Ice-free Period Research Articles

Reconstructing ice conditions in the southern Chukchi Sea during the last millennium based on chemical composition of sediments and diatom assemblages

Using transfer functions, this study reconstructed the ice-free period (IFP) that occurred 4.7 kya in the southern Chukchi Sea, based on the comparison between the observed data and the chemical composition of sediments accumulated during the observation period. During the analysis, a double normalization of the chemical element contenton rubidium and minimax - was implemented for the first time. It was established that the duration of the IFP varied between 90 and 140 days/year. The highest values are observed in the 21st century and 4–5 kya, coinciding with Pacific water inflow through the Bering Strait. The reconstruction of water masses based on diatom thanatocoenosis has revealed the considerable impact of the Alaskan coastal current on the duration of the IFP. The penetration of its waters to the west during the following time periods - 2750-2550, 1450–800, 350–0 cal yr BP - led to an increase in the duration of the IFP in the central part of the sea by 10–15 days, relative to background values. As a result, the identified variations in the duration of the IFP in the southern Chukchi Sea do not coincide with global climate events of the last millennium, but are clearly demonstrated by an increase in the IFP during the Little Ice Age. Currently, the influence of the Alaskan coastal water is summed up by the effect of increasing global temperatures and Pacific water inflow, which has led to a sharp increase in the IFP in the last few decades.

Modeling of Water Fluxes and Budget in Nam Co Basin during 1979–2013

AbstractIn this study, we established a hydrologic modeling framework over the Nam Co Lake basin by linking a glacier-melt scheme with a physically based, distributed land surface hydrologic model, and a heat-balance model was used for water surface evaporation. Hydrologic processes including evapotranspiration from land regions, runoff from both glacierized and nonglacierized areas, and lake surface evaporation were continuously modeled for 1979–2013, and then lake level changes were reconstructed. Rainfall runoff, snowmelt runoff, and glacier runoff contributed 59%, 28%, and 13% of total runoff, respectively. For the high-altitude region, runoff was mostly generated from glaciers. The lake had a positive water budget in most of the years with an average lake level depth of 128.8 mm, resulting in a total rise of approximately 4.5 m. Precipitation and precipitation-induced runoff were the main water supplies and played a dominant role in lake growth. Although the glacier runoff only contributed 13% of the total runoff, it played an important role in controlling the water level. The rising temperature led to increasing evaporation in two ways: one was providing an energy source for evaporation, and the second was extending the ice-free period. This mitigated the recent expansion of the lake, but on the other hand, it led to increasing glacier runoff into the lake. Hence, the rising temperature had two diametrically opposed effects on lake water balance.

Resilience of pond communities to extreme thermal regime shifts: an alpine–montane reciprocal transplant experiment

Elevational gradients are ideal ecological venues for testing how communities respond to environmental changes associated with global warming. Recent warming rates have been shown to increase with elevation, hypothetically translating into heat waves that more adversely affect cold-adapted alpine communities than lower montane communities exposed to cold waves. We tested this hypothesis by conducting a replicated two-factor (source × elevation) experiment involving a reciprocal transplant of regional alpine and montane pond communities across two elevational sites (2345 m versus 1390 m asl). At each elevation, half of the mesocosms were inoculated with zooplankton and sedimentary egg-banks collected from alpine ponds while the other mesocosms were similarly seeded with zooplankton and sediment collected from montane ponds in 2016. After overwintering, the mesocosms were sampled for temperature and plankton during the ice-free periods of 2017 and 2018. The mesocosms at the low elevation were 8.0 ± 1.2 °C °C warmer than those at the high elevation. Elevation significantly affected total zooplankton biomass, whereas source effects were not significant. Elevation effects revealed that the temperature difference between sites affected the phenology of species within the assembled communities, but not their total biomass. Functional trait analysis revealed that the warmer environment selected for smaller body size and asexual reproduction as a warmer thermal regime stimulated several small parthenogenetic herbivores while suppressing larger, obligate sexual omnivores. Nevertheless, thermal regime shifts did not substantially affect the abundance-weighted mean functional identities of either transferred pond community, highlighting ponds as potential sources of functional insurance against increasingly extreme climate events.

Wind-Driven Coastal Upwelling near Large River Deltas in the Laptev and East-Siberian Seas

The Lena, Kolyma, and Indigirka rivers are among the largest rivers that inflow to the Arctic Ocean. Their discharges form a freshened surface water mass over a wide area in the Laptev and East-Siberian seas and govern many local physical, geochemical, and biological processes. In this study we report coastal upwelling events that are regularly manifested on satellite imagery by increased sea surface turbidity and decreased sea surface temperature at certain areas adjacent to the Lena Delta in the Laptev Sea and the Kolyma and Indigirka deltas in the East-Siberian Sea. These events are formed under strong easterly and southeasterly wind forcing and are estimated to occur during up to 10%–30% of ice-free periods at the study region. Coastal upwelling events induce intense mixing of the Lena, Kolyma, and Indigirka plumes with subjacent saline sea. These plumes are significantly transformed and diluted while spreading over the upwelling areas; therefore, their salinity and depths abruptly increase, while stratification abruptly decreases in the vicinity of their sources. This feature strongly affects the structure of the freshened surface layer during ice-free periods and, therefore, influences circulation, ice formation, and many other processes at the Laptev and East-Siberian seas.

Seasonal cycle of benthic denitrification and DNRA in the aphotic coastal zone, northern Baltic Sea

Current knowledge on the seasonality of benthic nitrate reduction pathways in the aphotic, density stratified coastal zone of the Baltic Sea is largely based on data from muddy sediments, neglecting the potential contribution of sandy sediments. To gain a more comprehensive understanding of seasonality in this part of the Baltic Sea coast, we measured rates of benthic denitrification, anammox and dissimilatory nitrate reduction to ammonium (DNRA) monthly in the ice-free period of 2016 in both sandy and muddy aphotic sediments, northwestern Gulf of Finland. No anammox was observed. The seasonal cycle of denitrification in both sediment types was related to the hydrography-driven development of bottom water temperature. The seasonal cycle of DNRA was less clear and likely connected to a combination of bottom water temperature, carbon to nitrogen ratio, and substrate competition with denitrification. Denitrification and DNRA rates were 50-80 and 20% lower in the sandy than in the muddy sediment. The share of DNRA in total nitrate reduction, however, was higher in the sandy than in the muddy sediment, being (by ~50%) the highest DNRA share in sandy sediments so far measured. Our data add to the small pool of published studies showing significant DNRA in both cold and/or sandy sediments and suggest that DNRA is currently underestimated in the Baltic coastal nitrogen filter. Our results furthermore emphasize that the various environmental conditions of a coastal habitat (light regime, hydrography, and geomorphology) affect biogeochemical element cycling and thus need to be considered in data interpretation.

Water column changes under ice during different winters in a mid-latitude Mediterranean high mountain lake

Winter limnology has been developed mainly in northern-temperate or subarctic lakes, while mid-latitude Mediterranean high mountain lakes have been less studied during the ice-covered season. We present a five-year study in one of these lower latitude high mountain lakes, conducted with multiprobes located at two different depths recording high-frequency data. We have studied highly contrasted winters regarding temperature and snowfall. The results of a principal component analysis and a subsequent hierarchical clustering show that bottom oxygen depletion under ice is strongly influenced by winter cover thickness and transparency. A thick and opaque winter cover (dark mode) leads to an intense oxygen depletion until anoxia, while a thin and clear winter cover (clear mode) allows higher dissolved oxygen saturation due to oxygen production by photosynthesis. Under unusual conditions of cold and dry climate, only a weak decrease in bottom dissolved oxygen was observed. The extent of dissolved oxygen depletion and its relationship with meteorological parameters and climate patterns are further investigated with generalized additive models. Winter cover thickness and phenology are driven by the joint effect of the North Atlantic Oscillation and East Atlantic climatic patterns. Ice phenology could also influence the following ice-free period given the correlation of lake heat content with the ice-off date and the ice cover length. We propose some features jointly occurring in Lake Cimera as a model for mid-latitude Mediterranean high mountain lakes, including (yet not exclusive) the occurrence of very thick winter covers, the prevalence of dark mode, the relatively high and similar through the years oxygen depletion rates, and high water temperatures during the ice-free periods. It is unclear how the ongoing climate change will affect the prevalence of dark over clear modes due to the expected antagonistic effects of warmer temperatures and lower snowfalls.

Interrelated ecological impacts of climate change on an apex predator.

Climate change has broad ecological implications for species that rely on sensitive habitats. For some top predators, loss of habitat is expected to lead to cascading behavioral, nutritional, and reproductive changes that ultimately accelerate population declines. In the case of the polar bear (Ursus maritimus), declining Arctic sea ice reduces access to prey and lengthens seasonal fasting periods. We used a novel combination of physical capture, biopsy darting, and visual aerial observation data to project reproductive performance for polar bears by linking sea ice loss to changes in habitat use, body condition (i.e., fatness), and cub production. Satellite telemetry data from 43 (1991–1997) and 38 (2009–2015) adult female polar bears in the Baffin Bay subpopulation showed that bears now spend an additional 30 d on land (90 d in total) in the 2000s compared to the 1990s, a change closely correlated with changes in spring sea ice breakup and fall sea ice formation. Body condition declined for all sex, age, and reproductive classes and was positively correlated with sea ice availability in the current and previous year. Furthermore, cub litter size was positively correlated with maternal condition and spring breakup date (i.e., later breakup leading to larger litters), and negatively correlated with the duration of the ice‐free period (i.e., longer ice‐free periods leading to smaller litters). Based on these relationships, we projected reproductive performance three polar bear generations into the future (approximately 35 yr). Results indicate that two‐cub litters, previously the norm, could largely disappear from Baffin Bay as sea ice loss continues. Our findings demonstrate how concurrent analysis of multiple data types collected over long periods from polar bears can provide a mechanistic understanding of the ecological implications of climate change. This information is needed for long‐term conservation planning, which includes quantitative harvest risk assessments that incorporate estimated or assumed trends in future environmental carrying capacity.

<p><strong>New Chrysophycean cyst morphotypes and their ecology in Finland</strong></p>

Despite multiple studies on chrysophyte stomatocysts globally, detailed surveys of these resting stages have remained scarce in Northern Europe. This is the first description of new chrysophyte cyst morphotypes in concordance with the International Statospore Working Group guidelines, based on scanning electron microscope images from lake sediment material in Finland. A nationwide chrysophyte cyst survey revealed 18 new cyst morphotypes with different surface ornamentation types. Environmental background information on the locations and the quantitatively calculated optimums and tolerances for electric conductivity, pH, total phosphorus and ice-free period are also provided.

Amderma open water period characteristics based on satellite observation of the sea ice concentration, archives for the 1979-2018 period

The aim of this study is to estimate the Amderma station (the Kara Sea) ice-free period using sea ice concentration satellite datasets in comparison to observation data. The work follows the research performed for the Western Coast of the Yamal (Marresalya) being the part of the Arctic coastal dynamics study. The OSISAF, JAXA and NSIDC (resolution 25 km, 1 day, 1979-2018) sea ice concentration datasets were used to characterize the water area adjacent to the station within the 30-50 km radius. The threshold (15%-concentration) and the author's "sliding window" methods were used to detect open water start and end dates. According to the satellite data, the ice-free period in the 30-50-kilometer water area along the Amderma coast is shifted by 2-3 weeks closer to December if compared to observations. At Amderma station (in the contrast to Marresalya), there are no significant trends in ice-free period start dates. On the adjacent water area, the destruction of the ice cover occurs earlier by 3-6 weeks if compared to the 1980’s, and the end date by 3-6 weeks later. The duration of the open water period over 40 years has increased by 32-36 days at the station and by 52-120 days (40-100%) in the adjacent water area.

Shifts in phenology of zooplankton due to climate change

Freshwater zooplankton is recognized as sensitive indicator of environmental changes. limate change has already altered abundance, species composition, structure of freshwater zooplankton and the timing of seasonal behavior, events and life-history parameters. In recent decades, due to climate warming, the ice-free period, the biological summer period, the river runoff have increased in Lake Onego. We have identified 5 phenological phases (winter, spring, early summer, late summer, autumn) on the base of the ratio of the main taxonomic groups of zooplankton using discriminant analysis. The date of the beginning and the end of each phenophase, the duration of the phenological phases were determined. omparison of long-term data with current data showed a phenological phases shifts. Early summer phenophase has occurred about 30 days earlier. Autumn phenophase has occurred on average 23 days earlier. Knowledge of phenology zooplankton in Petrozavodsk bay of Lake Onego makes it possible to detail the mechanisms of its functioning and to describe the response to climate change.

Multi-scale observations of the co-evolution of sea ice thermophysical properties and microwave brightness temperatures during the summer melt period in Hudson Bay

Monitoring the trend of sea ice breakup and formation in Hudson Bay is vital for maritime operations, such as local hunting or shipping, particularly in response to the lengthening of the ice-free period in the Bay driven by climate change. Satellite passive microwave sea ice concentration products are commonly used for large-scale sea ice monitoring and predictive modelling; however, these product algorithms are known to underperform during the summer melt period due to the changes in sea ice thermophysical properties. This study investigates the evolution of in situ and satellite-retrieved brightness temperature (TB) throughout the melt season using a combination of in situ passive microwave measurements, thermophysical sampling, unmanned aerial vehicle (UAV) surveys, and satellite-retrieved TB. In situ data revealed a strong positive correlation between the presence of liquid water in the snow matrix and in situ TB in the 37 and 89 GHz frequencies. When considering TB ratios utilized by popular sea ice concentration algorithms (e.g., NASA Team 2), liquid water presence in the snow matrix was shown to increase the in situ TB gradient ratio of 37/19V. In situ gradient ratios of 89/19V and 89/19H were shown to correlate positively with UAV-derived melt pond coverage across the ice surface. Multi-scale comparison between in situ TB measurements and satellite-retrieved TB (by Advanced Microwave Scanning Radiometer 2) showed a distinct pattern of passive microwave TB signature at different stages of melt, confirmed by data from in situ thermophysical measurements. This pattern allowed for both in situ and satellite-retrieved TB to be partitioned into three discrete stages of sea ice melt: late spring, early melt and advanced melt. The results of this study thus advance the goal of achieving more accurate modeled predictions of the sea ice cover during the critical navigation and breakup period in Hudson Bay.

Тривалість фази збереження та руйнування у випадках відкладень ожеледі категорії СГЯ (стихійні) на території України у місяці холодного періоду року протягом 1991– 2016 рр.

The article deals with the question of the duration of the preservation and destruction phase which were calculated for ice-free periods of the category of SHP and were observed on the territory of Ukraine in the month of the cold period of the year during certain periods 1991–2000, 2001-2010 and 2011-2016. It was established that the duration of the preservation phase and the destruction of ice-oily deposits in the category of SHP is very volatile and ranges from near-instant destruction after reaching a maximum diameter of several hours or several dozen hours. However, there are cases where the duration of this phase can be 4 days in a row and more than several hundred hours. The study found that for the most part during the investigated period, the glacial deposits of the SHP category were dominated by non-prolonged conservation and degradation phases, regardless of the region where the sediment was formed, and regardless of the overall duration of the sediment itself, which could be significant. In 2001–2010 and 2011–2016, unlike in the period of 1991-2000, in January and December, the number of cases of ice-ousted categories of SHP increased. Moreover, in January, especially in 2011–2016, the number of cases with a significant duration of the phase of preservation and destruction of ice deposits of the category of SHP was increased. From the above we can draw a number of conclusions, namely: – During 1991–2000, the phases of preservation and destruction of ice-clay deposits in the category of HPAs were mostly non-prolonged and ranging from several hours to several dozen hours. The most prolonged phases of preservation and destruction of deposits of iced ice of category SHHA were in cases of sediments in Lower Zirgozakh in January 1996, in March 1998 in Kropivnitsky and most often in November 1999 in Gadyach, Dolynska, Komissarivka, Mariupol, Prisheby, and also in 2000 It is in Novodnistrovsk, Separate, Lyubashevtsi, Serbs, Voznesensk, December 1997 in Loshkarivka, Kryvy Rih, Nikopol, Lyubashevtsi, Prisheb and especially in Donetsk. – In 2001–2010, the amount of ice-cream deposits in the category of SHP increased slightly. In addition, the duration of the preservation and destruction phase compared to the previous period changed slightly, taking into account the individual months. So, in January, along with the relatively long phases of preservation and destruction of ice-clay deposits of the category of SHP (up to several dozen hours), in 2010 deposits with very long phases of conservation and destruction in Debaltsevo and especially in Mysovoye were observed. In December of this period, the long phases of preservation and destruction of deposits of iced ice of category SHP were observed in 2004 in Dar’yivka, and in 2008 in Vinnitsa and Ovruch. In the remaining months, the duration of the conservation and destruction phase was overwhelmingly within a few hours, at least to several dozen golds (11–25 hours) – Unlike in the years 1991-2000 and 2001-2010, in January the number of cases of ice deposits of the category of SHP increased in the five-year period of 2011–2016. They met practically in most regions. Significantly increased cases with them, where the duration of the preservation and destruction phase was significant and exceeded the duration of 4 consecutive days. Such cases were observed in January 2013 in Rava-Ruska, Kamianets Buzka and Poltava, in January 2014 – in Rava-Ruska, Ternopil, Amvrosiyivka, Rosdilna, Mykolayiv, Ochakov, and Simferopol. In December 2012, a similar accident happened in Evpatoria.

Interannual, summer, and diel variability of CH4and CO2effluxes from Toolik Lake, Alaska, during the ice-free periods 2010–2015

Accelerated warming in the Arctic has led to concern regarding the amount of carbon emission potential from Arctic water bodies. Yet, aquatic carbon dioxide (CO2) and methane (CH4) flux measurements remain scarce, particularly at high resolution and over long periods of time. Effluxes of methane (CH4) and carbon dioxide (CO2) from Toolik Lake, a deep glacial lake in northern Alaska, were measured for the first time with the direct eddy covariance (EC) flux technique during six ice-free lake periods (2010-2015). CO2 flux estimates from the lake (daily average efflux of 16.7 ± 5.3 mmol m-2 d-1) were in good agreement with earlier estimates from 1975-1989 using different methods. CH4 effluxes in 2010-2015 (averaging 0.13 ± 0.06 mmol m-2 d-1) showed an interannual variation that was 4.1 times greater than median diel variations, but mean fluxes were almost one order of magnitude lower than earlier estimates obtained from single water samples in 1990 and 2011-2012. The overall global warming potential (GWP) of Toolik Lake is thus governed mostly by CO2 effluxes, contributing 86-93% of the ice-free period GWP of 26-90 g CO2,eq m-2. Diel variation in fluxes was also important, with up to a 2-fold (CH4) to 4-fold (CO2) difference between the highest nighttime and lowest daytime effluxes. Within the summer ice-free period, on average, CH4 fluxes increased 2-fold during the first half of the summer, then remained almost constant, whereas CO2 effluxes remained almost constant over the entire summer, ending with a linear increase during the last 1-2 weeks of measurements. Due to the cold bottom temperatures of this 26 m deep lake, and the absence of ebullition and episodic flux events, Toolik Lake and other deep glacial lakes are likely not hot spots for greenhouse gas emissions, but they still contribute to the overall GWP of the Arctic.

The major Late Albian transgressive event recorded in the epeiric platform of the Langshan Formation in central Tibet

Abstract Global sea-level changes strongly impact within-basin depositional patterns and the evolution of palaeoclimate, palaeogeography and palaeoecology. During the long, worldwide ice-free period in the mid-Cretaceous greenhouse time interval, high-frequency global sea-level changes were recorded in sedimentary archives. However, the causes of these global sea-level changes are still debated. In central Tibet, the 1 km-thick Langshan Formation has been dated to the late Aptian to early Cenomanian based on larger benthic foraminifera and accumulated in an epeiric seaway, thus, it provides a good opportunity to reconstruct the sea-level change and their controlling factors. Eleven distinct microfacies corresponding to three sedimentary environments have been identified in the Langshan Formation. Calcispheres marlstone and bioclastic wackestone with calcispheres were deposited in an open marine environment; coral rudstone, rudist rudstone and benthic foraminifera–rudist wackestone characterize were deposited in a rudist bank environment; and orbitolinids floatstone–rudstone, green algae packstone, bioclastic grainstone, orbitolinids wackestone with small benthic foraminifera, spicules wackestone and small benthic foraminifera wackestone–mudstone were deposited in a lagoonal environment. The Langshan Formation accumulated on an epeiric platform. This unit documents a sudden deepening event from a rudist bank to an open marine environment during the late Albian ( c. 107 Ma). Integrating these findings with regional data from the literature, we infer that this deepening event was a widespread, roughly synchronous feature across the globe, and was controlled by a global sea-level rise related to the decay of polar ice sheets or the release of water from continental aquifers.

Snow Deposition and Melting as Drivers of Polychlorinated Biphenyls and Organochlorine Pesticides in Arctic Rivers, Lakes, and Ocean.

Concurrent sampling of freshwater (lakes and rivers), seawater, snow, air, and zooplankton for a range of legacy polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) was undertaken in the Canadian High Arctic during ice-covered, melting, and ice-free conditions. Overall, there was a general trend of higher fluvial PCB/OCP concentrations associated with the spring snow melt (early-mid June), while much lower concentrations were detected during the snow-free season (end of July). In contrast, PCB concentrations in two Arctic lakes (West and East Lakes, Melville Island) and in ocean waters, sharply increased in the ice-free period, likely because of inputs from the ice/snow layer melting and river runoff. The resulting air-water fugacity ratios and fluxes followed a remarkable shift during the sampling campaign. PCBs and OCPs shifted from equilibrium during ice/snow-covered conditions toward a clear net volatilization of PCBs and most of the OCPs during snow/ice-free conditions. Differences in the bioaccumulation factor for PCB/OCPs in zooplankton between West and East Lakes were observed, likely because of zooplankton being exposed to more contaminated food in West Lake due to higher turbidity related to in-lake disturbances.

Quantifying DOC and Its Controlling Factors in Major Arctic Rivers during Ice-Free Conditions using Sentinel-2 Data

The six largest Arctic rivers (Yenisey, Lena, Ob’, Kolyma, Yukon, and Mackenzie) drain the organic-rich Arctic watersheds and serve as important pools in the global carbon cycle. Satellite remote sensing data are considered to be a necessary supplement to the ground-based monitoring of riverine organic matter circulation, especially for the ice-free periods in high-latitudes. In this study, we propose a remote sensing retrieval algorithm to obtain the chromophoric dissolved organic matter (CDOM) levels of the six largest Arctic rivers using Sentinel-2 images from 2016 to 2018. These CDOM results are converted to dissolved organic carbon (DOC) concentrations using the strong relationship (R2 = 0.89) between the field measurements of these two water constituents. The temporal-spatial distributions of the DOC in the six largest Arctic rivers during ice-free conditions are depicted. The performance of the retrieval algorithm verifies the capacity of using Sentinel-2 data to monitor riverine DOC variations due to its improved spatial resolution, better band placement, and increased observation frequency. River discharge, watershed slopes, human activities, and land use/land cover change drove much of the variation in the satellite-derived DOC. The seasonality, geography, and scale would affect the correlation between DOC concentration and these influence factors. Our results could improve the ability to monitor DOC fluxes in Arctic rivers and advance our understanding of the Earth’s carbon cycle.

Long-term trends in hypolimnetic volumes and dissolved oxygen concentrations in Boreal Shield lakes of south-central Ontario, Canada

Temperature–oxygen profiles, collected biweekly to monthly for ∼40 years, were used to calculate end-of-summer volume-weighted hypolimnetic oxygen (VWHO) concentrations in six small lakes located in south-central Ontario, Canada. Coherent decreases in thermocline depth and increases in hypolimnetic volume, mean hypolimnetic dissolved oxygen (DO) concentration, and VWHO were observed in five of the six study lakes. All lakes underwent an abrupt increase in VWHO and mean hypolimnetic DO after 2010. In four of the six study lakes, the highest hypolimnetic DO concentrations were observed in years where chlorophyll a concentrations were low, whereas at five of the six study lakes the highest hypolimnetic volumes were observed when dissolved organic carbon concentrations were relatively high. Warmer spring or winter air temperatures were associated with higher hypolimnetic DO concentrations at two sites, and longer ice-free periods were associated with smaller hypolimnetic volumes at two sites. These results suggest that the recent VWHO increases in the studied south-central Ontario lakes may be a function of multiple drivers that include changes in primary production, lake water transparency, and regional climatic factors.

Soil moisture dynamics modelling of a reclaimed upland in the early post-construction period

Mine reclamation landscapes typically comprise layers of mine waste materials such as tailings sands, capped with a cover soil. In addition to the arrangement and placement of these materials, their hydraulic properties govern the performance of the built system. Soil evolution due to freeze–thaw cycling can result in dramatically altered soil hydraulic properties compared to the as-built material. Therefore, prediction of present and future hydrologic behaviour relies on understanding the nature and magnitude of this change and the elapsed time associated with stabilization. This research quantifies the transient hydraulic properties of mine reclamation materials at a constructed upland within a reclaimed watershed, and models the effect of this evolution on the partitioning of soil moisture between evaporation and groundwater recharge. Soil moisture dynamics were simulated using HYDRUS-1D for the ice-free period two, three, and five years after construction. A capillary barrier between the fine-grained cover soil and coarse-grained tailings sand regulated percolation past the interface. Soil evolution of the cover soil was responsible for an increase in saturated hydraulic conductivity by an order of magnitude, decrease in air-entry pressure by a factor of 4, and decrease in the van Genuchten n parameter by a factor of 2. The altered soil hydraulic properties associated with the weathered cover soil ultimately resulted in a 64% increase in groundwater recharge as a consequence of the capillary barrier weakening. The cover soil exhibited minor spatial heterogeneity in soil hydraulic properties, and did not contribute substantial uncertainty to the estimates of groundwater recharge and evaporation. Cover soil thickness exerted a strong influence on the partitioning of soil moisture. Reclaimed uplands will provide the most recharge to downgradient ecosystems in the period following the completion of soil evolution (~4 years) but preceding substantial vegetation development.

Decadal trends in water chemistry of Alpine lakes in calcareous catchments driven by climate change

High mountain lakes are considered sensitive indicators of the effects of natural and anthropogenic drivers, including atmospheric deposition and climate change. In this study, we assess long-term trends in the chemistry of a group of high altitude lakes in the Western Alps, Italy, lying in bedrock with a relevant presence of basic, soluble rocks. An in-depth investigation was performed on two key-sites (Lakes Boden Inferiore and Superiore) for which continuous chemical data are available for a period of 30 years. A group of 10 additional lakes in the same area was also considered; these lakes were sampled at the end of the ice-free period during irregular surveys in the period 1980–2017. Water samples were analysed for the main chemical variables, including pH, electrical conductivity, major ions (Ca2+, Mg2+, Na+, K+, HCO3−, Cl−, SO42−, NO3−) and algal nutrients (phosphorus and nitrogen compounds, reactive silica).A steep increase in conductivity and ion concentrations was detected at the key-sites: conductivity increased from 40–45 to 60–70 µS cm−1 over the period 1984–2017; sulphate concentrations more than doubled over the same period (from 50–60 to 120–180 µeq L−1) and base cations increased from 400–500 to 600–750 µeq L−1. An increase in the solute content was also detected in the survey lakes (average conductivity from 39 ± 20 to 57 ± 23 µS cm−1). The analysis of meteorological data revealed a significant increase of air temperature (0.019 °C y−1 over the period 1950–2017), mainly in spring and summer (0.033 °C y−1), and a decrease of snow cover depth and duration. Meteo-climatic drivers were identified as the responsible for the chemical changes occurred in the lakes. Climate-driven effects on weathering rates were mainly indirect and occurred by affecting the flow paths of water at both surface and subsurface level. Cryosphere modification (reduced snow cover and permafrost thawing) also played a role.

Dissolved Organic Matter and Associated Trace Metal Dynamics from River to Lake, Under Ice-Covered and Ice-Free Conditions.

The present study investigates the changes in dissolved organic matter (DOM) composition and its influences on trace metal dispersion from the Shuya River (SR) in the Petrozavodsk Bay of Lake Onega during ice-covered and ice-free periods. Humic substances (HS) found in the SR dominated the composition of DOM through the river-bay-lake continuum in both periods. When the bay was ice-covered, both the aromaticity and the size of HS varied in the water column according to a horizontal stratification and decreased in the bay, while under ice-free conditions, they decreased along the river-lake gradient, suggesting in both cases a decrease in the proportion of HS with high aromatic character. These findings were associated with an overall decrease in the proportion of HS components that have the highest molecular masses. The quantification of metal bound to HS revealed that these characteristics were associated with a decrease in the binding capacity of the HS for Fe and Al but not Cu while dispersing in the bay to the lake. Pb was found to bind on HS, but its behavior in the bay could not be related to the HS dispersion nor to the changes in HS properties.