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The Three Gorges Region in China is currently subject to a large-scale land use change, which was induced by the construction of the Three Gorges Dam on the Yangtze River. The relocation of towns, villages, and agricultural areas is expected to affect the water balance and increase erosion rates and sediment yields in the affected catchments. Hydrologic and water quality models are frequently used to assess the impact of land use changes on water resources. In this study, the eco-hydrological Soil and Water Assessment Tool (SWAT) model is applied to the Xiangxi Catchment in the Three Gorges Region. This paper presents the calibration and validation of streamflow and sediment loads at Xingshan gauging station. The calibration of daily streamflow resulted in a satisfactory fit of simulated and observed data, which is indicated by Nash-Sutcliffe efficiency (NSE) values of 0.69 and 0.67 for the calibration (1981-1986) and validation (1988-1993) periods, respectively. In contrast, the model was not able to simulate the monthly average sediment loads correctly, as indicated by very low NSE values of 0.47 (calibration) and 0.08 (validation). This might be due to inadequate representation of spatial rainfall variability by the available climate stations, insufficient input data, uncertainties in the model structure, or uncertainties in the observed sediment loads. The discussion of these possible reasons for the incorrect prediction of sediment loads by SWAT reveals the need for further research in the field of hydrological and water quality modeling in China. [ABSTRACT FROM AUTHOR]

Development of hypoxia in Japan has been confirmed in the inner part of almost every major bay of Japan on the Pacific Coast from Tokyo southward. This paper presents multiple aspects (present condition, hydraulic mechanism, effect upon fisheries, historical progress and nutrient budget between sediment and water) using Mikawa Bay, where Japan's most serious hypoxia occurs, as an example. Although hypoxia basically results from the increase of nutrient load input from domestic and livestock sources, the intense reclamation of shallows (including tidal flats) and the large reduction in river flow due to farmland irrigation drastically accelerated dissolved oxygen deficiency. Oxygen‐deficient waters in Mikawa Bay are large enough to strip the water purification capacity of the remaining shallows. Unfortunately, the shallows have turned from a purifier to a source of nutrient load. These conditions are more or less common in all bays where the dissolved oxygen–deficient waters have been reported. To break this cycle, dissolved oxygen deficiency must be contained to the extent that the purification capacity of the shallows can be restored to an efficient level. For this purpose, the first thing to do is to restore tidal flats over an extensive area and to recover sufficient water flow, which may be a more urgent imperative than reducing the nutrient load input. [ABSTRACT FROM AUTHOR]