Long-term global arctic lake monitoring

Huser et al. 2022: Freshwater Biology 67 Special Issue

Water chemistry

• Near arctic, sub arctic low arctic and high arctic lakes all have diffrent water chemistry, influenced by soil and nearby forest composition
• Dissolved Carbon is lowest in high arctic lakes
• Total phosphorus is much higher in slump lakes (formed by melting permafrost) (thermokarst)

Temporal trends

• There is long term water chemistry monitoring data for arctic lakes in Canada, Sweden, Finland

pH increase

• Acid rain regulations resulted in lakes becoming less acific over time

Overall

• Not clear trends in one direction, there are lots of local variations

Biodiversity global patterns

Gaston 2000: Nature 405: 220-227

Species richness decreases with latitude and elevation and increases with annual ppt

Plankton

Schartau et al. 2022 Freshwater Biology 67 Special Issue

Plankton data is not very consistently monitored. In the arctic, their species richness tends to decrease towards the poles, but the trend is less clear in zooplankton compared to phytoplankton

• This could be due to better dispersal in phytoplankton (they're smaller)
• Or due to lower overall species richness in phytoplankton

Benthic macroinvertebrates

Lento et al. 2022 Freshwater Biology 67 Special Issue

Alpha Diversity has a peak around mid arctic latitudes in Fennoscandia, also with higher temperatures

Freshwater Fish diversity

Laske et al. 2022 Freshwater Biology 67 Special Issue

Highest alpha diversity in the Scandanavian and Russian Taiga ($n=72$ species), lowest in the Faroe islands ($n=1$ species)

Food web considerations

Lau et al. 2022 Freshwater Biology 67 Special Issue

FEC = Focal Ecosystem Components

• Overall the important species to the base of the food webs are more present in terrestrial areas in Scandanavia compared to oceanic islands
  Food web level species richness: A Principal Component Analysis of the FECs results in some different clusterings of ecosystems

Diversity hotspots and cold spots

• Diversity is correlated with these focal ecosystem components
• A map of biodiversity zones:
  !Kahilainen_Arctic_lakes, p.27

Intraspecific diversity patterns

• Within fish species there can be a lot of variation
  • Color and size morphological differences
  • Speciation#Morphology
• An interesting map shows different fish species and their number of different phenotypes:

Blain et al. 2023 Global Ecology and Biogeography 32: 2257-2270

We can also examine their Functional Traits like gill raker count, which is typically higher in planktivorous species - this correlation is visible in the data.

A Principal Component Analysis of their ecotype-environment relationships

Climate Change and Arctic lakes

Permafrost thaw

• Contains pathogens, pollutants and mercury
• Mercury is bound to carbon and held in permafrost - it will be released into the atmosphere, but also the lakes

Evaporation

Forest fires

• In Alaska these happen on grasslands also
• Annual tundra area burned - higher temperature and lower precipitation correlated with burned area in Alaskan fiers
• Industrial development

Industrial development

• Linear development for oil and gas in Canada
• Tar sands

Algal blooms

Lake archives show that microfossils associated with algal blooms have massively increased in Arctic lakes

Future trends in lake communities?

Distribution changes

Range expansion of warm adapted species

• A 2006 study of perch and whitefish in North America shows prediction of expanding range
  • Reist et al. 2006 Ambio 35: 370-380.
• Each species has a temperature optimum for growth rate
• In Finland also, perch is taking over northern lakes based on long-term monitoring
  • Smålas 2023 Ecology and Evolution 13: e10185
  • Catch per unit area analysis shows that perch are taking over

Range retraction of cold adapted species

• Arctic char have had their range retracted to only far northern lakes pretty much in Sweden
  • Hein et al. 2012 Ambio 41: 303-312.

Community and food web responses

• Sometimes it's hard to tell if a species is warm- or cool-adapted
• McMeans et al. 2020 Ecology Letters 23: 922-938 describes a method for classifying arctic fish species into "thermal guilds" based on optimal thermal preference and the season they are most active

Rewiring food webs

• Cold adapted species move deeper into the lake as temperature increases, this can have big effects on the food web that are hard to measure.

Kahlainen's studies of the Tornio-Muoniojoki watercourse gradient

• He was based in Kilpisjärvi studying freshwater aquatic ecosystems
• Productivity, temperature and precipitation increases as the watercourse flows south to the Baltic sea.
• Sampling of fish, zooplankton and benthic macroinvertebrates in 19 different tributary lakes
• Salmonids most common in upper reaches, then perch, then (?)
  • See Hayden et al. 2017

Food web biomass

• Keva et a. 2021 Analyzed trends in subarctic food webs - a clear increase in phytoplankton biomass with temperature
• Intertivorous fish also increase, despite not having a large increase in invertebrates
• Overall, an increasing temperature will result in eutrophic lakes where most of the biomass is at the small invertivorous fish trophic level and zooplankton (hourglass shape)
  !Kahilainen_Arctic_lakes, p.59

Effect of mercury increase in food webs

Kozak et al. 2021

• Food webs accumulate mercury faster in upper lakes that are simpler, in more complex webs the rate of mercury update is slower