Fresh groundwater discharge insignificant for the world’s oceans but important for coastal ecosystems

Abstract

The flow of fresh groundwater may provide substantial inputs of nutrients and solutes to the oceans. However, the extent to which hydrogeological parameters control groundwater flow to the world's oceans has not been quantified systematically. Here we present a spatially resolved global model of coastal groundwater discharge to show that the contribution of fresh groundwater accounts for~0.6% (0.004%-1.3%) of the total freshwater input and~2% (0.003%-7.7%) of the solute input for carbon, nitrogen, silica and strontium. However, the coastal discharge of fresh groundwater and nutrients displays a high spatial variability and for an estimated 26% (0.4%-39%) of the world's estuaries, 17% (0.3%-31%) of the salt marshes and 14% (0.1-26%) of the coral reefs, the flux of terrestrial groundwater exceeds 25% of the river flux and poses a risk for pollution and eutrophication.

Submarine groundwater springs are characterized by distinct fish communities

“…Although globally, fresh SGD amounts to only a small percentage of river discharge (Luijendijk, Gleeson, & Moosdorf, 2020; Taniguchi, Burnett, Cable, & Turner, 2002) tropical coasts export more than 56% of all fresh SGD (Zhou, Sawyer, David, & Famiglietti, 2019). In coastal ecosystems nutrient‐rich fresh SGD increases primary production and sustains higher primary and secondary consumer biomass (Dale & Miller, 2008; Encarnação et al., 2015; Hata et al., 2016; Lecher & Mackey, 2018; Piló et al., 2018; Utsunomiya et al., 2017; Waska & Kim, 2011).…”

“…The influx of fresh groundwater is a locally important pathway for inland‐derived nutrients, especially to tropical coastal marine environments (Luijendijk et al., 2020; Zhou et al., 2019). Recorded nitrate and phosphate concentrations were higher than previously reported for Trou aux Biches lagoon (Hurbungs, Jayabalan, & Chineah, 2002).…”

234U/230Th coral growth dating yields reliable ages in restricted basins despite anomalous δ234Ui values

“…Dutton et al, 2015), (iii) late Quaternary cyanobacterial mounds that dominate Cape Heraion at Locality 1 (Fig 1. c) may provide evidence of rising groundwater altering the water chemistry (Portman et al, 2005), and (iv) coral growth occurs in the footwalls along coastal margins (localities 2-9, Fig. 1a) that are subject to episodic fault-related uplift and freshwater influx from rivers and groundwater (Luijendijk et al, 2020). A study of the Holocene coastal marginal marine environment along the southern western Gulf of Corinth (Soter et al, 2001) provides an analogue to conditions during previous highstands.…”

HESS Opinions: Improving the evaluation of groundwater representation in continental to global scale models

“…This is partially reasonable because local to regional peculiarities of hydrology, politics and culture are paramount to groundwater resource management (Foster et al 2013) and groundwater dynamics in different continents are less directly connected and coupled than atmospheric dynamics. Regional groundwater analysis is a mature, well-established field (Hill & Tiedeman, 2007;Kresic, 2009;Zhou & Li, 2011;Hiscock & Bense, 2014;Anderson et al 2015a) and regional approaches may be preferable for some issues and objectives; yet, important global aspects of groundwater both as a resource and as part of the Earth System are emerging (Gleeson et al 2020). First, our increasingly globalized world trades virtual groundwater and other groundwater-dependent resources in the food-energy-water nexus, and groundwater often crosses borders in transboundary aquifers.…”

“…As the main storage component of the freshwater hydrologic cycle, groundwater systems support baseflow levels in streams and rivers, and thereby ecosystems and agricultural productivity and other ecosystem services in both irrigated and rainfed systems (Scanlon et al, 2012;Qiu et al, 2019;Visser, 1959;Zipper et al, 2015Zipper et al, , 2017. When pumped groundwater is transferred to oceans Wada et al, 2012;Döll et al, 2014a;Wada, 2016;Caceres et al, 2020;Luijendijk et al 2020), resulting sealevel rise can impact salinity levels in coastal aquifers, and freshwater and solute inputs to the https://doi.org/10.5194/hess-2020-378 Preprint. Discussion started: 24 August 2020 c Author(s) 2020.…”