Ecosystem services from coastal wetlands

Prof Catherine Lovelock

Seagrass

Mangroves

Saltmarshes (and salt flats) and brackish marshes

The benefits people obtain from ecosystems

Millennium Ecosystem Assessment

Todays focus

• Fisheries (commercial and recreational)

• Coastal protection

• Mitigation of CO2 emissions

Biodiversity

Culture, recreation, education

Nutrients enter estuarine

wetlands from nearby

terrestrial areas dissolved

in run-off or as particles of

detritus

Crabs and other animals can transfer nutrients (often in

the form of detritus) into and out of the sediment.

Microbes recycle nutrients, taking up nutrients, grazed,

decomposed and exchange nitrogen with the

atmosphere.

Groundwater and riparian vegetation can play a

significant role in reducing nitrogen entering streams,

protecting downstream water quality

Filtration and exchange as

water moves

Animals transform and move

nutrients across landscapes

*Sediment trapping *

Todays focus

• Fisheries (commercial and recreational)

• Coastal protection

• Mitigation of CO2 emissions

Seagrass meadows are nurseries for some fisheries

species (e.g. prawns)

Proximity to seagrass meadows linked to increased fish

populations in nearby reefs and mangroves

Economic losses of AU$235 000/year when 12 700 ha of

seagrasses in South Australia was lost (Barbier et al. 2011)

“seagrass restoration efforts costing $A10,000 ha-1 have a potential payback time of less than five years, and that restoration costing $A 629,000 ha-1 can be justified on the basis of enhanced commercial fish recruitment where these twelve fish species are present” Blandon and Ermgasson 2014

Fish need mangroves Mangroves are nurseries for some fish species

Mangrove forests are rich in resources for both grazers and

predators – linked to commercially important fish species

Economic value of mangroves for fisheries was estimated at

US$37,500 per hectare (Aburto Oropeza et al. 2008)

Mumby et al. 2003

Coastal protection Mangrove forests and seagrass provide protection from

waves - dissipate energy

Mangrove protection is important during storms

Roots, stems, foliage and sediments attenuate waves

(effectiveness depends on water depth, width of the

vegetation, density etc….)

Economic value estimated at $10 000 per hectare for

prevention of typhoon damage

Attenuation of waves

• inducing wave breaking as the main damping mechanism

• dissipating energy through flow separation

• dissipating energy through friction on rough surfaces

• dissipating energy through porous friction

• producing a barrier effect that reflects energy in the offshore direction

• combination of the above mechanisms

But also vulnerable to storms

Keeping up with sea level rise

• Coral reefs, mangroves, seagrass and saltmarsh all have some capacity to increase in elevation over time(unlike concrete walls)

• Important for maintenance of coasts (coastal protection and other services)

Darwin worked this out in 1842:

Sea level rise – instrumental record and predictions

Church et al. 2011

IPCC 2013

Mangrove forests, seagrass and saltmarsh may keep up with sea level rise

Increasing elevation of the soil surface over time occurs due to:

Sediment deposition

Root growth

Low rates of subsidence (tectonic, oil, gas, water extraction, compaction)

Measurements

surface elevation

change

shallow subsidence or

expansion

deep land movement

0

~12

Dep

th (

m)

RSET (36 pt/site)

DE = f(sediment accretion + sub-surface processes)

sediment accretion (marker bed, tiles)

• Rod Surface Elevation Tables

Coastal wetlands are vulnerable to sea level rise

Mangroves, saltmarsh and

seagrass may not be able to

keep up with predicted future

rates of sea level rise

Predictions for what will happen

in mangroves:

Seaward fringe inundated

too long and dies (retreat)

Landward forests expand –

e.g. invasion of saltmarsh

Barriers will prevent

movement – “squeeze”

*Seagrass predictions – cover

later if interested

Modeling change with sea level rise Models can help visualize the future

See http://drownyourtown.tumblr.com/

Where will mangrove forests exist in the future

Digital elevation models of land surface

Sea level predictions

Knowledge of vertical accretion and other processes

Modeled vegetation change using SLAMM

Consequences of gains in surface elevation

• Sustained coastal protection, even with sea level rise

• Carbon sequestration

Blue carbon

Reducing Emissions from Deforestation and Forest Degradation in Developing Countries (~2008)

2009

Carbon sequestered in mangroves, seagrass and saltmarshes

• 25% of CO2 emitted to the atmosphere from activities of humans comes from land-use change

• Strategies developed to reduce this source and encourage CO2 fixation in ecosystems

Blue Carbon: Mitigation and conservation

IPCC greenhouse gas accounting (Kyoto 2005, IPCC 2006 guidance) – Countries ‘pledge’ to reduce emissions and techniques for counting carbon available Coastal wetland management activities that

affect carbon (e.g. losses and gains) are to be counted: Wetland supplement to 2006 assessment released in 2013 Other mechanisms: Clean Development

Mechanism (IPCC - CDM), REDD+, voluntary markets (e.g. Verified Carbon Standard)

Australia: Emissions White Paper April 2014

Looking for low cost options

Mangrove, saltmarsh and seagrass sediments are

globally significant stocks of carbon

High productivity (roots)

Low oxygen in sediments slows down

decomposition

Plants trap carbon from elsewhere

Soil volumes increase over time

• Seagrass has less carbon per unit area compared to mangroves, but

• Global area of seagrass is very large (could be up to 600 000 km2 compared to mangroves 150 000 km2)

• Dependent on species and environment

Reef Catchments

• Large areas of coastal habitats

• Carbon stocks in mangroves are substantial

Saltm

arsh

es

Bra

ckish m

arsh

es

Gra

ssland

s

Inland

wet

land

sBar

e

Melaleu

ca/C

asua

rina

Sea

gras

s

Man

grov

es

Rai

nfor

ests

Euc

alyp

t

Clear

ed

To

tal carb

on s

tock (

mill

ions o

f T

onne

s)

0

10

20

30

40

50

Saltm

arsh

es

Bra

ckish m

arsh

es

Gra

ssland

s

Inland

wet

land

sBar

e

Melaleu

ca/C

asua

rina

Sea

gras

s

Man

grov

es

Rai

nfor

ests

Euc

alyp

t

Clear

ed

Are

a o

f ve

ge

tatio

n

(ha)

0

100000

200000

300000

400000

500000

NA NA

Probably underestimated

Opportunities – case studies

• Hunter River • Potential for

restoration through reestablishing tidal flows (cheap)

• Carbon + other benefits

Rogers et al. 2014

Floodgates closed – 3000 ha of wetlands: C burial by 2100 – 330 000 tonnes Floodgates open – 8000 ha of wetlands: C burial by 2100 – 600 000 tonnes

Mangroves, seagrass meadows and

saltmarshes are valuable assets

Supporting fisheries production

Coastal protection

Climate regulation (carbon dioxide

sequestration)

Regulates water quality

Biodiversity

Culture/recreation/education

Management for maintaining ecosystem services

Plan for climate change

Secure land for coastal wetland landward expansion

Remove barriers to landward movement of the ecosystem (pond walls,

roads, dykes)

Redraw boundaries around wetland reserves

Ensure sediment supply is maintained for accretion (dams and levees)

Reduce unsustainable extraction

Restore *Restoring seagrass meadows is difficult and expensive

because water quality has to be improved before restoration can work

– best to prevent losses.

Maintaining seagrass requires management of land-based nutrient and

sediment inputs as well as preventing direct disturbance (e.g. dredging)

Monitoring networks (e.g. Seagrass Watch)

Responses of seagrasses to sea level rise

Light limitation

Desiccation, hydrodynamic limitation

• Losses on deep edge, especially with poor water quality? • Increases in shallow water?

Habitat distribution model

Seagrass

Roelfsema et al. 2009

Secchi Depth

EHMP

Wave height

SWAN model

Depth

LiDAR and Deep Reef

Saunders et al. 2013

Predicted seagrass distribution in 2100

10 km

Habitat

no change

Habitat gain

Habitat loss

Land

Non-seagrass habitat

• 1.1 m SLR • 17% decline

in area • Need 30%

increase in water quality to offset this loss