IJERD – International Journal of Environmental and Rural Development (2014) 5-2

Research article
erd

Variation of Important Nutrients Proportion on
Phytoplankton Distribution in Bang-tabun Bay,
Phetchaburi Province, Thailand
BOONTARIKA THONGDONPHUM*
Faculty of Agricultural Technology, Rajamangala University of Technology Thanyaburi,
Pathum Thani, Thailand
Email: Boontarika_T@exchange.rmutt.ac.th

SHETTAPONG MEKSUMPUN
Faculty of Fishery, Kasetsart University, Bangkok, Thailand

CHARUMAS MEKSUMPUN
Faculty of Fishery, Kasetsart University, Bangkok, Thailand

NISSARA THAWONSODE
Faculty of Fishery, Kasetsart University, Bangkok, ThailandBANTHITA SAWASDEE
Faculty of Agricultural Technology, Rajabhat Mahasarakham University, Mahasarakham,
ThailandReceived 4 January 2014

Accepted 11 August 2014(*Corresponding Author)

Abstract Bang-tabun Bay, the estuarine area is situated close to the Phetchaburi rivermouth, Phetchaburi Province. Petchaburi River flows in the west of the Kingdom and exits
into the Gulf of Thailand. This research study was conducted with sample collection ofaquatic environmental quality from September 2011 to May 2012. The results indicatedthe increasing level of NH4+, NO2-+NO3-, Si(OH)4 and PO43- in this area, which lead to thephytoplankton bloom phenomenon, thus, implied the mesotrophic to eutrophic status of
the area. Three phyta and 54 genera of phytoplankton were discovered in the river mouth.
The dominant groups were diatoms (Thalassionema), cyanobacteria (Trichodesmium), anddinoflagellates (Ceratium). In this study, Ceratium was classified to be the dominantgroup. Analysis of DIN:P and Si:P molar ratios of surface water were applied to examine
the factors influencing the abundance of phytoplankton in the estuarine systems. Thus, thechange of phytoplankton abundance should be considered to assess the water quality, andthereby more efficient aquatic environmental conservation of Bang-tabun Bay further.
Keywords nutrient proportion, phytoplankton, and Bang-tabun bay

INTRODUCTION
Bang-tabun Bay is located in the western part of the Gulf of Thailand. Petchaburi River isapproximately 118 kilometer in length with the catchment of 6,219 square kilometer. Runs fromPetchaburi province and flows toward the lower plain before discharging into the Gulf of Thailand(REO8, 2011). Pollution problems in the gulf can occur according to untreated municipal andindustrial wastewater, eutrophication, trace metals contamination and petroleum hydrocarbon(Cheevaporn and Menasveta, 2003). Eutrophication can be defined as excessive by algae growthwhen high concentration of nutrients, particularly phosphates and nitrates enrich in the water body
(Tantanasarit et al., 2013). The term 'harmful algal bloom' covers two characteristics that arecaused by microalgae and negative impact on anthropogenic activities (Zingone and Enevoldsen,2000). Regional Environmental Office 8 (REO8, 2011) reported that utilization of land along theⒸ ISERD100

IJERD – International Journal of Environmental and Rural Development (2014) 5-2

Petchaburi River was estimated to be 58% forest and 29% agricultural areas, in Phetchaburiprovince, respectively. Here, the river supports a resident population about 466,079 people or 1,772
people per square kilometer that related to the deterioration of water quality induced mainly bysewage, domestic discharges, and agricultural utilization (REO8, 2011). Those activities could becontributed to phytoplankton bloom phenomena along the coastal zones of this area.
OBJECTIVEThis study aims to assess the aquatic environmental factors and related impacts by utilization to thevariation of phytoplankton. The findings could be used to estimate a dissolved inorganic nutrient
ratio that achieves levels for serious consideration of nutrient criteria for water resources
conservation management and thereby sustainable utilization of this area.
METHODOLOGY
Sampling Sites and Survey Plan
The surveys were conducted at 18 sampling stations covered Bang-tabun Bay, the stations of whichwere grouped into two different characteristics: sub-tidal channel (B1-B12) and bivalve culture flat
areas in the upper (U1 and U2), middle (M1 and M2), and lower (S1-S2) areas, spanning from
September 2011 to May 2012 (Fig.1). According to the rainfall patterns, Thailand is under theinfluence of monsoon winds (TMD, 2012). The seasons can thus be divided into rainy season(May- September), and winter season (October-February).

1470000

B12
U11469000

U2

B11
B51468000

B2
B11467000
1466000

B10
M1B3

S1

B4

B6

M2

B7
S21465000

B9B8

1 km598000 599000 600000 601000 602000 603000 604000 605000 606000 607000 608000

sub-tidal channel (B1-B12) and bivalve culture flat areas in the upper (U1 and U2),
middle (M1 and M2), and lower (S1-S2)

Fig. 1 Survey stations of 18 major stations within two different characteristic of Bang-tabun
Bay, Petchaburi Province, Thailand
Sample Collection and Analysis
The general water quality factors, namely temperature, dissolved oxygen (DO), salinity, and pH
were measured with a multi-parameter probe (YSI-6600 Sonde instrument) at the sampling sites.
Samples of surface water (30 cm deep) were pre-filtered through GF/F (Whatman) and then stored
at 4oC before transporting to the laboratory for analysis of nutrients, including ammonium (NH4+),
nitrite and nitrate (NO2-+NO3-), silicate (Si(OH)4), and orthophosphate (PO43-), with a SKALARⒸ ISERD

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segmented flow analyzer. The samples for chlorophyll a (Chl a) and total suspended solids (TSS)
measurement were analyzed by the spectrophotometric method and the freeze-dried technique,respectively. Phytoplankton samples were collected and preserved in formaldehyde buffered
solution before being classified and enumerated with a Sedgewick-Rafter counting chamber undera light microscope.
Data Analysis
Comparisons of water quality in terms of temperature, salinity, DO, pH, Chl a, and TSS among thesampling periods and zones were performed using average levels and distribution characteristics.
Least Significant Differences (LSD) or Tamhane's T2 of Post Hoc test of the one-way analysis ofvariance (ANOVA) was used for the environmental variation comparison, and the level ofconfidence greater than 95% (p < 0.05) was considered to indicate a statistically significant impact.
The Mann-Whitney test was used where a normal distribution was not observed. The relationships
between nutrients as dissolved inorganic nitrogen (DIN; NH4++NO2-+NO3-) and orthophosphate
phosphorus (P), Chl a, and total phytoplankton density were analyzed using the Spearman rankcorrelation coefficient (rs). In this study, a confidence interval of more than 95% (p < 0.05) was
considered to indicate a statistically significant impact.
RESULTS AND DISCUSSION
Environmental Factors
The results indicated that freshwater runoffs had influence on water quality in the Bang-tabun Bay,
which in turn contributed to varying water quality by seasonal variation. Water temperatures wasslightly decreased with the seasons (p < 0.05), and low level of salinity was detected during
September 2011 due to the large freshwater discharges into the Bang-tabun Bay. The pH levelvaried from 7.22 to 8.67 for the entire study area. DO varied and was markedly decreased tounsuitable levels (< 4 mg/l) during the rainy season. Levels of TSS and Chl a were between 5.40 to147.65 mg/L and 3.58 to 29.64 g/L, respectively, with the both of highest levels in May 2012.
Thongdonphum et al. (2011) reported that Chl a of approximately 10 g/L has been regarded as theinitial level for eutrophication in the estuarine zone. The Mae Klong River (in the eastern part), had
Chl a levels 1.34 to 14.69 g/L (Thongdonphum et al., 2013), while the Tha Chin Estuary, locatedclosely to the study area, had a very high levels of Chl a in excess of 20 g/L and reached 535 g/L
when Noctiluca red tide outbreak is occurred (Meksumpun and Meksumpun, 2008).
Table 1 Water quality (mean±SD) in the Bang-tabun Bay during the study periods
Parameters
Temp (oC)
Salinity (psu)
DO (mg/L)pH
Chl a (g/L)
TSS (mg/L)
NH4+ (M)
NO2-+NO3- (M)
Si(OH)4 (M)
PO43- (M)

Study periods
December 201125.27 ± 0.64
21.70 ± 1.11
7.79 ± 0.95
8.49 ± 0.15
10.39 ± 5.07
15.68 ± 13.34
43.25 ± 13.98
2.78 ± 2.62
68.15 ± 28.47
2.00 ± 1.29

September 201130.65 ± 0.95
18.17 ± 5.17
6.03 ± 2.747.89 ± 0.31
11.98 ± 4.92
20.45 ± 16.37
30.71 ± 11.25
6.01 ± 4.17
126.65 ± 52.07
2.77 ± 1.58May 201230.92 ± 0.63
21.64 ± 2.96
3.41 ± 0.58
7.47 ± 0.13
12.31 ± 5.83
78.98 ± 45.67
40.98 ± 8.82
8.00 ± 2.84
137.98 ± 32.88
3.53 ± 0.78

The levels of NH4+ and NO2-+NO3- varied significantly (p < 0.05) with seasons. Levels ofNH4+ varied from 13.89 to 71.86 M, with the highest level found in December 2011. NO2-+NO3concentrations ranged between undetectable to 15.82 M. High concentration levels were found inⒸ ISERD102

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September 2011, which was probably the results of land utilization of agriculture, of which ricefields and aquaculture areas that covering the river mouth (REO8, 2011). Si(OH) 4 concentrations
ranged from 24.94 to 241.72 M with high concentration levels particularly in the rainy season (p< 0.05). PO43- levels ranged from 0.63 to 5.65 M with noticeably higher levels than therecommended level of 0.48 M from the ASEAN marine water quality (Chongprasith et al., 1999).
Phytoplankton Distribution
Phytoplankton community variation was related to local nutrient loads and hydrographic condition,
turbulence and human impact (Álvarez-Góngora and Herrera-Silveira, 2006). The phytoplankton
community consisted of 54 genera, namely 4 Cyanophyceae, 7 Chlorophyceae, 33
Bacillariophyceae (diatoms), 1 Dictyochophyceae, and 9 Dinophyceae (dinoflagellate). The amountof phytoplankton varied from 180 to 1.37x105 unit cells/L with the highest density in December
2011. The results showed that dinoflagellate was the most dominant group. Other species, such as
Trichodesmium sp., Protoperidinium sp., and Noctiluca scintillans, were also found, while
Ceratium sp. was dominant species when the red tide phenomenon is occurred. The results ofstatistical analysis implied that dissolved inorganic nutrients had influenced on phytoplankton
density. Spearman rank correlation coefficient (rs) indicated that phytoplankton density highly
significant (p < 0.01) received enhancement from NO2-+NO3-, Si(OH)4, and PO43- (rs = -0.762, 0.745, and -0.484, respectively). Those nutrients play the key roles of phytoplankton blooming,
while NH4+ concentration were surplus for phytoplankton growth in this area.
Nutrients Proportion for Phytoplankton
The results of nutrient proportion were calculated for dissolved inorganic nitrogen (DIN;NH4++NO2-+NO3-), orthophosphate (P; PO43-) and silicate (Si; Si(OH)4) and compared with
Redfield ratios of N:Si:P (16:16:1) based on the work of Brzezinski (1985). The results of DIN:Pand Si:P molar ratios varied by season and were mostly higher than Redfield ratios, especially inDecember 2012 when there is an accumulation process in the water column. In this study, thelevels of DIN:P ratios had related to phytoplankton density with the power function of Y =828.1e0.109X in which r2 = 0.344, when Y = phytoplankton density and X = DIN:P levels (Fig. 2).
Such variation reflected high load of nutrients that involved the natural runoff and agricultural land
uses which was consequentially influence such nutrient loads (Thongdonphum et al., 2011). Thus,
PO43- levels could be monitored and used for managing water quality.

Fig. 2 Relationships between of DIN:P ratios and phytoplankton density found in theBang-tabun Bay during study periodsⒸ ISERD

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CONCLUSION
This study has revealed that phytoplankton can play an important role in nutrients, particularly
phosphate from the water column as the crucial influencing factor of phytoplankton growth. DINlevels were surplus for the Bang-tabun Bay. The levels of phosphate could be used to monitor andmanage eutrophication and/or red tide phenomenon. The study results could be applied to estimate
the level of phytoplankton density for more efficient management of water resources andutilization.
ACKNOWLEDGEMENTS
The authors would like to express deep gratitude to all the staff members of the Marine
Environmental Laboratory (Department of Marine Sciences) and the Sediment and Aquatic
Environment Research Laboratory (Department of Fishery Biology), Faculty of Fisheries, Kasetsart
University, for their in valuable advice and assistance.
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