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標題: Time Series and Spatial Analysis on the Trophic Status in Te-Chi Reservoir
作者: Leung, William Kachu
關鍵字: Additive decomposition method;相加性季節變動模式;Te-Chi reservoir;Trophic Status Index;Time series;Spatial analysis;德基水庫;優養化;時間數列;空間分析
出版社: 水土保持學系
中 文 摘 要
在時間性方面以德基水庫中總磷資料計算優養指數TSI(Trophic Status Index),並利用相加性分解方法進行德基水庫水質優養化時間數列分析。通常影響時間數列的成份包括:(T)長期趨勢,(S)季節變動,(C)循環變動,及(I)不規則變動。其中比較通用的模式之一有相加性季節變動模式 (additive decomposition method): Y=T+S+C+I。我們從結果分析得知:(1)德基水庫TSI指標呈規律變化,其高峰期由四月到十月,為期七個月。(2)長期趨勢隨時間增加而變化,其關係為 T=50.978+0.0728t。(3)循環變動週期會從二、三年後減少至一年或一年半。為了比較相加性與相乘性季節變動模式在水庫優養化時間數列分析上之優劣,研究結果顯示,兩模式經總變異統計方法統一單位後,利用敘述統計和t-test進行比較驗證,發現兩模式中之共同因子 -- 長期趨勢(T)、季節變動(S),及循環變動(C)都具有相同的性質與變化情形。至於在預測能力方面,結果則顯示相乘性模式的誤差平方和(=4392.821)較相加性模式(=4520.047)為低,具有較精確的預測能力。

The subject of this study is trophic status of Tei-Chi reservoir to use as time analysis and spatial analysis.
The objective of time analysis is to apply the additive
decomposition method as well as TSI (Trophic Status Index) to maturate a practical procedure for time series analysis of an eutrophication conditions in reservoirs to exhibit trend and seasonal effects. The basic idea behind this model is to determine the trophic variation including trend (T), seasonal (S), cyclical (C), and irregular (I) changes. The results indicate that (1) TSI has regular change with a long high peak for seven months from April to October yearly, (2) the long-term trend (T) increases with time(t) as following relationship : T=50.978+0.0728t, and (3) circular change period decreases from two or three years to about one year. The methodology is feasible to present the eutrophication change numerically. Otherwise the study was to compare the suitability of additive and multiplicative decomposition method for time series analysis of eutrophication in Te-Chi reservoir. Besides the comparisons of same factors between two models, the precisions for forecast abilities of models were also examined. The statistical data and t-test indicated that trend (T), seasonal (S), and cyclical (C) change of two models had same property and variation after standardization in units. As for forecast ability, sum of square due to error (SSE) of multiplicative model (=4392.821) was lower than that of additive model (=4520.047), i.e., multiplicative model could forecast eutrophication more precise. But the differences between two models were negligible. Consequently, both multiplicative and additive model could forecast eutrophication trend in Te-Chi reservoir efficiently.
In spatial analysis was to investigate the relationship between trophic status of Tei-Chi reservoir and watersheds streams, and to evaluate the regions influence by ANOVA and multiple comparison method. The results indicated that water quality for upper part of reservoir (within 28 ~ 46 section) belonged to a serious eutrophication, as well as the middle and down part were better due to effective function of protective zone. For tributaries of reservoir, Li-San effluent and rivers of upper watershed were main contamination sources. On the other hand, the reason causing bad water quality of watershed didnt come from Wu-Ling farm, but contamination of non-point source in upper part of watershed. Finally, the data presented that outlet of Tei-Chi reservoir had better water quality due to natural self-purification of reservoir
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