. The Arctic is a water-rich region, with freshwater systems covering about 16 % of the northern permafrost landscape. Permafrost thaw creates new freshwater ecosystems, while at the same time modifying the existing lakes, streams, and rivers that are impacted by thaw. Here, we describe the current state of knowledge regarding how permafrost thaw affects lentic (still) and lotic (moving) systems, exploring the effects of both thermokarst (thawing and collapse of ice-rich permafrost) and deepening of the active layer (the surface soil layer that thaws and refreezes each year). Within thermokarst, we further differentiate between the effects of thermokarst in lowland areas vs. that on hillslopes. For almost all of the processes that we explore, the effects of thaw vary regionally, and between lake and stream systems. Much of this regional variation is caused by differences in ground ice content, topography, soil type, and permafrost coverage. Together, these modifying factors determine (i) the degree to which permafrost thaw manifests as thermokarst, (ii) whether thermokarst leads to slumping or the formation of thermokarst lakes, and (iii) the manner in which constituent delivery to freshwater systems is altered by thaw. Differences in thaw-enabled constituent delivery can be considerable, with these modifying factors determining, for example, the balance between delivery of particulate vs. dissolved constituents, and inorganic vs. organic materials. Changes in the composition of thaw-impacted waters, coupled with changes in lake morphology, can strongly affect the physical and optical properties of thermokarst lakes. The ecology of thaw-impacted lakes and streams is also likely to change; these systems have unique microbiological communities, and show differences in respiration, primary production, and food web structure that are largely driven by differences in sediment, dissolved organic matter, and nutrient delivery. The degree to which thaw enables the delivery of dissolved vs. particulate organic matter, coupled with the composition of that organic matter and the morphology and stratification characteristics of recipient systems will play an important role in determining the balance between the release of organic matter as greenhouse gases (CO2 and CH4), its burial in sediments, and its loss downstream. The magnitude of thaw impacts on northern aquatic ecosystems is increasing, as is the prevalence of thaw-impacted lakes and streams. There is therefore an urgent need to quantify how permafrost thaw is affecting aquatic ecosystems across diverse Arctic landscapes, and the implications of this change for further climate warming.

/pdf/reviews-and-syntheses-effects-of-permafrost-thaw-on-arctic-51iclrryox.pdf

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

Endorheic (hydrologically landlocked) basins spatially concur with arid/semi-arid climates. Given limited precipitation but high potential evaporation, their water storage is vulnerable to subtle flux perturbations, which are exacerbated by global warming and human activities. Increasing regional evidence suggests a probably recent net decline in endorheic water storage, but this remains unquantified at a global scale. By integrating satellite observations and hydrological modelling, we reveal that during 2002–2016 the global endorheic system experienced a widespread water loss of about 106.3 Gt yr−1, attributed to comparable losses in surface water, soil moisture and groundwater. This decadal decline, disparate from water storage fluctuations in exorheic basins, appears less sensitive to El Nino–Southern Oscillation-driven climate variability, which implies a possible response to longer-term climate conditions and human water management. In the mass-conserved hydrosphere, such an endorheic water loss not only exacerbates local water stress, but also imposes excess water on exorheic basins, leading to a potential sea level rise that matches the contribution of nearly half of the land glacier retreat (excluding Greenland and Antarctica). Given these dual ramifications, we suggest the necessity for long-term monitoring of water storage variation in the global endorheic system and the inclusion of its net contribution to future sea level budgeting.

/pdf/recent-global-decline-in-endorheic-basin-water-storages-1pyjol8eju.pdf

Recent global decline in endorheic basin water storages.

A regional-scale assessment of Himalayan glacial lake changes using satellite observations from 1990 to 2015

Regional differences of lake evolution across China during 1960s–2015 and its natural and anthropogenic causes

Permafrost carbon feedback (PCF) modeling has focused on gradual thaw of near-surface permafrost leading to enhanced carbon dioxide and methane emissions that accelerate global climate warming. These state-of-the-art land models have yet to incorporate deeper, abrupt thaw in the PCF. Here we use model data, supported by field observations, radiocarbon dating, and remote sensing, to show that methane and carbon dioxide emissions from abrupt thaw beneath thermokarst lakes will more than double radiative forcing from circumpolar permafrost-soil carbon fluxes this century. Abrupt thaw lake emissions are similar under moderate and high representative concentration pathways (RCP4.5 and RCP8.5), but their relative contribution to the PCF is much larger under the moderate warming scenario. Abrupt thaw accelerates mobilization of deeply frozen, ancient carbon, increasing 14C-depleted permafrost soil carbon emissions by ~125–190% compared to gradual thaw alone. These findings demonstrate the need to incorporate abrupt thaw processes in earth system models for more comprehensive projection of the PCF this century.

/pdf/21st-century-modeled-permafrost-carbon-emissions-accelerated-10ix5h2bbq.pdf

21st-century modeled permafrost carbon emissions accelerated by abrupt thaw beneath lakes

Monitoring decadal lake dynamics across the Yangtze Basin downstream of Three Gorges Dam

Detailed bathymetric data were collected for 28 thermokarst lakes across the Arctic Coastal Plain (ACP) of northern Alaska from areas with distinctly different surficial sediments and topography. Lakes found in the low-relief coastal area have developed in marine silts that are ice-rich in the upper 6–10 m. The lakes tend to be shallow (~ 2 m), of uniform depth and lack prominent littoral shelves. Further inland on the ACP, lakes have formed in relatively ice-poor aeolian sand deposits. In this hilly terrain, average lake depth is less (~ 1 m) despite deeper (3–5 m) central pools. This bathymetry reflects the influence of broad, shallow littoral shelves where sand, eroded from bluffs at the lake margin, is deposited concurrently with deep penetration of the talik beneath the basin centre. Lakes in the ACP-Arctic Foothills transition zone to the south have developed in loess uplands. These yedoma deposits are extremely ice-rich, and residual lakes found inside old lake basins (alases) are generally 2–4 m deep, reflecting continued talik development and ground subsidence following drainage of the original lake. However, where the expanding lake encroaches on the flanks of the upland at actively eroding bluffs, near-shore pools develop that can be 6–9 m deep. It appears that thawing of ice-rich permafrost during lake expansion causes ground subsidence and formation of deep pools above ablating ice wedges. These data suggest that thermokarst lake morphometry largely depends on the characteristics of the substrate beneath the lake and the availability of sediments eroded at the lake margin. Copyright © 2012 John Wiley & Sons, Ltd.

Thermokarst Lakes on the Arctic Coastal Plain of Alaska: Geomorphic Controls on Bathymetry

Drained thaw lake basin recovery on the western Arctic Coastal Plain of Alaska using high-resolution digital elevation models and remote sensing imagery

Regional-to global-scale lake maps can now be produced using existing technology and freely available data and serve as powerful tools for a variety of lake-and water-related studies. The accuracy of these studies depends in part on the accuracy of the lake map that they use. Mapping lakes using remote sensing requires a careful study of error and uncertainty. Errors in lake maps are caused by sensor-specific, lake-specific, and processing-specific factors. These can be further broken down to spatial, spectral/radiometric, and temporal factors. In this study, we analyse and compare these factors using modern and historical Landsat images along with intensive ground surveys of lakes in northern Alaska. Percentage error in lake area relative to lake size decreases for larger and more circular lakes, making a minimum size threshold an effective error mitigation practice. Image resampling involved in image transformation significantly increased error in lake area and is easily avoided by performing co-registration in the vector domain. Spectral properties varied for individual lakes due to depth, suspended sediment, vegetation, and other in situ factors, necessitating a normalized water index and independently derived threshold values for each lake. For lake change detection studies, spatially degrading a finer resolution image to the resolution of the coarser image a common practice does not significantly affect the difference in observed lake area. Due to the large numbers of lakes, particularly in the climatologically sensitive Arctic region, small errors in individual lake areas can compound to significantly impact results on regional to global scales. This study is intended to inform future static and multitemporal lake remote-sensing studies by evaluating errors and uncertainties in lake area, as measured by remote sensing.

Quantifying sources of error in multitemporal multisensor lake mapping

Satellite-based daily lake areas in the Yangtze Basin, China, 2000-2011

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