Quantifying the submarine groundwater discharge to the Great Barrier Reef Lagoon, Australia

Abstract:

Submarine groundwater discharge (SGD) is a recognized pathway for nutrient enrichment in coastal environments. However, most large scale studies have been conducted in the northern hemisphere such as the Gulf of Mexico and the eastern U.S. seaboard creating substantial uncertainty in global estimates. SGD inputs into other significant coastal areas such as to the Great Barrier Reef (GBR) are not yet well understood. In this study, we constructed a three-dimensional large-scale groundwater flow model supported by hydrogeological modelling (incorporating the diverse hydrologic conditions and heterogeneous subsurface materials in the model) to estimate SGD rates to the world’s largest coral reef ecosystem, the GBR, from the adjacent unconfined aquifers. The contributing recharge area comprised ~400,000 km² land area, extending tens to hundreds of kilometers inland. Preliminary results indicate that ~18 km³/yr (10–28 km³/yr) of groundwater directly enters the GBR lagoon. The findings of this study provide new insights into the distributed nature of SGD and the contributing areas that can supply anthropogenic contaminants to the GBR system via SGD. The results are also helpful to define the subterranean domains which are crucial to evaluate the current status and future prospects of coastal chemical budgets, coastal ecosystem processes and marine ecosystem services, and to develop integrated coastal management strategies.