For the long term I cant really tell but for day to day terms its like STEEM gets distributed via this pool. You kind of need to think that the pool has 703468"liters" (STEEM) currently in it. On the one side it gets filled and on the other it is getting spit out to users. The +5690 is the difference between how much came in and how much out over one day. So for today less out :D

There is no reset in that form. If the pool gets to 0 I assume you still be getting rewards but less untill more gets added than distributed.