We often hear the term “diffuse discharge” in regional plans and consent conditions, especially when talking about dairy farming and freshwater quality. But what does it actually mean in practice?
A diffuse discharge is a loss of contaminants into the environment that doesn’t come from a single point such a pipe or outlet. Instead, it occurs across the land surface or through the soil, often gradually and over a wider area.
On dairy farms, this can include:
- Nitrogen leaching from urine patches
- Runoff from paddocks during heavy rain
- Sediment loss from bare or pugged soils
- Nutrients or effluent residues moving across land
- Stock access to streams or drains causing direct inputs into those waterways
What is the difference between a “normal” discharge and a “diffuse” discharge? Here is a table with the main differences:
| NORMAL DISCHARGE | DIFFUSE DISCHARGE |
| – Effluent discharged through an irrigation system – Discharges from a treatment system or pondWater released from a controlled outlet – Clearly defined discharge point – Typically managed through discharge consents | – Not from one single outletInfluenced by rainfall, soil type, and farming practices – Harder to measure directly – Occurs across the land surface or through soil – They are managed through land use controls |
In the Bay of Plenty, diffuse discharges are not typically consented on their own. Instead, they are managed through a combination of Regional Natural Resources Plan (RNRP) rules around land use and freshwater management, conditions attached to land use consents or discharge consents and National policy direction under the National Policy Statement for Freshwater Management (NPS-FM).
The management of Diffuse Discharges are usually focused on reducing nutrient losses (particularly nitrogen and phosphorus), minimising sediment entering waterways, protecting critical source areas and waterways and managing cumulative effects within catchments.
Even though they are harder to “see,” diffuse discharges are a major contributor to:
- Eutrophication (algal growth in waterways)
- Reduced water clarity
- Elevated nutrient levels in groundwater and surface water
- Long-term catchment degradation
What can be done on-farm?
From a practical perspective, diffuse discharges cannot be eliminated entirely, but they can be reduced through good management practices, such as:
- Avoiding grazing on wet or vulnerable soils
- Managing winter grazing carefully and avoiding high-risk areas
- Fencing off waterways and providing alternative stock water
- Improving effluent application timing and soil moisture management
- Identifying and managing critical source areas (where runoff concentrates)
- Maintaining good pasture cover to reduce soil exposure
Overall, managing diffuse discharges is about reducing risk across the whole farm system, rather than controlling a single point of discharge, and making small, consistent changes that improve long-term water quality.
Natalia Zefferino
Environmental Consultant