廢棄煤礦捨石山與鄰近次生林土壤之化育： 生物、母質與時間因子影響

Abstract

煤礦曾是臺灣重要的採礦產業之一，為早期推動工業化的重要基礎。然而採礦過程，不僅破壞天然植被或改變地形而造成地表退化，其中地下採礦開採時挖掘出的石塊與棄土，因集中堆積形成小山丘狀的地形，而得捨石山之名。由於有關捨石山之土壤性質在自然演育下情況的研究較少，因此本文初步進行捨石山土壤之植生與物理化學性質調查，探討捨石山人為土壤經30餘年自然化育情況下，其土壤性質與鄰近非捨石山土壤之比較。實驗結果顯示，捨石山人為土壤剖面化育較為簡單，僅為A-C土壤層化育，並無化育B層。捨石山人為土壤含石率亦高，土壤含石率超過50 %，下層土壤含石率甚至可達80 %。然而，捨石山土壤呈現較暗顏色，其小於2 mm以下之土壤有機碳量與全氮量較鄰近次生林土壤高，土壤pH亦較次生林低，CEC同樣呈現捨石山土壤高於次生林土壤。選擇性鐵鋁萃取數據顯示，捨石山土壤具有較低Feo/Fed (無定型鐵與游離鐵比例)數值與較高Fed/Fet (游離鐵與全鐵比例)數值，就風化程度而言，鐵鋁萃取數值結果顯示捨石山土壤具備一定程度風化作用，甚至高於鄰近次生林土壤。 儘管土壤野外調查結果顯示土壤剖面仍處於化育初始階段，然而上述土壤化學性質分析結果並不符合我們的預期，我們初步推測土壤分析結果僅為參與土壤化育性質的分析結果，並未實際考慮土壤母質差異之影響，因此我們進一步分析岩塊性質。從岩塊分析的結果可得知，捨石山岩塊與非捨石山之次生林區域岩塊性質亦有明顯差異，尤其是有機碳、全氮含量、Feo/Fed及Fed/Fet數值，顯示捨石山土壤高風化指數亦受到岩石本身所影響。由於捨石山與次生林土壤岩石母質並不相同，若直接比較捨石山與鄰近非捨石山土壤性質差異，可能忽略部分土壤生成因子的影響。我們的結果證明捨石山土壤化育性質除受時間影響外，亦受到生物與岩石母質的影響，且其土壤化學性質僅能說明部分參與土壤化育的結果，無法完全反應土壤風化程度。

Coal mining once played a pivotal role in Taiwan’s early industrial development. However, such activities have resulted in substantial land surface degradation due to the disruption of vegetation and significant alterations to local topography. Among the anthropogenic landforms generated by coal mining, "Coal Waste Heap (Sheshishan)"—mounds or hills composed of waste rock and spoil materials excavated during subsurface mining operations, is one of the obvious landscape features. These geomorphic features, characterized by steep slopes and heterogeneous substrate composition, represent a unique form of anthropogenic geomorphology. Despite their ecological and pedological relevance, the soil formation processes and edaphic properties of coal waste heap landscapes remain understudied under natural post-mining succession. This study intends to present a preliminary assessment of the vegetation structure and soil physicochemical properties developed within the coal waste heap approximately after three decades of natural succession. The objective is to elucidate the current state of soil development in these anthropogenic deposits and to compare their properties with adjacent secondary forest soils.Our results indicate that soils in coal waste heap exhibit incipient pedogenic development, with profiles primarily exhibiting A–C horizon and lacking an illuvial B horizon, indicative of limited pedogenetic horizon differentiation. These soils are characterized by a high coarse fragment content, with lithic fragment volume exceeding 50% in the soils, even reaching up to 80% in some subsoil horizons. Nevertheless, surface horizons exhibit darker color, higher soil organic carbon (SOC) and total nitrogen (TN) contents relative to the adjacent secondary forest soils. Soil pH is comparatively lower, while cation exchange capacity (CEC) is higher, suggesting an accumulation of organic matter and increased colloidal activity in the coal waste heap soils. Selective extraction analyses of pedogenic iron and aluminum specieation further support ongoing weathering processes. Lower Feo/Fed ratios (oxalate-extractable to dithionite-extractable Fe) and higher Fed/Fet ratios (dithionite-extractable to total Fe) observed in coal waste heap soils suggest a relative dominance of crystalline over amorphous Fe phases, implying advanced mineral transformation and a notable degree of pedogenic weathering—potentially exceeding that of the adjacent secondary forest soils. Our field observations suggest that the profile development remains in the early stages, while the chemical indices predominantly reflect the properties in the coal waste heap soils are not at the incipient development as we supposed. To further interpret the unexpected pedochemical trends, a geochemical analysis of the lithic fragments was conducted. The results reveal significant differences in geochemical composition between the rocks from coal waste heap and those from adjacent secondary forest soils, particularly in SOC, TN, Feo/Fed, and Fed/Fet values. These differences indicate that the stronger weathering indices in coal waste heap soils are likely influenced not only by time factor but also by the intrinsic properties of the parent material, which differ lithologically from those of the surrounding landscape. This study concludes that the pedogenesis of coal waste heap soils is governed by a complex interplay between biotic factors, parent material heterogeneity, and environmental conditions. The chemical properties of the soil matrix reflect only the weathered fraction of the substrate, and thus cannot fully represent the weathering status of the entire soil body. These findings underscore the need for integrated geomorphic, pedologic, and geochemical approaches when assessing anthropogenic soil landscapes undergoing natural rehabilitation.