WATER QUALITY OF TAM GIANG – CAU HAI LAGOON SYSTEM AND
ENVIRONMENTAL CARRYING CAPACITY OF CONCENTRATED AQUACULTURE
AREA IN SAM CHUON LAGOON, VIETNAM
PhD student: Le Cong Tuan;
Supervisors: Prof. Massimo Sarti, Prof. Alessandra Negri
The natural resources of 22.000ha of Tam Giang – Cau Hai lagoon system in recent years showed
over-exploitation, mainly in reduced water quality, exhausted aquatic animal resources. Most
concentrated area of aquaculture as Sam Chuon lagoon showed the overlap, polluted by organic
matter, nutrient, and disease over break (Department of fishery, Vietnam, 2006). In order to
effectively manage the area and re-planning base on full comprehension about the lagoon included
environment carrying capacity are urgently needed.
The hypothesis of the research: 1) Water quality parameters of Tam Giang – Cau Hai lagoon
system does not exhibit significant seasonal changes and overall satisfies the Vietnamese standards
for coastal areas. 2) The development of aquaculture in the concentrated aquaculture area is not
exceeding yet the environment carrying capacity of the lagoon.
The purposes of the research: 1) Evaluate the state of water quality in the Tam Giang – Cau Hai
lagoon based on main parameters and preliminary lagoon zoning with salinity based. 2) Estimate
environment carrying capacity of concentrated aquaculture area (CAA) at Sam Chuon lagoon and
provide suggesting scenarios for sustainable develop of aquaculture in the area.
Contents and methodologies: Measured and analysis 36 sites on 12 transects along Tam Giang –
Cau Hai lagoon system for Temperature, pH, Salinity, DO, BOD5, COD, TN, TP, Total coliform,
fecal coliform in 4 months, and in the concentrated aquaculture area for temperature, pH, Salinity,
DO, BOD5, COD, TN, TP during the same time. In parallel, 13 ponds representative of exit
aquaculture models in high and low tide area of 4 communes were used to study temperature, pH,
Salinity, DO, BOD5, COD, TN, TP in the period of April, May, June, July and August. Estimate
water exchange between CAA of Sam chuon lagoon and Tam Giang – Cau Hai lagoon in the
purpose use for calculate environmental carrying capacity of CAA, measured tidal level, depth,
velocity, salinity, in representative of maximum, average and minimum tidal cycle of dry season.
Method for analyzing waste and nutrient concentration in water was used Standard Methods for
Examination of Water and Wastewater (APHA, USA, 1995). For measure the water exchange
Standard methods of marine hydroteorological centre-Vietnam (1981) was followed. Estimate
Environmental carrying capacity was applied methods of Christensen M.S., 2005. For aquaculture
survey, we used combined Geographic Information System, Global position system and
Participatory Rural Appraisal techniques in the top-down and bottom-up survey. Following
Vietnamese standards were used to discuss in the thesis 1) Coastal water quality standard. 2) Water
quality standard for industrial effluents discharged into coastal waters used for protection of aquatic
life. 3) Water quality - Surface water quality standard, 4) The procedure for intensive culture of
Tiger shrimp. All the statistic test applied in the research based on Statistical Package for the Social
Sciences version 11.0 (SPSS), The GMAV software package (University of Sydney), and
Permanova v.1.6 (M.J. Anderson, department of statistics, University of Auckland, 2005).
The main finding and conclusion:
- The depth of Tam Giang – Cau Hai lagoon in range from >0 to 11m, most the parts of Tam Giang
– Cau Hai lagoon have depth around 1-3m and the deepest site toward to Thuan An inlet up to 11m.
The depth of the lagoon is very suitable to develop pond and cage aquaculture.
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- Water quality parameters in terms of temperature, BOD, COD, TN, TP in Tam Giang – Cau Hai
lagoon sanctified the Vietnamese standards for coastal areas [66]. Some areas in Tam Giang – Cau
Hai lagoon, pH of water already exceeded the Vietnamese standards for coastal and lagoon areas
[66]. This information has to be carefully consideration in future planning of lagoon activities,
especially for apply and locate sustainable culture species and models.
- Salinity stratification and quick changed in Tam Giang – Cau Hai lagoon during the summer and
raining seasons, it bring negative affected to aquaculture production in term difficult to select culture
species, models, and cannot prevent salinitization impact.
- Decline of oxygen in some places can be the evident of high concentrated of aquatic organism and
partial accumulation of organic matter in Tam Giang – Cau Hai lagoon. These places, dissolved
oxygen concentration are lower than the Vietnamese standards for coastal and lagoon areas [66].
This is the dark points have to be consideration in the development planning for aquaculture.
- The big alarm for water quality in the Tam Giang – Cau Hai lagoon is bacteria pollution. Total
coliform in lagoon water was higher than allowable standard from 3 to 30 times. In many places
showed 430 to 750 times higher than the Vietnamese standards for coastal and lagoon areas [66],
especially high density of fecal coliform, it could be the cause of diseases on aquatic animals and
local people [77].
- There are 3 sub-lagoon zones with salinity based can be consider for suitable aquaculture models in
Tam Giang – Cau Hai lagoon: 1) Fresh-brackish water area is suitable for fresh aquaculture as pond
and cage culture of silver carp (Hypophthalmichthys molitrix), grass carp (Ctenopharyngodon
idella), common carp (Cyprinus carpio), and catfish and eel (Anguilla anguilla). 2) Brackish water is
very sensitive area with quick and high changing of salinity so the suitable models is pond culture
with wide salinity tolerant species as tilapia (Oreochromis niloticus, Oreochromis mosambica), tiger
shrimp (Penaeus monodon), Cyprinus centralus, greasy-back shrimp (Metapenaeus ensis). 3)
Brackish - saline water area is suitable with all the aquaculture models with brackish water species
as mud crab (Scylla serrata) and high salinity tolerance species as snappers (Lutjanus sp.), groupers
(Epinephelus sp.), rabbit fish (Siganus guttatus) and black kingfish (Rachycentron canadum).
- Overall water quality situation at Tam Giang – Cau Hai lagoon system was not different among the
fresh-brackish, brackish, brackish-saline and saline water areas but different between dry and rain
seasons.
- The cause of water polluted, reduced water exchange, and algae bloom in Sam Chuon lagoon are
unplanned development, and used fresh feed, homemade feed [67]. One of the solutions for long
term develops of aquaculture and increase environmental carrying capacity of the lagoon has to
reduce and then stop these harmful activities.
- The development of aquaculture area in the lagoon has exceeded the environmental carrying
capacity for organic matter (BOD, COD) of the Sam Chuon lagoon. Future development of
aquaculture in CAA of Sam Chuon lagoon has to reduce aquaculture area or apply the friendly
environmental models or apply organic matter waste treatment techniques.
The possibility scenarios can be applied to get better environmental carrying capacity is keep the
same area of 157.9 ha of high tide pond then reduce 46.8 ha of low tide pond area.
Recommendation: update the result of water quality and environment carrying capacity in the replanning of aquaculture area in the Tam Giang – Cau Hai lagoon system and the Sam Chuon and use
the master plan for sustainable development of aquaculture in term of environmental carrying
capacity at Sam Chuon lagoon.
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