Lakes380 – what does the data tell us?

Lakes380 – Our lakes’ health: past, present, future is the largest scientific study ever undertaken on lakes in Aotearoa New Zealand. The programme, jointly led by GNS Science and Cawthron Institute, has sampled around 10% of the 3,800 lakes larger than 1 hectare – about the size of a rugby field. The researchers have taken water, surface sediment and sediment cores from lakes across the motu (country) and are analysing the material contained in the samples. The aim of the study is to gain an understanding of the current and historical health of our lakes.

Sediment cores tell a story

Sediments are the fragments of inorganic materials like sand, soil or residue from volcanic eruptions and organic materials like plant remains that are carried and deposited by wind, water or ice. Over the years, layer after layer of sediment builds up, trapping and preserving pollen, leaves, wood and inorganic materials. This process can happen over hundreds to thousands of years.

Sediment cores taken from the lakebed are split and sampled for pollen, aquatic animal remains, microscopic algae and environmental DNA from things that once lived in or near the lake. Pieces of organic matter are removed from the sediment for radiocarbon analysis to determine the age of the layers of mud in the sediment core. This information, along with high-resolution scans, provides evidence of change caused by volcanic eruptions, landslides, climate change or other natural events. It also provides evidence of changes caused by human habitation in the lake catchment – for example, deforestation and changes to farmland.

Te ao tuatahi – the land before human arrivals

Some of the sediment cores provide information from a very long time ago. Skelton Lakes are alpine lakes high up in the Garvie Mountain Range of Southland. Scientists have been able to sample pollen and algae dating back around 4,000 years! The lakes are above the treeline, but the sediments show that the valleys below the lakes were initially covered with podocarps (especially mataī) and smaller trees such as mountain toatoa with beech trees slowly becoming established.

Human settlement

There are several clues as to when humans settled in a lake catchment. These clues, along with mātauranga and oral histories, are often used as evidence of Māori settlement.

The clues, known as proxies, include charcoal, algae and pollen spores. Charcoal, which is produced from fires, becomes more evident due to human use. Freshwater algae naturally occur in lake systems. Shifts in algal communities and their abundance indicate changes that happened within the lake catchment.

The third proxy is pollen. Many plants produce and spread pollen grains as part of their reproductive process. The types and abundance of pollen can be used to determine how the plants within and around a lake have changed.

Evidence of Māori settlement is marked by a noticeable increase in pollen from bracken fern. Bracken fern is commonly associated with landscape disturbance – it is one of the first plants to appear when land has been burned to reduce forests. Further evidence of land-use change is seen with the arrival of European settlers. In many of the lowland and coastal lake catchments, forests were reduced to create pastures and plantations of non-native trees like pines. Pollen samples from these lake environments reflect the monoculture of pasture grass or pine species.

The evidence of change provided by charcoal, algae and pollen samples from lake sediment cores is clearly seen in the graphic of Lake Moawhitu, pictured below.

Diversity of lakes and lake conditions

For a small country, Aotearoa has an amazing diversity of lakes. The country’s unique geography is responsible for this diversity, and it’s also helping to protect lots of our lakes. Many of the alpine and highland lakes are in locations that are difficult to access. Although sediment cores show evidence of human settlements in the wider regions, a good number of these lakes continue to be surrounded by native forest and are in pristine condition.

Lowland and coastal lakes – like Moawhitu – are often in poorer condition than high country or alpine lakes. These lakes are often shallow and are located in catchment areas modified for agriculture or urban developments. Nutrient (nitrogen and phosphorus) leaching causes excessive algal growth, which can deplete oxygen in the lake water. Poor water quality directly impacts aquatic life, native fish populations, mahinga kai practices and more.

Lakes380 datasets – public resources for local and global use

Fortunately, scientists no longer have to guess about the conditions of many of the lakes in Aotearoa New Zealand. The Lakes380 project is providing data about a selection of lakes from across the North Island, South Island and Chatham Islands, with a mix of lowland, high country and alpine locations. The data will be useful to identify lakes in need of protection and to help set realistic and attainable aspirations when working to restore water quality. The Lakes380 datasets will become public resources for everyone in Aotearoa New Zealand and the global scientific community.

To see examples of lake data from different areas and altitudes, download the PDFs below:

Coastal lakes

• Lake Moawhitu – Marlborough
• Tomahawk Lagoon – Otago

Lowland lakes

• Lake Kahuparere – Northland
• Lake Pupuke – Auckland
• Lake Wiritoa – Manawatū Whanganui
• Lake Ōkataina – Bay of Plenty
• Lake Kāurupātaka – West Coast

Highland lakes

• Kaweka/Kuripapango Lakes – Hawke’s Bay
• Lake Marion – Canterbury
• Ōtūroto (Lake Heron) – Canterbury

Alpine lakes

• Lake McRae – Marlborough
• Skelton Lake – Southland
• Lake Bright – Southland