Below the surface: Unveiling submarine groundwater discharge at Playa de la Estación

Abstract

Submarine groundwater discharge (SGD) is the outflow of an aquifer into the coastal ocean and is affected by oceanic, geologic, and anthropogenic processes. The basal aquifer of Santa Cruz Island, Galápagos, Ecuador has been over-pumped and poorly managed, resulting in saltwater intrusion, a brackish aquifer, and contamination of recreational sites such as Las Ninfas Lagoon. Further exploitation and contamination of the aquifer may harm coastal ecosystems and increase the potential for invasive species to establish and flourish. This study identifies the salinity gradient associated with SGD at Playa de la Estación, one of the few beach accesses on Santa Cruz Island. We consistently found low salinity near the shoreline ranging from 8-18 ppt. Although low salinity output was consistently observed, rainfall varied over the course of the study and was ruled out as a potential cause for the low salinity measured. There appears to be three main points of SGD seepage that also consistently had the lowest dissolved oxygen content averaging at 4.2 (mg/L) while the overall average was approximately 7.8 (mg/L). The island was thought to be waterless and lacking SGD, thus the existence and impacts of this phenomenon have been historically overlooked and underestimated. Uncontaminated SGD is beneficial and a preferred environment for native marine life in other regions of the Pacific Ocean, and anthropogenic alteration and contamination of the aquifer can change an ecosystem drastically. By identifying SGD seepage points, the water quality of the aquifer can be better understood and managed. Due to its scarcity, the groundwater of Santa Cruz must be studied in terms of aquifer health and SGD. Because SGD is seeping into the Galapagos Marine Reserve, further investigation can provide valuable foresight to those responsible for its protection.