Inflow characteristics of pollutant loads from surrounding rivers into Lake Shinji.

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  • SUGAI Ryukichi
    Shimane Environment & Health Public Corporation
  • MIZOYAMA Isamu
    Miyoshi Offce of River and National Highway, Chugoku Regional Development Bureau, Ministry of land, Infrastructure, Transport and Tourism
  • SUGAHARA Shogo
    Graduate School of Science and Engineering, Shimane University
  • SEIKE Yasushi
    Graduate School of Science and Engineering, Shimane University

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  • 周辺部河川からの宍道湖への汚濁負荷流入特性
  • シュウヘンブ カセン カラ ノ シンジコ エ ノ オダク フカ リュウニュウ トクセイ

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Abstract

<p>　In this study (1993-2003), the Loading-flow rate (LQ) equations for rivers and drainages, flowing into Lake Shinji were determined by applying the least-squares method to logarithmic regression curves based on data from loadings and flows. Our results showed that values for “b” from the equation, loading = a (flow rate)b (L=aQb) in the Hii River, were higher under flood flow conditions than values calculated under normal flow conditions, with the exception of total inorganic nitrogen (TIN).<br>　The percentages of pollutant loadings from the Hii River to Lake Shinji were 60, 40, 62, 31, and 36% for chemical oxygen demand (COD), total nitrogen (TN), total inorganic nitrogen (TIN), total phosphorus (TP), and phosphate (PO4-P) respectively.<br>　Pollutant loadings of TN, TP from other rivers to Lake Shinji were higher than the Hii River, although the percentage of total amount of river water (approximately 20%) from other rivers were lower than the Hii River. As a result of a cluster analysis, indicators of water pollution were divided into five groups, revealing that the TIN/PO4-P ratio from inflows into the west bank region of Lake Shinji (with the exception of the Hii River) were higher than those of other rivers. <br>　The percentages of the particulate portion of phosphorus (PP) in the Hii River, under both flood flow conditions and normal flow conditions, were higher than those of COD and TN. In addition, our results revealed that the TN/TP ratio was smaller under flood flow conditions (6.0) than that under normal flow conditions (29), indicating that relative phosphorus loadings were increased under flood flow conditions.</p>

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