Hydrodynamics Modeling of Khung Krabaen Lagoon, Chanthaburi Province, Thailand

Khung Krabaen Lagoon (KKBL) is a small low-inflow water body. There are vast areas of tidal flat occupied nearly 60% of the lagoon that host some of the most productive seagrass habitats in the region. The lagoon is surrounded by mangrove forest and intensive shrimp farms behind it. The KKBL was used as an intake and recipient water for the farms. However due some shrimp disease epidemics and possibly deteriorated water quality, the farms are now taking the intake water from the outer sea through very expensive (to construct and to maintain) irrigation system. Objective of this study is to investigate the KKBL’s hydrodynamics using a numerical simulation model validated with measured data. The simulation model was setup two-dimensionally based on the Delft3D model. Results suggested that water currents inside, at the mouth and at the outer sea of the lagoon are mainly governed by tide and wind. Offshore of the lagoon, there are strong tidal currents flowing along northwest and southeast direction. The tidal currents flow into the lagoon through its mouth before dispersion rapidly inside the lagoon. Mean circulation largely varied seasonally and had direct correlations outer sea seasonal mean currents and the monsoons

Influence of local wind field on seasonal circulations in the upper Gulf of Thailand

Previous results of circulation in the upper Gulf of Thailand using a 2-dimensional model suggested counter-clockwise circulation and a clockwise gyre during the northeast and the southwest monsoons, respectively. A review of previous reports relevant to circulation, and the results of surface chlorophyll-a distribution estimated by OCTS (Ocean Color and Temperature Scanner) data support the results during the northeast monsoon. Anyway, residual circulation analyzed from oceanographic buoys deployed in the upper gulf illustrated both clockwise and counter-clockwise circulations during the southwest monsoon. Therefore, the objective of this study is trying to investigate the current patterns and their controlling factors especially during the southwest monsoon. The 2-dimenional circulation model is applied again but this time uses meteorological wind data from local stations around the study area as inputs. The experiments also include investigation of current patterns due to the difference of wind gradients in east-west and north-south direction. The results show that counter-clockwise circulation can be developed during the southwest monsoon when wind magnitude in the east or the south is significantly stronger than that in the west or the north, respectively, which possibly happens in the real situation. It can be concluded that the circulation patterns in the area are controlled by not only wind direction but also its gradient. We also found that external flows through the open boundary can change the patterns of circulation just in the southernmost area

The Modification of Water Column Conditions in the Gulf of Thailand by the Influences of the South China Sea and Monsoonal Winds

Water column conditions in the Gulf of Thailand (GoT) were analyzed by considering four major factors including surface heat fluxes, freshwater inputs from river discharge and atmospheric fluxes, tidal and wind stirrings. The analytical results suggested that surface heat fluxes and tidal stirring are the most important factors to control water column conditions, followed by freshwater fluxes. Well-mixing was predicted to occur from November to February resulted from relatively large tidal stirring, surface heat loss and low freshwater input, but the climatological density data suggested stratification during this period because of local freshwater accumulation. The South China Sea (SCS) and the northeast wind played significant contributions to freshwater accumulation by generating surface water flow into the gulf during the northeast monsoon. On the other hand, the development of stable and strong stratification during the southwest monsoon was enhanced by SCS subsurface water intrusion and surface outflow induced by the southwest wind. Strong surface heat fluxes coincident with SCS intrusion in April and May make water stratification more complex. This phenomenon generates double thermocline and multi stratified water in some GoTarea

Spatial and temporal variations of Biological Production in the Asia-Pacific Marginal Seas

This research project consists several main activities which are considered to be able to improve research capability in the Asia-Pacific region, especially in the collaborating countries. In terms of research, the project focused on discerning spatial and temporal variations of marine biological production in the Asia-Pacific marginal seas (the East China Sea, the South China Sea, the Strait of Malacca, and the Gulf of Thailand) utilizing multisensor satellite observations and coupled hydrodynamic-biogeochemical model. As part of the research achievements, one paper was accepted (in press) for publication in Remote Sensing. Other three or four papers are now under preparation for submission to high impact journals. To achieve research objectives, four (4) young scientists from collaborating countries were also involved in the project, that at once allowing them to improve their research capability and to enter international scientific community. In order to expand international networking and/or research collaboration in the near future, international mini-workshop on the western Pacific Ocean and marginal seas biogeochemical variability was also held in Japan Agency for Marine-Earth Science and Technology (JAMSTEC) in February 2014. As feedback of this research project and research continuation, it has been discussed and planned to propose Japan Society for the Promotion of Science (JSPS) Postdoctoral Fellowships for foreign researchers.Project Reference Number: ARCP2012-21NSY-Siswanto, Final Report submitted to APN ; The original publication is available at APN via http://www.apn-gcr.org/resources/items/show/176

MODIS-derived green Noctiluca blooms in the upper Gulf of Thailand: Algorithm development and seasonal variation mapping

In recent decades, red tides of non-toxic harmful algal blooms have frequently occurred in monsoon-influenced tropical areas, particularly the green form of Noctiluca scintillans (hereafter green Noctiluca). However, our understanding of the mechanism of red tide formation is hindered by spatial and temporal constraints of field data. In this study, we used moderate resolution imaging spectroradiometer (MODIS) ocean color data along with a locally developed algal-bloom classification algorithm to investigate the seasonal variability of dominant red tides across the upper Gulf of Thailand (uGoT). During our July 2018 observation, a super green Noctiluca bloom with extraordinarily high chl-a (>1,469 mg m-3) displayed a distinct spectral reflectance characteristic among red tides in blue-to-green and red-to-near infrared wavelengths. According to the distinctive in situ hyperspectral characteristics of uGoT algal blooms, we developed a classification algorithm for MODIS normalized at 488, 531, and 667 nm, which successfully discriminated green Noctiluca in three levels of blooms, namely, super (100%), strong (>80%), and weak (>40%), from other algal blooms (i.e., dinoflagellates, diatoms, cyanobacteria, and mixed red tide species) as well as non-bloom oceanic and coastal waters using MODIS data, as confirmed by uGoT red tide reports. Monthly MODIS-based discrimination composites from 2003 to 2021 revealed seasonal variability in the surface distribution and bloom frequency of green Noctiluca and other red tides according to the Asian monsoon seasons: the southwest monsoon (May–September) and the northeast monsoon (October–January of the following year). Green Noctiluca blooms occurred farther from the shore and estuaries than other red tides (dinoflagellates and cyanobacteria), and were much more frequent than other red tides between the Tha Chin and Chao Phraya River mouths during the non-monsoon period (February to April). The frequency and distribution of green Noctiluca blooms, as well as other algal blooms, varied with the monsoon season. By comparing MODIS-derived algal blooms to monsoon-induced factors (i.e., sea surface winds, precipitation, and river discharge), we present an unprecedented overview of the spatial and temporal dynamics of red tides throughout the uGoT under Asian monsoon conditions. This research contributes to our understanding of the impact of climate change on phytoplankton dynamics

Seasonal Variations in Water Column Stratification in the Gulf of Thailand

Water column conditions in terms of vertical well mixing and stratification are important to phases of physical and biochemical environments such as vertical material exchanges and primary productivity of phytoplankton. Water stratification plays as a barrier to nutrient mixing between surface and subsurface waters. Primary productivity in such area is then limited by nutrient availability. In contrast, the stratification in a high eutrophic area can generate hypoxia or anoxia in near bottom water due to organic material decomposition. The objective of this study is to investigate the seasonal variations of water column stratification in the Gulf of Thailand (GoT) from the distributions of temperature and salinity profiles. Other controlling factors such as surface heat flux, freshwater discharge, rainfall, tidal and wind stirrings were also included in this study

Water Characteristics in the Cambodian Water in November 2015

The abstract of Water Characteristics in the Cambodian Water in November 2015Twenty four oceanographic survey stations were carried out by CTD, seabird 911 plus equipped onboard RV Koyo Maru in the Cambodian water during 10 - 21 November 2015 cover 101.989o E to 103.635o E and 9.084o N to 11.236o N. Its results including temperature, salinity, density and Dissolved Oxygen (DO) were used to determine water characteristics and their causes. The results showed that water profile was complex in some station because of water masses intrusion from the North and Northeast of the study area. This water masses occupied at the depth from the surface to 40 m in North and Northeast. Its thickness, however was continuously less when it flowing southward. This water masses characteristic was high temperature, low salinity and low density. Additionally, low oxygen condition (about 2.6 ml/l) in near bottom water was found in some study area when the bottom depth deeper than 40 m. Even though, DO near the bottom in deep area was low but not low enough to harm to organism. The study results show that strong water stratification led to low oxygen in the study area

Hydrodynamics Modeling of Khung Krabaen Lagoon, Chanthaburi Province, Thailand

Khung Krabaen Lagoon (KKBL) is a small low-inflow water body. There are vast areas of tidal flat occupied nearly 60% of the lagoon that host some of the most productive seagrass habitats in the region. The lagoon is surrounded by mangrove forest and intensive shrimp farms behind it. The KKBL was used as an intake and recipient water for the farms. However due some shrimp disease epidemics and possibly deteriorated water quality, the farms are now taking the intake water from the outer sea through very expensive (to construct and to maintain) irrigation system. Objective of this study is to investigate the KKBL’s hydrodynamics using a numerical simulation model validated with measured data. The simulation model was setup two-dimensionally based on the Delft3D model. Results suggested that water currents inside, at the mouth and at the outer sea of the lagoon are mainly governed by tide and wind. Offshore of the lagoon, there are strong tidal currents flowing along northwest and southeast direction. The tidal currents flow into the lagoon through its mouth before dispersion rapidly inside the lagoon. Mean circulation largely varied seasonally and had direct correlations outer sea seasonal mean currents and the monsoons

Vertical diffusivity and water qualities in the upper Gulf of Thailand in March 2009

Field observation in the upper Gulf of Thailand (UGoT) in March 2009 was conducted to prove the relationship between vertical diffusivity (water turbulence) and chlorophyll-a (Chl-a), addressed by numerical model results of our previous study. Relationships between Chl-a and water properties, including salinity, temperature, density, dissolved oxygen (DO), dissolved inorganic nitrogen (DIN) and phosphorous (DIP), dissolved silicate (DSi) and turbulence, were investigated. Blooming areas did not exactly correspond to the area of freshwater influences and high nutrients, except DSi. Insignificant relationships between Chl-a and environmental parameters were found in the correlation analysis. The correlation line indicated that no relationship is evident in the case of Chl-a and DIN. Proportional relationships seem to happen for Chl-a and DIP, and Chl-a and DSi, while reverse relationships for Chl-a and Kz. Further investigations are required to clarify the occurrence mechanism of red tide in UGoT.Proceedings of 4th JSPS-VAST Joint Seminar on \u27Coastal Marine Science\u27, Hai Phong, Viet Nam, 26-28 October 2009Oceanograph