Nitrogen is essential to help plants and animals grow, and is also known as a nutrient.
Excess nitrogen can create significant problems when it enters waterways where it can cause excessive algae and aquatic plant growth, and contaminate drinking water.
Nitrogen can enter waterways from a range of sources including industrial discharges, wastewater treatment plants, leaky septic systems, fertiliser run-off from pasture and crop paddocks, and run-off from animal manure/urine.
The biggest source of nitrogen in New Zealand’s waterways is urine from farm animals. Urine contains urea which is rich in nitrogen. While urine can act as an economical fertiliser, it's concentrated in small patches, and too much can mean that grass can’t grow fast enough to take up all the nitrogen, particularly in winter. The excess nitrogen seeps down into groundwater or washes off the paddock into streams or through the soil and drains. Lost nitrogen fertiliser is a much smaller source of nitrogen in freshwater than urine.
Effect on people and our environment
Nitrogen can also contaminate drinking water, causing serious illness, and posing severe risk to some people including infants and the elderly. It can also pose a risk to pets and stock.
Both common forms of nitrogen in water – nitrate and ammonia – cause problems. Nitrate can kill sensitive organisms like young fish species. Ammonia is highly toxic to fish and other creatures that live in water, so direct discharge of ammonia-rich wastes such as raw sewage or dairy shed effluent can be particularly damaging.
Excess nitrogen in waterways also causes damage to ecosystems by promoting the overgrowth of large plants called macrophytes, and tiny algae called periphyton and phytoplankton.
The result is that excessive plant growth can lead to dramatic drops in oxygen levels, leaving fish and other aquatic creatures unable to breathe.
We test monthly for the two forms of nitrogen that get into water (nitrates & ammonia) at a number of groundwater bores, and surface water sites (rivers, streams, lakes) around Southland.
Environment Southland has completed scientific modelling, using the latest information and data, to better understand the gap between where our water quality is now and where it needs to be to meet our goals for improved freshwater quality - the Murihiku Southland draft freshwater objectives.
Several modelling studies have been undertaken to predict (estimate) the size of load reductions needed to achieve the objectives related to nitrogen in rivers, lakes and estuaries.
The estimated reduction in nitrogen load to achieve the national bottom lines is 47%. To achieve the proposed Southland Water and Land Plan standards the reduction required is 66%, and to achieve the draft Murihiku Southland freshwater objectives it is 70%.
Read the report here > Report - Nutrient load reduction modelling - lakes, rivers, estuaries (LWP) (PDF, 3.3MB)
There are a number of things you can do to take action. Find out more about what you can do.
Table of load reductions needed for each of the reporting catchments to meet the Murihiku Southland draft freshwater objectives:
Total Nitrogen reduction (%)
Waiau Catchment (Waiau Estuary)
Te Waewae Bay Western Coastal Zone
Aparima & Pourakino Catchment (Jacobs River Estuary)
Waimatuku & Taunamau Catchments
Orepuki Coastal Zone
Bluff Zone (Bluff Harbour & Awarua Bay)
Ōreti & Invercargill Catchments (New River Estuary)
Waituna Catchments (Waituna Lagoon)
Matāura Catchments (Toetoes Estuary)
Tokanui Coastal Zone
Waikawa Catchment (Waikawa Harbour)
Catlins (Longbeach) Zone
This modelling analysis helps to build our understanding. Before any decisions on limits and actions are made, we’ll need to consider the social, economic, and cultural impacts of any decisions and work our way back if those impacts are too significant.
There is work being completed for on-farm mitigations and how far they will take us to achieving these reductions. It’s clear that adoption of on-farm mitigations won’t get us all the way to where we need to be, but they are a good place to start and provide for a strong foundation.
We’re looking at how we can build on many of the good initiatives already underway and support new technologies and innovation.
Closing the gap is a big challenge and will take time. We’re keen to hear from you and to understand how we can support you to take action.
For more information go to the environmental challenges page.