Interesting. The water influences the proportion of nitrogen in the vegetation and the ratio of C4 to C3. Everything is intimately interconnected. Can't resist another quote from the article:

"The coincidence in time of megafauna extinction and ecosystem collapse shortly after the arrival of modern humans, and the lack of similar changes during dramatic climate change earlier in the Quaternary, suggests there may be a causal link."

I promise I won't do it again.