What was the white area that developed on mulch after a heavy rain?

Question: After a severe rain storm the other day, this white area developed under a grouping of trees, on some mulch. The next day it began turning black. What would be happening and are the plants near by or the trees in jeopardy of getting some form of fungus or disease? Answer: Jonathan Foster, Home read more What was the white area that developed on mulch after a heavy rain?