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

Abstract

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.

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

“…As in previous studies (Hu & Cai, 2013;Ruiz-Halpern et al, 2015), R was very low in the oligohaline portion of the NewRE and NeuseRE, and increased rapidly with salinity to a midestuary maximum ( Figure 5). At this point, R decreased as low alkalinity river water mixed with seawater with a DIC:TA ratio less than 1.…”

“…Climate change is expected to alter current hydrologic patterns, and these changes will affect estuarine carbon (C) cycling on seasonal to decadal scales (Dhillon & Inamdar, ; Najjar et al, ). In addition to these longer‐term effects, episodic events like storms and droughts are also expected to increase with climate change and will contribute significantly to estuarine CO 2 fluxes on an annual scale, although the nature of that change will depend on a variety of system‐specific features (Crosswell et al, ; Evanset al, ; Hunt et al, ; Ruiz‐Halpern et al, ). Both episodic and seasonal variations in river discharge strongly affect air‐water CO 2 exchange in estuaries (Bauer et al, ; Borges & Abril, ; Cai, ; Chen et al, ); however, quantitative relationships between estuarine C cycling and catchment hydrology remain relatively poorly defined.…”

Spatial and temporal variability of CO2and CH4gas transfer velocities and quantification of the CH4microbubble flux in mangrove dominated estuaries

“…a,b). Raymond and Cole's () parameterization ( k 600 = 1.91 e 0.35 u ) has also been used in recent mangrove CO 2 flux studies (Bouillon et al ; Maher et al ; Ruiz‐Halpern et al ) and was a good fit to our data, but the estimated fluxes still varied from an underestimation of 67% to an overestimation of 65% (mean = 10% underestimation) and estimated CH 4 fluxes from an underestimation of 79% to an overestimation of 86% (mean = 5% underestimation). The combined parameterization of O'Connor and Dobbins () and Ho et al () was also a good fit to our measured fluxes and overestimated the CO 2 and CH 4 flux on average by 20% with a variation between 36% underestimation and 66% overestimation for CO 2 and an underestimation of 59% and overestimation of 87% for CH 4 (Fig.…”

Effects of Estuarine Acidification on an Oyster-Associated Community in New South Wales, Australia

“…Acidic water collects in drainage ditches and is distributed to surrounding water bodies via outflow drains, thereby exposing aquatic organisms to acidified environments (Wilson & Hyne 1997). During rain events, pulses of acidified water may impact sites several km downstream of the outflow drain (Ruiz-Halpern et al 2015). These acidification events are short lived, on the order of days (Macdonald et al 2007), weeks (Wilson et al 1999), or rarely, months (Sammut et al 1995).…”