State of the Arctic Freshwater Biodiversity Report: Findings

Arctic freshwater ecosystems are highly threatened by climate change and human development which can alter the distribution and abundance of species and affect biodiversity and the ecosystem services on which many Arctic peoples depend.

• Long-term trends of increasing water temperature and decreasing ice cover in freshwater systems have been observed in many areas of the Arctic. Warmer and wetter climate will generally lead to higher concentrations of dissolved organic matter, minerals, and nutrients. Furthermore, impacts related to human population growth (e.g., from increased infrastructure, development, and resource exploration/exploitation) have the potential to contribute to further degradation and nutrient enrichment of freshwater systems in the Arctic.
• These changes could significantly affect lake and river ecosystem processes, causing decreased light penetration in lakes, nutrient enrichment, and sedimentation, and leading to changes in biodiversity, occurrence, and biomass of Arctic species.
• With continued warming, the boundaries of Arctic climatic zones (e.g., sub-, low, and high Arctic, as defined by the Arctic Biodiversity Assessment) are expected to shift and cause an overall reduction in the spatial extent that can be considered part of the Arctic ecoregion, based on temperature and vegetation conditions.
• Warmer water temperatures in Arctic rivers and lakes may lead to an increase in overall biodiversity as southern species expand their ranges northward, but the highly cold-adapted and cold-tolerant species that currently inhabit the Arctic will be at risk due to competition from non-native species and face possible extirpation when their thermal tolerances are exceeded.
• Cold-water endemic species unique to the Arctic, such as Arctic char, may suffer regional losses with the potential for extinctions in extreme cases.

Patterns of biodiversity vary across the Arctic, but ecoregions that have historically warmer temperatures and connections to the mainland generally have higher biodiversity than those with cold temperatures (high latitude or altitude) or on remote islands.

• Fennoscandian lakes (in particular, inland non-mountainous regions) are biodiversity hotspots for macrophytes, zooplankton, benthic macroinvertebrates, and fish in lakes. Lakes in Coastal Alaska are most diverse with regards to diatom and phytoplankton species and among the most diverse ecoregions for fish in the Arctic. Ecoregions in Canada, Greenland, Iceland, and Russia were less diverse for many of the lake biotic FECs.
• Fennoscandia, coastal Alaska, and western and southern Canada have the most diverse ecoregions across riverine diatoms, benthic macroinvertebrate, and fish FECs.
• The warmer climate in Fennoscandia and southern ecoregions of Canada as well as the strong geographical connectivity to the mainland explains the overall high biodiversity of these areas. Similarly, high connectivity of the Alaskan coastal region and lack of ice cover in the last glaciation may have contributed to high biodiversity of many FECs.
• Biodiversity in mountainous and alpine ecoregions of North America and Fennoscandia is generally lower than that of surrounding ecoregions for both lakes and rivers. This likely reflects harsh environmental conditions generally found in mountainous regions or possibly the effect of dispersal barriers to species such as migrating fish.
• Biodiversity is lower on remote islands where movement and introduction of species can be limited; this is particularly evident in Greenland, Iceland, the Faroe Islands, Svalbard, and Wrangel Island.

Temperature is the overriding and predominant driver for most FECs, but climate, geographical connectivity, geology, and smaller-scale environmental parameters such as water chemistry are all key drivers of Arctic freshwater biodiversity.

• Biodiversity of benthic macroinvertebrates in rivers and lakes decreased at higher latitudes, particularly above 68°N. This northward decline in diversity was strongly related to decreasing maximum summer temperatures, indicating that tolerance for cold temperatures limits the number of benthic macroinvertebrate species that can inhabit the high Arctic.
• Latitudinal trends were weaker for other FECs, but high-latitude lakes and rivers showed differences in diversity and composition of fish, plankton, diatoms, and macrophytes compared to lower-latitude systems. The differences reflected temperature and precipitation gradients as well as barriers to movement, glaciation history, and bedrock geology, which affects water chemistry.
• Cyanobacteria species, of which some are toxin-producing, were most abundant in lakes during the warmest years on record. As temperatures continue to increase, cyanobacteria blooms can be expected to become more common.

Available long-term monitoring records and research data indicate that freshwater biodiversity has changed over the last 200 years, with shifts in species composition being less dramatic in areas where temperatures have been more stable.

• Long-term fish monitoring records from Iceland indicate declining abundance of Arctic char and increasing dominance of Atlantic salmon and brown trout since the 1980s. At the same time there has been an increase in spring and fall water temperatures that might affect spawning and hatching time of Arctic char.
• Diatoms in lake sediment cores show shifts in community composition over the last 200 years, with changes in the dominant species that reflect changes in the temperature zones in the water column of lakes.
• Changes in diatom composition over the last 200 years were weakest in eastern Canadian coastal ecoregions (e.g., northern Labrador and Quebec) where temperatures have historically been more stable with less evidence of warming.

Existing data are not sufficient to describe biodiversity patterns in all ecoregions, and increased sampling is required to improve understanding of biodiversity change.

• Differences in composition among stations were most often due to finding new species, which suggests that additional sampling (more stations) is required to accurately estimate the number of species present in Arctic freshwater systems.
• Better coordination and harmonized sampling, sample processing, and data storage across the Arctic will improve our ability to detect and monitor changes in freshwater biodiversity.
• There is a substantial lack of data for large parts of the North American and Russian Arctic and few long term data sets for Arctic lakes and rivers.
• Differences in sampling methods, sample processing, and data storage limit spatial comparisons, for example, where different lake habitats (shallow or deep water) are sampled or vastly different sampling equipment or approaches are used.