都市淡水水體碳匯調查

Abstract

本研究旨在探討都市湖泊在全球碳循環中的角色，特別是其作為碳源或碳匯的潛力與實際表現。都市湖泊由於位處人口密集的城市環境，經常受到污染物與營養鹽（如氮、磷）的輸入影響，導致水體優養化，進而影響其碳通量。本研究以台灣兩座代表性的都市水體—龍潭大池與大湖公園為研究對象，透過為期一年的實地採樣與氣體通量測量，分析二氧化碳（CO₂）與甲烷（CH₄）之排放情形，並探討其與環境因子間的關聯性。結果顯示，龍潭大池在多數時期呈現低於全球平均值的溫室氣體通量，甚至在某些季節具有碳匯的特徵，顯示其具有吸收CO₂的潛力。反之，大湖公園的甲烷排放通量明顯較高，並在部分時期超過全球平均值的兩倍，是顯著的碳排放源。此現象可能與該湖泊底泥厚度、厭氧環境，以及初級生產力有關。研究也發現甲烷通量在日間普遍高於夜間，推測可能受到光合作用強度與氣體溶解度變化的共同影響。統計分析顯示甲烷通量在季節間變異顯著，特別是在冬夏間的差異，可能與氣溫變化相關；而CO₂通量則未顯示出明確的時間與季節變化趨勢。透過冗餘分析（RDA），本研究進一步探討水質參數與氣體通量之間的關係。結果指出，葉綠素、總磷、硝酸鹽氮、有機碳、溶氧與光照等因子與甲烷通量密切相關，這些指標與湖泊的優養化程度與初級生產力密切相關；CO₂通量則與葉綠素、顆粒性有機碳、溶解性有機碳、pH值、溶氧與總磷等變項有明顯關聯，反映出都市湖泊中碳排放或吸收主要受到藻類光合作用與水質條件的雙重影響。研究也發現，相較於其他類型水體（如自然湖泊與水庫），都市湖泊特別是小型湖泊，其甲烷通量普遍較高，並具有顯著的貢獻潛力。此結果與全球研究一致，指出小型湖泊是內陸水域碳排放的重要熱點，尤其在氣候變遷加劇與都市化進程下，其重要性不容忽視。研究結果顯示，都市湖泊雖具有部分碳匯潛力，但在甲烷排放方面仍可能是重要的碳源，應透過改善水質、降低營養鹽輸入及生態系統管理等方式加以控制，提升其在碳中和政策中的貢獻潛力。

This study aims to explore the role of urban lakes in the global carbon cycle, particularly their potential and actual performance as carbon sources or sinks. Urban lakes, situated in densely populated areas, are often affected by inputs of pollutants and nutrients such as nitrogen and phosphorus, leading to eutrophication, which in turn influences their carbon fluxes. This research focuses on two representative urban water bodies in Taiwan—Longtan Large Tourist Pond and Dahu Park —and analyzes carbon dioxide (CO₂) and methane (CH₄) emissions through year-round field sampling and flux measurements. The results show that Longtan Large Tourist Pond generally exhibited greenhouse gas fluxes lower than the global average and even demonstrated characteristics of a carbon sink during certain seasons, indicating a potential for CO₂ absorption. In contrast, Dahu Park exhibited significantly higher methane emissions, with some periods reaching more than twice the global average, identifying it as a notable carbon source. This phenomenon is likely related to factors such as sediment thickness, anoxic conditions, and primary productivity. The study also found that methane fluxes were generally higher during the day than at night, possibly due to the combined effects of photosynthetic activity and wind speed variations. Statistical analysis revealed significant seasonal variation in CH₄ flux, particularly between winter and summer, which may be associated with temperature changes, whereas CO₂ fluxes did not show clear temporal or seasonal patterns. Redundancy analysis (RDA) was conducted to examine the relationships between water quality parameters and gas fluxes. The results indicate that chlorophyll-a, total phosphorus, nitrate, organic carbon, dissolved oxygen, and light intensity were closely associated with methane flux, reflecting the influence of eutrophication and primary productivity. CO₂ flux, on the other hand, was significantly correlated with variables such as chlorophyll-a, particulate and dissolved organic carbon, pH, dissolved oxygen, and total phosphorus, suggesting that both algal photosynthesis and water quality jointly affect carbon emissions or uptake in urban lakes. The study also observed that, compared to other water bodies such as natural lakes and reservoirs, urban lakes—especially small-sized ones—tend to have higher methane fluxes and substantial emission potential. This finding aligns with global research pointing out that small lakes are important hotspots of carbon emissions in inland waters, especially under accelerating climate change and urbanization. While urban lakes may possess some carbon sink potential, they are likely significant methane sources. Thus, measures such as water quality improvement, reduction of nutrient inputs, and ecosystem management are essential to enhance their contribution to carbon neutrality goals.