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Water level changes in seasonal wetlands

Water level changes in seasonal wetlands. Mass Solute Balance and Evaporation. Mark Wiltermuth NDSU Geol 628 Geochemistry 2010. Reference.

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Water level changes in seasonal wetlands

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  1. Water level changes in seasonal wetlands Mass Solute Balanceand Evaporation Mark Wiltermuth NDSU Geol 628 Geochemistry 2010

  2. Reference Heagle, D., M. Hayashi and G. van der Kamp (2007). Use of solute mass balance to quantify geochemical processes in a prairie recharge wetland. Wetlands 27: 806-818.

  3. Pond water chemistry • Subject: northern prairie recharge wetland • Objective: Identify key geochemical processes and quantify their rates • Method: Combined water and solute mass balance approach • Key Processes: Sulfate reduction, carbonate mineral reactions, and processes adding CO2 to the pond

  4. Implications to the Ecosystem • Water chemistry affects the plant and animal communities of a wetland • Salinity influences the plant and invertebrate community • Source of salinity: Glacial till; oxidation of sulfur and dissolution of carbonate

  5. Hydrology • Three types of wetlands: recharge, flow-through, discharge • Hydrologic cycle of closed basins • Inflow: Precipitation and Runoff, and Groundwater • Outflow: Evaporation, Groundwater • Chemical transport: infiltration carries solutes into groundwater • Evaporation: deposit solutes, oxidize reduced species

  6. Model: Mass Solute Balance • Water balance: ΔVolume= Area ( Precip + Runoff – Evap – Infilt) • Use of a conservative species as a tracer (Chloride) • Groundwater inflow and outflow • Sulfur redox reactions

  7. Model: Mass Solute Balance • Normalized Masses of species to first observed concentration to compare to Chloride • Changes in Chloride reflect changes do to hydrology • Differences between normalized mass of other species indicates reactions • Solute mass balance: [ P(Cp) + R(CR) – fI{I + E}(C) + B ]

  8. Model: Mass Solute Balance • Use Chloride to find fI because B=0 for conservative species • Can now solve for I and E (so just solved a hydrology problem) • Use mass balance for other species, change B to represent the addition or removal of species by reactions

  9. Evaporation Question • How does evaporation alone change the water chemistry? • How can the water chemistry changes be modeled using PHREEQC?

  10. Phreeqc Modeling • Evaporation by reaction TITLE Seasonal Wetland 25% Evaporation SOLUTION 1 Initial Water 11-May 1994 units mg/L pH 7.18 temp 18.0 Ca 28 Mg 11 Cl 4.5 S(6) 2.56 Alkalinity 167 as HCO3 REACTION 1 H2O -1.0 13.875 moles

  11. Evaporation: Saturation Index

  12. Log of number of moles: S

  13. Log of number of moles: C

  14. Discussion • Modeling precipitation, runoff and evaporation • Changes in chemistry through transport in a wetland system

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