Well, matching an audio environment is a real artform, kind of like matching a complex lighting situation. It can very easily seem "off" without you being able to put your finger on it.
So I can't really give general recommendations without having heard the recording or what the environment should sound like. But usually, there are two things that you will notice immediately that should be different:
1. In a studio environment, there is no reverb. In any real situation, you will find some reverb, and you'll have to add some of it to your voice. Probably only a very slight amount, and if you can find an "open space" preset, that would be good. A beach does not have much reverb, but there has to be some feedback from the environment.
2. More importantly: In a studio situation, your actor will talk very close to the mic, and on the beach he will not. This is called near-field-effect on microphones and will produce overaccentuated very low frequencies and sharp high consonants. To match a studio recording to a real world sound atmosphere, it will certainly help to apply a graphic equalizer and take down the lower frequencies (a falloff starting at maybe 200 or 250 Hertz, steepening slowly and reaching something like -12dB at 80 Hertz). You can also fall off on the very high frequencies (above 8kHz) to get rid of the sharp consonants or (if you have it) apply a De-Esser to the track.
The EQ alone should get you a lot more natural sounding audio. Finally, I want to throw in that for almost any speech recording, I will apply a compressor with a ratio of 4-5 to reduce the huge amplitude range of the human voice. Just sayin'...
Good luck!
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Oh, if you really want to get into it: Try to find (or simulate) a recording that sounds like the one you would like. Then do an echo- and a spectral analysis. That way you can artificially create a room echo and see what EQ settings you have to apply. But this might be too advanced...