199

ORIGINAL PAPER

Characteristics of Water Quality and Nitrogen-AssociatedBacterial Functions in Mekong Delta Mangroves
Tomomi INOUE* and Tetsumi ASANO
National Institute for Environmental Studies
16-2 Onogawa Tsukuba, Ibaraki 305-8506, Japan*e-mail: tomomi.inoue@nies.go.jp
0Abstract
Rapid changes, such as urbanization and artificial field expansion, are occurring in mangrove regions
worldwide. To assess the characteristics of nitrogen-related processes in mangrove forests in the Mekong
delta in relation to conditions in the surrounding environment, we measured water quality: inorganic nitrogen,inorganic phosphate and heavy metals; and nitrogen-associated bacterial activities: nitrogen-fixing activity
and nitrogen-consuming activity. The water quality results suggest that key changes in Mekong delta mangroves include a high input of ammonium, phosphorus and heavy metals from cities and aquaculture farms
upstream. The current value of mangrove soil bacterial nitrogen fixation in the Mekong delta, 0.87-24.57
mg N m-2 d-1, has dropped to within the previously reported order of other mangrove regions. We determinedthat the addition of ammonium had reduced soil nitrogen fixation to less than half that of the control treatment.
The addition of aquaculture pond water also suppressed soil nitrogen fixation. We postulated that if drainage
from the artificial systems upstream continuously supplies the mangroves downstream, part of the mangrove
soil nitrogen will shift from atmospherically-derived nitrogen to anthropogenically-derived nitrogen. If thenitrogen input from the upstream region exceeds the nitrogen-consuming capacity of the mangrove forest,
effects on plant growth due to excessive ammonium and eutrophication of the surrounding ocean will be aconcern.
Key words: heavy metals, mangrove, nitrogen, nitrogen fixation, phosphorus, water characteristics

1. Introduction
Mangrove plants form highly productive ecosystems
on coastlines of tropical and subtropical regions. These
ecosystems support large plant and animal communities,
many of which are economically and ecologically important (Bunt, 1992). Despite their importance in ecosystems, mangrove areas have been continuously declining around the world (Spalding et al., 2010), and the
Mekong delta is no exception (Hong, 2004). In the pastfew decades, many mangrove forests in the Mekong delta
have been converted to fields for aquaculture and agriculture. Furthermore, expanding urbanization in neighboring areas typically brings environmental change to mangrove ecosystems. The effects of these human-induced
impacts on mangrove ecosystems have become a serious
concern. The disappearance of habitats because oflarge-scale deforestation affects the animals living in theforest, and also fish and shellfish in neighboring water
bodies. In addition to these obvious changes, subtler
changes should also be discussed. For example, qualitative changes to the remaining mangrove forests causedby the intrusion of nutrient loadings and other chemicals
Global Environmental Research
17/2013: 199-206
printed in Japan

from sewage, aquaculture and agriculture have not been
fully studied. To assess some of these changes, this study
focused on one key element, nitrogen. Nitrogen is one of
the most important elements for plant growth, and thus
the nitrogen level in the rooting zone of the soil reflects
the conditions for plants. The coastline, the habitat for
mangrove plants, is generally a nitrogen-exporting region.
Large amounts of organic matter containing some nitrogen are continuously lost from the mangrove forest to theocean by tidal processes (Boto ＆ Robertson, 1990). Boto
＆ Bunt (1981) calculated the amount of nitrogen exported via tidal activity from a large mangrove forest in
northern Australia, and found that approximately 13% of
the average annual forest net primary production nitrogenrequirement was lost in this manner. Therefore, to maintain mangrove plant growth, the tidal nitrogen loss needs
to be balanced by nitrogen inflows. There are two main
nitrogen inflow pathways: (i) imports from the freshwater or terrestrial surroundings, and (ii) bacterial nitrogen
fixation. The supplied nitrogen is mainly consumed by(a) plant growth; (b) bacterial assimilation; and (c)bacterial nitrification–denitrification in mangrove forests.
To assess the characteristics of nitrogen-related processes©2013 AIRIES

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T. INOUE and T. ASANO

in the Mekong delta mangrove forests in relation to theconditions of the surrounding environment, we measured
water quality and nitrogen-associated bacterial activities.

2. Study Area and Methods
2.1 Sampling sites
Water quality and bacterial activities were measured
in the following mangrove ecosystems of the Mekong
delta in Vietnam: Ho Chi Minh, Soc Trang and Ca Mau(Fig. 1). The Can Gio mangrove forest is a 30,000 ha
second-growth forest located 20-30 km downstream
from the center of Ho Chi Minh City. The species plantedin the forest was Rhizophora apiculata. The current forest thus mainly comprises R. apiculata, while there arenaturally occurring species such as Avicennia spp. andSonneratia spp. Because of its ecological importance,
this forest has been acknowledged as a UNESCO
Biosphere Reserve since 2000. Although the forest is not
currently a candidate for large-scale deforestation followed by conversion to fields, it is surrounded by many
paddy fields and aquaculture ponds. Furthermore, thegrowth of Ho Chi Minh City has been significant in thepast few decades, as it has become highly populated andits industrial area has expanded.
The Soc Trang mangrove forest is located on a sandbank, Cu Lao Dung, formed in the estuary of the mainstream of the Mekong River. Here, the afforested mangrove, Sonneratia caseolaris is distributed from thefringe of the coastline to about 1 km inland. Behind themangrove forest, many paddy fields, aquaculture ponds
and houses have been constructed, and shrimp farming is
the main form of aquaculture. There are two types ofcultivation: (i) separate shrimp ponds and mangrove
forest farms, and (ii) mixed farms where the shrimp
ponds consist of a series of long channels dug through themangrove forest. The separated farms are currently
dominant in Cu Lao Dung. Drainage from these artificial
systems runs into man-made canals and finally out to theocean through the mangrove forest.
The Ca Mau peninsula of the lower Mekong delta has
51,000-52,000 ha second-growth mangrove forest. Man-

Fig. 1 Aerial photograph of field sites in the Mekong delta.

grove plants, mainly R. apiculata, are distributed fromthe fringe of the coastline to about 1 km inland. The
center of Ca Mau is located 40-50 km inland from thecoastline. Ca Mau has grown into one of the biggest commercial centers in the Mekong delta. The population has
increased year by year, and many aquaculture ponds havebeen constructed. Shrimp farming is the main form ofcommercial aquaculture, and mixed-type farms are currently dominant in Ca Mau Province.
Sampling stations (n = 32) were located in thesemangrove ecosystems (Table 1), and categorized into thefollowing six groups: (i) canals in urban areas, (ii) rivers,(iii) canals through aquaculture farms, (iv) separate-type
shrimp farms, (v) mixed-type shrimp farms, and (vi)mangroves.
2.2 Water sampling procedure
Water from the canal or river was collected in a 1-liter
polypropylene bottle and 30 ml of the water was immediately filtered through a 0.2-µm filter (DIDMIC-25cs,
cellulose acetate, ADVANTEC, Tokyo, Japan) with aplastic syringe (ss-30ESZ, TERUMO, Tokyo, Japan) to
remove bacteria. The sampling procedure was repeatedthree times at each sampling station during the lowest
tidal conditions in September 2009.
In the middle of the forest, soil pore water was collected with a water-sampling tube rather than using thesampling procedure described above. The watersampling tube comprised three parts: (a) an unglazed
Table 1 A list of the sampling stations in the Mekong delta.
StationCategory
Location
Can Gio1
Urban area
10˚47′36.08″ 106˚41′51.01″
2
Urban area
10˚44′13.05″ 106˚42′11.03″
3
Urban area
10˚46′29.03″ 106˚42′25.03″
10˚39′58.05″ 106˚46′30.03″
4River
10˚35′03.07″ 106˚49′32.02″
5River
10˚31′23.00″ 106˚52′09.01″
6River
10˚23′38.02″ 106˚55′14.00″
7River
10˚31′19.64″ 106˚51′31.78″
8
Mangrove forest
Soc Trang
09˚29′36.44″ 106˚13′57.42″
9River
09˚29′26.05″ 106˚14′16.32″
10
River
11
Shrimp pond (S)09˚30′33.98″ 106˚13′53.94″
12
Shrimp pond (S)09˚30′29.99″ 106˚14′07.13″
13
Shrimp pond (S)09˚31′30.55″ 106˚13′18.96″
14Canal in shrimp farm (S) 09˚30′28.77″ 106˚13′57.86″
15
Canal in shrimp farm (S) 09˚30′22.90″ 106˚14′07.11″
16
Canal in shrimp farm (S) 09˚30′14.06″ 106˚14′15.05″
09˚29′34.44″ 106˚14′16.91″
17
Mangrove forest
09˚30′01.98″ 106˚14′14.11″
18
Mangrove forest
Ca Mau19
Urban area
09˚10′49.09″ 105˚08′58.04″
20
Urban area
09˚10′39.00″ 105˚08′55.00″
21
Shrimp pond (S)08˚53′20.09″ 105˚18′51.02″
22
Shrimp pond (S)08˚53′18.84″ 105˚18′47.19″
23
Shrimp pond (S)08˚53′19.27″ 105˚18′45.17″
24
Canal in shrimp farm (S) 08˚53′21.14″ 105˚18′42.25″
08˚53′26.61″ 105˚18′46.79″
25
Mangrove forest
26
Shrimp pond (M)08˚39′30.03″ 105˚04′02.06″
27
Shrimp pond (M)08˚39′28.07″ 105˚04′04.82″
28
Shrimp pond (M)08˚39′10.99″ 105˚03′43.94″
29
Shrimp pond (M)08˚39′28.03″ 105˚04′01.03″
30
Mangrove forest (M)08˚39′26.77″ 105˚03′59.81″
31
Mangrove forest (M)08˚39′09.68″ 105˚03′47.13″
32
Mangrove forest (M)08˚39′19.15″ 105˚04′14.06″(S) Separate-type shrimp farm; (M) Mixed-type shrimp farmMekong Delta Mangroves: Water Quality and Bacteria

tube (2 mm diameter, 10 cm length), (b) a teflon-lined
tube (2 mm diameter, 30 cm length), and (c) a hollow
needle. The unglazed tube was buried in the sediment to
depth of 10-20 cm. To collect the soil pore water, theneedle was inserted into the silicon lid of a vacuumsealed glass vessel, and soil pore water was drawn into
the vessel through the teflon-lined tube. The first 2 ml ofwater were discarded and the next 30 ml were filteredthrough the 0.2-µm filter as described above. The
samples were held below 5°C in a cooler bag prior tochemical analysis.
2.3 Chemical analysis of water
The dissolved inorganic nitrogen (NO2-, NO3- andNH4+) and phosphate concentrations in the water samples
were measured with an auto-analyzer (AACS-II, BRAN+
LUBBE, Norderstedt, Germany). Dissolved inorganic
heavy metal concentrations (As, Pb, Cd, Cr, Cu, Zn, Ca,
Fe, Mn, Mo, Sr and Ti) were measured by an inductively
coupled plasma atomic emission spectrometer (ICP-JA,
Nippon Jarrell-Ash, Kyoto, Japan) after diluting thesamples in 1 N nitric acid.
2.4 Bacterial activity
The potential activity of soil nitrogen-consuming
bacteria was determined using the following procedure.
A 49-ml soil core collected at a soil depth of 1–6 cm wastransferred to a 200 ml teflon flask together with 120 mlof the surrounding water. The solution was adjusted to
100 µM ammonium by adding ammonium chloride, andshaken in the dark at 28°C. After 0.3, 3 and 6 h from thestart of the incubation, 30 ml of the solution from eachflask was filtered through the 0.2-µm filter. The concentration of inorganic nitrogen in the solution was determined using the auto-analyzer. The potential activity ofthe bacteria consuming the inorganic nitrogen was determined by the decrease in inorganic nitrogen in the samples with time, using a linear regression analysis.
Soil nitrogen fixation was indirectly measured using
the acetylene reduction technique (Hardy et al., 1986). A
5 ml soil core (1 cm in diameter, 5 cm in height) from a
1-6 cm soil depth collected within the mangrove forest
was transferred to a 50 ml glass vial with 5 ml of thesurrounding water. Fifteen vials were prepared for each
forest. The vials were purged with argon to provide ananoxic atmosphere, and sealed with teflon–silicon septa.
For five of the vials, 4 ml of the gas phase were evacuatedand replaced with acetylene via the Teflon–silicon septa.
Five other vials were prepared without acetylene as blanktest. The remaining five vials were used to assess
eutrophication, and were incubated with added ammonium. The vials were shaken in the dark at 28°C, and
0.2 ml of the gas phase was sampled at 0.3, 5 and 10 hafter the acetylene was introduced. Ethylene concentrations in the gas samples were determined with a gas chromatograph equipped with a Porapak N column and FID
detector (GC-4000, GL Science Inc., Tokyo, Japan). The
activity of the nitrogen-fixing enzyme nitrogenase wasdetermined from the accumulation of ethylene in the201vials with time, using a linear regression analysi.

3. Results and Discussion
3.1 Water characteristics
3.1.1 Inorganic nitrogen and inorganic phosphate
Very high concentrations of inorganic nitrogen weredetected in the urban regions, Stations 1-3, 19 and 20(Fig. 2). Most of the dissolved inorganic nitrogen in thewater was present as ammonium, NH4+. This suggeststhat nitrogen in the urban system is mainly draining out
as ammonium, and/or that the bacterial metabolic processes in these canals are mainly anaerobic, which convert dissolved nitrogen to the reduced ammonium form.
In the downstream river waters (Stations 4-7, 9 and 10),
total inorganic nitrogen concentration was decreased.
Most of the dissolved inorganic nitrogen was present as
nitrite and nitrate, probably because of bacterial nitrification processes in the aerobically stirred stream. In theseparate-type shrimp ponds (Stations 11-13 and 21-23),
total inorganic nitrogen concentration in the pond water
was comparatively low and mainly present in the form ofammonium. However, in the canals receiving drainage
from the ponds (Stations 14-16 and 24), a comparatively
higher total inorganic nitrogen level was detected. Whilemost of it was in the form of ammonium, one-third appeared as nitrite and nitrate. In the mixed-type shrimp
farm systems (Stations 30-32), the total inorganic nitrogen concentration in the water was extremely high andmost of it appeared as ammonium.
The phosphate concentration was remarkably high in
the urban regions (Fig. 3). The phosphate concentrationin water was lower in the downstream river. The separate-type shrimp farm systems showed high levels of
dissolved phosphate, both in pond waters and in thecanals receiving drainage from the ponds. Levels of dissolved phosphate in the mixed-type shrimp farm systems
remained at a low level. The phosphate levels in the two

Fig. 2 Inorganic nitrogen dissolved in water in the Mekong delta.
Results are expressed as mean ± standard error (n = 3–6).
Different letters indicate significant differences (p < 0.05).

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T. INOUE and T. ASANO

types of shrimp farm systems contrasted with the levels
of inorganic nitrogen (total inorganic nitrogen was highin the mixed-type systems and low in the separate-typesystems) (Fig. 4).
Most of the mangroves (Stations 8, 17, 18 and 25)
were categorized as low-nutrient areas (Fig. 4). Concentrations of dissolved inorganic nitrogen and phosphate intropical mangrove forests are generally reported to below (within the µM range) because of the rapid and efficient uptake of dissolved materials by bacteria (Alongi
et al., 1992). An exception was the mangroves in mixedtype shrimp farms (Station 30), which fell within the
category of mixed-type shrimp ponds (high levels of
inorganic nitrogen while phosphate levels were low).

Fig. 3 Inorganic phosphate dissolved in water in the Mekong
delta. Results are expressed as mean ± standard error(n = 3–6). Different letters indicate significant differences(p < 0.05).

Fig. 4 Water characteristics of mangrove ecosystems in the
Mekong delta.

3.1.2 Heavy metals
Of the metals analyzed, comparatively high levels ofarsenic, cadmium and lead were detected; mean values
exceeded the World Health Organization (WHO) standard for drinking water in some categories (Fig. 5). Highlevels of arsenic and cadmium were detected in the
shrimp farm systems and the canals receiving drainage
from the separate-type ponds. This observation suggeststhat the shrimp farm system may be a source of the two
metals in drainage waters. Although the concentrationlevels were not as high, titanium showed a similar pattern
to that of arsenic and cadmium. High levels of lead weredetected in the urban regions and their river waters; meanvalues exceeded the WHO standard for drinking water inthese two categories. In addition to lead, the iron concentration was higher in the urban regions compared withthe other categories. One interpretation of this could bethat the urban system may be a source of lead and iron. In
mangrove soil pore water of these regions, higher concentrations of lead, manganese, chromium, zinc andmolybdenum were detected compared with those of theother stations. These elements might accumulate in thesoil through the ability of soil particles to adsorb metal
ions, and the bacterial mineralization process allows
them to become soluble. Relatively high levels of calcium and strontium in the shrimp farm systems may be
attributed to the influence of seawater, because thisgenerally contains comparatively high levels of these twoelements compared with freshwater. Furthermore, separate-type shrimp ponds need the addition of CaCO3 inorder to regulate the pH conditions of the water, because
these types of ponds tend to become acidic due to oxidation of pyrite. This may be a reason for the higher concentration of calcium in separate-type ponds than in
mixed-type ponds.
3.1.3 Bacterial activity
On a dry-weight basis, the potential activity of inorganic nitrogen-consuming bacteria was considerably
higher in root materials than in soil, probably because of
the high nitrogen requirements of root cells (Fig. 6). The
background soil nitrogen-consuming activity was calculated as 1.5-3.9 g N m-2 d-1 (Table 2). This value can only
be applied to the top 1-6 cm of soil and therefore the rateof inorganic nitrogen consumption over the entire mangrove forest, including deeper soil, must be higher than
this. There may be an effective nitrogen-exporting process in the mangrove root zone; that is, a nitrification–
denitrification process. The first step in this process is theoxidation of ammonium nitrogen in soil pore water toform nitrite-N. The nitrite-N is reduced in the anoxic
zone to form gaseous-N, which is then lost to the atmosphere. This process is accelerated when oxic and anoxic
conditions co-exist, as is the case in the mangrove rootzone. Most mangrove species develop aerial root systems
to transport oxygen through internal lacunae (gas-spacecontinua) to their root tips, which are buried in hypoxic
sediments. A portion of this oxygen diffuses toward therhizosphere via the root surface, and forms a thin oxida-

Mekong Delta Mangroves: Water Quality and Bacteria

203

Fig. 5 Dissolved metal concentrations in the Mekong delta. Orange lines indicate the standard for drinking
water set by the World Health Organization. Results are expressed as mean ± standard error (n = 3–6).
Letters indicate significant differences (p < 0.05).
Table 2 Background upper-soil inorganic-nitrogenconsuming activity in mangrove soils.
StationCan Gio8
Soc Trang
17
18
Ca Mau25
30

Fig. 6 Inorganic nitrogen-consuming bacterial activity by soil androots in Mekong delta mangrove forests. Results are
expressed as mean ± standard error (n = 5). Different letters
indicate significant differences (p < 0.05).

N-consuming potential[gN area m-2 day-1]
3.5 ± 0.2
2.2 ± 0.4
1.5 ± 0.5
3.9 ± 0.5
3.6 ± 0.3
Mean ± SDtive layer. It has been reported that the soil redox potential is higher in the mangrove rhizosphere than in the
non-rhizosphere (Thibodeau & Nickerson, 1986; McKee
et al., 1988; McKee, 1993). It is likely that nitrification
would occur in this oxic zone.
The potential of nitrogen-fixing activity was significantly higher in root materials than in soil (P < 0.05,
Fig. 7). This can be interpreted to mean that nitrogenfixing bacteria are more abundant in the mangrove
rhizosphere than in bulk soil or in the bacteria colonizing
root materials. Detection of nitrogen-fixing activity inmangrove root materials (Inoue et al., 2011a) has beenreported in previous studies. Inoue et al. (2011b) reported
that nitrogen content (C:N) was significantly higher inthe mangrove root zone than 10 cm away from the rootzone. The high levels of nitrogen may be due to dead root204

T. INOUE and T. ASANO

Fig. 7 Nitrogen-fixing activity by soil and roots under control, ammonium fertilization (2.8 ppm NH4+)and shrimp-pond-water-added conditions, respectively, in the Mekong delta. Results are expressed
as mean ± standard error (n = 5).

Fig. 8 Balance between nitrogen consumption andfixation.

detritus, which is abundant in the root zone, or to highlevels of bacterial nitrogen immobilization in the rootzone.
In Can Gio and Soc Trang mangroves, the balance
between nitrogen consumption and fixation was negativein the top 1-6 cm of mangrove soils, while it was substantially positive in root materials (Fig. 8), indicating that
nitrogen input to mangrove roots was guaranteed bynitrogen fixation itself. In contrast, the nitrogen balance
was negative in both soil and root materials in the Ca
Mau mangroves.
3.1.4 Effect of ammonium input on nitrogen fixation
The water quality results suggest that one of the key
changes occurring around the mangrove forests is highnitrogen input from the urban areas upstream. Apart fromthe mangroves in the Ca Mau region, the addition ofammonium (2.8 ppm NH4+) reduced the potential ofmangrove soil nitrogen-fixing activity to less than half ofthe control treatment (Fig. 7). Ammonium is relatively
important in regulating nitrogen fixation in aquatic environments, because of the repression of nitrogenase
synthesis and rapid reversible inhibition of nitrogenase
activity (Capone, 1988). In contrast to the soil, thepotential nitrogenase activity of root material was not
reduced by the addition of NH4+ (Fig. 7). This suggeststhat the composition of nitrogen-fixing bacteria differs
between the bulk soil and the rhizosphere (or in root
materials), and the bacteria associated with root materials
are insensitive to NH4+. Some sulfate-reducing bacteria,such as those in the genus Desulfovibrio, are known to beinsensitive to NH4+ (Welsh et al., 1997). In Ca Mau
mangroves, the addition of ammonia did not reduce thepotential nitrogenase activity of either soil or root material. At Stations 30-32, the ammonium concentration insoil pore water was already high and thus the potential
nitrogenase activity might have already been suppressed.
Compared with the previously reported values (Potts,
1979; Hicks & Silvester, 1985; Boto & Robertson, 1990;
Woitchik et al., 1997; Kristensen et al., 1998; Alongi
et al., 2000; Sjoling et al., 2005), the value of bacterial
nitrogen-fixing activity in the Can Gio forest (Station 7)
and that in one of the Soc Trang forests (Station 18) analyzed in this study was not remarkably low comparedwith that in other forests. The values in the Ca Mau region (Stations 25 and 30) and in the other Soc Trangforest (Station 17) were comparatively low (Fig. 9). The
Soc Trang forest, Station 17, is located on the seaward
fringe, and thus the low bacterial nitrogen-fixing activity
might be attributed to its low soil organic matter (0.9%),
because the oxidation of organic matter is essential forMekong Delta Mangroves: Water Quality and Bacteria

205

Fig. 9 Nitrogen-fixing activity of soil analyzed in mangrove forests. Egypt 1979 (Potts, 1979);
New Zealand 1985 (Hicks & Silvester, 1985); Australia 1990 (Boto & Robertson,1990); Tanzania 2005 (Sjoling et al., 2005); Thailand 1998 (Kristensen et al., 1998);
Kenya 1997 (Woitchik et al., 1997) and Vietnam 1996 (Alongi et al., 2000).

nitrogen fixation. Alongi et al. (2000) analyzed soil
nitrogenase activity in three mangrove forests in the Ca
Mau region in 1996 (the 1996 Vietnam values in Fig. 9).
Compared with the values in 1996 and those obtained inthis study, the bacterial nitrogen-fixing activity in the Ca
Mau region seems to have fallen remarkably in thesethirteen years. Because the three mangrove forests inAlongi et al. (2000) are not the same forests studied here,some conditions such as forest age and surrounding
circumstances were not the same, and thus the resultsfrom the two studies cannot simply be compared. However, there is the possibility that expansion of mixed-type
shrimp farm areas have led to a reduction in the activityof nitrogen-fixing bacteria. A high level of ammonium
drainage from the upstream regions in this study would
affect the nitrogen balance in downstream mangrove
ecosystems. Consequently, part of the mangrove soil
nitrogen would shift from atmospherically derived N toanthropogenically derived N. If the nitrogen input fromthe artificial systems exceeded the nitrogen-consuming
capacity of the mangrove forest, effects on plant growth
due to excessive ammonium and eutrophication of thesurrounding ocean would occur. Finally, addition of theshrimp pond water also reduced potential nitrogenase
activity in the soil in the Soc Trang forest (Station 18) toless than half that of the control treatment (Fig. 7). The
water characteristics results indicate that the shrimp pond
water contained comparatively high levels of arsenic,
cadmium, calcium, strontium and titanium (Fig. 5). The
effect of heavy metals on nitrogen-associated bacteria inmangrove forests needs to be examined.

Acknowledgments
We thank Mr. Le van Shin, Manager of the Can Gio
Mangrove management board, and Mr. Cat Van Thanh,Vice Manager of the Can Gio Mangrove management

board; Mr. Ly Hoa Khuong, Coordinator of the Soc Trang
Province People’s Committee; Mr. Vo Nguon Thao,
Manager of the Forest Science Institute of Vietnam; andthe staff of the Minh Hai Wetlands Forest ResearchCenter, for their kind assistance with field work andproviding critical comments and advice. We would also
like to express our sincere gratitude to the organizers of
Action for Mangrove Reforestation (ACTMANG),
Messrs. Motohiko Kogo, Seiji Suda and Chiharu
Miyamoto, for their kind encouragement and assistancewith fieldwork. We wish finally to express our appreciation to Dr. Seiichi Nohara, researcher at the National
Institute for Environmental Studies; and Ms. Junko
Yamamura, technical expert of the Global Environmental
Forum, for their encouragement and support. This work
has been partly supported by a Grant-in-Aid for environmental studies by the Ministry of the Environment,
Japan.
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Tomomi INOUE
Tomomi INOUE is a senior researcher at the
National Institute for Environmental Studies
Japan (NIES). Her interest is in the ecophysiology
of wetland plants. In 2006 she joined the five-year
NIES core project focusing on the Mekong river
basin, and through her work on mangroves herinterest and involvement with these astonishingplants has developed.

Tetsumi ASANO
Tetsumi ASANO is a core member of Action for
Mangrove Reforestation (ACTMANG). He
worked as a staff member of the International
Society for Mangrove Ecosystems (ISME) from1992 to 1993. He moved to Vietnam as a resident
representative of ACTMANG in 1993, and will besupervising the reforestation of mangroves fortwenty years.

(Received 30 December 2012, Accepted 7 May 2013)