Ecosystem Health of Wetlands of the Great Barrier Reef Catchment: Tully-Murray Floodplain Case Study

Research Report

R. G. Pearson¹, A. H. Arthington² and P. C. Godfrey²
with contributions from J. Wallace³, F. Karim³ and M. Ellison¹

¹ School of Marine and Tropical Biology, James Cook University, Townsville
² Australian Rivers Institute, Griffith University, Brisbane
³ CSIRO Davies Laboratory, Townsville

ISBN 978-1-921359-63-7
Report completed June 2010
Published by the RRRC March 2011

MTSRF Project 3.7.3 - Freshwater indicators and thresholds of concern

Extract from Report Summary

This project aimed to measure and understand the ecological processes, linkages and interdependencies that govern the biodiversity, physical condition, ecological health, temporal trends and resilience of rivers and floodplain wetlands in catchments of the Great Barrier Reef (GBR).

Summary of key findings:

• The most serious factors affecting health in Wet Tropics streams and wetlands are changes to habitats (flow modification, loss of riparian vegetation, weed invasion, infrastructure).
• Water-quality effects of agriculture are evident in streams and lagoons, particularly in systems that are not flushed throughout the year. In perennial streams (e.g. Russell-Mulgrave) and lagoons (e.g. Tully-Murray), dilution ameliorates impacts.
• The diverse aquatic invertebrate assemblages of Wet Tropics waterways are sensitive to habitat and water quality changes; they are good indicators of local ecological conditions.
• Wet tropics waterways provide essential habitat, including nursery habitat, for unique fish assemblages, which are very good indicators of the physical characteristics, hydrological connectivity and ecological condition of sub-catchments and floodplain lagoons.
• The presence of alien fishes is a strong indicator of disturbance in the broader landscape, and an early warning indicator of the potential for further disturbance from increasing numbers of individuals and species (e.g. tilapia).
• The alien ponded-pasture grass Hymenachne amplexicaulis and other alien plants that now occupy Wet Tropics waterways are avoided by most native fish species.
• Surrogate measures such as the Cassowary Coast Regional Council's (previously, Cardwell Shire's) Floodplain Project Values and Threats scores can provide rapid assessment of waterway ecosystem health.
• Connectivity pathways of streams and wetlands to estuaries, coasts and the Reef are an essential feature of Wet Tropics waterways, and can be compromised by infrastructure, flow regulation, weeds and water quality barriers.
• Ecological condition of floodplain lagoons may serve as a powerful indicator of climate change, because they are vulnerable to sea-level rise and hydrologic alterations, especially loss of flood pulses, dry-season base flow and connectivity between rivers and wetlands.
• Hydrological connectivity between individual lagoons and the stream network is vital for maintenance of fish assemblages and normal waterway function.
• The special nature of the Tully-Murray wetlands as a unique assemblage of Wet Tropics habitats, with functional links to the GBR lagoon, needs to be specially recognised.