A trilinear diagram is commonly used to present data on natural water. Which data does it display?

• A. It maps groundwater flow directions
• B. The percentage composition of major cations and anions in natural water
• C. The mineralogy of sediments
• D. The temperature profile of groundwater

Answer: (B)

A trilinear diagram is a visual tool for showing the major-ion chemistry of natural waters. It takes the concentrations of the main dissolved ions and expresses them as percentages or milliequivalents, placing the cations (such as calcium, magnesium, sodium, and potassium) on one ternary diagram and the anions (bicarbonate/carbonate, chloride, sulfate) on another. The two plots are connected into a central representation that helps identify the water type and how it has been influenced by processes like rock-water interaction, ion exchange, or mixing. This is why it’s used to display the relative proportions of major ions in water. It is not used for mapping groundwater flow directions, mineralogy of sediments, or temperature profiles.