In an estuary, the concentration C of a dissolved nutrient (measured in mg/L) depends on the water’s salinity S (measured in ‰). Tidal motion causes the salinity to vary over time t (measured in hours). Researchers monitoring the water quality want to understand how quickly the nutrient concentration is changing at a particular instant.
(a) Identify the independent variable and the two dependent variables in this situation.
(b) Describe, in complete sentences and with correct symbolic notation, how the instantaneous rate of change dtdC can be expressed in terms of two simpler rates that involve S. Explain the reasoning behind your relationship without performing any numerical calculation.