Groundwater dynamics in subterranean estuaries of coastal unconfined aquifers: Controls on submarine groundwater discharge and chemical inputs to the ocean

Robinson, C. E.; Xin, Pei; Santos, Isaac R.; Charette, Matthew A.; Li, Ling; Barry, David Andrew

doi:10.1016/j.advwatres.2017.10.041

Cited by 204 publications

(151 citation statements)

References 244 publications

(343 reference statements)

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“…We combine bottom up (i.e., groundwater derived fluxes) and top down (i.e., a response in the water column) evidence to assess whether groundwater may be an important source of DOM to surface waters into the 12 systems under investigation. Combining bottom up and top down evidence builds confidence when interpreting the biogeochemical response of surface waters to groundwater exchange (Robinson et al ). Even large groundwater sources may be minor relative to other local sources of DOM (such as surface runoff), so the absolute flux estimates need to be put in perspective.…”

Section: Discussionmentioning

confidence: 96%

Groundwater as a source of dissolved organic matter to coastal waters: Insights from radon and CDOM observations in 12 shallow coastal systems

Webb

Santos

Maher

et al. 2018

Limnology & Oceanography

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The influence of groundwater and pore‐water exchange on dissolved organic matter (DOM) dynamics in coastal surface waters remains poorly understood. Here, we combine bottom up (i.e., groundwater‐derived flux estimates) and top down (i.e., water column response) evidence to assess whether groundwater exchange drives DOM dynamics in shallow coastal waters. We rely on automated chromophoric DOM (CDOM, a proxy for DOM) and radon (222Rn, groundwater proxy) measurements over tidal time scales in 12 shallow systems, including tidal freshwater wetlands, estuaries, mangroves, coral reefs, coastal lakes, a saltmarsh, and a residential canal estate. Groundwater‐derived dissolved organic carbon (DOC) fluxes ranged from 2 ± 2 mmol m−2 d−1 in a coral reef to 1941 ± 1325 mmol m−2 d−1 in a mangrove tidal creek. These groundwater fluxes replaced surface water DOC inventories on time scales ranging from ~ 0.5 d to several weeks. Systems with short replacement times displayed positive correlations between radon and CDOM in surface waters. Groundwater exchange diluted surface water DOC in four systems. Using multiple lines of evidence, we interpreted groundwater to be an important source of DOM to surface waters in 4 out of the 12 systems, including an offshore coral reef lagoon with low surface water DOC concentrations. Groundwater discharge was a negligible source of DOM in systems with high surface water DOC and CDOM concentrations such as tidal freshwater wetlands and coastal lakes. This investigation highlights the high variability in groundwater‐derived DOC fluxes and responses in the water column, and demonstrates that submarine groundwater discharge and advective pore‐water exchange should be considered in coastal carbon budgets.

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Section: Discussionmentioning

confidence: 96%

Groundwater as a source of dissolved organic matter to coastal waters: Insights from radon and CDOM observations in 12 shallow coastal systems

Webb

Santos

Maher

et al. 2018

Limnology & Oceanography

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“…Wave pumping and bottom water currents cause advective pore water flow within surficial sediments, while tidal pumping induces advective flow into deeper layers (Santos et al, 2012). Combined with fresh groundwater discharge, these factors often shape a seawater circulation cell (Robinson et al, 2018;Santos et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Seasonality of Organic Matter Degradation Regulates Nutrient and Metal Net Fluxes in a High Energy Sandy Beach

et al. 2020

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During seawater circulation in permeable intertidal sands, organic matter degradation alters the composition of percolating fluids and remineralization products discharge into surficial waters. Concurrently, coastal seawater nutrient and organic matter composition change seasonally due to variations in pelagic productivity. To assess seasonal changes in organic matter degradation in the intertidal zone of a high energy beach (Spiekeroog Island, southern North Sea, Germany), we analyzed shallow pore waters for major redox constituents (oxygen [O2], manganese [Mn], and iron [Fe]) and inorganic nitrogen species (nitrite [NO2−], nitrate [NO3−], and ammonium [NH4+]) in March, August, and October. Surface water samples from a local time series station were used to monitor seasonal changes in pelagic productivity. O2 and NO3− were the dominating pore water constituents in March and October. Dissolved Mn, Fe, and NH4+ were more widely distributed in August. Seasonal changes in seawater temperature as well as organic matter and nitrate supply by seawater were assumed to affect microbial rates and degradation pathways. Pore water and seawater variability led to seasonally changing constituent effluxes to surface waters. Mn, Fe, and NH4+ effluxes are minimal in March and reached their maximum in August. Furthermore, the intertidal sands switched from a net dissolved inorganic nitrogen sink in March to a net source in August. In conclusion, seasonal effects on intertidal pore water biogeochemistry affect constituent fluxes across the sediment‐water interface. The seasonality of the beach bioreactor must be considered when fluxes are extrapolated to annual timescales.

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“…The present regression model forms a new basis for examining and predicting groundwater tables, particularly those driven by irregular multifrequency surface water fluctuations. The predicted hysteresis effect of antecedent surface water fluctuations on the groundwater behavior may in turn influence soil conditions (e.g., moisture and oxygen availability) and reactive transport of dissolved constituents (e.g., carbon, nutrients, metal, and organic contaminants) (Boano et al, ; Robinson et al, ).…”

Section: Resultsmentioning

confidence: 99%

Predictability and Quantification of Complex Groundwater Table Dynamics Driven by Irregular Surface Water Fluctuations

Xin

Wang

Shen

et al. 2018

Water Resources Research

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Shallow groundwater interacts strongly with surface water across a quarter of global land area, affecting significantly the terrestrial eco‐hydrology and biogeochemistry. We examined groundwater behavior subjected to unimodal impulse and irregular surface water fluctuations, combining physical experiments, numerical simulations, and functional data analysis. Both the experiments and numerical simulations demonstrated a damped and delayed response of groundwater table to surface water fluctuations. To quantify this hysteretic shallow groundwater behavior, we developed a regression model with the Gamma distribution functions adopted to account for the dependence of groundwater behavior on antecedent surface water conditions. The regression model fits and predicts well the groundwater table oscillations resulting from propagation of irregular surface water fluctuations in both laboratory and large‐scale aquifers. The coefficients of the Gamma distribution function vary spatially, reflecting the hysteresis effect associated with increased amplitude damping and delay as the fluctuation propagates. The regression model, in a relatively simple functional form, has demonstrated its capacity of reproducing high‐order nonlinear effects that underpin the surface water and groundwater interactions. The finding has important implications for understanding and predicting shallow groundwater behavior and associated biogeochemical processes, and will contribute broadly to studies of groundwater‐dependent ecology and biogeochemistry.

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Groundwater dynamics in subterranean estuaries of coastal unconfined aquifers: Controls on submarine groundwater discharge and chemical inputs to the ocean

Cited by 204 publications

References 244 publications

Groundwater as a source of dissolved organic matter to coastal waters: Insights from radon and CDOM observations in 12 shallow coastal systems

Groundwater as a source of dissolved organic matter to coastal waters: Insights from radon and CDOM observations in 12 shallow coastal systems

Seasonality of Organic Matter Degradation Regulates Nutrient and Metal Net Fluxes in a High Energy Sandy Beach

Predictability and Quantification of Complex Groundwater Table Dynamics Driven by Irregular Surface Water Fluctuations

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