The phrase "sulfate concentrations" refers to the amount of sulfate present in a substance or solution. It indicates how much sulfate is found in that particular sample. Full definition
This has led to a large decrease in sulfur emissions, and less atmospheric deposition of sulfate to agricultural fields, and consequently, declining sulfate concentrations in rivers. (sciencedaily.com)
I assume there's enough evidence to estimate the influence of sulfate concentrations on heat flux thanks to all of the eruptions on record. (tamino.wordpress.com)
When we looked at a whole variety of fields with tile drainage systems, we found that some had very low sulfate concentrations — just a few milligrams per liter. (sciencedaily.com)