I bounded enough funds in order to be nominated. But the minum amount of DOT changes frequently. Will I loose the status of a nominator if my bonded amount falls below the threshold?
You will not lose your nomination "status" if your current bond falls below the current minimum active bond. However, you will not be able to earn rewards if your bonded funds are always below the minimum active bond.
You can think of it as a large queue of nominators that are trying to get rewards. However, there are only a limited number of nominators that can earn rewards per era (election round), so the nominators with more bond will have priority and be selected over those who have less bond. The minimum active bond is just a figure to give you an idea of what's the minimum bond that is likely to place you in the set of nominators who may receive rewards. Keep in mind that the minimum active stake may and will change often.
It may be that, even if your bonded funds are below the current minimum active stake, you'll be selected for rewards in later eras. But if you want to be on the safe side, you should aim at keeping an eye on the minimum active bond and bond above it.
Nomination pools are a good option if you consider the minimum stake "too high". In pools, multiple nominators bond their stake together and each nominator may bond as low as 1 DOT and still be able to earn rewards (due to the fact that the pool members collectively nominate as one nominator).