Apologies for the impersonal nature of this message - I'm struggling to keep this to 280 characters!
Thanks for asking about mosquitoes here in the UK. You're absolutely right: mosquitoes are almost certainly going to be (one of many) species that colonise my little tub - particularly Culex pipiens (primarily a bird-feeding mosquito). Though some larval-predators (including newts and damselfly nymphs) may colonise in time, it's true that some adult mosquitoes are likely to emerge from this water-body.
However I'd like to point out that, here in the UK, the advice is that small pools like this are not a disease risk. In other words, our mosquito species are currently a nuisance to humans rather than an imminent disease threat. Of course, this may well change in future as climate-change modifies the distribution of disease-harbouring mosquitoes and therefore -importantly- I am in regular contact with the UK Mosquito Consortium and the London School of Tropical Medicine on this issue. If this advice changes, then I will be the first to take note and end this project, as will hundreds of UK wildlife conservation organisations that also encourage activities like these and have done for many, many years. (Incidentally, the UK Mosquito Consortium and the London School of Tropical Medicine are aware of this project and have given it their support as an educational activity to talk about succession and about the wider value of freshwater in urban and sub-urban areas).
In the last few weeks, I've been made aware that this tiny one-person project does not translate well to an American audience. Please understand that this kind of pond-dipping has a rich and character-filled history in Britain - particularly among quirky Victorians eager to explore their freshwater delights with a microscope and gather a greater understanding and appreciation of ecological succession. I see the same magic that I think they saw and I can only apologise if I'm not expressing that clearly and with enough vim.
Again, thanks for your concern -it is valued and appreciated- and apologies for the impersonal nature of this message.
Warm wishes, Jules