I think it may be hard to get a clear answer, to easy to slice the data to say what you want it to.
For example the nitrogen pollution from specifically nitrogen base fertilizer vs manure used as fertilizer vs animal waste from cows, pigs and poultry are all different.
This is a good read and relevant for context I think.
Nutrient pollution and greenhouse gas emissions related to crop agriculture and confined animal feeding operations (CAFOs) in the US have changed substantially in recent years, in amounts and forms. This review is intended to provide a broad view of ...
www.ncbi.nlm.nih.gov
I feel horrible for all the farmers facing bankruptcy and losing their way of life, also the fishermen facing the same thing.
I am a SCUBA dive, and I can say we are destroying our reefs and fish populations. To compare the reefs I was diving in the 80's and 90's to today is so saddening.