The Tail of Two Rivers in Tasmania: The Derwent and Huon Estuaries

Abstract

The Derwent and Huon Rivers are two relatively small river systems in the southeast of Tasmania (Australia). They terminate in estuaries that are very similar in structure and function. Historically, runoff from their adjoining catchments has been very dilute, but coloured by dissolved organic matter. Their location in cool, temperate latitudes results in a maritime climate that is changeable, but delivers regular rainfall, and therefore river flow, throughout the year. Marked seasonal cycles in nutrient levels and biological activity are seen in neighbouring coastal waters. Discharge from both rivers does not have the same seasonal signature; it is consistently enriched in dissolved organic matter (including nitrogenous forms) and depleted in inorganic nitrogen and phosphorus. Small variations in chemistry of the riverine end-members seem to ensue from intra-catchment differences in geology, soils and vegetation influenced by localised rainfall patterns. Silicon manifestly displays this behaviour in the Huon system.