Nice (for the first Look)
I believe that you should but some relections for the winter trees in the right
and some work on the merge area (it's a little obvious)
Good Luck ....

agree with the comments above and i'd add some sun or warm light to the summer part

The water looks frozen for winter, so no reflection would necessarily be seen, particularly if the sky is overcast...

I would make the sky above summer a more intense cyan blue, to differentiate it from the overcast winter sky. Although there are summer clouds, they are obscuring too much summer sky, so you may have to replace some of them with a summer sky image cloned in.

Very creative concept.

sky (fixed)
thanks to you guys!