Explain the concept of pollutant loadings and mass balance in streams and how they help identify pollutant sources.

• A. Concentrations alone determine pollutant impacts without regard to flow.
• B. Using concentrations and flow to estimate mass moving into/out of a stream; mass balance helps quantify sources, sinks, and in-stream fate.
• C. Mass balance focuses only on the chemical composition of the stream water.
• D. Mass balance is not applicable to streams.

Answer: (B)