Map of lake TN, TP, and TN:TP by Sarah Collins
This map is from this article by Sarah Collins et al. It clearly shows how spatial patterns in TP and TN alone do not lead to similar patterns in the ratio of TN:TP. Also, spatial pattern in TN and TP are similar, but not identical and there are some interesting outliers, e.g., Michigan lakes. See the article for details on these cool patterns.