Underground sources of nutrient contamination to surface waters in Bangkok, Thailand.

Radon-222 is very concentrated in groundwater relative to surface waters and thus serves as an effective groundwater discharge tracer. We observed spikes in radon data from an earlier (2004) survey of the Chao Phraya River that appeared to correspond to locations where major canals ("klongs") enter the river. We returned in 2006 and conducted more detailed surveys along some of the main klongs on the western (Thonburi) side of the Chao Phraya to evaluate this possibility.

Evaluating ground water-sea water interactions via resistivity and seepage meters.

We investigated submarine ground water discharge and salt water-fresh water interactions at two locations along the shoreline of the Upper Gulf of Thailand to evaluate mechanisms of water and material transport into the coastal zone. Our data set illustrates the value of using a combined approach consisting of automatic seepage meters to monitor flow rates while assessing the conductivity (salinity) of the subterranean fluids via remote resistivity measurements. Negative correlations between electric conductivities of fluids measured directly inside seepage meter chambers and the remotely assessed resistivities of subsurface pore water show that such measurements may evaluate the spatial distribution of flow rates as well as the subterranean water quality in the coastal zone.

Evaluation of time-space distributions of submarine ground water discharge.

Submarine ground water discharge (SGD) rates were measured continuously by automated seepage meters to evaluate the process of ground water discharge to the ocean in the coastal zone of Suruga Bay, Japan. The ratio of terrestrial fresh SGD to total SGD was estimated to be at most 9% by continuous measurements of electrical conductivity of SGD. Semidiurnal changes of SGD due to tidal effects and an inverse relation between SGD and barometric pressure were observed.