Sources, transformations and fate of particulate and dissolved organic carbon – implications for the GBR

Led by: Michele Burford, GU


Project Summary

Organic carbon has traditionally been poorly studied in marine systems, but recent studies suggest that GBR microalgae can utilise organic matter, and that eroded soil carbon parameters can ameliorate marine algal responses to catchment nutrients. This suggests that organic carbon may play an important role in marine ecosystems than previously thought. Additionally, GBR organic carbon concentrations are increasing, but the mechanisms are unclear. The proposed study would review the literature, develop a conceptual model, and undertake data analysis on organic carbon in the GBR and catchments, and examine links to ecosystem effects. This will improve monitoring and management of water quality in the GBR.


Project Description

A recent water quality monitoring report on the GBR inshore waters identified an increase in both particulate and dissolved organic carbon (POC, DOC) over time at a broad range of sites across the GBR (Fig. 1, Lonborg et al. 2016). The reasons for the increase are unclear. POC can have either terrestrial or marine origins. Terrestrial sources include soils, plant detritus, and other organic material. Marine sources are typically dominated by living algae or marine snow, which may be a mixture of algae, bacteria and detritus. DOC is a complex array of molecules, some of which are readily utilized by bacteria and microalgae (Lonborg et al. in press), and others which are not easily accessed to micro-organisms or may inhibit growth (e.g. Neilen et al. 2017). Additionally, breakdown of organic carbon by bacteria can reduce oxygen levels, causing hypoxia with flow-on effects to fish and other animal species, e.g. Wong et al. (2011). Terrestrial DOC is typically leached from soils and vegetation, while marine sources come from algal leakage, animal excretion products, and breakdown of organic matter originating from algae, bacteria and other organisms.

A recent study by Qld DSITI and Griffith University found that the effect of fine sediment from GBR catchments on marine algal photosynthesis can be more accurately estimated using measures of soil nitrogen and organic carbon, rather than nitrogen alone (Garzon-Garcia et al. 2017). This suggests that organic carbon may play a mediating role in facilitating nitrogen bioavailability for algae. A recent study by Lonborg et al. (2017) also showed that organic compounds (which typically contain carbon, nitrogen and phosphorus) can play a major role in contributing the nutrient requirements of microalgae in the GBR, although the sources were unclear. The sources, transformations and fate of organic carbon in aquatic systems is complex. This combined with the limited global understanding of organic carbon processes in coastal areas makes this a challenging area of research, monitoring, modelling and management.

Therefore the proposed study would undertake a literature review of the latest available information on terrestrial and marine organic matter, and links to marine ecosystem effects. This will utilize information from studies around the world, but with a focus on coastal marine systems that are likely to be most applicable to the GBR. Additionally, the effect of wetland and intertidal areas on affecting organic matter concentrations in coastal systems will also be examined. One of the challenges of studying organic carbon in coastal systems is to differentiate terrestrially-derived from marine-derived carbon. The literature review will also examine if there are techniques for effective differentiation of these two sources, e.g. tracer methods.

With the literature review as a framework, a conceptual model of the complex processes will be developed, and hypotheses set for potential explanations for the increase in organic carbon in the GBR over time. Information will also be gleaned from the existing eReef biogeochemical model (Mark Baird, CSIRO). The existing monitoring data on POC and DOC concentrations in the GBR will be analysed against potential drivers to try and explain the increase in concentrations over time.

The information from the study will be used to inform the future water quality monitoring program, and options for revising this, based on available information on the possible mechanistic links between catchment inputs, organic carbon measures and ecosystem responses. It may be possible to identify concentrations at which POC and DOC have significant impacts on the functioning of GBR ecosystems. Additionally, the study will identify knowledge gaps requiring future research to provide a clearer understanding of the complex role of organic carbon.


Specifically the aims are to:

  1. Undertake a literature review on terrestrial and marine POC and DOC with a focus on sources, transformations and fate in marine systems.
  2. Develop a conceptual model of key processes relating to organic carbon in the GBR, and set hypotheses for testing potential drivers using the existing water quality data
  3. Analyse water quality data from inshore GBR monitoring to determine factors correlating with POC and DOC increases over time
  4. Examine the implications of our current state-of-knowledge of terrestrial and marine POC and DOC for future water quality and ecosystem monitoring and management of the GBR


This study will link with existing programs, i.e. GBR Marine Monitoring Program (MMP) and RIMReP. The MMP was the source of data showing the increase in DOC. Therefore, the project findings may have implications for MMP/RIMReP program design.


The information gained from this study will be used to:

  1. Improve water quality monitoring systems in the GBR
  2. Improve interpretation of organic carbon monitoring data in the GBR
  3. Identify potential causes of trends in organic carbon in the GBR and set hypotheses for further experimental testing

The results from this study will be communicated to all relevant stakeholders in the GBR in the form of a report at the end of the study. Additionally, a summary of the results will be presented at various fora with interested stakeholders at the end of the study. This will include visiting GBRMPA and interested Government departments.



Garzon-Garcia A, Burton J, Moody P, De Hayr R, Franklin H, Burford M. (2017). Sources of Bioavailable Particulate Nutrients: Phase 2. Indicators of the Bioavailability of Particulate Nutrients to Algae in Freshwater and Marine Conditions. Department of Science, Information Technology and Innovation.

Lønborg C, Devlin M, Waterhouse J, Brinkman R, Costello P, da Silva E, Davidson J, Gunn K, Logan M, Petus C, Schaffelke B, Skuza M, Tonin H, Tracey D, Wright M and Zagorskis I (2016). Marine Monitoring Program: Annual Report for inshore water quality monitoring: 2014 to 2015. Report for the Great Barrier Reef Marine Park Authority. Australian Institute of Marine Science and JCU TropWATER, Townsville 229 pp.

Lonborg, C., Alvarex-Salgado, X. A., Duggan, S., Carreira, C. Organic matter bioavailability in tropical coastal waters: The Great Barrier Reef. Limnology and Oceanography, in press

Neilen, A.D. Hawker; D.W., O’Brien, K.R., Burford, M.A. 2017. Phytotoxic effects of terrestrial dissolved organic matter on a freshwater cyanobacteria and green algae species is affected by plant source and DOM chemical composition. Chemosphere, 184, 969-980.

Wong, V.N.L., Johnston, S.G., Burton, E.D., Bush, R.T., Sullivan, L.A., Slavich, P.G. 2011. Anthropogenic forcing of estuarine hypoxic events in sub-tropical catchments: Landscape drivers and biogeochemical processes. Science of the Total Environment 409, 5368–5375.


NESP 2017 Research Priority Alignment

This project aligns with the NESP 2017 Research Priorities under Theme 1:

Theme 1: Improved understanding of the impacts, including cumulative impacts, and pressures on priority freshwater, coastal and marine ecosystems and species

  • Improve our knowledge of cumulative pressures on environmental and social values of the Great Barrier Reef to determine more effective management actions.


Project Keywords

Dissolved organic carbon; Particulate organic carbon; Monitoring; Ecosystem health; Catchments.


Project Funding

This project is jointly funded through GU, JCU and the Australian Government’s National Environmental Science Programme.


Project Publications






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