecosystem,
the energy stored within moves with them.
Energy Flows While Nutrients
Cycle

While energy flows
into, through, and
out of biological
systems, nutrients
move between the
abiotic environment
and living organisms,
and nutrient mass is
conserved
throughout the
process.
Nutrient Cycling and Scale


When ecologists refer to
nutrient cycling, they
generally do so within the
context of spatial scale.
The pattern of input,
internal cycling, and
output discussed above
occurs microscopically
(even inside single-celled
organisms), at the global
level, and at all scales in
between.
Biogeochemical Cycles
 This
scale progression continues up to the
level of the whole planet. At the global
scale, nutrients move
within biogeochemical cycles.
 The components of cycles at this scale
are living organisms (the biosphere); rocks
and soil (the lithosphere); oceans, lakes,
rivers, and other water bodies (the
hydrosphere); and the atmosphere.
Nitrogen
Cycling in
Ecosystems
Nitrogen Cycling
 As
a nutrient moves between the abiotic
and biotic components of an ecosystem,
it shifts between different inorganic and
organic forms.
Nitrogen Cycling
 The
primary reservoir for Nitrogen is the
atmosphere.


79% of air is N2.
N=N Triple bond is hard to beak – it takes
lots of energy to break the bond and use
each nitrogen to build other molecules.
Nitrogen Cycling
 Five
major stages of chemical
transformation involved in the movement
of nitrogen into, around, and out of an
ecosystem:





Nitrogen Fixation
Immobilization
Mineralization
Nitrification
Denitrification
Nitrogen Fixation
 Microorganisms
fix atmospheric nitrogen
and convert it into forms that plants can
readily utilize.
 Most of the fixed nitrogen plants draw
from the soil or water is in one of three
forms: ammonium (NH4+), nitrite (NO2-) or
nitrate (NO3-).
Nitrogen Fixation
 Plant
life is
dependent upon
microorganisms for
their nitrogen and so
symbiotic relationshi
ps have evolved
between plants and
these nitrogen fixers.


Mutualism
Legumes (beans,
peas)
Nitrogen Fixation
 Nitrogen
can also be fixed by lightening
or released when we burn fossil fuels.
Immobilization


After inorganic nitrogen entering
an ecosystem from the
atmosphere is fixed, it is then
converted into organic
compounds by plants and
microorganisms.
The amount of plant-available
nitrogen in the soil affects the
rate of net primary productivity,
the amount of nitrogen in plant
tissue, and the nitrogen
available to herbivores and
other consumers.
Mineralization


Mineralization (or
“decay”) is the
opposite of
immobilization.
When dead organisms
and animal waste
decompose, the
organic forms of
nitrogen contained in
that material are
converted back into
ammonia and
ammonium.
Mineralization



Litter quality reflects how easily dead matter is
decomposed.
It is determined by nitrogen and phosphorus
concentrations, lignin content of plant
material, and the ratio of carbon to nitrogen.
Litter of higher quality is considered to have
higher nitrogen, lower lignin, and a lower C:N
ratio.

High quality litter is easier for decomposers to
break down.
Nitrification


Much of the ammonium
produced during
decomposition is
converted first into nitrites
(NO2-) and then into
nitrates (NO3-), which are
much more soluble than
ammonium and thus much
more mobile.
This chemical
transformation is
called nitrification.
Nitrification
 Many
legumes convert the ammonia
formed during nitrogen fixation into nitrites
and nitrates within their root systems.
 However, the majority of nitrification is
performed by free-living bacteria in soil or
water.
Denitrification


Denitrification removes
nitrogen from an
ecosystem and returns it
to the atmosphere.
Denitrifying bacteria are
responsible for this
chemical transformation.

When oxygen is not
available, these bacteria
use nitrate instead of
O2 in order to break
down organic matter.
Nitrogen Cycling in Terrestrial
Ecosystems
 Water
moving through the soil carries free
nitrites and nitrates. High rates of
streamflow can therefore, lead to losses of
nitrogen from the ecosystem.
 The process of converting nutrients from a
solid to dissolved form that leads to loss
from the system is called leaching.


Decreased soil fertility
Increased nitrogen in water downstream
Nitrogen Cycling in Terrestrial
Ecosystems

Disturbances, whether naturally occurring
phenomena or human-caused disruptions
of the ecosystem, can produce large
increases in the amount of nitrogen that
water carries out of the ecosystem.
Nitrogen Cycling in Aquatic
Ecosystems
 Nutrients
leaving a terrestrial ecosystem
enter a stream, river, lake, estuary, or
ocean.
 The amount of nutrients flowing into a
water body is strongly influenced by the
nutrient dynamics of the surrounding
landscape or watershed.

For example, large amounts of nitrogen
can come from fertilizer runoff, sewage,
and animal waste.
Nitrogen Cycling in Aquatic
Ecosystems



Aquatic plants and algae can use nitrites,
nitrates and ammonium dissolved in the
surrounding water.
Cyanobacteria fix atmospheric nitrogen and
convert it into ammonium, and aquatic
nitrifying bacteria convert it into nitrites and
nitrates.
Nitrogen is immobilized and stored in aquatic
sediments in a similar way as it is in soil.
Nitrogen Cycling in Aquatic
Ecosystems
 Aquatic
ecologists often to refer to
"nutrient spiraling": an atom of a nutrient
travels through a cycle, but is displaced
downstream by the current as it goes. The
faster the current, the more elongated
the spiral.
Impacts of Disturbance
 The
movement of
water and cycling of
nutrients in
ecosystems can be
greatly affected by
disturbance.
 In forestry plantations,
a repeated
disturbance occurs
when timber is
harvested.
The Hubbard Brook Experiment


The Hubbard Brook
experiment was
designed to
investigate how a
forest and its
vegetation affects the
loss of nutrients from
the ecosystem.
They studied two
adjacent tracts of
land for 3 years to
gather baseline data,
and then clearcut one
of them.
The Hubbard Brook Experiment


The clearcut and undisturbed forest areas were
compared through time to see how nutrient
dynamics differed between the two.
They discovered that the loss of nitrates in
streamflow from the clearcut area was 40 to 50
times greater than from the intact forest.
Impact of
Human Activity
Impacts of Human Activity
 Humans
significantly impact how nutrients
move around the planet.
 Our agricultural, forestry, and industrial
pursuits all affect the cycling of carbon,
nitrogen, phosphorus, sulfur, and water.

For example, human activities have at least
doubled the rate fixed nitrogen is being
added to terrestrial ecosystems.
Impacts of Human Activity
 Disturbing
these biogeochemical cycles
causes phenomena such as acid rain, the
greenhouse effect, and eutrophication.
Humans are Nitrogen Fixers
 Anthropogenic
sources of nitrogen are
estimated to add the same amount of
nitrogen to the atmosphere as natural
processes.
 Industrial nitrogen fixation greatly
increases crop yields, but also produces
large amounts of nitrous oxide,
a greenhouse gas, and nitric oxide, an
important contributor to smog and acid
rain.
Humans are Nitrogen Fixers
 The
production of synthetic nitrogen
fertilizer adds nitrate or ammonium
directly to the soil, bypassing part of the
natural nitrogen cycle.
 The denitrification systems in many
ecosystems are not able to keep up with
the high rates of artificial nitrogen fixation
occurring with fertilizer use in agriculture
and forestry, widespread planting of
legumes, and burning fossil fuels.
Humans are Nitrogen Fixers
 Primary
production in estuaries is typically
considered nitrogen limited and excess
nitrogen inputs into oceans cause algal
blooms in marine waters.
Acid Rain


The term "acid rain" refers to rain
water that has been mixed with
pollutants, decreasing its pH to
4.5 or lower.
Burning fossil fuels, smelting ore,
and other industrial processes
release large amounts of SO2 into
the atmosphere. Nitrous oxides
are primarily produced by fuel
combustion in vehicles and
power plants. When these gases
enter the atmosphere, they react
with water vapor to form sulfuric
and nitric acids and other
secondary pollutants.
Effects of Acid Rain - Aquatic




Acid deposition directly impacts the biota living in
freshwater aquatic systems.
If the pH of freshwater falls below 6.0, many
aquatic invertebrates die and fish species decline.
Once pH drops below 5.0, fish cannot survive,
decomposers can no longer break down dead
organic matter, and the ecosystem becomes
severely denuded.
As fish stocks dwindle and water quality declines,
waterbirds, amphibians, and mammals also suffer.
Effects of Acid Rain - Terrestrial
 Any
significant change in soil pH will
affect plants growing in that soil.
 Because plant species have different pH
tolerances, shifts in soil pH can alter
competitive dynamics and thus the
composition of local plant communities.
Effects of Acid Rain - Terrestrial
 Although
acid rain does not immediately
kill trees directly, it reduces their vitality
and ability to regenerate.
 Prolonged exposure to acid rain
significantly impacts nutrient cycling in
forest ecosystems.

Over the long run, this indirect effect is
especially harmful to trees.
Impacts of Acid Rain on
Nutrient Cycling
 Acidic
water dissolves nutrients in the soil
and washes them out via streamflow.
 Trees are subjected to a double
whammy: their supply of nutrients
declines, and their ability to use remaining
nutrients is impeded.
 A forest's capacity to withstand these
effects depends on how well its soil buffers
acidification.
Phosphorous Cycling
 The
Phosphorous cycle does not include a
significant atmospheric component.
 Most phosphorous is found in sediments
and mineral deposits.
Phosphorous Cycling
 Weathering
of rocks slowly releases
phosphorus into terrestrial and aquatic
ecosystems.
 Since rock weathering is a slow process,
most undisturbed terrestrial ecosystems
are normally phosphorus-limited.
 Like the case with nitrogen, phosphorus
cycles between inorganic and organic
forms within an ecosystem, and some is
lost via leaching and streamflow.
Human Impact on
Phosphorous Cycle
 Phosphate
rock is mined for use in
fertilizers, industrial processes, and the
manufacture of detergents. Globally, the
artificial transfer of phosphorus from rocks
to soil is about five times faster than
natural weathering.
 Agricultural and human sewage, even
after being treated, still contains high
concentrations of phosphorus, which also
flows into aquatic ecosystems.
Eutrophication



Eutrophication takes place when water
bodies receive large inputs of nutrients,
stimulating plant growth, particularly algae.
The increased plant growth in turn increases
inputs into decomposer systems (with more
plants present, there are more plants dying)
which leads to deoxygenation of the water.
Deoxygenation can cause aquatic animals to
die, thus causing significant change to the
local community.
Eutrophication

Phosphorus
enrichment of
aquatic systems can
lead to sudden
blooms of
phytoplankton and
aquatic vegetation.
Indeed, phosphorus
has long been
thought the main
culprit responsible for
the eutrophication of
lakes.
Eutrophication
 Although
we now recognize that limiting
both phosphorus and nitrogen pollution is
critical for maintaining healthy aquatic
ecosystems, how best to accomplish this
goal remains the focus of much current
research.
Lake Washington
 In
the 1940s and
1950s, the local
human population
grew rapidly and
huge amounts of
phosphorus-rich
sewage effluent (20
million gallons per
day at one stage!)
were deposited into
the lake.
Lake Washington
 In
the 1950s, local residents noticed that
the lake water was becoming
progressively cloudier and smellier, fish
were dying, and phytoplankton were
blooming every summer.

These are classic symptoms of phosphorus
enrichment.
Carbon Cycling
 More
than 99% of Earth's carbon is tied up
in rocks, particularly limestone, and cycles
very slowly.
 So the major fluxes of carbon involve less
than 1% of the total carbon on Earth, and
of that, most involve carbon dioxide
(CO2).
Carbon Cycling

Because oceans are
so huge, the biggest
pool of CO2 is actually
in the deeper ocean
waters, and, on the
timescale of decades
to millennia, oceans
are the primary
regulator of
atmospheric CO2.
Carbon Cycling



Carbon dioxide that diffuses into the surface
waters of oceans from the atmosphere is used
by photosynthesizing plankton and
macrophytes.
This carbon moves through the food web of
the marine community from lower to higher
trophic levels.
Marine organisms such as clams, oysters,
coral, and some algae store carbon in their
shells and cells as calcium carbonate.
Carbon Cycling
 When
these organisms die, their bodies
and shells drop to the ocean floor where
they accumulate as carbon-rich deposits.
 Over long periods of time, these deposits
form the sedimentary rocks like limestone
where most of the Earth's carbon is stored.
 But over shorter time periods (decades to
centuries) this is an important flux of
carbon from the surface to deep ocean.
Terrestrial Carbon Cycling
 The
CO2 in the atmosphere cycles not
only with that in the ocean's surface, but
also with living matter on land.
 The terrestrial fluxes of CO2 are closely
linked to energy flow.

Plants take up atmospheric CO2 during
photosynthesis, as they capture solar
energy, and virtually all organisms release
CO2 during respiration, as they consume
stored energy.
Terrestrial Carbon Cycling
 After
organisms die, decomposers release
carbon that was tied up in their bodies.
 Fires can also release carbon.
Terrestrial Carbon Cycling


The two major carbon pools
on land are in the
aboveground biomass (for
example, the wood of trees
holds much of the carbon in
an old-growth forest) and in
the soils, where carbon is
stored in dead material that
has not fully decayed.
Given enough time and the
right conditions, carbon
stored in the soil can be
transformed into fossil fuels
like coal, oil, and natural gas.
Human Effects on the Carbon
Cycle
 The
exchanges of
carbon among land, sea
and atmosphere have
been disturbed by the
rapid release of
atmospheric CO2 from
fossil fuel burning,
deforestation and other
land use changes, and
by the release of
methane (CH4) from
agriculture and industry.
Human Effects on the Carbon
Cycle

This plot represents continuous data for atmospheric
CO2, which show regular seasonal fluctuations, and
mean CO2 levels per year, depicted as the smooth
line superimposed on the seasonal variation.
Climate Change
 Increases
in atmospheric CO2 have
alarmed scientists because of probable
effects on Earth's climate.
Climate Change
 Increased
emissions of carbon dioxide,
methane, and other greenhouse gases
are thought to be increasing annual
mean temperatures around the world.
 Greenhouse gases trap radiation emitted
from the Earth's surface, warming the
atmosphere.
Climate Change

With continued increase in atmospheric carbon,
scientists predict that weather patterns will become
more erratic and unpredictable, Northern
Hemisphere winters will become warmer and
wetter, and sea levels will rise around the world due
to the melting of polar ice and thermal expansion
of oceans.