The problem with our water
There’s been a lot of talk lately about land use change and its impact on water quality in Southland. However, do we have any evidence that water quality is actually declining? The short answer is “yes”. Scientific monitoring and investigations confirm that Southland has both water quality and quantity issues.
To better understand why our region’s water quality is an issue today, we need to have a brief look at how our landscape has changed, particularly over the past 30 years or so.
Southland was colonised relatively early in New Zealand’s history and has undergone a dramatic change in vegetation cover over the past 150 years. From the 1860s to the late 1900s, European settlers and their descendants converted about 43% of mainland Southland to pasture and forestry, resulting in the dramatic loss of native vegetation.
The changing face of farming – the last 30 years
By 1985 agricultural expansion into undeveloped areas had largely stopped. However, how we have used agricultural land has changed significantly over recent years. For example, the biggest land use change over the past 30 years has been the conversion of sheep and beef farms to dairy.
The 1990s saw the start of dramatic changes to farming in Southland. Cheap land prices and rising international prices for dairy products resulted in the rapid conversion of sheep and beef farms to dairy. In 2010/11, the average South land herd size was 555 cows – over four times that before the 1990s ‘boom’.
How does this change affect our water?
Intensive agriculture has put our natural systems under a pressure that they’ve never had to cope with before. Environmental pressures from these land use changes can be severe. The large scale loss of indigenous vegetation across the region has accelerated erosion processes, reduced biodiversity and led to the increased sedimentation of the region’s water bodies.
The recent shift to high nutrient loss, intensive land uses such as dairying, winter cropping and intensive beef and sheep farming has meant that we are seeing significant declines in soil and water quality across the region.
What’s polluting the water?
- In Southland there are three main issues that affect water quality:Sediment (e.g. mud and silt) – accumulates on the bottom of our rivers, lakes and estuaries. It is a problem because it can make the water murky, block fish gills, smother the habitat that macroinvertebrates and fish live in and promote slime algae growth. Sediment can come from heavy rainfall, disturbance of the riverbed or bank by heavy machinery or through direct discharges
- Nutrients – particularly Nitrogen (N) and Phosphorus (P), which are needed by all plants to grow. These nutrients typically come from stock urine/dung or fertiliser. However, too much N and/or P in our waterways causes problems with excess slime algae and aquatic plant growth.
- Bacteria (e.g. E.coli) – faecal bacteria including E.coli are an indication of potentially disease-causing organisms that can make humans and animals sick.
Our ongoing monitoring programme aims to better understand long-term trends in water quality, where contaminants are coming from and how we can best look after the quality of our waterways.
- Go to the Land Air Water Aotearoa (LAWA) website to look at online water quality data for Southland.