To identify whether or not there are sulfates in a water source, one must understand the different types. Sodium, Potassium, and Magnesium are some of the most common heavier metal sulfates that are readily soluble (easily dissolved) in water. Due to their solubility, they are commonly found in high concentrations. Calcium is the fifth most common Sulfate, and it is relatively less soluble than its counterparts (i.e. unless exposed to cold water). Once a sulfate dissolves, it reduces itself into a sulfide.
Sulfide is a non-metallic element that occurs naturally in numerous minerals in soil and rock formations that contain groundwater. Some of which are Barite (BaSO4), Epsomite (MgSO4-7H2O), and Gypsum (CaSO4-2 H2O). The reversible reaction between sulfide and sulfate in a natural environment is often called the “sulfide cycle.” Natural sources of sulfide include volcanoes, fertilizers, and the decomposition of organic matter and ocean salts. Atmospheric fallout is one of the primary vehicles of sulfide transport.
Where do Sulfates come from?
- Mining, smelters, paper milling, textiles, and tanneries. (Sulfates and sulfuric acids)
- Abandoned coal mines (Iron pyrite (FeS)
- Surface waters (sulfates)
- Destruction and deposition of waste rock in mine dumps (Sulfates)
- Fertilizers (Sulfates)
Are sulfates important in my water source?
Sulfates are helpful for understanding oxidation-reduction conditions in groundwater and, therefore, predicting the fate of contaminants, (i.e. industrial solvents).
- Contributes to the salinity of irrigation water, Na, Ca, Mg, Cl and HCO3.
- Contributes to water’s conductivity, dissolved solids, and water quality parameters regulated by international standards.
- Contributes to the limited uptake of calcium and increases the absorption of sodium and potassium, resulting in a disturbance in the cationic balance within the plant.
- Contributes to the harm of mineral nutrition of the plant through its effects on the uptake and metabolism of nutrients.
What are the average Sulfate ranges of soil?
Sulfate: 0 – 20 meq/l
Electrical Conductivity: 0-3 dS/m
Dissolved Solids: 0 – 2000 mg/l
pH: 6.5 to 8.4
Do Sulfates Influence Water Quality through Electrical Conductivity?
There is a correlation between Sulfates and electrical conductivity. Assuming that Sulfate is the predominant anion in irrigation water, its increase parallels the other.
Electrical Conductivity Range
0-500 mhos/cm: Excellent
500-1500 mhos/cm: Good
1500-3000 mhos/cm: Fair (may have adverse effects on water quality)
3000-5000 mhos/cm: Poor (can be used in permeable soils with careful management methods)
5000-6000 mhos/cm: Very Poor
Are their solutions to mitigate sulfate conditions?
- Proper Waste Management
- Proper Fertilizer Management
- Proper Wetland Management
- Mining of low sulfur minerals
- Infiltration/salinity problems generated by high sulfate concentrations can be mitigated with good agricultural practices