TBH, I wouldn't know where to tell you to start in that field. I work with utilities and I started out capturing electricity networks and got that by saying I "knew a bit of CAD".
I think ESRI is a player in the enviromental area, making yourself familiar with the tools would be a good start, they offer courses (though I have no idea how much they cost). You can't guarantee every job will use it but it's def one of the biggest players.
ESRI Training ESRI Natural resources apps
You might also want to check out
GRASS, one of the biggest open source GIS systems.