The runoff of suspended, substances, nitrogen, and phosphorus by enforced draining during the ploughing season Experiments in paddy fields

Abstract

山田 佳裕 1) ，井桁 明丈 2) ，中島 沙知 3) ，三戸 勇吾 3) ，小笠原貴子 4) ， 和田 彩香 4) ，大野 智彦 5) ，上田 篤史 2)，8) ，兵藤不二夫 2) ，今田 美穂 2) ， 谷内 茂雄 2) ，陀安 一郎 6) ，福原 昭一 7) ，田中 拓弥 2) ，和田英太郎 2)，9)The runoff of suspended substances，nitrogen，and phosphorus by enforced draining during the ploughing season Experiments in paddy fieldsThe runoff of suspended substances (SS)，nitrogen，and phosphorus by enforced draining during the ploughing season was calculated from experiments in two paddy fields．The area of a paddy field was 3000m 2 ．The total fluxes were 33 kg (SS)， 85 g (total-N)， and 46 g (total-P) in Field A， with a small decrease in water levels (8mm)， 110kg (SS)，589 g (total-N)，and146 g (total-P) in Field B with a major decrease in water levels (72mm)． Furthermore， the nitrogen/phosphorus ratios (mol ratios) of the waste water by the enforced draining were 4.1 (Field A) and 8.8 (Field B)．In comparison with N/P of the phytoplankton (16)，it was found that the phosphorus flowed out efficiently with the enforced draining．Increasing the supply of the phosphorus to Lake Biwa is not desirable in view of the current problems of eutrophication．The careless water management of paddy fields was a crucial factor in any plan to improve the water quality of Lake Biwa．

Radiocesium discharge from paddy fields with different initial scrapings for decontamination after the Fukushima Dai-ichi Nuclear Power Plant accident

“…Table 4 shows a comparison among the results of this study and other recent studies related to SS discharge due to puddling, [31][32][33][34] showing signicant variability. However, SS (kg ha À1 ) aer puddling is roughly in proportion to discharged water (mm).…”

“…Several recent studies have demonstrated that the discharge of muddy water was increased by puddling during irrigation. [27][28][29][30][31] Thus, the volume of drainage water may affect SS discharge.…”

Time Dependence of the 137Cs Concentration in Particles Discharged from Rice Paddies to Freshwater Bodies after the Fukushima Daiichi NPP Accident

“…The major causes of soil wash-off from paddy fields are runoff of turbid paddy water during puddling, enforced drainage after puddling, runoff of paddy water during heavy rainfall, and soil erosion during the nonirrigation period. Many studies have used monitoring and modeling to evaluate the soil wash-off from paddy field. ,− However, to estimate the particulate 137 Cs wash-off from paddy fields, parametrization of the particulate 137 Cs concentration in the discharged suspended solid (SS) is essential.…”

Dissolved oxygen concentration in river sediment of the Lake Biwa tributaries, Japan

“…As a result, the analysis revealed that the proportion of paddy fields has a significant effect on the particle size composition (Table 4). In rice farming, plowing, irrigating, and rice planting release large quantities of muddy water into the rivers (Yamada et al 2006). Fine particles of paddy soil origin are abundant in the muddy waters and the river sediments downstream.…”

“…The paddy field supplies the river with many substances (Takeda et al 1991;Kondoh et al 1993;Kawara et al 1996;Sugimoto et al 2008;Wang et al 2009). During plowing, irrigating, and rice planting, water rich in particles of paddy field soil is discharged from the paddy fields into the rivers, and this discharge causes turbidity in the river water and the water in Lake Biwa (Yamada et al 2006). Fine particles supplied from the paddy fields settle on the riverbed.…”