Abstract:

The mixing between river water and seawater is a key interface process in the estuary.The mixing scale and rate concern the dispersion range and fate of the material transported by river. The aim of this paper is to calculate the transport rate of river plume in the estuary by using naturally occurring tracer ²²⁴Ra and ²²⁶Ra. In August 2010, we collected twenty groundwater samples, thirteen river water samples and twelve mixing samples in the estuary to measure the salinity,²²⁴Ra and ²²⁶Ra activities. The results showed that，1)²²⁴Ra and ²²⁶Ra activities in the groundwater samples were generally higher than those in the river water samples; 2)²²⁴Ra activity was generally higher than ²²⁶Ra activity in every sample; 3)²²⁴Ra activity largely increased when river water mixed with seawater, however,²²⁶Ra activity increased slightly. Based on the differences of radioactive half-life between ²²⁴Ra and ²²⁶Ra, and only eddy diffusion mixture occurring between river water and seawater, the transport rate for river plume in the estuary was calculated to be 140.2-142.5 m/h.

Key words: groundwater, river water, seawater, 224Ra, 226Ra, transport rate, Min River estuary