What do you mean by one website? It is possible to have more than one wordpress installation on one domain.
It is possible to set up a domain so that you have mysite.com as one wordpress installation and mysite.com/nicheOne as a second wordpress installation and mysite.com/nicheTwo as a third and so on. If you are clever you set them up as multisite installation so some things are done from one dashboard.
There are others who go the route of sub domains so the address for the first niche becomes nicheOne.mysite.com
You still have most of the disavantages of having multiple websites which leads to you doing some tasks once for each website so multiplying the time and effort needed to maintain your online presence. Yet you are only using one domain.
It depends on your technical abilty and the time and effort you are willing to put in to maintian and grow each site.
God's Lily is "a voice for those frustrated by the slow progress towards a fair society where the needs of the weakest are met in a way that it strengthens them rather than weakens them further" . If that includes you then hop on over and have a look around. If you like what you see it would be a good idea to sign up to receive our blog broadcasts. Oh and you will get a couple of pdf files that explain the what and why behind the site when