Submarine groundwater discharge impacts on coastal nutrient biogeochemistry

Santos, Isaac R.; Chen, Xiaogang; Lecher, Alanna L; Sawyer, Audrey H.; Moosdorf, Nils; Rodellas, Valentí; Tamborski, Joseph; Cho, Hyung‐Mi; Dimova, Natasha; Sugimoto, Ryo; Bonaglia, Stefano; Li, Hailong; Hajati, Mithra‐Christin; Li, Ling

doi:10.1038/s43017-021-00152-0

Cited by 232 publications

(125 citation statements)

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“…Furthermore, NH 4 + was stable throughout the 24-h time-series measurement tidal cycle, suggesting that a reduced form of N was characteristic of the STE at this location (Figure 5). This condition is also mirrored alongside Mobile Bay's eastern shoreline, where organic-rich surface coastal sediment promoting a high concentration of NH 4 + and DON was reported as well as other coastal aquifers worldwide (Montiel et al, 2019b;Santos et al, 2021). NH 4 + and DON in the STE can be either physicochemically generated from the mineralization of coastal organic deposits or, in the case of NH 4 + , a product of microbially mediated dissimilatory nitrate reduction to ammonium (DNRA) process, which was also observed in the eastern Mobile Bay (Bernard et al, 2015;Adyasari et al, 2020).…”

Section: Disl Piermentioning

confidence: 77%

Storm-Driven Fresh Submarine Groundwater Discharge and Nutrient Fluxes From a Barrier Island

et al. 2021

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Quantifying and characterizing groundwater flow and discharge from barrier islands to coastal waters is crucial for assessing freshwater resources and contaminant transport to the ocean. In this study, we examined the groundwater hydrological response, discharge, and associated nutrient fluxes in Dauphin Island, a barrier island located in the northeastern Gulf of Mexico. We employed radon (222Rn) and radium (Ra) isotopes as tracers to evaluate the temporal and spatial variability of fresh and recirculated submarine groundwater discharge (SGD) in the nearshore waters. The results from a 40-day continuous 222Rn time series conducted during a rainy season suggest that the coastal area surrounding Dauphin Island was river-dominated in the days after storm events. Groundwater response was detected about 1 week after the precipitation and peak river discharge. During the period when SGD was a factor in the nutrient budget of the coastal area, the total SGD rates were as high as 1.36 m day–1, or almost three times higher than detected fluxes during the river-dominated period. We found from a three-endmember Ra mixing model that most of the SGD from the barrier island was composed of fresh groundwater. SGD was driven by marine and terrestrial forces, and focused on the southeastern part of the island. We observed spatial variability of nutrients in the subterranean estuary across this part of the island. Reduced nitrogen (i.e., NH4+ and dissolved organic nitrogen) fluxes dominated the eastern shore with average rates of 4.88 and 5.20 mmol m–2 day–1, respectively. In contrast, NO3– was prevalent along the south-central shore, which has significant tourism developments. The contrasting nutrient dynamics resulted in N- and P-limited coastal water in the different parts of the island. This study emphasizes the importance of understanding groundwater flow and dynamics in barrier islands, particularly those urbanized, prone to storm events, or located near large estuaries.

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Section: Disl Piermentioning

confidence: 77%

Storm-Driven Fresh Submarine Groundwater Discharge and Nutrient Fluxes From a Barrier Island

et al. 2021

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“…The main lateral contribution to surface and subsurface waters is via currents or (anti-)cyclonic eddies (e.g., Montes et al, 2014;Grasse et al, 2016;Thomsen et al, 2016). Further sources from land like submarine groundwater discharge or riverine input are either unknown or neglectable, as the study area is bordered by the Atacama Desert (e.g., Hutchins et al, 2002;Santos et al, 2021).…”

Section: Discussionmentioning

confidence: 99%

Controls on the Silicon Isotope Composition of Diatoms in the Peruvian Upwelling

et al. 2021

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The upwelling area off Peru is characterized by exceptionally high rates of primary productivity, mainly dominated by diatoms, which require dissolved silicic acid (dSi) to construct their frustules. The silicon isotope compositions of dissolved silicic acid (δ30SidSi) and biogenic silica (δ30SibSi) in the ocean carry information about dSi utilization, dissolution, and water mass mixing. Diatoms are preserved in the underlying sediments and can serve as archives for past nutrient conditions. However, the factors influencing the Si isotope fractionation between diatoms and seawater are not fully understood. More δ30SibSi data in today’s ocean are required to validate and improve the understanding of paleo records. Here, we present the first δ30SibSi data (together with δ30SidSi) from the water column in the Peruvian Upwelling region. Samples were taken under strong upwelling conditions and the bSi collected from seawater consisted of more than 98% diatoms. The δ30SidSi signatures in the surface waters were higher (+1.7‰ to +3.0‰) than δ30SibSi (+1.0‰ to +2‰) with offsets between diatoms and seawater (Δ30Si) ranging from −0.4‰ to −1.0‰. In contrast, δ30SidSi and δ30SibSi signatures were similar in the subsurface waters of the oxygen minimum zone (OMZ) as a consequence of a decrease in δ30SidSi. A strong relationship between δ30SibSi and [dSi] in surface water samples supports that dSi utilization of the available pool (70 and 98%) is the main driver controlling δ30SibSi. A comparison of δ30SibSi samples from the water column and from underlying core-top sediments (δ30SibSi_sed.) in the central upwelling region off Peru (10°S and 15°S) showed good agreement (δ30SibSi_sed. = +0.9‰ to +1.7‰), although we observed small differences in δ30SibSi depending on the diatom size fraction and diatom assemblage. A detailed analysis of the diatom assemblages highlights apparent variability in fractionation among taxa that has to be taken into account when using δ30SibSi data as a paleo proxy for the reconstruction of dSi utilization in the region.

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“…Nutrient inputs from land via rivers and groundwater can also fertilize coastal ecosystems (Valiela et al 1990). The importance of river inputs is well established; however, two decades of research on groundwater discharge into coastal seas have also highlighted the importance of groundwater‐derived nutrients as an essential flux into coastal ecosystems (Taniguchi et al 2019; Santos et al 2021).…”

Section: Figurementioning

confidence: 99%

Nutrient fluxes from rivers, groundwater, and the ocean into the coastal embayment along the Sanriku ria coast, Japan

Nakajima

Sugimoto

Kusunoki

et al. 2021

Limnology & Oceanography

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External nutrient supply from the land and ocean is crucial for sustaining high primary productivity in coastal seas. Submarine groundwater discharge (SGD) is recognized as one of the most important sources of terrestrial nutrients. However, the relative importance of SGD-derived nutrients from different sources in coastal ecosystems controlled by offshore exchange has not been well quantified. Here, we assessed water and nutrient budgets in the semi-enclosed bay along the Sanriku ria coast, where the intrusion of nutrient-enriched oceanic water is substantial. We conducted seasonal sampling campaigns and monitored the groundwater level throughout the year. Water and nutrient fluxes from fresh groundwater, saline groundwater, river water, and oceanic water were estimated using a hydrological method and radium (Ra) mass balance model. The results indicated that oceanic water was a dominant source, accounting for 99.5%, 86%, 97%, and 84% of the total influx of water, dissolved inorganic nitrogen, dissolved inorganic phosphorus, and dissolved silica, respectively. Although the mean fluxes of land-derived nutrients were small, the contribution increased to 28-59% in October, when nutrient fluxes of oceanic water weakened. Of the terrestrial sources, SGD dominated (41-94%), particularly saline SGD (>99% of total SGD). We concluded that an efficient supply of the primary limiting nutrient from land to the coastal ecosystem can accelerate coastal primary production during certain seasons, even if oceanic nutrients are typically the dominant source.Coastal seas are among the most productive regions of the Earth's biosphere, wherein land and ocean physical and biogeochemical processes interact (Jickells 1998). The external supply of nutrients is essential for sustaining the high primary productivity of coastal seas. Offshore seawater serves as a significant nutrient source in coastal seas (Kobayashi and Fujiwara 2008;Sugimoto et al. 2016). The magnitude and timing of oceanic nutrient flux is greatly influenced by physical processes, such as the movement of ocean current paths (e.g., Yoder et al. 1981;Sugimoto et al. 2009), wind intensity (e.g., Graham and Largier 1997;Carstensen and Conley 2004), and river discharge (e.g., Schubel and Pritchard 1986;Watanabe et al. 2017). Nutrient inputs from land via rivers and groundwater can also fertilize coastal ecosystems (Valiela et al. 1990).

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Submarine groundwater discharge impacts on coastal nutrient biogeochemistry

Cited by 232 publications

References 259 publications

Storm-Driven Fresh Submarine Groundwater Discharge and Nutrient Fluxes From a Barrier Island

Storm-Driven Fresh Submarine Groundwater Discharge and Nutrient Fluxes From a Barrier Island

Controls on the Silicon Isotope Composition of Diatoms in the Peruvian Upwelling

Nutrient fluxes from rivers, groundwater, and the ocean into the coastal embayment along the Sanriku ria coast, Japan

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