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Why are seagrasses disappearing globally?
- Nutrient inputs
- Sediment inputs
What water quality do seagrass require in Western Port? Perran - - PowerPoint PPT Presentation
What water quality do seagrass require in Western Port? Perran - - PowerPoint PPT Presentation
What water quality do seagrass require in Western Port? Perran Cook, Dougal Greer, Andy Longmore, Brent Wormersley, David Ball, Michael Keough, John Beardall, Randall Lee, Ralph MacNally Why are seagrasses disappearing globally? Nutrient
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Seagrasses are disappearing globally, why?
- Inputs of nutrients (nitrogen) - eutrophication
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Why have seagrasses disappeared in Western Port?
Sediment input
Benthic exchange
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Sediment input
Benthic exchange
Why have seagrasses disappeared in Western Port?
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Sediment input
Benthic exchange
Why have seagrasses disappeared in Western Port?
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Sediment input
Benthic exchange
Why have seagrasses disappeared in Western Port?
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Sediment input
Benthic exchange
Why have seagrasses disappeared in Western Port?
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Sediment input
Benthic exchange
Why have seagrasses disappeared in Western Port?
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Sediment input
Benthic exchange
Why have seagrasses disappeared in Western Port?
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Aims of this project
- To identify the key factors (light or nutrients?)
controlling the current seagrass distribution within Western Port
- To quantify this relationship to obtain
thresholds (and hence water quality) needed for seagrass growth
- To investigate the possibility of using leaf
chemistry as a sentinel to stress
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Method
- Take existing habitat map, overlay with WQ,
light TSS
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Method
- Take existing habitat map, overlay with WQ,
light TSS
%Cover Driver (e.g. light) Critical threshold
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Method
- Relate leaf chemistry to key drivers (nitrogen
and light)
%Cover or leaf chemistry Driver (e.g. light) Critical threshold Can we use leaf chemistry as a sentinel for change?
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What do carbon isotopes tell us?
Isotope scale Light Heavy Photosynthesis Light limited Light replete Deep water Turbid water Shallow water Clear water
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Carbon isotopes in Western Port
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A comparison with Port Phillip Bay
Shallow sites in the NE
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Undertstanding the sediment driver
- Suspended sediments are derived from the
catchment and re-suspension within Western Port
- To understand this complex driver we used a
hydrodynamic model which simulates resuspension by waves and currents
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Modelled mean significant wave height
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Mean modelled current velocities
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Sediment type
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Total suspended sediments
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From suspended sediments to light
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The light field!
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Total Suspended solids
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Conclusions
- We believe light limitation is the key issue in
Western Port
- Spatial analysis of the data is currently
underway to identify the key thresholds of light, TSS and elevation in this dynamic environment
- Work is continuing to develop the use of