Why is that natural accidental placed on that G? Does the slur extend the sharp on the previous measure to the next one? That wouldn't make sense for the bass though.
This is known as a Courtesy Accidental. The purpose is to clearly indicate to the reader that a note that was given an accidental in a previous measure will return to the pitch indicated in the key signature in this occurrence, which is especially helpful for sight reading. It is called a Courtesy Accidental because the convention is that an accidental from a previous measure does not carry over into the next but as a courtesy, the accidental is placed there to remind the reader/player to return to the pitch indicated by the key signature. This can be done with any type of accidental.
The Courtesy Accidental is also included in the bass basically for the same reason. Advanced sight readers essentially get used to keys/tonalities and can use this to more easily read dense music, so when an accidental appears in one clef, a Courtesy Accidental is placed in the other clef to make sure the reader returns to the key signature. This "cross-clef" Courtesy Accidental can also be useful in preventing ambiguities that may occur in more modern pieces that might actually have a G in one clef and a G# in the other.
I notice that sometimes too. My theory is that the measure before always has the note sharped or flatted. I haven't found one otherwise, and it's true here (in the measure before, G is sharp). The natural is there to remind you that in the key signature that note is natural. I would just ignore it.