I'm working on a large scale publishing site. I can increase search rankings almost immediately by improving internal linking to targeted pages, sometimes by 40 positions but after a day or two these same rankings drop down again, not always as low as before but significantly lower than their highest position.

My theory is that the uplift generated by the internal linking is subsequently mitigated by other algorithmic factors relating to content quality or site performance or is this unlikely?

Does anyone else have experience of this phenomenon or any theories?