Gullaya Wattayakorn

Mixing, trapping and outwelling in the Klong Ngao mangrove swamp, Thailand

The Klong Ngao estuary in Thailand is a 7-5-km long tidal creek facing the Andaman Sea and drains 11.5 km 2 of mangrove swamps. Physical processes in the estuary differ greatly from the wet season to the dry season. In the dry season, vertical homogeneity prevails and the swamp behaves like an evaporation pond. Salt and water are trapped upstream, longitudinal gradients result and, through tidal dispersion, nutrient outwelling may result for SiO 2, possibly NO 2 and NO3, but not PO 4. The outflow is trapped in a coastal boundary layer. In the wet season, short-lived local floods generate a strong stratification in salinity and episodical flushing of the estuary and may make measurements of nutrient budgets inconclusive. The Klong Ngao mangrove swamp traps land-derived sediments in the wet season.

Trace metal transport in a tropical estuary

Abstract The distributions of soluble and particulate trace metals in the Bang Pakong Estuary, Thailand were studied during high (wet) and low (dry) discharge conditions. Particulate trace metals and particulate organic C concentrations are controlled by physical processes. Dissolved Cu and Ni are, in general, conservatively mixed through the estuary. The behavior of Fe and Pb result in net removal during estuarine transport. Fe removal appears to be due to decreased solubility as pH increases in estuarine waters. Mn is removed at low salinities, when riverine concentrations are high, and remobilized at higher salinities. Dissolved Cd, Co and Zn concentration distributions have mid-estuary maxima which coincide with nutrient maxima. The metal-nutrient relationship is interpreted as the result of metal regeneration during organic matter decomposition.

Groundwater Discharge as an Important Land-Sea Pathway into Manila Bay, Philippines

Abstract A multidisciplinary approach was taken to assess the potential importance of groundwater seepage to nutrient inputs into Manila Bay, Philippines. Three lines of seepage meters were installed in transects along the coast at Mariveles, Bataan Province, during the period 8–10 January 2005. The overall average seepage flux was 5.1 ± 5.4 cm d−1 (n = 73) with a range of 0–26 cm d−1 and a calculated integrated shoreline flux of 12.4 m3 m−1 d−1. Additional methodologies employed included automatic seepage meters, resistivity measurements, sampling for nutrient analyses in both seepage meters and ambient seawater, and use of natural radon as a groundwater tracer. Seepage meter and tracer results provided consistent results of estimates of submarine groundwater discharge into Manila Bay. Many lines of evidence suggest that seepage fluxes are not steady state but are modulated by the tides. Resistivity profiles show that the saline-freshwater interface moves on a tidal timescale, consistent with the observed drop in salinity of the seepage waters as low tide approaches. Our results show that dissolved inorganic nitrogen (DIN) fluxes via submarine groundwater discharge are comparable in magnitude to DIN fluxes from each of the two major rivers that drain into Manila Bay.

ENVIRONMENTAL ISSUES IN THE GULF OF THAILAND

The Gulf of Thailand is a semi-enclosed tropical sea located in the South China Sea (Pacific Ocean), surrounded by the countries Malaysia, Thailand, Cambodia and Vietnam. The Gulf covers roughly 320,000 km². The boundary of the Gulf is defined by the line from Cape Camau in southern Vietnam (just south of the mouth of the Mekong River) to the coastal city of Kota Bharu on the east coast of Peninsular Malaysia. It is relatively shallow; the mean depth is 45 m, and the maximum depth only 80 m. The general shape of the Gulf’s bottom topography can be considered elliptic parabolic. It is separated from the South China Sea by two ridges that limit water exchanges with the open South China Sea. The first extends southeast from Cape Camou for about 60 nautical miles with an average sill depth of less than 25 m. The second ridge, which extends off Kota Bharu for approximately 90 nautical miles, has an average sill depth of 50 m. There is a narrow, deeper channel between the two ridges with the observed depth of 67 m (Emery and Niino, 1963). The Gulf may be divided into two portions, Upper Gulf and Lower Gulf. The Upper Gulf at the innermost area has an inverted U-shape. The Upper Gulf is the catchment basin of four large rivers on the northern side and two on the western coast. Numerous rivers discharge freshwater and sediment into the Gulf. Among them, the Chao Phraya River has the biggest volume transport next to the Mekong River. The average runoff per year of the Chao Phraya is 13.22 x 10 3 and that of 3

Nutrient capital in different aged forests of the mangrove Rhizophora apiculata

Abstract Partitioning and storage of mineral nutrients and trace elements were examined in tree components and soils of differently aged (3-, 5- and 25-year-old) forests of the mangrove Rhizophora apiculata in southern Thailand. Despite lack of replication of forests, three patterns of element partitioning and forest nutrient capital emerged: (1) concentrations of most (but not all) elements in various tree parts declined with increasing tree age; (2) the soil pool size of most elements decreased with increasing stand age; and (3) the proportion of C, N, Na, Mn, Zn and Mo in total living biomass increased with increasing forest age. Most elements were stored in soils and dead roots, supporting the concept that wet tropical forests do not store proportionally more nutrients in their biomass than in soils, as compared to temperate and boreal forests. The large element pools stored in dead roots may serve as a conservation mechanism. Our data suggest that the proportion of element capital stored in forest biomass increases, but decreases in soils as forests age, suggesting net accumulation with forest maturity. Mean residence time for total forest N increased from 0.3 years for the 3-year-old forest to 0.5 years for the 5-year-old forest to 0.6 years for the 25-year-old forest. Compared with other forests, N turnover is very rapid, mirroring the tight coupling between production and decomposition processes in these wet tropical ecosystems.

Biogeochemical budgets and processes in Bandon Bay, Suratthani, Thailand

Abstract Water, salt, dissolved nitrogen, and dissolved phosphorus budgets have been constructed for Bandon Bay for the wet and dry periods of 1997 and 1998. The two-box model shows that while most of the dissolved N and P loading is taken up in the estuarine section of Tapi River and Bandon Bay, a significant portion is exported to the Gulf of Thailand. In general, the export fluxes are higher during the wet season than in the dry season. The export flux of DIN is normally dominated by NH 4 , and generally greater than the export flux of DON, while DIP is exported at about the same rate as that of DOP. Bandon Bay appears to be in balance metabolically ( p − r =0), suggesting a very high efficiency within the Bay for recycling organic material. The system consumes about 3% more organic matter than it produces in the dry season and produces about 4% more organic matter than it consumes in the wet season. Tapi Estuary is a net denitrifying system while Bandon Bay is slightly net nitrogen fixing. The presence of benthic algae on the mud flats and the mangrove fringe around the bay could account for nitrogen fixation in the bay. Seasonal variations in biogeochemical rates were attributable to differences in magnitude of freshwater inputs. Under conditions of high river flow, overall rates of net production were enhanced by increased nutrient delivery.

GC/MS based analyses of individual organic constituents of chao phraya river water and estimated discharge rates into the upper gulf of Thailand

Abstract Detailed GC/MS based chemical analyses of organic concentrates from the Chao Phraya River obtained from a water sample collected in the Bangkok metropolitan area indicated that hydrocarbons of petroleum or combustion sources may be minor constituents of the dissolved lipophilic fraction relative to biogenic hydrocarbons and industrial chemicals. Using published data on river discharge and the concentrations measured in an integrated sample, tentative input rates into the Upper Gulf of Thailand for characterized chemicals are calculated.