科研之友
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摘要
Estuaries are dynamic hot spots for carbon cycling and atmospheric evasion. Here we assess the dynamics and drivers of CO2 in a hydrologically modified subtropical Australian estuary. Over 1year, 10 high-resolution spatial surveys of pCO(2), radon, chromophoric dissolved organic matter, chlorophyll a, and physicochemical parameters were conducted from the estuary mouth to a weir located 25km upstream. The riverine respiratory quotient revealed that processes besides water column respiration were driving high CO2 within the tidal river (salinity<2) but not in the estuary (salinity>2). Conservative mixing plots for pCO(2) and Rn-222 implied that groundwater may be a contributing source of CO2 during most surveys, but not during dry conditions. A multiple linear regression model explained 88% of the annual pCO(2) variability, indicating that mixing, metabolism, temperature, and groundwater inputs were key drivers of CO2. Inputs from an upstream wastewater outfall potentially fuel observed seasonal algal blooms, resulting in the lowest daytime CO2 emissions periods. Postbloom surveys had the highest daytime CO2 emissions. The average tidal river CO2 atmospheric flux rate was 37953mmol m(-2) day(-1). The average estuarine CO2 flux was 7817mmol m(-2) day(-1), equating to 286mol m(-2) yr(-1). Although the tidal river surface area was similar to 10 times smaller than the estuary, about one third (35%) of the CO2 emissions were derived from the tidal river. Our results suggest that CO2 emissions along the tidal river-estuary continuum are dynamic over small temporal and spatial scales and that a combination of hydrological and biological processes is a controlling factor of this variability. Plain Language Summary Estuaries are dynamic hotspots for carbon cycling and atmospheric emissions of the greenhouse gas carbon dioxide (CO2). Understanding the drivers and emissions of CO2 is important for global carbon budgets. Here we assess the seasonal drivers of CO2 in a subtropical Australian estuary. Over one-year, spatial surveys of pCO(2) and associated drivers were measured from the estuary mouth to a weir located 25km upstream. Our analysis revealed processes besides water column respiration were driving high CO2 within the tidal river but not in the estuary. Conservative mixing plots implied groundwater may be contributing to the source of CO2 upstream. A modeling exercise indicated the mixing of seawater, metabolism, seasonality and groundwater inputs were important predictors of CO2. Inputs from the upstream wastewater outfall potentially fuel observed seasonal algal blooms, resulting in lowest daytime CO2 emissions whilst post-bloom surveys had the highest daytime CO2 emissions. The average estuarine CO2 flux was 28 6 mol m(-2) yr(-1), which is in line with recent global estimates. Our results suggest that CO2 emissions along the tidal river-estuary continuum are dynamic over small temporal and spatial scales and that a combination of hydrological and biological processes are controlling factors of this variability.
- 出版日期2018-6
