Evaluating the costs and benefits of agricultural land conversion to wetlands

Nathan Waltham

Led by: Dr Nathan Waltham, JCU


Project Summary

Government (e.g. Major Integrated Projects, MIPs) and private investors (e.g. Kilter Rural Group, WWF, and Greening Australia) are increasingly interested in nitrogen reduction projects, particularly via conversion of land to wetlands. Investing in such projects requires understanding the environmental benefits to be accrued and cost-effectiveness. The best way to provide these data is to evaluate already constructed land-wetland conversion sites that resemble what future projects might look like. This project will collect data from previously completed land-wetland conversion sites, on construction and ongoing maintenance costs, and the water quality and biodiversity benefits. In doing so it will provide explicit data for government and private investors to make informed decisions on future investments of this kind.


Project Publications
Final Report






Project Video


Project Description

Data on the construction and ongoing maintenance costs for wetlands and sediment basins has never been collected systematically, nor in terms of the N cost effectiveness for farmers. This project will overcome a lack of cost and performance relationships for wetland conversion projects by evaluating (cost effectiveness of wetlands per unit present value, expressed in terms of N-removal effectiveness, and biodiversity effectiveness) and synthesising information on costs and outcomes offered to farmers. This will be achieved via on-ground wetland condition assessment (water quality, biodiversity, hydrology), and on-site data collection to quantify the full costs of wetland construction and ongoing maintenance. These data are necessary to inform emerging restoration programs (e.g. Greening Australia, The Nature Conservancy, Kilter Rural Group, WWF and NRM groups), the newly approved Major Integrated Projects (MIPs) in the Wet Tropics and Burdekin regions, and to facilitate market funded investment/trading schemes showing keen interest to invest in water quality improvement restoration projects in GBR catchments.

How Research Addresses the Problem

Year 1 – in the first year the project team will complete a survey and scientifically evaluate the ecological benefits (e.g. water quality efficacy, hydrology and ecological inventory of flora and fauna), and economic costs (cost effectiveness analysis for farm conversions) of five (5) land conversion wetland-based nitrogen management sites (targeting a gradient of wetland sizes, types, connectedness within the water network, and whether historical data exits for comparison – final sites will be chosen between Cairns and Mackay in partnership with NRM groups, industry and government). Research in the first year will immediately achieve two end-user benefits:

  • Qualitative and quantitative data to provide immediate information to inform the government funded MIPs program:
    1. Data Set 1 – In conjunction with NRM groups, landholders and wetland construction contractors, data will be collected on the cost and effectiveness of wetland treatment technologies.
    2. Data Set 2 – As a separate exercise, on-site interviews will be conducted with landholders to record, retrospectively, the nature and timescale of the construction work involved, on-going maintenance requirements for the wetland and cropping performance of the elevated paddock(s). Landholders’ perceptions of the benefits and effectiveness of the constructed wetland and their views on barriers and enablers influencing wetland conversion will also be collected.
    3. Data Set 3 – Ecological condition, water balance and water quality efficacy of land conversion works completed. In addition to water quality (focusing on sedimentation/deposition, nutrients (for example measuring nutrient decay rates), temperature, dissolved oxygen, pH, conductivity – note that pesticides/herbicides are out-of-scope due to the significant budget necessary for analysis), additional condition measures will include vegetation species, weeds/pests, fish, birds, crustacean and turtles. Where appropriate flow gauge data is available, inflow and outflow (water balance) calculations will be estimated. Cultural and Indigenous services will be also captured as part of these data.
  • These data will provide the confidence, both in terms of investment costs (effectiveness) and environmental performance, necessary to attract significant funding from national and international private investor groups for wetland restoration projects in GBR catchments. In addition, during year 1, the project team will generate a data collection (methods) template so that future projects will be able to capture data (economics and environmental) in a consistent and reportable format. These data could be directly uploaded (some care is necessary with commercial confidentially) in a consistent and meaningful way into Queensland WetlandInfo (GIS polygons collected for each wetland in addition to ancillary data such as depth, volume, design, and other distinguishing features important).

Construction costs will be expressed in terms of representative input requirements per hectare of wetland converted (e.g. contractor days with specific plant and equipment requirements). Maintenance costs will be expressed in terms of representative input requirements per hectare per year for each type of maintenance operation (e.g. contractor days with specific equipment requirements for weed management or sediment removal per hectare per year). Economic benefits arising from improved cropping performance of the elevated paddocks will be expressed in terms of representative percentage increases in yield per hectare per year.

Regression-based approaches will be applied to the collated data to develop relationships to predict the different cost and benefit elements as functions of site characteristics. It is possible that costs per hectare will reduce as the total area of wetland converted increases. If so, then representative costings will be estimated across a range of wetland sizes. Economic costs and benefits will be converted into monetary values using current pricing and net revenues for the different inputs and for production output. Environmental benefits will be expressed in relevant physical outcomes per hectare per year (e.g. kg DIN per removed hectare per year)

Year 2 and 3 – An inventory of technical reports and data from previously completed drainage works, wetland construction and cost effectiveness will be completed across the study area. These data will be sourced from reports generated from farmer project sites through to major programs (e.g. SIIP), which will then be collated, evaluated and spatially mapped. This will be completed by firstly collating all relevant available consultancy reports, government documents and background information generated, and creating a single data repository. These reports will then be used to produce a synthesis of the information. The assembled inventory and subsequent analyses of these data (e.g. multi-dimensional scaling and regressions) will then serve to develop relationships to predict different cost elements as a function of site characteristics, and potentially then expected land conversion wetland-based nitrogen management benefits for future projects.  Finally, these data will be mapped spatially and collated for uploading into WetlandInfo (Queensland Government).

In addition, we will continue to expand the farm on-ground surveys (following our established methods proposed in Year 1, step 1 a-c). By expanding field surveys, and working with the Queensland Government catchment modelling group, we will build a solid data set around the understanding of wetlands and sediment basins, in addition to providing ecological function/benefits, cultural value and N cost-effectiveness for farmers. The federal government wetlands section has also indicated a strong need for these data to assist with future investment in restoration and water quality projects in the GBR catchments.


Linkage with other policy, management recovery plans and strategies

This project has linkages with:

  • Wet Tropics Major Infrastructure Project program;
  • Greening Australia Reef Aid program;
  • Reef 2050 – Long Term Sustainability Plan – 1) Target EHT3 – There is no net loss of the extent, and a net improvement in the condition, of natural wetlands and riparian vegetation that contribute to Reef resilience and ecosystem health; 2) Target WQT2 – There is no net loss of the extent, and an improvement in the ecological processes and environmental values, of natural wetland;
  • Reef Plan 2013 – Long Term Goal – Land and Catchment Management targets 2018 – There is no net loss of the extent, and an improvement in the ecological processes and environmental values, of natural wetlands;
  • Queensland Wetland Program Strategy – Phase 2 Strategic Management Plan (May 2013);
  • Advance Queensland funding (GBR wetland biogeochemical process of nutrients – lead by Dr F Adame);
  • Water quality improvement, system repair, land use management and species conservation needs outlined in the Wet Tropics WQIP (2015-2020);
  • Queensland Regional Natural Resource Management Investment program 2016-2017;
  • Great Barrier Reef Water Science Taskforce (May 2016) – key recommendation Monitoring, modelling, evaluation and reporting for improved decision making and adaptive management;
  • Queensland Regional Natural Resource Management Investment program: 2016-17. Landscape Resilience – Improving coastal wetland ecosystems through improved understanding of best irrigation management practice in the Lower Burdekin;
  • Addresses water quality, system repair and coastal ecosystem health concerns raised during the recent rounds of “Walking the landscape” facilitated by the Queensland Government Wetlands program

Linkage to other NESP projects

  • NESP Marine Biodiversity Hub (Project B4) – Underpinning the repair and conservation of Australia’s threatened coastal –marine habitats (Completed 2016)
  • NESP Tropical Water Quality Hub (Project 2.2) A tradable permit scheme for cost effective reduction of nitrogen runoff in the sugarcane catchments of the Great Barrier Reef (completed February 2016)
  • NESP Tropical Water Quality Hub (Project 2.1.2) – Framework to transition low-lying cane land to reduce DIN in wet tropic catchments (submitted April 2017)
  • NESP Tropical Water Quality Hub (Project 3.3.2) – Science evaluation of coastal wetland systems repair projects across GBR catchments (completion December 2019)
  • NESP Tropical Water Quality Hub (Project 3.1.6) Exploring trading in water quality credits as a cost-effective approach for managing water quality in the Great Barrier Reef (completion December 2018).
  • NESP Tropical Water Quality Hub (Project 4.8) Project 25 farmers, water quality, and on-farm decision making

Linkage to on-ground action and practice change

This project in the first year will complete a case study of five farm locations which have constructed wetland/sediment basins for water treatment. These sites will be inspected, and farmers will be interviewed to understand the full lifecycle costs of drainage works, associated farming practices and operating costs. Data (water quality, habitat, vegetation, fauna, hydrology) will be collected to construct an inventory of the ecological condition of the drainage works (including constructed wetlands). The first year deliverables will include a methods proforma to capture ecological and economic data using consistent, rigorous methodologies. This methodology will provide a means for MIPs project sites to capture data, consistently, for the purposes of reporting and increasing our learnings and capacity more broadly. In addition, collection of these data could be useful in pollutant export models, as undertaken by the Department of Natural Resources and Mines. In addition, Commonwealth Environmental Water Office has expressed the need for these data to not only examine the return on wetland-land conversion investment, but to provide the department with a tool (data) to assess the likely cost effectiveness of future investment in wetland construction and systems repair.

Overall this project has direct linkage with a farm enhancement project being planned with WWF, Green Fleet, and Queensland Trust for Nature by providing a clearer indication of the direct and indirect benefits (environmental and economic). Data from this project is also likely to be beneficial for another funded project through the Reef Trust that involves The Nature Conservancy and the Kilter Rural Group (Victorian financial services) that are looking for investment projects in the GBR catchment – feasibility study for this project is currently being undertaken with Reef Trust funding (due late September 2017).


NESP 2017 Research Priority Alignment

This project aligns with the NESP 2017 Research Priorities under Themes 1 and 2, namely;

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

  • Develop practical improvements to land management practices that will influence behavioural change and improve outcomes for tropical water quality and ecosystem health.

Theme 2: Maximise the resilience of vulnerable species by reducing other pressures, including poor water quality.

  • Identify practical management actions capable of protecting and improving water quality on the Great Barrier Reef.


Project Keywords

Wetland-based nitrogen management; Private investors markets; Dissolved inorganic nitrogen; Wetlands ; Systems repair.


Project Funding

This project is jointly funded through JCU, GU, Queensland Government (EHP), Queensland Trust for Nature and the Australian Government’s National Environmental Science Program.