A comparison of CO₂ dynamics and air‐water fluxes in a river‐dominated estuary and a mangrove‐dominated marine estuary

Abstract

The fugacity of CO2 (fCO2 (water)) and air‐water CO2 flux were compared between a river‐dominated anthropogenically disturbed open estuary, the Hugli, and a comparatively pristine mangrove‐dominated semiclosed marine estuary, the Matla, on the east coast of India. Annual mean salinity of the Hugli Estuary (≈7.1) was much less compared to the Matla Estuary (≈20.0). All the stations of the Hugli Estuary were highly supersaturated with CO2 (annual mean ~ 2200 µatm), whereas the Matla was marginally oversaturated (annual mean ~ 530 µatm). During the postmonsoon season, the outer station of the Matla Estuary was under saturated with respect to CO2 and acted as a sink. The annual mean CO2 emission from the Hugli Estuary (32.4 mol C m−2 yr−1) was 14 times higher than the Matla Estuary (2.3 mol C m−2 yr−1). CO2 efflux rate from the Hugli Estuary has increased drastically in the last decade, which is attributed to increased runoff from the river‐dominated estuary.

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

“…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).…”

“…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, ). Our findings support this understanding; we show that river‐borne CO 2 ([CO 2 ] river ) was indeed larger in the river‐dominated NeuseRE than in the marine‐dominated NewRE, by a factor of 2.6–5.2.…”

The post-monsoon carbon biogeochemistry of the Hooghly–Sundarbans estuarine system under different levels of anthropogenic impacts

“…Different aspects of C cycling in the Hooghly-Sundarbans system have been reported by Ray et al (2015Ray et al ( , 2018. Barring Samanta et al (2015), which has wider spatial and temporal coverages with respect to DIC in the Hooghly, other studies are severely limited in spatial coverage with focus on the middle to lower parts of the Hooghly estuary and a few locations in the Sundarbans (one location by Ray et al, 2015Ray et al, , 2018; three locations by Akhand et al, 2016). Given the vast expanse of these estuaries, the extrapolation of data Ghosh, (1973), Khan (1995) No information available Dissolved metal flux Increased from 230 % to 1770 % annually Samanta and Dalai (2018) No information available from these studies for the entire ecosystem may lead to overestimation and underestimation.…”

“…Earlier, the major focus of biogeochemical studies in the Hooghly and the estuaries of the Sundarbans had been on the biogeochemistry of trace gases (Mukhopadhyay et al, 2002;Biswas et al, 2004Biswas et al, , 2007Ganguly et al, 2008Ganguly et al, , 2009Dutta et al, 2013Dutta et al, , 2015Dutta et al, , 2017 with the exception of one comprehensive study on nutrient budgets at the Hooghly estuary (Mukhopadhyay et al, 2006). Recently, attempts have been made to understand different aspects of C cycling in these two estuaries (Samanta et al, 2015;Ray et al, 2015Ray et al, , 2018Akhand et al, 2016). Samanta et al (2015) comprehensively studied DIC dynamics in the Hooghly estuary, whereas Akhand et al (2016) focused on DIC and pCO 2 at the Hooghly-Matla estuary.…”

“…Recently, attempts have been made to understand different aspects of C cycling in these two estuaries (Samanta et al, 2015;Ray et al, 2015Ray et al, , 2018Akhand et al, 2016). Samanta et al (2015) comprehensively studied DIC dynamics in the Hooghly estuary, whereas Akhand et al (2016) focused on DIC and pCO 2 at the Hooghly-Matla estuary. Different aspects of C cycling in the Hooghly-Sundarbans system have been reported by Ray et al (2015Ray et al ( , 2018.…”