The Subterranean Estuary: Technical Term, Simple Analogy, or Source of Confusion?

Abstract

Twenty years ago, the term subterranean estuary was proposed by Moore (1999, https://doi.org/10.1016/S0304-4203(99)00014-6) as a call of attention to the ocean sciences community about the importance of coastal groundwater systems, which can compete in relevance and impact to oceans with fresh runoff coming from the continent. Coastal aquifers were presented as an analogy to surface estuaries in that water of different density comes together and establishes a saline wedge underlying fresher water. In the past two decades, the use of this term has expanded. Initially limited to studies with an oceanographic viewpoint considering the impact of groundwater on the ocean, it is now common in the literature, competing with classical hydrogeological terminology such as coastal aquifer or seawater intrusion and reaching publications with a traditional hydrogeological focus. The popularity of this terminology suggests that it fills a need not met by existing coastal hydrogeological terms, although these classical terms have their roots in a long history of study of coastal groundwater. This term may serve to enhance communications between the traditionally disparate communities of hydrogeology and ocean sciences—imbricating saltwater intrusion studies with marine sciences and bringing an opportunity to enhance interactions. But does the term also carry an element of confusion? This essay is intended to open a discussion within the coastal research community about the use and meaning of terminology in future studies of coastal and offshore groundwater systems.

Saltwater Intrusion and Submarine Groundwater Discharge: Acceleration of Biogeochemical Reactions in Changing Coastal Aquifers

“…In addition to "transition zone" Jiao and Post (2019) suggested that the term "mixing zone" or "coastal aquifer" would be adequate to describe the system. Duque et al (2020) proposed changing the term "subterranean estuary" to "subterranean mixing and reaction field." We do not advocate these changes.…”

Habitat Partitioning in the Marine Sector of Karst Subterranean Estuaries and Bermuda's Marine Caves: Benthic Foraminiferal Evidence

“…Karst subterranean estuaries (KSEs) are an environment created from the two-and three-way mixing of saline groundwater, rain, and oceanic water in the subsurface on carbonate landscapes, and this hydrographic framework promotes unique physical processes, biogeochemical cycling, and biological communities. Research on subterranean estuaries has significantly increased in the last 20 years (Moore, 1999;Gonneea et al, 2014;Brankovits et al, 2017Brankovits et al, , 2018Pain et al, 2019Pain et al, , 2020Duque et al, 2020). Traditionally, the biologic-focused study (fauna and ecosystems) of caves that are flooded by a KSE have been described with the adjectives anchialine or marine cave environments (Iliffe et al, 1983(Iliffe et al, , 1984Stock et al, 1986;Bishop et al, 2015).…”

Coastal Groundwater Flow at the Nearshore and Embayment Scales: A Field and Modeling Study

“…Nearly 25% of the world's population lives within 100 km of a coastline (Nicholls & Small, 2002), and the freshwater‐saltwater interface marks the seaward boundary of fresh groundwater supplies on which many coastal communities depend. As discussed by Duque et al (2020), the freshwater‐saltwater interface also marks the transition from potable groundwater resources to the subterranean estuary (Moore, 1999), where significant biogeochemical transformations occur and submarine groundwater discharge (SGD) exports nutrients, metals, and carbon to the coastal ocean (Burnett et al, 2003; Moore, 2010). Thus, knowledge of the location of the freshwater‐saltwater interface is critical for the continuum of studies that span coastal aquifers.…”