I have been meaning to see if I can find some urban pollution numbers to do with yard and garden fertilization. I have worked in landscaping and in agriculture and I have to say that when it comes to responsible use of fertilizer the homeowners and lawn care companies do their share of damage over applying fertilizer on yards and landscaping that are planted in a shallow amount of topsoil layered over very poor soil in the case of the Ozarks, solid rock which has no nutrient retention value, after the fertilizer comes the over watering which transports the nutrients.
As someone who has set in classrooms full of Ag students and listened to their take on the environment the problem not only of over fertilization but most environmental issues is generational. As more and more people who are involved agricultural production become educated and move away from the "well that's how dad did it" mindset combine with the fact that fertilizer cost money and that cost is going up the problem of over application should fade more so because producers are starting to realize that over fertilization is as good as throwing away money than any other, but there will always be a few that refuse to realize the impact they have on everyones world and their own bottom line.
The issue that the amount of nutrients in the water this year is skyrocketing is largely because of the drought. No one I have ever met can tell me if its going to rain in a month let alone two months or more, which means when row crop farmer fertilizes in most cases late April he has no clue if its going to rain in May, June and July when his crop would use the nutrients. In the case that no rain falls and your crop dies and the nutrients are not used but left in a fallow field and then like this spring very large amounts of rainfall before the next crop can even be planted the nutrients in the soil will leach down through the soil which will filter to a point in a good situation in a bad situation if the fertilizer is applied after the last rainfall and remains on top of the soil which becomes baked hard and loses its ability to take on water very well followed by rain which will become largely runoff and taking with it anything small and water soluble, like most fertilizers. Is the actual size of the kill due to the amount of fertilizer used? yes. Is the fact that if every producer did exactly what they should this would still happen? yes. Unless you follow the idea that no fertilizer should be used and in case we should all get used to spending 30% or more of our income on food instead of the average 9.4% here in the USA. As stated above someone somewhere will pay the cost of producing food be it at the store, people in the gulf, or people starving when they can't buy and don't have the resources to grow their own or when we refuse to give it to them.