Masumi Koriyama

Effect of nutrient concentration and salinity on diel vertical migration of Chattonella marina (Raphidophyceae)

Abstract Vertical migration plays an important role in the development of Chattonella populations in the natural environment; however, this behaviour has remained largely undescribed. In the present study, the diel vertical migration of Chattonella marina in the Ariake Sea was examined along with nutrient concentrations and salinity at four sampling sites during the bloom in the summers of 2008, 2009 and 2010. Cells of Chattonella were abundant at the surface (0 m depth) in the daytime in most cases. However, when surface salinity was 9, which is the lower limit for growth, the population accumulated at a depth of 2 m, where salinity was 15, suggesting that Chattonella moves to avoid water with low salinity. Chattonella cells actively migrated, even under nutrient-replete conditions (mean DIN concentration, 12.73 µM). The present study demonstrates that Chattonella cell migration is independent of nutrient availability. In addition, Chattonella cells stop upward migration when the surface salinity is low (< 15). These insights are important for making predictions of Chattonella population dynamics after heavy rains.

Measurement of LAI in the Watershed Using Terra-ASTER Data

Leaf area index (LAI) is an important factor to identify the water balance in the area of forest as a biological factor influencing directly on the evapotranspiration occurs in the forest area. This study is purposed to estimate the LAI on the forest area in summer and winter by applying the Terra-Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data to the LAI estimation method based on the absorption and scattering process of the vertical element of electromagnetic waves and the characteristics of reflection spectrum of soil-vegetation. Estimated LAI was derived from application of ASTER data on the northern forest area of Saga City as the target region in this study. LAI measured directly by means of LAI-2000 on the observation point inside the target region was compared to the estimated LAI derived from the ASTER data. This study proved that LAI estimation method was a feasible and accurate method as indicated by the high relationship (r=0.91) between LAI derived from ASTER data and LAI measured directly.

BURROW - FORMATION BY MACROBENTHOS IN THE MUDDY TIDAL FLAT AND ITS EFFECTS ON THE NITRIFICATION-DENITRLFICATION PROCESS

The relationships between burrow-formation by macrobenthos and nitrification-denitrification process in the muddy tidal flat located in the interior pails of the Make Sea, which supports the purification action of environment, were investigated on the basis of the field measured and experimental data. It was showed that the burrow - formation by Neanthes japonica, etc. in the low tide made redox potential discontinuity layer (RPD layer) near the surface layer in the muddy tidal flat and caused the nitrification, and the disappearance of the burrow in the high tide erased RPD layer and caused the denitrification. An equation for the relation between denitrification rate and NO3-concentration and temperature in the muddy tidal flat was presented. The properties of denitrification were made clear by this equation.