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Water quality
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Marine Blueprint
Water Quality: safeguarding a national asset
Water quality is at the heart of the health of the Great Barrier Reef and its
World Heritage coral, mangrove and lagoon ecosystems. Good water quality is
essential for sustaining commercial fisheries, tourism and recreational angling.
Water quality science is the study of how water's characteristics: temperature,
salinity, acidity, clarity, oxygen content, nutrient and suspended sediment
levels, organic matter content and toxic pollutant loads, affect aquatic
organisms, aquatic ecosystems and human uses of water.
Scientific evidence gathered by AIMS and other institutions over the past 30
years clearly shows that human activities have increased inputs of nutrients and
sediment to reef waters and point to a decline in water quality in some parts of
the Reef. This affects the coral – especially close to the coast – and fish
populations, the tourism and fishing industries and the coastal communities
which depend on them. Management efforts to maintain good water quality in the
Reef will influence how we develop marine industries in the future.
The main marine water quality issues facing the Great Barrier Reef are:
- the increased loads of suspended sediment and nutrients
entering Reef and coastal waters from the land as a result of agriculture,
grazing, industrial and urban development. Increased sediment runoff
ultimately increases sedimentation on coastal reefs, reduces the clarity of
coastal waters and restricts the growth of light-requiring plants and
animals. Increased nutrient inputs stimulate algal growth on reefs and in
reef waters, coral disease, and may influence crown-of-thorns starfish
outbreaks.
- the contamination of reef waters and sediments by
pesticides, chemicals, oils and waste from agriculture, industry and urban
areas which affects marine life.
- the impact of rising seawater temperatures and increasing
seawater acidity as a result of enhanced inputs of greenhouse gases to the
atmosphere and the enhanced uptake of CO2 by the oceans.
Increased acidity of seawater reduces the capacity of corals and other
calcifying organisms to build the calcium carbonate skeletons, shells and
scales which also form reefs and sediments.
Runoff
Increased runoff of sediment, nutrients and chemicals from the land is the
greatest immediate challenge to the state of water quality in the GBR, and the
coastal marine ecosystems that fringe the northern half of Australia.
Well documented by research carried out over almost 30 years, the increased
sediment and nutrient loads now carried by runoff have multiple impacts which
range from smothering inshore corals under layers of silt, cutting the light
which is essential for the growth of corals and seagrass and favouring the
growth of reef algae which can displace corals. AIMS is developing bioindicators
that can detect sub-lethal stress in organisms caused by reduced water quality.
The potential build up of toxic chemicals from agricultural, industrial and
domestic activity which can weaken the health and resilience of corals and other
organisms, making them more susceptible to disease outbreaks or climate impacts.
AIMS scientists estimate that average yearly inputs of nitrogen from the land
have nearly doubled from 23,000 to 43,000 tonnes over the past 150 years, while
phosphorus inputs have tripled from 2,400 tonnes to 7,100 tonnes. In wet years,
these inputs can be many times higher.
AIMS scientists consider that most of this material is eventually flushed out of
the GBR lagoon, transferred to the atmosphere or buried in coastal sediments,
but net levels in reef waters may be increasing slowly. The Great Barrier Reef
lagoon is so large and complex that processes within it that control the fate of
nutrients – how long they remain there, what life forms exploit them and where
they go – is only partly understood.
One of AIMS’ most vital missions is to understand and interpret the nutrient
cycle in the Reef and in Australia’s tropical northern waters. The scientific
insights and date gathered by AIMS researchers are critical inputs to
Australia’s Reef Water Quality Protection Plan, acknowledged as setting a
world-best standard for minimising human water quality impacts in reef waters.
Murky water
Light is an important factor for the growth and survival of coral reefs. While
corals can grow and form reefs over a wide range of water clarity conditions,
the nature of the reefs and their continued survival depends on getting
sufficient light. A variety of new and old data is now suggesting that coastal
waters in some parts of the Great Barrier Reef are becoming more turbid due to
increased loads of fine sediment and organic particles which are continually
being resuspended from the bottom by waves and currents. Past and current
research by AIMS oceanographers and reef scientists is defining how reef
organisms are affected by fine sediment and how coastal reef communities are
responding to enhanced sediment runoff.
Ocean Acidification
Much of the additional CO2 being added to the
atmosphere by enhanced fossil fuel burning, land use and industrial activities
eventually dissolves in the ocean. This dissolved CO2
causes a gradual acidification of surface seawaters which alters the natural pH
balance of the oceans and reduces the ability of corals and other calcifying
organisms to produce their chalky skeletons. Ocean acidification is another
subtle, but significant, water quality stress affecting coral reef ecosystems.
Disease
Reef scientists worldwide have reported an upsurge in coral diseases, including
on the GBR. This increase is thought to be linked to increased stress on corals
caused by a combination of reduced water quality, disturbance and climate
change. This issue is covered further in the Marine Blueprint on Marine
Microbiology.
Contaminants
A variety of chemicals used in land- and marine-based activities have been shown
to have toxic effects on corals. These chemicals can affect photosynthesis by
the symbiotic algae living in corals, disrupt coral reproduction and inhibit the
successful settlement of coral larvae. Chemicals which can influence corals
include high levels of nutrients, herbicides and insecticides, industrial
wastes, oils, solvents and industrial chemicals that mimic natural hormones.
For further information, please contact:
Dr Britta Schaffelke
Team Leader, Water Quality in the GBR
07-4753 4382
b.schaffelke@aims.gov.au
March 19, 2008
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