  Our subject is an electromagnetic field near the plane interface dividing a
conductive and a dielectric media, under conditions supporting the surface
plasmon-polariton (SPP) propagation. The conductive medium is described by the
hydrodynamic electron-gas model which 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 the silver-vacuum interface
as an example. A set of the "field" and material contributions to the energy,
spin and momentum are explicitly identified in respect to their physical
origins, and the orbital (canonical) and spin (Belinfante) momentum
constituents are separately examined. In this context, a procedure for the
spin-orbital momentum decomposition in 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.
