Seasonal variability of the inorganic carbon system in a large coastal plain estuary

Abstract

Abstract. Carbonate geochemistry research in large estuarine systems is limited. More work is needed to understand how changes in land-use activity influence watershed export of organic and inorganic carbon, acids, and nutrients to the coastal ocean. To investigate the seasonal variation of the inorganic carbon system in the Delaware Estuary, one of the largest estuaries along the US east coast, dissolved inorganic carbon (DIC), total alkalinity (TA), and pH were measured along the estuary from June 2013 to April 2015. In addition, DIC, TA, and pH were periodically measured from March to October 2015 in the nontidal freshwater Delaware, Schuylkill, and Christina rivers over a range of discharge conditions. There were strong negative relationships between river TA and discharge, suggesting that changes in HCO − 3 concentrations reflect dilution of weathering products in the drainage basin. The ratio of DIC to TA, an understudied but important property, was high (1.11) during high discharge and low (0.94) during low discharge, reflecting additional DIC input in the form of carbon dioxide (CO 2 ), most likely from terrestrial organic matter decomposition, rather than bicarbonate (HCO − 3 ) inputs due to drainage basin weathering processes. This is also a result of CO 2 loss to the atmosphere due to rapid water transit during the wet season. Our data further show that elevated DIC in the Schuylkill River is substantially different than that in the Delaware River. Thus, tributary contributions must be considered when attributing estuarine DIC sources to the internal carbon cycle versus external processes such as drainage basin mineralogy, weathering intensity, and discharge patterns. Longterm records in the Delaware and Schuylkill rivers indicate shifts toward higher alkalinity in estuarine waters over time, as has been found in other estuaries worldwide. Annual DIC input flux to the estuary and export flux to the coastal ocean are estimated to be 15.7 ± 8.2 × 10 9 mol C yr −1 and 16.5 ± 10.6 × 10 9 mol C yr −1 , respectively, while net DIC production within the estuary including inputs from intertidal marshes is estimated to be 5.1 × 10 9 mol C yr −1 . The small difference between riverine input and export flux suggests that, in the case of the Delaware Estuary and perhaps other large coastal systems with long freshwater residence times, the majority of the DIC produced in the estuary by biological processes is exchanged with the atmosphere rather than exported to the sea.

Simulated Arctic Ocean Response to Doubling of Riverine Carbon and Nutrient Delivery

“…For simplicity, in the ORCA1-PISCES model it is assumed that the riverine A T :C T ratio is 1.0. Conversely, the observed A T :C T ratio in rivers ranges from 0.6 in the Congo River (Wang et al, 2013) to 1.1 in the Delaware Estuary (Joesoef et al, 2017). In the Mississippi River, that ratio is 1.0 (Cai, 2003).…”

Carbon dynamics and CO<sub>2</sub> and CH<sub>4</sub> outgassing in the Mekong delta

“…Most estuarine environments are net heterotrophic ecosystems (Gattuso et al, 1998;Testa et al, 2012), leading to the production and emission to the atmosphere of CO 2 and CH 4 . The production of CO 2 and CH 4 is modulated by various physical features resulting from estuarine geomorphology such as water residence time (Borges et al, 2006;Joesoef et al, 2017), tidal amplitude and vertical stratification (Borges, 2005;Koné et al, 2009;Crosswell et al, 2012;Joesoef et al, 2015), and connectivity with tidal flats and salt marshes (Middelburg et al, 2002;Cai, 2011). Highly eutrophic (Cotovicz Jr. et al, 2015) or strongly stratified estuarine systems (Koné et al, 2009) can exceptionally act as sinks of CO 2 due to high carbon sequestration, although high organic matter sedimentation can concomitantly lead to high CH 4 production and emission to the atmosphere (Koné et al, 2010;Borges and Abril, 2011).…”

Alkalinity and dissolved inorganic carbon exports from tropical and subtropical river catchments discharging to the Great Barrier Reef, Australia

“…River inorganic carbon concentration and discharge commonly follow power law trends, suggesting that the slope is representative of the degree of dilution (Joesoef, Kirchman, Sommerfield, & Cai, 2017;Zhong, Li, Tao, Yue, & Liu, 2017). Accordingly, the daily concentration (C d ) of the studied rivers was calculated based on the regression equation of the relationship of measured concentration and daily river discharge (Q d ) in each river system:…”

“…F I G U R E 3 Daily river discharge, daily precipitation, and cumulative loads of DIC and TAlk in the Johnstone, Herbert, Burdekin, and Fitzroy rivers. DIC and TAlk loads were calculated based on the concentration-discharge relationships (Figure 2) TAlk (1.11) during high discharge periods and low ratios (0.94) during low discharge periods have been also found in freshwater end-members in river estuaries of the U.S. east coast (Joesoef et al, 2017). The additional DIC input may be explained by increased CO 2 production from terrestrial (soil) organic matter decomposition during high discharge periods combined with less CO 2 degassing due to high water throughput in the river (Joesoef et al, 2017;Mayorga et al, 2005).…”

“…DIC and TAlk loads were calculated based on the concentration-discharge relationships (Figure 2) TAlk (1.11) during high discharge periods and low ratios (0.94) during low discharge periods have been also found in freshwater end-members in river estuaries of the U.S. east coast (Joesoef et al, 2017). The additional DIC input may be explained by increased CO 2 production from terrestrial (soil) organic matter decomposition during high discharge periods combined with less CO 2 degassing due to high water throughput in the river (Joesoef et al, 2017;Mayorga et al, 2005). A few exceptions were found in the Burdekin river during dry periods in the summer months and with high pH (> 8.4), where DIC:TAlk ratios were less than one, suggesting increased contribution of [CO 3…”