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. (1)Density driven circulation (2)Tidal pumping (3)Wave setup (4)Fresh groundwater discharge Robinson et al., 2007 Submarine groundwater discharge driving forces

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. Patos Mangueira Mirim Atlantic Ocean Brazil

5. 222 Rn survey results – Aug/2006

6. Groundwater and Lagoon water tracer concentrations

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

8. Modeling 222 Rn-derived groundwater discharge Approach 1: Steady state J ben + 222 I 226 - 222 I 222 - J atm - J hor = 0 Inputs - Outputs = 0 Approach 2: Non-steady state (irrigation canals disturbed by pumping) dI 222 /dt = 222 I 226 + J ben - 222 I 222 - J atm - J hor Inventory rate of change = Inputs - Outputs

9. Offshore 222 Rn transects

10. Determining mixing losses m: slope of the log-linear curve K h : mixing coefficient (m 2 /d) : decay constant Determine mixing coefficients from 222 Rn and conductivity transects Neglecting advection and Production: Mixing coefficients K h in th order of 10 3 m 2 /day Use iterative approach to adjust 222 Rn concentrations along the transect

11. Estimated advection rates Mixing contributes an average of ~6% (maximum of 12%) of the total 222 Rn losses Advection rates in the irrigation canals from the south are much higher Extrapolated water fluxes (~50000 m 3 /day) represent only 2% of the direct rainfall

13. Major ions in Mangueira Lagoon and Groundwater GW

14. Groundwater-derived ion fluxes F Cl SO 4 HCO 3 Na K Ca Mg

15. 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.