Transcript E Chapter 14 Impacts of Disturbances etc

Kaiser part three; Impacts
Chapter 14: Disturbances etc
IMPACTS FROM DISTURBANCES,
POLLUTION, AND CLIMATE
CHANGE
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Kaiser part three; Impacts
Chapter 14: Disturbances etc
Chapter 14 overview
1 Introduction
2 Ecological significance of disturbances
(Sources, scales, restitution rates, the IDH hypothesis)
3 Measuring the effect of disturbances
(Univariate measures, distribution measures, multivariate measures, detection, experimental
design, pitfalls)
4 Anthropogenic causes of disturbances
(River transport/agriculture, eutrophication, hydropower plants, oil industry, marine mining,
chemical vaste)
5 Climate change
(Temperature effects, precipitation variation, ocean currents/circulation, multifactor interactions)
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Kaiser part three; Impacts
Chapter 14: Disturbances etc
Chapter 14 internal build-up
The problem: Human activity all over the world is connected with a series of changes in marine
ecosystems. Many activities concern exploitation of biological and mineral resources, while other
types of impacts concern vaste from industry and agriculture. The resulting changes in marine
ecosystems have often been sudden and catastrophal, other times more subtle and not detected
before after many years.
The approach: To assess the ecological significance of human acitivity it is necessary to
understand how the marine environment react to ecological disturbances and changes in the
environment. It is particularly important to understand the temporal and spatial scales for which
the changes are relevant.
The analysis: To judge whether ecological changes are responses on manmade disturbances or
only general climatic changes, very rigorous experimental designs as well as extensive
monitoring are necessary. At the same time, it is important to assess with which statistical power
the various types of changes can be detected.
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Kaiser part three; Impacts
Chapter 14: Disturbances etc
Chapter 14 executive summary
• Disturbances of marine ecosystems have occurred naturally in all places at all times.
• Responses on disturbances in terms of species diversities appear general and predictable
• Anthropogenic effects must be distinguishable from natural changes (by experimental design)
• The continental shelves are most sensitive to anthopogenic disturbances (fisheries, aquaculture, oil
industry, shipping, tourism and pollution)
• Eutrophication caused by agriculture activity have resulted in poisonous algae blooms and mass
deaths of marine fauna.
• Resistant pollution (e.g. plastics) have complex and hard-to-detect damage effects
• The consentration of the world population in coast-near areas makes them vulnerable to changes in
the ocean level caused by man-made global warming
• Increased amounts of precitation will increase the freshwater runoff and sedimentation in estuarine
and coastal systems, and thereby affect density-driven ocean currents (regions of freshwater
influence), which in turn change the distribution of plant- and animal societies.
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Kaiser part three; Impacts
Chapter 14: Disturbances etc
The problem...
World population in year 2000 was
ca 6 billions. The increase has been
exponential for a long time.
Year
Today the increase is
approx. 1.2% p.a.
Population
(in billions)
2010
6.8
2020
7.6
2030
8.3
2040
8.9
2050
9.4
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The increasing world population
puts pressure on natural
resources, both terrestrial and
marine. The world has an
increasing demand for protein.
The need for energy has
increased dramatically, too, and
the use of fossile fuel is
believed to be one cause of the
rapid global warming we are
witnessing today.
It must be expected that the
need for energy will increase
even more, as new and large
population groups demand their
share of the welfare.
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Chapter 14: Disturbances etc
The geographic distribution of the world population
shows that the densiest areas are those where the
inhabitants now demand their share of the welfare,
and therefore will need huge resources in form of food
and energy. It is expected that this will lead to large
milieu problems in those areas, and an increased
pressure also on natural marine resources.
Population densities vary between
countries. Some nations have
large populations and therefore
strong national interests relative to
natural resources and energy.
India and China are typical
examples of this.
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Chapter 14: Disturbances etc
Population densities in year 2000
"Hotspots" in population densities are found in both developed
and undeveloped countries.
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Chapter 14: Disturbances etc
DISTURBANCES
Definition: Disturbances were defined by Picket & White (1985) as "any time-limited
event which tears up existing ecosystems, societies or population structures and
changes resources, substrate availability or the physical environment".
Natural: Distubances act on different scales and with different frequencies. Natural
disturbances, such as ocean-level change, ocean temperatures and ocean currents,
usually take place over extended time periods. Other natural phenomena have a
shorter time scale (hurricanes and cyclones, pests).
Antropogenic: Oil spill, destruction of coral reefs by trawling, eutrophication, and
poisonous vaste.
Common to both is that they can affect a wide specter of marine habitats, and that
they are processes which contribute to the diversity in all ecosystems.
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The increased exploitation of natural resources needed to serve a growing world
population has both direct and indirect disturbing effects on marine ecosystems.
Even activities far from the ocean, like hydropower plants, mountain mining (rivertransported pollution), nuclear power plants (leakage of radionucleotides), and
chemical industry (river-transported vaste) eventually ends up affecting marine
habitats and ecosystems.
A more subtle and slow-working impact, but not less serious, is the increasing
deforestation several places on earth. It leads to soil-erosion and increased rivertransport of soil, humus and mud which may cover benthic habitats, and reduced
light conditions in areas with coral reefs. Reduced light can also lead to changes in
the composition and hierarchy of marine food webs (example: the coronate jellyfish
Periphylla periphylla).
These anthropogenic disturbances of biological systems come on top of the natural
fluctuations. The new danger now is that mankind with its activities also affects the
climate, and thereby the natural fluctuations.
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Scale: There is a tight coupling between the time- and space scales in which
disturbances occur. On the smallest scale we have the instantaneous chemical
reactions between sediment particles, viral-, and bacterial processes. Futher on
via minute-scale predation and metre-scale bioturbidity to tidal cycluses. The
seabed is a mosaic of small societies on different stages of change and
recolonization, and together these societies characterize the habitat.
The physical disturbance which
results from a single waving crab
(Uca sp.) is negligible, but the joint
activity of a whole population can
turn the sediment surface upside
down during one single tidal cyclus.
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Restitution rates: For small-scale disturbances the restitution times are short; from seconds to
weeks, but they increases strongly with the geographic and temporal scale. It may take years and
decades to heal the damage to a coral reef which has been destroyed by bottom trawling. When the fish
fauna in coastal waters in South Norway was almost wiped our some decades ago, it took surprisingly
short time (one or two years) before it was intact again. Therefore, aspects of the mobility of the involved
organisms is also part of the picture with respect to recolonosation.
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Different models have been suggested to describe
how animal societies react on a disturbance, in form of
changes in the societiy's species diversity. Her are two
of them:
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Pearson & Rosenberg
model
The IDH hypothesis (Intermediate
Disturbance Hypothesis)
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How to measure effects of human activities
One-variable indexes:
Variation in the occurrence of one particular species has often been used to
describe the effects of disturbances. However; this approach does not target
changes in the very structure of the society which results from the variation in
one or a few species. In most cases the effects of human activity are not
species-specific, but may have very different effects on the various
components of the society. Wrong scale in the approach can easily lead to
wrong conclusions.
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Distribution indexes:
Measures which comprises a set
of species counts in a single
sample in one graph or
histogram.
There are a rich flora of such
indexes, whereof some may be
more sensitive and thereby
better fit than others, depending
on the circumstances.
The graph to the right shows a
situation where a plot of
"Taxonomic distinctness" ()
proved more effective than the
common Shannon-Wiener
diversity index (H).
[Cf the textbook page 469]
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Multivariate techniques:
These techniques combine two or more
samples with respect to which degree
they contain the same species or different
species with variable frequency. They can
include both the species themselves, or
their respective occurrence or biomass).
The graph to the right shows a MDS
(multidimensional scaling) plot of fish and
benthic societies in the Irish Sea by use of
bottom trawl. Closeness on the plot
means similarity of species composition
and numeric value.
MDS plott
(MDS plot. Cf textbook p. 470 for figure
caption). (Multi-Dimensional Scaling)
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How to detect changes :
If we shall have any possibility to detect effects of human avtivity it is, in light of the
enormously complex interactions in marine ecosystems, critically important to ask
the right question. Long-term ecological changes are strongly influenced by a
fluctuating environment, and it can be very difficult to sort out the importance of
single factors among a multitude of milieu effects. Sometimes it is necessary to do
laboratory experiments as a support to time series of climatic or ecological data.
Monitoring time series must be designed so that they have the necessary statistical
power for detecting trends in a time series.
• Type I error: To conclude with difference when there in fact is no difference.
• Type 2 error: To conclude with no difference when there in fact is a difference.
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Special topics
• A priori hypothesis testing
• A posteriori hypothesis testing
• Significance level in multiple
tests of the same hypothesis
• The importance of pilot studies
and resampling
• Joint significance level from
multiple tests (Fisher's omnibus test)
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Experimental design
Experiments must be planned so that the data obtained are suitable for the
relevant statistical procedures and tests. Examples of basic pre-requisites
are:
1. If Anova is planned, at least replicate measurements are needed, so that a
mean and variance can be calculated.
2. If frequencies of categorial variables are used, sample size is crucial for
detecting significant differences.
3. If trend analysis (increase/decrease) is used, at least 6 plots are necessary
for detecting significance at the 5% niveau.
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The cause of changes in marine ecosystems
River transport of terrestrial discharge
Estuaries are strongly influenced by the freshwater runoff, and the materials
which the rivers carries with them to the sea. Worldwide, ca 70% of the
sediments are contributed by rivers. Powerplants, agricultural discharge,
flood debris, size of the precipitation area and estuary decide how strong
the sedimentation is. The big rivers in the world; the Amazonas and the Nile
create enormous deltas which in historic time have been important settling
areas for mankind and birth places of civilications.
Eutrophication
Rivers supply nutrients to the estuaries,
and initiate phytoplankton blooms which
may spread over vast distances with
ocean currents and thus result in substantial downstream ecosystem disturbances.
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Powerplant
constructions
Egypt
The building of the Aswan dam resulted
in a temporary decline of Mediterranean
fisheries. It is assumed that the reduced
transport of phosphorous during dam
construction eventuallly was more than
compensated by increased supply from
water plants downstream after the
building of the dam.
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Natural conditions / eutrophication
In the northern Gulf of Mexico, on the Louisiana continental shelf just by the
outlet of Mississippi, there are large areas with anoxic conditions in the bottom
water in March-December. The severity of the conditions may vary from year
to year.
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Oil- and gas exploitation on the ocean floor
Release of hydrocarbons and boreslam from drilling platforms affects the
surrounding seafloor considerably. The effect is seen as a gradient out
from the platform, some places out to 100 meters, but in the North Sea
up to 6 km. Such releases have been substantially reduced with modern
technology, so that today the effects from release from shipping is
actually much larger that the one from oil production.
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OIL SPILL
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OIL SPILL
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OIL SPILL
Oil in water affects plankton, nekton,
(incl. fish), aquaculture, birds and
marine mammals.
Oil on the beaches affects coastlines,
marinas, freshwater production and
seabirds and other animals that live
by the sea.
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OIL SPILL
Exxon Valdez
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The oil tankship Exxon
Valdez was grounded on
Bligh Reff at the Kodiak
Island, Alaskan Gulf 24.
March 1989. It released
large amounts of raw oil
into the marine nvironment.
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OIL SPILL
The Exxon Valdez oil spill killed, with certainty, more than
1000 sea otters along the west coast of USA. Some
estimates suggest that the number was actually three times
larger. This catastrophy, and many others, has had serious
consequences for endangered sea otter stock wherever they
are found.
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Amoco Cadiz
The tanker Amoco Cadiz
grounded and spilt large
amounts of oil on the
beaches of Bretagne,
France, in March 1978.
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DISTURBANCES
Amoco Cadiz
Gannet killed by oil spill
Oil destroys the isolating effect of the bird’s
plumage and the birds flying ability. The
bird will freeze to death, be caught by
predators (incl. domestic pets), or succumb
by poisoning.
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Seagull, killed by oil spill
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OIL SPILL
PHYSICS
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OLJESPILL
Plankton is the fundament of all marine food webs. Plankton is very sensitive
for the toxic oil products, and many planktonic organisms die at high oil
consentrations. Many other organisms in the food web suffer when the plankton
biomass decreases.
Fish has sensitive organs for detecting oil and are often able to leave
contaminated areas if not caught in some way. Juvenile fish are more
vulnerable than adults, and a decimation at this life stage will have long-term
effects on the stock.
Predators in the marine milieu, like scavengers, birds and man, eat in turn the
contaminated fish and accumulate toxic compounds in the long run.
Oil compounds do not taste good, and both wild fish and farmed fish may not
hit the market and thus lead to economic losses. Farmed fish are usually not
able to leave the contaminated areas and can be deemed not edible.
In open waters, marine mammals such as whales often have the possibility to
leave contaminated areas and thus reduce the danger to their health
themselves. However, those that live closer to the shore (dolphins and seals)
risk contact with oil compounds on the shores, and get fur damage and food
toxification as a resulst.
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MINERAL MINING ON THE OCEAN FLOOR
Exploitation of mineral aggregates (nodules) from the deep ocean floors results
in intense local disturbance which can last for decades.
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Contaminants
The most important contaminants are radionucleotides and organic compounds from
energy plants and the industry. PCB (polychlorated biphenyls) are shown to reduce
hatchability in bird eggs, while toxic mercury accumulates in bird’s feathers.
Heavy metals generally accumulate and have toxic effects high up in the food chain
(top predators like fish, birds, polar bear), while fat-soluble dioxins have toxic effects
e.g. through mother’s milk in mammals.
Different flame-inhibitors are shown to give hormonal disturbances in fishes, and may
lead to disturbances in sexual expression (”gender benders”).
Radioactive compounds fra nuclear plants have leaked to the sea and led by ocean
currents long distances in the East Atlantic. Leakages from the English nuclear plant
Sellafield have been traced in plant- and animal tissues even in the inner parts of
Norwegian fjords.
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Climate change
The UN climate panel has concluded that the ongoing worldwide
temperature increase is an effect of human activity in form of release of
climate gases (carbon dioxide, methane a.a.) and water vapour.
In the North Sea and along the Norwegian coast there is an ongoing rise
in temperature which is unusually strong. Temperature rises have also
been recorded earlier (e.g. in the 1930ies), and it is at present not clear if
we have entered an irreverible process. The high coastal temperatures are
also reflected in increased bottom water temperatures in the Trondheimsfjord during the last 30 years. (next slide).
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From the TBS hydrographical time series in the Trondheimsfjord
The temperatures have oscillated (~ 8-10 year ampl.), with an upgoing trend In the last 1012 years. In 2007 an ”all times high” was recorded at 500 m depth. The situation in the fjord
reflects that on the coast.
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Ocean currents in the East Atlantic connects the various regions and make no area
isolated from the others. Thus, all types of pollution can reach even the northernmost
regions. For example, dioxins have reached alarming consentrations in polar mammals
and birds.
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Interaction between factors
In the foregoing, different factors that influence the marine ecosystems have been treated
separately for the sake of simplicity. In reality they often work in concert, and the effect can
be additive or synergetic.
It is notoriously difficult to predict the end outcome of the change in one factor in an
ecosystem, because the interplay is so intense and complex between organisms, and
between organisms and their environment. The outcomes may be very different, dependent
on the particular situation in time and space.
One knows about the occurrence of cascade reactions, where originally small disturbances
can ”run away” and lead to substantial overthrowings in the ecosystems.
Times with extensive changes are Bonanza for opportunistic species. Many of these are
evolutionary very old forms with simple life functions. Having survived through hundreds of
millions of years of evolution, one can say that they have proved the success of their
design.
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