| Summary: | 碩士 === 國立臺灣海洋大學 === 水產養殖學系 === 105 === Duckweed is an aquatic plant that can play the best role in an aquaponics system for its being very productive and capable of cleaning the water in which the aquatic animal inhabits. Here we used Spirodela polyrhiza, one of the most studied duckweed species. In Experiment 1 (Chapter 2), we successfully employed image analysis system to get covering area of duckweed and estimate duckweed fresh dry weight through weight-area correlation analysis. Considering the convenience and popularity of smart phone, we would prefer it for image taking than digital camera. Equipped with this effective tool to estimate duckweed biomass, we were then able to find out the factors affecting duckweed growth in the following experiments, such as light source and photoperiod (Experiment 2 – Chapter 3) and light intensity and nitrogen nutrient (Experiment 3 – Chapter 4). Both LED white and fluorescent T5 achieved better duckweed growth and nutrient stripping than LED blue, but no difference in between of the former two. LED white was the preferred light source for its higher energy saving than fluorescent T5. Photoperiod had no effects on duckweed growth. However, 16L:8D was chosen for its higher nutrient stripping than 12L:12D but similar performance as 24L:0D. Light intensity at 55, 110 and 220 PPFD (mol m-2s-1) exhibited no effects on duckweed growth and nutrient stripping. Concomitantly, light intensity at 55 mol m-2s-1 should be used if the facility environment met, such as light tube specification and accommodation space. The highest nitrogen nutrient level, 40 mg L-1 total nitrogen (TN) was recommended since it resulted in higher duckweed growth than the other two lower levels, 20 and 10 mg L-1 TN. While the optimal light regime and nutrient level for duckweed’s growth and nutrient stripping became available, we were readily to conduct aquaponics study with duckweed (Experiment 4 – Chapter 5). Red tilapia (Oreochromis niloticus) and red swamp crayfish (Procambarus clarkii) were chosen as the animals since finfish and crustacean, respectively, may exhibit different nitrogen metabolism and affect nitrogen nutrient cycle in the system. Although total ammonia nitrogen and total nitrogen concentration in crayfish aquaponics system were higher than those in tilapia system, the duckweed growth remained similar. Disregarding the difference in animal or plant density at present study, duckweed can effectively improve water quality in either tilapia or crayfish aquaponics system as compared to tilapia or crayfish alone aquaculture system.
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