Students help restore mauri to the Oruarangi Stream

An industrial purple dye spill devastated the Oruarangi Stream ecosystem in 2013. It’s hard to believe such an event could have a positive outcome, but it was the inspiration behind a Participatory Science Platform project involving students from Aorere College, Makaurau Marae, Wai Care, NIWA and Ngā Pae o te Māramatanga.Together, they are working to restore mauri to the local awa (stream).

The project is a mix of science and local history and has become the stepping stone for further citizen science projects in the South Auckland community.

Oruarangi Stream – an awa of local significance

Oruarangi Stream holds special significance to local iwi. Their papakāinga is Auckland’s oldest settlement. The stream was an important link to the Manukau Harbour – providing both food and navigation. The Mangere Wastewater Treatment Plant disrupted the stream’s flow for 40 years. Upgrades to the treatment plant in 1998 once again connected the stream to the harbour, and Makaurau Marae members worked to clean up and restore the stream. (Read about the history of this area in the article Ihumātao – past and present.)

In 2013, more than 1,000 litres of methyl violet dye spilled into a local catchment pit and was carried through the Oruarangi Stream. The effect on freshwater and sea life was devastating. But there is a silver lining to this tragedy.

Restoring mauri to Oruarangi Stream

In 2015, year 9 students from Aorere College teamed up with youth and elders from Makaurau Marae. They learned about the local history and stories associated with the stream. Armed with a better understanding of the link between people and place, the group worked to learn about and help restore the stream’s ecosystems. Science experts from Wai Care and NIWA guided students as they investigated water-quality testing, species diversity and ecosystems and what they can do to improve them.

Water-quality monitoring protocols

A range of standard water-quality indicators are measured on site. Physical factors include water clarity, pH, temperature and streambed type. Biological factors include micro and macroinvertebrates, plants and larger animals. Water and streambed substrate samples are often collected for off-site analysis.

Water clarity

Water clarity is an important indicator of stream health. Just like plants growing on land, aquatic plants need sunlight to grow. Aquatic plants provide food and protection for other species. Plants also produce oxygen. Stream water can become cloudy (turbid) with sediments from erosion, run-off or algae. Turbidity blocks sunlight and limits plant growth and the oxygen that plants produce. Sediments in the water also absorb heat, raising the water temperature and reducing dissolved oxygen supplies. Sediment can block the gills of aquatic animals.

pH

pH measures the acidity or alkalinity of the water. A pH of 7.0 is considered neutral. The optimal pH for many aquatic species is between 7.0 and 9.0.

Vegetation and geology can influence stream pH. Accidental spills or run-off alter pH. For example, higher than usual alkaline readings indicate an excess of lime fertiliser or detergents, both of which may cause unwanted plant growth.

Temperature

Water temperature is mostly determined by weather, but there are land-use practices that influence temperature. Macroinvertebrates – an important part of aquatic food webs – tend to prefer cool, fast-running water. Streamside vegetation provides shade and helps to keep water cool. Removing vegetation and damming waterways, which slows or reduces water flows, can cause water to warm.

Substrate

The streambed substrate (soft or hard bottom) influences the types of organisms that live in a stream. Soft-bottomed, muddy streams often have a slower flow and more plants. Stony, gravelly, hard bottoms usually have faster flows and support a more varied invertebrate community. Changes to a stream’s substrate will affect the ecosystem it supports.

Biological monitoring

Macroinvertebrates are used to assess water quality. They are easily collected in most aquatic environments. Some species, like mayflies and caddisflies, are sensitive to physical and chemical changes to their habitat. They are called indicator species because their presence or absence is an indicator of water quality. These species like cold, rushing water so they are harder to find in slow-moving streams in warmer areas, even if the water quality is considered to be good. Macroinvertebrates are affected by decreases in oxygen levels as well as by pH, temperature and substrate changes.

Macroinvertebrates are part of aquatic food webs that include larger species like eels, fish and birds.

Community outcomes

The project established more than just baseline data from which to judge water quality in the Oruarangi Stream. The students learned scientific protocols in a relevant and meaningful context. Strong personal links developed between students, the marae community and science professionals. The timeline River investigations and the nature of science documents many of these moments.

Makaurau Marae hopes to continue with the project, bringing in new students each year to collect and compare data, monitor changes to water quality and species diversity and continue with the restoration of mauri to their awa.

Mauri is an integral part of being Māori. Dr Kepa Morgan established a 'mauri model' in order to aid environmental workers and iwi in their work to determine environmental impacts and solutions in situations like water contamination.