  We analyze the electromagnetic field near a plane interface between a
conductive and a dielectric media, under conditions supporting surface
plasmon-polariton (SPP) propagation. The conductive medium is described by the
hydrodynamic electron-gas model that enables a consistent analysis of the
field-induced variations of the electron density and velocity at the interface
and its nearest vicinity. The distributions of electromagnetic dynamical
characteristics: energy, energy flow, spin and momentum are calculated
analytically and illustrated numerically, employing silver-vacuum interface as
an example. A set of the "field" and material contributions to the energy, spin
and momentum are explicitly identified and classified with respect to their
physical origins and properties, and the orbital (canonical) and spin
(Belinfante) momentum constituents are separately examined. In this context, a
procedure for the spin-orbital momentum decomposition in the presence of free
charges is proposed and substantiated. The microscopic results agree with the
known phenomenological data but additionally show specific nanoscale structures
in the near-interface behavior of the SPP energy and momentum, which can be
deliberately created, controlled and used in nanotechnology applications.
