Nitrate Reductase Activity, Nitrate Uptake and Iodine Speciation in the Marine Environment

NITRATE REDUCTASE ACTIVITY, NITRATE UPTAKE AND IODINE SPECIATION IN THE MARINE ENVIRONMENT Chin-Chang Hung Old Dominion University, 1999 Director: Dr. George T. F. Wong The present method for the determination o f new production (NP) by measuring the uptake o f added ISN 0 3' suffers from a number o f limitations. In an attempt to improve this situation, this research examined the possibility o f estimating I5N 0 3' uptake by measuring the activity o f nitrate reductase (NRA). In addition, because it has long been suspected that the biological reduction o f I0 3‘ to T may be mediated by nitrate reductase (NR), this research investigated the ability of NR to catalyze the reduction o f iodate to iodide. An improved method for the determination ofNRA was developed. The sensitivity of this method is about five times higher than methods used in previous studies. NRA and isN0 3uptake (NU) were determined over a wide range of nitrate concentrations in the East China Sea and in the adjoining Kuroshio Current in May, 1996. In lightand nitratereplete waters ([N 03']> 1 pM, %PAR > 10%, PAR: photosynthetically active radiance), NRA was linearly related to NP so that NRA may be used for estimating NP. A high ratio of NU/NRA was found in nitrate-depleted ([N 03*]<1 pM) and light-replete (%PAR >10%) conditions. The high ratio o f NU/NRA data might have been caused by an overestimation ofNU due to the stimulation o f the addition of l5N 0 3* to nitrate-deficient water. This result revealed that NRA may be a reliable index for estimating new production in oligotrophic waters. In comparing NU in the literature with our NU values in different hydrographic realms, the NU values estimated from NRA fall well with recently reported values in similar types of waters. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. NRA and iodine speciation were measured in the East China Sea in May, 1996. The results suggest that the reduction of iodate to iodide in the upwelling areas is caused by the enzyme NR. In the process of iodate reduction, the depletion of iodate and the enrichment o f iodide relative to the composition of the source water o f a surface water mass represent an integration of NRA through the residence time o f the water mass. A method for estimating the reduction of iodate to iodide by NR by using I25I0 3' was developed. The reduction o f I0 3‘ to I' by NR was observed in the cultures o f S. costatum and in natural phytoplankton assemblages. The rates were 0.008 to 0.019 n mol I" txg chi aA h '1 in natural samples. The iodate reduction rate was linearly related to NRA, suggesting that iodate reduction may be coupled to nitrate reduction. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGMENTS I would like to give my sincere thanks to Dr. George Wong who gave me much help and encouragement since I came to Old Dominion University. During the period of writing my dissertation. Dr. Wong spent much time in reading and correcting my dissertation. Also, I want to greatly express my thanks to my committee members-Drs. William Dunstan, Louis Codispoti and John Donat-who spent much time reading and correcting my dissertation and they assisted me greatly in my dissertation work. I am deeply grateful to other professors, EC. -EC. Liu, James Yuan, G. -C. Gong , F. -EC. Shiah, Y. -L.L. Chen, Gregory Cutter, and David Burdige who gave me much assistance in my field experiments and provided many significant discussions and comments on my dissertation. Additionally, I also want to give thanks to my friends and classmates: Vincent Kelly, Lisa Drake. Xianhao Cheng, Keun-Hyung Choi, Claudette Lajoi, Christina Dryden, Shi-Jun Fan, Rusty Hall, Carley Moritz, Paul Richardson, Li Zhang, Steve Kibler, and Rob Wardwell. They gave me help, comments, and encouragements about my experiments. Moreover, I greatly appreciate the help given to me by R.C. ECidd, Dana Oblak, Holly Park and Nikki Moore since I came to ODU. Furthermore, I want to thank the captains and the crew ofR/V Ocean Researcher I and II for their assistance in taking sample collections. Finally, I would like to dedicate this dissertation to my parents whose love and support fill my heart. My wife, Hsiao-Feng, has given me infinite support, sacrifice, and love so that I can finish my degree. I am constantly aware o f how much I appreciate them. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS Page LIST OF TABLES. viii LIST OF FIGURES. ix Chapter