Dune Lakes Kaitiaki Partnership Project 2024
The dune lakes of Northland are rare and precious ecosystems of national and international importance. Many of them are in excellent condition, but others are slowly degrading and need our help. Most are found on private land, so we work with landowners to help care for them. We also work with the Department of Conservation and District Councils when dune lakes are in their care.
The project is a partnership, with NRC working with iwi and landowners to achieve mutual goals for dune lakes in Te Taitokerau.
Northland’s dune lakes are fragile ecosystems, easily damaged by high nutrient levels and pest fish and plants. We will work with our partners to achieve the vision and goals of iwi, landowners and the public for these special places. We will improve water quality and the habitat of Threatened and At-Risk species through a range of workstreams that specifically target threats to the lakes and the creatures that call them home.
We will:
- Collaborate with tangata whenua, landowners and other partners
- Protect Threatened and At-Risk species that live in and around lakes
- Survey for and eradicate pest plants in and around lakes
- Exclude stock through fencing
- Remove pines and replant with natives
- Remedy nutrient and sediment inputs
- Improve water quality in dune lakes
We will ask our project partners what they want for their dune lakes, and we’ll write up a plan with them that incorporates their vision for improved lake health. NRC will support the implementation of these plans with staff time and resources.
There are around 30 Threatened and 40 At Risk species that live in or around dune lakes in Te Taitokerau, including native freshwater plants, fish and insects. We will monitor these species to understand their population distribution and to find ways to improve their status and prevent their decline.
Surveillance for pest plants will be carried out in four of our High Value lakes that have public access. The main vector of weed spread between waterbodies is by people using them, so these lakes have a higher risk of new weed incursions. We need to be able to treat any new infestations fast, if they occur.
NRC has been treating several lakes to kill hornwort (Ceratophyllum demersum). The results are promising, with major reductions of hornwort. We have also reduced egeria (Egeria densa) in another lake. However, our goal is eradication, so more work will be done in the summer of 2024-2025 to assess progress and see if more treatments are required.
Hornwort (Ceratophyllum demersum) - an exotic water weed we will control in Northland lakes.
A range of weed removal options have been used in Northland previously, including mechanical removal, biological control (grass carp) and treating the lakes with targeted herbicides. The most successful long-term option to date is herbicide.
Endothall (Aquathol K) is an herbicide that targets the invasive aquatic weeds Lagarosiphon major and hornwort. It can do so without affecting native plants or fish, as it is broken down into its constituent elements of oxygen, carbon, hydrogen and potassium by microbes in the lake-bed.
In the spring of 2020, Council used Endothall to successfully control Lagarosiphon major in Lake Ngatu. We have surveyed the lake each year since then and the weed has not been seen. We will continue to monitor the lake to check it has been eradicated.
Lagarosiphon is one of the exotic waterweeds we plan to eradicate from Northland lakes. (Photo credit: Trevor Reed).
Hornwort has been controlled in six other water bodies since 2021, using Diquat (Reglone) and Endothall. The weed has been significantly reduced in all cases. We will continue to monitor and control the weed with the aim of eradicating it from these water bodies.
Exotic waterweeds are easily spread unintentionally, by a range of activities such as boating, duck hunting, eel fishing with nets, digger operations and farm drains. The weeds can easily outgrow the native plant community, choking a lake to the point of collapse and resulting in an algal state and with algal blooms becoming frequent.
Algae and cyanobacteria blooms can blanket a lake, smothering the remaining native plants and depleting oxygen, which can kill fish and other aquatic life. A toxic algal bloom can make the water unfit for consumption and/or skin contact by people or animals. Aquatic weeds also affect recreational activities such as boating and swimming.
The weeds grow from fragments, so tiny pieces caught on gear, boats and trailers can be transferred to another unaffected waterbody and grow there.
The best way of protecting lakes and waterways from pests is by preventing them moving around and being introduced to new sites. Once pests have infested a new lake it is expensive to try to control them and not always successful.
You can help stop the spread of weeds and other pests by using the ‘Check, Clean, Dry’ (CCD) method before moving between waterways.
- CHECK all your clothes and equipment and remove any fragments of weeds or algae
- CLEAN all your clothes and equipment that had been in contact with the water
- DRY all your clothes and equipment thoroughly and then wait for at least 48 hours before you use it in another waterbody.
See Check, Clean, Dry to protect our waterways for more information.
Fencing is the most important tool to improve the quality of water in lakes. We work with landowners to support stock-proof fencing around all lakes. All livestock must be effectively excluded from lakes greater than one hectare under the Northland Regional Plan.
See Keeping stock out of waterways for more information.
Dune lakes are usually closed systems, with no or minor inflows and outflows. This means that anything that enters the lake stays there.
Sediment (eroded soil) is an issue when it washes into waterways because it is often phosphorus rich. Too much phosphorus and nitrogen contribute to poor water quality and can produce algal blooms in lakes.
It is estimated that 192 million tonnes of soil are lost from erosion in New Zealand every year, with 44 percent of this from areas in pasture.
Land use intensification, the draining of wetlands and inappropriate land management cause increased levels of erosion. The sediment results in economic, cultural and environmental effects such as:
- reduced soil fertility
- increased impacts from flooding
- infrastructure damage
- algal growth from increased phosphorus
- water turbidity
- smothering of shellfish beds
Best practice sediment reduction takes a two-pronged approach, using in-field action and edge-of-field action:
In-field action will prevent erosion occurring in the first place by binding soil to prevent its mobilisation and reduce rainfall impacts. Actions include:
- increase pasture density,
- spaced tree planting on pasture,
- well-maintained farm tracks and races
- conversion to forestry, native or exotic of highly erodible land.
Edge-of-field measures aim to mitigate erosion that does occur by reducing run-off speed and trapping suspended sediment. Measures include:
- riparian fencing and planting,
- sediment retention infrastructure such as swales, traps and bunds,
- retaining or creating wetlands.
Other benefits of sediment mitigation include the reduction of nitrogen, phosphorus and E. coli, helping to maintain soil health and fertility. Edge-of-field measures also contribute to more effective ecosystem services on-site and off-site, such as flood mitigation and the protection of habitat for native and endangered plants and wildlife.
Best practice land use will lead to reduced sediment and phosphorus reaching lakes in surface water flows. With less nutrients entering the lakes, water clarity is improved or maintained, weed and cyanobacteria growth are reduced, and low-nutrient-need native submerged plants (macrophytes) can recover.
See these web sites for more information:
Water quality in Northland’s dune lakes is, on average, declining. Fifteen dune lakes are monitored for water quality each month and the results can be found at LAWA and NRC’s Environmental Data Hub.
The causes of water quality decline are many, but include stock-access, water runoff with associated nutrients and sediment from surrounding land, drought, storms, exotic pest fish and invasive weeds.
Project work includes eradicating waterweeds such as hornwort, educating the wider community about threats to dune lakes, fencing out stock, replanting riparian margins and reducing the impact of run-off and nutrients getting into lakes. All these actions will improve water quality in the long term.
Contact the Biodiversity Team by:
Freephone: 0800 002 004 | Email: [email protected]