蓮華池試驗集水區淨輻射與土壤熱能變化特性之探討

Abstract

本研究的目的在於探討森林地區輻射能量的變化以及土壤的熱性質。以蓮華池五號集水區為試驗地，設置淨輻射計、土壤熱流量板，以及在不同深度埋設土壤溫度計、張力計。藉由自2005年五月至2006年四月收集到之淨輻射、土壤熱通量以及不同深度土壤溫度與土壤水分勢能資料的分析，探討本試驗地各項淨輻射、土溫、土壤熱能變化的特性，茲將研究結果摘要如下。 冬季因日射量及氣溫較低，地表長波輻射易由稀疏之樹冠層射出林外，因此林內淨輻射對林外淨輻射之比率較低。夏季降雨量多，土壤潮濕，潛熱通量較高，加上氣溫較高，顯熱通量亦高，故夏季土壤熱通量佔林內淨輻射量的比例非常低。而冬季則由於顯熱通量與潛熱通量較其它季節更低，且此時土壤熱通量為地表熱量的供應來源，因此佔林內淨輻射的比例也就相對較高。 淺層土壤溫度的日變化呈正弦曲線變化，土壤越深，則土壤溫度的正弦曲線變化其振幅越小，週期的起始也隨著土壤深度增加而延遲。試驗地於2005年九月至十月發生土溫的逆轉，土壤由吸熱狀態轉變為放熱狀態，一直到2006年三月到四月才又翻轉回來。 降雨時土壤水分勢能很快就能反應降雨的情況，其中以淺層土壤變化速度最快，在重力水(即pF值1.8以下)與毛管移動水的情形土壤熱傳導係數與土壤水分勢能具有明顯相關，土壤水分勢能越高，土壤熱傳導係數越高。在毛管水非移動水的情形土壤熱傳導係數與土壤水分勢能則沒有明顯相關。地表無有機物覆蓋處測得的土壤熱傳導係數平均值為1.095 Jm-1℃-1S-1，較有機物覆蓋處平均值0.5736Jm-1℃-1S-1大。地表無有機物覆蓋處測得的土壤熱傳導係數日變動的幅度也較無有機物覆蓋處高。

This study is to investigate radiation energy variation and soil thermal properties in forest area. Experimental plot was selected in Lienhuachi experimental watershed No. 5. Radiometer, heat flux plate, and soil thermometers and tensiometers embedding at different depths were set. Data involving net radiation, soil temperature, and soil water potential were collected during May 2005 to April 2006. From analyzed data, the characteristics of net radiation within and without the forest, soil temperature, and soil thermal change with soil water situation were understood. Results are summarized as follows: Decreasing solar radiation, decreasing air temperature, and defoliation during winter could cause earth radiation emission through out the canopy. Therefore, the net radiation ratio of within the forest to without the forest was lower. In summer, more latent heat flux and sensible heat flux caused relatively less proportion of soil heat flux to net radiation within the forest. In winter, latent heat flux and sensible heat flux were less than other seasons. Besides, soil heat flux became heat source of earth surface that could increase the proportion to net radiation. Daily soil temperature variation at the shallow part of soil appeared in sine curve. The amplitude of sine curve was decreasing with soil depth increasing. Also, the start of sine curve period delayed with soil depth increasing. During September to October 2005, the overturn of soil temperature occurred, soil heat from endothermic state converted to exothermic state. The process reverted to original state during March to April 2006. Among the rainfall occurred, it was therefore fair that soil water potential at the shallow part changed fastest. In gravitational water condition (pF value below 1.8) and in mobile capillary water condition, soil thermal conductivity would be significantly negative correlation with soil water potential, but in non-mobile capillary water condition, soil thermal conductivity would not be significantly correlation with soil water potential. The mean of the soil thermal conductivity obtained from non-organic matter covered surface was 1.095 Jm-1℃-1S-1, and that of the organic matter covered soils was 0.5736 Jm-1℃-1S-1. Furthermore, the daily variation amplitude of the soil thermal conductivity obtained from non-organic matter covered surface was larger than that of the organic matter covered surface.