Freshwater ecosystems in the Arctic: understanding environment-biodiversity linkages in a changing climate

This winter many extreme weather events have been recorded around the globe. Temperatures broke records in February and 2016 is expected to become the hottest year on record. Although partly due to the El Niño phenomenon, anthropogenic climate change is also responsible and the Arctic isn’t exempt. NASA show January temperatures were up to 13.3°C above average in parts of the Arctic and for the second year running the maximum extent of Arctic sea ice  this winter was at a record low. Sea ice regulates global temperature by reflecting sunlight back into space, so a decrease in sea ice will alter weather and climate over the Northern Hemisphere and potentially further afield. However, in our research we hope to uncover the impacts of such drastic changes on Arctic freshwater ecosystems.

 The Arctic is often considered an inhospitable landscape, inhabited by few species. However, in the summer the Arctic transforms into a highly productive landscape dominated by wetlands. The snow and ice accumulated over the long winter melt as summer returns so that lakes, ponds, streams and rivers become major features, in some areas water covers 90-percent of the surface. These freshwaters provide habitats for a wide variety of species. Below the water surface fish thrive and juvenile stages of aquatic insects develop before emerging as aerial adults during the summer to mate and complete their life cycle. Above the surface, these ecosystems are a vital breeding ground for migratory bird species that time their annual migration to nest in the Arctic tundra, from as far away as New Zealand, to coincide with the snow melting. The insect emergence is one of their major food sources.

Our research is focused on streams in the Zackenberg valley, a remote area of Northeast Greenland. The only way of arriving is a five hour chartered flight by Twin Otter aircraft from Akureyri, in northern Iceland, that transports scientists, food and equipment to this isolated Arctic research station. At the station there are typically about 25 people with the goal of researching and monitoring the effects of climate change in this pristine Arctic environment.

In Zackenberg, we are exploring how aquatic insects in streams will be affected by a warming Arctic climate. In a future with reduced snowfall, shrinking glaciers and thawing ground, the source of stream water is predicted to change from meltwater to being sourced from rainfall, wetlands and groundwater. As a consequence stream habitats will become warmer and transport less glacier rock flour, altering a habitat many species are adapted to and depend upon. Winter weather conditions and snowfall at Zackenberg over the last three years have been highly variable and because of this, we have discovered that aquatic insect communities are highly variable between years.

In a changing Arctic climate, our results lead us to believe that insects especially adapted to cold, unstable environments are likely to become locally extinct, whereas more generalist species that are able to survive in and adapt to a wide variety of habitat conditions will likely thrive. Warmer, more stable conditions could lead to increased insect abundance.

Looking at the broader consequences of climate change on freshwater ecosystems in the Arctic, key fish species such as Arctic char could become threatened by warmer waters and competition from more southerly species moving northwards. There could be knock-on impacts on the rest of the tundra ecosystem and potentially lead to asynchronous timing of the nesting cycles of migratory birds, with the timing of insect emergence, leaving newly hatched chicks without enough food ahead of their long journeys south. However the potential increase in insect abundance could potentially provide more food for migratory birds if emergence timing is synchronous.

In conclusion, the relationship between water source, stream habitat and aquatic insect community has been identified for environments across the Arctic (e.g. Birmingham-based research also in Svalbard and Northern Sweden). However, marked fluctuations in aquatic insect community structure in streams under a changing climate have potential effects on the wider ecosystem and migratory birds that are uncertain. Nevertheless, collecting long-term data sets to monitor changes is crucial to better predict consequences of a changing climate in the Arctic.

Authors:

Catherine Docherty

Doctoral Researcher, School of Geography, Earth and Environmental Sciences

 Professor Alexander Milner

Professor of River Ecosystems, School of Geography, Earth and Environmental Sciences

 Professor David Hannah

Head of School, Professor of Hydrology, School of Geography, Earth and Environmental Sciences