I couldn’t bring myself to give this blog a fancy title. “The State of the Environment” really says it all. These large and comprehensive reports released by the Ministry for the Environment (MfE) about environmental health in New Zealand, come out every 5 years. With the last one released in December 2007, we can expect a new one at the end of this year.
Measuring water quality
To begin with, water quality is measured using key indicators such as:
- Concentrations of nutrients
- Concentrations of bacteria
- Visual clarity
- Water temperature
- Dissolved oxygen
- Richness of invertebrate species in rivers
Today I’m going to focus on nutrient concentrations.
Nutrient concentrations are arguably one of the most significant indicators of ecosystem health, which impact upon many of the other indicators, such as dissolved oxygen concentration.
Nutrients are beneficial for many aquatic plants, however an over abundance of nitrogen and phosphorus especially, may lead to algal blooms and weed growth. Nitrogen and phosphorus enter water ways mainly as a result of fertilization and stock effluent in agricultural catchments.
So what did the 2007 SotE report say about freshwater nutrient concentrations?
Findings for rivers and lakes:
- From 1989- 2003 there was an increase of total nitrogen (TN) and dissolved reactive phosphorus (DRP) from 0.5%-1%. This indicates a long term trend of nutrient enrichment.
- There has been a decrease in total phosphorus (an indicator of poor fertilizing practice), and ammoniacal nitrogen (primarily from sheep and cow effluent). This is likely a result of applying effluent to land, rather than discharging it into waterways.
- Urban streams have the highest levels of nutrient enrichment, followed by agricultural catchments. Median nutrient concentrations for both are higher than the AZNECC upper guidelines for river health.
- This is significant as agricultural and urban land use combined comprise 44% of total catchment land use in New Zealand.
- 75/134 monitored lakes have high- very high nutrient levels. 13% of these are hypertrophic (which means that nutrient levels are extreme, and water quality is very poor). This mainly occurs in shallow lakes, such as Lake Ellismere near Christchurch.
- On a brighter note, our most enriched rivers are still lower than the average level of enrichment of rivers in Europe, USA and Asia.
Monitoring was also carried out to determine groundwater quality. One third of monitored groundwater sites have elevated levels of nitrate, a form of nitrogen which can cause “blue baby syndrome”. This is likely due to leaching through the soils of fertilizer and stock effluent. 5% of sites exceeded the safe level for New Zealand drinking water (11.3 mg per L), especially in the Waikato and Manawatu regions.
How is this explained?
Urban steams were generally found to have the lowest water quality. The main causes of this are bacteria and nutrients leaking from damages sewage pipes, and runoff to streams from contaminated surfaces such as roads. Roads can be covered in particulate pollutants from exhaust emissions, brake linings and tire wear.
Agriculture showed high levels of nutrient concentrations, with TN and DRP showing an increasing trend. Because of a shift from low intensity agriculture (such as sheep farming) to high intensive agriculture (such as dairy farming) in recent years, increased amounts of nutrients and sediment are entering our water ways.
Point sources of pollution (such as water flow from an effluent pipe) have been legislated against under the Resource Management Act 1991, so the current problem is non-point sources, such as overland runoff, and stock in waterways.
What is being done about this?
There are several initiatives underway discussed in the SotE report to improve fresh water quality. These include:
- Support from the Taranaki Regional Council for riparian planting on stream banks in Taranaki. Riparian plants filter water flowing into the waterway, and lower nutrient and sediment levels.
- The Dairying and Clean Streams Accord: This is an agreement signed by Fonterra, local councils and the Ministries for the Environment and for Agriculture and Forestry. It sets targets to exclude stock from waterways, and decrease effluent discharge, amongst others.
- And, the development of a Cultural Health Index for Streams and Waterways (CHI) by Ngāi Tahu, which facilitates water quality monitoring by local iwi.
To conclude, It must be remembered that these statistics and information come from a report released five years ago. It is my hope that the initiatives in place will help to halt the increasing nutrient trends, and if possible begin to lower nutrient concentration in our freshwater.
It is with baited breath that I await the next State of the Environment Report, which will enable us to evaluate the effectiveness of New Zealands strategies to protect this vital resource.