Studies on hydraulic and biochemical phonomena of an irrigation reservoir and ponded water in a paddy field
2008
Yoshinaga, I.(National Agricultural Research Center for Kyushu Okinawa Region, Itoman (Japan))
Water environment conservation in rural area is an important issue. In Japan seventy-eight percent of irrigation reservoirs are in a eutrophicated state, where the bloom of phytoplankton may occur. Massive growth of phytoplankton produces unsightly bad-smelling scum, preventing the use of water for agricultural and recreational purposes. Especially, excessive growth of cyanobacterium Microcystis on freshwater systems is a serious problem nowadays. Some Microcystis species produce toxins that cause fatal poisoning of livestock and humans. To predict and prevent nuisance Microcystis blooms in freshwater systems, it is necessary to understand the conditions that lead to Microcystis dominance. One of the specific characteristics of regulating reservoirs for irrigation is artificial exchange of water (hydraulic turnover rate) due to paddy irrigation demand. Artificial exchange of water will affect hydrodynamic conditions, which will change environmental conditions for phytoplankton growth. To our knowledge, few studies have examined both the physical and the biochemical phenomena in irrigation reservoirs, especially focusing on the relationship between the hydraulic turnover rate and Microcystis dominance. The objective of this study was to understand both the physical and the biochemical phenomena in irrigation reservoir using the data of field measurement and numerical simulation. In addition, this study also aimed to understand nitrogen discharging phenomena from paddy field, which may have impacts on water environment of closed water bodies in all downstream watersheds.
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