Contribution of Three Rivers to Floodplain and Coastal Productivity in the Gulf of Carpentaria
Total Page:16
File Type:pdf, Size:1020Kb
Contribution of three rivers to floodplain and coastal productivity in the Gulf of Carpentaria Final report (component 1) by Michele A. Burford, Stephen J. Faggotter and Rob Kenyon © Griffith University, 2020 Contribution of three rivers to floodplain and coastal productivity in the Gulf of Carpentaria: Component 1 final report is licensed by the Griffith University for use under a Creative Commons Attribution 4.0 Australia licence. For licence conditions see creativecommons.org/licenses/by/4.0 This report should be cited as: Burford MA, Faggotter SJ & Kenyon R. 2020. Contribution of three rivers to floodplain and coastal productivity in the Gulf of Carpentaria: Component 1 final report. Griffith University, Brisbane. Cover photographs Front cover: Flinders River estuary (photo: Stephen Faggotter). Back cover: Gilbert River estuary (photo: Stephen Faggotter). This report is available for download from the Northern Australia Environmental Resources (NAER) Hub website at nespnorthern.edu.au The Hub is supported through funding from the Australian Government’s National Environmental Science Program (NESP). The NESP NAER Hub is hosted by Charles Darwin University. ISBN 978-1-925800-46-3 August, 2020 Printed by Uniprint Contents List of figures ...............................................................................................................................ii List of tables ............................................................................................................................... v Acronyms................................................................................................................................... vii Acknowledgements .................................................................................................................. viii Executive summary .................................................................................................................... 1 Component 1: Effect of flow on fisheries species in Flinders, Gilbert and Mitchell Rivers .. 1 1. Introduction .......................................................................................................................... 4 1.1 Background .................................................................................................................. 4 1.2 Objectives ..................................................................................................................... 5 1.3 Characterisation of study sites ..................................................................................... 6 2. Methodology ........................................................................................................................ 9 2.1 Objective 1 – End of system nutrient loads ................................................................. 9 2.2 Objective 2 – Estuarine primary productivity ............................................................. 11 2.2.1 Physicochemical and water column sampling .................................................... 13 2.2.2 Sediment parameters.......................................................................................... 14 2.3 Objective 3 – Banana prawn densities ...................................................................... 16 2.4 Objective 4 – Tracer methods to determine prawn movement ................................. 18 2.5 Objective 5 – Modelling prawn fisheries and flow ..................................................... 18 3. Results and discussion ..................................................................................................... 19 3.1 Objective 1 – End of system nutrient loads ............................................................... 19 3.2 Objective 2 – Estuarine primary productivity ............................................................. 21 3.2.1 Water quality ....................................................................................................... 21 3.2.2 Benthic algal biomass, production/respiration and sediment nutrients.............. 32 3.2.3 Effect of nutrient additions on benthic productivity ............................................. 36 3.3 Objective 3 – Banana prawn densities ...................................................................... 38 3.3.1 Prawn abundances across estuaries .................................................................... 38 3.3.2 Spatial distribution of prawns within estuaries ...................................................... 40 3.3.3 Areal extent of habitat ............................................................................................ 43 3.4 Objective 4 – Tracer methods to determine prawn movement ................................. 47 3.5 Objective 5 – Modelling prawn fisheries and flow ..................................................... 49 4. Conclusions and recommendations.................................................................................. 50 References ............................................................................................................................... 52 Appendix 1: Hydrographs ........................................................................................................ 55 Appendix 2: Sampling sites ...................................................................................................... 58 Appendix 3: Broadley et al, paper modelling fisheries catch with flow alterations ................. 61 Appendix 4: Maps of nutrient concentrations in three rivers ................................................. 100 Appendix 5: Mudflat and sandflat grain size analysis ........................................................... 105 Appendix 6: Size distribution of prawns ................................................................................. 106 Contribution of three rivers to floodplain and coastal productivity in the Gulf of Carpentaria | i List of figures Figure 1. Location of the three study rivers in north Queensland. ............................................ 7 Figure 2. (a) Mean annual rainfall (mm) and (b) evaporation (mm) in the three study catchments, Mitchell, Gilbert and Flinders Rivers (generated by J. Coates-Marnane, Bureau of Meterology data). .................................................................................................... 8 Figure 3. Annual flow (GL) from 1984 to 2011 based on modelled end-of-system flow (generated by A. Broadley, CSIRO data). Red dashed line represents mean annual flow across the years. ...................................................................................................................... 8 Figure 4. Hydrograph (ML day-1) in three rivers over the period of the study, based on DNRM gauging station data at Dunbar (139.4 km from Mitchell River mouth), Burke Development Rd (102.5 km from Gilbert River mouth) and Walkers Bend (103 km from Flinders River mouth). Arrows show sampling times. ........................................................... 10 Figure 5. Google Earth maps showing water quality sampling sites in each estuary and associated floodplume sampling. Top left: Mitchell; top right: Gilbert; bottom left: Flinders. Heli = helicopter transect sampling, Plume = floodplume transect sampling from boat, WQ = routine water quality sampling sites associated with sediment sampling sites, River T = estuary transect sites. ............................................................................................ 14 Figure 6. Incubation and measuring equipment used for measuring primary productivity in mudflat samples. Photos: Michele Burford, Stephen Faggotter. .......................................... 16 Figure 7. Salinity transects in Flinders River estuary and nearshore area. ............................ 23 Figure 8. Salinity in the Mitchell and Gilbert River estuaries and nearshore zone. ................ 23 Figure 9. Photos of Flinders River estuary and nearshore area showing scale of unprecedented flood in Febuary 2019. Photos: Michele Burford. ........................................ 24 Figure 10. Total nitrogen and phosphorus floodplume sampling in two wet seasons and comparison with estuarine concentrations in the Mitchell River estuary. ............................. 26 Figure 11. Map of total phosphorus and nitrogen concentrations in the Flinders estuary and nearshore. ....................................................................................................................... 26 Figure 12. Transect of water column chlorophyll a concentrations in the Mitchell, Gilbert and Flinders River estuaries on each sampling occasion. .................................................... 27 Figure 13. Correlations between water quality parameters for all sampling occasions in the three estuaries. R2 values are only provided for significantly correlated parameters, i.e. P < 0.05. ................................................................................................................................. 29 Figure 14. Correlation between salinity and nutrient parameters in Flinders River estuary during 24 h sampling across the tidal cycle in March 2019 trip. ........................................... 30 Figure 15. Photos showing examples of intertidal mudflats (left) and sandflats (right) at the mouth an estuary. Photos: Stephen Faggotter. .................................................................... 32 Figure 16. Sediment chlorophyll a concentrations (mg m-2) in (a) mudflat and (b) sandflat habitats in the three estuaries on each sampling occasion.