  Nuclear Stellar Discs have been observed in the vast majority of barred disc
galaxies including the Milky Way. Their intense star formation is sustained by
the intense gas inflows driven by their surrounding bars and frequently
supports a large-scale galactic fountain. Despite their central role in galaxy
evolution, their chemical evolution remains largely unexplored. Here we present
the first systematic, multizonal modelling of the chemical evolution of these
nuclear stellar discs. We argue that the chemical composition of nuclear
stellar discs is best understood relative to the bar tips from which their gas
is drawn. We make predictions of the detailed abundance profiles within the
nuclear stellar disc under different accretion scenarios from the galactic bar
and show by which observable differences they can be decided. We show that with
their difference to normal disc star formation, nuclear discs offer a unique
laboratory to break parameter degeneracies in chemical evolution models. This
allows us to identify the effects of the main gas parameters and disentangle
them from the global enrichment history. We show this for the example of the
ejection fractions from the outer and nuclear disk.
