Examination of a simple, but quantitative parameter, Sf/So, the ratio of average salinity of a coastal waterway/marine source water salinity, both geographically and temporally, identified five major types of coastal environment around Australia: (i) runoff-dominated annually - found mostly on the eastern seaboard, where rainfall is near continuous year-round ; (ii) seawater-dominated annually- large embayments with small runoffs; (iii) evaporation-dominated annually - found on the fringes of arid climate zones of western Australia, such as Shark Bay and in South Australia, Spencer and St. Vincents Gulf; (iv) runoff-dominated in the summer monsoon and evaporation-dominated in the winter - e.g. the northern Australian estuaries near moist-tropical and semi-arid zones with summer rains; and (v) runoff-dominated in the winter and evaporation-dominated in the summer-e.g. the estuaries and coastal lakes of southwestern Australia. A general equation of salt and water mass balances, including an evaporation term, was used to estimate freshwater residence time, a proxy for dissolved anthropogenic input. Geographic and temporal variation in climate forcing factors, notably seasonal variation in rain-fall and runoff and the net of evaporation and precipitation, exert major controls on residence time and flushing of Australian coastal environments. The inverse of the residence time (1/T day-1) is an important parameter in the estimation of quantities of dissolved anthropogenic inputs flushed from the coastal environment to the sea. As such, it is one important parameter for evaluating coastal water quality.
