Reduction in Riverine Freshwater Supply Changes Inorganic and Organic Carbon Dynamics and Air‐Water CO₂ Fluxes in a Tropical Mangrove Dominated Estuary

Abstract

Estuaries are biogeochemically active zones where both particulate and dissolved matter undergoes vigorous transformations (Bianchi, 2007), mostly in ways that make these waters net heterotrophic (Gattuso et al., 1998;Testa et al., 2012), eventually leading to emission of substantial amounts of CO 2 to the atmosphere (Laruelle et al., 2010(Laruelle et al., , 2013. However, net autotrophy with the accompanying CO 2 sink is sometimes observed in some estuaries (Crosswell et al., 2017;Maher & Eyre, 2012). Besides the trophic state,

Drivers of inorganic carbon dynamics and air–water CO2 fluxes in two large tropical estuaries: Insights from coupled radon (222Rn) and pCO2 surveys

“…DO exhibited no significant control on p CO 2 (water); thus, aerobic respiration of organic matter was not a major biogenic driver of p CO 2 (water). This result is consistent with the results of previous studies (Akhand et al 2021a,b) that physical mixing is dominant over biological controls as the major driver of p CO 2 (water) in the Hooghly and Matla estuaries.…”

“…Previous studies using hourly time series or discrete data have often underestimated or overestimated air–water gas fluxes because of their inability to capture tidal maxima and minima (Rosentreter et al 2018). Only one study, which collected data four times during an annual cycle, has reported high temporal resolution p CO 2 (water) and air–water CO 2 flux data for the Matla estuary (Akhand et al 2021b), and no previous study has to our knowledge collected high‐temporal‐resolution data from the Hooghly estuary. However, our air–water CO 2 flux data (Table 1) are also in good agreement with the annual data (hourly diurnal sampling twice each month) of Akhand et al (2016).…”

Reviews and Syntheses: Carbon biogeochemistry of Indian estuaries

“…To our knowledge, no data exists to evaluate fresh groundwater contributions to estuarine pCO2 for Indian estuaries. However, Akhand et al (2021) reported porewater pCO2 values up to 5423 µatm in the Indian Sundarbans mangroves. Using mean annual soil temperature and porewater salinity from Dutta et al, (2013), we estimate that this equates to a CO2 concentration of 137 µM.…”

“…These estimates suggest a limited contribution of Indian estuaries to global estuarine CO2 and CH4 fluxes. In terms of anthropogenic greenhouse gas emissions, India emits 2.8 Gt CO2eq annually of which 79%, 14%, and 5% are contributed by CO2, CH4, Mangroves are both a large sink (i.e., soil C burial) and source of greenhouse gases to the atmosphere (Chauhan et al, 2008;Krithika et al, 2008;Dutta et al, 2013Dutta et al, , 2015Dutta et al, , 2017Barnes et al, 2011;Biswas et al, 2007;Akhand et al, 2021). Compiling a large mangrove dataset in the east coast of India, Banerjee et al (2014) estimated mean CO2 and CH4 fluxes from the mangrove surrounding water to be 20.18 mol m -2 yr -1 and 0.027 -17502 mmol m -2 yr -1 , respectively.…”

“…In general, the C biogeochemistry of Indian estuaries bordered by extensive mangrove systems, has received more attention than estuaries less influenced by mangroves (Biswas et al, 2004(Biswas et al, , 2007Mukhopadhyay et al, 2002;Dutta et al, 2013Dutta et al, , 2015Dutta et al, , 2017Dutta et al, , 2019aDutta et al, , 2019bDutta et al, , 2021Ray et al, 2011Ray et al, , 2013Ray et al, , 2015Ray et al, , 2018Ganguly et al, 2011;Krithika et al, 2008;Borges et al, 2003;Akhand et al, 2016Akhand et al, , 2021. Some studies have focused on key drivers of OM cycling (Sarma et al, 2012(Sarma et al, , 2014Dutta et al, 2019aDutta et al, , 2021Rao et al, 2016;Ray et al, 2011Ray et al, , 2013Biswas et al, 2004Biswas et al, , 2007Mukhopadhyay et al, 2002), and others more on quantitative assessments of C budgets (Dutta et al, 2013(Dutta et al, , 2015(Dutta et al, , 2017 and export fluxes (Ray et al, 2018;Krishna et al, 2015Krishna et al, , 2019.…”