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Climate warming is changing Arctic freshwater ecosystems

October 25, 2019
The Delta River in Alaska. Much of the river’s watershed consists of arctic tundra, which is at risk from climate warming. Image: Bureau of Land Management | Flickr Creative Commons

Biodiversity in arctic lakes, rivers and wetlands is increasingly threatened by climate warming, according to a report published earlier this year. It is suggested that warming is shrinking the extent of what can be considered ‘Arctic’ environments, and with it the range and diversity of aquatic species that they support.

The State of the Arctic Freshwater Biodiversity report was produced by the Circumpolar Biodiversity Monitoring Program Freshwater Group of the Arctic Council Conservation of Arctic Flora and Fauna (CAFF) Working Group. The report – the first of is kind – provides a synthesis of the state of knowledge about biodiversity in Arctic freshwater ecosystems, and its trends and trajectories.

Patterns of biodiversity vary across the Arctic, with temperature and connection to the mainland two key drivers of biodiversity. In other words, it is generally the coldest and most isolated Arctic islands that support the lowest freshwater biodiversity, and the warmest and most connected (often at lower latitudes) that support the highest biodiversity.

However, warming temperatures across the Arctic are shifting where cold-adapted species can survive. Long-term observations show increasing water temperatures and decreasing ice cover in freshwater ecosystems across many parts of the Arctic. A shift to warmer, wetter climates has the potential to significantly impact aquatic systems: altering the seasonality of water flows; increasing concentrations of dissolved organic matter, sediments, minerals and nutrients in water bodies; and opening up new regions to human settlement and development.

The Arctic Council has eight nation state members: Canada, the Kingdom of Denmark (Greenland), Finland, Iceland, Norway, the Russian Federation, Sweden and the United States (Alaska). The report considers ecosystems in the Arctic Circle, largely at the northern range of these states.

The report suggests that with continued climatic warming, the boundaries of the Arctic climatic zones are expected to shift northwards. In other words, the area of ‘Arctic’ environment in the polar region is expected to shrink.

Warmer water temperatures in Arctic rivers and lakes may increase overall biodiversity, as southern species expand their population range northward. However, specialist cold-adapted and tolerant species which currently occupy Arctic freshwaters are likely to be put at risk, both by their shrinking habitat, and by competition from non-native species.

Cold-adapted species such as the Arctic char are likely to be put at risk by climate warming in Arctic regions. Image: Christa Rohrbach | Flickr Creative Commons

The report suggests that cold-water endemic species unique to the Arctic, such as the Arctic char, are likely to suffer regional losses, or even local extinctions as a result.

For example, long-term monitoring records from Iceland indicate a declining abundance of Arctic char and increasing dominance of Atlantic salmon and brown trout since the 1980s. This shift has coincided with an increase in spring and autumn water temperatures, which are likely to affect that spawning and hatching cycles of the Arctic char.

Temperature increases are also predicted to cause more cyanobacteria blooms across Arctic freshwaters. Long-term data in the report shows that cyanobacteria blooms – some of which were toxic – were most abundant in Arctic lakes during the warmest years on record. As climate warming continues, such blooms are likely to become more abundant, potentially causing ecological and human health issues.

The research by the Circumpolar Biodiversity Monitoring Program Freshwater Group which underpins the report is designed to help establish a long-term monitoring environmental framework for Arctic freshwaters. This framework is intended to facilitate rapid detection of, and responses to, changes in Arctic water quality and aquatic biodiversity.

Monitoring of Arctic freshwaters is carried out through the identification of Focal Ecosystem Components. These are ‘indicator’ species – such as fish, invertebrates and plants – whose population dynamics can indicate shifts in the wider ecosystem.

The report suggests, however, that existing scientific monitoring is not sufficient to describe freshwater biodiversity in all Arctic ecoregions. This is often due to challenge and cost of monitoring vast and remote areas. The authors argue for the need for increased and better harmonised monitoring efforts across the Arctic to better understand and manage the changes to freshwater ecosystems in this unique region.

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Read The State of Arctic Freshwater Biodiversity report here.

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