Hydrological, geochemical and land use drivers of greenhouse gas dynamics in eleven sub-tropical streams
Luke Andrews, Praktan D. Wadnerkar, Shane White, Xiaogang Chen, Rogger E. Correa, Luke C. Jeffrey, Isaac R. Santos
Abstract
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 (CO 2 ), nitrous oxide (N 2 O) and methane (CH 4 ) from eleven Australian freshwater streams with varying catchment land uses yet similar hydrology, geomorphology, and climate. These sub-tropical streams were a source of CO 2 (74 ± 39 mmol m −2 day −1 ), CH 4 (0.04 ± 0.06 mmol m −2 day −1 ), and N 2 O (4.01 ± 5.98 µmol m −2 day −1 ) to the atmosphere. CO 2 accounted for ~ 97% of all CO 2 -equivalent emissions with CH 4 (~ 1.5%) and N 2 O (~ 1.5%) playing a minor role. Episodic rainfall events drove changes in stream GHG due to the release of soil NO x (nitrate + nitrite) and dissolved organic carbon (DOC). Groundwater discharge as traced by radon ( 222 Rn, a natural groundwater tracer) was not an apparent source of CO 2 and CH 4 , but was a source of N 2 O in both agricultural and forest catchments. Land use played a subtle role on greenhouse gas dynamics. CO 2 and CH 4 increased with catchment forest cover during the wet period, while N 2 O and CH 4 increased with agricultural catchment area during the dry period. Overall, this study showed how DOC and NO x , 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 CO 2 and CH 4 emissions, but increase N 2 O.