The chemistry, fluxes, and sources of carbon dioxide in the estuarine waters of the Satilla and Altamaha Rivers, Georgia

Abstract

The pH, alkalinity (Alk), and dissolved inorganic carbon (DIC) in estuarine waters of several rivers of Georgia in the southeastern United States are reported. Although they discharge into a narrow area in the South Atlantic Bight, the rivers along the coast of Georgia differ significantly in their drainage area (Piedmont rivers vs. coastal plain rivers), chemical composition (contents of carbonate and humics), and discharge rates. Large differences in pH, DIC, and Alk between these rivers clearly reflect the differences of material inputs to the rivers. Dramatic pH increases in the early stage of mixing (more obvious for the coastal plain rivers) reflect the low buffering capacity of the river waters despite the high content of humic substances. Flux of riverine DIC to the South Atlantic Bight is estimated to be 52.5 X lo9 mol yr-*. We suggest that the presently available world total riverine DIC flux to the ocean could have much uncertainty if the small river fluxes are important. Calculated pC0, values from the pH and DIC measurements are extremely high in low-salinity areas (1,000 to >6,000 patm at salinity < 10) as are the corresponding CO, fluxes to the atmosphere (20 to >250 mol m-* yr-I at salinity <lo). Data presented suggest that the most likely causes that sustain the high pC0, values and high water-to-air fluxes in the estuaries are CO, inputs from organic carbon respiration in the tidally flooded salt marshes and groundwater.Carbon dioxide is biogeochemically important in estuarine and coastal waters. It is closely linked to the organic carbon pool through photosynthesis and respiration. CO, is also a greenhouse gas and therefore its air-sea exchange is an important issue for climate change study. The coastal ocean, with its small area but large atmospheric CO, flux, plays an important role in determining whether the whole ocean is autotrophic or heterotrophic (Smith and Hollibaugh 1993; Kempe 1995). Because of these and other roles, the fluxes, sources, and mechanisms of CO, transport and transformation are among the most important current issues in marine and freshwater biogeochemistry (Degens et al. 1991;Walsh 1991;Brink et al. 1992;Smith and Hollibaugh 1993; Kempe 1995). However, we have little knowledge of the most important sources (other than riverine) and processes that determine the inorganic carbon flux to coastal oceans.There are few systematic studies on the chemistry and flux of CO, in estuarine and coastal waters over a large salinity range. Most biogeochemical studies in the estuarine mixing zone have focused on nutrients and trace metals (Boyle et al. 1974;Li and Chan 1979;Kaul and Froelich 1984; Windom and Smith 1985). Alkalinity and dissolved inorganic carbon (DIC) are viewed as conservative in most estuaries (e.g. Columia River by Park et al. 1972; upper Chesapeake Acknowledgments Discussions with W. Wiebe, L. Pomeroy, T. Dai, R. Wiegert, M. A. Moran, M. Alber, R. Hodson, A. Chalmers, and J. Blanton were very helpful. M. A. Moran, M. Sun, and J. Hoppema helped to sha...

Plutonium in groundwater at the 100K-Area of the U.S. DOE Hanford Site

“…DIC data was obtained by acidification of 0.5 mL of a water sample and the subsequent quantification of CO 2 with the IR detector (Li-Cor 6252). This method has a precision of 0.1-0.2% (Cai and Wang, 1998). TAlk was determined by Gran titration.…”

Spatial variability in surface-water &lt;i&gt;p&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt; and gas exchange in the world's largest semi-enclosed estuarine system: St. Lawrence Estuary (Canada)

“…Although the K 1 and K 2 formulations from Lueker et al (2000) are recommended for best practices by Dickson et al (2007), they are not suitable for the low-salinity conditions found in estuaries (S P < 19) (Orr et al, 2015). The revised equations for K 1 and K 2 from Cai and Wang (1998) are applicable over a larger range of salinities (0 to 40) and, thus, were used to examine the carbonate system in the estuarine waters of our study area.…”

“…Because direct pCO 2 measurements were not available from the RV Coriolis II cruises, pCO 2 (water) (µatm) and DIC (µmol kg −1 ) were calculated from the measured pH (total or NBS scale) and TAlk (µmol kg −1 ), at in situ temperature ( • C), salinity (S P ), and pressure (dbar), using the program CO2SYS (MATLAB version 1.1; van Heuven et al, 2011) and the carbonic acid dissociation constants (K 1 , K 2 ) of Cai and Wang (1998) for estuarine waters. Wherever data were avail-able, the contributions to TAlk from phosphate and silicate were included in the calculations.…”

“…A preliminary analysis revealed that respiration (upper estuary), photosynthesis (lower estuary), and temperature (Gulf of St. Lawrence) controlled the spatial variability in surface-water pCO 2 . Whereas we used the dissociation constants of Cai and Wang (1998) …”

“…With an estimated global efflux of 0.10-0.15 Pg C yr −1 (Chen et al, 2013;Laruelle et al, 2013), estuarine CO 2 degassing is thought to counterbalance CO 2 uptake on the continental shelves (Chen and Borges, 2009;Laruelle et al, 2010;Cai, 2011). Almost every estuary on Earth, for which data are available, is generally supersaturated with CO 2 with respect to the atmosphere (Cai and Wang, 1998;Frankignoulle et al, 1998;Borges, 2005;Borges et al, 2005Borges et al, , 2006Chen and Borges, 2009;Laruelle et al, 2010;Cai, 2011;Chen et al, 2012;Bauer et al, 2013;Chen et al, 2013;Regnier et al, 2013), with CO 2 partial pressures (pCO 2 ) ranging from 400 to 10 000 µatm (in contrast, the atmospheric pCO 2 in coastal zones was approximately 360-385 µatm in the year 2000) (Cai, 2011). Although estuaries are generally net sources of CO 2 , there is considerable variability and uncertainty in estimates of their CO 2 emissions, reflecting the limited spatial and temporal coverage of pCO 2 measurements in estuaries as well as their heterogeneous nature (hydrological and geomorphological differences, differences in magnitude and stoichiometry of 3222 A.…”