No abstract

Numerous attempts have been conducted in order to recover emergent plants and submerged plants in various lakes. However, floating-leaved plants, which make water quality worse, have been rarely focused. The purpose of this paper is to evaluate the effect of mowing down the floating-leaved plants area partially in Lake Suwa, where floating-leaved plants-dominated state is observed in shallow zone. We measure water temperature, turbidity and water velocity inside and outside of the floating-leaved plants area. It is confirmed that 1) The variation range of water temperature inside of floating-leaved plants area is smaller than that of outside. 2) Floating-leaved plants lessen the vertical water circulation. 3) Outside of floating-leaved plants area is easier to be influenced by cold water than inside when cold water intrude into water grass area. 4) Turbidity inside of floating-leaved plants area is higher than outside. 5) The leaves of floating-leaved plants become the resistance of surface current.

No abstract

The water quality and physical process within bays are strongly affected by climatic phenomena such as regional air pressure distributions, ocean currents and typhoons. The present study reveals that the water mass inside Ohfunato Bay is strongly related to the sea level along the Pacific coast over a scale of 3,000km from Nemuro (Hokkaido) to Naha (Okinawa). Low salinity water associated with the Oyashio ocean current intrudes in Ohfunato Bay from April to October in the average year. Finally, it was found that low salinity water is carried by typhoon from ocean into Ohfunato Bay.

Numerous studies in biological and chemical processes have been conducted in Lake Suwa, only a few of which were concerned with physical processes that strongly affect a lake' s biochemical dynamics. To gain a better understanding of the corresponding physical dynamics (e.g., current pattern and discharge), we deployed an updated current instrument (i.e., an Acoustic Doppler Current Profiler, ADCP), which is accepted world ･ wide for its accuracy and high resolution as well as for its ability to resolve the spatial and temporal variations of currents. Using the ADCP, we measured discharges of the dominant inflows and current patterns of a submerged macrophytic area near the shore together with an outflowing area (nearby Kamaguchi floodgate). Our results show that (1) the discharges observed in the dominant inflows (the Kami, Miya and To rivers) are different from those reported by Nagano Prefecture, whereas the outflowing discharge at Kamaguchi Floodgate is similar to that in the Nagano Prefecture report, and (2) the vertical distributions of velocity outside the submerged macrophytic area differ from those inside the area, whose horizontal velocities were reduced by macrophyte-induced turbulence, and (3) the current patterns near the outflow showed a strong velocity in the northeast, rather than in the southwest region.