Carbon dioxide hydrodynamics along a wetland-lake-stream-waterfall continuum (Blue Mountains, Australia)

The small-scale spatial variability in dissolved carbon dioxide (CO2) and water-air CO2 flux dynamics were investigated within first-order catchments of the upper Blue Mountains Plateau (New South Wales, Australia). Water samples were collected at 81 locations during winter and summer over two consecutive years across seven aquatic ecosystem types: wetland, impoundment, lake, tributary stream, mainstem, escarpment complex, and urban-aquatic interface. Dissolved [CO2] ranged from 15 to 880 mu M (94 to 4760%Sat), and dissolved [O-2] from 0 to 350 mu M (0 to 101%Sat). CO2 supersaturation was typically highest in wetlands and vegetated impoundments of the upper plateau, and decreased downstream approaching atmospheric equilibrium at the escarpment waterfalls. Gas transfer velocities ranged from 0.18 m d(-1) in lentic waters to 292 m d(-1) at the bottom of waterfalls due to bubble-mediated transfer. The first-and second-order streams represented only 4.8% of the total open water area yet contributed to 61% of the total water-air CO2 outgassing. The lake, escarpment and mainstem group systems had narrow diel and seasonal CO2 concentration variability, while wetlands and vegetated impoundments had the widest ranges. Our high resolution spatio-temporal sampling was essential to identifying CO2 outgassing hotspots in these geomorphically diverse catchments. Overall, >95% of excess dissolved CO2 traversing the upper Blue Mountains Plateau was outgassed to the atmosphere. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study investigated the small-scale spatial variability in dissolved carbon dioxide (CO2) and water-air CO2 flux dynamics in first-order catchments of the upper Blue Mountains Plateau in New South Wales, Australia. The results showed that wetlands and lakes had the highest CO2 supersaturation, while CO2 approached atmospheric equilibrium at escarpment waterfalls. High resolution sampling was essential in identifying CO2 outgassing hotspots, with over 95% of excess dissolved CO2 outgassed to the atmosphere in these geomorphically diverse catchments.