What two land-uses were contributing excess nitrogen to the watershed and what event washed these excess nutrients into the river?

Ithink that b is correct but just in case wait to see if someone else answers

Ibelieve is d but i’m not 100% sure

You should never redesign your experiment. try and see what in your experiment you made a mistake on or try and test your experimemt with somebody else. see if they get the right results.