Title: Nutrient Cycles in Marine Ecosystems
1Nutrient Cycles in Marine Ecosystems
- Inputs and outputs to the reservoir of dissolved
nutrients - The biological uses of nutrients
- Nutrient Availability and Productivity
2- Nutrient chemical that an organisms needs to
live and grow (or a substance used in an
organisms metabolism) which must be taken from
the environment
3Demonstrate an understanding that there is a
reservoir of nutrients dissolved in the surface
layer of the ocean
4- Algae require light for photosynthesis
- Light intensity decreases with depth so
photosynthesis is restricted to the surface layer - Known as the photic zone
- Varies from 30 m to 150 m (much less in turbid
water) - Surface layer contains many ions
5Remember These?
Ion Mean concentration in seawater (ppt)
chloride 19.345
sodium 10.752
sulphate 2.701
magnesium 1.295
calcium 0.416
hydrogen carbonate 0.145
6- These ions, together with nitrate and phosphate
ions, form a reservoir of nutrients for the
growth of algae and other primary producers - Nitrate and phosphate ions occur at loc
concentrations in sea water - Mean concentration of nitrate is 0.5 ppm
- Mean concentration of phosphate is 0.07 ppm
7The Sea-Surface Microlayer
- incredibly thin (few hundred µm)
- important for the chemistry of the ocean
- covers 71 of surface of the planet therefore
it is the largest single ecosystem - not well understood (difficult to sample such a
tiny vertical section of the water column) - critical link between ocean and atmosphere
- Receives and transmits
- energy
- gases
- solids
- collects matter transported by winds from above
and by water below
8The Sea-Surface Microlayer
- The upper meter of seawater is divided in to
sublayers, each with its own biological and
chemical features. Within the surface layer, (the
upper 60 cm), the first 0.05 mm contains an
especially dense concentration of minerals,
organic chemicals, protozoans and
micro-organisms. The upper 70 mm has dense
concentrations of slightly larger organisms,
including fish eggs, fish larvae, and
crustaceans. Larger, floating jellyfish and
seaweeds are found in the upper 30 cm. There are
many transient creatures that move up and down in
tune to the sunlight.
9The Sea-Surface Microlayer
- The plants and animals that live in the water
excrete many organic compounds, such as amino
acids, proteins, and fatty acids that serve as
nutrients for bacterial growth. These rise to the
surface where they are concentrated the thin
organic skin of the water. This happens in fresh
water as well as salt water. - When aquatic organisms die, the oils in their
bodies may float to the surface before they
completely decompose. - The thin layer of oily material on the surface
of the sea is an important part of the water
cycle as it helps control the rate of
evaporation. It is also a highly nutritious food
source for many species of microscopic plants and
animals (ie plankton). - On calm days we say the sea is "slick calm" or
"oily calm" because the microscopic layer of oil
is evenly distributed on the surface.
10The Sea-Surface Microlayer
- Wind pushes the oil into long ribbons of calm
water known as "wind slicks" or "wind rows." - You can see these on most days when looking at
the sea from an overlook or from a boat. - Samples show the plankton and nutrients are
thousands of times more concentrated in the
windrows than in water only a few cm deeper or in
adjacent areas. - Unfortunately, the oily surface of the sea is
also the first to receive pollutants from the
atmosphere. Scientists believe more than 30 per
cent of all ocean pollution comes from tiny
particles of dust and smoke in the air - often
called fallout. - This settles on the most sensitive and vulnerable
part of the ocean - its skin. - The pollutants contain pesticides, heavy metals,
and industrial and motor vehicle toxins such as
sulphuric acid, chlorine, and dioxin.
11Wind Slicks
12The Sea-Surface Microlayer
- A polluted surface microlayer has the potential
to poison much of the complex marine food web,
including fish, crustaceans, whales, and
seabirds. - Destruction of the microlayer may alter the
exchange of materials between the atmosphere and
the ocean, thereby affecting global climate. - Oil pollution also floats on the surface of the
sea and quickly contaminates this fragile
environment with chemical toxins. - Oil, even a very thin layer, spreading over the
surface of the water at the same time fish are
releasing their floating eggs can devastate their
reproductive success
13The Sea-Surface Microlayer
- Heavy metals, and other toxins, are hundreds of
times more concentrated in the surface windrows
of the sea than in deeper water. Pesticides are
found concentrated millions of times greater than
in the rest of the water. - As the ozone layer in the upper atmosphere breaks
down from air pollution, ultraviolet radiation
increases. This has been shown to have a severe
impact on the phytoplankton and the eggs of sea
creatures when they concentrate at the surface.
14The Sea-Surface Microlayer
- Three processes transport matter to the oceans
surface from below - Molecular diffusion
- Slow process due to random motion of all
molecules - Convective motion
- Vertical circulation of water from transfer of
heat - Rising air bubbles
- Bubbles created by waves and wind rise through
seawater because of their buoyancy - absorb inorganic/organic matter which is
ejected into air when bubble bursts at surface
15The Sea-Surface Microlayer
- Result of this atmospheric and oceanic flux of
material is the enrichment of both dissolved and
particulate matter in the surface microlayer - The concentrated materials represent a surface
coating that can reduce significantly the
transfer of gases and water vapor across the
air-sea interface - Influences the chemistry of lowermost atmosphere
and uppermost ocean (and possibly, the climate in
the long run)
16Explain the process by which the reservoir of
dissolved nutrients is replenished, including
upwelling, runoff from the land, and dissolving
of atmospheric gases
- Upwelling is the movement of water from deep in
the ocean to the surface layer, where the
nutrients become available to primary producers - Upwelling brought about by several processes
- Deflection of deep water currents upwards
- Movement of water away from the coast (due to
wind) - Upwelling Animation
17Mechanisms that create ocean upwelling
- Wind
- Coriolis Effect
- Ekman Transport
18Upwelling refers to deep water that is brought to
the surface.
Areas of upwelling are created by surface winds
that pull water away from an area. This deficit
of water on the surface invites water to come up
from deeper regions.
19To understand upwelling, you must be familiar
with how the Coriolis Force affects ocean surface
currents. The Coriolis Effect acts on moving
water, because it is not attached to the rotating
Earth. As water flows over the rotating earth,
it appears to deflect to the right in the
Northern Hemisphere and the left in the Southern.
20- Coriolis Effect link
- Coriolis Video
21Due to friction between the layers of water in
the ocean and the Coriolis Effect, the net result
of wind blowing across the surface of the water
is transportation of a layer of water 90 degrees
to the direction of the wind. This is known as
Ekman Transport.
22Seasonal upwelling
Wind
Wind
Onshore winds pile water up on shore, thus
surface water will be forced downward. This is
downwelling.
Offshore winds take water away from shore, thus
water from depth will upwell to the surface.
23Upwelled water also contains nutrients
(nitrate, phosphate, silicate) and dissolved
gases (oxygen and carbon dioxide) that are not
utilized at depth because of a lack of
sunlight.Now on the surface, these nutrients
and gases help to fuel photosynthesis by small
algae called phytoplankton.
24Phytoplankton photosynthesize using specialized
color pigments called chlorophyll. Thus, Ocean
Color maps are another way to identify areas of
upwelling. Where on this ocean color map are
high phytoplankton concentrations?
25Even though upwelling areas account for only 1
of the ocean surface, they support 50 of the
worlds fisheries.
26Productivity (phytoplankton growth) of an area
is determined by the rate and the duration of
upwelling.
- Rate of upwelling determines phytoplankton cell
size.
- Duration of upwelling determines the total amount
of phytoplankton.
small vs. large
few vs. many
27Classification of upwelling systems in terms of
rate and duration
After Thurman, H.V. (1994)
28-Moderate rates of upwelling for long duration (8
months or longer) provide the ultimate
combination for a large fishery. -With too low
or too high a rate, phytoplankton are small, so
there is a trophic level between the algae and
the fish.therefore the fish receive less energy.
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30Stormwater Runoff
- the most common pollutant of streams, rivers, and
oceans.
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32Demonstrate an understanding that the reservoir
of dissolved nutrients is depleted by uptake into
organisms in food chains
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35Explain how productivity may be limited by the
availability of dissolved nutrients
36Primary production is the total amount of carbon
(C) in grams converted into organic material per
square meter of sea surface per year (gm C/m2/yr).
General Marine Productivity
- Factors that limit plant growth and reduce
primary production include solar radiation and
nutrients as major factors and upwelling,
turbulence, grazing intensity and turbidity as
secondary factors. - Only 0.1 to 0.2 of the solar radiation is
employed for photosynthesis and its energy stored
in organic compounds.
37- Macronutrients and micronutrients are chemicals
needed for survival, growth and reproduction in
large and small quantities, respectively. - Upwelling and turbulence return nutrients to the
surface. - Overgrazing of autotrophs depletes the population
and leads to a decline in productivity. - Turbidity reduces the depth of light penetration
and restricts productivity even if nutrients are
abundant.
38Productivity varies greatly in different parts of
the ocean in response to the availability of
nutrients and sunlight.
- In the tropics and subtropics sunlight is
abundant, but it generates a strong thermocline
that restricts upwelling of nutrients and results
in lower productivity. - High productivity locally occurs in areas of
coastal upwelling, in the tropical waters between
the gyres, and in coral reefs.
39- In temperate regions productivity is distinctly
seasonal. - Polar waters are nutrient-rich all year but
productivity is only high in the summer when
light is abundant.
40Variations in Primary Productivity
41Mixing plays an important role in the limitation
of primary production by nutrients.
- Mixing plays an important role in the limitation
of primary production by nutrients. - Inorganic nutrients, such as nitrate, phosphate,
and silicate acid are necessary for phytoplankton
to synthesize their cells and cellular machinery.
- Because of gravitational sinking of particulate
material (such as plankton, dead or fecal
material), nutrients are constantly lost from the
photic zone, and are only replenished by mixing
or upwelling of deeper water. - Summer increased solar heating, reduced winds
leads to vertical stratification (thermocline)
which makes it more difficult for upwellings
42Mixing plays an important role in the limitation
of primary production by nutrients.
- Between mixing events, primary production (and
the resulting processes that leads to sinking
particulate material) constantly acts to consume
nutrients in the mixed layer - In many regions, this leads to nutrient
exhaustion and decreased mixed layer production
in the summer - Even in the presence of abundant light not
always a limiting factor! - As long as the photic zone is deep enough,
primary production may continue below the mixed
layer where light-limited growth rates mean that
nutrients are often more abundant
43Primary productivity varies from 25 to 1250 gm
C/m2/yr in the marine environment and is highest
in estuaries and lowest in the open ocean.
- In the open ocean primary productivity
distribution resembles a bulls eye pattern
with lowest productivity in the center and
highest at the edge of the basin. - Water in the center of the ocean is a clear blue
because it is an area of downwelling, above a
strong thermocline and is almost devoid of
biological activity.
44- Continental shelves display moderate productivity
between 50 and 200 gm C/m2/yr because nutrients
wash in from the land, and tide- and wave-
generated turbulence recycle nutrients from the
bottom water. - Polar areas have high productivity because there
is no pycnocline to inhibit mixing. - Equatorial waters have high productivity because
of upwelling. - Centers of circulation gyres, which occupy most
of the open ocean, are biological deserts.
45The Sargasso Sea and Vertical Profiles
46Remember.
- Although rate of productivity is very low for the
open ocean compared to areas of upwelling, the
open ocean has the greatest biomass productivity
because of its enormous size.
47Irons Influence
- Micronutrient iron (used as cofactor in enzymes
and important processes like nitrogen fixation)
has been discovered to have a significant role in
oceanic primary productivity - Major source of irons to oceans is the dust from
the Earths deserts (carried through wind) - In regions far removed from deserts or that are
not reached by dust carrying winds (eg North
Pacific ocean), lack of iron can severely limit
the amount of primary productivity - Known as HNLC (High-Nutrient, Low-Chlorophyll)
regions, because the scarcity of iron both limits
phytoplankton growth and leaves a surplus of
other nutrients - Some scientists have suggested introducing iron
to these areas as a means of increasing primary
productivity and sequestering carbon dioxide from
the atmosphere.
48Demonstrate an understanding that the nutrients
taken up by organisms in food chains may sink to
the sea floor in faeces or after death, may be
incorporated into coral reefs, or may be removed
by harvesting
49MARINE ENERGY FLOW AND NUTRIENT CYCLES
50DETRIVORES AND DETRITUS
- Some heterotrophs (e.g., earthworms, flies,
beetles, crabs, sea cucumbers, ants, vultures,
hyenas, etc.) depend on detritus (dead organic
material/biomass), rather than live organic
material. - Note animals can be both a herbivore and a
detrivore, or a carnivore or omnivore and a
detrivore, i.e., they eat both living and dead
organisms.
51DETRIVORES AND DETRITUS
- In some ecosystems more energy for the support of
higher trophic levels in the ecosystem comes from
detritus than from living plants and animals
(note this can be true in terrestrial,
freshwater and marine ecosystems), with detritus
serving as an energy source for an interacting
system of herbivores, carnivores and decomposers.
E.G., APHOTIC ZONE
52Marine Snow
53Marine Snow
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55DECOMPOSERS
- Decomposers play a very important role in
mineralisation by breaking down organic
substances into inorganic compounds that are
again available for reuse by producers.
56Show that each of the nutrient cycles listed
below can be summarized as shown in Fig 4.1 and
state the biological use of each nutrient
- nitrogen which is used to make proteins
- carbon which is used to make all organic
materials - magnesium which is used to make chlorophyll
- calcium which is used to make bones, corals, and
shells - phosphorous which is used to make DNA and bone
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58Ecology
Biological Processes Geological Processes
59The Carbon Cycle
- Key role in Earths thermostat
- Absorbed by ocean, utilized by plants in
photosynthesis, humans in digestion - Sinks (storage) in lithosphere (largest reservoir
limestone and other sedimentary rock),
hydrosphere (ocean), atmosphere (CO2) and in the
biosphere (dead animals, wood, plants) - Released by fires, decomposition, volcanoes, and
human respiration
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61The Oxygen Cycle
- Essential for animals
- Taken in during respiration
- Released by plants in photosynthesis
- Disrupted by the same factors that disrupt the
carbon cycle - Clear cutting of trees
- Increased burning of fossil fuels
- Pollution to phytoplankton containing water
62The Nitrogen Cycle
- 78 of troposphere is N2, 0 utilized in
respiration - Present in proteins, moves through food chain
- Most complex cycle
- Disrupted by
- Burning fuel (releases nitric oxides)
- Increased use of fertilizer
- Removal from topsoil
- Addition to aquatic ecosystems
63Conversion of Atmospheric Nitrogen to usage
nitrogen
N2
Soil
Acid soil
bacteria
NH4
NH3
64Nitrogen Cycle
- N2 gas is modified by nitrogen fixing bacteria
into ammonia (NH3) (nitrogen fixation) - Bacteria turn nitrogenous waste and detritus into
ammonia (ammonification) - NH3 is converted into nitrite (N02) which is used
to produce nitrate (N03) (nitrification) - Other bacteria convert nitrite into gas which
enters the air (denitrification)
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66The Phosphorous Cycle
- Very slow process
- Found only in sedimentary rocks and water (not in
atmosphere) - Released as rocks erode
- Travels through food chain
- Released by decomposition
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68The Sulfur Cycle
- Most stored underground
- Released by volcanoes and swamps
- Plants assimilate the sulfur
- Bacteria break it down
- 99 of all that reaches atmosphere is by humans
(industries, burning fuel, refining petroleum)
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