Assessment of the feasibility in using constructed mangrove wetland to clean mariculture effluent

• Main Authors: Yung-MingSu, 蘇永銘
• Other Authors: Ya-Fu Lee
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/67121054711578784674

博士 === 國立成功大學 === 生命科學系碩博士班 === 100 === Constructed wetlands represent an environmentally and economically friendly tool in wastewater treatment and for controlling water pollution. This study aimed to investigate the growth, morphology, and leaf photosynthetic pigment content of native mangroves in Taiwan, including grey mangroves (Avicennia marina (Forsk.) Vierh.), red mangrove (Rhizophora stylosa Griff.), and black mangroves (Lumnitzera racemosa Willd.), treated with different hydraulic residence times (HRT: 0.5, 1, and 2 days and one drained treatment as control), to clean mariculture effluent, and their pollutant removal efficiency. The experiments set up 45 microcosms planted in monoculture over a ten month period. The seedlings of all three mangrove species survived under all mariculture wastewater treatments, but longer HRTs induced greater stress and suppressed mangrove growth. For A. marina and L. racemosa, the percent change in stem height, stem biomass, leaf biomass, root biomass, net primary productivity (NPP), and relative growth rate (RGR) were highest with the 0.5-d HRT treatment. For R. stylosa, none of the components of biomass showed any significant difference among treatments. However, the percent change in stem height, NPP, and RGR were highest with the drained treatment. The percent change in leaf number, leaf area, and leaf area ratio of the three mangrove species decreased with increasing HRT. The specific leaf area showed no significant difference among all treatments for A. marina and R. stylosa. However, this parameter declined as HRT increased in the case of L. racemosa. At the intermediate stage of the experimental period, chlorophyll a, chlorophyll b, and total chlorophyll contents were lowest with 2-d HRT treatment for R. stylosa and L. racemosa and with 0.5-d HRT treatment for A. marina. The ratios of chlorophyll a/b in the three species decreased by the greatest extent in the drained treatment, followed by in the 0.5-d, and the least in the 2-d treatment. At the end of the experiment, the chlorophyll contents of A. marina and R. stylosa showed no significant difference among the treatments. For L. racemosa, the chlorophyll a, total chlorophyll contents, and chlorophyll a/b ratio were significantly lower with the 2-d HRT treatment than with the drained and 0.5-d HRT treatments. The all mangrove microcosms removed pollutants from the mariculture effluent with efficiencies of 15.40 ± 2.16% (mean ± SE) for SS, 18.86 ± 2.55% for BOD5, 32.51 ± 3.39% for NH4+-N, 21.17 ± 2.77% for NOx--N, and 23.11 ± 1.23% for TP. Compared with the unplanted group, all of the three planted groups consistently presented greater efficiencies for SS, BOD5, and TP removal. However, no species displayed consistently superior performance in removing all pollutant parameters. Microcosms operating at 2-d HRT exhibited higher removal efficiency for each pollutant than those operating at 0.5-d HRT, but operating at 0.5-d HRT exhibited better mass removal rate for pollutant than those operating at 2-d HRT. The results of the study indicate that under waterlogging conductions, the growth of A. marina and L. racemosa was better than that of R. stylosa, but three plants all decreased with increasing HRT. The longer HRT the better pollutant removal efficiency, but the mass removal rate was reverse. Therefore, growing A. marina and L. racemosa with a 0.5-d HRT regime and periodic draining of wastewater is the most appropriate design for the management of constructed mangrove wetland in southern Taiwan.