湖泊為一重要的水資源,然而目前湖泊水質優養化評價,仍缺乏一共通、可靠的綜合評估指標,本文嘗試以灰關聯分析法針對宜蘭地區湖泊水質監測資料進行多指標優養化綜合評估,並探討此方法與常用卡爾森優養指標法在評估結果上的差異。研究結果顯示:(1)灰關聯分析具有湖泊水質多指標綜合評估功能,灰關聯度的計算採用傳統公式或修飾公式,對所湖泊優養等級之評定結果影響不大。(2)採灰關聯分析法(修飾公式)所判別的五湖泊中四個呈普養等級,一個則呈普/優養等級,優養化程度較採用卡爾森綜合優養指標法判定之結果為輕。(3)灰關聯分析過程中湖泊水質監測數據是否經無因次處理,會影響某些湖泊優養等級之評定結果,需謹慎為之。(4)湖泊水質監測數據總磷的測定偵測極限須提高,以避免優養化綜合評估結果因主觀採用數值之不同而出現歧異。
Lake is an important water resource. However, a common accepted and reliable synthetic evaluation index for lake water quality is not found. In this study, grey relational analysis were used to evaluate the eutrophic status for the lakes of Yilan Area. Results obtained from grey relational analysis were compared with that obtained from Carlson trophic state index as well. The analysis results indicate that (1) grey relational analysis can be successfully established for eutrophic state evaluation. No mater Deng's formula or Wen's modified formula was applied for the calculation, there is no big difference in the results of eutrophic state classification. (2) In the 5 evaluated lakes (calculated by Wen's modified formula), 4 of them were classified as mesotropic. One lake was classified as mestropic/eutrophic. In general, a better eutrophic status of lake is obtained from grey relational analysis rather than that rated by Carlson trophic state index. (3) Data were normalized or not before grey relational analysis, the outcome of trophic state classification is different in some lakes. Therefore, data pretreatment for grey relation analysis need to be carefully considered. (4) For the evaluation of eutrophic status for lakes, we found that the detection limit of total phosphorus need to be improved to avoid the different rating that caused by data with total phosphorus below detection limit.