Paul Daly (Fianna Fail) | Oireachtas source

I would like clarification on something that was mentioned a while ago about the rise in levels after the drought of 2018. The witnesses stated it was because farmers used extra chemical nitrogen because that was the advice that was given. Do they have scientific proof of this? Is it just because they know extra nitrogen was used and they are correlating the two? The habits of many people and industries changed when there were water shortages and the drought happened. To use the same example I used earlier, there was a lot more grime gathered on the roads because they were dry and then it was washed into rivers. Are the witnesses making a correlation because they know farmers were advised to put on more chemical nitrogen? Do they have specific and scientific proof that the reason there was a rise after 2018 was because farmers were advised to use more chemical nitrogen?