鴛鴦湖湖水溶解性有機碳之來源探討

Abstract

鴛鴦湖為位於台灣北部之中高海拔湖泊，其湖色呈現深褐色且偏酸性，被認為可能由溶解性有機碳(DOC)所造成。為進一步了解DOC在此湖泊生態系所扮演的角色，本研究乃探討湖水中DOC的來源以及其對藻類生長的影響。實驗採集湖區陸域的杜鵑、扁柏之凋落物及附生苔蘚進行淋洗、萃取湖周之表土和分離純化湖水中的藻類，以分析淋洗液、土壤、湖水及藻液的DOC。結果顯示，高比例的DOC為深褐色、不易被分解的腐植物質。湖水DOC的苯環化程度(SUVA254)相當高。在偏酸性雨水的淋洗下，苔蘚產生更酸的淋洗液。降雨量為影響湖水DOC濃度、pH值、水色(A440)的重要因子，且這些變量間有高度的相關性。由螢光光譜儀所做之激發－發射矩陣光譜(EEMs)及用高效液相層析(HPLC)儀所做之分子量檢測顯示，湖水的DOC以外源性的腐植物質為主，其性質與杜鵑和蘚的淋洗液較為接近。以鴛鴦湖湖水之DOC對分離自此湖的藻類做培養試驗，結果顯示DOC濃度愈高，則藻類生長愈多。對照藻液的EEMs圖譜，顯示藻類生長時會產生小分子的有機物及大分子的腐植物質，但因其在水中的濃度很低，僅在湖水量較少時較能看出其對湖水DOC性質的貢獻。綜言之，在扁柏為優勢植被的鴛鴦湖集水區中，林下的灌木及苔蘚等附生植物的淋洗液以及表土有機質層中的腐植物質可能為鴛鴦湖湖水DOC之重要來源，也是使土壤及湖水酸化的主要原因。

Yuan-yang Lake is a subalpine lake situated in northern Taiwan. The lake water is characterized by brown color with low pH. In order to know more about the role of dissolved organic carbon (DOC) in the lake ecosystem, this study is attempted to elucidate the sources of DOC and its effect on algae in this lake. Litters from dominant plants, rhododendron and cypress, and epiphytic liverworts were collected and used for leaching experiments. In addition, surface soil of forest was collected and extracted for comparison with lake water. The results showed that DOC in lake water was contributed mainly by the refractory, humic substances (HS). High values of SUVA254 in lake water suggested that it is in high degree of aromaticity. The acidity of leachates from epiphytic liverworts was higher than rain water. The amount of precipitates was an important factor that affected the DOC concentration, pH, and color (A440) in lake water. The results of excitation-emission matrices (EEMs) and high performance liquid chromatographic (HPLC) analysis showed that a high similarity existed between the fluorescence plots and molecular weight spectra between lake water and the leachates of rhododendron and epiphytes, suggesting that DOC in lake water should be mainly allochthonous in origin. In experiments of cultivating the algae isolated from lake with DOC, it is revealed that algae grew faster in higher concentrations of DOC. The plots of EEMs showed that algal cells produced low molecular weight molecules and high molecular weight HS. However, owing to low algal density in lake water, the role played by the algal-derived DOC in lake water was minor and could be negligible. The source of DOC and its effects on algae in this lake were discussed. This study provides data showing that the DOC in YYL is contributed mainly by the leachates from forest under-layers and epiphytes.