Environment Southland

Water Story

Haere mai and welcome to our new and evolving Water Story. This is a place where you can learn more about how our fresh waterways are doing and what some of the key stresses on them are. We’ll also be sharing and profiling some of the great things that are going on across the region in an effort to help maintain and improve them. We hope you’ll come on this journey with us.

What affects our water?

Ki uta ki tai, from the mountains to the sea – there is a connectedness to our environment. Our actions in one part of the system can have impacts and flow-on effects in another. Water moves through the landscape, above and below, interacting with land, air and us. Every part of its journey shapes it, and so it does with us.

The Southland setting

Freshwater bodies can include lakes, rivers, wetlands, estuaries and groundwater. They are complex systems which affect, and are affected by, the land, air and coastal environments: no two catchments are the same 1.

Did you know?

The Southland region is the second largest in New Zealand, covering over 12% of New Zealand's total land area, at 34,000 square kilometres. Just over half (53%) of Southland is managed as conservation estate, while farmland occupies 85% of the non-conservation land. Approximately 91,000 people live in the region.

Southland contains a large amount of freshwater, both as surface water (e.g. rivers) and groundwater (e.g. aquifers). The region has six of New Zealand's 25 largest lakes (as measured by surface area), including Lakes Te Anau, Manapōuri, and Hauroko (which are also New Zealand's three deepest lakes). There are also tens of thousands of kilometres of rivers and streams. Four major river catchments - the Waiau, Aparima, Ōrerti and Matāura – cover 54% of the region (18,552 square kilometres), with the remainder of the region's area made up of the Fiordland & Islands catchment (including Stewart Island) and smaller coastal catchments.

Before Māori arrival, an estimated 8% (268,500 hectares) of land in Southland was in wetlands and swamps, most of it across the Southern Plains. Wetlands perform a significant cleansing role in the environment and are important connectors between surface and ground water.

Between 1840 and 2015, it is estimated that the area of wetlands on privately owned land reduced by over 96% - from around 220,000 hectares to 8,486 hectares. Between 2007 and 2015, wetlands on private land were further reduced by more than 10% (1,235 hectares).

Historical clearance and altered drainage of land for farming and human occupation has since made the area more prone to erosion, increased water runoff, reduced area of wetlands and riparian habitat, and an increased loss of contaminants to waterways (e.g. sediment, nutrients and micro-organisms). The installation of artificial drainage, e.g. mole and tile or open drains, to enable farming has often led to direct channels (or pathways) for losses of nutrients to enter surface water, bypassing some restorative, natural processes.

Southland's water and land is highly connected. This environment has influenced the development of agriculture and forestry and, in turn, has been altered by the expansion of these sectors: agriculture and primary production being the main contributors to Southland's economy.

Agricultural land use has intensified significantly in recent years, especially through the expansion of dairying in the region. The number of dairy cows has increased 7-fold since the early 2000s. In New Zealand, from 1994 to 2015, sheep numbers decreased 41% while dairy cattle increased by 69%. The largest numbers of dairy cattle are in Waikato (1.76 million), followed by Canterbury (1.25 million) and Southland (0.73 million). Canterbury and Southland had the largest increases in dairy cattle numbers from 1994 to 2015, with Southland having the largest increase overall by percentage, seeing dairy cattle numbers rise by about 539% (StatsNZ2).

Key sources of strain on our freshwater bodies

Many things can impact negatively on our freshwater systems, from pest plants to physical modifications such as river straightening. The main issues affecting our water quality, however, have come from land use; with nutrients (nitrogen and phosphorus), fine sediment, and disease-causing micro-organisms (referred to as microbes) having had the most impact 3.

Southland physiographic zones

To better understand how contaminants move through Southland's landscape, explore Southland's physiographic zones.

The activities we do on the land, mainly urban and agricultural activities, can cause excess nutrients and E.coli - a type of bacteria commonly found in the intestines of warm-blooded mammals (including people) and birds – to wash into our water bodies through run-off, or filter through the land into groundwater. Phosphorous often enters surface water attached to sediment.

Urban issues

In urban environments, contaminants enter water bodies mainly through stormwater and wastewater networks, illegal connections to the networks, and leaky pipes, pumps, and connections.

Before wastewater became reticulated, water quality issues were more visible for towns on poorly drained land than towns on medium to well drained land. Where land is poorly drained, wastewater can pond and flow towards surface water bodies (rivers, lakes, streams and estuaries). Where land is well drained, wastewater flows downwards to groundwater. With the effects of wastewater on surface water being more visible, smaller towns on poorly drained soils tended to have a wastewater scheme earlier than similar towns on medium to well-drained soils.

There are now a range of different wastewater situations across the region. The wastewater schemes of some towns have aging infrastructure and capacity issues, while other towns have received either new systems or upgrades (e.g. Browns, Wyndham, Edendale, Gore and Invercargill). There are also towns that have declining populations and could face difficult decisions about their levels of service in the future. A number of towns (e.g. Mossburn, Athol, and Waikaia) do not have a wastewater scheme, with residents relying on on-site treatment systems. A few towns, particularly Te Anau, have seasonal variations in population that places greater pressure on their scheme at different times of the year.

Rural issues

Nitrogen losses from forestry vary depending on the history of the land, management of the forest, and time since planting. Forestry operations can expose soil and increase losses of suspended sediment, particularly during afforestation and harvesting. During these times, shrub clearance, loosening of soil and infrastructure works can make the soil vulnerable to erosion from rainfall and wind, and increase the risk of large sediment loads to enter waterways. Trees also use a lot of water for growth. They can also change the hydrology of a catchment through the harvest residue or 'slash' being washed in to waterways and damming or restricting the flow. This can lead to downstream problems; for example, the risk of flood or problems at the source (turbulence, high velocities or hidden obstacles underwater).

In agricultural areas, nutrients and pathogens (organisms that can cause disease) come from animal waste and urine, and fertilisers. Since the late 1970s, agricultural practices have intensified in some areas of New Zealand, indicated by higher stocking rates and yields, increased use of fertiliser, pesticides, and food stocks, and moves to more intensive forms of agriculture, such as dairying. Agricultural land use is the world's greatest contributor to diffuse pollution (run-off from the land or filtration through the soil). However, since diffuse discharges are hard to measure, it is difficult to determine the relationship between specific land use and water quality.

Nutrients occur naturally and are necessary for plants to grow4. However, high nutrient concentrations can result in too much growth of algae in water (this algae is generally periphyton (5.4MB PDF) in rivers and phytoplankton in lakes). Excessive algae in water can decrease oxygen levels, prevent light from penetrating water, and change the composition of freshwater plant and animal species that live there. High concentrations of nitrogen can be toxic to species and make water unsafe to drink.

Fine sediment is a pervasive contaminant in freshwater environments. It alters the physical condition of stream habitat, by filling in the spaces between stream bed substrates (the underlying layers) and smothering benthic surfaces – the ecological region at the lowest level of a body of water. It can alter stream chemistry and act as a source of nutrients to drive eutrophication - which is when a body of water becomes overly enriched with minerals and nutrients subsequently inducing excessive growth of plants and algae. Eutrophication is a leading cause of damage to many freshwater and coastal marine ecosystems. Fine sediment also makes waterbodies less attractive and less safe for recreation.

1 https://www.es.govt.nz/Document Library/Research and reports/Various reports/Science reports/Urban and Industry Report.pdf .
2 http://archive.stats.govt.nz/browse_for_stats/environment/environmental-reporting-series/environmental-indicators/Home/Land/livestock-numbers/livestock-numbers-archived-19-04-2018.aspx.
3 https://www.es.govt.nz/environment/rivers-lakes-and-streams/Pages/default.aspx.
4 http://www.mfe.govt.nz/sites/default/files/media/Environmental reporting/our-fresh-water-2017_1.pdf (4.4MB PDF).