Nonpoint sources are difficult to regulate and usually vary spatially and temporally (with season, precipitation, and other irregular events).

The number of burrows used by desert tortoises varies spatially and temporally, from approximately 5 to 25 per year.

The environment of deposition for these sediments has changed, varying spatially and temporally.

Simple and exact solutions are precluded by the fact that the system's constituents either influence each other in a complex way, or depend on temporally varying external forces.

The water distribution varies both geographically and temporally depending on the operational requirements of the water system.

The relative importance of the component acids in precipitation varies spatially and temporally, but in general similar values apply in eastern North America and Europe.

The extent to which various taxa are eaten by Spotted Owls varies temporally.

Nano Niagara Separation of Charged Particles by a Spatially and Temporally varying Electric Field.

(The current atmospheric concentration is about 390 ppm, but the degree of acidification in the ocean today varies regionally and temporally.)

The yellowfin whitings' diet also varies spatially and temporally, which appears to be a function of prey availability at different sites and periods of the year.