Pathogen Pathways – Soil Risk Index
1. Executive summary
Microbial contamination of water bodies is widespread in New Zealand. Recognising this, the New Zealand Ministry of Agriculture and Forestry established the consortium-based Pathogen Transmission Routes Research Program (PTRRP) to quantify the relative significance of key microbial transmission routes from farm animals to water bodies. The final PTRRP report has been completed.
The purpose of this report, separately funded by the New Zealand Ministry of Agriculture and Forestry, Science Policy Unit, is to focus on models to depict spatially the risk of microbial transport from farm animal excreta and effluent irrigation of animal waste from land to water.
Objective
To present spatial outputs from models describing the relative risk of transport of microbes across and through the land surface from farm animals to waterways, for both the North Island and South Island of New Zealand.
Risk-based approach to assessment
Relative risks of microbial transport associated with:
- Surface runoff
- Bypass flow through soil
- Flow through the vadose zone
are presented spatially. Relative risk associated with surface runoff and bypass flow are combined to present relative risk of microbial contamination of surface water, while relative risk associated with bypass flow and vadose zone transport are combined to present relative risk of microbial contamination of ground water. Maps of optimal riparian buffer strip width based on the final Best Management Practices Report of the PTRRP are also presented.
This report models and spatially predicts the risks associated with transport of microbes from farm animals to waterways for the North and South Island of New Zealand at a maximum scale of 1:50 000.
Conclusions
- In the central North Island and Taranaki regions, soils and vadose zone material derived from tephra have physical properties which minimise the transmission of microbes to water bodies.
- Soils with well-developed soil structure and soils with a drainage impediment both relatively poorly attenuate transmission of microbes through soil.
- Skeletal alluvial soils on gravelly vadose zone material relatively poorly attenuate transmission of microbes to ground water.
- Microbial transport through the vadose zone is poorly understood.
Recommendations
- Vadose zone processes including spatial effects of weathering and temporal wetness characteristics require further investigation.
- Where microbial transport through soil is poorly understood, further investigation is required.
- Information about soils in some soil map polygons, especially those from older soil surveys, requires upgrading.
- Soil map units relating to general soil surveys of the North or South Islands are likely to require upgrading.
Contact for Enquiries
Phil Journeaux
Manager
North Island Regions
Sector Performance Policy
MAF Policy
Private Bag 3123
Hamilton
NEW ZEALAND
Phone: +64 7 957 8313
Fax: +64 7 957 8315
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