Estuaries and Coasts

, Volume 36, Issue 6, pp 1237–1252 | Cite as

Spatial Distribution of Dissolved Radon in the Choptank River and Its Tributaries: Implications for Groundwater Discharge and Nitrate Inputs

  • Karen L. Knee
  • Thomas E. Jordan


The Choptank River, Chesapeake Bay’s largest eastern-shore tributary, is experiencing increasing nutrient loading and eutrophication. Productivity in the Choptank is predominantly nitrogen-limited, and most nitrogen inputs occur via discharge of high-nitrate groundwater into the river system’s surface waters. However, spatial patterns in the magnitude and quality of groundwater discharge are not well understood. In this study, we surveyed the activity of 222Rn, a natural groundwater tracer, in the Choptank’s main tidal channel, the large tidal tributary Tuckahoe Creek, smaller tidal and non-tidal tributaries around the basin, and groundwater discharging into those tributaries, measuring nitrate and salinity concurrently. 222Rn activities were <100 Bq m−3 in the main tidal channel and 100–700 Bq m−3 in the upper Choptank River and Tuckahoe Creek, while the median Rn activities of fresh tributaries and discharging groundwater were 1,000 and 7,000 Bq m−3, respectively. Nitrate-N concentrations were <0.01 mg L−1 throughout most of the tidal channel, 1.5–3 mg L−1 in the upper reaches, up to 13 mg L−1 in tributary samples, and up to 19.6 mg L−1 in groundwater. Nitrate concentrations in tributary surface water were correlated with Rn activity in three of five sub-watersheds, indicating a groundwater nitrate source. 222Rn and salinity mass balances indicated that Rn-enriched groundwater discharges directly into the Choptank’s tidal waters and suggested that it consists of a mixture of fresh groundwater and brackish re-circulated estuarine water. Further sampling is necessary to constrain the Rn activity and nitrate concentration of discharging groundwater and quantify direct discharge and associated nitrogen inputs.


Groundwater discharge Radon Choptank River Chesapeake Bay Nitrate 



We thank Adina Paytan and Rick Peterson for the use of their RAD7 radon detectors and for advice about carrying out the study. Micah Ryder helped obtain and analyze geographic data, and David Culver generously provided access to GIS software. Dana Brenner, Nancy Goff, Christina Hill, Ryan Ihnacik, Alanna Lecher, Ginny Leviton, Joe Miklas, and Amelia Snyder assisted with sample collection and analysis. Rick Peterson, Thomas Fisher, and two anonymous reviewers provided comments that improved the quality of this manuscript. Financial support for this research came from a Smithsonian Institution Postdoctoral Fellowship (to K. Knee) and National Science Foundation grants (DEB-0919181 and DEB-0919141 to T. Jordan and T. Fisher).


  1. Benitez, J.A. 2002. Historical land cover changes (1665–2000) and impact on N and P export from the Choptank watershed. Ph.D. dissertation, University of Maryland College Park.Google Scholar
  2. Böhlke, J.K., and J.M. Denver. 1995. Combined use of groundwater dating, chemical, and isotopic analyses to resolve the history and fate of nitrate contamination in two agricultural watersheds, Atlantic Coastal Plain, Maryland. Water Resources Research 31: 2319–2339.CrossRefGoogle Scholar
  3. Borges, A.V., B. Delille, L.-S. Schiettecatte, F. Gazeau, G. Abril, and M. Frankignoulle. 2004. Gas transfer velocities of CO2 in three European estuaries (Randers Fjord, Scheldt, and Thames). Limnology and Oceanography 49: 1630–1641.CrossRefGoogle Scholar
  4. Bouwman, A.F., G. Van Drecht, and K.W. van der Hoek. 2005. Surface N balances and reactive N loss to the environment from global intensive agricultural production systems for the period 1970–2030. Science in China. Series C, Life Sciences 48: 767–779.CrossRefGoogle Scholar
  5. Burnett, W.C., J.E. Cable, R.D. Corbett and J.P. Chanton. 1996. Tracing groundwater flow into surface waters using natural 222Rn. Groundwater Discharge in the Coastal Zone: Proceedings of an International Symposium 8:22–36. LOICZ Reports Studies.Google Scholar
  6. Burnett, W.C., G. Kim, and D. Lane-Smith. 2001. A continuous radon monitor for assessment of radon in coastal ocean waters. Journal of Radioanalytical and Nuclear Chemistry 249: 167–172.CrossRefGoogle Scholar
  7. Burnett, W.C., and H. Dulaiova. 2003. Estimating the dynamics of groundwater input into the coastal zone via continuous 222Rn measurements. Journal of Environmental Radioactivity 1–2: 21–35.CrossRefGoogle Scholar
  8. Burnett, W.C., P.K. Aggarwal, A. Aureli, H. Bokuniewicz, J.E. Cable, M.A. Charette, E. Kontar, S. Krupa, K.M. Kulkarni, A. Loveless, W.S. Moore, J.A. Oberdorfer, J. Oliveira, N. Ozyurt, P. Povinec, A.M.G. Privitera, R. Rajar, R.T. Ramessur, J. Scholten, T. Stieglitz, M. Taniguchi, and J.V. Turner. 2006. Quantifying submarine groundwater discharge in the coastal zone via multiple methods. Science of the Total Environment 367(2–3): 498–543.CrossRefGoogle Scholar
  9. Burnett, W.C., R.N. Peterson, I.R. Santos, and R.W. Hicks. 2010. Use of automated radon measurements for rapid assessment of groundwater flow into Florida streams. Journal of Hydrology 380: 298–304.CrossRefGoogle Scholar
  10. Cable, J.E., G.C. Bugna, W.C. Burnett, and J.P. Chanton. 1996. Application of 222Rn and CH4 for assessment of groundwater discharge to the coastal ocean. Limnology and Oceanography 41(6): 1347–1353.CrossRefGoogle Scholar
  11. Cable, J.E., and J.B. Martin. 2008. In situ evaluation of nearshore marine and fresh pore water transport into Flamengo Bay, Brazil. Estuarine, Coastal and Shelf Science 76: 473–483.CrossRefGoogle Scholar
  12. Caraco, N.F., and J.J. Cole. 1999. Human impact on nitrate export: an analysis using major world rivers. Ambio 28: 167–170.Google Scholar
  13. Caraco, N.F., and J.J. Cole. 2001. Human influence on nitrogen export: a comparison of mesic and xeric catchments. Marine and Freshwater Research 52: 119–125.CrossRefGoogle Scholar
  14. Charette, M.A., and K.O. Buesseler. 2004. Submarine groundwater discharge of nutrients and copper to an urban subestuary of Chesapeake Bay (Elizabeth River). Limnology and Oceanography 49: 376–385.CrossRefGoogle Scholar
  15. Cooper, S.R., and G.S. Brush. 1993. A 2,500-year history of anoxia and eutrophication in Chesapeake Bay. Estuaries and Coasts 16: 617–626. doi: 10.2307/1352799.CrossRefGoogle Scholar
  16. Corbett, D.R., W.C. Burnett, P.H. Cable, and S.B. Clark. 1997. Radon tracing of groundwater input into Par Pond, Savannah River Site. Journal of Hydrology 203: 209–227.CrossRefGoogle Scholar
  17. Corbett, D.R., W.C. Burnett, P.H. Cable, and S.B. Clark. 1998. A multiple approach to the determination of radon fluxes from sediments. Journal of Radioanalytical and Nuclear Chemistry 236: 247–253.CrossRefGoogle Scholar
  18. Dulaiova, H., R. Peterson, W.C. Burnett, and D. Lane-Smith. 2005. A multi-detector continuous monitor for assessment of 222Rn in the coastal ocean. Journal of Radioanalytical and Nuclear Chemistry 263: 361–363. doi: 10.1007/s10967-005-0063-8.CrossRefGoogle Scholar
  19. Dulaiova, H., M.E. Gonneea, P.B. Henderson, and M.A. Charette. 2008. Geochemical and physical sources of radon variation in a subterranean estuary – implications for groundwater radon activities in submarine groundwater discharge studies. Marine Chemistry 110: 120–127.CrossRefGoogle Scholar
  20. Dulaiova, H., R. Camilli, P.B. Henderson, and M.A. Charette. 2010. Coupled radon, methane and nitrate sensors for large-scale assessment of groundwater discharge and non-point source pollution to coastal waters. Journal of Environmental Radioactivity 101(7): 553–563.CrossRefGoogle Scholar
  21. Fisher, T.R., K.-Y. Lee, H. Berndt, J.A. Benitez, and M.M. Norton. 1998. Hydrology and chemistry of the Choptank basin. Water, Air, and Soil Pollution 105: 387–397.CrossRefGoogle Scholar
  22. Fisher, T.R., J.D. Hagy III, W.R. Boynton, and M.R. Williams. 2006. Cultural eutrophication in the Choptank and Patuxent estuaries of Chesapeake Bay. Limnology and Oceanography 51: 435–447.CrossRefGoogle Scholar
  23. Fisher, T.R., A.B. Gustafson, A.I. Koskelo, R.J. Fox, T. Kana, K.A. Beckert, J.P. Stone, T.E. Jordan, K.W. Staver, A.J. Sutton, G. McCarty and M. Lang. 2010. The Choptank Basin in Transition: Intensifying Agriculture, Slow Urbanization, and Estuarine Eutrophication. Chapter 7 in Coastal Lagoons: Critical Habitats of Environmental Change. New York, Taylor and Francis, p. 137–168.Google Scholar
  24. Freeze, R.A. and J.A. Cherry. Groundwater. Englewood Cliffs, NJ, USA. Prentice-Hall, 1979. 604 pp.Google Scholar
  25. Garrison, G.H., C.R. Glenn, and G.M. McMurtry. 2003. Measurement of submarine groundwater discharge in Kahana Bay, O`ahu, Hawai`i. Limnology and Oceanography 48(2): 920–928.CrossRefGoogle Scholar
  26. Glibert, P.M., R. Magnien, M.W. Lomas, J. Alexander, C. Tan, E. Haramoto, M. Trice, and T.M. Kana. 2001. Harmful algal blooms in the Chesapeake and coastal bays of Maryland, USA: Comparison of 1997, 1998, and 1999 events. Estuaries and Coasts 24: 875–883. doi: 10.2307/1353178.CrossRefGoogle Scholar
  27. Hammond, D.E., H.J. Simpson, and G. Mathieu. 1977. Radon 222 distribution and transport across the sediment-water interface in the Hudson River estuary. Journal of Geophysical Research 82: 3913–3920. doi: 10.1029/JC082i027p03913.CrossRefGoogle Scholar
  28. Hussain, N., T.M. Church, and G. Kim. 1999. Use of 222Rn and 226Ra to trace groundwater discharge into the Chesapeake Bay. Marine Chemistry 65: 127–134.CrossRefGoogle Scholar
  29. Hwang, D.-W., G. Kim, W.-C. Lee, and H.-T. Oh. 2010. The role of submarine groundwater discharge (SGD) in nutrient budgets of Gamak Bay, a shellfish farming bay, in Korea. Journal of Sea Research 64: 224–230.CrossRefGoogle Scholar
  30. Jordan, T.E., D.L. Correll, and D.E. Weller. 1997. Effects of agriculture on discharges of nutrients from coastal plain watersheds of Chesapeake Bay. Journal of Environmental Quality 26(3): 836–848.CrossRefGoogle Scholar
  31. Kalbus, E., F. Reinstorf, and M. Schirmer. 2006. Measuring methods for groundwater-surface water interactions: A review. Hydrology and Earth System Sciences 10: 873–887.CrossRefGoogle Scholar
  32. Kettle, A.J., and M.O. Andreae. 2000. Flux of dimethylsulfide from the oceans: A comparison of updated data sets and flux models. Journal of Geophysical Research 105: 26,793–26,808.CrossRefGoogle Scholar
  33. Kim, G., K.-K. Lee, K.-S. Park, D.-W. Hwang, and H.-S. Yang. 2003. Large submarine groundwater discharge (SGD) from a volcanic island. Geophysical Research Letters 30: 2098–2101.CrossRefGoogle Scholar
  34. Knee, K.L., and A. Paytan. 2012. Submarine groundwater discharge: A source of nutrients, metals and pollutants to the coastal ocean. In: Wolanski, E. and D.S. McLusky, eds. Treatise on Estuarine and Coastal Science 4: 205–233.Google Scholar
  35. Kroeger, K.D., M.L. Cole, and I. Valiela. 2006. Groundwater-transported dissolved organic nitrogen exports from coastal watersheds. Limnology and Oceanography 51: 2248–2261.CrossRefGoogle Scholar
  36. Kroeger, K.D., P.W. Swarzenski, W.J. Greenwood, and C. Reich. 2007. Submarine groundwater discharge to Tampa Bay: Nutrient fluxes and biogeochemistry of the coastal aquifer. Marine Chemistry 104: 85–97.CrossRefGoogle Scholar
  37. Lambert, M.J., and W.C. Burnett. 2003. Submarine groundwater discharge estimates at a Florida coastal site based on continuous radon measurements. Biogeochemistry 66: 55–73. doi: 10.1023/B:BIOG.0000006057.63478.fa.CrossRefGoogle Scholar
  38. Lee, K.-Y., T.R. Fisher, T.E. Jordan, D.L. Correll, and D.E. Weller. 2000. Modeling the hydrochemistry of the Choptank River Basin using GWLF and Arc/Info: 1. Model calibration and validation. Biogeochemistry 49: 143–173. doi: 10.1023/A:1006375530844.CrossRefGoogle Scholar
  39. Lee, K.-Y., T.R. Fisher, and E. Rochelle-Newall. 2001. Modeling the hydrochemistry of the Choptank River basin using GWLF and Arc/Info: 2. Model validation and application. Biogeochemistry 56: 311–348. doi: 10.1023/A:1013169027082.CrossRefGoogle Scholar
  40. Lorite-Herrera, M., K. Hiscock, and R. Jiménez-Espinosa. 2009. Distribution of dissolved inorganic and organic nitrogen in river water and groundwater in an agriculturally-dominated catchment, south-east Spain. Water, Air, and Soil Pollution 198: 335–346.CrossRefGoogle Scholar
  41. Marshall, H.G., and L. Burchardt. 2004. Monitoring phytoplankton populations and water quality parameters in estuarine rivers of Chesapeake Bay, USA. Oceanological and Hydrobiological Sciences 33: 55–64.Google Scholar
  42. McCarty, G.W., L.L. McConnell, C.J. Hapeman, A. Sadeghi, C. Graff, W.D. Hively, M.W. Lang, T.R. Fisher, T. Jordan, C.P. Rice, E.E. Codling, D. Whitall, A. Lynn, J. Keppler, and M.L. Fogel. 2008. Water quality and conservation practice effects in the Choptank River watershed. Journal of Soil and Water Conservation 63: 461–474.CrossRefGoogle Scholar
  43. Mulligan, A.E., and M.A. Charette. 2006. Intercomparison of submarine groundwater discharge estimates from an unconfined aquifer. Journal of Hydrology 327: 411–425.CrossRefGoogle Scholar
  44. Mullinger, N.J., A.M. Binley, J.M. Pates, and N.P. Crook. 2007. Radon in chalk streams: Spatial and temporal variation of groundwater sources in the Pang and Lambourn watersheds, UK. Journal of Hydrology 339: 172–182.CrossRefGoogle Scholar
  45. Paerl, H.W. 1999. Cultural eutrophication of shallow coastal waters: Coupling changing anthropogenic nutrient inputs to regional management approaches. Limnologica 29: 249–254.CrossRefGoogle Scholar
  46. Paerl, H.W. 2006. Assessing and managing nutrient-enhanced eutrophication in estuarine and coastal waters: Interactive effects of human and climatic perturbations. Ecological Engineering 26: 40–54.CrossRefGoogle Scholar
  47. Peterson, R.N., I.R. Santos, and W.C. Burnett. 2010. Evaluating groundwater discharge to tidal rivers based on a Rn-222 time-series approach. Estuarine, Coastal and Shelf Science 86: 165–178.CrossRefGoogle Scholar
  48. Phillips, P.J., J.M. Denver, R.J. Shedlock, and P.A. Hamilton. 1993. Effect of forested wetlands on nitrate concentrations in ground water and surface water on the Delmarva Peninsula. Wetlands 13: 75–83. doi: 10.1007/BF03160867.CrossRefGoogle Scholar
  49. Rapaglia, J.P., and H.J. Bokuniewicz. 2009. The effect of groundwater advection on salinity in pore waters of permeable sediments. Limnology and Oceanography 54: 630–643.CrossRefGoogle Scholar
  50. Santos, I.R., W.C. Burnett, T. Dittmar, I.G.N.A. Suryaputra, and J. Chanton. 2009. Tidal pumping drives nutrient and dissolved organic matter dynamics in a Gulf of Mexico subterranean estuary. Geochimica et Cosmochimica Acta 73: 1325–1339.CrossRefGoogle Scholar
  51. Santos, I.R., R.N. Peterson, B.D. Eyre, and W.C. Burnett. 2010. Significant lateral inputs of fresh groundwater into a stratified tropical estuary: Evidence from radon and radium isotopes. Marine Chemistry 121: 37–48.CrossRefGoogle Scholar
  52. Santos, I.R., R.N. Glud, D. Maher, D. Erler, and B.D. Eyre. 2011. Diel coral reef acidification driven by porewater advection in permeable carbonate sands, Heron Island, Great Barrier Reef. Geophysical Research Letters 38: 1–5.CrossRefGoogle Scholar
  53. Schwartz, M.C. 2003. Significant groundwater input to a coastal plain estuary: Assessment from excess radon. Estuarine, Coastal and Shelf Science 56: 31–42.CrossRefGoogle Scholar
  54. Slomp, C.P., and P. Van Cappellen. 2004. Nutrient inputs to the coastal ocean through submarine groundwater discharge: controls and potential impact. Journal of Hydrology 295: 64–86.CrossRefGoogle Scholar
  55. Smith, V.H., and D.W. Schindler. 2009. Eutrophication science: where do we go from here? Trends in Ecology & Evolution 24: 201–207.CrossRefGoogle Scholar
  56. Staver, L.W., K.W. Staver, and J.C. Stevenson. 1996. Nutrient inputs to the Choptank River estuary: Implications for watershed management. Estuaries and coasts 19: 342–358. doi: 10.2307/1352455.CrossRefGoogle Scholar
  57. Street, J.H., K.L. Knee, E.E. Grossman, and A. Paytan. 2008. Submarine groundwater discharge and nutrient addition to the coastal zone and coral reefs of leeward Hawai`i. Marine Chemistry 109: 355–376.CrossRefGoogle Scholar
  58. Tango, P., W. Butler and C. Wazniak. 2004. Assessment of harmful algae bloom species in the Maryland Coastal Bays. In: Wazniak C, Hall M, editors. Maryland’s Coastal Bays Ecosystem Health Assessment 2004. Annapolis, MD: Maryland Department of Natural Resources;
  59. Taniguchi, M., W.C. Burnett, J.E. Cable, and J.V. Turner. 2002. Investigation of submarine groundwater discharge. Hydrological Processes 16: 2115–2129.CrossRefGoogle Scholar
  60. Weil, R.R., R.A. Weismuller, and R.S. Turner. 1990. Nitrate contamination of groundwater under irrigated coastal plain soils. Journal of Environmental Quality 19: 441–448.CrossRefGoogle Scholar
  61. Wilson, J., and C. Rocha. 2012. Regional scale assessment of Submarine Groundwater Discharge in Ireland combining medium resolution satellite imagery and geochemical tracing techniques. Remote Sensing of Environment 119: 21–34.CrossRefGoogle Scholar

Copyright information

© Coastal and Estuarine Research Federation (outside the USA) 2013

Authors and Affiliations

  1. 1.Department of Environmental ScienceAmerican UniversityWashingtonUSA
  2. 2.Smithsonian Environmental Research CenterEdgewaterUSA

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