In this study, water quality was observed in urban rivers, natural rivers, and irrigation drainage networks in order to elucidate the mechanism of water purification function of wetlands in Monsoon Asia. The results showed that EC value of urban rivers and irrigation drainage area was about the same in the rainy season, but in the dry season, EC of urban rivers was about two times higher than that of irrigation drainage area. Urban rivers in Laos receive both domestic wastewater and rainwater runoff, which is thought to dilute the water quality load to about twice as much during the rainy season as during the dry season. On the other hand, EC of wastewater from irrigated drainage areas was almost constant with small fluctuations throughout the year. This may be due to the dilution effect of drainage from rice paddies during the dry season.

The aim of this project was to develop a set of species distribution models as a tool for assessing biodiversity in the Mekong Delta, Ben Tre, Vietnam. A series of field surveys on fish fauna and physical environment was conducted jointly with Thuyloi University, Vietnam. In the fish fauna survey, fishing gears were selected according to a local condition, and species name and body length were recorded with geographic location. Physical environment survey was conducted using a CTD profiler in the five major rivers in the region (namely, Tien river, Ham Luong river, Balai river, Ben Tre channel, and Binh Chanh river). As a result, over 70 fish species were observed in the region, of which species distributions were affected by salinity gradient. Spatiotemporal salinity distributions in the region was complex due to nested channel structures and tidal gates established to alleviate saline water intrusion. Such information will be used for modelling the dynamics of species distributions.

This study aimed at the development of a framework for simulating the dynamics of water flows and fish behaviours in irrigation channels and rivers. We conducted a series of field surveys and numerical analysis on fish ecohydraulics, in which advanced measurement methods such as acoustic Doppler current profiler (ADCP) were employed to measure high resolution hydrodynamic data. Data-driven models using machine learning were employed for modelling fish species distributions and its dynamics. Process-based models were used for modelling 1D or 2D hydrodynamics in the target reach, based on which habitat heterogeneity was assessed in order to link it with species richness.

An integrated analysis model of flow field, thermal environment and dissolved nitrogen dynamics was developed considering the interaction among spatial components (irrigation and drainage canal and paddy fields) for the water environment in a paddy dominated basin. This numerical model consists of three components; a model that can represent flow condition of paddy ponding water surrounding numerous rice bunches, a model that expresses how the temperature environment in the paddy field and the nitrogen concentration distribution in the paddy water change depending on the flow field of the paddy water, the temperature of the irrigation water, and the weather conditions, and a model that represents the spatiotemporal distribution of water temperature and nitrogen concentration throughout the paddy irrigation area.

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