光線強度與營養鹽濃度對微囊藻營養鹽攝取之影響

Abstract

台灣地區水庫藻華問題嚴重，不但會使淨水成本增加，亦會依優勢藻種之不同，產生不同的問題。優勢之藻種常為藍綠藻，而藍綠藻中之微囊藻更是台灣水庫常發生的優勢藻種，其為人所注目之原因，係因為有部分微囊藻藻種會產生藻毒素，對人體健康產生影響。 微囊藻常在春末夏初之際，於熱分層水域中，成為優勢藻種。造成此現象之因素，主要是因為微囊藻具有浮力調控之機制，藉由浮力調控機制垂直上下移動；以及藻體會瞬間攝取超過生長所需之營養鹽並儲存於體內。因此微囊藻可以停留於光線充足之表水層進行光合作用，以及至下層水體攝取營養鹽，克服光線與營養鹽之分層之問題，充分利用營養鹽與光線，大量生長。 本研究採集現場環境水體中之微囊藻，使其藻細胞生理狀態為飢餓，以不同光線強度照光，添加氮磷營養鹽於水體之中，量測水體營養鹽濃度之變化，計算藻體內營養鹽含量以及攝取率。實驗結果顯示，藻類具有超量攝取營養鹽並儲存於體內之能力，且營養鹽攝取速率受到外部營養鹽濃度(S)、從外部攝取進入藻體內之營養鹽含量(△Q)以及光線強度(I)影響。外部營養鹽濃度(S)高、光線強度(I)強皆會使攝取率增加，而從外部攝取進入藻體內之營養鹽含量(△Q)愈大，則會使攝取率降低。 本研究並利用Morel 與Okada and Sudo模式，模擬光線強度(I)、外部營養鹽濃度(S)以及藻體攝取之磷營養鹽濃度(△Q)等不同之情況下，磷攝取率之大小期待找到一個最佳模式，應用於實際環境之中，做為預測微囊藻生長及評估改善之工具。 Morel 模是簡化後，最佳參數為：可增加之體內營養鹽含量Qmax-Qmin=27 P-μg•SS-mg-1，半飽和營養鹽濃度係數Ks=0.847 P-mg•L-1。Qkada and Sudo模式簡化後，利用實驗數據找出之最佳參數為：Qmax-Qmin=23.5 P-μg•SS-mg-1，Ks=0.3863 P-mg•L ，半飽和體內營養鹽含量Kq=10.8 P-μg•SS-mg-1。兩模式所得之預測值與實測值相比，比較其相關性(Morel model：R=0.82，slope=0.805； Okada and Sudo model：R=0.84，slope=0.645)。

The algal bloom is a serious problem in reservoirs, not only would increase the cost of water treatment, but also result in various problems due to different algal species. Blue-green algae are often the dominant species. Microcystis is one of blue-green algae, and often dominates in reservoirs. We are also concerned about on Microcystis due to some species of Microcystis is able to produce toxins which pose serious health risks to human and animals. Microcystis is dominant algae in stratified lakes from late spring to early autumn. There are two mechanisms help the Microcystis dominance. The first mechanism is buoyancy regulation which allows Microcystis to overcome the vertical separation of light and nutrients in a stratified lake. The second mechanism is that Microcystis uptakes and stores nutrients more than the amount needed for growth. Therefore, Microcystis can stay in sufficiency of light in surface water for photosynthesis, and uptake nutrient in lower water. Microcystis overcomes the problem of light and nutrient separation, and blooms in stratified subtropical reservoirs. In this study, we sampled Microcystis from Hsin-Shan reservoir. In order to deplete the intracellular polyphosphate storage, we put change in nutrient free water under light with 14 : 10-h light :dark cycle for 3days. When the experiment began, we added nutrients in water under different irradiance intensities, and measured the changes of nutrient concentrations in water. The amounts of changes were used to calculate the N and P cell quota and uptake rates. The results show that Microcystis has the ability which can uptake and store nutrient in cells. The uptake rate is increases with light intensity, increases with external nutrient concentration and decreases with cell quota. We use Morel model and Okada and Sudo model to simulate the uptake under different irradiance intensity (I), external nutrient concentration(S) and nutrient concentration. The best fitting parameters in Morel model are：maximum allowed uptake , Qmax-Qmin=27 P-μg•SS-mg-1, helf saturated nutrient concentration , Ks=0.847 P-mg•L-1. The best fitting parameters in Okada and Sudo model are： maximum allowed uptake , Qmax-Qmin=23.5 P-μg•SS-mg-1, helf saturated cell quota , Kq=10.8 P-μg•SS-mg-1, helf saturated nutrient concentration , Ks=0.3863 P-mg•L-1. Morel model has R=0.82 , slope=0.805； Okada and Sudo model has R=0.84 , slope=0.645.