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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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slide1

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

slide2

Submarine groundwater discharge driving forces

  • Density driven circulation
  • Tidal pumping
  • Wave setup
  • Fresh groundwater discharge

Robinson et al., 2007

slide3

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

slide4

Brazil

Patos

Mirim

Atlantic

Ocean

Mangueira

slide7

Summer – Jan/2007

Pumps on

Pumps on

Time (h)

222Rn time series – Vitor Barbosa Canal

Winter – Aug/2006

slide8

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

slide10

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

slide11

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

slide14

F Cl SO4 HCO3 Na K Ca Mg

Groundwater-derived ion fluxes

slide15

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.