top of page
  • Writer's pictureShelby Deegan

Hydroelectricity production could be undoing carbon sequestration in New Zealand

Written By: Shelby Deegan

Edited By: Justin Weir

Hydroelectric power has long been a part of New Zealand's energy grid, powering homes and businesses alike since the late nineteenth century. However, the use of hydroelectric power has recently come under scrutiny — due to its potential to disrupt the natural carbon absorption capacity of fjords in New Zealand.

Samples from deep sediments have been used to find that roughly 20% of New Zealand’s annual emissions are absorbed by fjords (Ewing, 2022). Fjords are formed through a process called glaciation, in which glaciers move very slowly throughout geological time. Throughout Earth’s history, the planet has cycled through different glacial phases. In the transition from a glacial to an interglacial period, glaciers retreat and flow toward the sea. In doing so, deep valleys are eroded and then flooded by the subsequent rising sea levels (Oceana Canada). The resulting valleys are called fjords, containing both saltwater from the ocean and freshwater from upstream rivers, glacial meltwater, and rainfall (Oceana Canada). This unique mixing creates an important habitat for orcas, seals, invertebrates, and cold-water corals (Oceana Canada).

The unique environment of fjords also gives them the ability to sequester large amounts of carbon. They’re often surrounded by lush, forested peaks, making them well-positioned to collect the carbon-rich soils that run off the forested slopes (Deng, 2015). Although fjords are not found in much of the world and account for only about 0.3% of Earth’s surface area, they sequester a disproportionately high 11% of the total carbon absorbed by marine sediment (Deng, 2015). In fact, fjords are burying the largest amount of organic carbon per unit-area in the world (GNS Science).

In New Zealand, fjords are also being used to slow climate change more directly through hydroelectric dams. The Manapōuri Power Station is the largest hydroelectric power station in the country, completed in 1971 (Engineering NZ). It uses a fjord’s natural 178-meter drop to generate hydroelectric power, up to a capacity of 850 megawatts (Engineering NZ). Given New Zealand’s goal to produce the entirety of its energy through renewable sources, more pressure is likely to be placed on the station in the coming years.

Recently, however, it was discovered that the Manapōuri station itself might actually be threatening the fjord’s ability to act as a carbon sink — increasing net emissions in the region (Ewing, 2022). The Manapōuri station generates power by flushing fresh water through a 10km tunnel into the Doubtful Sound fjord; however, this results in oxygenation that could be disrupting the natural burial of carbon (Ewing, 2022).

Fjords make effective carbon sinks because they are characterized by a lack of oxygen, which prevents the decomposition of organic matter (NBC). This results in an accumulation of organic matter on the fjord floor, where it is gradually covered by sediment and locked away for hundreds, or even thousands of years. So, carbon can become isolated and stored for an extensive period of time before it is released into the atmosphere. However, hydroelectric dams can interfere with this process. The turbines and generators required for hydroelectric energy production often draw water from the depths of the fjord, bringing oxygen-rich water down to the fjord floor. Injection of oxygen into the accumulation area alters the sequestration process — leading to a breakdown of the accumulated organic matter, and the release of stored carbon into the atmosphere as CO2 (NBC).

At the same time, the oxygenation of fjords has negative impacts on local ecosystems. The increased oxygen levels cause changes in water chemistry, killing some species and altering the balance of the food chain. This can have cascading effects on the entire ecosystem, affecting not only the plants and animals that live in the fjord, but also those that rely on it.

Recently, a research team from the University of Otago has been granted $8.5 million NZD (~$7.25 million CAD) from the Ministry of Business, Innovation, and Employment’s Endeavour Fund in order to examine how changes in fjord circulation, from both the power station and climate change, will impact the fjord’s ability to sequester carbon (Lewis, 2021). The researchers state that when a certain level of freshwater input is reached, the carbon sequestration of fjords could drastically change, causing a large decrease in the efficiency of carbon absorption, and increasing emissions. The team aims to discover the level at which these detrimental inputs occur, and what happens when these tipping points are crossed (GNS Science). This sort of research is vital for developing and implementing effective environmental management strategies (GNS Science).

Although fjords are a rare geological phenomenon globally, they are also found in Canada (National Geographic Society). As Canada also targets net-zero emissions by 2050, understanding the impacts of hydroelectric power use will be essential, because of the country’s heavy reliance on hydroelectric power. Canadian fjords provide fisheries, eco-tourism, aquaculture, artisanal fishing, and hunting (Oceana Canada). Their health is crucial to many Canadians’ livelihoods, and must be considered when decisions are made surrounding the implementation of hydroelectric power. Despite not being on many Canadians’ radar, the research being done in New Zealand could have profound implications for which kinds of renewable energy Canada should seek to prioritize.



Deng, B. (2015, May 4). Fjords soak up a surprising amount of carbon. Nature News. Retrieved February 9, 2023, from

Ewing, I. (2022, July 5). Manapōuri power station may be undoing fjord's natural carbon absorption. Newshub. Retrieved February 9, 2023, from

Fjord. National Geographic Society. (n.d.). Retrieved February 9, 2023, from

Fjords. Oceana Canada. (2022, October 11). Retrieved February 9, 2023, from

Lewis, J. (2021, September 12). Carbon Sink Research attracts $8.6M funding. Otago Daily Times Online News. Retrieved February 9, 2023, from

Manapouri Power Station. Engineering NZ. (n.d.). Retrieved February 9, 2023, from

NBCUniversal News Group. (2015, May 4). Fjords are unexpected natural allies against climate change: Study. Retrieved February 9, 2023, from

New Zealand fjord sediment records - potential carbon sinks: GNS science: Te Pῡ Ao. GNS Science | Te Pῡ Ao. (n.d.). Retrieved February 9, 2023, from,crucial%20ecosystem%20for%20regulating%20climate.


bottom of page