In recent years, it has become apparent that carbon dioxide (CO2) emissions from inland water bodies and lakes are an important component of the global carbon cycle. Large-scale lake heterotrophy is thought to be a major driver of CO2 production and may mask other processes such as groundwater input. This study uses radon (222Rn, a natural groundwater tracer) to quantify groundwater discharge, and estimates CO2 outgassing to determine the contribution of groundwater-derived CO2 inputs into Lake Ainsworth (New South Wales, Australia). Lake Ainsworth was a source of CO2 to the atmosphere throughout the study period with outgassing rates ranging from 10.6 to 152.3 mmol m2 day−1. Annual groundwater fluxes were determined using a radon mass balance equated to about 55 ± 50 % of the total volume of water input (via direct precipitation and groundwater) into the lake. In spite of large uncertainties, groundwater seepage was a source of CO2 supersaturation in Lake Ainsworth equivalent to 13 ± 25 % of total CO2 outgassing rates. Hence, groundwater discharge may need to be considered for carbon budgets of other lakes.
- Atmospheric flux
- Permeable sediments
- Submarine groundwater discharge