- 學位論文
南海有光層海水溶解態磷物種分析與季節變化初探
Seasonal Variations of Dissolved Phosphorus in the Euphonic Zone of Oligotrophic South China Sea
摘要
磷（phosphorus）是生物成長所需要的主要營養鹽之一，而磷的缺乏通常是淡水或是海洋環境裡浮游植物生長的限制因子。然而，多位學者早已證實浮游植物可以攝取有機磷替代最容易被吸收利用的磷酸鹽，營養鹽內循環也可以將有機磷顆粒帶回上層海水，而溶解性有機磷佔上層海水中的總溶解態磷很大比例的事實，更一再暗示了溶解性有機磷在上層水體中的重要性。因此，本研究選用1976年由Koroleff所提出的過硫酸鉀氧化劑水解法進行有機磷的消化，針對部分實驗條件略作修改以期達到最佳的回收率。在抗壞血酸鉬藍還原比色法定量無機磷酸鹽的配合之下，測量南海時間序列（SEATS）計畫中時序測站的溶解性無機磷酸鹽與總溶解態磷濃度，而獲得其相扣而得的溶解性有機磷濃度。 南海有光層內的溶解態磷物種確實存在季節性的變化，冬夏兩季的溶解態無機磷酸鹽與總溶解態磷的濃度較高，而春季與秋季的濃度則偏低。季節性的變化除了與水體密度層結構改變有關，亦可能與東北季風盛行期間沙塵暴夾帶大量的無機磷礦物進入南海海域有極大的關連。南海有光層內溶解性有機磷濃度在表水50公尺以淺的濃度範圍是0.11 ~ 0.20 μM，有光層內的季節性變化不大，而且濃度隨著深度增加而逐漸降低，水深200公尺以後的濃度已經幾近於零。南海有光層內溶解態有機磷與無機磷的比例，大致呈現由表水往下迅速遞減的趨勢，在水深10公尺以淺，因為無機磷酸鹽濃度非常低而導致秋季的DOP/DIP比例高達38，而冬季最低約為1~2。除了表水之外，春夏秋三個季節的DOP/DIP與螢光最大值訊號無明顯的關聯性，但在次表層皆有一個DOP/DIP的相對高值。南海營養鹽躍層深度較淺且有東北季風挾帶而來的沙塵，磷酸鹽濃度非常充足，因而有光層內的生物對於溶解態有機磷的需求不高，溶解性有機磷幾乎不會有太大的濃度變化。
並列摘要
Phosphorus (P) is an essential macronutrient required for all living organisms. Several evidences suggest that phosphorus may limit primary production rates in the oligotrophic marine habitats, which has stimulated great interests in P dynamics. In the ocean, total dissolved phosphorus (TDP) pool, according to the operational definition, is generally partitioned into dissolved inorganic P (DIP, mostly orthophosphate) and dissolved organic P (DOP, mostly phosphorus esters and phosphonates). In this study, a modified alkaline persulfate oxidation method together with standard molybdenum blue method, was examined and employed for quantitatively converting a range of organic phosphorus compounds to orthophosphate, and provided the direct measurements of total dissolved phosphorus in seawater samples. Field observations of the concentration changes in dissolved phosphorus pool in the South China Sea were made at Station KK1 (18.25°N, 115.67°E) several times from August 2003 to May 2004. Both TDP and DIP concentrations measured in the euphotic zone showed strong seasonal variations and covariant trends with higher concentrations found in summer and winter. The DOP concentrations in the upper 200 m ranged from 0 to 0.3 μM decreasing with depth showed distinct seasonal patterns, and subsurface maximum found in corresponding to that of Chlorophyll-a. As DOP/DIP ratios in the upper 60m showed strong seasonal variations and declined with increasing depth. These results suggest that relatively consistent DOP concentrations in surface water may sustain the nutrient recycling supplying for the growth of living organisms.