One of the fields you may get to work in is the examination of the condition of the environment. Which part of the environment research you will need, depends on where you work. In a county or municipal autority you may be asked to search old aireal photos and old archives to find places where there could be old sites which are polluted. When you find a suspect site, a company would then be asked to examine if there is an pollution. They may make test drillings to find old oil leaks or try to find chemicals left by an old factory.
One of the things you could be asked to do, is to examine the condition of a river or stream. What determines the sort of plant and animal life, you will find in the stream, is the type and condition of the bottom materials, the amount of oxygen in the water, how fast it flows, the pollution level and so on.
You don't always have to measure and analyze to see if there is a problem. You identifies the condition of a stream by seeing which animals and plants that exist in the stream. If the stream was polluted within the last few days, you won't find the sort of animals that you should find.
Somtimes the places that look polluted, are not polluted. When a ditch has dirty water, it is usually not because it is polluted, it is because there are a lot of dead leaves in it. That gives the same result as if there had been an emmision of a pollutant: The water is grey and smells. Luckily nature can handle that sort of 'pollution'. They have always been there, they are part of nature. They are not supposed to be cleaned up, just to be left to handle themselves. By the way: Nature is using the organismes thart lives in such places, when it cleanes up our manmade pollutions.