新海橋人工溼地水生植物生長與水質淨化效能

Abstract

熱帶與亞熱帶的環境可能因颱風或暴風雨形成的氾濫導致重大改變，這些天災影響人工濕地處理污染物的效能被大多數在溫帶進行的研究所忽視。因此本研究調查淡水河流域的新海橋第二期人工濕地於2007年柯羅莎(KROSA)颱風干擾前後濕地系統污染去除效能的差異，結果顯示在柯羅莎颱風干擾之前，新海二期表面流式人工濕地有效移除64.3％的生化需氧量、98.9％氨氮與39.5％的總磷。柯羅莎颱風在濕地範圍造成大規模的氾濫並且沖走多數水生植物族群的地上部，並在每個處理單元的底部遺留淤積物，儘管溼地系統內的水流動在颱風過後隨即恢復，但是其污染去除效能僅有37.7％的生化需氧量、35.1％氨氮與31.8％的總磷。比較颱風干擾前後人工濕地處理的水質，結果顯示污染物去除量的效能被颱風影響，因此建立高流量的引道並評估其他預防方式將可保護易受颱風干擾區域的人工濕地。 3.29公頃的新海二期人工濕地每天處理4000立方公尺的家庭廢水與城市逕流，其蘊含的生物量具有生產生質能源和碳吸存的潛力，栽植多種類的水生植物也能促進生物多樣性。於2007年3月至2008年3月期間調查人工濕地內植物地上部的每季生物量變化，發現水生植物地上部生物量與碳存量累積於2007年9月達到高峰，其總量分別為16,737公斤與6,185公斤。柯羅莎颱風於2007年10月淹沒新海二期人工濕地，但水生植物在沒有人為補植下卻有明顯恢復，水丁香比颱風干擾前位於優勢的香蒲更快地在溼地內恢復覆蓋，觀察水生植物族群於颱風干擾後自行恢復覆蓋的能力，顯示在人工濕地收獲生物量的可行性，試驗區域內收獲的生物量80％灰化後可產生11,846千瓦小時的能源以供1個月之用。 新海二期人工濕地系統污染處理效能與水生植物地上部植物組織內的總磷和總氮累積的相關性，19種水生植物中含量最佳的為蕹菜 (Ipomoea aquatica)與台灣水龍(Ludwigia x taiwanensis) ，總氮含量分別為3.82%與3.52% (w/w)，其總磷含量則分別為0.64%與0.83% (w/w)，整體植物累積的吸收量從2007年3月至2007年9月達到高峰，總氮含量從213公斤增加到403公斤，總磷含量則從41公斤增加至75公斤。2007年3月至2008年3月間總氮累積於植物組織內和進流汙染物去除的比率分別為1.57％、2.76％、1.51％與3.2％，同一期間的總磷累積於植物組織內和進流汙染物去除的比率分別為1.71％、8.0％、0.58％與10.1％，水生植物地上部吸收溼地系統內營養物質的移除量於生長季節則更為明顯。

Typhoons and hurricanes in subtropical/tropical regions can induce significant environmental changes. It may be a mass flooding or inundations. However, the damage to the pollutant removal efficiencies of constructed wetlands brought about by these natural disturbances has been neglected in major studies conducted in temperate climates. Therefore, this study compares the pollutant removal performance of the Hsin-Hai Bridge phase Ⅱ constructed wetland in the Danshui River Basin, before and after the system was inundated with flooding from Typhoon Krosa in 2007. The pollutant removal performance of the free water surface (FWS) constructed wetland was investigated monthly from September 2006 to April 2008. Results of the study demonstrated that this FWS wetland effectively removed 64.3% BOD, 98.9% NH4–N, and 39.5% Total-P before Typhoon Krosa. However, the extensive flooding caused by Typhoon Krosa swept over most of the aboveground plant community and deposited the sediment onto the bottom of each compartment. Subsequently, reduced pollutant removal efficiencies were observed. Only 37.7% BOD, 35.1% NH4–N, and 31.8% Total-P were removed after this event, although the flow regime was immediately restored. Comparing the water quality data for the FWS wetland before and after Typhoon Krosa revealed the immediate, quantitative damage to the pollutant removal performance caused by the typhoon's inundation. Consequently, a high-flow bypass and additional preventive measures would protect any constructed wetland in areas subject to typhoons. Wetland biomass has potentials for bioenergy production and carbon sequestration. Planted with multiple species macrophytes to promote biodiversity, the 3.29 ha constructed wetland has been treated 4000 cubic meter per day (CMD) domestic wastewater and urban runoff. This study investigated the seasonal variations of aboveground biomass of the constructed wetland, from March 2007 to March 2008. The overall aboveground biomass was 16,737 kg and total carbon content 6185 kg at the peak of aboveground accumulation for the system emergent macrophyte at September 2007. Typhoon Korsa flood this constructed wetland at October 2007, however, significant recovery for emergent macrophyte was observed without human intervention. Endemic Ludwigia sp. Recovered much faster, compared to previously dominated typha. Self-recovery ability of the macrophyte community after typhoon validated the feasibility of biomass harvesting. Incinerating of 80% biomass harvested of experimental area in a nearby incineration plant could produce 11,846 kWh for one month. This study investigated the correlations between the system treatment efficiencies and total nitrogen (TN) and total phosphorus (TP) accumulations of aboveground tissues of the wetland macrophytes. Among 19 emergent macrophytes studied, the optimal TN contents, 3.82% and 3.52% (w/w) were found for water spinach (Ipomoea aquatica) and Ludwigia x taiwanensis; while the optimal TP contents were found for the above two macrophytes at 0.64% and 0.83% (w/w). The accumulations of total plant TN and TP uptakes increased from 213 to 403 kg and 41 to 75 kg from March 2007 to the peak at September 2007, respectively. The TN ratios between plant tissue accumulations and the removals from the influents were 1.57%, 2.76%, 1.51% and 3.2% from March 2007 to March 2008. In the same period, the TP ratios between plant tissue accumulations and the removals from influents were 1.71%, 8.0%, 0.58% and 10.1%. The roles of the uptakes by aboveground portions of emergent macrophytes in system nutrient removals from the influents were more significant during growth seasons.