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Paul Boon
Institute for Sustainability & Innovation
Victoria University, Melbourne
Salinization of Melaleuca-
dominated wetlands of the
Gippsland Lakes, Australia
Australian distribution of Melaleuca
Gippsland Lakes
The Gippsland Lakes
Lakes Entrance
Opened in 1889
Melbourne
Dowd Morass study site
Lakes Entrance
Gippsland Sustainable Water Strategy (2010)
Lakes Entrance
LaTrobe Rv & Dowd Morass Melaleuca wetlands
Saltmarshes
LaTrobe Rv – Dowd
Morass estuary
Early 1950s RAAF photo from Eric Bird
November 2010
Phragmites beds
Retreat of Phragmites australis
Consequences of
artificial opening
Death of Eucalyptus camaldulesis
Death of Melaleuca ericifolia
Within Dowd Morass:
Death of adult plants
Little floristic diversity
Loss of sexual reproduction
Root suckers
Morass kept full to prevent saline
intrusions since 1992
Year
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
Wa
ter
Dep
th (
m)
0.0
0.2
0.4
0.6
0.8
1.0
Parks Victoria drawdown
Full even over drought
But salinity is still very high
PV’s salinity goal (< 4000 EC)
½ seawater salinity
Rehabilitation predictions
Re-instating a dry phase in Dowd Morass would
• Improve condition of adult Melaleuca
• Allow Melaleuca to recruit sexually
• Increase floristic diversity of understorey
Risks included
• Activating acid sulfate soils
• Increasing water-column and sediment salinity
• Being too short to achieve desired outcomes
• Too ambitious with too little resources
Experimental manipulations
Lake Wellington
LaTrobe River
Big Drain
Little Drain
1 km
N
Pre-existing levees
Lake
Wellington
Beyond-BACI experimental design
Control (Flooded)
Impact
(Drawdown)
Heywood’s
levee
Reference
Water in
Water out
Passive draw-down 2003-2004
Going well – then vandalism
Duck season
vandalism
2nd intervention: active draw-down 2005
Response to
2004 vandalism
in 2005: Pumping!
• 1 x 12” pump
• 1 x 10” pump
Pumped continuously for 28 days in early 2005
Active draw-down
2005
Beyond-BACI vegetation assessment
45 x 100-m long transects across wetland
• 20 in Control (flooded) sites
• 20 in Impact (drawdown) sites
• 5 in Reference (shoreline) sites
Dates: April 2003 (B), June 2004 (D), April 2005 (D), April 2006 (A)
Variables:
• Continuous water depth and salinity (data loggers)
• Water depth along transects every 0.5 m (36,000 data pts)
• Vegetation floristics and structure (overstorey &
understorey cover and floristics etc) (>120,000 data pts)
Wate
r le
vel (m
AH
D)
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
Impact
Control
Impact (Interpolated)
Apr 0
3
Jul 0
3
Oct 0
3
Jan
04
Apr 0
4
Jul 0
4
Oct 0
4
Jan
05
Apr 0
5
Jul 0
5
Oct 0
5
Jan
06
Apr 0
6
Jul 0
6
Oct 0
6
Survey 3 Survey 4
Impact
Control
Vandalism
Pumpingcommences
Survey 1 Survey 2
Drawdown 2 commences
Drawdown 1 commences
30
25
20
15
10
5
0
Storm Storm Storm
Ele
ctr
ical conductivity (
mS
cm
-1)
No big difference
between Control
and Impact water
levels
B) Salinity
A) Water level
2003 2004 2005 2006
Impact
Control
Confounding
variability in
salinity between
Control and
Impact sites
Results
Alternative: non-BACI (gradient) analysis
Instead of ANOVA,
use gradient analysis
Classification of the hydrology as per
Brownlow et al. (1994)
Four water regimes In Dowd Morass
1
2
3
4
Permanently wet
Driest sites
Gradient analysis much better than
original BACI-ANOVA approach
Water regimes 1 (dry) – 4 (wet)
Species richness
Raulings, Morris & Boon (2010) Freshwater Biology 55: 701-715
Raulings, Morris & Boon (2011) Freshwater Biology 56: 2347-2369
Projective
cover
wet
dry
wet
dry
What causes the diversity of
hydrologies? Microtopographic relief
Caused by Melaleuca, Phragmites
and Paspalum humps
Photo by Matt Hatton
Implications for wetland rehabilitation
Success after 1 year
Large-scale hummock creation, 2006
Results after 4 years
July 2010
More information?
Copies of two technical handbooks (2005, 2007)
Summary hand-out of papers to date
Over some beers tonight