不同水生植物吸收營養鹽之研究

Abstract

用自然生態方法處理水質是未來重要的循環水處理技術之一，用水生植物淨化水質的好處是低成本、低污染、零耗能、高效率及改善生態環境，永續經營等。本研究利用四種不同種類的水生植物：挺水植物（輪傘莎草）、浮葉植物（龍骨瓣莕菜）、漂浮植物（大萍）及沉水植物（水蘊草），在三種不同濃度的水中（水耕液水、池溏水、純水），計量對營養鹽吸收速率和對水質改善的能力。 結果顯示，在前14天的平均吸收速率，沉水植物（水蘊草）有較好的吸收營養鹽效果，每天每公斤鮮重植物能吸收125.351 mg磷酸根離子（PO43-），0.795 mg亞硝酸根離子(NO2-)，11.081 mg銨離子（NH4+）和12.816 mg鈣離子（Ca2+），另外對陽離子的消減有顯著作用，因為沉水植物的整個植物體，包括根、莖、葉都具有吸收營養鹽能力，並在水中進行光合作用時，產生大量碳酸氫離子和氫氧根離子，使水質pH值上升，能使更多的陽離子被結合沉降，另外對水中溶氧有增加的作用。其次是漂浮植物（大萍），能有效降底水中導電度，並能吸收19.578 mg硝酸根離子(NO3-)，1.719 mg亞硝酸根離子(NO2-)和14.823 mg氯離子（Cl-），但會使水中溶氧和pH值降低，與沉水植物形成一個互補關係。第三是挺水植物（輪傘莎草），除了有不錯的吸收營養鹽能力外，對邊坡鞏固和抑制藻類生長有重要作用。最後是浮葉植物（龍骨瓣莕菜），對各離子的吸收狀況都沒有顯著效果，而且會使水中pH值和溶氧降低，不建議放入水中淨化水質。另外，研究結果得知營養鹽濃度愈高，吸收速率愈快。並且四種植物在14天後的吸收速率開始變緩。 本研究以量化水生植物的收支速率和水生植物對水質淨化的效果，提供將來在改善水質施工設計上參考之依據，合理配置不同水生植物的比例，達到最有效的改善效果。

Using natural ecosystems to improve water quality is an important technology for the future circulating water treatment. The benefits of using aquatic plants to purify water quality are low cost, low pollution, zero energy consumption, high efficiency, improving the ecological environment and sustainable development. In this study observes the situation of plants absorbing nutrients with four different types of aquatic plants: emergent plants (Cyperus involucratus Rottb), floating-leaved plants (Nymphoides cristata (Roxb.) O. Kuntze), floating plants (Pistia stratiotes Linn), submerged plant (Egeria densa Planch), in three different concentrations of water (hydroponic water, lake water, pure water). The results showed that submerged plants (Egeria densa Planch) had better absorption of nutrients in the first 14 days. They could absorb 125.351 mg phosphate (PO43-), 0.795 mg nitrite (NO2-), 11.081 mg ammonium (NH4+) and 12.816 mg calcium ion (Ca2+) per kilogram per day. They also had significant reduction of cation base on two points. First, the whole plant, including roots, stems and leaves can absorb nutrients. Second, when submerged plants photosynthesis under the water, they produced large amounts of hydroxide ions and bicarbonate ions increasing the water pH value and binding more cations settlement. Moreover, submerged plants increased dissolved oxygen in water. Secondary, floating plants (Pistia stratiotes Linn) had effectively reduced the conductivity of the water and could absorb 19.578 mg nitrate (NO3-), 1.719 mg nitrite (NO2-) and 14.823 mg Chloride (Cl-) per kilogram per day. Floating plants reduced dissolved oxygen and pH. They just formed a complementary relationship with the submerged plants. The third, emergent plants (Cyperus involucratus Rottb) had a good nutrient absorption capacity, slope consolidation and algae growth inhibition. Finally, floating-leaved plants (Nymphoides cristata (Roxb.) O. Kuntze) had no significant effect in nutrient absorption and they reduced the water pH and dissolved oxygen. Hence it is not recommended in water purification. In addition, this study found out that the higher nutrient concentration, the faster the absorption rate. It also found out that four different types of aquatic plants had been absorption stagnation after 14 days. This study aimed to quantify the rate of nutrient revenue and expenditure of aquatic plants and the effect of aquatic plants on water purification. It can provide a data base for future reference improving water quality in the construction design. Hoping that it can achieve the most effective improvement by rational allocation of the proportion of four different types of aquatic plants.