HR: 15:05h
AN: OS52F-05    [PDF]
TI: The Interannual Response of Physical and Chemical Parameters in Suboxic/Anoxic Bottom Waters of the Chesapeake Bay During Late July 2002 and Early August 2003.
AU: * Montbriand, P J
EM:
AF: Kettering University, 1700 W. Third Ave., Flint, MI 48504 United States
AU: Glazer, B T
EM:
AF: Graduate College of Marine Studies, University of Delaware, 700 Pilottown Road, Lewes, DE 19958 United States
AU: Lewis, B L
EM: blewis@kettering.edu
AF: Kettering University, 1700 W. Third Ave., Flint, MI 48504 United States
AU: Luther, G W
EM:
AF: Graduate College of Marine Studies, University of Delaware, 700 Pilottown Road, Lewes, DE 19958 United States
AU: Ma, S
EM:
AF: Graduate College of Marine Studies, University of Delaware, 700 Pilottown Road, Lewes, DE 19958 United States
AU: Nuzzio, D B
EM:
AF: Graduate College of Marine Studies, University of Delaware, 700 Pilottown Road, Lewes, DE 19958 United States
AU: Nuzzio, D B
EM:
AF: Analytical Instrument Systems, Inc., POB 458, Flemington, NJ 08822 United States
AU: Theberge, S
EM:
AF: Merrimack College, Dept. of Chemistry, 315 Turnpike St., New Andover, MA 01845 United States
AB: The severity of seasonal anoxia in Chesapeake Bay varies annually with changes in freshwater and nutrient inputs. The years 2002 and 2003 are a case in point. Whereas in 2002 the region was under drought conditions, 2003 has been the second wettest year on record. Average freshwater discharge into the Bay for 2003 was over 75 billion gallons per day, compared to only 28.6 bgd in 2002 (Roylance, 2003),. Combined with high nutrient inputs, this has resulted in the most severe hypoxia recorded in twenty years of monitoring. In early July, 2003, approximately forty percent of waters in the mainstem of Chesapeake Bay had DO levels $<$ 5 mg/L (Chesapeake Bay Program, 2003). Interannual variations in DO levels are reflected in the water column concentrations of redox-sensitive chemical species. Here we report water column hydrography and redox chemistry at a station just south of the Chesapeake Bay Bridge (east of Annapolis, MD) for one week periods in late July, 2002 (7/24 - 7/29) and early August, 2003 (8/2 - 8/7). A combination of CTD casts, discrete bottle sampling and in situ voltammetric microelectrode profiling was used to examine redox conditions in the water column. Vertical profiles of physical and chemical parameters were measured several times each day, including temperature, salinity and density, dissolved oxygen and sulfide, nitrate/nitrite/ammonia, and dissolved Mn and Fe(II). A rosette-mounted AIS Model DLK-Sub-III electrochemical analyzer was used to measure oxygen and sulfide in real time. While vertical profiles displayed the pattern generally expected for an oxic/suboxic/anoxic interface, physical and chemical signals in the lower water column fluctuated on several time scales, from as short as a few minutes to quite dramatic interannual differences. During both years, the strongest short-term response had a periodicity of several hours, in response to tidal fluctuations and the resulting oscillation of the anoxic water mass (Sanford et al., 1990; Montbriand et al., 1992). During the 2002 occupation, we also observed a gradual shoaling of the pycnocline over the six-day sampling period, following the passage of a storm, and, during one cast, a sudden shift in the depth and thickness of the suboxic layer, likely due to passage of an internal wave. In 2003, conditions in the water column were strikingly different than those observed the previous year. Water column salinities ranged from only about 7 psu at the surface to less than 16 psu near the bottom, compared to approx. 12 to 21 psu in 2002. Nitrite concentrations were much lower throughout the water column, with maximum values only about one-fourth those observed in 2002. In contrast, the more intense suboxic/anoxic conditions during 2003 allowed the buildup of manganese, iron and sulfide to much higher levels. Maximum dissolved manganese and iron concentrations were nearly 14 and 4 micromolar, respectively, in 2003, compared to only 7.5 and 1.5 micromolar in 2002. Maximum sulfide concentrations were in 2003 were greater than 90 micromolar, more than three times the levels observed the previous year. References Chesapeake Bay Program. 2003. At: www.chesapeakebay.net Montbriand et al., AGU 2002 Fall Meeting. Roylance, F.D. 2003. IN: The Baltimore Sun, 10/8/03. Sanford, et al. 1990. J. of Mar. Research, 48:567-590.
DE: 4235 Estuarine processes
DE: 4536 Hydrography
DE: 4834 Hypoxic environments
DE: 4851 Oxidation/reduction reactions
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting