1. Mass Solute Balance and Evaporation Mark Wiltermuth NDSU Geol 628 Geochemistry 2010

2. 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.  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 CO 2 to the pond

4.  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.  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.  Water balance: Δ Volume = Area ( Precip + Runoff – Evap – Infilt)  Use of a conservative species as a tracer (Chloride)  Groundwater inflow and outflow  Sulfur redox reactions

7.  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(C p ) + R(C R ) – f I {I + E}(C) + B ]

8.  Use Chloride to find f I 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.  How does evaporation alone change the water chemistry?  How can the water chemistry changes be modeled using PHREEQC?

10.  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 Alkalinity167 as HCO3 REACTION 1 H2O -1.0 13.875 moles

11. % Evap151025507595 Anhydrite CaSO4 -3.67-3.64-3.6-3.47-3.19-2.74-1.83 Aragonite CaCO3 -0.79-0.76-0.71-0.57-0.270.231.26 Calcite CaCO3 -0.64-0.61-0.57-0.43-0.120.381.41 CH4(g) CH4 -122.81-122.82-122.85-122.93-123.09-123.59-123.98 CO2(g) CO2 -1.99-1.98-1.95-1.87-1.7-1.39-0.68 Dolomite CaMg(CO3)2 -1.43-1.37-1.28-0.390.612.68 Gypsum CaSO4:2H2O -3.43-3.4-3.36-3.23-2.95-2.5-1.59 H2(g) H2 -36.9-36.91-36.92-36.96-37.04-37.24-37.52 H2O(g) H2O -1.7 H2S(g) H2S -124.01-124.03-124.06-124.15-124.34-124.89-125.4 O2(g) O2 -11.82-11.81-11.78-11.7-11.54-11.13-10.58 Sulfur S -93.08-93.09-93.11-93.16-93.26-93.61-93.85

12. % Evap 151025507595 SO4-2-4.62-4.61-4.58-4.51-4.36-4.09-3.49 CaSO4-5.74-5.71-5.67-5.54-5.26-4.81-3.90 MgSO4-5.91-5.88-5.84-5.71-5.43-4.98-4.06 HSO4--9.96-9.95-9.93-9.86-9.71-9.46-8.91 CaHSO4+-12.16-12.13-12.09-11.95-11.66-11.17-10.14

13. % Evap151025507595 HCO3--2.56-2.55-2.52-2.44-2.27-1.98-1.30 CO2-3.38-3.36-3.33-3.26-3.08-2.78-2.07 CaHCO3+-4.79-4.75-4.71-4.56-4.24-3.71-2.56 MgHCO3+-4.97-4.94-4.89-4.75-4.43-3.89-2.73 CO3-2-5.70-5.68-5.65-5.57-5.39-5.08-4.37 CaCO3-5.91-5.88-5.84-5.70-5.39-4.90-3.87 MgCO3-6.34-6.31-6.26-6.12-5.82-5.32-4.28

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