@article{oai:repository.naro.go.jp:00001723,
 author = {吉田, 正則 and YOSHIDA, Masanori and 村上, 敏文 and MURAKAMI, Toshifumi and 吉川, 省子 and YOSHIKAWA, Seiko and 藤原, 伸介 and FUJIHARA, Shinsuke},
 journal = {近畿中国四国農業研究センター研究報告, BULLETIN of THE NATIONAL AGRICULTURAL RESEARCH CENTER for WESTERN REGION},
 month = {Feb},
 note = {In the Shimanto River Basin in Shikoku, Japan, agricultural activity has been suspected to lead pollution of the Shimanto River. However, the causal relationships between the agricultural activities and changes in water quality are not evident. To reveal these relationships, we analyzed the concentrations and effluent characteristics of N, P, and inorganic ions in the waters of a river, mountain stream, and drainage ditch in an 815-ha watershed in the Shimanto River Basin. The results are as follows. 1) The annual mean specific loads of total N (T-N) and total P (T-P) in precipitation were 18.7 and 0.69 kg ha^-1, respectively. The corresponding precipitation-weighted average concentrations were 0.60 and 0.02 mgL^-1, respectively. 2) Manual measurement of data revealed that the concentrations and effluent loads of T-N, T-P, K^+, and NO_2+3^- -N increased markedly after the river flowed through a low, flat valley in the watershed, and that the concentration of NH_4^+ -N increased abruptly during the year and increased more gradually during the winter. 3) Analysis of automatically measured data revealed that a portion of the effluent T-N load from forested mountainous areas could be temporarily stored in the aquifer below the low, flat valley. The T-N concentration in the river water showed a typical pattern of variation in which the concentration decreased during rainy periods and increased during dry periods after rain. However, the T-N concentration in the river water also showed unusual changes during the drainage of flood water after paddling of paddy fields, drainage of wastewater from a pig barn, and drainage after a heavy rainstorm in which precipitation reached more than 300 mm day^-1. 4) Sudden or gradual increases in the T-N concentration of the river water in winter (i.e. the dry season) were ascribed to inflows of wastewater from the pig barn. Increases in the T-N concentration of the river water during the spring, when there was little rainfall, were ascribed to the drainage of flood water after paddling of paddy fields. 5) Water quality characteristics affected by flow through the low, flat valley were T-N, T-P, NH_4^+ -N, NO_2+3^- -N, and PO_4^3- -P. The proportions of these compounds added from the low, flat valley ranged from 49% to 84%. Most of these compounds were thought to be originated from agricultural and livestock industries, because effluent loads from rural communities (another potential source of these compounds) in the low, flat valley were negligible.},
 pages = {75--89},
 title = {四万十川の一流域における窒素, リン, 無機イオンの濃度変動および負荷流出特性},
 volume = {8},
 year = {2009},
 yomi = {ヨシダ, マサノリ and ムラカミ, トシフミ and ヨシカワ, セイコ and フジハラ, シンスケ}
}