I have read a number of articles and the facts associated with the benefit of the EU to UK science are quite simple. The UK receives more from the EU in scientific funding than it pays in and has done very well out of being part of the EU. Freedom of movement for students, graduate students, post-docs and above within the EU allows EU individuals to travel and work within the majority of EU countries. UK science is strong and therefore is a commensurately strong draw for the most talented individuals from the EU. If you haven't yet seen this video by an EU Law Expert, Professor Dougan, then I urge you to, it is an eye opening, honest and factual account of what the UK gains from the EU (in general). He also gives his views on EU Immigration in this article.
The uncertainties surrounding Brexit are significantly more complex. I could go through a number of possible avenues, however, the future relationship of the UK with the EU is a complete unknown. Herein lies the problem, there is no plan. As a result of this uncertainty, UK science faces a period of uncertainty. With access to funding, scientists have more money for research, with access to the free market job positions can be filled by the very best candidates in the UK and EU. However, this also provides UK citizens with ability to study and research abroad. Over the years this has led to the development of a fantastic multi-cultural and highly productive scientific community, which needs to be retained.
In my own research all of my papers have been published and supported with the help of EU partners (and some specific European Research Council grants), specifically in Italy, although EU money supporting the work was not sourced within the UK. What does this mean? On the face of it, nothing. We will continue to work with our European colleagues, it will just be a bit more expensive for us to work abroad! Volcanology in particular is an area which requires significant international collaboration. Often when discussing my job with others I get the reply "But there are no [active] volcanoes in Britain". The UK volcanology community will therefore continue to collaborate internationally, within and without of the EU, regardless of what happens to our relationship with the EU. It is just a question of how difficult that will become.
Until we know more on what the future relationship will be uncertainties will prevail over the next few years. I sincerely hope that this decision does not leave Early Career Scientists with a reduction in job prospects, not just in the UK, but throughout the EU. More than ever, we need to come together as a community, the decision has been made and we need to make it work for everyone.