- Email: [email protected]
Radium mass balance and submarine groundwater discharge in Sepetiba Bay, Rio de Janeiro State, Brazil
Journal of South American Earth Sciences 39 (2012) 44e51
Contents lists available at SciVerse ScienceDirect
Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames
Radium mass balance and submarine groundwater discharge in Sepetiba Bay, Rio de Janeiro State, Brazil Joseph M. Smoak a, *, Christian J. Sanders b, Sambasiva R. Patchineelam b, Willard S. Moore c a
University of South Florida (USF), Environmental Science, St. Petersburg, FL, USA Universidade Federal de Fluminense (UFF), Departamento de Geoquímica Niterói-RJ, Brazil c Department of Earth and Ocean Sciences, University of South Carolina, Columbia, SC, USA b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 February 2012 Accepted 6 July 2012
Radium-226 and 228Ra activities were determined in water samples from within and adjacent to Sepetiba Bay, Rio de Janeiro State (Brazil) in 1998, 2005 and 2007. Surface waters in Sepetiba Bay were substantially higher in 226Ra and 228Ra compared to ocean end member samples. Using the residence time of water in the bay we calculated the flux required to maintain the observed enrichment over the ocean end members. We then applied a radium mass balance to estimate the volume of submarine groundwater discharge (SGD) into the bay. The estimates of SGD into Sepetiba Bay (in 1010 L day1) were 2.56, 3.75, and 1.0, respectively for 1998, 2005, and 2007. These estimates are equivalent to approximately 1% of the total volume of the bay each day or 50 L m2 day1. It is likely that a substantial portion of the SGD in Sepetiba Bay consists of infiltrated seawater. This large flux of SGD has the potential to supply substantial quantities of nutrients, carbon and metals into coastal waters. The SGD found here is greater than what is typically found in SGD studies along the eastern United States and areas with similar geologic characteristics. Considering there are many coastal areas around the world like Sepetiba Bay, this could revise upward the already important contribution of SGD to coastal as well as oceanic budgets. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Radioactivity 226 Ra 228 Ra Coastal waters SGD
1. Introduction While rivers are an obvious source of freshwater to coastal systems, groundwater discharge from coastal aquifers has been receiving increased acceptance as an important contributor to coastal waters (Moore, 1996; Corbett et al., 1999; Burnett et al., 2001, 2003, 2008; Taniguchi et al., 2002; Santos et al., 2008; Charette and Moore, 2008). Input of subterranean water, referred to as Submarine Groundwater Discharge (SGD), typically is a mixture of infiltrated seawater and terrestrially derived freshwater and includes all advective fluid flow between the land and the continental shelf, regardless of the source or composition of the fluids (Burnett et al., 2003). This source of water is important for the biogeochemical flux of materials to coastal waters (Charette et al., 2001; Moore et al., 2002; Crotwell and Moore, 2003; Charette and Buesseler, 2004; Hwang et al., 2005; Kim et al., 2005). It is estimated that fresh terrestrial SGD alone supplies approximately 6% of the total freshwater runoff to the world’s oceans (Zekster and Loaiciga, 1993; reviewed by Burnett et al., 2003). Moore (2010)
* Corresponding author. E-mail address: [email protected] (J.M. Smoak). 0895-9811/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jsames.2012.07.004
found SGD into the South Atlantic Bight along the east coast of the United States to be approximately three times the total volume of river water supplied to the bight and a significant source of nutrients to the South Atlantic Bight (Moore et al., 2002). Several investigations have reported substantial nutrient input via SGD, which may contribute to coastal eutrophication (Capone and Slater, 1990; LaRoche et al., 1997; Herrera-Silveira, 1998; Charette et al., 2001; Burnett et al., 2007). Direct measurements (e.g. seepage meters) of SGD are difficult on a regional scale. However, radium isotopes have been shown to be powerful tools to quantify SGD fluxes and indicate the sources (Charette and Moore, 2008). The direct parent of each radium isotope is a thorium isotope. Thorium is strongly adsorbed to sediment and provides a source of radium, which is generated on a range of time scales. In freshwater, radium is strongly adsorbed to particles. However, under reducing conditions, low pH and/or increasing salinity, radium can be released into solution. These characteristics make radium an excellent tracer of brackish SGD. The goal of the present study is to determine the source of 226Ra and 228Ra to Sepetiba Bay and use that information to estimate SGD to the bay. We examine 226Ra and 228Ra in the waters of Sepetiba Bay, adjacent coastal waters outside of the bay, wells surrounding the bay, and river water entering the bay. Radium-226, a product in
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51
the 238U decay series, has a 1600-year half-life. Radium-228, produced through the 232Th decay series, has a 5.75-year half-life. Sepetiba Bay waters are enriched in these two radium isotopes compared to the ocean waters adjacent to the bay. The sources of enrichment from a mass balance approach are used to determine the fraction that is supplied by SGD. We estimate the volume of SGD using radium activity in brackish well water from around the bay. Most SGD studies have been conducted on the east coast of the United States and in areas with similar geological characteristics. However, as suggested by a few studies (Kim et al., 2003; Oliveira et al., 2003; Hwang et al., 2005), areas with different geological characteristics may produce substantially different SGD fluxes. We investigate an area quite different from most of these previous
45
studies to test the hypothesis that high elevation near the coast and permeability of the underlying geology could produce substantially higher SGD fluxes. If correct, considering the number of coastal areas like Sepetiba Bay around the world this could revise upward the already important contribution of SGD to coastal as well as oceanic budgets. 2. Study area Sepetiba Bay (Fig. 1) is located 60 km west of Rio de Janeiro City, Brazil. The bay is located between south latitude 22 55’ 00” and 23 03’ 60” and west longitude 43 56’ 30” and 43 36’ 20”. The volume of the bay is approximately 2.56 109 m3 with an average
44o W
44o 20’ W
21
20 23o S
23 Sepetiba Bay
17 25
19
23
29
18 26 24
27 Ilha Grande 0
28
5
10
km
O2 O3 O1
23o 20’ S
44o W
43o 45’ W
22o 55’ S
4 5 16 9 15 2
14 X
10 3 8
12
7
23o S
6
1 11
13
0
2.5
5
km
Fig. 1. Map of Sepetiba Bay and the surrounding area showing sampling stations for the water column (-), sulfide-rich well (3), and brackish wells (C).
46
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51
depth of 6 m. Tidal regime is micro tidal with amplitude of less than 2 m. Rodrigues (1990) determined the residence time of water in the bay to be 99 h. Sepetiba Bay covers a total area of approximately 519 km2 and the drainage basin is 2500 km2. The drainage basin is highly industrialized with hydro-metallurgical plants, iron and steel works, chemical factories, printing presses and rubber industry (FEEMA, 1989). The regional climate is humid subtropical with mean annual temperature around 24 C and mean annual precipitation of 1800 mm (1400e2500 mm range). Maximum rainfall occurs between December and March (summer) and minimum between June and August (winter). Cold fronts are frequent between September and November (spring). There are nine rivers that drain into Sepetiba Bay. These nine rivers are responsible for an annual freshwater input of 5.7e7.6 109 m3. The São Francisco River is responsible for 86% of the riverine input. The São Francisco River receives additional water from outside of the natural drainage basin via a large water diversion. Metaigneous and igneous rocks showing granitic to granodioritic compositions are dominant in the geological terranes of the study area and surroundings (Leonardos and Fyfe, 1974; Zorita, 1979; Chaves and Pires, 1984; Junho et al., 1993; Porto, 1993). These rocks contain various U and Th isotopes, the ultimate source of the radium isotopes, mainly in the form of accessory minerals such as zircon, allanite, sphene and monazite. Such accessory minerals (except allanite) are highly resistant to the weathering process and therefore will be concentrated as placer deposits. The soil and sediments derived from these parent rocks have been accumulating in low-lying drainage basins and in the coastal plain. Brazil placer deposits produce half the world’s supply of monazite. The world production of thorium is based almost exclusively on extraction from monazite. Since it belongs to the 232Th decay series, 228 Ra tends to be enriched in samples from this region relative to 226 Ra. Allanite is an abundant phase in rocks of the region (Guimarães, 1999) and because of its low resistance to weathering, must be considered the most probable source of the 228Ra enrichment in surface waters (Lauria and Godoy, 2002; Lauria et al., 2004).
4. Results The distribution of radium isotopes in the surface waters of Sepetiba Bay, the waters adjacent to Sepetiba Bay and ocean waters are given in Table 1. Sampling stations are shown in Fig. 1. Table 2 shows the activity of 228Ra and 226Ra in the brackish wells. Samples collected from within Sepetiba Bay were enriched in both 226 Ra and 228Ra relative to ocean end members. Ocean end members were determined from three samples collected on the Atlantic side of Ilha Grande. Refractometer salinity measurements recorded one of the samples (station O3) to be 36 and the other two (stations O1 and O2) at 34. The 36 sample had 7.86 dpm 100 L1 of 226Ra and 9.29 dpm 100 L1 of 228Ra while the mean of the three was 7.89 dpm 100 L1 for 226Ra and 9.56 dpm 100 L1 for 228Ra. Stations 27 and 28 appear to be in locations suitable for ocean end members but were collected on an outgoing tide and had substantially more 228Ra and somewhat greater 226 Ra values than stations O1, O2 or O3. The enrichment determined by subtracting the average 228Ra and 226Ra values in the ocean end member from the average 228Ra and 226Ra values within the bay yields an enrichment of 4 dpm 100 L1 for 226Ra and 25 dpm 100 L1 for 228 Ra in 1998 (n ¼ 4), 5 dpm 100 L1 for 226Ra and 20 dpm 100 L1 for 228 Ra in 2005 (n ¼ 4) and 2 dpm 100 L1 for 226Ra and 13 dpm 100 L1 for 228Ra in 2007 (n ¼ 8). The total enrichment determined by multiplying the enrichment activity by the total volume of the bay (2.56 1012 L) yields total enrichments (in 1010 dpm) within Sepetiba Bay of 9.2 and 64.5 for 226Ra and 228Ra respectively in 1998, 12.3 and 51.9 for 226Ra and 228Ra respectively in 2005 and 5.2 and 33.0 for 226Ra and 228Ra respectively in 2007. Given the 99-h residence time for Sepetiba Bay water (Rodrigues, 1990) the flux to maintain the enrichment was (in 1010 dpm day1) 2.2, 3.0, and 1.3 for 226Ra and 15.6, 12.6, and 8.0 for 228Ra in 1998, 2005 and 2007 respectively. The São Francisco River supplies 86% of the total riverine freshwater to the bay. The waters at the mouth of the São Francisco River contained 29.4 dpm 100 L1 226Ra and 71.1 dpm 100 L1 228Ra. The three brackish (salinity 15e20) groundwater wells on the shore adjacent to Sepetiba Bay have an average concentration of 63 dpm 100 L1 for 226Ra and 175 dpm 100 L1 for 228Ra. However, a single sulfide-rich saline-well had values that far exceeded any other values (226Ra 540 dpm 100 L1 and 228Ra 2380 dpm 100 L1).
3. Methods In 1998, 2005 and 2007 water samples of 20e40 l were collected from three different brackish artesian wells (Coroa Grande, Sepetiba Beach and Pedra de Guaratiba), the primary river (São Francisco), 16 stations within Sepetiba Bay, 15 stations in the adjacent waters outside Sepetiba Bay, and three open ocean sites. A refractometer was used to measure salinity. Water samples were immediately filtered through a 1 mm cartridge filter. Sample volume was recorded and the water sample was pumped through a column of manganese-coated acrylic fiber in order to remove Ra in a quantitative manner (Moore, 1976). The Mn-fibers were leached with HCl in a Soxhlet extraction apparatus to remove the long-lived radium isotopes. Radium was co-precipitated with BaSO4 and aged for 3 weeks, which allowed 222Rn and its daughters to reach secular equilibrium with 226Ra. Subsequently all samples were measured in a well-type hyperpure germanium detector for 226 Ra and 228Ra activities (Moore, 1984). The estimated error for these measurements is about 7%. Radium enrichment was calculated by subtracting the average 228 Ra and 226Ra values in the ocean end member from the average 228 Ra and 226Ra values within the bay. Total enrichment was determined by multiplying the enrichment activity by the total volume of the bay (2.56 1012 L). The fluxes were determined by dividing the total enrichment by the Sepetiba Bay water residence time of 99 h (Rodrigues, 1990).
5. Discussion Rivers entering the bay, diffusion from bay sediments, release from sediment via resuspension, and SGD are all potential sources of radium that can support the observed enrichments. We examine these sources to complete a radium mass balance for Sepetiba Bay. The contribution from rivers, diffusion, and the release from sediment via resuspension are evaluated and subtracted from the total enrichment to estimate the contribution via SGD. This is a “flux-bydifference” approach which is most useful with non-point source fluxes (Charette and Moore, 2008; and references within). The radium contribution from SGD was used along with the concentration of radium in brackish groundwater wells to estimate the volume of SGD. 5.1. Total flux to support enrichment 5.1.1. Radium-226 Sepetiba Bay water has a residence time of 99 h (Rodrigues, 1990), therefore fluxes of (in 1010 dpm day1) of 2.2, 3.0, and 1.3 were required to support the observed 226Ra enrichment during 1998, 2005 and 2007 sampling periods respectively. This was calculated by dividing the total 226Ra enrichment by the residence time. Decay was not a factor because bay water residence time is short in comparison to the half-life of 226Ra.
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51
47
Table 1 Radium activity in waters in and around Sepetiba Bay. Samples collected in December 1998, May 2005 and June 2007. Sampling year Bay waters 1998 1998 1998 1998 2005 2005 2005 2005 2007 2007 2007 2007 2007 2007 2007 2007 Adjacent waters 1998 1998 1998 1998 1998 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005 Ocean end members 2005 2005 2005 Mean
226
Ra (dpm 100 L1)
228
Ra (dpm 100 L1)
Station
LAT
LON
13.00 12.00 10.00 11.00 11.25 14.12 12.84 12.60 8.51 6.15 8.28 10.91 10.84 12.04 12.23 10.38
42.00 33.00 33.00 31.00 30.77 32.66 28.26 27.65 19.32 10.77 22.24 29.49 24.50 25.32 24.04 23.91
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
S 23 S 22 S 23 S 22 S 22 S 23 S 23 S 23 S 22 S 23 S 23 S 23 S 23 S 23 S 22 S 22
01.998 59.836 00.708 56.005 56.200 01.456 01.780 01.099 58.371 01.056 02.119 01.060 02.265 00.869 58.957 57.727
W 43 50.951 W 43 50.312 W 43 43.844 W 43 48.706 W 43 49.500 W 43 42.955 W 43 51.127 W 43 56.057 W 43 53.641 W 43 54.561 W 43 51.931 W 43 48.311 W 43 47.440 W 43 41.968 W 43 43.781 W 43 45.682
11.00 13.00 9.00 9.00 10.00 10.65 12.39 12.46 12.50 11.05 11.19 13.38 11.54 9.56 8.51 9.76
30.00 33.00 27.00 27.00 27.00 25.56 19.47 32.79 27.44 16.98 25.18 15.46 16.73 17.95 14.36 17.34
17 18 19 20 21 21 21 22 23 24 25 26 27 28 29 29
S 23 S 23 S 23 S 22 S 22 S 23 S 23 S 23 S 23 S 23 S 23 S 23 S 23 S 23 S 23 S 23
0 0.784 06.584 03.950 58.602 56.878 02.582 02.582 58.583 58.583 09.034 03.663 07.669 07.024 12.602 04.132 04.132
W W W W W W W W W W W W W W W W
8.19 7.61 7.86 7.89
9.92 9.46 9.29 9.56
O1 O2 O3
5.1.2. Radium-228 Using the 99-h residence time (Rodrigues, 1990) the observed enrichment of 228Ra required fluxes of (in 1010 dpm day1) 15.6, 12.6, and 8.0 in 1998, 2005 and 2007 respectively. The estimates were made in the same manner as with 226Ra. 5.2. Contribution from river 5.2.1. Radium-226 Radium-226 supplied by the river was determined using two approaches. First, the maximum discharge of all rivers entering the bay of 2.08 1010 L day1 and a suspended sediment concentration in the river of 63 mg L1 were used (Rodrigues, 1990). This gives a sediment discharge of 1.31 109 g day1. We used the activity of samples reported by Lauria et al. (2004) to estimate the desorbable 226Ra from the river sediments. Lauria et al. (2004) reported a maximum activity of 2.5 dpm g1 of 226Ra from samples collected in the western coastal zone of the State of Rio de Janeiro. Key et al. (1985) estimated the loss of 226Ra via desorption in Amazon River sediments was 0.93 dpm g1 while Smoak et al. (1996) determined desorption in Amazon River sediments to be that less than 0.6 dpm g1 via a desorption Table 2 Brackish wells around Sepetiba Bay. Wells
226
Pedra de Guarariba Sepetiba Beach Coroa Grande
55 78 55
Ra (dpm 100 L1)
228
Ra (dpm 100 L1)
197 155 173
(surf) (bottom)
(surf) (bottom)
S 23 1 6.813 S 23 10:987 S 23 13.266
43 44 44 43 43 44 44 43 43 44 44 44 44 44 44 44
5 7.975 02.816 00.530 56.533 57.605 06.246 06.246 56.701 56.701 32.127 25.635 22.917 03.167 002.470 14.077 14.077
W 44 1 6.009 W 44 16.974 W 44 25.494
experiment. In this calculation we maximized the contribution from the river by using an estimate of 1 dpm g1 desorbable radium based on Key et al. (1985) which is 40% of the total radium. Using 1 dpm g1 as the desorbable amount, sediments entering the bay via the rivers desorb a total of 1.31 109 dpm day1. In addition to the input via desorption the river also carries 5 dpm 100 L1 of dissolved radium, which supplies a total of 1.04 109 dpm day1. Therefore the combined contribution from desorption and dissolved 226Ra from the rivers is 2.4 109 dpm day1. The second approach to calculating the 226 Ra river supply was to multiply the maximum river volume discharge from all rivers entering the bay by the 226Ra concentration measured at the mouth of the São Francisco River after desorption would have occurred during the 2007 sampling period salinity 30). This calculation yields (29.4 dpm 100 L1; 6.1 109 dpm day1. We use the latter calculation to maximize the contribution from the river, and hence, minimize the contribution from SGD. Using the 6.1 109 dpm day1 value the river’s contribution to the total enrichment of 226Ra is 27%, 21% and 49% respectively for 1998, 2005 and 2007. 5.2.2. Radium-228 As with 226Ra, we first used the activity of samples reported by Lauria et al. (2004) to estimate the desorbable 228Ra from the river sediments. Lauria et al. (2004) reported a maximum activity of 7 dpm g1 of 228Ra from these samples collected in the western coastal zone of the State of Rio de Janeiro. We estimated based on the discussion in Section 5.2.1 that of this total activity approximately 40% (2.8 dpm g1) of the 228Ra might be desorbable. Sediments
48
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51
entering the bay via the rivers desorb a total of 3.67 109 dpm day1 from river sediments. In addition to the input via desorption the river also carries 10 dpm L1 of dissolved radium which supplies a total of 2.08 109 dpm day1. Therefore the combined contribution from desorption and dissolved 228Ra from the rivers is 5.8 109 dpm day1. The second approach using the river mouth value of 228Ra (71.1 dpm 100 L1) yields 1.48 1010 dpm day1. Like 226 Ra we used the river mouth estimate. Using this approach the river contribution to the total enrichment of 228Ra is 10%, 12% and 19% for 1998, 2005 and 2007 respectively. 5.3. Contribution via sediment diffusion 5.3.1. Radium-226 As sea level along the central Brazilian coast was higher over the past 6000 years (Angulo and Lessa, 1997; Martin, 2003), the sediments within the bay and surrounding the bay from the mangrove system had previously desorbed Ra and can only supply 226Ra that is produced from its 230Th parent. The production is very slow (l ¼ 4.3 104 yr1) therefore regeneration would supply little 226 Ra on the time scale of a few days. The diffusion flux was calculated using the parent activity estimated from Lauria et al. (2004), the production term, the radium diffusion coefficient, and the partition coefficient (Krest et al., 1999). This equation gives the supply in dpm m2 day1. The value is multiplied by the area of the bay (519 km2) and yields 1.31 108 dpm day1. This is approximately 1% in 2007 and less than 1% in 1998 and 2005 of the total flux of 226Ra required to support the observed enrichment.
estimate the input of SGD. The supply of 226Ra via resuspension was 1.15 108 dpm, 4.98 107 dpm and 5.27 107 dpm for 1998, 2005 and 2007, respectively. The 226Ra input via resuspension were all less than 1% of the total enrichment for each sampling period. The supply of 228Ra was 9.06 1010 dpm, 3.91 1010 dpm and 4.14 1010 dpm for 1998, 2005 and 2007, respectively. The 228Ra input via resuspension was 58% for 1998, 31% for 2005 and 52% for 2007. 5.5. Radium input via SGD The sediment resuspension supply of 226Ra was calculated, and we used the highest estimate from the river to maximize the river contribution. Even with these efforts to maximize the contribution, these sources along with the diffusion only contributed a fraction of the total input required to maintain the observed enrichment. The dominate source of 226Ra to the bay must be supplied by SGD. After subtracting the river, diffusion, and sediment resuspension there is an additional flux of 1.6 1010 dpm day1, 2.4 1010 dpm day1, and 0.63 1010 dpm day1, respectively for 1998, 2005 and 2007, which must be supplied by SGD (Fig. 2). This is an average of 67% of the total required 226Ra flux.
5.3.2. Radium-228 The production is greater than for 226Ra (l ¼ 0.122 yr1 for 228Ra) therefore regeneration supply will be greater. Radium-228 is produced from the ingrowth of the 232Th parent (Lauria et al., 2004). The 228Ra diffusion flux was calculated in the same manner as it was for 226Ra and yields 6.16 109 dpm day1. This is approximately 4%, 5% and 8% respectively for 1998, 2005 and 2007 of the total flux of 228 Ra required to support the observed enrichment. 5.4. Supply from sediment resuspension The only component missing to estimate SGD is the 228Ra and Ra supplied from any sediment resuspension. The supply from resuspension depends on the depth of resupension, sediment dry bulk density, parent radionuclide adsorbed and days between resuspension events. The dry bulk density was the same for each isotope (dry bulk density estimated from grab samples 2.0 g cm3) and parent radionuclide adsorbed was previously discussed (see Section 5.2). Days between resuspension events and depth of resuspension need to be determined. Due to the difference in the production of 226Ra and 228Ra the days between events will supply substantially different activity of 226Ra compared to 228Ra. We approach this with a simple box model assuming complete resuspension and desorption within the calculated sediment depth. We solve for the resuspension input from each isotope that will yield the same volume input of SGD from both 226Ra and 228Ra (SGD volume is discussed in Section 5.6.). Since the groundwater volume input calculated from 228Ra and 226Ra must be equal, and the resuspension input is determined from the depth and time between events (which must be the same for each isotope), we are able to simultaneously solve for radium input via resuspension and volume of SGD. While the depth and days between events must be the same for each isotope, there is not a unique solution; there are multiple combinations for depth and days that yield the same estimated volume of SGD. Therefore although we cannot calculate a specific depth and days between events, we can determine the input of each isotope and 226
Fig. 2. Source of
226
Ra in Sepetiba Bay in given year.
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51
The same approach was used to calculate 228Ra input via SGD. Once the other sources were subtracted the remaining flux was 4.47 1010 dpm day1, 6.57 1010 dpm day1, and 1.76 1010 dpm day1, respectively for 1998, 2005 and 2007, which must be supplied by SGD (Fig. 3). This is an average of 34% of the total required 228Ra flux. 5.6. SGD volume 226
49
Table 3 SGD volume in Sepetiba Bay. Year
Volume (1010 L day-1)
1998 2005 2007
2.56 3.75 1.0
228 228
Ra and Ra value from the brackish groundwater The mean wells around Sepetiba Bay were 63 dpm 100 L1 and 175 dpm 100 L1, respectively. If these are the average 226Ra and 228 Ra concentrations for brackish SGD entering the bay then, 2.56 1010 L day1, 3.75 1010 L day1 and 1.0 1010 L day1 of SGD are required to support the SGD flux for 1998, 2005, and 2007, respectively (Table 3). Most investigations of SGD with radium use the highest activity groundwater, which is typically brackish water to prevent overestimating the SGD. The well water samples used were all within the 15e20 salinity range. A single sulfide-rich saline-well had 540 dpm 100 L1 226Ra and 2380 dpm 100 L1
Ra. If the sulfide-rich saline-well value is used and we assume the same SGD activity contribution, the SGD volume decreases by an order of magnitude. However, the fact that this water is highly reducing implies that exchange of this water with oxidizing surface waters is limited. Thus, it is unlikely that this water represents a substantial fraction of SGD. The average brackish SGD volume over the three sampling periods is equivalent to approximately 1% of the total volume of the bay each day. In order to compare the SGD rate with other studies we normalize the rate to the entire area of the bay. However, it is unlikely that SGD is actually distributed equally over the entire area. The normalize SGD rate is approximately 50 L m2 day1. This is a high value when compared to enclosed water bodies on the eastern coast of the United States (Krest et al., 2000; Charette et al., 2001; Kelly and Moran, 2002) and within range of the values determined by Oliveira et al. (2003) from several embayments approximately 150 km to the west of our site. However, it is substantially less than that observed in the waters around Jeju Island (Kim et al. 2003) and Yeoja Bay (Hwang et al., 2005), Korea. The high elevation of the land near the bay and the permeability of the sediments might enhance the submarine groundwater discharge to this bay. It must also be considered that the input of SGD might not be as large throughout the year as this data only represent three distinct sampling periods. Other investigations of SGD have observed temporal variations in discharge rates (Cable et al., 1997; Kelly and Moran, 2002; Moore, 2006). In examining the source of SGD to the bay we consider the supply of rainfall to the drainage basin. The rainfall within the drainage basin minus evapo-transportation and surface runoff represents recharge and hence potential terrestrially derived freshwater to the bay via SGD. Even accounting for seasonal variations, poor delineation of the drainage basin, the area of aquifer recharge being somewhat larger than the surface area of the drainage basin, and augmentation from outside the drainage basin, it is impossible for terrestrially derived freshwater to be the complete source of the SGD. The SGD volume is in substantial excess of the total rainfall volume within the drainage basin. The most likely explanation is that much of the SGD consists of infiltrated seawater that has reacted with deeper permeable sediments and rocks to increase its Ra activity. In some cases SGD has been found to have a seawater component of 80e90% (Burnett et al., 2003). While we are unable to quantify the fraction from seawater infiltration, we estimate it to be an important contribution of the total SGD due to the limited supply of terrestrially derived water via recharge.
6. Conclusion
Fig. 3. Source of
228
Ra in Sepetiba Bay for given year.
The waters of Sepetiba Bay are enriched in radium as compared to the adjacent ocean waters. The river can support approximately 32% on average of the calculated 226Ra flux. Sediment diffusion of 226 Ra from 230Th can supply approximately 1% or less of the required flux. Radium-226 from sediment resuspension would supply less than 1%. The remaining 226Ra flux required must be supplied by SGD. This is approximately 67% of the total 226Ra flux required to maintain the enrichment.
50
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51
The same mass balance approach used for estimating Ra enrichment was applied to 228Ra. The river can support approximately 13% on average of the calculated 228Ra flux. Sediment diffusion of 228Ra from 230Th can supply approximately 5%. Radium-228 from sediment resuspension would supply approximately 47%. Diffusion and resuspension are more important sources of 228Ra as compared to 226Ra due to the much faster rate of ingrowth. The remaining 228Ra from SGD was approximately 34% of the total 228Ra flux required to maintain the enrichment. Using the concentration of 226Ra and 228Ra in the brackish groundwater wells, it was determined that on average 2.6 1010 L day1 of SGD must enter the bay. This is 1% of the total volume of the bay entering each day and greater than the total input from all rivers entering the bay. This value is more than the maximum freshwater contribution possible from the drainage basin therefore the dominant supply of SGD must be from infiltrated seawater. We conclude that SGD is an important source of water to Sepetiba Bay and could be an important source of other constituents. As the Sepetiba Bay drainage basin is highly industrialized, future investigations should consider not only nutrient and carbon fluxes as part of these other constituents, but also metals. Many coastal areas in the world are more like Sepetiba Bay than most of the previous SGD studies as a result the SGD contribution to coastal and oceanic budgets might need to be revised upward. 226
Acknowledgments Reviews by Luis Troccoli Ghinaglia and Julio Mendes greatly enhanced the manuscript. This study was supported by Fundação de Amparo à Pesquisa do Estado de Rio de Janeiro (FAPERJ) Grant (E-26/101.952/2009) to C.J.S. and Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq). J.M.S. received partial support from Fulbright and Universidade Federal de Fluminense (UFF), Departamento de Geoquímica, Niterói-RJ, Brazil.
References Angulo, R.J., Lessa, G.C., 1997. The Brazilian sea-level curves: a critical review with emphasis on the curves from the Paranaguá and Cananéia regions. Marine Geology 140, 141e166. Burnett, W.C., Wattayakorn, G., Taniguchi, M., Dulaiova, H., Sojisuporn, P., Rungsupa, S., Ishitobi, T., 2007. Groundwater-derived nutrient inputs to the Upper Gulf of Thailand. Continental Shelf Research 27, 176e190. Burnett, W.C., Taniguchi, M., Oberdorfer, J., 2001. Measurement and significance of the direct discharge of groundwater into the coastal zone. Journal of Sea Research 46, 109e116. Burnett, W.C., Bokuniewicz, H., Huettel, M., Moore, W.S., Taniguchi, M., 2003. Groundwater and pore water inputs to the coastal zone. Biogeochemistry 66, 3e33. Burnett, W.C., Peterson, R., Moore, W.S., Oliveira, J., 2008. Radon and radium isotopes as tracers of submarine groundwater discharge e results from the Ubatuba, Brazil SGD assessment intercomparison. Estuarine, Coastal and Shelf Science 76, 501e511. Cable, J.E., Burnett, W.C., Chanton, J.P., 1997. Magnitude and variations of groundwater seepage along a Florida marine shoreline. Biogeochemistry 38, 189e205. Capone, D.G., Slater, J.M., 1990. Interannual patterns of water table height and groundwater derived nitrate in nearshore sediments. Biogeochemistry 10, 277e288. Charette, M.A., Moore, W.S., Burnett, W.C., 2008. Uranium- and thorium-series nuclides as tracers of submarine groundwater discharge. In: Radioactivity in the Environment, vol. 13, chapter 5, pp. 155e191. Charette, M.A., Buesseler, K.O., 2004. Submarine groundwater discharge of nutrients and copper to an urban subestuary of Chesapeake Bay (Elizabeth River). Limnology and Oceanography 49, 376e385. Charette, M.A., Buesseler, K.O., Andrews, J.E., 2001. Utility of radium isotopes for evaluating the input and transport of groundwater-derived nitrogen to a Cape Cod estuary. Limnology and Oceanography 46, 465e470.
Chaves, M.L.C., Pires, F.R.M., 1984. Distribuição, gênese e significado economico de granitos dos Morros da Bica e Inacio Dias, Rio de Janeiro, RJ. XXXIII Congresso Brasileiro de Geologia, 28 Oct.e4 Nov. Rio de Janeiro, p. 162. Corbett, D.R., Chanton, J.P., Burnett, W.C., Dillon, K., Rutkowski, C., Fourqurean, J., 1999. Patterns of groundwater discharge into Florida Bay. Limnology and Oceanography 44, 1045e1055. Crotwell, A.M., Moore, W.S., 2003. Nutrient and radium fluxes from submarine groundwater discharge to Port Royal Sound, South Carolina. Aquatic Geochemistry 9, 191e208. FEEMA, 1989. Qualidade das águas do estado do Rio de Janeiro 1987-1989-Baia de Guanabara e Sepetiba. Fundação estadual de engenharia de meio ambiente, Rio de Janeiro, p 180. Guimarães, M.T., 1999. Geologia e geoquimica do complexo granítico de Mangaratiba-Conceição de Jacarei, RJ. Dissertação de mestrado, Universidade Federal Fluminense, Niteroi, p. 159. Herrera-Silveira, J., 1998. Nutrient-phytoplankton production relationships in a groundwater-influenced tropical coastal lagoon. Aquatic Ecosystem and Health Management 1, 373e385. Hwang, D.W., Kim, G., Lee, Y.W., Yang, H.S., 2005. Estimating submarine inputs of groundwater and nutrients to a coastal bay using radium isotopes. Marine Chemistry 96, 61e71. Junho, M.C., Baptista Filho, J., Correa Neto, A.V., 1993. A zona de enclaves da PrainhaGrumari, Maciço da Pedra Branca, Rio de Janeiro. Anais da Academia Brasileira de Ciências 65 (4), 341e356. Kelly, R.P., Moran, S.B., 2002. Seasonal changes in groundwater input to a wellmixed estuary estimated using radium isotopes and implications for coastal nutrient budgets. Limnology and Oceanography 47, 1796e1807. Key, R.M., Stallard, R.F., Moore, W.S., Sarmiento, J.L., 1985. Distribution and flux of 226 Ra and 228Ra in the Amazon River estuary. Journal of Geophysical Research 90, 6995e7004. Kim, G., Lee, K.K., Park, K.S., Hwang, D.W., Tang, H.S., 2003. Large submarine groundwater discharge (SGD) from a volcanic island. Geophysical Research Letter 30. Kim, G., Ryu, J.W., Yang, H.S., Yun, S.T., 2005. Submarine groundwater discharge (SGD) into the Yellow Sea revealed by 228Ra and 226Ra isotopes: implications for global silicate fluxes. Earth and Planetary Science Letter 237, 156e166. Krest, J.M., Moore, W.S., Rama, 1999. 226Ra and 228Ra in the mixing zones of the Mississippi and Atchafalaya Rivers: indicators of groundwater input. Marine Chemistry 64, 129e152. Krest, J.M., Moore, W.S., Gardner, L.R., Morris, J., 2000. Marsh nutrient export supplied by groundwater discharge: evidence from Ra measurements. Global Biogeochemical Cycles 14, 167e176. LaRoche, J., Nuzzi, R., Waters, R., Wyman, K., Falkowski, P.G., Wallace, D.W.R., 1997. Brown tide blooms in Long Island’s coastal waters linked to interannual variability in groundwater flow. Global Change Biology 3, 397e410. Lauria, D.C., Godoy, J.M., 2002. Abnormal high natural radium concentration in surface waters. Journal of Environmental Radioactivity 61, 159e168. Lauria, D.C., Almeida, R.M.R., Sracek, O., 2004. Behavior of radium, thorium and uranium in groundwater near the Buena Lagoon in the Coastal Zone of the State of Rio de Janeiro, Brazil. Environmental Geology 47, 11e19. Leonardos, O.H., Fyfe, W.S., 1974. Ultrametamorphism and melting of a continental margin: the Rio de Janeiro region, Brazil. Mineralogy and Petrology 46, 201e214. Martin, L., 2003. Holocene sea-level history along Eastern-Southeastern Brazil. Anu. Inst. Geociênc., Univ. Fed. Rio Janeiro 26:13e24. Moore, W.S., 1976. Sampling 226Ra in the deep ocean. Deep-Sea Research 23, 647e651. Moore, W.S., 1984. Radium isotope measurements using germanium detectors. Nuclear Instruments and Methods in Physics Research, Section B 223, 407e411. Moore, W.S., 1996. Large groundwater inputs to coastal waters revealed by 226Ra enrichments. Nature 380, 612e614. Moore, W.S., Krest, J., Taylor, G., Roggenstein, E., Joye, S., Lee, R., 2002. Thermal evidence of water exchange through a coastal aquifer: implications for nutrient fluxes. Geophysical Research Letters 29. Moore, W.S., 2006. Radium isotopes as tracers of submarine groundwater discharge in Sicily. Continental Shelf Research 26, 852e861. Moore, W.S., 2010. A reevaluation of submarine groundwater discharge along the southeastern coast of North America. Global Biogeochemical Cycles 24, GB4005. http://dx.doi.org/10.1029/2009GB003747. Oliveira, J., Burnett, W.C., Massilli, B.P., Braga, E.S., Farias, L.A., Christoff, J., Furtado, V.V., 2003. Reconnaissance of submarine groundwater discharge at Ubatuba coast, Brazil, using 222Rn as a natural tracer. Journal of Environmental Radioactivity 69, 37e52. Porto Jr., R., 1993. Petrologia das rochas graníticas das Serras da Pedra Branca e Misericórdia, município do Rio de Janeiro. Master Dissertation, Depto. de Geologia, UFRJ, 222 p. Rodrigues, P.P.G.W., 1990. Aporte de metais pesados para a Baia de Sepetiba e seu comportamento na região estuarina. Niteroi., Dissertação (Mestrado em Geoquimica) Departamento de Geoquimica, Universidade Federal Fluminense, Niteroi, p. 161. Santos, I.R., Burnett, W.C., Chanton, J., Mwashote, B., Suryaputra, I.G.N.A., Dittmar, T., 2008. Nutrient biogeochemistry in a Gulf of Mexico subterranean estuary and groundwater-derived fluxes to the coastal ocean. Limnology and Oceanography 53, 705e718.
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51 Smoak, J.M., DeMaster, D.J., Kuehl, S.A., Pope, R.H., McKee, B.A., 1996. The behavior of particle-reactive tracers in a high turbidity environment: 234Th and 210Pb on the Amazon continental shelf. Geochimica et Cosmochimica Acta 60, 2123e2137. Taniguchi, M., Burnett, W.C., Cable, J.E., Turner, J.V., 2002. Investigation of submarine groundwater discharge. Hydrological Processes 16, 2115e2129.
51
Zekster, I.S., Loaiciga, H.A., 1993. Groundwater fluxes in the global hydrologic cycle: past, present and future. Journal of Hydrology 144, 405e427. Zorita, M.E., 1979. Geoquímica de Las Rocas Graníticas de La Regiõn de SuruíMunicípio de Magé-RJ. Dissertação de mestrado, Universidade Federal Fluminense, Niteroi, p. 96.
Contents lists available at SciVerse ScienceDirect
Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames
Radium mass balance and submarine groundwater discharge in Sepetiba Bay, Rio de Janeiro State, Brazil Joseph M. Smoak a, *, Christian J. Sanders b, Sambasiva R. Patchineelam b, Willard S. Moore c a
University of South Florida (USF), Environmental Science, St. Petersburg, FL, USA Universidade Federal de Fluminense (UFF), Departamento de Geoquímica Niterói-RJ, Brazil c Department of Earth and Ocean Sciences, University of South Carolina, Columbia, SC, USA b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 February 2012 Accepted 6 July 2012
Radium-226 and 228Ra activities were determined in water samples from within and adjacent to Sepetiba Bay, Rio de Janeiro State (Brazil) in 1998, 2005 and 2007. Surface waters in Sepetiba Bay were substantially higher in 226Ra and 228Ra compared to ocean end member samples. Using the residence time of water in the bay we calculated the flux required to maintain the observed enrichment over the ocean end members. We then applied a radium mass balance to estimate the volume of submarine groundwater discharge (SGD) into the bay. The estimates of SGD into Sepetiba Bay (in 1010 L day1) were 2.56, 3.75, and 1.0, respectively for 1998, 2005, and 2007. These estimates are equivalent to approximately 1% of the total volume of the bay each day or 50 L m2 day1. It is likely that a substantial portion of the SGD in Sepetiba Bay consists of infiltrated seawater. This large flux of SGD has the potential to supply substantial quantities of nutrients, carbon and metals into coastal waters. The SGD found here is greater than what is typically found in SGD studies along the eastern United States and areas with similar geologic characteristics. Considering there are many coastal areas around the world like Sepetiba Bay, this could revise upward the already important contribution of SGD to coastal as well as oceanic budgets. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Radioactivity 226 Ra 228 Ra Coastal waters SGD
1. Introduction While rivers are an obvious source of freshwater to coastal systems, groundwater discharge from coastal aquifers has been receiving increased acceptance as an important contributor to coastal waters (Moore, 1996; Corbett et al., 1999; Burnett et al., 2001, 2003, 2008; Taniguchi et al., 2002; Santos et al., 2008; Charette and Moore, 2008). Input of subterranean water, referred to as Submarine Groundwater Discharge (SGD), typically is a mixture of infiltrated seawater and terrestrially derived freshwater and includes all advective fluid flow between the land and the continental shelf, regardless of the source or composition of the fluids (Burnett et al., 2003). This source of water is important for the biogeochemical flux of materials to coastal waters (Charette et al., 2001; Moore et al., 2002; Crotwell and Moore, 2003; Charette and Buesseler, 2004; Hwang et al., 2005; Kim et al., 2005). It is estimated that fresh terrestrial SGD alone supplies approximately 6% of the total freshwater runoff to the world’s oceans (Zekster and Loaiciga, 1993; reviewed by Burnett et al., 2003). Moore (2010)
* Corresponding author. E-mail address: [email protected] (J.M. Smoak). 0895-9811/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jsames.2012.07.004
found SGD into the South Atlantic Bight along the east coast of the United States to be approximately three times the total volume of river water supplied to the bight and a significant source of nutrients to the South Atlantic Bight (Moore et al., 2002). Several investigations have reported substantial nutrient input via SGD, which may contribute to coastal eutrophication (Capone and Slater, 1990; LaRoche et al., 1997; Herrera-Silveira, 1998; Charette et al., 2001; Burnett et al., 2007). Direct measurements (e.g. seepage meters) of SGD are difficult on a regional scale. However, radium isotopes have been shown to be powerful tools to quantify SGD fluxes and indicate the sources (Charette and Moore, 2008). The direct parent of each radium isotope is a thorium isotope. Thorium is strongly adsorbed to sediment and provides a source of radium, which is generated on a range of time scales. In freshwater, radium is strongly adsorbed to particles. However, under reducing conditions, low pH and/or increasing salinity, radium can be released into solution. These characteristics make radium an excellent tracer of brackish SGD. The goal of the present study is to determine the source of 226Ra and 228Ra to Sepetiba Bay and use that information to estimate SGD to the bay. We examine 226Ra and 228Ra in the waters of Sepetiba Bay, adjacent coastal waters outside of the bay, wells surrounding the bay, and river water entering the bay. Radium-226, a product in
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51
the 238U decay series, has a 1600-year half-life. Radium-228, produced through the 232Th decay series, has a 5.75-year half-life. Sepetiba Bay waters are enriched in these two radium isotopes compared to the ocean waters adjacent to the bay. The sources of enrichment from a mass balance approach are used to determine the fraction that is supplied by SGD. We estimate the volume of SGD using radium activity in brackish well water from around the bay. Most SGD studies have been conducted on the east coast of the United States and in areas with similar geological characteristics. However, as suggested by a few studies (Kim et al., 2003; Oliveira et al., 2003; Hwang et al., 2005), areas with different geological characteristics may produce substantially different SGD fluxes. We investigate an area quite different from most of these previous
45
studies to test the hypothesis that high elevation near the coast and permeability of the underlying geology could produce substantially higher SGD fluxes. If correct, considering the number of coastal areas like Sepetiba Bay around the world this could revise upward the already important contribution of SGD to coastal as well as oceanic budgets. 2. Study area Sepetiba Bay (Fig. 1) is located 60 km west of Rio de Janeiro City, Brazil. The bay is located between south latitude 22 55’ 00” and 23 03’ 60” and west longitude 43 56’ 30” and 43 36’ 20”. The volume of the bay is approximately 2.56 109 m3 with an average
44o W
44o 20’ W
21
20 23o S
23 Sepetiba Bay
17 25
19
23
29
18 26 24
27 Ilha Grande 0
28
5
10
km
O2 O3 O1
23o 20’ S
44o W
43o 45’ W
22o 55’ S
4 5 16 9 15 2
14 X
10 3 8
12
7
23o S
6
1 11
13
0
2.5
5
km
Fig. 1. Map of Sepetiba Bay and the surrounding area showing sampling stations for the water column (-), sulfide-rich well (3), and brackish wells (C).
46
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51
depth of 6 m. Tidal regime is micro tidal with amplitude of less than 2 m. Rodrigues (1990) determined the residence time of water in the bay to be 99 h. Sepetiba Bay covers a total area of approximately 519 km2 and the drainage basin is 2500 km2. The drainage basin is highly industrialized with hydro-metallurgical plants, iron and steel works, chemical factories, printing presses and rubber industry (FEEMA, 1989). The regional climate is humid subtropical with mean annual temperature around 24 C and mean annual precipitation of 1800 mm (1400e2500 mm range). Maximum rainfall occurs between December and March (summer) and minimum between June and August (winter). Cold fronts are frequent between September and November (spring). There are nine rivers that drain into Sepetiba Bay. These nine rivers are responsible for an annual freshwater input of 5.7e7.6 109 m3. The São Francisco River is responsible for 86% of the riverine input. The São Francisco River receives additional water from outside of the natural drainage basin via a large water diversion. Metaigneous and igneous rocks showing granitic to granodioritic compositions are dominant in the geological terranes of the study area and surroundings (Leonardos and Fyfe, 1974; Zorita, 1979; Chaves and Pires, 1984; Junho et al., 1993; Porto, 1993). These rocks contain various U and Th isotopes, the ultimate source of the radium isotopes, mainly in the form of accessory minerals such as zircon, allanite, sphene and monazite. Such accessory minerals (except allanite) are highly resistant to the weathering process and therefore will be concentrated as placer deposits. The soil and sediments derived from these parent rocks have been accumulating in low-lying drainage basins and in the coastal plain. Brazil placer deposits produce half the world’s supply of monazite. The world production of thorium is based almost exclusively on extraction from monazite. Since it belongs to the 232Th decay series, 228 Ra tends to be enriched in samples from this region relative to 226 Ra. Allanite is an abundant phase in rocks of the region (Guimarães, 1999) and because of its low resistance to weathering, must be considered the most probable source of the 228Ra enrichment in surface waters (Lauria and Godoy, 2002; Lauria et al., 2004).
4. Results The distribution of radium isotopes in the surface waters of Sepetiba Bay, the waters adjacent to Sepetiba Bay and ocean waters are given in Table 1. Sampling stations are shown in Fig. 1. Table 2 shows the activity of 228Ra and 226Ra in the brackish wells. Samples collected from within Sepetiba Bay were enriched in both 226 Ra and 228Ra relative to ocean end members. Ocean end members were determined from three samples collected on the Atlantic side of Ilha Grande. Refractometer salinity measurements recorded one of the samples (station O3) to be 36 and the other two (stations O1 and O2) at 34. The 36 sample had 7.86 dpm 100 L1 of 226Ra and 9.29 dpm 100 L1 of 228Ra while the mean of the three was 7.89 dpm 100 L1 for 226Ra and 9.56 dpm 100 L1 for 228Ra. Stations 27 and 28 appear to be in locations suitable for ocean end members but were collected on an outgoing tide and had substantially more 228Ra and somewhat greater 226 Ra values than stations O1, O2 or O3. The enrichment determined by subtracting the average 228Ra and 226Ra values in the ocean end member from the average 228Ra and 226Ra values within the bay yields an enrichment of 4 dpm 100 L1 for 226Ra and 25 dpm 100 L1 for 228 Ra in 1998 (n ¼ 4), 5 dpm 100 L1 for 226Ra and 20 dpm 100 L1 for 228 Ra in 2005 (n ¼ 4) and 2 dpm 100 L1 for 226Ra and 13 dpm 100 L1 for 228Ra in 2007 (n ¼ 8). The total enrichment determined by multiplying the enrichment activity by the total volume of the bay (2.56 1012 L) yields total enrichments (in 1010 dpm) within Sepetiba Bay of 9.2 and 64.5 for 226Ra and 228Ra respectively in 1998, 12.3 and 51.9 for 226Ra and 228Ra respectively in 2005 and 5.2 and 33.0 for 226Ra and 228Ra respectively in 2007. Given the 99-h residence time for Sepetiba Bay water (Rodrigues, 1990) the flux to maintain the enrichment was (in 1010 dpm day1) 2.2, 3.0, and 1.3 for 226Ra and 15.6, 12.6, and 8.0 for 228Ra in 1998, 2005 and 2007 respectively. The São Francisco River supplies 86% of the total riverine freshwater to the bay. The waters at the mouth of the São Francisco River contained 29.4 dpm 100 L1 226Ra and 71.1 dpm 100 L1 228Ra. The three brackish (salinity 15e20) groundwater wells on the shore adjacent to Sepetiba Bay have an average concentration of 63 dpm 100 L1 for 226Ra and 175 dpm 100 L1 for 228Ra. However, a single sulfide-rich saline-well had values that far exceeded any other values (226Ra 540 dpm 100 L1 and 228Ra 2380 dpm 100 L1).
3. Methods In 1998, 2005 and 2007 water samples of 20e40 l were collected from three different brackish artesian wells (Coroa Grande, Sepetiba Beach and Pedra de Guaratiba), the primary river (São Francisco), 16 stations within Sepetiba Bay, 15 stations in the adjacent waters outside Sepetiba Bay, and three open ocean sites. A refractometer was used to measure salinity. Water samples were immediately filtered through a 1 mm cartridge filter. Sample volume was recorded and the water sample was pumped through a column of manganese-coated acrylic fiber in order to remove Ra in a quantitative manner (Moore, 1976). The Mn-fibers were leached with HCl in a Soxhlet extraction apparatus to remove the long-lived radium isotopes. Radium was co-precipitated with BaSO4 and aged for 3 weeks, which allowed 222Rn and its daughters to reach secular equilibrium with 226Ra. Subsequently all samples were measured in a well-type hyperpure germanium detector for 226 Ra and 228Ra activities (Moore, 1984). The estimated error for these measurements is about 7%. Radium enrichment was calculated by subtracting the average 228 Ra and 226Ra values in the ocean end member from the average 228 Ra and 226Ra values within the bay. Total enrichment was determined by multiplying the enrichment activity by the total volume of the bay (2.56 1012 L). The fluxes were determined by dividing the total enrichment by the Sepetiba Bay water residence time of 99 h (Rodrigues, 1990).
5. Discussion Rivers entering the bay, diffusion from bay sediments, release from sediment via resuspension, and SGD are all potential sources of radium that can support the observed enrichments. We examine these sources to complete a radium mass balance for Sepetiba Bay. The contribution from rivers, diffusion, and the release from sediment via resuspension are evaluated and subtracted from the total enrichment to estimate the contribution via SGD. This is a “flux-bydifference” approach which is most useful with non-point source fluxes (Charette and Moore, 2008; and references within). The radium contribution from SGD was used along with the concentration of radium in brackish groundwater wells to estimate the volume of SGD. 5.1. Total flux to support enrichment 5.1.1. Radium-226 Sepetiba Bay water has a residence time of 99 h (Rodrigues, 1990), therefore fluxes of (in 1010 dpm day1) of 2.2, 3.0, and 1.3 were required to support the observed 226Ra enrichment during 1998, 2005 and 2007 sampling periods respectively. This was calculated by dividing the total 226Ra enrichment by the residence time. Decay was not a factor because bay water residence time is short in comparison to the half-life of 226Ra.
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51
47
Table 1 Radium activity in waters in and around Sepetiba Bay. Samples collected in December 1998, May 2005 and June 2007. Sampling year Bay waters 1998 1998 1998 1998 2005 2005 2005 2005 2007 2007 2007 2007 2007 2007 2007 2007 Adjacent waters 1998 1998 1998 1998 1998 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005 Ocean end members 2005 2005 2005 Mean
226
Ra (dpm 100 L1)
228
Ra (dpm 100 L1)
Station
LAT
LON
13.00 12.00 10.00 11.00 11.25 14.12 12.84 12.60 8.51 6.15 8.28 10.91 10.84 12.04 12.23 10.38
42.00 33.00 33.00 31.00 30.77 32.66 28.26 27.65 19.32 10.77 22.24 29.49 24.50 25.32 24.04 23.91
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
S 23 S 22 S 23 S 22 S 22 S 23 S 23 S 23 S 22 S 23 S 23 S 23 S 23 S 23 S 22 S 22
01.998 59.836 00.708 56.005 56.200 01.456 01.780 01.099 58.371 01.056 02.119 01.060 02.265 00.869 58.957 57.727
W 43 50.951 W 43 50.312 W 43 43.844 W 43 48.706 W 43 49.500 W 43 42.955 W 43 51.127 W 43 56.057 W 43 53.641 W 43 54.561 W 43 51.931 W 43 48.311 W 43 47.440 W 43 41.968 W 43 43.781 W 43 45.682
11.00 13.00 9.00 9.00 10.00 10.65 12.39 12.46 12.50 11.05 11.19 13.38 11.54 9.56 8.51 9.76
30.00 33.00 27.00 27.00 27.00 25.56 19.47 32.79 27.44 16.98 25.18 15.46 16.73 17.95 14.36 17.34
17 18 19 20 21 21 21 22 23 24 25 26 27 28 29 29
S 23 S 23 S 23 S 22 S 22 S 23 S 23 S 23 S 23 S 23 S 23 S 23 S 23 S 23 S 23 S 23
0 0.784 06.584 03.950 58.602 56.878 02.582 02.582 58.583 58.583 09.034 03.663 07.669 07.024 12.602 04.132 04.132
W W W W W W W W W W W W W W W W
8.19 7.61 7.86 7.89
9.92 9.46 9.29 9.56
O1 O2 O3
5.1.2. Radium-228 Using the 99-h residence time (Rodrigues, 1990) the observed enrichment of 228Ra required fluxes of (in 1010 dpm day1) 15.6, 12.6, and 8.0 in 1998, 2005 and 2007 respectively. The estimates were made in the same manner as with 226Ra. 5.2. Contribution from river 5.2.1. Radium-226 Radium-226 supplied by the river was determined using two approaches. First, the maximum discharge of all rivers entering the bay of 2.08 1010 L day1 and a suspended sediment concentration in the river of 63 mg L1 were used (Rodrigues, 1990). This gives a sediment discharge of 1.31 109 g day1. We used the activity of samples reported by Lauria et al. (2004) to estimate the desorbable 226Ra from the river sediments. Lauria et al. (2004) reported a maximum activity of 2.5 dpm g1 of 226Ra from samples collected in the western coastal zone of the State of Rio de Janeiro. Key et al. (1985) estimated the loss of 226Ra via desorption in Amazon River sediments was 0.93 dpm g1 while Smoak et al. (1996) determined desorption in Amazon River sediments to be that less than 0.6 dpm g1 via a desorption Table 2 Brackish wells around Sepetiba Bay. Wells
226
Pedra de Guarariba Sepetiba Beach Coroa Grande
55 78 55
Ra (dpm 100 L1)
228
Ra (dpm 100 L1)
197 155 173
(surf) (bottom)
(surf) (bottom)
S 23 1 6.813 S 23 10:987 S 23 13.266
43 44 44 43 43 44 44 43 43 44 44 44 44 44 44 44
5 7.975 02.816 00.530 56.533 57.605 06.246 06.246 56.701 56.701 32.127 25.635 22.917 03.167 002.470 14.077 14.077
W 44 1 6.009 W 44 16.974 W 44 25.494
experiment. In this calculation we maximized the contribution from the river by using an estimate of 1 dpm g1 desorbable radium based on Key et al. (1985) which is 40% of the total radium. Using 1 dpm g1 as the desorbable amount, sediments entering the bay via the rivers desorb a total of 1.31 109 dpm day1. In addition to the input via desorption the river also carries 5 dpm 100 L1 of dissolved radium, which supplies a total of 1.04 109 dpm day1. Therefore the combined contribution from desorption and dissolved 226Ra from the rivers is 2.4 109 dpm day1. The second approach to calculating the 226 Ra river supply was to multiply the maximum river volume discharge from all rivers entering the bay by the 226Ra concentration measured at the mouth of the São Francisco River after desorption would have occurred during the 2007 sampling period salinity 30). This calculation yields (29.4 dpm 100 L1; 6.1 109 dpm day1. We use the latter calculation to maximize the contribution from the river, and hence, minimize the contribution from SGD. Using the 6.1 109 dpm day1 value the river’s contribution to the total enrichment of 226Ra is 27%, 21% and 49% respectively for 1998, 2005 and 2007. 5.2.2. Radium-228 As with 226Ra, we first used the activity of samples reported by Lauria et al. (2004) to estimate the desorbable 228Ra from the river sediments. Lauria et al. (2004) reported a maximum activity of 7 dpm g1 of 228Ra from these samples collected in the western coastal zone of the State of Rio de Janeiro. We estimated based on the discussion in Section 5.2.1 that of this total activity approximately 40% (2.8 dpm g1) of the 228Ra might be desorbable. Sediments
48
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51
entering the bay via the rivers desorb a total of 3.67 109 dpm day1 from river sediments. In addition to the input via desorption the river also carries 10 dpm L1 of dissolved radium which supplies a total of 2.08 109 dpm day1. Therefore the combined contribution from desorption and dissolved 228Ra from the rivers is 5.8 109 dpm day1. The second approach using the river mouth value of 228Ra (71.1 dpm 100 L1) yields 1.48 1010 dpm day1. Like 226 Ra we used the river mouth estimate. Using this approach the river contribution to the total enrichment of 228Ra is 10%, 12% and 19% for 1998, 2005 and 2007 respectively. 5.3. Contribution via sediment diffusion 5.3.1. Radium-226 As sea level along the central Brazilian coast was higher over the past 6000 years (Angulo and Lessa, 1997; Martin, 2003), the sediments within the bay and surrounding the bay from the mangrove system had previously desorbed Ra and can only supply 226Ra that is produced from its 230Th parent. The production is very slow (l ¼ 4.3 104 yr1) therefore regeneration would supply little 226 Ra on the time scale of a few days. The diffusion flux was calculated using the parent activity estimated from Lauria et al. (2004), the production term, the radium diffusion coefficient, and the partition coefficient (Krest et al., 1999). This equation gives the supply in dpm m2 day1. The value is multiplied by the area of the bay (519 km2) and yields 1.31 108 dpm day1. This is approximately 1% in 2007 and less than 1% in 1998 and 2005 of the total flux of 226Ra required to support the observed enrichment.
estimate the input of SGD. The supply of 226Ra via resuspension was 1.15 108 dpm, 4.98 107 dpm and 5.27 107 dpm for 1998, 2005 and 2007, respectively. The 226Ra input via resuspension were all less than 1% of the total enrichment for each sampling period. The supply of 228Ra was 9.06 1010 dpm, 3.91 1010 dpm and 4.14 1010 dpm for 1998, 2005 and 2007, respectively. The 228Ra input via resuspension was 58% for 1998, 31% for 2005 and 52% for 2007. 5.5. Radium input via SGD The sediment resuspension supply of 226Ra was calculated, and we used the highest estimate from the river to maximize the river contribution. Even with these efforts to maximize the contribution, these sources along with the diffusion only contributed a fraction of the total input required to maintain the observed enrichment. The dominate source of 226Ra to the bay must be supplied by SGD. After subtracting the river, diffusion, and sediment resuspension there is an additional flux of 1.6 1010 dpm day1, 2.4 1010 dpm day1, and 0.63 1010 dpm day1, respectively for 1998, 2005 and 2007, which must be supplied by SGD (Fig. 2). This is an average of 67% of the total required 226Ra flux.
5.3.2. Radium-228 The production is greater than for 226Ra (l ¼ 0.122 yr1 for 228Ra) therefore regeneration supply will be greater. Radium-228 is produced from the ingrowth of the 232Th parent (Lauria et al., 2004). The 228Ra diffusion flux was calculated in the same manner as it was for 226Ra and yields 6.16 109 dpm day1. This is approximately 4%, 5% and 8% respectively for 1998, 2005 and 2007 of the total flux of 228 Ra required to support the observed enrichment. 5.4. Supply from sediment resuspension The only component missing to estimate SGD is the 228Ra and Ra supplied from any sediment resuspension. The supply from resuspension depends on the depth of resupension, sediment dry bulk density, parent radionuclide adsorbed and days between resuspension events. The dry bulk density was the same for each isotope (dry bulk density estimated from grab samples 2.0 g cm3) and parent radionuclide adsorbed was previously discussed (see Section 5.2). Days between resuspension events and depth of resuspension need to be determined. Due to the difference in the production of 226Ra and 228Ra the days between events will supply substantially different activity of 226Ra compared to 228Ra. We approach this with a simple box model assuming complete resuspension and desorption within the calculated sediment depth. We solve for the resuspension input from each isotope that will yield the same volume input of SGD from both 226Ra and 228Ra (SGD volume is discussed in Section 5.6.). Since the groundwater volume input calculated from 228Ra and 226Ra must be equal, and the resuspension input is determined from the depth and time between events (which must be the same for each isotope), we are able to simultaneously solve for radium input via resuspension and volume of SGD. While the depth and days between events must be the same for each isotope, there is not a unique solution; there are multiple combinations for depth and days that yield the same estimated volume of SGD. Therefore although we cannot calculate a specific depth and days between events, we can determine the input of each isotope and 226
Fig. 2. Source of
226
Ra in Sepetiba Bay in given year.
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51
The same approach was used to calculate 228Ra input via SGD. Once the other sources were subtracted the remaining flux was 4.47 1010 dpm day1, 6.57 1010 dpm day1, and 1.76 1010 dpm day1, respectively for 1998, 2005 and 2007, which must be supplied by SGD (Fig. 3). This is an average of 34% of the total required 228Ra flux. 5.6. SGD volume 226
49
Table 3 SGD volume in Sepetiba Bay. Year
Volume (1010 L day-1)
1998 2005 2007
2.56 3.75 1.0
228 228
Ra and Ra value from the brackish groundwater The mean wells around Sepetiba Bay were 63 dpm 100 L1 and 175 dpm 100 L1, respectively. If these are the average 226Ra and 228 Ra concentrations for brackish SGD entering the bay then, 2.56 1010 L day1, 3.75 1010 L day1 and 1.0 1010 L day1 of SGD are required to support the SGD flux for 1998, 2005, and 2007, respectively (Table 3). Most investigations of SGD with radium use the highest activity groundwater, which is typically brackish water to prevent overestimating the SGD. The well water samples used were all within the 15e20 salinity range. A single sulfide-rich saline-well had 540 dpm 100 L1 226Ra and 2380 dpm 100 L1
Ra. If the sulfide-rich saline-well value is used and we assume the same SGD activity contribution, the SGD volume decreases by an order of magnitude. However, the fact that this water is highly reducing implies that exchange of this water with oxidizing surface waters is limited. Thus, it is unlikely that this water represents a substantial fraction of SGD. The average brackish SGD volume over the three sampling periods is equivalent to approximately 1% of the total volume of the bay each day. In order to compare the SGD rate with other studies we normalize the rate to the entire area of the bay. However, it is unlikely that SGD is actually distributed equally over the entire area. The normalize SGD rate is approximately 50 L m2 day1. This is a high value when compared to enclosed water bodies on the eastern coast of the United States (Krest et al., 2000; Charette et al., 2001; Kelly and Moran, 2002) and within range of the values determined by Oliveira et al. (2003) from several embayments approximately 150 km to the west of our site. However, it is substantially less than that observed in the waters around Jeju Island (Kim et al. 2003) and Yeoja Bay (Hwang et al., 2005), Korea. The high elevation of the land near the bay and the permeability of the sediments might enhance the submarine groundwater discharge to this bay. It must also be considered that the input of SGD might not be as large throughout the year as this data only represent three distinct sampling periods. Other investigations of SGD have observed temporal variations in discharge rates (Cable et al., 1997; Kelly and Moran, 2002; Moore, 2006). In examining the source of SGD to the bay we consider the supply of rainfall to the drainage basin. The rainfall within the drainage basin minus evapo-transportation and surface runoff represents recharge and hence potential terrestrially derived freshwater to the bay via SGD. Even accounting for seasonal variations, poor delineation of the drainage basin, the area of aquifer recharge being somewhat larger than the surface area of the drainage basin, and augmentation from outside the drainage basin, it is impossible for terrestrially derived freshwater to be the complete source of the SGD. The SGD volume is in substantial excess of the total rainfall volume within the drainage basin. The most likely explanation is that much of the SGD consists of infiltrated seawater that has reacted with deeper permeable sediments and rocks to increase its Ra activity. In some cases SGD has been found to have a seawater component of 80e90% (Burnett et al., 2003). While we are unable to quantify the fraction from seawater infiltration, we estimate it to be an important contribution of the total SGD due to the limited supply of terrestrially derived water via recharge.
6. Conclusion
Fig. 3. Source of
228
Ra in Sepetiba Bay for given year.
The waters of Sepetiba Bay are enriched in radium as compared to the adjacent ocean waters. The river can support approximately 32% on average of the calculated 226Ra flux. Sediment diffusion of 226 Ra from 230Th can supply approximately 1% or less of the required flux. Radium-226 from sediment resuspension would supply less than 1%. The remaining 226Ra flux required must be supplied by SGD. This is approximately 67% of the total 226Ra flux required to maintain the enrichment.
50
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51
The same mass balance approach used for estimating Ra enrichment was applied to 228Ra. The river can support approximately 13% on average of the calculated 228Ra flux. Sediment diffusion of 228Ra from 230Th can supply approximately 5%. Radium-228 from sediment resuspension would supply approximately 47%. Diffusion and resuspension are more important sources of 228Ra as compared to 226Ra due to the much faster rate of ingrowth. The remaining 228Ra from SGD was approximately 34% of the total 228Ra flux required to maintain the enrichment. Using the concentration of 226Ra and 228Ra in the brackish groundwater wells, it was determined that on average 2.6 1010 L day1 of SGD must enter the bay. This is 1% of the total volume of the bay entering each day and greater than the total input from all rivers entering the bay. This value is more than the maximum freshwater contribution possible from the drainage basin therefore the dominant supply of SGD must be from infiltrated seawater. We conclude that SGD is an important source of water to Sepetiba Bay and could be an important source of other constituents. As the Sepetiba Bay drainage basin is highly industrialized, future investigations should consider not only nutrient and carbon fluxes as part of these other constituents, but also metals. Many coastal areas in the world are more like Sepetiba Bay than most of the previous SGD studies as a result the SGD contribution to coastal and oceanic budgets might need to be revised upward. 226
Acknowledgments Reviews by Luis Troccoli Ghinaglia and Julio Mendes greatly enhanced the manuscript. This study was supported by Fundação de Amparo à Pesquisa do Estado de Rio de Janeiro (FAPERJ) Grant (E-26/101.952/2009) to C.J.S. and Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq). J.M.S. received partial support from Fulbright and Universidade Federal de Fluminense (UFF), Departamento de Geoquímica, Niterói-RJ, Brazil.
References Angulo, R.J., Lessa, G.C., 1997. The Brazilian sea-level curves: a critical review with emphasis on the curves from the Paranaguá and Cananéia regions. Marine Geology 140, 141e166. Burnett, W.C., Wattayakorn, G., Taniguchi, M., Dulaiova, H., Sojisuporn, P., Rungsupa, S., Ishitobi, T., 2007. Groundwater-derived nutrient inputs to the Upper Gulf of Thailand. Continental Shelf Research 27, 176e190. Burnett, W.C., Taniguchi, M., Oberdorfer, J., 2001. Measurement and significance of the direct discharge of groundwater into the coastal zone. Journal of Sea Research 46, 109e116. Burnett, W.C., Bokuniewicz, H., Huettel, M., Moore, W.S., Taniguchi, M., 2003. Groundwater and pore water inputs to the coastal zone. Biogeochemistry 66, 3e33. Burnett, W.C., Peterson, R., Moore, W.S., Oliveira, J., 2008. Radon and radium isotopes as tracers of submarine groundwater discharge e results from the Ubatuba, Brazil SGD assessment intercomparison. Estuarine, Coastal and Shelf Science 76, 501e511. Cable, J.E., Burnett, W.C., Chanton, J.P., 1997. Magnitude and variations of groundwater seepage along a Florida marine shoreline. Biogeochemistry 38, 189e205. Capone, D.G., Slater, J.M., 1990. Interannual patterns of water table height and groundwater derived nitrate in nearshore sediments. Biogeochemistry 10, 277e288. Charette, M.A., Moore, W.S., Burnett, W.C., 2008. Uranium- and thorium-series nuclides as tracers of submarine groundwater discharge. In: Radioactivity in the Environment, vol. 13, chapter 5, pp. 155e191. Charette, M.A., Buesseler, K.O., 2004. Submarine groundwater discharge of nutrients and copper to an urban subestuary of Chesapeake Bay (Elizabeth River). Limnology and Oceanography 49, 376e385. Charette, M.A., Buesseler, K.O., Andrews, J.E., 2001. Utility of radium isotopes for evaluating the input and transport of groundwater-derived nitrogen to a Cape Cod estuary. Limnology and Oceanography 46, 465e470.
Chaves, M.L.C., Pires, F.R.M., 1984. Distribuição, gênese e significado economico de granitos dos Morros da Bica e Inacio Dias, Rio de Janeiro, RJ. XXXIII Congresso Brasileiro de Geologia, 28 Oct.e4 Nov. Rio de Janeiro, p. 162. Corbett, D.R., Chanton, J.P., Burnett, W.C., Dillon, K., Rutkowski, C., Fourqurean, J., 1999. Patterns of groundwater discharge into Florida Bay. Limnology and Oceanography 44, 1045e1055. Crotwell, A.M., Moore, W.S., 2003. Nutrient and radium fluxes from submarine groundwater discharge to Port Royal Sound, South Carolina. Aquatic Geochemistry 9, 191e208. FEEMA, 1989. Qualidade das águas do estado do Rio de Janeiro 1987-1989-Baia de Guanabara e Sepetiba. Fundação estadual de engenharia de meio ambiente, Rio de Janeiro, p 180. Guimarães, M.T., 1999. Geologia e geoquimica do complexo granítico de Mangaratiba-Conceição de Jacarei, RJ. Dissertação de mestrado, Universidade Federal Fluminense, Niteroi, p. 159. Herrera-Silveira, J., 1998. Nutrient-phytoplankton production relationships in a groundwater-influenced tropical coastal lagoon. Aquatic Ecosystem and Health Management 1, 373e385. Hwang, D.W., Kim, G., Lee, Y.W., Yang, H.S., 2005. Estimating submarine inputs of groundwater and nutrients to a coastal bay using radium isotopes. Marine Chemistry 96, 61e71. Junho, M.C., Baptista Filho, J., Correa Neto, A.V., 1993. A zona de enclaves da PrainhaGrumari, Maciço da Pedra Branca, Rio de Janeiro. Anais da Academia Brasileira de Ciências 65 (4), 341e356. Kelly, R.P., Moran, S.B., 2002. Seasonal changes in groundwater input to a wellmixed estuary estimated using radium isotopes and implications for coastal nutrient budgets. Limnology and Oceanography 47, 1796e1807. Key, R.M., Stallard, R.F., Moore, W.S., Sarmiento, J.L., 1985. Distribution and flux of 226 Ra and 228Ra in the Amazon River estuary. Journal of Geophysical Research 90, 6995e7004. Kim, G., Lee, K.K., Park, K.S., Hwang, D.W., Tang, H.S., 2003. Large submarine groundwater discharge (SGD) from a volcanic island. Geophysical Research Letter 30. Kim, G., Ryu, J.W., Yang, H.S., Yun, S.T., 2005. Submarine groundwater discharge (SGD) into the Yellow Sea revealed by 228Ra and 226Ra isotopes: implications for global silicate fluxes. Earth and Planetary Science Letter 237, 156e166. Krest, J.M., Moore, W.S., Rama, 1999. 226Ra and 228Ra in the mixing zones of the Mississippi and Atchafalaya Rivers: indicators of groundwater input. Marine Chemistry 64, 129e152. Krest, J.M., Moore, W.S., Gardner, L.R., Morris, J., 2000. Marsh nutrient export supplied by groundwater discharge: evidence from Ra measurements. Global Biogeochemical Cycles 14, 167e176. LaRoche, J., Nuzzi, R., Waters, R., Wyman, K., Falkowski, P.G., Wallace, D.W.R., 1997. Brown tide blooms in Long Island’s coastal waters linked to interannual variability in groundwater flow. Global Change Biology 3, 397e410. Lauria, D.C., Godoy, J.M., 2002. Abnormal high natural radium concentration in surface waters. Journal of Environmental Radioactivity 61, 159e168. Lauria, D.C., Almeida, R.M.R., Sracek, O., 2004. Behavior of radium, thorium and uranium in groundwater near the Buena Lagoon in the Coastal Zone of the State of Rio de Janeiro, Brazil. Environmental Geology 47, 11e19. Leonardos, O.H., Fyfe, W.S., 1974. Ultrametamorphism and melting of a continental margin: the Rio de Janeiro region, Brazil. Mineralogy and Petrology 46, 201e214. Martin, L., 2003. Holocene sea-level history along Eastern-Southeastern Brazil. Anu. Inst. Geociênc., Univ. Fed. Rio Janeiro 26:13e24. Moore, W.S., 1976. Sampling 226Ra in the deep ocean. Deep-Sea Research 23, 647e651. Moore, W.S., 1984. Radium isotope measurements using germanium detectors. Nuclear Instruments and Methods in Physics Research, Section B 223, 407e411. Moore, W.S., 1996. Large groundwater inputs to coastal waters revealed by 226Ra enrichments. Nature 380, 612e614. Moore, W.S., Krest, J., Taylor, G., Roggenstein, E., Joye, S., Lee, R., 2002. Thermal evidence of water exchange through a coastal aquifer: implications for nutrient fluxes. Geophysical Research Letters 29. Moore, W.S., 2006. Radium isotopes as tracers of submarine groundwater discharge in Sicily. Continental Shelf Research 26, 852e861. Moore, W.S., 2010. A reevaluation of submarine groundwater discharge along the southeastern coast of North America. Global Biogeochemical Cycles 24, GB4005. http://dx.doi.org/10.1029/2009GB003747. Oliveira, J., Burnett, W.C., Massilli, B.P., Braga, E.S., Farias, L.A., Christoff, J., Furtado, V.V., 2003. Reconnaissance of submarine groundwater discharge at Ubatuba coast, Brazil, using 222Rn as a natural tracer. Journal of Environmental Radioactivity 69, 37e52. Porto Jr., R., 1993. Petrologia das rochas graníticas das Serras da Pedra Branca e Misericórdia, município do Rio de Janeiro. Master Dissertation, Depto. de Geologia, UFRJ, 222 p. Rodrigues, P.P.G.W., 1990. Aporte de metais pesados para a Baia de Sepetiba e seu comportamento na região estuarina. Niteroi., Dissertação (Mestrado em Geoquimica) Departamento de Geoquimica, Universidade Federal Fluminense, Niteroi, p. 161. Santos, I.R., Burnett, W.C., Chanton, J., Mwashote, B., Suryaputra, I.G.N.A., Dittmar, T., 2008. Nutrient biogeochemistry in a Gulf of Mexico subterranean estuary and groundwater-derived fluxes to the coastal ocean. Limnology and Oceanography 53, 705e718.
J.M. Smoak et al. / Journal of South American Earth Sciences 39 (2012) 44e51 Smoak, J.M., DeMaster, D.J., Kuehl, S.A., Pope, R.H., McKee, B.A., 1996. The behavior of particle-reactive tracers in a high turbidity environment: 234Th and 210Pb on the Amazon continental shelf. Geochimica et Cosmochimica Acta 60, 2123e2137. Taniguchi, M., Burnett, W.C., Cable, J.E., Turner, J.V., 2002. Investigation of submarine groundwater discharge. Hydrological Processes 16, 2115e2129.
51
Zekster, I.S., Loaiciga, H.A., 1993. Groundwater fluxes in the global hydrologic cycle: past, present and future. Journal of Hydrology 144, 405e427. Zorita, M.E., 1979. Geoquímica de Las Rocas Graníticas de La Regiõn de SuruíMunicípio de Magé-RJ. Dissertação de mestrado, Universidade Federal Fluminense, Niteroi, p. 96.