These are turbo-props. The jet bit is only a power supply to turn a propeller. It doesn't provide thrust like in a 747 or military jet. Its air intake is covered by a filter system just like any piston engine. For a given fuel consumption, the amount of air moving in/out of a turbine engine is roughly proportional to a piston engine.
Piston engines have air intakes too. A 600ish HP turbine is also moving a lot less air than you probably think.. it's not a high-bypass jet on an airliner.
Small/medium sized turbines are used all the time on helicopters, which routinely see backwoods operation.