Presentation by Danghan Xie, University of Utrecht, The Netherlands, at the Delft3D and XBeach User Day: Coastal morphodynamics, during Delft Software Days - Edition 2019. Wednesday, 13 November 2019, Delft.

1. Credit by Artist: Yuhau Fang, China, Age 9Credit by Artist: A. Basheer, India, 9th Grade
Danghan Xie(1), Christian Schwarz(1), Muriel Z.M. Brückner(1), Maarten G. Kleinhans(1), Dunia H. Urrego(2), Zeng Zhou(3) & Barend van Maanen(1,2)
(1) Faculty of Geosciences, Utrecht University, Utrecht, Netherlands
(2) College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom
(3) College of Harbour, Coastal and Offshore Engineering, Hohai University, Nanjing, China
under sea level rise and human pressure
Mangrove diversity loss may be inevitable

2. Mangroves – A multifunctional coastal ecosystem
• Biodiversity reserves and organisms’ habitats.
• Coastal protection from natural hazards
• Water and air purifier
• Carbon storage and sequestration
• Food production (fish, shell fish and algae)
• A source for food, medicine and fuelwood
• Tourist and recreation
Photo credit by: mangrove.at
`Photo credit by: ieyenews
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3. Climate change and human actions – 2 potential threats
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4. Sea level rise
Phan et al. (2015)
Human infrastructure
• How do mangrove forests respond to
different combinations of sea level rise
rates, sediment supplies, and the presence
of barriers?
Climate change and human actions – 2 potential threats
Photo credit by: Qian Zhang
Sediment supply limitation
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5. White mangrove
Black mangrove
SLR
Sediment
deposition/erosion
Multiple mangrove species
Sediment
supply
Sediment transport
MWL
Red mangrove
Schematic of 1D eco-morphodynamic model:
Comprehensive treatment of
sediment transport processes:
Erosion/deposition and transport of
sediment between regions
Multiple mangrove species:
Dynamic growth of red, black and
white mangroves
Human barriers:
Barriers are incorporated in the model,
restricting the upland movement of
water and vegetation
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6. Coco et al. (2013)
Delft3D Matlab
Mangrove model from van Maanen et al. (2015)
Vegetation model from van Oorschot et al. (2016)
Saltmarsh model from Brückner et al (submitted)
Vegetation model based on:
Working structure of eco-morphodynamic model:
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7. Coco et al. (2013)
Delft3D Matlab
Working structure of eco-morphodynamic model:
Vegetation life processes:
Colonization, growth and mortality
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8. Coco et al. (2013)
Delft3D Matlab
Working structure of eco-morphodynamic model:
Vegetation life processes:
Colonization, growth and mortality
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9. Coco et al. (2013)
Delft3D Matlab
Working structure of eco-morphodynamic model:
Fitness and competition
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white black red
Mangrove:
Modified from Krauss et al. (2008) van Maanen et al. (2015)

10. Mangrove assemblage diversity index (ADI):
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1. richness 2. evenness
𝐴𝐷𝐼 = − ෍
𝑖=1
𝑛
𝑝𝑖 ∙ ln 𝑝𝑖
where 𝑝𝑖 is the proportional extent
of species i relative to the total
forest extent.

11. Low SSC High SLR
All mangrove species shift to upland Mangroves expand to both seaward and landward
High SSC Low SLR
Year 30, 100, 200, 300
* SSC= Sediment supply concentration; SLR=sea level rise
Impacts of sediment supply concentration and sea level rise
time
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12. Low SSC High SLR High SSC Low SLR
I am a dyke…
Extinction of white mangrove
All mangrove species shift to upland, extinction happens Mangroves expand to seaward but blocked on
upland
Impacts of human barriers
Loc.1
Loc.2
Loc.3
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13. Bed level accumulation rate decreases while inundation period increases → species are linked!!! 9
Impacts of human barriers
High SSC Low SLR

14. Barriers play a role in promoting vertical accretion!
Movement of seaward forest edge averaged over 300 years
With barriersWithout barriers
Retreat
Expansion
Retreat
Expansion
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Retreat Expansion

15. Movement of the seaward forest edge may reverse!
With barriersWithout barriers
Temporal evolution of the seaward forests edge
Continuous retreat
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Continuous expansion
Continuous
retreat
Shifts
Continuous expansion
Shifts:
(Retreat to expansion
Expansion to retreat)

16. Losses in mangrove diversity with rising sea level might be inevitable!
With barriersWithout barriers
Changes of mangrove assemblage diversity in 300 years
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Species loss
Species unevenness

17. Forest extent can increase under high SSC despite SLR, but it does not
necessarily mean an increase in diversity.
Questions?
Barriers may enhance sediment accretion but obstruct mangrove
landward migration, potentially causing extinction of species.
Mangrove species are linked through complex biophysical
interactions and play a critical role in defining forest structural changes.
Sediment accretion across the intertidal area may vary over time…
(historical/current accretion rates may be misleading).
Key messages
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Danghan Xie | PhD Candidate | Utrecht
University | d.xie@uu.nl