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Abstract There is limited information on how the nutrient and freshwater input affects water column carbonate chemistry in the estuaries along the northern Gulf of Mexico. In this study, we assess the seasonal and spatial variability in carbonate chemistry in the Barataria Basin, a eutrophic estuary adjacent to the mouth of the Mississippi River. Eleven stations were sampled along a salinity gradient during the winter (January), spring (April), summer (July), and fall (October) of 2021. Surface and bottom water samples were collected for the analyses of dissolved inorganic carbon (DIC); total alkalinity (TA); and nitrite plus nitrate (NO2 + NO3), phosphate (PO4), and dissolved silica (SiO4). Dissolved CO2(pCO2) was measured in the surface water. Seasonal surface DIC and TA values ranged from 1553 to 2582 μmol kg−1and 1217 to 2217 μmol kg−1, respectively. DIC and TA varied seasonally and showed an increasing trend from fresh stations to saline stations. The highest DIC and TA values were observed during the fall season, likely due to the increased contribution of DIC and TA from adjacent marshes as a result of enhanced porewater exchange. In contrast to DIC and TA, pCO2decreased with the increase of salinity. The seasonal and spatial patterns in carbonate chemistry could not be explained solely by physical mixing and reflected complex interactions between biogeochemical processes driven by nutrient supply and temperature as well as tidal flushing and material exchanges with adjacent marshes.
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Interpreting biogeochemical processes through the relationship between total alkalinity and dissolved inorganic carbon: Theoretical basis and limitations
Abstract The marine carbonate system is influenced by anthropogenic CO2uptake, biogeochemical processes, and physical changes that involve freshwater input and removal. Two frequently used parameters to quantify seawater carbonate system are total alkalinity (TA) and total dissolved inorganic carbon (DIC). To account for the physical changes, both TA and DIC are usually normalized to a reference salinity (i.e., nTA and nDIC), and then the relationship between nTA and nDIC is used to identify major biogeochemical processes that regulate the carbonate system, based on process‐specific reaction stoichiometry. However, the theoretical basis of this interpretation has not been holistically examined. In this study, we validated this method under idealized conditions and discussed the associated assumptions and limitations. Furthermore, we applied this method to interpret field TA and DIC data from a lagoonal estuary in the northwestern Gulf of Mexico. Our results demonstrated that evaluating field data that encompass multiple stations and time periods could be problematic. In addition, various combinations of biogeochemical processes can lead to the same nTA–nDIC relationship, even though the relative importance of each individual process may vary significantly. Therefore, the stoichiometric relationship relying solely on TA and DIC data is not a definitive approach for uncovering dominant biogeochemical processes. Instead, measurements of process‐specific parameters are necessary.
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- Award ID(s):
- 2319434
- PAR ID:
- 10495441
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography: Methods
- ISSN:
- 1541-5856
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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