Groundwater seepage as a driver of CO2 evasion in a coastal lake (Lake Ainsworth, NSW, Australia)

Groundwater seepage as a driver of CO2 evasion in a coastal lake (Lake Ainsworth, NSW, Australia)

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.