Using Ra isotopes to examine transport processes controlling benthic fluxes into a shallow estuarine lagoon

Hancock, Gary; Webster, Ian T.; Ford, Phillip W.; Moore, Willard S.

doi:10.1016/s0016-7037(00)00469-5

Cited by 82 publications

(49 citation statements)

References 23 publications

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“…Funding for this work was provided by the Rhode Island Sea Grant Program (Project Award R/CL-013) and a United States Geological Survey award to the University of Rhode Island Water Resource Center (Project 03). Elsinger and Moore 1980;Fanning et al 1981;Bollinger and Moore 1993;Hancock and Murray 1996;Moore 1996;Rama and Moore 1996;Moore 1997a,b;Scott 1998;Hussain et al 1999;Krest et al 1999Krest et al , 2000Charette et al 2001;Scott and Moran 2001;Burnett et al 2002). The application of Ra isotopes as tracers of groundwater input to coastal systems is based on balancing the input of 226 Ra from groundwater with the removal of excess 226 Ra due to tidal flushing.…”

Section: Acknowledgmentsmentioning

confidence: 99%

“…The residence time of Ra within the estuary (T, d) can be estimated using (Moore 1997a(Moore , 2000, 224 224…”

Section: Constraining the Residence Time Of Ra Within The Estuary-shomentioning

confidence: 99%

“…The only remaining source that may account for the observed 226 Ra and 228 Ra enrichment is input of Ra-enriched groundwater. 224 Ra data may be used to constrain the residence time of Ra within the Pettaquamscutt estuary (Hancock and Murray 1996;Torgerson et al 1996;Rama and Moore 1996;Hancock et al 2000;Charette et al 2001). 224 Ra is enriched at brackish salinities, analogous to 226 Ra and 228 Ra (Fig.…”

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confidence: 99%

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Seasonal changes in groundwater input to a well‐mixed estuary estimated using radium isotopes and implications for coastal nutrient budgets

Kelly

Moran

2002

Limnology & Oceanography

162

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Abstract226 Ra (half-life 1,600 yr) and 228 Ra (half-life 5.75 yr) were used as tracers to determine seasonal changes in groundwater input to the Pettaquamscutt estuary from June 1999 to June 2000. Ra isotopes were observed to be in excess of activities due to input from streams, Rhode Island Sound water, and particle desorption. The source of excess 226 Ra and 228 Ra within the estuary is attributed to groundwater transport of Ra derived from the weathering of bedrock within the Pettaquamscutt watershed. Short-lived 224 Ra (half-life 3.66 d) was used to calculate an average residence time of the estuary of 8 Ϯ 4 d. Box models used to constrain seasonal changes in groundwater input to the estuary indicate highest groundwater input in the summer (6.4-20 L m Ϫ2 d Ϫ1 ) and lowest values in the winter (2.1-6.9 L m Ϫ2 d Ϫ1 ). These Ra-derived groundwater fluxes are similar to rates of aquifer recharge over the annual cycle. Using these Ra-derived groundwater fluxes, the input of inorganic nitrogen and phosphorus from groundwater to the Pettaquamscutt was estimated at 61-180 mmol m Ϫ2 yr Ϫ1 and 4.4-13 mmol m Ϫ2 yr Ϫ1, respectively.

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Section: Acknowledgmentsmentioning

confidence: 99%

“…The residence time of Ra within the estuary (T, d) can be estimated using (Moore 1997a(Moore , 2000, 224 224…”

Section: Constraining the Residence Time Of Ra Within The Estuary-shomentioning

confidence: 99%

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confidence: 99%

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Seasonal changes in groundwater input to a well‐mixed estuary estimated using radium isotopes and implications for coastal nutrient budgets

Kelly

Moran

2002

Limnology & Oceanography

162

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“…In marine environments, radium isotopes have been used to quantify water and solute fluxes through this reaction zone by modeling diffusion across the interface (e.g., Hancock et al 2000;Nozaki et al 2001), bioturbation (e.g., Cochran 1980;Sun and Torgersen 2001), tidal flushing of the sediments (e.g., Webster et al 1994;Rama and Moore 1996), or groundwater discharge (e.g., Moore 1997;Krest et al 2000;Burnett et al 2002). 223 Ra and 224 Ra, with their short half-lives (Table 1), promise to be useful for quantifying rates of exchange over short timescales, as occurs in this reaction zone, but only a few studies have examined the geochemistry of these isotopes in groundwater or pore water (e.g., Webster et al 1994;Hancock et al 2000;Sun and Torgersen 2001). Several recent studies have used these isotopes to model coastal or estuarine residence times Charette et al 2001;Kelly and Moran 2002), but many questions remain concerning the processes that control the distribution of radium in these systems.…”

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confidence: 99%

Using natural distributions of short‐lived radium isotopes to quantify groundwater discharge and recharge

Krest

Harvey

2003

Limnology & Oceanography

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Radium activity in pore water of wetland sediments often differs from the amount expected from local production, decay, and exchange with solid phases. This disequilibrium results from vertical transport of radium with groundwater that flows between the underlying aquifer and surface water. In situations where groundwater recharge or discharge is significant, the rate of vertical water flow through wetland sediment can be determined from the radium disequilibrium by a combined model of transport, production, decay, and exchange with solid phases. We have developed and tested this technique at three sites in the freshwater portion of the Everglades by quantifying vertical advective velocities in areas with persistent groundwater recharge or discharge and estimating a coefficient of dispersion at a site that is subject to reversals between recharge and discharge. Groundwater velocities (v) were determined to be between 0 and Ϫ0.5 cm dϪ1 for a recharge site and 1.5 Ϯ 0.4 cm d Ϫ1 for a discharge site near Levee 39 in the Everglades. Strong gradients in 223 Ra and 224 Ra usually occurred at the base of the peat layer, which avoided the problems of other tracers (e.g., chloride) for which greatest sensitivity occurs near the peat surface-a zone readily disturbed by processes unrelated to groundwater flow. This technique should be easily applicable to any wetland system with different production rates of these isotopes in distinct sedimentary layers or surface water. The approach is most straightforward in systems where constant pore-water ionic strength can be assumed, simplifying the modeling of radium exchange.

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“…The naturally occurring radium isotopic suite ( 226 Ra, 228 Ra, 223 Ra, and 224 Ra) has great potential for evaluating and quantifying many of these limnological processes. These isotopes have previously been used in salt marsh (Rama and Moore 1996;Krest et al 2000;Kelly and Moran 2002), estuarine (Hussain et al 1999;Hancock et al 2000;Charette et al 2001), and coastal marine (Moore 1999) regions to examine groundwater inflow to, and determination of residence time of water in, these environments. Although these isotopes behave identically chemically, their range of half-lives ( 226 Ra ϭ 1,601 yr; 228 Ra ϭ 5.8 yr, 223 Ra ϭ 11.4 d, and 224 Ra ϭ 3.7 d) allows the examination of time-dependent processes that occur during mixing and transport.…”

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Radium isotopes in Cayuga Lake, New York: Indicators of inflow and mixing processes

Kræmer¹

2005

Limnol. Oceanogr.

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Using Ra isotopes to examine transport processes controlling benthic fluxes into a shallow estuarine lagoon

Cited by 82 publications

References 23 publications

Seasonal changes in groundwater input to a well‐mixed estuary estimated using radium isotopes and implications for coastal nutrient budgets

Seasonal changes in groundwater input to a well‐mixed estuary estimated using radium isotopes and implications for coastal nutrient budgets

Using natural distributions of short‐lived radium isotopes to quantify groundwater discharge and recharge

Radium isotopes in Cayuga Lake, New York: Indicators of inflow and mixing processes

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