Abstract:  The degree of increased discharge of nitrogen and phosphorus from Great Barrier Reef (GBR) rivers, associated with agricultural development of the catchments in the last 200 years, varies greatly between the 35 individual major rivers. Changes to discharge in the far northern section of the GBR have been minimal while changes in the central and southern GBR have been of the order of 2 – 5 times increases in both nitrogen and phosphorus. Thus the degree of increased nutrient loading of communities such as coral reefs and seagrass meadows also varies spatially to a great degree, both from north (low loading) to central and south (high loading) as well as cross-shelf with higher loading to inshore systems and progressively less loading as distance from the coast and river mouths increase. The impacts of increased nutrient loading in the GBR include increased outbreaks of the crown of thorns starfish, a predator on coral; increased susceptibility of coral to bleaching in nutrient enriched conditions; decreased water clarity associated with increased suspended particulate matter and subsequent effects on phototrophic organisms such as coral and seagrass; and changes in the relationship between coral and macroalgae on coral reefs. Overall these impacts are manifest in the overall status of the ecosystems of the GBR with coral, seagrass and dugongs (which feed on seagrass) being in best condition in the far northern region of the GBR, including the Torres Strait section, but in poor condition in the central and southern GBR. While other factors such as climate change are also implicated in these differences it is well established that nutrient enrichment plays a major role.

Biography:  Dr Jon Brodie’s research interests are in the sources of pollutants in catchments, transport of pollutants to the marine environment, the dispersal of land-based pollutants in coastal and marine environments and the effects of terrestrial pollutants on marine ecosystems. He is particularly interested in the following research areas: water quality in tropical coastal marine environments; the effects of sediments, nutrients, pesticides and other contaminants on coral reef and seagrass bed ecosystems; catchment sources of sediment, nutrient and pesticide discharge to coastal environments; land use practices which lead to enhanced rates of sediment, nutrient and pesticide discharge to coastal environments; river plume dynamics and biological, physical and chemical processes occurring in river plumes; temporal and spatial dynamics of water quality on the Great Barrier Reef; water quality management systems in coral reef environments. Jon has published over 100 peer reviewed articles in this field as well as more than 300 technical reports, books and book chapters. He is also heavily involved in policy advice to Australian governments regarding management of water quality issues for the Great Barrier Reef. Jon was the lead author of the Scientific Consensus Statement documenting the status of knowledge and management for water quality issues affecting the Great Barrier Reef for the Queensland and Federal Governments in 2008, 2013 and 2016/2017 leading groups of more than 50 scientists and policy experts and has been closely involved in the Water Quality Improvement Planning process for the GBR NRM regions over the last 10 years.