Reef Plan Marine Monitoring Program - Project - Inshore water quality monitoring (AIMS)

Introduction

The management of water quality is essential to ensure the long-term protection of the coastal and inshore reefs of the Great Barrier Reef (GBR). The land management initiatives under the Australian and Queensland Government's Reef Water Quality Protection Plan 2009 (Reef Plan) are key tools to improve the water quality entering the GBR. Ongoing long-term water quality monitoring at 20 fixed sites (Figure 1) is part of the Reef Plan and is fundamental to determine the status and long-term trends of marine water quality of the coastal and inshore GBR lagoon.

The 8th year of long-term water quality monitoring was completed in June 2013. An index of water quality derived from long term means are shown in Figure 2. The water quality index score is overall ‘very good’ or ‘good’ in the Wet Tropics and Burdekin Regions, a steady decline in water quality found in the Mackay Whitsunday Region reaching an overall moderate index score, while in the Fitzroy Region the water quality is variable but still reaches a score of ‘good’.

Water quality in the inshore GBR lagoon shows distinct gradients away from river mouths and is influenced over short time periods by river floods and by wind-driven resuspension of seafloor sediments. The natural seasonal differences and extreme variability in river discharges since the start of the MMP sampling (a few drier years at the start of the program and extreme wet seasons during the past years) is the factor best explaining the changes in water quality. A longer time series will be required to distinguish the influences of land management changes from the high temporal variability in the marine water quality data.

This page summarises one component of the Reef Rescue Marine Monitoring Program (MMP). Information about the whole program and links to other components can be found here.

Methods

The MMP site-specific water quality monitoring in the inshore lagoon has started in 2005 at 14 fixed coral reef sites in four Natural Resource Management Regions (NRM) regions, the Wet Tropics (5 sites), Burdekin (3), Mackay Whitsunday (3) and Fitzroy regions (3). As part of the regular monitoring we collect water samples that are analysed for a comprehensive suite of dissolved and particulate nutrients and carbon, suspended solids, chlorophyll a , temperature and salinity. We also use sensors with data logging capacity for continuous measurements of temperature, chlorophyll a and turbidity. Sampling of the longest available time series of water quality data for the Great Barrier Reef (GBR) (since 1989) has also continued at 6 sites in coastal waters between Cape Tribulation and Cairns.

 

Figure 1. The map shows a summary of the inshore water quality monitoring and coral reef monitoring. This map is downloadable as a KMZ. This layer shows three main datasets:

  • Turbidity and chlorophyll from 2007-2013, measured by water quality loggers.
  • Nutrient data (particulate nitrogen, particulate phosphorus, suspended solids, Secchi depth) from 2005-2013, gathered by direct water sampling.
  • Cover of hard coral, soft coral and macroalgae from 2005-2013.

To identify areas/sites with potential water quality issues, we developed a simple water quality index to generate an overall assessment of water quality at each of the 20 water quality sampling locations (Figure 1). The index is based on all available data to June 2013 using four-year running means and includes a scaling step in the comparison to the GBR Water Quality Guidelines (GBRMPA 2010). The index aggregates scores given to four indicators/indicator groups:

  1. A combined score for suspended solids concentration in water samples; Secchi depth; and turbidity measurements by FLNTUSB instruments, where available.
  2. Chlorophyll a concentration in water samples;
  3. Particulate nitrogen concentrations in water samples;
  4. Particulate phosphorus concentrations in water samples.

These scores were converted into a “traffic light” colour scheme for reporting the status of inshore water quality (see Figure 2), consistent with other marine condition reporting under the Paddock to Reef Monitoring, Modelling and Reporting Program and colours reflect the status of water quality: red (very poor), orange (poor), yellow (moderate), light green (good), dark green (very good).

Key results

The site-specific monitoring has been effective in identifying regional hotspots of impaired water quality. In the summary assessment for 2009 to 2013, the water quality index is overall ‘very good’ or ‘good’ in the Wet Tropics and Burdekin Regions, while a steady decline in water quality is found in the Mackay Whitsunday Region reaching a moderate index score and in the Fitzroy Region the water quality is variable but still reaches a score of ‘good’.

Fig 2 Water Quality Index

The monitoring data show increases in mean turbidity and concentrations of suspended solids, chlorophyll and nutrients, both dissolved and particulate, and declines in Secchi depth that correspond to increased river flow in all regions. This is particularly pronounced at reef sites which are close to the coast and frequently exposed to riverine flood plumes. The increased turbidity and suspended solids concentrations during the high-flow years of ~2008-2012 led to an increased supply of fine sediment to the reef substratum.

An example of the variability of the water quality variables turbidity and chlorophyll over short time periods is shown in Figure 3 using data collected at Snapper North in the Wet Tropics NRM region. Note the higher turbidity values following high river discharge events.

Fig 3 Time Series Chlorophyll Turbidity

Management of coastal water quality in the GBR region is undertaken at the ecosystem-scale, along the catchment-to-reef continuum. However, the impacts of land runoff have to be considered as part of global change and we need to better understand the complex responses and thresholds of coastal ecosystems, especially in interaction with other anthropogenic pressures on the coastal zone and with climate change. The success of the Reef Plan, the investments under Reef Rescue to improve land management and the legislated agricultural regulation under the Reef Protection Package is being assessed by the Paddock to Reef Program. As part of this overarching program, the Reef Rescue MMP focuses on measuring and assessing the condition of the receiving waters adjacent to the GBR catchments. The detection of trends following management intervention on the catchment could take years to decades as improved land management practices will take many years to become effective in reducing pollutant loads at the end of catchment. Ongoing and consistent monitoring is particularly crucial in complex systems such as the inshore GBR lagoon, which is influenced by a range of factors other than land runoff, to be able to show that the marine impacts of increased loads of nutrients, sediments and pesticides will be reversed when the loads are reduced.

Reports from this project

These reports cover the work of this project in detail:

AttachmentSize
gbr-aims-wq-feb-2012.kmz217.91 KB

Photos