Linking catchments to the coast - can the development of northern Australia negatively impact on the health and productivity of estuaries?

Increased development in catchments and coastal regions is threatening the health of rivers, estuaries and coastal regions. Freshwater inputs can play an important role in driving productivity, or alternatively high nutrient loads can seriously impact on the health of these systems. One approach to understanding the links between freshwater inputs and estuaries is to quantify all the loads of nutrients entering the estuary to determine the component that is driving productivity in the system. Recent studies within the Tropical Rivers and Coastal Knowledge program have examined freshwater inputs in a tropical macrotidal estuary, Darwin Harbour. The city of Darwin is situated in this harbour. Surprisingly, on a whole-of-harbour scale, nutrients from the sea, rather than rivers or urban inputs were the major source for the harbour. This is the result of the macrotidal regime. However, when urban inputs, particularly sewage inputs to creeks, were examined in more detail, it was found that sewage inputs can have substantial localised effects. This study highlights that generalizations cannot be made about freshwater inputs and their effect on estuaries, and a thorough understanding of the physical, chemical and biological properties of each system is needed in order to effectively manage the estuarine health.