Why did Russia Dump the U.S. Dollar for Euro as Reserve Currency and what effect will it have?

They have not actually dumped US Notes, they have changed the proportion of their monetary holdings. The EURO now represents about 47.5% of their holdings as opposed to the Dollar which represents 41.5%. Although this change makes the EURO it's basic reserve currency it has not affected the official peg of the dual currency basket which is $0.55 - 0.45 EURO.