Duration Of Ice Cover Research Articles

Spatial-Temporal Distribution of the Freeze–Thaw Cycle of the Largest Lake (Qinghai Lake) in China Based on Machine Learning and MODIS from 2000 to 2020

The lake ice phenology variations are vital for the land–surface–water cycle. Qinghai Lake is experiencing amplified warming under climate change. Based on the MODIS imagery, the spatio-temporal dynamics of the ice phenology of Qinghai Lake were analyzed using machine learning during the 2000/2001 to 2019/2020 ice season, and cloud gap-filling procedures were applied to reconstruct the result. The results showed that the overall accuracy of the water–ice classification by random forest and cloud gap-filling procedures was 98.36% and 92.56%, respectively. The annual spatial distribution of the freeze-up and break-up dates ranged primarily from DOY 330 to 397 and from DOY 70 to 116. Meanwhile, the decrease rates of freeze-up duration (DFU), full ice cover duration (DFI), and ice cover duration (DI) were 0.37, 0.34, and 0.13 days/yr., respectively, and the duration was shortened by 7.4, 6.8, and 2.6 days over the past 20 years. The increased rate of break-up duration (DBU) was 0.58 days/yr. and the duration was lengthened by 11.6 days. Furthermore, the increase in temperature resulted in an increase in precipitation after two years; the increase in precipitation resulted in the increase in DBU and decrease in DFU in corresponding years, and decreased DI and DFI after one year.

Shifted dynamics of plankton communities in a restored lake: exploring the effects of climate change on phenology through four decades

Lake surface temperatures have increased globally in recent decades. Climate change can affect lake biota directly via enhanced water temperatures, shorter ice cover duration and prolonged stratification, and indirectly via changes in species interactions. Changes in the seasonal dynamics of phytoplankton and zooplankton can further affect whole lake ecosystems. However, separating the effects of climate change from the more direct and dominating effects of nutrients is a challenge. Our aim was to explore the ecological effects of climate change while accounting for the effects of re-oligotrophication in Lake Mjøsa, the largest lake in Norway. While restoration measures since the 1970s have resulted in strongly reduced nutrient levels, the surface water temperature has increased by almost 0.4°C decade-1 during the same period. We analysed long-term trends and abrupt changes in environmental and biological time series as well as changes in the seasonal dynamics of individual plankton taxa. The general long-term trends in phenology were diverging for phytoplankton (later peaks) vs. zooplankton (earlier peaks). However, individual taxa of both phytoplankton and zooplankton displayed earlier peaks. Earlier peaks of the phytoplankton group Cryptophyceae can be explained by increased spring temperature or other climate-related changes. Earlier onset of population growth of certain zooplankton species (Limnocalanus macrurus and Holopedium gibberum) can also be explained by climatic change, either directly (earlier temperature increase) or more indirectly (earlier availability of Cryptophyceae as a food source). In the long run, climate-related changes in both phytoplankton and zooplankton phenology may have implications for the fish communities of this lake.

The disappearance of ice cover on temperate lakes (Central Europe) as a result of climate warming

This paper presents changes in the ice regime of lakes located in the northern part of Poland. It has been established that in the period 1960–2019, there was a successive decline in the ice extent of lakes, clearly visible in individual parameters; formation of ice cover is delayed by 3.0 days/decade (on average for all lakes), its decline occurred earlier by 3.8 days/decade, and the length of ice cover is shorter by 6.8 days/decade. Moreover, the maximum thickness of the ice cover is becoming thinner, and this process has progressed at an average rate of 2.3 cm/decade. The aforementioned situation shows strong relations with air temperature. It was particularly evident in the late 1980s, when a change in the thermal regime took place, which was documented in most of the analysed parameters, as demonstrated in the study. It has been established that from that period up to now, the decline of ice cover tends to start 19 days earlier, the duration of ice cover is shorter by 22 days, and the ice cover is 8 cm thinner, on average. The observed transformation affects the imbalance of the existing equilibrium in lakes, which can be related to both biotic and abiotic processes.

Wintertime growth in Atlantic salmon under changing climate: the importance of ice cover for individual growth dynamics

Understanding the dynamic nature of individual growth in stream-dwelling salmonids may help forecast consequences of climate change on northern fish populations. Here, we performed an experimental capture–mark–recapture study in Atlantic salmon (Salmo salar) to quantify factors influencing wintertime growth variation among juveniles under different scenarios for ice-cover reduction. We applied multiple imputation to simulate missing size observations for unrecaptured fish and to account for individual-level variation in growth rates. The salmon parr exhibited substantial body length shrinkage in early winter, suppressed growth through midwinter, and increased growth rates in late winter and particularly in spring. Unexpectedly, the presence of ice cover had no direct effects on wintertime growth. Instead, our results implied increasing energetic costs with reducing ice cover; individuals exposed to absent or shortened ice-covered period gained mass at a lowered rate in spring, whereas the present, long ice-covered period was followed by rapid growth. This study emphasizes natural resilience of Atlantic salmon to wintertime environmental variation, which may help the species to cope with the reductions in ice-cover duration due to climate change.

The Role of Climate and Lake Size in Regulating the Ice Phenology of Boreal Lakes

AbstractWe quantified the relationships between seasonal air temperatures and ice phenology for a 0.54 km2 boreal lake in Northwestern Ontario, Canada using a 50‐year time series (1970–2019). Significant temporal trends in the duration of ice cover (−4.0 days decade−1) occurred over the study period and both ice‐on and ice‐off dates were highly predictable from seasonal air temperatures. While temporal trends in ice‐off dates were not significant, ice‐on dates trended later by 2.2 days decade−1, and both ice‐off dates and the duration of ice‐cover became increasingly variable over the study period. For three consecutive winter seasons, we also evaluated regional variations of ice‐phenology and snow and ice‐thickness from 9 to 30 boreal lakes across a lake size gradient (0.02–26 km2) using ground based and satellite observations. Regional variation of ice‐on dates (30–45 days), ice‐off dates (10–21 days), and total duration of ice‐cover (22–38 days) between lakes displayed significant nonlinear relationships to lake size across all years. Regional variation of ice‐off dates was structured according to lake size, and appeared driven by relationships between lake size, snow thickness, and ice thickness. Multiple linear regression and generalized additive modeling approaches to predict ice‐on and ice‐off dates at the regional scale by integrating the effects of air temperature and lake size had similar performance, explaining >90% of the variance of observed.

The vulnerability of lakes to climate change along an altitudinal gradient

Studies of future 21st century climate warming in lakes along altitudinal gradients have been partially obscured by local atmospheric phenomena unresolved in climate models. Here we forced the physical lake model Simstrat with locally downscaled climate models under three future scenarios to investigate the impact on 29 Swiss lakes, varying in size along an altitudinal gradient. Results from the worst-case scenario project substantial change at the end of the century in duration of ice-cover at mid to high altitude (−2 to −107 days), stratification duration (winter −17 to −84 days, summer −2 to 73 days), while lower and especially mid altitude (present day mean annual air temperature from 9 °C to 3 °C) dimictic lakes risk shift to monomictic regimes (seven out of the eight lakes). Analysis further indicates that for many lakes shifts in mixing regime can be avoided by adhering to the most stringent scenario.

Climate Change-Driven Regime Shifts in a Planktonic Food Web.

AbstractPredicting how food webs will respond to global environmental change is difficult because of the complex interplay between the abiotic forcing and biotic interactions. Mechanistic models of species interactions in seasonal environments can help understand the effects of global change in different ecosystems. Seasonally ice-covered lakes are warming faster than many other ecosystems and undergoing pronounced food web changes, making the need to forecast those changes especially urgent. Using a seasonally forced food web model with a generalist zooplankton grazer and competing cold-adapted winter and warm-adapted summer phytoplankton, we show that with declining ice cover, the food web moves through different dynamic regimes, from annual to biennial cycles, with decreasing and then disappearing winter phytoplankton blooms and a shift of maximum biomass to summer season. Interestingly, when predator-prey interactions were not included, a declining ice cover did not cause regime shifts, suggesting that both are needed for regime transitions. A cluster analysis of long-term data from Lake Baikal, Siberia, supports the model results, revealing a change from regularly occurring winter blooms of endemic diatoms to less frequent winter bloom years with decreasing ice cover. Together, the results show that even gradual environmental change, such as declining ice cover duration, may cause discontinuous or abrupt transitions between dynamic regimes in food webs.

Chlorophyll-a concentrations in 82 large alpine lakes on the Tibetan Plateau during 2003–2017: temporal–spatial variations and influencing factors

ABSTRACT As essential parts of the unique ecosystem of Tibetan Plateau (TP), the sizes and associated physical properties of alpine lakes have long been investigated. However, little is known about one of the most critical biogeochemical properties, i.e. the Chlorophyll-a (Chl-a) concentrations. Here, for the first time, we presented a comprehensive investigation of the temporal–spatial variations in Chl-a in 82 lakes (>50 km2) across the entire TP region, based on MODIS observations in the period of 2003–2017. The results showed that the 82 lakes exhibited an average long-term mean Chl-a of 3.3 ± 4.3 mg m−3, with high Chl-a lakes concentrated in the eastern and southern inner TP basin and northeastern parts of the TP. An interannual trend analysis revealed that lakes exhibiting (significantly) decreasing Chl-a trends and (significantly) increasing Chl-a trends were comparable in numbers but differed in distribution patterns. A correlation analysis indicated that at least 70% of the interannual variability in Chl-a values of lakes was significantly correlated with one of the four environmental factors (wind speed, ice cover duration, lake water surface temperature and surface runoff) and lake size. In addition, glacier meltwater tended to reduce lake Chl-a while salinity levels showed minor influences.

Methylmercury Transport and Fate Shows Strong Seasonal and Spatial Variability along a High Arctic Freshwater Hydrologic Continuum.

The presence of toxic methylmercury (MeHg) in Arctic freshwater ecosystems and foodwebs is a potential health concern for northern Indigenous people. Addressing this issue requires a better understanding of MeHg production, fate during transport, and uptake into foodwebs. We used methylation assays and spatiotemporal surveys of MeHg concentrations, during the ice-covered and open water seasons, across a hydrologic continuum (composed of thaw seeps, lake/ponds, and a wetland) to identify Hg methylation hotspots and seasonal differences in MeHg cycling unique to Arctic ecosystems. Ponds and saturated wetland soils support methylation hotspots during the open water season, but subsequent export of MeHg to downstream ecosystems is limited by particle settling, binding of MeHg on soil organic matter, and/or demethylation in drier wetland soils. During the ice-covered season, MeHg concentrations in lake waters were approximately ten-fold greater than in summer; however, zooplankton MeHg concentrations were paradoxically five times lower at this time. Despite limited evidence of snow-phase methylation, the snowpack is an important MeHg reservoir. Changes in ice-cover duration will alter MeHg production and bioaccumulation in lakes, while increased thaw and surface water flow will likely result in higher methylation rates at the aquatic-terrestrial interface and more efficient downstream transport of MeHg.

Lake Phenology of Freeze-Thaw Cycles Using Random Forest: A Case Study of Qinghai Lake

Lake phenology is essential for understanding the lake freeze-thaw cycle effects on terrestrial hydrological processes. The Qinghai-Tibetan Plateau (QTP) has the most extensive ice reserve outside of the Arctic and Antarctic poles and is a sensitive indicator of global climate changes. Qinghai Lake, the largest lake in the QTP, plays a critical role in climate change. The freeze-thaw cycles of lakes were studied using daily Moderate Resolution Imaging Spectroradiometer (MODIS) data ranging from 2000–2018 in the Google Earth Engine (GEE) platform. Surface water/ice area, coverage, critical dates, surface water, and ice cover duration were extracted. Random forest (RF) was applied with a classifier accuracy of 0.9965 and a validation accuracy of 0.8072. Compared with six common water indexes (tasseled cap wetness (TCW), normalized difference water index (NDWI), modified normalized difference water index (MNDWI), automated water extraction index (AWEI), water index 2015 (WI2015) and multiband water index (MBWI)) and ice threshold value methods, the critical freeze-up start (FUS), freeze-up end (FUE), break-up start (BUS), and break-up end (BUE) dates were extracted by RF and validated by visual interpretation. The results showed an R2 of 0.99, RMSE of 3.81 days, FUS and BUS overestimations of 2.50 days, and FUE and BUE underestimations of 0.85 days. RF performed well for lake freeze-thaw cycles. From 2000 to 2018, the FUS and FUE dates were delayed by 11.21 and 8.21 days, respectively, and the BUS and BUE dates were 8.59 and 1.26 days early, respectively. Two novel key indicators, namely date of the first negative land surface temperature (DFNLST) and date of the first positive land surface temperature (DFPLST), were proposed to comprehensively delineate lake phenology: DFNLST was approximately 37 days before FUS, and DFPLST was approximately 20 days before BUS, revealing that the first negative and first positive land surface temperatures occur increasingly earlier.

Distribution patterns of epiphytic reed-associated macroinvertebrate communities across European shallow lakes

So far, research on plant-associated macroinvertebrates, even if conducted on a large number of water bodies, has mostly focused on a relatively small area, permitting limited conclusions to be drawn regarding potentially broader geographic effects, including climate. Some recent studies have shown that the composition of epiphytic communities may differ considerably among climatic zones. To assess this phenomenon, we studied macroinvertebrates associated with the common reed Phragmites australis (Cav.) Trin. ex Steud in 46 shallow lakes using a common protocol. The lakes, located in nine countries, covered almost the entire European latitudinal range (from <48°N to 61°N) and captured much of the variability in lake size and nutrient content in the region. A Poisson Generalized Linear Mixed Model (GLMM) showed the number of macroinvertebrate epiphytic taxa to be negatively associated with water conductivity and positively associated with medium ice cover duration (approximately 1 month). A Gamma GLMM showed a positive effect of chlorophyll a on the density of macroinvertebrates, and a significantly greater density in lakes located at the lowest and highest latitudes. Individual taxa responded differently to lake environmental conditions across climate zones. Chironomidae dominated in all climate zones, but their contribution to total density decreased with increasing latitude, with progressively greater proportions of Naidinae, Asellidae, Ephemeroptera and Trichoptera. Our study demonstrates that epiphytic macroinvertebrate fauna, even when analyzed at low taxonomic resolution, exhibits clear differences in diversity, relative abundance of individual taxa and total density, shaped both by geographic and anthropogenic variables. The results were discussed in the context of climate change. To our best knowledge this is the first study to examine epiphytic fauna carried out on a European scale.

Assessment of machine learning classifiers for global lake ice cover mapping from MODIS TOA reflectance data

The topic of satellite remote sensing of lake ice has gained considerable attention in recent years. Optical satellite data from the Moderate Resolution Imaging Spectroradiometer (MODIS) allow for the monitoring of lake ice cover (an Essential Climate Variable or ECV), and dates associated with ice phenology (freeze-up, break-up, and ice cover duration) over large areas in an era where ground-based observational networks have nearly vanished in many northern countries. Ice phenology dates as well as dates of maximum and minimum ice cover extent (for lakes that do not form a complete ice cover in winter or do not totally lose their ice cover in summer) are useful for assessing long-term trends and variability in climate, particularly due to their sensitivity to changes in near-surface air temperature. Existing knowledge-driven (threshold-based) retrieval algorithms for lake ice cover mapping that use top-of-atmosphere (TOA) reflectance products do not perform well under lower solar illumination conditions (i.e. large solar zenith angles), resulting in low TOA reflectance. This research assessed the capability of four machine learning classifiers (i.e. multinomial logistic regression, MLR; support vector machine, SVM; random forest, RF; gradient boosting trees, GBT) for mapping lake ice cover, water and cloud cover during both break-up and freeze-up periods using the MODIS/Terra L1B TOA (MOD02) product. The classifiers were trained and validated using samples collected from 17 large lakes across the Northern Hemisphere (Europe and North America); lakes that represent different characteristics with regards to area, latitude, freezing frequency, and ice duration. Following an accuracy assessment using random k-fold cross-validation (k = 100), all machine learning classifiers using a 7-band combination (visible, near-infrared and shortwave-infrared) were found to be able to produce overall classification accuracies above 94%. Both RF and GBT provided overall and class-specific accuracies above 98% and a more visually accurate depiction of lake ice, water and cloud cover. The two tree-based classifiers offered the most robust spatial transferability over the 17 lakes and performed consistently well across ice seasons. However, only RF was relatively insensitive to the choice of the hyperparameters compared to the other three classifiers. The results demonstrate the potential of RF for mapping lake ice cover globally from MODIS TOA reflectance data.

On thinning ice: Effects of atmospheric warming, changes in wind speed and rainfall on ice conditions in temperate lakes (Northern Poland)

Northern Hemisphere lakes are losing their ice cover due to climate change. Here we explored six decades of observational data (1961–2017) showing trends in air temperature, wind speed and precipitation over northern Poland, as well as changes in the ice conditions for five lakes with different morphometry. We evaluated whether and to what extent climatic effects, including atmospheric warming, changing wind speed and rainfall during fall and winter, influence ice conditions in morphometrically different lakes in Northern Poland. Our analysis demonstrated that ice cover duration and thickness decreased at rates of 5.4 days decade−1 and 2.5 cm decade−1, respectively. Ice conditions were influenced (65–75%) by the direct effects of air temperature change and to some extent by an interaction of warming with wind speed and precipitation (5–10%). While stronger autumnal winds result in longer ice cover duration, the effect of precipitation is bimodal with either an enhancement of ice formation by autumnal rain or accelerated ice loss during spring. To project future changes in ice conditions, we used a 1D hydrodynamic lake model forced with four climate model projections under low, medium and high Representative Concentration Pathway (RCP) scenarios. Our simulations demonstrate that current ice conditions will stabilize under the low emission scenario (RCP 2.6) but decrease under both the medium and high emission scenarios (RCP 6.0 and 8.5). During the 21st century, the lakes are projected to lose their ice at a rate between 4.5- and 10-days decade−1 and ice thickness will decrease by between 3.0 and 5.0 cm decade−1. The rate of change will be greater in smaller rather than larger lakes and more so for those situated further inland. The probability of ice-free winters will increase for all lakes and among all future scenarios by between 4 and 69% with the highest potential frequency of ice-free winters in smaller and deeper but relatively wind-exposed lakes.

Phenology of alpine zooplankton populations and the importance of lake ice-out

AbstractThe prolonged ice cover inherent to alpine lakes incurs unique challenges for aquatic life, which are compounded by recent shifts in the timing and duration of ice cover. To understand the responses of alpine zooplankton, we analyzed a decade (2009–2019) of open-water samples of Daphnia pulicaria and Hesperodiaptomus shoshone for growth, reproduction and ultraviolet radiation tolerance. Due to reproductive differences between taxa, we expected clonal cladocerans to exhibit a more rapid response to ice-cover changes relative to copepods dependent on sexual reproduction. For D. pulicaria, biomass and melanization were lowest after ice clearance and increased through summer, whereas fecundity was highest shortly after ice-off. For H. shoshone, biomass and fecundity peaked later but were generally less variable through time. Among years, ice clearance date varied by 49 days; years with earlier ice-out and a longer growing season supported higher D. pulicaria biomass and clutch sizes along with greater H. shoshone fecundity. While these large-bodied, stress tolerant zooplankton taxa were relatively resilient to phenological shifts during the observation period, continued losses of ice cover may create unfavorably warm conditions and facilitate invasion by montane species, emphasizing the value of long-term data in assessing future changes to these sensitive ecosystems.

Nematode responses to an Arctic sea-ice regime: morphometric characteristics and biomass size spectra

Body size is one of the most important traits of organisms that affects their behavioral life histories, physiologies, and energy requirements. For sediment-dwelling organisms, such as free-living nematodes, body size is a direct adaptation for living in sediments with a particular particle size, but other environmental factors, e.g., water depth and food availability, directly or indirectly shape nematode morphology. Nevertheless, our knowledge of meiofaunal organisms sizes still lags far behind that of other aquatic fauna, particularly for high-latitude fauna. Therefore, to gain insight into the nematode community size structure, we investigated eight stations located in the seasonal sea-ice zone north of Svalbard (Yermak Plateau, Nansen Basin, and Northern Svalbard shelf) during Arctic spring. Sample locations covered a wide depth gradient, different sea-ice concentrations and subsequent bloom stages. Our study provides previously unavailable data on nematode morphometry for this Arctic region during ecologically important spring to summer transition times. We analyzed nematode biomass, body shape and morphometric attributes, along with respective feeding types and life stage information. Our results show that differences in nematode densities, biomass and allometric attributes most likely reflect differences in the flux of organic material to the seafloor and in the biogeochemical properties of the sediments. Nematode assemblages appeared to respond to spatial gradients in ice cover duration and therefore pelagic productivity from the northern Svalbard shelf to the Yermak Plateau as evidenced by decreasing density, biomass and body size. Considering the entire community, as well as different life stages, average individual body weight decreased northward. Biomass dominance in the lower weight classes and the significantly lower abundance of long and thick morphotype nematodes observed on the Yermak Plateau than in the two other regions were striking. This was in contrast with the assemblage observed on the shelf, where prevailing environmental conditions influenced the presence of other morphotypes - markedly longer and wider organisms. Ongoing changes in sea-ice cover and primary production in the Arctic may significantly affect nematode functioning, as they are expected to have pronounced impacts on nematode morphological characteristics. In this regard, the size-based approach becomes a useful tool for detecting changes in the community and has important implications for predicting the direction of change with regard to benthic productivity.

Variability of Sedimentation Processes in Northern Part of East Novaya Zemlya Trough in the Anthropocene

The lithological and mineralogical characteristics of sea surface sediments, composition of microfossils, contribution of organic matter, and element composition have been studied in a core from the northern part of East Novaya Zemlya Trough. Sedimentation rates were calculated based on the radioisotopes 210Pb and 137Cs. Lithological, biogeochemical, and geochemical studies showed a low variability of the sedimentation conditions over the last 250 years. However, even small changes in microfossils, as well as lithological and geochemical parameters, make it possible to trace some short-term climate changes in this area, probably controlled by atmospheric circulation. The core shows a clear binomial structure, reflecting changes in sedimentation at the end of the Little Ice Age (LIA) and afterward. For the northern part of the East Novaya Zemlya Trough, low sea surface temperatures and an increase in the duration of ice cover at the end of the LIA in the 1780s−1810s have been reconstructed. Since the 1810s, the hydrodynamic activity of water masses intensified sharply due to glacier melting (especially after the 1840s). In addition, an increase in sea surface temperatures can be assumed, except for the cooling of the 1910s. Later, circulation of water masses increased, contributing to the supply of terrigenous material to the deep parts of the trough.

Winter Climate Shapes Spring Phytoplankton Development in Non‐Ice‐Covered Lakes: Subtropical Lake Taihu as an Example

AbstractWinter warming plays a vital role in spring phytoplankton community succession in temperate lakes due to variation of ice cover duration in winter. How winter conditions affect spring phytoplankton in subtropical lakes without winter ice cover is, however, largely unknown. In this study, covering 26 years, we elucidated the effects of both climate conditions and nutrient levels in winter on the phytoplankton community (expressed as Morpho‐Functional Groups) in spring in Lake Taihu, a large shallow subtropical lake in China. During this period, wind speed declined significantly in both winter and spring from 1992 to 2017 and the sunshine hours increased slightly from 2000 to 2017. The biomass of eight dominant phytoplankton groups showed increasing trends from 1992 to 2017, while it declined for one group, which mainly included filamentous green algae such as Ulothrix sp. Nonmetric multidimensional scaling (NMDS) results indicated that wind speed and sunshine duration in winter and spring were the most important factors affecting the spring phytoplankton community in Lake Taihu. Also, partial least squares path modeling (PLS‐PM) suggested that the spring phytoplankton community was strongly affected by winter conditions. Our study indicated that the “climate memory” effects on phytoplankton, resulting from winter and acting on the following spring, not only occur in north temperate winter ice‐covered shallow lakes but also in subtropical lakes without ice‐covered in winter.

Ice Regime of the Kozłowa Góra Reservoir (Southern Poland) as an Indicator of Changes of the Thermal Conditions of Ambient Air

Ice phenomena are construed as the occurrence of ice in water irrespective of its structure, form, and duration. One of the most frequently discussed research problems is the possibility of using long-term ice phenology as an indicator of changes of the thermal conditions of ambient air. The study used correlation analysis and regression models in order to determine changes in the parameters studied over time. In order to compare the ice regime of the study reservoir and other lakes in the region, discriminant function analysis, principal components analysis (PCA), and canonical redundancy analysis (RDA) were applied. During the 52 winter seasons studied (1964–2015), there were weak but still statistically significant trends concerning the increase in air temperature in the region (by 0.3 °C per decade), the reduction in the number of days with ice cover (by 8.6 days per decade) and the decline in the maximum and average thicknesses of lake ice (by 2.0 cm and 1.2 cm per decade). The low average depth and volume capacity are reflected in the rapid freezing rate of the reservoir, and its location results in a longer duration of ice cover, greater ice thickness, and later dates of its melting.

Hydrologic control on winter dissolved oxygen mediates arsenic cycling in a small subarctic lake

AbstractThe seasonal development of an ice cover is a characteristic feature of subarctic lakes, yet the biogeochemical cycling of redox sensitive elements under ice, including arsenic (As), is poorly understood. We conducted comprehensive geochemical characterization of lake waters, sediment pore waters and lake sediments over two consecutive years to develop a conceptual model of As, iron (Fe), and sulfur (S) dynamics under ice in a shallow subarctic lake (mean depth 2.0 m) impacted by more than 60 yr of As pollution from local gold mining emissions. Lake sediments were a source of As to overlying waters during both winters when oxygen was depleted from interfacial sediments through the reductive dissolution of As‐bearing Fe (oxy)hydroxides, but the influence on lake water chemistry was distinctly different between years and dependent on winter hydrology of the lake. When the lake was hydrologically disconnected from the upstream watershed, anoxia developed through the entire water column and high concentrations of As (&gt; 100 μg L−1) and Fe (&gt; 1000 μg L−1) were measured in lake water. During the second winter, open‐water flow persisted at the lake inlet, which replenished dissolved oxygen in the under‐ice water column, suppressed the upward migration of the Fe and SO4 redox boundaries, and limited sediment As efflux. These findings demonstrate how changing hydrology, specifically ice cover duration, and hydrological connectivity can influence the winter cycling of As, Fe, and S in shallow subarctic lakes.

Lake trout growth is sensitive to spring temperature in southwest Alaska lakes

AbstractIn high‐latitude lakes, air temperature is an important driver of ice cover thickness and duration, which in turn influence water temperature and primary production supporting lake consumers and predators. In lieu of multidecadal observational records necessary to assess the response of lakes to long‐term warming, we used otolith‐based growth records from a long‐lived resident lake fish, lake trout (Salvelinus namaycush), as a proxy for production. Lake trout were collected from seven deep, oligotrophic lakes in Lake Clark National Park and Preserve on in southwest Alaska that varied in the presence of marine‐derived nutrients (MDN) from anadromous sockeye salmon (Oncorhynchus nerka). Linear mixed‐effects models were used to partition variation in lake trout growth by age and calendar‐year and model comparisons tested for a mean increase in lake trout growth with sockeye salmon presence. Year effects from the best mixed‐effects model were subsequently compared to indices of temperature, lake ice, and regional indices of sockeye salmon escapement. A strong positive correlation between annual lake trout growth and temperature suggested that warmer springs, earlier lake ice break‐up, and a longer ice‐free growing season increase lake trout growth via previously identified bottom‐up increases in production with warming. Accounting for differences in the presence or annual escapement of sockeye salmon with available data did not improve model fit. Collectively with other studies, the results suggest that productivity of subarctic lakes has benefitted from warming spring temperatures and that temperature can synchronise otolith growth across lakes with and without sockeye salmon MDN.