Narrow Results

During the summer of 2005, we carried out an intensive field survey of current velocity, salinity, temperature, and water density in Inohana Lake, Japan, which is a semi-enclosed and highly stratified estuary. Field and meteorological data were used to investigate the characteristics of currents, and to estimate water-volume and salt fluxes as a measure of water and material exchanges. We undertook a test using a simple box model based on the average salinity and river discharge, and obtained the exchanges of waters between Inohana and Hamana Lakes and within Inohana Lake, respectively. In terms of water exchanges between the two lakes and within Inohana Lake, wind effects were dominant over tide. In terms of water exchange rate between the two lakes, the water-volume flux was about five times as great as freshwater inflow. The water-volume flux between two lakes estimated from the box model showed good agreement with the observed ones by the ADCP. In the box model, the contribution of advection was larger than that of diffusion for the vertical water exchange. The vertical salt flux was estimated using two methods: the direct estimation from field data and a turbulent diffusion model. The turbulent diffusion model showed good agreement with the direct estimation by removing fluctuations with frequency less than 0.2 Hz from the velocity and salinity data.

The study examined the summertime behavior of phosphorus (P) and estimated P fluxes in the Inohana Lake Estuary, Shizuoka, Japan through a field observation conducted in the summer of 2007 and a box model approach. The sedimentation flux of P was significantly correlated with the overlying chlorophyll-a concentration. The box model provided a good estimate of the summer-averaged water flux. The P mass balance method yielded the release flux of P, which approximated the observed value. For the P exchange between the Inohana Lake Estuary and Hamana Bay, on the net flux, particulate P flows out into Hamana Bay through the upper layer, while dissolved P (phosphate P) flows into the Inohana Lake Estuary through the lower layer. For the P exchange between the upper and lower layers, the upward transport of P from the lower layer was more than 10 (~100) times greater than the downward transport of P. The results showed that P accumulates in the bottom sediment during the summer. This study indicates the possibility that the P input from Hamana Bay is dominant over the river P input in summer season with significant density stratification.