I know my last post was rather tedious, but I think seeing it that way helps to get the point across.
And, yes, PapaBear, nothing about a pond is static. The contaminant input will vary with the seasons. Over such a long period some contaminants are altered by the biomass to a form that settles out; and, if contaminant levels are lower, appetite improves and more feeding occurs, so inputs increase, etc., etc.
The point to absorb is a year of deteriorating conditions with equilibrium at 10 times the weekly input of contamination, vs a couple of months with equilibrium at less than 3 times the weekly contamination is a huge difference. DickB's 10% per day through constant trickle is on an entirely different plane.... equilibrium takes 50 days (not much different that 35% weekly water changes), but the ambient contamination is less than 1.5 weeks' worth and there is virtually no significant fluctuation.