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