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Tracing anthropogenically-driven groundwater discharge into a coastal lagoon from Brazil

Tracing anthropogenically-driven groundwater discharge into a coastal lagoon from Brazil. Isaac R. Santos ; William Burnett; Richard Peterson; Jeffrey Chanton Department of Oceanography, Florida State University, Tallahassee, FL, USA Felipe Niencheski; Carlos F.F. Andrade; Idel B. Milani

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Tracing anthropogenically-driven groundwater discharge into a coastal lagoon from Brazil

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  1. Tracing anthropogenically-driven groundwater discharge into a coastal lagoon from Brazil Isaac R. Santos; William Burnett; Richard Peterson; Jeffrey Chanton Department of Oceanography, Florida State University, Tallahassee, FL, USA Felipe Niencheski;Carlos F.F. Andrade; Idel B. Milani Department of Chemistry, Fundaçao Universidade do Rio Grande, Rio Grande, Brazil Axel Schmidt; Kay Knoeller Helmholtz Centre for Environmental Research, Leipzig, Germany

  2. Submarine groundwater discharge driving forces • Density driven circulation • Tidal pumping • Wave setup • Fresh groundwater discharge Robinson et al., 2007

  3. Hypotheses 1 - The annual irrigation creates extreme conditions that seasonally change groundwater discharge into Mangueira Lagoon 2 - Dredging of irrigation canals alters the groundwater fluxes

  4. Brazil Patos Mirim Atlantic Ocean Mangueira

  5. 222Rn survey results – Aug/2006

  6. Groundwater and Lagoon water tracer concentrations

  7. Summer – Jan/2007 Pumps on Pumps on Time (h) 222Rn time series – Vitor Barbosa Canal Winter – Aug/2006

  8. Approach 2: Non-steady state (irrigation canals disturbed by pumping) Inventory rate of change = Inputs - Outputs dI222/dt = 222I226 + Jben - 222I222 - Jatm - Jhor Modeling 222Rn-derived groundwater discharge Approach 1: Steady state Inputs - Outputs = 0 Jben + 222I226 - 222I222 - Jatm - Jhor = 0

  9. Offshore 222Rn transects

  10. Determining mixing losses Determine mixing coefficients from 222Rn and conductivity transects Neglecting advection and Production: m: slope of the log-linear curve Kh: mixing coefficient (m2/d) : decay constant Mixing coefficients Kh in th order of 103 m2/day Use iterative approach to adjust 222Rn concentrations along the transect

  11. Estimated advection rates Mixing contributes an average of ~6% (maximum of 12%) of the total 222Rn losses Advection rates in the irrigation canals from the south are much higher Extrapolated water fluxes (~50000 m3/day) represent only 2% of the direct rainfall

  12. Major ions in Mangueira Lagoon and Groundwater GW GW GW

  13. F Cl SO4 HCO3 Na K Ca Mg Groundwater-derived ion fluxes

  14. Conclusions 1) No major seasonal changes in groundwater advection rates driven by irrigation 2) Advection rates in the canals were ~2 orders of magnitude higher than along the lagoon shoreline contribution ~80% of total groundwater inputs. 3) In spite of the small volume contribution (<2% of total water inputs), groundwater should not be neglected in dissolved species budgets 4) Anthropogenic changes in the water cycle may have a major effect on groundwater discharge in some coastal environments.

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