Estuarine canal estate waters: Hotspots of CO2 outgassing driven by enhanced groundwater discharge?

Macklin, Paul A.; Maher, Damien T.; Santos, Isaac R.

doi:10.1016/j.marchem.2014.08.002

Cited by 53 publications

(25 citation statements)

References 52 publications

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“…Hence, the metabolic balance of a given estuary is closely linked to the hydrology of its watershed. This idea is supported by previous findings linking seasonal to annual variation in CO 2 flux with changes in freshwater delivery, through both surface (Akhand et al, 2016;Drupp et al, 2011;Flecha et al, 2015;Guo et al, 2009;Yao et al, 2007;Zhai et al, 2005) and groundwater channels (Call et al, 2015;Jeffrey et al, 2016;Macklin et al, 2014;Santos et al, 2010). Watershed-scale hydrology may also drive complex changes in the buffering capacity of estuarine waters, impacting calcifying organisms (Barton et al, 2012;Hofmann et al, 2010), pH-sensitive processes like nitrification (Beman et al, 2010;Huesemann et al, 2002), and even animal behavior (Dodd et al, 2015;Leung et al, 2015).…”

Section: Introductionsupporting

confidence: 71%

“…In marine‐dominated estuaries like the NewRE, however, internal production of CO 2 , rather than riverine inputs appear to drive CO 2 oversaturation. While submarine groundwater discharge may be a significant DIC source in some estuaries (Call et al, ; Macklin et al, ; Santos et al, ), this source has been determined to be small in both the NeuseRE (Fear et al, ; Null et al, ) and NewRE (Crosswell et al, ). Previous studies have identified river‐dominated estuaries as large CO 2 sources, relative to marine‐dominated ones (Akhand et al, ; Jiang et al, ).…”

Section: Discussionmentioning

confidence: 99%

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Watershed‐Scale Drivers of Air‐Water CO₂ Exchanges in Two Lagoonal North Carolina (USA) Estuaries

et al. 2018

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Riverine loading of nutrients and organic matter act in concert to modulate CO2 fluxes in estuaries, yet quantitative relationships between these factors remain poorly defined. This study explored watershed‐scale mechanisms responsible for the relatively low CO2 fluxes observed in two microtidal, lagoonal estuaries. Air‐water CO2 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 CO2 to the atmosphere, 12.5 and 16.3 mmol C m−2 d−1 in the NeuseRE and NewRE, respectively. Large‐scale pCO2 variations were driven by changes in freshwater age, which modulates nutrient and organic carbon supply and phytoplankton flushing. Greatest pCO2 undersaturation was observed at intermediate freshwater ages, between 2 and 3 weeks. Biological controls on CO2 fluxes were obscured by variable inputs of river‐borne CO2, which drove CO2 degassing in the river‐dominated NeuseRE. Internally produced CO2 exceeded river‐borne CO2 in the marine‐dominated NewRE, suggesting that net ecosystem heterotrophy, rather than riverine inputs, drove CO2 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 CO2 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.

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Section: Introductionsupporting

confidence: 71%

Section: Discussionmentioning

confidence: 99%

Watershed‐Scale Drivers of Air‐Water CO₂ Exchanges in Two Lagoonal North Carolina (USA) Estuaries

et al. 2018

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“…This is further supported by DO supersaturation (N 100%) coinciding with pCO 2 N 550 μatm well above equilibrium with the atmosphere (~390 μatm). The concurrent supersaturation of both DO and CO 2 implies that photosynthetic uptake of CO 2 during times of DO N 100% was small compared to other CO 2 sources such as porewater as also observed in an Australia estuary (Macklin et al, 2014).…”

Section: Carbon Dynamicsmentioning

confidence: 69%

Porewater exchange as a driver of carbon dynamics across a terrestrial-marine transect: Insights from coupled 222Rn and pCO2 observations in the German Wadden Sea

et al. 2015

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“…In a nearby creek in the region,

{normalP}_{{CO}_{2}}

concentrations in groundwater were on average 8087 Pa (or up to 20‐fold higher than surface waters) demonstrating that even small groundwater inputs may drive surface water CO 2 dynamics (Atkins et al ). Although our 222 Rn survey was not designed to provide a quantitative estimation of groundwater discharge, the significant correlations found between

{normalP}_{{CO}_{2}}

and 222 Rn provide an indication that groundwater is a likely source of CO 2 to the estuary as found in other nearby estuaries (Atkins et al, 2013; Macklin et al, ; Maher et al, In Press). During flooding, most of the water entering the estuary comes from overland flow.…”

Section: Drivers Of Co2mentioning

confidence: 99%

High CO₂ evasion during floods in an Australian subtropical estuary downstream from a modified acidic floodplain wetland

et al. 2014

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Dissolved CO 2 dynamics associated with flooding and postflood recovery were investigated in the lower estuary of the Richmond River and a tributary draining an acidic wetland. Heavy rains (up to 133 mm d 21 ) resulted in large discharge volumes (up to 250 3 10 6 m 3 d 21 ) flushing the estuary in less than a day. Maximum values of the partial pressure of CO 2 (P CO 2 , 2006 Pa or 19,801 latm) occurred during the postflood recovery period. High P CO2 values were related to the transport of floodplain metabolic products via surface runoff and groundwater as well as the low pH (4.22) of waters draining a modified wetland with coastal acid sulphate soils. Aerobic respiration alone could not explain the high concentrations of CO 2 in the estuary and an area of low buffering developed in the 0-20 salinity range. P CO2 was correlated with freshwater discharge in the Richmond River main channel (R 2 5 0.82; p < 0.05; n 5 9) but not in the acidified tributary (R 2 5 0.17; p > 0.05; n 5 7). Air-water fluxes of CO 2 were at the high end of the range for aquatic systems (maximum 1413 mmol C m 22 d 21 , mean 252 mmol C m 22 d 21 ). This study highlights the large spatiotemporal variability of P CO 2 , the importance of episodic flooding events, the role of adjacent modified acidic wetlands, and the role of groundwater discharge as a source of CO 2 to estuaries. Global estimates of CO 2 air-water fluxes in estuaries may be under estimated due to the lack of high-resolution data to capture short-term episodic events (e.g., flooding), in tropical and subtropical areas.

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Estuarine canal estate waters: Hotspots of CO2 outgassing driven by enhanced groundwater discharge?

Cited by 53 publications

References 52 publications

Watershed‐Scale Drivers of Air‐Water CO₂ Exchanges in Two Lagoonal North Carolina (USA) Estuaries

Watershed‐Scale Drivers of Air‐Water CO₂ Exchanges in Two Lagoonal North Carolina (USA) Estuaries

Porewater exchange as a driver of carbon dynamics across a terrestrial-marine transect: Insights from coupled 222Rn and pCO2 observations in the German Wadden Sea

High CO₂ evasion during floods in an Australian subtropical estuary downstream from a modified acidic floodplain wetland

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Estuarine canal estate waters: Hotspots of CO2 outgassing driven by enhanced groundwater discharge?

Cited by 53 publications

References 52 publications

Watershed‐Scale Drivers of Air‐Water CO2 Exchanges in Two Lagoonal North Carolina (USA) Estuaries

Watershed‐Scale Drivers of Air‐Water CO2 Exchanges in Two Lagoonal North Carolina (USA) Estuaries

Porewater exchange as a driver of carbon dynamics across a terrestrial-marine transect: Insights from coupled 222Rn and pCO2 observations in the German Wadden Sea

High CO2 evasion during floods in an Australian subtropical estuary downstream from a modified acidic floodplain wetland

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Watershed‐Scale Drivers of Air‐Water CO₂ Exchanges in Two Lagoonal North Carolina (USA) Estuaries

Watershed‐Scale Drivers of Air‐Water CO₂ Exchanges in Two Lagoonal North Carolina (USA) Estuaries

High CO₂ evasion during floods in an Australian subtropical estuary downstream from a modified acidic floodplain wetland