Hydrological, geochemical and land use drivers of greenhouse gas dynamics in eleven sub-tropical streams

Luke F Andrews,Rogger E Correa,Isaac R Santos,Luke C Jeffrey,Xiaogang Chen,Shane A White,Praktan D Wadnerkar

doi:10.1007/s00027-021-00791-x

Luke F Andrews, Rogger E Correa + Show 5 more

Open Access

https://doi.org/10.1007/s00027-021-00791-x

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Abstract

Greenhouse gas (GHG) emissions from freshwater streams are poorly quantified in sub-tropical climates, especially in the southern hemisphere where land use is rapidly changing. Here, we examined the distribution, potential drivers, and emissions of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) from eleven Australian freshwater streams with varying catchment land uses yet similar hydrology, geomorphology, and climate. These sub-tropical streams were a source of CO2 (74 ± 39 mmol m−2 day−1), CH4 (0.04 ± 0.06 mmol m−2 day−1), and N2O (4.01 ± 5.98 µmol m−2 day−1) to the atmosphere. CO2 accounted for ~ 97% of all CO2-equivalent emissions with CH4 (~ 1.5%) and N2O (~ 1.5%) playing a minor role. Episodic rainfall events drove changes in stream GHG due to the release of soil NOx (nitrate + nitrite) and dissolved organic carbon (DOC). Groundwater discharge as traced by radon (222Rn, a natural groundwater tracer) was not an apparent source of CO2 and CH4, but was a source of N2O in both agricultural and forest catchments. Land use played a subtle role on greenhouse gas dynamics. CO2 and CH4 increased with catchment forest cover during the wet period, while N2O and CH4 increased with agricultural catchment area during the dry period. Overall, this study showed how DOC and NOx, land use, and rainfall events interact to drive spatial and temporal dynamics of GHG emissions in sub-tropical streams using multiple linear regression modelling. Increasing intensive agricultural land use will likely decrease regional CO2 and CH4 emissions, but increase N2O.

Highlights

Freshwater systems have been recognised as an important source of greenhouse gases (GHGs), especially CO2, to the atmosphere (Cole et al 2007; Drake et al 2018; Li et al 2018; Marx et al 2017)
In the absence of rainfall, streams tend to have longer water residence times which allow for internal aquatic processes and slow groundwater seepage to exert a stronger influence on GHG dynamics (Herreid et al 2020; Marx et al 2017; Smith and Kaushal 2015)
Insights into our hypotheses that land use drives GHGs in streams were obtained by establishing links between geochemical proxies (DOC, N Ox, and dissolved oxygen (DO)) and GHGs within streams (Atkins et al 2017; Seitzinger and Kroeze 1998; Stanley et al 2016)

Summary

Introduction

Freshwater systems have been recognised as an important source of greenhouse gases (GHGs), especially CO2, to the atmosphere (Cole et al 2007; Drake et al 2018; Li et al 2018; Marx et al 2017). 40 Page 2 of 19 into streams occurs during rainfall events or via groundwater discharge (Dinsmore et al 2013; Marx et al 2017). Rainfall events tend to alter stream pH, temperature, and dissolved oxygen (DO), which, in turn, affect the microbial production of GHGs in stream sediments as well as their solubility and fluxes at the air–water interface (Borges et al 2015,2018a; Webb et al 2016). In the absence of rainfall, streams tend to have longer water residence times which allow for internal aquatic processes (such as microbial respiration and photodegradation) and slow groundwater seepage to exert a stronger influence on GHG dynamics (Herreid et al 2020; Marx et al 2017; Smith and Kaushal 2015)

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