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PROCESSES AFFECTING THE BEHAVIOR OF REDOX-SENSITIVE CHEMICAL SPECIES IN CHESAPEAKE BAY Maria Lourdes San Diego-McGlone Old Dominion University, 1991 Director: Dr. Gregory A. Cutter Traditionally, estuarine flux calculations have assumed steady state and tidally averaged conditions. These assumptions cause two potential problems: one, this approach is unable to resolve the mechanistic details of the processes involved and two, estuaries are dynamic environments in which a wide range of biogeochemical processes occur on time scales of hours to months. Several processes can affect long-term (seasonal) and short-term (hourly) variations in the chemical composition of an estuary, including (1) biogeochemical reactions in the water column, (2) advective transport, and (3) diffusion from underlying sediments. Estuarine biogeochemistry may also be affected by redox reactions. The purpose of the study was to establish whether estuarine redox reactions are controlled by a complex interaction of processes 1 to 3, and whether these reactions subsequently affect the fluxes of redox sensitive chemical species through the Bay. To investigate this, short-term and long-term studies were conducted in the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. changing redox environment of the Chesapeake Bay. The redox species examined include those which directly and indirectly participate in redox cycling. Redox species directly involved in redox cycling include oxygen, iron, manganese, hydrogen sulfide, nitrogen species, arsenic and antimony species, while phosphate is indirectly involved in redox cycles. Silicate was used as a non-redox tracer. For the short-term study, a Lagrangian drifter was used to track a parcel of bottom water, and thus allow monitoring of in situ water column processes and sedimentwater exchange (i.e., influence of advection minimized). In addition, a fixed (Eulerian) station was established to integrate processes 1 to 3. Porewater profiles of the different redox species were utilized to calculate sediraent-water exchange rates, seasonal (long-term) changes in porewater and water column profiles, as well as horizontal transects along the salinity gradients, were used to calculate fluxes and establish the coupling between benthic inputs and the inventory of redox sensitive chemical species in bottom waters of the Bay. Estuarine modeling was used on the long-term (seasonal) data sets from the upper Bay to estimate riverine and estuarine (output and internal) fluxes. During summer, there was estuarine flux (internal production) for ammonia, phosphate, iron, manganese, and silicate. A comparison of these estuarine fluxes and benthic fluxes from cores taken in the upper Bay showed Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. that the total flux of materials produced within this portion of the estuary is strongly influenced by sedimentwater exchange, particularly for ammonia (up to 100%) and phosphate (up to 100%). This was also the case for the metals, iron and manganese, (100%) during summer. Benthic flux of silicate was a more important contribution to the estuarine flux of silicate (10 to 15%) in summer. The mechanistic details of the coupling of the transport and in situ biogeochemical processes mentioned above (processes 1 to 3) were closely examined by the short-term study. At the fixed station, large hourly variations in the concentration of redox species indicate that advection controls Eulerian behavior. Advective flux was estimated from horizontal gradients, established from spatial variability of the benthic flux along the drifter track, and the calculated current velocity. From the Lagrangian study, maximum concentrations usually occurred when the water mass passed over areas with higher benthic fluxes. This was illustrated by the behavior of sulfide, manganese, and arsenic. Overall, the concentration of redox sensitive chemical species were controlled by in situ reactions and benthic sources, but the variability in concentration at a fixed point was primarily due to advection. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS It would be impossible for me to list all those who have helped me with this work. Some do not know me and are unaware of how much their papers, books, and manuscripts have added to my understanding of oceanography. For those who have closely been a part of my formative years as a chemical oceanographer, I wish particularly to thank... Greg Cutter for his valuable guidance, support, expertise, confidence, and the necessary push to complete this work. David Burdige, Denny Kirwan, and Ed Sholkovitz for providing significant comments and suggestions for the improvement of this work. A special thanks to Ed Sholkovitz for allowing me to participate on his cruises aboard the R.V. Warfield. Doug McGlone for being the 'love of my life' and 'joy of my heart'...and for putting up with his 'not so ideal' wife. My Tatay and Nanay for their love, trust, unending support, and for encouraging me to go for my dreams. My six brothers Butch, Edwin, Edgar, Alvin, Alex and Francis; Menchie, Karl, Justin, Inday, Ging-ging, Dodong, and other members of the household for their love, care, understanding, and for believing in me. The McGlones Mom, Dave, Greg, Jan, Ryan, Rob, Katy, Chelsea, Dad, Joan and Grandma for their constant support and tireless encouragement, and for warmly taking me in as part of the family. Gil Jacinto for his invaluable friendship and for those early days when we were 'groping'oceanographers, and all other friends at UP Marine Science Institute who inspire me to make a contribution to oceanography back home. Lynda Cutter for her lab expertise and assistance, and for the fantastic celebration parties. Bob Kluckhohn for his redhead (the first I've seen!), his help on my cruises, and his 'unique' humor. Joel Radford-Knoery for having answers to almost any question (plus his 'go read the book' response), his camaraderie, and doses of French culture. Lisa Ramirez for the friendship and the medieval mysteries. David Velinsky for becoming a good friend, for the help during the early days of graduate school and for being there along the way.

Processes Affecting the Behavior of Redox-Sensitive Elements in Chesapeake Bay