23 Aug 2021
23 Aug 2021
Status: a revised version of this preprint is currently under review for the journal BG.

Carbon dynamics at the river-estuarine transition: a comparison among tributaries of Chesapeake Bay

Paul Bukaveckas Paul Bukaveckas
  • Center for Environmental Studies, Virginia Commonwealth University

Abstract. Sources and transformation of C were quantified using mass balance and ecosystem metabolism data for the upper segments of the James, Pamunkey and Mattaponi Estuaries. The goal was to assess the role of external (river inputs & tidal exchange) vs. internal (metabolism) drivers in influencing the forms and fluxes of C. C forms and their response to river discharge differed among the estuaries based on their physiographic setting. The James, which receives the bulk of inputs from upland areas (Piedmont and Mountain), exhibited a higher ratio of inorganic to organic C, and larger inputs of POC. The Pamunkey and Mattaponi receive a greater proportion of inputs from lowland (Coastal Plain) areas, which were characterized by low DIC and POC, and elevated DOC. We anticipated that transport processes would dominate during colder months when discharge is elevated and metabolism is low, and that biological processes would predominate in summer, leading to attenuation of C through-puts via de-gassing of CO2. Contrary to expectations, highest retention of OC occurred during periods of high through-put, as elevated discharge resulted in greater loading and retention of POC. In summer, internal cycling of C via production and respiration was large in comparison to external forcing despite the large riverine influence in these upper estuarine segments. The estuaries were found to be net heterotrophic based on retention of OC, export of DIC, low GPP relative to ER, and a net flux of CO2 to the atmosphere. In the James, greater contributions from phytoplankton production resulted in a closer balance between GPP and ER, with autochthonous production exceeding allochthonous inputs. Combining the mass balance and metabolism data with bioenergetics provided a basis for estimating the proportion of C inputs utilized by the dominant metazoan. The findings suggest that invasive catfish utilize 15 % of total OM inputs and up to 40 % of allochthonous inputs to the James.

Paul Bukaveckas

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-209', Anonymous Referee #1, 15 Nov 2021
  • RC2: 'Comment on bg-2021-209', Anonymous Referee #2, 07 Dec 2021

Paul Bukaveckas


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Short summary
Inland waters play an important role in the global carbon cycle by storing, transforming and transporting carbon from land to sea. Comparatively little is known about carbon dynamics at the river-estuarine transition. A study of tributaries of Chesapeake Bay showed that biological processes exerted a strong effect on carbon transformations. Peak carbon retention occurred during periods of elevated river discharge and was associated with trapping of particulate matter.