If you are in the U.S. and happen to be in an area with a sizable Latino population, then Spanish is THE way to go, as it is a WIIIIIIIDELY spoken language throughout the world, and is easily the most relevant second language in the U.S., as well as many other places.
Simply being fluent in Spanish will lead to better careers and more open doors. Where I live (Oregon) the Latino population is immense, and being able to speak Spanish is a great way to set yourself above the competition.
Now, this may not apply you too much since you plan on being a researcher, so it would depend more on where you would want to do research at. If, for some reason, you decided that Spain's ecosystem is perfect for some soil sampling and animal research, then learn Spanish. On the other hand, if doing experiments on gravity up high on the Tibetan Mountains sounds like a better deal to you, learn Mandarin :)
Basically, unless you are particularly partial to a language, learn what will BENEFIT you most, and not, to put it callously, what you like the most.
For example, I have chosen to study Spanish over either French or Italian, simply because Spanish is MUCH more relevant where I live. And since its more practical, I have grown to appreciate it much more than what were once my "preferred" languages of study.
One thing to take note of though is, learning a language is ridiculously difficult if you do not have opportunities to speak it regularly with others. Be sure you have the resources necessary to immerse yourself in a language if you plan on being fluent at all. Learning a language is much different than learning other things, such as math or science.
Good luck in college! By the way, may I ask which one you are attending?