Japan Society of Hydrology and Water Resources Acta Medica Okayama 1882-3416 14 4 2020 Estimation of long-term external nutrient loading from watersheds to Lake Biwa by a combined rainfall-runoff model and loading-discharge curve approach 143 149 EN Huu Le Tien Graduate School of Environmental and Life Science, Okayama University Kenji Okubo Graduate School of Environmental and Life Science, Okayama University Phuong Ho Thi School of Chemical, Biological and Environmental Technologies, Vinh University Mitsuyo Saito Graduate School of Environmental and Life Science, Okayama University External nutrient loadings to Lake Biwa were estimated using a combined tank model and loading-discharge curve approach. The model was applied to collective drainage basins of the lakefs Imazu (northwest), Hikone (northeast), and Otsu (south) areas. The hourly model was conducted using particular discharges from Kita (Ado) river, Takatoki (Ane) river, and Yasu River to obtain loading curves for phosphate (PO4) and silica (SiO2) by assimilating measured concentrations (2002–2003). The tank model was updated by adding an evapotranspiration routine and direct paths of groundwater discharges to the lake floor. The daily model was calibrated through analysis of water budget among the basin, inflow, lake and outflow, and then validated. The model was established and combined into a loading-discharge curve to determine the long-term external nutrient loadings entering the lake (1980–2017). Seasonal variation in nutrient loadings increased during spring and summer and decreased during winter. Annual phosphate-phosphorus (PO4-P) loading ranged from 217 to 296 tons yr–1 in the North Basin and 45 to 76 tons yr–1 in the South Basin, while SiO2 loading fluctuated from 16,027 to 32,655 tons yr–1 and 2,518 to 5,490 tons yr–1 in the North and South Basins, respectively. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 2014 Seto Inland Sea tidal flow simulation 93 100 EN Shinya MORIFUJI Hiroshi SUITO Janne ROPPONEN Kenji OKUBO No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 2014 Simplified approach to evaluate total external loading to Kojima Lake 76 92 EN Shin-ichi NISHIMURA Kenji OKUBO Hidenori MORITA Jari KOSKIAHO Sirrka TATTARI No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 2014 Total loading curves applied to Lake Pyhäjärvi 69 75 EN Kenji OKUBO Jari KOSKIAHO Anne-Mari VENTELÄ Timo HUTTULA No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 2014 (Abstract for Journal paper) Waves in two shallow lakes in different latitudes with climate change perspective – measurements and forecasts 57 57 EN Ting Feng WU Kenji OKUBO Timo HUTTULA Janne ROPPONEN No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 2014 The sink of sediments suspended by waves in Lake Pyhäjärvi 48 56 EN Kenji OKUBO Timo HUTTULA Hiroshi SUITO Janne ROPPONEN Akiko MANO Takashi NAKAZAWA No potential conflict of interest relevant to this article was reported.

‰ͺŽR‘εŠwŠΒ‹«—HŠw•” Acta Medica Okayama 1341-9099 1 1 1996 Turbid intrusion below the thermal staircase in the seasonal thermocline of Lake Biwa 77 89 EN Kenji Okubo Hiroshi Morikawa Takashi Kimoto Yuji Tanaka 10.18926/fest/11615 Thermal 'staircase', a layer of constant temperature between the sheets of the steep gradients, was formed in the seasonal thermocline, which was 2.5 m above the bottom at a point of 18 m deep on the boundary slope in Lake Biwa. Following a sediment resuspension event when a moderate onshore wind blew, bed materials should be suspended up to the thermocline, then settled down forming a staircase above the turbid intrusion. Comparing the observed downward hear flux with the settling flux of sediment, it was found that double-diffusive convection would play an important role on the formation of the whole structure consisting of the staircase and turbid intrusion along with chemical anomalies and dense population of phytoplankters, which were fed by nutrients supplied from the bottom sediment under a typical condition of drought. Laboratory experiments were conducted to demonstrate the thermal and sediment processes in the stratified lake. Resuspension process due to surface and internal waves was examined using a tank with a sloping bottom, while the settling process was investigated by using a deep, diffusive tank. Formative process and scales of the staircase and intrusion were discussed relating with the intensity of resuspension and the buoyancy fluxes. No potential conflict of interest relevant to this article was reported.

‰ͺŽR‘εŠwŠΒ‹«—HŠw•” Acta Medica Okayama 1341-9099 3 1 1998 Surface Air Temperature Distribution : A Study from Southwest Bangladesh 97 104 EN Kenji Okubo 10.18926/fest/11568 Surface air temperature distribution over the Ganges Delta Region of southwest Bangladesh and its tendency of warming are discussed through the analyses based upon the long-term temperature data from 1900-93. The data consist of two parts corresponding to the time-periods: 1973-93 and 1900-72. The study area is one of most affected places by the annual monsoon hydrological cycle and the present observation from these temperature data indicate that the surface air temperature gradient in the north-south direction is significant in the rainy season and that the temperature of the region is at an increasing tendency; the warming rate during the data periods (1900-93) on the long-term mean annual basis is estimated as 0.77Ž at Satkhira of the Khulna division and 0.29Ž as an areal average including the Barisal division, for the time difference of about half a century between the data periods before and after 1972. No potential conflict of interest relevant to this article was reported.