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アラスカ・ユーコン河流域における物質輸送機構 : 観測とモデリング

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Title: アラスカ・ユーコン河流域における物質輸送機構 : 観測とモデリング
Other Titles: Material-loading processes in the Yukon River basin, Alaska : Observations and modelling
Authors: 知北, 和久 Browse this author →KAKEN DB
和田, 知之 Browse this author
工藤, 勲 Browse this author →KAKEN DB
Keywords: ユーコン河
Issue Date: 31-Mar-2016
Publisher: 低温科学第74巻編集委員会
Journal Title: 低温科学
Journal Title(alt): Low Temperature Science
Volume: 74
Start Page: 43
End Page: 54
Abstract: 2006年6月~2009年9月の3年余の期間,アラスカ・ユーコン河最下流部のUSGS水位観測点(PLS地点)で浮遊物質濃度,懸濁態炭素(POC)濃度,懸濁態窒素(PON)濃度の1時間連続データを得た.ユーコン河流域(面積8.57×105km2)の約75%は不連続永久凍土をもつ森林域,1.1%は高山氷河域である.6月~9月の夏期には,ユーコン河の流量と浮遊物質濃度は氷河と凍土の融解と数日間にわたる数回の降雨によって大きく変動する.4月下旬~5月初旬には,融雪増水に伴う河氷の破砕(breakup)が生じ,この後は6月初旬まで融雪出水が続く.2007~2009年の3回の融雪出水について,年間の流量・土砂流出量・POCフラックス・PONフラックスに対する寄与を評価した.結果として,年間の流量に対し14.1-24.8%,土砂流出量に対し8.7-22.5%,POCフラックスに対し11.6-23.7%,PONフラックスに対し10.3-24.5%の寄与があった.2006~2008年夏期の日平均流量と日平均土砂流出量の時系列について,それぞれタンク・モデルおよび計算流量のベキ関数を適用して,その再現を試みた.結果として,モデル計算は観測結果との間にr=0.88-0.94(流量)とr=0.73-0.93(浮遊物質濃度)の高い相関を示し,モデルによる再現が共に妥当であることがわかった.土砂流出量から得られる浮遊物質濃度に対する数値解析から,流送土砂の給源が氷河域と河道にあると推定された.感度解析では,温暖化による気温上昇が氷河融解流出に与える効果について議論した.
Hourly time series of discharge, suspended sediment concentration, POC (particulate organic carbon) and PON (particulate organic nitrogen) were obtained at the lowest gauging station, PLS (Pilot Station) of U. S. Geological Survey in the Yukon River basin, Alaska, in June 2006 - September 2009. The river basin (area, 8.57×105 km2) is occupied by 1.1 % glacierized mountainous regions and ca. 75 % lower forest regions with discontinuous permafrost. Thereby, the Yukon River discharge in summer consists of glacier-melt and permafrost-melt discharges over the summer and a few rainfall runoffs for several days. Focusing on the snowmelt runoff in late April or early May to early June, its contribution to annual discharge, sediment load, POC flux and PON flux was estimated. As a result, the three snowmelt runoffs in 2007, 2008 and 2009 occupied 14.1 - 24.8% of annual discharge, 8.7 - 22.5% of annual sediment load, 11.6 - 23.7% of annual POC flux, and 10.3 - 24.5% of annual PON flux. The discharge and suspended sediment concentration time series in the summers of 2006-2008 were simulated by the tank model and a power function of modeled discharge, respectively. The simulated results were agreeable to the observed ones with the correlation coefficient, r=0.88-0.94 for discharge and r=0.73-0.93 for suspended sediment concentration. In the simulation of suspended sediment concentration, it was suggested that the sediment source is located in the glacierized regions and river channels. As a sensitivity analysis, the effect of an increase in air temperature, due to global warming, on the glacier-melt discharge is discussed.
Type: bulletin (article)
Appears in Collections:低温科学 = Low Temperature Science > 第74巻

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