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Watershed‐Scale Drivers of Air‐Water CO 2 Exchanges in Two Lagoonal North Carolina (USA) Estuaries
Author(s) -
Van Dam Bryce R.,
Crosswell Joseph R.,
Anderson Iris C.,
Paerl Hans W.
Publication year - 2018
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2017jg004243
Subject(s) - estuary , environmental science , watershed , nutrient , alkalinity , phytoplankton , hydrology (agriculture) , dissolved organic carbon , total organic carbon , ecosystem , total inorganic carbon , oceanography , ecology , environmental chemistry , carbon dioxide , geology , chemistry , biology , geotechnical engineering , organic chemistry , machine learning , computer science
Riverine loading of nutrients and organic matter act in concert to modulate CO 2 fluxes in estuaries, yet quantitative relationships between these factors remain poorly defined. This study explored watershed‐scale mechanisms responsible for the relatively low CO 2 fluxes observed in two microtidal, lagoonal estuaries. Air‐water CO 2 fluxes were quantified with 74 high‐resolution spatial surveys in the neighboring New River Estuary (NewRE) and Neuse River Estuary (NeuseRE), North Carolina, which experience a common climatology but differ in marine versus riverine influence. Annually, both estuaries were relatively small sources of CO 2 to the atmosphere, 12.5 and 16.3 mmol C m −2 d −1 in the NeuseRE and NewRE, respectively. Large‐scale p CO 2 variations were driven by changes in freshwater age, which modulates nutrient and organic carbon supply and phytoplankton flushing. Greatest p CO 2 undersaturation was observed at intermediate freshwater ages, between 2 and 3 weeks. Biological controls on CO 2 fluxes were obscured by variable inputs of river‐borne CO 2 , which drove CO 2 degassing in the river‐dominated NeuseRE. Internally produced CO 2 exceeded river‐borne CO 2 in the marine‐dominated NewRE, suggesting that net ecosystem heterotrophy, rather than riverine inputs, drove CO 2 fluxes in this system. Variations in riverine alkalinity and inorganic carbon loading caused zones of minimum buffering capacity to occur at different locations in each estuary, enhancing the sensitivity of estuarine inorganic C chemistry to acidification. Although annual CO 2 fluxes were similar between systems, watershed‐specific hydrologic factors led to disparate controls on internal carbonate chemistry, which can influence ecosystem biogeochemical cycling, trophic state, and response to future perturbations.