| 摘要: | 近年來，大氣層中溫室效應氣體(greenhouse gases)含量逐年增加進而
導致全球暖化及氣候變遷議的議題普遍受到國際間的重視。人工溼地為
一種低成本、省能源、容易操作、且兼具生態保育及景觀價值的廢水處
理程序，然而在淨化水質的生化程序中，無可避免的也會產生甲烷
(CH4)、氧化亞氮(N2O)溫室效應氣體而引起關切。人工溼地在國內外應
用的數目及面積規模均有逐年成長的趨勢，因此溫室氣體排放造成衝擊
的相關研究有其迫切需要。
本研究繼賴建志(2008)於民國96 年12 月~97 年6 月的7 個月期間調
查了嘉南藥理科技大學校園人工濕地N2O 與CH4 釋放通量研究之後，
持續以該溼地為調查對象，使用密閉罩法測量濕地不同位置點的溫室氣
體釋放通量，並同時監測濕地的廢水處理操作條件及監測濕地的水質變
化與環境條件。直到98 年6 月止，每個月採樣分析一次，本文因此收
集了該人工濕地為連續19 個月的溫室氣體長期監測資料進行統計分
析。本研究人工濕地系統由一個表面下流動式(SSF)溼地連結一個表面流
(FWS)溼地所構成，總濕地面積約3,800m2，收集經污水處理廠二級處理
後的放流水，研究期間平均日處理量317m3 / d。本年度的主要研究目的
包括：(1)調查人工溼地N2O 及CH4 釋放通量的時間與季節變化；(2)探
討人工溼地N2O 和CH4 釋放通量的空間分布變化；(3)探討N2O 和CH4
釋放通量與環境因子及水質間的關係；(4)有水生植物覆輓L植物覆?br>區域之氣體通量的比較；(5)探討日夜間變化對人工溼地溫室效應氣體產
量的影響；(6)比較不同類型人工溼地(FWS 與SSF 溼地)溫室氣體排放量
的差異，並與國內已建立的天然溼地溫室氣體排放資料進行比較。
II
研究結果顯示，SSF 濕地對N2O與CH4的釋放通量分別為3.83~87.37
μg N2O m-2 h-1 及-1.09~55.36 mg CH4 m-2 h-1，而FWS 濕地的釋放通量分
為−6.1~128.78 μg N2O m-2 h-1 及-4.17~28.86 mg CH4 m-2 h-1。氣體通量的
月份變化觀察結果顯示，SSF 及FWS 兩者濕地的最高N2O 通量都發生
在2008 年3 月與10 月，最低N2O 通量都發生在2008 年2 月；而兩者
濕地的最高CH4 通量都發生在2008 年9 月，SSF 濕地的最低CH4 通量
發生在2008 年2 月，FWS 濕地的最低通量則出現在2008 年1 月。若以
季節進行平均統計，發現冬季整個溼地的N2O 與CH4 平均通量明顯低
於春、夏或秋季的平均值(p<0.05)，而春、夏及秋季之間的通量並無明
顯差異(p>0.05)。在空間變化方面，N2O 的平均釋放通量沿著人工濕地
的流動距離而顯著下降(p<0.05)；CH4 的平均釋放通量隨人工濕地流動距
離的下降趨勢較不明顯，僅發現在SSF 單元進流端的CH4 通量明顯高
於出流端(p<0.05)。
本研究以單變數線性回歸將不同位置及不同時間所調查的氣體通量
與各項水質參數及氣溫的監測結果進行交叉分析，結果發現氣溫、水溫
及FWS 單元底泥溫度對三種溫室氣體通量有最一致的顯著正相關。同
時也發現氣體通量與氣溫的關係遵循著名的modified Arrhenius
equation(R=0.703~0.912, p<0.01)，N2O 與CH4 釋放通量的溫度校正係數
分別為1.042~1.098 及1.087~1.170。此結果說明季節變化導致的濕地溫
度變化，進而影響人工濕地中有關碳與氮物質的微生物轉化程序，會顯
著影響溼地N2O 及CH4 的釋放。
有水生植物存在的溼地區域，其N2O 與CH4 通量平均值均高於無水
生植物存在的溼地區域，其中以在SSF 單元所測的N2O 通量的差異性
最顯著(p<0.05)。本研究所調查的N2O 及CH4 通量值落於文獻中有關人
III
工溼地處理廢水所報導通量的範圍。若與國內天然溼地溫室氣體通量的
文獻值比較，本研究人工濕地的N2O 通量略高於、CH4 通量則明顯高於
天然溼地。
Because global warming and climate changes are following upon an
increase in atmospheric levels of greenhouse gases, there is intense concern
with the sources and emissions of the gases. Constructed wetland technology
is a natural treatment system for wastewater engineering and is characterized
by the advantages of moderate capital costs and very low energy
consumption and maintenance requirements. However, constructed wetlands
are inherently the net source of greenhouse gases such as methane (CH4),
nitrous oxide (N2O), and Carbon dioxide (CO2). Wetland construction and
the area covered by constructed wetlands are increasing domestically and
globally, thus there is an urgent need to elucidate the impact of constructed
wetlands on atmospheric burden of these gases.
Following the study conducted by Chien-Chih Lai in 2008, this study
monitored emission rates of nitrous oxide and methane as well as several
parameters of water quality simultaneously and monthly at various sampling
locations of a practical-scale constructed wetland system located in
Chia-Nan University of Pharmacy and Science during the period from
December 2007 to February 2009. The constructed wetland system has been
operated for tertiary treatment of campus wastewater for over three years,
and consists of a subsurface flow (SSF) wetland and followed by a free
water surface flow (FWS) wetland with a total surface area of 3,800 m2. The
objectives of the study were to: (1) investigate the spatial and temporal
variations in emission rate of greenhouse gases; (2) investigate the
relationship between gas emissions and water quality of the constructed
wetland to elucidate possible factors that can affect greenhouse gas emission;
(3) examine the differences in greenhouse gas emissions between in
V
vegetated and non-vegetated area in constructed wetlands; (4) investigate
variation of gas emission rate during a day-night cycle; (5) compare the
results obtained from the study with results of domestic natural wetlands
from literature and with results of constructed wetlands from literature.
The monitored results showed that gas emission fluxes ranged from
3.83~87.37 μg N2O m-2 h-1 and -1.09~ 55.36 mg CH4 m-2 h-1 for the SSF
wetland, and from −6.1~128.78 μg N2O m-2 h-1 and -4.17 ~ 28.86 mg CH4
m-2 h-1 for the FWS wetland. The N2O emission fluxes of the both wetlands
recorded in March and October 2008 were greater than that recorded in other
months, while their CH4 fluxes observed in September 2008 was highest
among the data monthly observed. The lowest flux of either N2O or CH4 was
measured in February 2008. When looking at the seasonal difference in N2O
and CH4 flux, we found that the gas flux determined in months of winter
season was significantly lower than those of spring, summer or fall (p<0.05),
and the difference in the gas flux among the spring, summer and fall was
insignificant (p>0.05).
The average emission flux of either N2O or CH4 was found to be
decreased (p<0.05) along the flow path of the SSF and FWS unit. There was
significant difference (p<0.05) in N2O flux between inlet and outlet of the
both wetlands as well as in CH4 flux between inlet and outlet of the SSF
units.
A variety of water quality parameters and air temperature were further
correlated with gas emission fluxes by using single variable linear regression
method. It was found that gas fluxes of N2O and CH4 correlated significantly
and positively with ambient temperature, water temperature and temperature
of the FWS sediment. Additionally, the relationship between the gas fluxes
and ambient temperature strongly followed the modified Arrhenius equation
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(R=0.703~0.912, p<0.01), with a temperature coefficient ranging from 1.042
~ 1.098 and 1.087 ~ 1.170 for N2O and CH4 emission, respectively. These
findings indicate that temperature variation caused by seasonal change
affected the biological processes responsible for carbon and nitrogen
transformation, which in turn influenced the gas emission in wetlands.
The average fluxes of N2O and CH4 measured in vegetated areas of both
the SSF and FWS units were greater than those in unvegetated area, in
which difference in N2O flux between vegetated and unvegetated area in the
SSF unit was most significant (p<0.05). The gas fluxes reported in this study
fall within the gas flux values reported by literature regarding constructed
wetlands for wastewater treatment. As compared to the reported values of
domestic natural wetlands from previous studies, the values of constructed
wetlands in the study showed slightly higher in N2O flux, considerably
higher in CH4 flux, and about the same order of magnitude in CO2 flux. |
