Reviews and syntheses: Effects of permafrost thaw on Arctic aquatic ecosystems

[摘要] The Arctic is a water-rich region, with freshwater systems covering about16 % of the northern permafrost landscape. Permafrost thaw creates newfreshwater ecosystems, while at the same time modifying the existing lakes,streams, and rivers that are impacted by thaw. Here, we describe the currentstate of knowledge regarding how permafrost thaw affects lentic (still) andlotic (moving) systems, exploring the effects of both thermokarst (thawingand collapse of ice-rich permafrost) and deepening of the active layer (thesurface soil layer that thaws and refreezes each year). Within thermokarst,we further differentiate between the effects of thermokarst in lowlandareas vs. that on hillslopes. For almost all of the processes that weexplore, the effects of thaw vary regionally, and between lake and streamsystems. Much of this regional variation is caused by differences in groundice content, topography, soil type, and permafrost coverage. Together, thesemodifying factors determine (i) the degree to which permafrost thawmanifests as thermokarst, (ii) whether thermokarst leads to slumping or theformation of thermokarst lakes, and (iii) the manner in which constituentdelivery to freshwater systems is altered by thaw. Differences inthaw-enabled constituent delivery can be considerable, with these modifyingfactors determining, for example, the balance between delivery ofparticulate vs. dissolved constituents, and inorganic vs. organicmaterials. Changes in the composition of thaw-impacted waters, coupled withchanges in lake morphology, can strongly affect the physical and opticalproperties of thermokarst lakes. The ecology of thaw-impacted lakes andstreams is also likely to change; these systems have unique microbiologicalcommunities, and show differences in respiration, primary production, andfood web structure that are largely driven by differences in sediment,dissolved organic matter, and nutrient delivery. The degree to which thawenables the delivery of dissolved vs. particulate organic matter, coupledwith the composition of that organic matter and the morphology andstratification characteristics of recipient systems will play an importantrole in determining the balance between the release of organic matter asgreenhouse gases (CO₂ and CH₄), its burial in sediments, and itsloss downstream. The magnitude of thaw impacts on northern aquaticecosystems is increasing, as is the prevalence of thaw-impacted lakes andstreams. There is therefore an urgent need to quantify how permafrost thawis affecting aquatic ecosystems across diverse Arctic landscapes, and theimplications of this change for further climate warming.

[学科分类] 地球化学与岩石