the figure you quoted is an average for Poland and may be completely irrelevant to the case we are talking about
And maybe they're relevant. In the absence of better data, they are the average figures for Poland. Now, ok, let's take your scenario of fewer paying tourists, but then the region (SE Poland) also has lower average wages, so even if you scale down the values of less tourist spend to the local average wage, it is still supporting large numbers of people.
let's assume that 10 per cent of visitors to the Poleski National Park are foreingers
Why so low, you've just plucked that out of the air to suit your argument. Why not 85% or 99%? You've got no idea whether your 10% is closer to the truth than my 99%, so let's not make up stuff.
People visiting that fairly remote region will of course be over-nighting. Ecotourists are generally out at dawn, as that is when the wildlife is most active, so of course that includes overnight stays.
Coal mining might employ more people in a short burst, until the coal is exhausted, but ecotourism is *renewable* for much longer, and they're cleaner jobs, and the industry wont leave vast scars on the landscape and throw up tonnes of dust.
Coal mining does indeed cause smog when you burn the stuff in Rzeszow and Krakow and other towns, which I mentioned.