Evidence of eutrophication in Arctic lakes

Paola Ayala-Borda,Michael Power,Connie Lovejoy,Milla Rautio

doi:10.1139/as-2020-0033

Abstract

Lakes and ponds are dominant components of Arctic landscapes and provide food and water for northern communities. In the Greiner Lake watershed, in Cambridge Bay (Nunavut, Canada), water bodies are small (84% <5 ha) and shallow (99% <4 m deep). Such characteristics make them vulnerable to eutrophication as temperatures rise and nutrient concentrations from the greening landscape increase. Here, we investigated and compared 35 lakes and ponds in the Greiner watershed in August 2018 and 2019 to determine their current trophic states based on their chemical composition and phytoplankton communities. The ponds had higher trophic status than the lakes, but overall, most sites were oligotrophic. Lake ERA5, located upstream of any direct human influence was classified as eutrophic due to high total phosphorus (32.3 μg·L−1) and a high proportion of Cyanobacteria (42.9% of total phytoplankton biovolume). Satellite imagery suggests the lake may have been eutrophic for the last 30 years. We hypothesize that the coupled effects of catchment characteristics and elevated local snow accumulation patterns promote higher nutrient leaching rates from the soils. We recommend further analysis and monitoring as eutrophication could become more widespread with ongoing climate change and the associated increases in temperature, precipitation, and catchment–lake coupling.

Highlights

Lakes and ponds are a striking component of many Arctic landscapes and provide migratory nesting birds, resident animals, and humans with food and fresh water
The ponds had an overall higher trophic status compared with the lakes, with 20% higher mean chlorophyll a (Chl a) and total phosphorus (TP), 30% higher total dissolved phosphorus (TDP), 62% higher total nitrogen (TN), 70% higher dissolved organic carbon (DOC) and a 40% higher phytoplankton biovolume (Table 1)
ERA5, was ranked as eutrophic according to both TP and Chl a, with a >40% prevalence of Cyanobacteria by phytoplankton biovolume

Summary

Introduction

Lakes and ponds are a striking component of many Arctic landscapes and provide migratory nesting birds, resident animals, and humans with food and fresh water. The water bodies experience strong seasonal fluctuations, from complete ice cover, with low or no light and hypoxic conditions during much of the year, to open water, water column mixing, full oxygenation, air temperatures above freezing and 24 h light cycles during the brief summer. Their limnological characteristics and those of the surrounding landscapes make them sensitive to small changes in the environment and within the context of Arctic freshwater science they are typically viewed as “sentinels of climate change” (Vincent et al 2009). An additional potential consequence of warming is the increasing prevalence of phytoplankton groups, such as Cyanobacteria, that prefer warmer temperatures and that have already been reported to respond to climate change in subarctic ponds (Przytulska et al 2017)

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Conclusion