Groundwater-derived nutrient inputs to the
Upper Gulf of Thailand
Abstract
We report here the first direct measurements of nutrient fluxes via groundwater discharge into the Upper Gulf of
Thailand. Nutrient and standard oceanographic surveys were conducted during the wet and dry seasons along the Chao
Phraya River, Estuary and out into the Upper Gulf of Thailand. Additional measurements in selected near-shore regions
of the Gulf included manual and automatic seepage meter deployments, as well as nutrient evaluations of seepage and
coastal waters. The river transects characterized the distribution of biogeochemical parameters in this highly contaminated
urban environment. Seepage flux measurements together with nutrient analyses of seepage fluids were used to estimate
nutrient fluxes via groundwater pathways for comparison to riverine fluxes.
Our findings show that disseminated seepage of nutrient-rich mostly saline groundwater into the Upper Gulf of
Thailand is significant. Estimated fluxes of dissolved inorganic nitrogen (DIN) supplied via groundwater discharge were
40–50% of that delivered by the Chao Phraya River, inorganic phosphate was 60–70%, and silica was 15–40%. Dissolved
organic nitrogen (DON) and phosphorus (DOP) groundwater fluxes were also high at 30–40% and 30–130% of the river
inputs, respectively. These observations are especially impressive since the comparison is being made to the river that is the
largest source of fresh water into the Gulf of Thailand and flows directly through the megacity of Bangkok with high
nutrient loadings from industrial and domestic sources.
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