Assessment of carbon sequestration and budget for two saline mangrove artificial wetlands functioned for different ecological services

二種不同生態服務功能之鹹水型紅樹林人造濕地之碳捕捉及碳收支能力評估研究

楊磊(Lei Yang) ； 蔡承斌(Chen-Bin Tsai) ； 袁中新(Chung-Shin Yuan) ； 鄭凱云(Kai-Yun Cheng) ； Hsing-Juh Lin

《濕地學刊》 7卷1期 (2018/12) Pp. 52-71

摘要

The saline aquaculture wastewater combined with local community sewage are treated by several salty constructed wetlands vegetated with mangroves in Southern Taiwan. The greenhouse gases (GHGs) of carbon dioxide (CO_2), methane (CH_4) and nitrous oxide (N_2O) are produced from different metabolic processes emitting into the atmosphere from the wetland systems and thus causing greenhouse effect, while the systems may also exhibit ability to sequestrate and store carbon in the sediments as carbon sinks. In this study, two salty artificial wetland, Datang Saline Constructed Wetland (DSCW) functioned for wastewater treatment and vegetated with black mangrove species of Avicennia marina, and Mangrove Wetland Park (MWP) functioned for mangrove conservation and vegetated with Rhizophora stylosa, were selected for assessment of carbon sequestration and carbon budget based on measuring GHGs emissions and net primary productivities. The average GHGs flux were then calculated, and compared with the net carbon sequestration flux with same unit of carbon dioxide equivalent (CO_2 eq.) to learn if the wetland exhibited carbon sink or source effects. According to the monitoring and calculating results, the total flux of three GHGs emitted for DSCW and MWP were 2,128 and 2,148 g CO_2 eq. /m^2-yr, respectively, while the flux of carbon output from the water bodies of DSCW and MWP were 781 and 1,030 g CO_2 eq. / m^2-yr, respectively. Hence, the total carbon output flux for DSCW and MWP were 2,909 and 3,178 g CO_2 eq. /m^2-yr, respectively. The flux of carbon sequestration, which could be regarded as carbon input flux and were transferred to CO_2 eq. from the net productivities of mangroves in wetlands, in DSCW and MWP were measured equal to 2,233 and 2,948 g CO_2 eq. /m^2-yr, respectively. The flux of carbon budget for DSCW and MWP were then calculated equal to -676 and -230 g CO_2 eq. /m^2-yr, respectively, which negative values revealed that both of the artificial wetlands, DSCW and MWP, exhibited carbon source effect. It was inferred that the large amounts of N_2O with high global warming potential (GWP) of 265 emitted from DSCW and MWP systems that treating the wastewater and receiving polluted lagoon seawater, respectively, both of which contained high nitrogenous nutrients, caused high values of total GHGs flux emitted from the wetland systems. It was concluded that both of the nitrogenous contents and environmental conditions suitable for microbial production of N_2O might be the main factors to assess the wetland systems presenting carbon sink or source effect.

關鍵字

Carbon sinks ； carbon source ； carbon budget ； carbon sequestration ； greenhouse effects ； saline mangrove constructed wetlands

並列摘要

位於南臺灣的大鵬灣為一感潮的海岸潟湖，其週遭有許多的海水養殖池，係抽取潟湖內之海水以養殖石斑魚為主。其所衍生出之海水養殖廢水，結合當地社區的生活污水，經由附近5座鹽水型紅樹林人工濕地處理後，再排入大鵬灣域內，以防止污染大鵬灣水質。然而不論是自然濕地或人造濕地，經由濕地系統內的不同生物及微生物之代謝過程中，均會產生二氧化碳(CO_2)、甲烷(CH_4)及氧化亞氮(N_2O)等溫室氣體(GHGs)，釋出於大氣中，從而產生溫室效應。然而濕地系統亦具有明顯碳的捕捉能力，將碳螯合及儲存於沉積物中，因而具有碳匯的功能。在本研究中，將選取大鵬灣五座鹹水型紅樹林人工濕地中的大潭人工濕地，紅樹林種為海茄冬(Avicennia marina)，以及1座紅樹林濕地公園，係以復育紅樹林之紅海欖(Rhizophora stylosa)的品種為其主要功能，並量測該人造濕地之3種溫室氣體排放量，以及其碳捕捉及碳收支的能力，以評估這二類不同功能之鹹水型紅樹林人造濕地是否呈現出碳匯或碳源的效應。根據監測和計算結果，大潭人工濕地及紅樹林濕地公園內之3種溫室氣體排放之總流通量計算出分別為2,128及2,148 g CO_2 eq. / m^2-yr，以及水體碳輸出通量分別為781及1,030 g CO_2 eq. / m^2-yr；因此，總碳排出通量分別為2,909及3,178 g CO_2 eq./ m^2-yr。而所測量計算出的碳捕捉通量（近似於紅樹初級生產力通量）則分別為2,233及2,948 gCO_2 eq./ m^2-yr，因此經碳收支平衡的計算，得到其數值分別為- 676及- 230 gCO_2 eq./m^2-yr。由計算結果為負值，顯示出這2座人造濕地皆呈現出碳源的效應。根據推斷，這是因為這2座人造濕地，1座處理含氮量較高的養殖廢水及生活污水，而另1座濕地公園承受含氮營養鹽的潟湖海水，致使全球溫室潛勢值(GWP)極高的N_2O，於換算為CO_2 eq.後(GWP=265)，釋出大量的溫室氣體所致。

並列關鍵字

鹹水型紅樹林人造濕地 ； 溫室效應 ； 碳捕捉 ； 碳收支 ； 碳源 ； 碳匯