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Life in New Zealand’s Geothermal Environments

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New Zealand’s geothermal activity occurs due to high heat flow in the Earth’s crust along the Pacific – Australasian tectonic plate boundary. Faults and fractures channel heat to the surface creating volcanoes, hot springs, geysers, heated soils, hot streams, and fumaroles.

Champagne Pool at Waiotapu. Photo Credit: GNS Science

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Why are geothermal areas colourful?The brightly coloured rocks and soils in geothermal areas arise in different ways, due to chemicals in the soil and the presence of pigmented microorganisms.

Hot, acidic gases and fluids interact with rock to form colourful clay minerals. For example salmon pink is cinnabar (mercury sulphide), orange is realgar (arsenic sulphide) and yellow to grey colours can be from sulphur-based minerals.

When geothermal water discharges out of a spring or geyser, it cools quickly and forms what is known as a sinter deposit. Pure silica is white, but sinters often contain traces of impurities or microorganisms which produce beautifully coloured forms. Some of the more common colours are pink from iron oxide or microbes, and grey to black, from iron sulfide (pyrite).

Microorganisms inhabit geothermal areas and can survive in very high temperatures. The type of microbes will depend largely on the temperature and the chemical composition of the surrounding water, and each is pigmented differently. At lower temperatures photosynthetic pigments produce blues, reds and greens, while some higher temperature microorganisms have carotenoid pigments that produce pinks, reds, yellows and browns.

What is that smell?That rotten egg smell in geothermal areas is due to hydrogen sulphide gas being released into the atmosphere. Fortunately if you live here, or visit often, you quickly get used to the smell!

The most well-recognised geothermal area in New Zealand is the Taupō Volcanic Zone (TVZ). This is a 100 km wide by 350 km long volcanic region of the central North Island.

Māori legend says that geothermal fields in the central North Island were created when Te Pupu and Te Hoata, goddesses of fire, emerged from the Earth’s core in search of Ngātoroirangi who had been stranded freezing on Mt Tongariro. Wherever they surfaced, they left geysers, hot springs and mud pools, leaving the path of geothermal activity that remains today.

Warm and hot waters are also discharging from springs throughout the country, including Ngawha and Northland, East Cape, the Hauraki and Auckland regions, around Tauranga, and along the Alpine Fault in the South Island such as Hanmer Springs.

Hot spring at Waimangu. The yellow and green colours are associated with photosynthetic microorganisms.

The Taupō Volcanic Zone sits over the subduction zone boundary where the Australasian and Pacific tectonic plates meet.

Photo Credit: Jean Power

New Plymouth

Wellington

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Taupō Volcanic Zone

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IsLANdsoN lANd Geothermal areas are unique habitats and ecosystems that challenge the survival ability of most life forms. Their physical characteristics include high temperatures, steep soil temperature gradients, exposure to steam, highly mineralised soils and waters, extreme pH, infertile soils, and the presence of toxic metals and gases.

Hoani, a hot spring at Tokaanu. Photo Credit: Jean Power

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TERRESTRIAL HABITATS Fumarole margins & warm microclimatesFumaroles are steam and gas vents. Constant steam allows frost-sensitive plants to survive at the fumarole margins.

Heated groundGeothermally heated soils result from heat flowing through the ground that is released at the surface as steam. Ground temperatures (15 cm deep) can range from 40°C to over 100°C. Some flora species such as the prostrate kanuka have evolved very shallow root structures to avoid the heated and acidic soils at deeper soil depths.

Cooled, hydrothermally altered soils Hydrothermally altered soils are often infertile. They have been changed by geothermal steam and become highly acidic, have low amounts of organic matter and phosphorus, and may contain toxic concentrations of metals and trace elements.

What can live in or near heated soils?While microorganisms thrive in extreme temperatures, the hot conditions prohibit any Eukaryotes, including any plant life and most invertebrates (insects), from residing in the hottest thermal areas. However, a complex variety of specialised microorganisms, plants and insects readily colonise areas adjacent to these heated areas.

cradles for early lifeThe unusual food webs in geothermal areas may mimic conditions of the Earth billions of years ago when life originated. It is generally thought that life (primordial microorganisms) began in environments adjacent to geothermal features full of gases and toxic metals!

Geothermal ecosystems have a longitudinal zonation, which means the plant and animal life changes with distance from the heat and geothermal fluid source. This makes these areas small “islands” of unique and specialised species and communities.

AQUATIC HABITATS Hot pools & springsMineral waters journey through heated rocks to discharge naturally at the surface. Temperatures range from 30-100°C and pH from less than 1 (highly acidic) to 10 (highly alkaline). Depending on their chemical composition and gas content, these mineralised waters can be bubbly, salty, acidic, smelly or even flammable!

Geothermal streamsidesMicrohabitats are created where hot and cold waters meet. This allows species, particularly those with tropical origins, to exist in areas that would otherwise be too cold.

What lives in or near Warm Water?Distinctive aquatic flora and fauna occur downstream from thermal springs. Closest to the high temperature water source (>60°C), aquatic communities are dominated exclusively by high-temperature microorganisms (bacteria and archaea). As the water cools downstream (<60°C), a diverse array of algae and fungi appear, and then soft-bodied organisms (invertebrates) begin to occur where temperatures are less than 50°C.

A diverse range of plants grows in this geothermal microhabitat at Waikite.

Fumarole and sinter terraces at Te Puia.

Photo Credit: Jean Power

Photo Credit: Jean Power

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Microorganisms, insects and plants have made geothermal areas their home by adapting to extremes of temperature, acidity and alkalinity, turbidity and toxicity.The unique ecosystem biodiversity is so closely linked to chemical and physical conditions within each niche that community composition can vary between neighbouring hot springs, or even within a single pool or at different soil depths.

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Array of geothermal habitats in a stream at Waimangu. Each colour indicates an environmental niche supporting different microbial life.

Photo Credit: Matthew Stott

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Some species and communities are endemic, that is, they are found only in these habitats and locations.

Where do they come from?Many of the plant, insect and larger species are now uniquely adapted for life in geothermal areas and are exclusively found in these extreme habitats. Other opportunistic species have adapted to tolerate geothermal conditions but are also found in non-geothermal areas.

The distribution and diversity of microorganisms within geothermal areas is thought to be a consequence of:

• physical dispersal by air, water, earth, and animals,

• natural selection to the environmental conditions, and

• beneficial DNA mutation by the species.

the geothermal food Web

Microorganisms are the backbone of the food web in all geothermal ecosystems, but even more so in environments where conditions do not allow photosynthesis. In these cases, microorganisms can use gases, such as methane and hydrogen sulphide, or metals, such as iron or arsenic, as energy sources. Other microorganisms are decomposers, with the ability to recycle nutrients from other organisms’ waste or break down plant material for energy and carbon. In turn, these primary producing microorganisms can be predated by other organisms in the food web.

Grazing insects such as shore flies and midges are found in abundance living and feeding on microbial mats (up to 50°C). Predatory insects live on the cooler edges of hot springs and streams and feed on the larvae and other detritus. The adult geothermal-living insects then become prey for land-based predatory insects and birds.

ANIMALS, BIRDS

PREDATORY INSECTSPARASITIC FLIES

EPHYDRID FLIES

MICROORGANISMS(e.g. ALGAE, FUNGI, BACTERIA, ARCHAEA)

Hot spring at Waimangu. Photo Credit: Jean Power

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exTremophILes Microorganisms are present in almost every environment on earth, including in the heated water-bodies and soils of geothermal environments. As a general definition, microorganisms are any life form that cannot be seen without magnification. Examples of microorganisms can be found in all three kingdoms of life including Eukaryotes (for example protozoa, algae and some fungi), Bacteria and Archaea.

Silica sinters growing at the margin of Champagne Pool, Waiotapu. Photo Credit: Bruce Mountain

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Some microorganisms, primarily bacterial and archaeal species, are the only life forms that survive such harsh conditions. Temperatures can be up to 122°C, the pH can range from highly acidic to strongly alkaline, and there can be elevated concentrations of salts and/or heavy metals. These unique forms of microorganisms are appropriately termed ‘extremophiles’.

Extremes of temperature

Where are they?While the individuals are invisible to the naked eye, these micro-communities can be “seen” in some characteristic features of a geothermal ecosystem.

A distinctive characteristic of algae and cyanobacteria is their ability to form microbial mats and films. Some mats change colour with the season and sunshine hours, being dark green in winter and orange in summer.

In some areas, the silica structures are shaped the way they are due to interaction with the microbial communities. For example, when silica precipitation and microbial mats occur together, the mats are encased in silica forming a spectacular structure.

Many of the pink, yellow and orange colours seen on silica terraces and structures are due to pigmented microorganisms.

microbial community membersMicroorganisms derive energy either via photosynthesis or via the chemical oxidation of organic or inorganic compounds. Photosynthetic microorganisms including algae, cyanobacteria and a small number of other bacterial species are capable of living in geothermal environments, but are limited to temperatures less than 65°C. Conversely, microorganisms generating energy from chemical oxidation processes use gases (e.g. methane or hydrogen), metals (e.g. iron) or organic compounds (e.g. sugars, fats or protein) as energy sources. They can be found at temperatures up to 100°C in New Zealand’s terrestrial environments.

Extremes of pH

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Scanning electron microscope image of thermophilic bacterium Chthonomonoas calidirosea.

Photo Credit: Kevin Lee

Whangapoa, hot spring near Atiamuri.

Photo Credit: Duncan Graham

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INseCTs Few invertebrate species live only in thermal areas. Most are pre-adapted to the high temperatures and low pH, or are found in geothermal waters as temporary visitors. Some proliferate in high abundance because there is less competition and fewer predators.

Chironomus larvae (midge) commonly found in geothermal areas. Photo Credit: Ian Hogg

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The factors regulating distribution are temperature, pH and food availability. Fewer invertebrates occur in close proximity to geothermal areas than in cooler neighbouring areas. The resident communities are also more diverse and abundant where different habitats are available, for example, sinter terraces support less life than areas populated by vegetation.

Invertebrate fauna includes:

• Residents – specialist species found only in geothermal ecosystems that do not occur in neighbouring colder areas.

• Adapters – species also resident in non-geothermal areas that are tolerant of geothermal conditions.

• Migrants - temporary visitors who transit areas influenced by geothermal heat and steam; some regularly, others only in winter.

• Foragers – these predatory insects do not reside in geothermal ecosystems, but visit to raid the carcasses of other invertebrates that have been killed or knocked down by rising steam near hot springs and streams.

Insect larvae living on a microbial mat in a geothermal seep at Ngatamariki.

Fly grazing on geothermal microbial mat.

Diptera (flies) and Coleoptera (beetles) have the greatest tolerance to high temperatures with individuals having been found in waters of up to 55 °C. The most common geothermal specialists are the Ephydridae (the shore fly), chironomid midge (Tanytarsus), the endemic mosquito (Culex rotoruae) larve and the larvae and adults of hydrophilid and dytiscid beetles.

Acclimatised macroinvertebrates include Odonata (damselflies), Chironomus (midges), Hemiptera (swimming bugs) as well as a range of other flies, beetles and a few snails.

acid versus alkaline environmentsAlkali-chloride and/or bicarbonate environments tend to have a community dominated by midges, ephydrid flies and cyanobacteria.

Acid-sulfate and/or chloride waters tend to have communities dominated by Chironomus flies along with various other Diptera flies and diatoms.

Photo Credit: Duncan Graham

Photo Credit: Duncan Graham

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geoThermAL plANts

In New Zealand, geothermal vegetation has been identified as an ecosystem of historically limited extent, and naturally rare, even in pre-human landscapes. Combinations of temperature, chemistry, hydrology, and localised protection from frosts, produce rare and unusual habitats for plants.

Otamakokore geothermal stream flowing from the Te Manaroa spring at Waikite. Photo Credit: Karen Houghton

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Heat flow through the soil is the most important factor in determining the vegetation that can thrive in geothermal areas.

Plants also must tolerate highly acidic soils with little organic material, phosphorus and aluminium, but high concentrations of metals and trace elements, such as arsenic.

Vegetation assemblages at geothermal sites include lichenfield, mossfield, herbfield, fernland, scrub, shrubland, rushland, sedgeland, reedland, forest, wetland and open water habitats.

They occur over a wide range of altitudes, from sea level to the summits of the Central North Island volcanoes and Mt Tarawera.

A number of plants found in geothermal sites in New Zealand are listed as threatened or at risk. These include orchids, grasses, ferns and prostrate kanuka.

Prostrate kanuka growing by a geothermal spring at Waimangu; this species dominates geothermally altered and heated soils in New Zealand.

Photo Credit: Julie Deslippe

Dicranopteris linearis (tangle fern) at Karapiti. This tropical fern only survives in New Zealand in warm geothermal areas.

What can i see?Prostrate kanuka only occurs in geothermal habitats. It is low in stature, becoming shorter as soil temperatures increase, and has shallow roots that enable it to survive in geothermal areas. Groundcovers are often a turf of unusual mosses, liverworts, and lichens.

Other species that are usually found only in warmer climates can also survive in the higher temperatures found in geothermal areas.

The constant presence of steam around hot springs, fumaroles and streams allows frost-sensitive species to survive. Some geothermal areas are home to rare tropical ferns and orchids that grow nowhere else in New Zealand.

Some plants that occur in non-geothermal areas can also adapt to tolerate conditions in geothermal habitats. Examples include the low fertility shrublands of mingimingi, manuka and monoao.

Photo Credit: Julie Deslippe

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exTremesurvivAl Geothermal habitats often generally have low biodiversity. There are limited types of species but they can be in a high abundance.The plant, animal and microbial species have evolved characteristics to help them survive in geothermal conditions.

Red pigmented spring at Te Kopia - the colour is due to microoganisms and precipitated iron. Photo Credit: Mathew Stott

Special characteristics of life in geothermal areas include smaller sizes and slower growth rates compared to their non-geothermal counterparts. Some plants have shallower roots and only intermittently flower.

Microorganisms have had to invent new ways of doing things too. For example, thermophilic microorganisms utilise temperature stable enzymes to carry out metabolic functions. Likewise extremophilic microorganisms often synthesise unusual fats to ensure the integrity of their cell membranes to these extreme conditions.

resilience to changeThese geothermal communities need to be resilient to changing environmental conditions.

Hot springs, geysers, mud pots, and fumaroles are dynamic surface features that are sensitive to any changes in their underground water supply.

Geothermal features are easily affected by natural events such as earthquakes and landslides. Man-made impacts also include the development of geothermal power stations and drilling of geothermal bores for domestic and commercial heating.

This can all result in natural changes to temperature, water levels and chemistry.

threatsDevelopment of geothermal fields, land use change and pest invasion have already had an impact on existing geothermal environments.

Extraction of geothermal energy for power generation and heating uses have affected surface activity, changed soil and hot spring temperatures, and resulted in ground subsidence.

Some flora and fauna that do not require the thermal features for their survival, but have learnt to adapt to thermal areas, have become threats to the unique geothermal species.

Additionally, some imported warm-water aquarium species have been released into the environment and now thrive only in warmer geothermal waters, competing with indigenous fauna and flora for resources.

Blackberry (Rubus fruticosus agg.) is a major problem in some areas, as is buddleia (Buddleja davidii), wild introduced conifers and some exotic grasses.

Animal stock and people can trample vegetation when areas are not fenced.

Protection of geothermal areasGeothermal areas are often protected because the geothermal features, fauna and flora are rare and easily damaged.

Five geothermal areas, White Island (Whakaari), Rotorua, Waimangu, Waiotapu and Tongariro, are considered to be of international significance and preservation takes precedence over development in these areas.

Management of geothermal systems aims to balance development activities with the protection of highly-valued surface features and ecosystems.

Landscape immediately following a hydrothermal eruption at Ngatamariki.

Monitoring geothermal environments is an important part of sustainable resource management.

Photo Credit: Bruce Mountain

Photo Credit: GNS Science

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moreiNformAtioN

ACkNowLedgemeNTs

www.1000springs.org.nz

www.gns.cri.nz/extremophiles

www.gns.cri.nz/geothermalecosystems

Geothermal research funding from the New Zealand Government.

FRONT/BACK COVER: Boiling springs at Whakarewarewa.Photo Credit: GNS Science

GNS Science Miscellaneous Series 77, ISBN 978-0-478-19910-9 ISSN 1177-2441 (Print), ISSN 1172-2886 (Online)May 2015