Presented by Dr. Nguyen Thanh Nho, Nguyen Tat Thanh University (NTTU) and Dr. Truong Van Vinh, Nong Lam University Ho Chi Minh City (NLU-HCM), on 10 November 2020 at "International workshop: Enhancing wetland management and sustainable development"

1. 11/16/2020 1
THE ROLES OF MANGROVE FOR METAL(LOID)S RETENTION
AND IMPLICATION FOR DESIGNING PAYMENT FOR
FOREST ENVIRONMENTAL SERVICES (PFES) IN VIET NAM
NGUYEN THANH-NHO(1) và TRUONG VAN VINH (2)
(1) Faculty of Environmental and Food Engineering, Nguyen Tat Thanh University
(2) Faculty of Forestry, Nong Lam University Ho Chi Minh City

2. Mangroves are forests of salt-tolerant trees and shrubs, growing in the
shallow tidal waters of estuaries and coastal areas, in the intertidal
zones of tropical and subtropical regions.
Mangroves?
2
Land
Sea
Nguồn: Selvam 2004

3. Mangrove distributions and characteristics?
o Cover close to 140,000 km2.
o extend from 30 0N to 38 0S.
Characterized by:
o High organic matter in soils.
o High clay content in soils.
3
Global mangrove distribution map (2013).
(http://www.mangrovewacth.org.au/index.php)

4. 4
Ecological benefits of Mangrove
Source: https://savecaramoanpeninsula.wordpress.com/2014/06/18/importance-of-mangroves/

5. Mangrove environmental service in Vietnam?
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Mangrove environmental services in Vietnam for which a PFES mechanism can be
developed (Pham và cộng sự 2020)

6. Sources and emission pathways of metal(loid)s
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Agricultural landscapes
Weathering processes
etc.
Sewage, industrial effluents
Urban and runoff
Conceptual model of physical, chemical and biological variables and processes
for behavior and toxicity of metal(loid)s. (Machado et al. 2016)

7. Why can mangrove be potential roles for metal(loid)s retention?
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=> induce different
biogeochemical
processes, affecting trace
metal(loid) distributions
and partitioning.
Classis estuarine zonation (Bianchi 2007).
Estuarine waters are characterized by strong gradients in e.g.
salinity, density, flow velocity, suspended matter composition.

8. Why can mangrove be potential roles for metal(loid)s retention?
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Alongi et al., 2014.
Mangrove
Estuary
Sink of metal(loid)s
Landward
River
Fine particle
deposition
Decrease in
flow velocity
Mangrove
biota
uptake
Mangrove sediments are
characterized by different
redox processes.
=> Trace metals bearing
phases may be dissolved.

9. Which method can be used to prove the role of mangrove for
metal(loid)s trapping?
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Two main questions need to be
answered:
1. How to confirm and prove that
mangrove can trap metal(loid)s
in water?
2. What method can be used to
determine and demonstrate?

10. Method can be used to prove the role of mangrove for
metal(loid)s trapping?
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Sampling sites:
- Sites are considered as input and output of contaminants that have
mangrove and without mangrove, respectively.
- Site is located at the river mouth.
Control sites (i.e.
input of mangrove)
Intervention sites
(within the
mangrove or without
mangrove)
Control site (output
of mangrove or
river mouth)

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Sample collection:
Samples
Filtrate and
Suspended
particulate
matter
Surface
sediment
Mangrorve
sediment
Mangrove
tissues
Method can be used to prove the role of mangrove for
metal(loid)s trapping?

12. Case study in Hai Phong city
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Where:
Control sites: 1, 4, 7
Intervention sites: 2, 3, 5, 6
Sampling sites expressing in yellow: mangrove-dominated area (Da Bac-Bach Dang River)
Sampling sites expressing in red: without mangrove area (Cam River)

13. Case study in Hai Phong City
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Water filtration to collect
filtrate and suspended
particulate matter
Sampling surface
sediment
Sampling mudflat to
mangrove sediment
Sampling at field

14. Case study in Hai Phong City
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Temporal variation of total metal(loid) concentration in water
At both
tributaries:
Concentrations of
metal(loid)s at
intervention sites
were higher than
those measured
at control sites.
 Site 1, 2 and 3: Cam River
 Site 4, 5 and 6: Da Bac-Bach Dang River

15. Case study in Hai Phong city
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At both tributaries:
Concentrations of
metal(loid)s at
intervention sites were
higher than those
measured at control sites.
 Site 1, 2 and 3: Cam River
 Site 4, 5 and 6: Da Bac-Bach Dang River

16. Case study in Hai Phong city
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Mangrove-dominated area: Da Bac-
Bach Dang River:
Concentrations of metal(loid)s at
output of mangrove (Site 6) were
lower than those measured at
input site (Site 5).
=> Potential role of mangrove for
contaminant reduction
 Site 1, 2 and 3: Cam River
 Site 4, 5 and 6: Da Bac-Bach Dang River

17. dy in Hai Phong city
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Map of distribution of different industries in Hai Phong (Note: this
distribution is compiled of companies with location data on
Google Maps)
=>Higher concentrations
at site 5 than site 6 could
be caused by iron and
steel production,
shipbuilding industry,
and charcoal port
5
6
Sampling site

18. Case study in Hai Phong city
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Interventions sites at without
mangrove area: Cam River:
Concentrations of metal(loid)s
at intervention sites (Site 3)
were higher than those
measured at Site 2.
 Site 1, 2 and 3: Cam River
 Site 4, 5 and 6: Da Bac-Bach Dang River

19. dy in Hai Phong city
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=> Increasing of
metal(loid)
concentration can be
orginated from iron
and steel facilities,
port, and
Shipbuilding
activities.
2
3
Sampling site
Map of distribution of different industries in Hai Phong (Note:
this distribution is compiled of companies with location data on
Google Maps)

20. Case study in Hai Phong city
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Metal(loid) concentrations in surface sediment
Concentration of metal(loid)s in order of:
Al > Fe > Mn > Zn > Cr > Pb > Cu > Ni > As> Cd
 Within the range of concentration
measured in other River in Vietnam:
 Sai Gon River (Strady et al. 2017)
 Thi Vai River (Costa-Boddeker et al. 2017)

21. Enrichment Factor
(EF) 𝑀𝑒 𝑠𝑜𝑖𝑙, 𝐴𝑙 𝑠𝑜𝑖𝑙: concentration of metal(loid)
and aluminium in sediment
𝑀𝑒 𝑐𝑟𝑢𝑠𝑡, 𝐴𝑙 𝑐𝑟𝑢𝑠𝑡 concentration of metal(loid)
and aluminium in crust surface (Wedepohl
1995)
Level Value Caterogisation
0
1
2
3
4
5
6
EF ≤ 1
1 ≤ EF ≤ 3
3 ≤ EF ≤ 5
5 ≤ EF ≤ 10
10≤ EF ≤ 25
25 ≤EF ≤ 50
50≤ EF
No enrichment
Minor enrichment
Moderate enrichment
Moderately severe enrichment
Severe enrichment
Very severe enrichment
Extremely severe enrichment
𝐸𝐹 =
(
𝑀𝑒
[𝐴𝑙]
) 𝑠𝑜𝑖𝑙
(
𝑀𝑒
[𝐴𝑙]
) 𝑐𝑟𝑢𝑠𝑡
Natural or
anthropogenic
source
Wedepohl, K.H., The composition of the continental crust. Geochimica et cosmochimica Acta, 1995. 59(7): p. 1217-1232.
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22. Case study in Hai Phong city
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Enrichment Factor of metal(loid)s in surface sediment
- Fe, Mn, Ni, Cu và Zn: 1 < EF< 3
(Minor enrichment).
- Cd và Pb: 3 < EF < 10
(Moderate to moderately
severe enrichment).
- Notably, As: 10 < EF < 25:
Severe enrichment.
Most of metal(loid)s may
originate from anthropogenic
activities

23. Index of Geo-accumulation (Igeo)
𝐼𝑔𝑒𝑜 = log2
𝐶 𝑛
𝐵𝑛 × 1.5
𝐶 𝑛: Metal(loid) concentration in sediment
𝐵𝑛: the background value for the metal n
1.5 is used because of possible variation in
background data due to lithological variation
Level Value Quantification
0
1
2
3
4
5
6
𝐼𝑔𝑒𝑜 ≤ 0
0 ≤ 𝐼𝑔𝑒𝑜 ≤ 1
1 ≤ 𝐼𝑔𝑒𝑜 ≤ 2
2 ≤ 𝐼𝑔𝑒𝑜 ≤ 3
3 ≤ 𝐼𝑔𝑒𝑜 ≤ 4
4 ≤ 𝐼𝑔𝑒𝑜 ≤ 5
5 < 𝐼𝑔𝑒𝑜
Uncontaminated
Uncontaminated to moderately contaminated
Moderately contaminated
Moderately to heavily contaminated
Heavily contaminated
Heavily to extremely contaminated
Extremely contaminated
Any increase
can be caused
by human
impact
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24. Case study in Hai Phong city
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- Cu, Zn, Cd and Pb: 0 < Igeo< 2:
moderately contaminated
- Notably, As: 3 < Igeo: Heavily
contaminated
Index of Geo-accumulation in surface sediment
Most of metal(loid)s were
caused by human activities

25. Case study in Hai Phong city
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Metal stock (t ha-1)
= (Csediment * BD * 50 * 100)/106
where:
Ctrầm tích: average total metal(loid) concentration in
the upper 50 cm (mg kg-1)
BD: average bulk density in the upper 50 cm (g cm-3)
50: length of the cores used for estimation of
metal(loid) stock (cm)
100: conversion factor from g cm-2 sang t ha-1
106: conversion factor of a metal(loid) concentration
in mg kg-1

26. Case study in Hai Phong city
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 Most of metal(loid) stocks
increased from mudflat to
the mangrove stand.
 Exept Mn, its stock was
lower in the mangrove
stand than other one.
Why???
Concentration of : Al > Fe >
Mn > Zn > Cr ~ Pb > Cu ~ Ni >
As > Cd

27. Case study in Hai Phong city
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Most of metal(loid) stocks increased
from mudflat to the mangrove stand.

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Metal(loid) accumulation in mangrove tissues
Leaf
Root
Interface between sediment-air
50 cm of
sediment
depth
Saplings
Mature trees
Saplings
Mature trees
Bioconcentration factor
(BCF) = Ctissue/ Csediment
Case study in Hai Phong city

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=> Mn was accumulated at high
concentration in different parts
of mangrove, notably in leaf.
Bioconcentration factor
(BCF) = Ctissue/ Csediment
Case study in Hai Phong city

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Summary
 Mangrove acts as natural sink that stores and contributes for reducing
metal(loid) contaminants in water flowing through its system.
 The method applied in the Hai Phong city can be deployed to other areas in
Vietnam.
 The results indicated that iron and steel manufacturing facilities, shipbuilding,
coal ports and ship ports can be main sources of metal(loid) emissions.
Protection of mangrove should be strengthened to enhance the value of their
ecological services.
It is necessary to develop a policy of payment for metal(loid) contaminant
reduction/ self-cleaning services to fund the conservation and expansion of
mangrove.
Case study in Hai Phong city

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