For example, to achieve a 30% reduction in the end-of-river
DIN concentration from a nutrient-rich river system requires a
substantially larger absolute reduction in DIN (in terms of lg L1)
than a 30% reduction from a nutrient-poor river system. Countering
this fact however, is the strong likelihood that the required effort
to achieve DIN improvements becomes more difficult (and
economically costly) the cleaner the river system (see e.g., Roebeling
et al., 2007).