Seasonal Lake Research Articles

Water safety assessment and spatio-temporal changes in Dongting Lake, China on the basis of water regime during 1980–2014

Abstract The drastic changes in water regime are of great importance for maintaining water security in lakes with violent seasonal fluctuations. Based on hydrological data of Dongting Lake, the second largest freshwater lake in China, during 1980–2014, a set of water safety assessment methods suitable for seasonal lakes was constructed. Results demonstrated the following. (1) The year 2003 was a major time point for changes in water regime in Dongting Lake between 1980 and 2014. (2) The water regime changes in different parts of Dongting Lake exhibited certain similarities in periodicity and overall change trends. Among them, South Dongting Lake presented the best water security status, followed by East Dongting Lake and West Dongting Lake. (3) Compared with 1980–2002, the complexity of the water safety level change in East Dongting Lake increased in 2003–2014, as manifested in the tendency of the distribution of water safety levels to change sharply. (4) The influence of dry years on the water safety of Dongting Lake was greater than that of rainy years. The multi-time, multi-scale and multi-target lake water safety assessment method based on water regimes provides new ideas and methods for global research on seasonal lake water safety.

Integrated rockfall hazard and risk assessment along highways: An example for Jiuzhaigou area after the 2017 Ms 7.0 Jiuzhaigou earthquake, China

This work addresses the integrated assessment of rockfall (including landslides) hazards and risk for S301, Z120, and Z128 highways, which are important transportation corridors to the world heritage site Jiuzhai Valley National Park in Sichuan, China. The highways are severely threatened by rockfalls or landslide events after the 2017 Ms 7.0 Jiuzhaigou earthquake. Field survey (September 14–18th, 2017, May 15–20th, 2018, and September 9–17th, 2018), unmanned aerial vehicle (UAV), and satellite image identified high-relief rockfalls and road construction rockfalls or landslides along the highway. Rockfall hazard is qualitatively evaluated using block count, velocity, and flying height through a 3D rockfall simulation at local and regional scales. Rockfall risk is quantitatively assessed with rockfall event probability, propagation probability, spatial probability, and vulnerability for different block volume classes. Approximately 21.5%, 20.5%, and 5.3% of the road mileage was found to be subject to an unacceptable (UA) risk class for vehicles along S301, Z120, and Z128 highways, respectively. Approximately 20.1% and 3.3% of the road mileage belong to the UA risk class for tourists along Z120 and Z128 highways, respectively. Results highlighted that high-relief rockfall events were intensively located at K50 to K55 (Guanmenzi to Ganheba) and K70 to K72 (Jiudaoguai to Shangsizhai Village) road mileages along S301 highway and KZ18 to KZ22 (Five Flower Lake to Arrow Bamboo Lake) road mileages, KZ30 (Swan Lake to Virgin Forests), and KY10.5 kilometers in Jiuzhai Valley. Rockfalls in these locations were classified under the UA risk class and medium to very high hazard index. Road construction rockfalls were located at K67 (Jiuzhai Paradise) and K75–K76 kilometers along S301 highway and KZ12 to KZ14 (Rhino Lake to Nuorilang Waterfall), KZ16.5 to KZ17.5 (Golden Bell Lake), KY5 (Lower Seasonal Lake), and KY14 (Upper Seasonal Lake) kilometers along Z120 and Z128 highway in Jiuzhai Valley. Rockfalls in these areas were within a reasonable practicable risk to UA risk class and very low to medium hazard index. Finally, defensive measures, including flexible nets, concrete walls, and artificial tunnels, could be selected appropriately on the basis of the rockfall hazard index and risk class. This study revealed the integration between qualitative rockfall hazard assessment and quantitative rockfall risk assessment, which is crucial in studying rockfall prevention and mitigation.

Modeling experiments on seasonal lake ice mass and energy balance in the Qinghai–Tibet Plateau: a case study

Abstract. The lake-rich Qinghai–Tibet Plateau (QTP) has significant impacts on regional and global water cycles and monsoon systems through heat and water vapor exchange. The lake–atmosphere interactions have been quantified over open-water periods, yet little is known about the lake ice thermodynamics and heat and mass balance during the ice-covered season due to a lack of field data. In this study, a high-resolution thermodynamic ice model was applied in experiments of lake ice evolution and energy balance of a shallow lake in the QTP. Basal growth and melt dominated the seasonal evolution of lake ice, but surface sublimation was also crucial for ice loss, accounting for up to 40 % of the maximum ice thickness. Sublimation was also responsible for 41 % of the lake water loss during the ice-covered period. Simulation results matched the observations well with respect to ice mass balance components, ice thickness, and ice temperature. Strong solar radiation, negative air temperature, low air moisture, and prevailing strong winds were the major driving forces controlling the seasonal ice mass balance. The energy balance was estimated at the ice surface and bottom, and within the ice interior and under-ice water. Particularly, almost all heat fluxes showed significant diurnal variations including incoming, absorbed, and penetrated solar radiation, long-wave radiation, turbulent air–ice heat fluxes, and basal ice–water heat fluxes. The calculated ice surface temperature indicated that the atmospheric boundary layer stratification was consistently stable or neutral throughout the ice-covered period. The turbulent air–ice heat fluxes and the net heat gain by the lake were much lower than those during the open-water period.

A grain size and n-alkanes record of Holocene environmental evolution from a groundwater recharge lake in Badain Jaran Desert, Northwestern China

Vertical water transport plays an important role in the development and maintenance of lakes in arid zones. However, previous study of this phenomenon has focused mainly on the effects of regional precipitation, rather than effects of groundwater recharge, on arid-zone environmental change. We selected a sedimentary profile from a seasonal lake basin located in the hinterland of the Badain Jaran Desert, northwestern China, to assess the Holocene environmental evolution of this region and its response to climate change. Our results show that peat deposition from 11 to 10 ka indicates humidification after Younger Dryas (YD) event; the lake sediment and lower EM2 and lower principal component analysis (PCA)-1 scores indicate relative more humid environment from 10 to 7.8 ka; the lake sediment and higher EM2 and higher PCA-1 scores indicate most humid environment from 7.8 to 5.8 ka; the transition from lacustrine facies to limnetic facies and increasing salinity indicate drying trend from 5.8 to 2.5 ka; the aeolian sand sediment and lowest EM2 and lowest PCA-1 scores indicate driest environment from 2.5 to 0.8 ka; and lacustrine facies and finest grain size indicate relative humid environment during the ‘Little Ice Age’ period. The environment was relative humid in early Holocene, most Humid in mid-Holocene, and dry in mid-late Holocene. The moisture pattern in the hinterland of the Badain Jaran Desert was synchronous with that in the northeastern of Tibetan Plateau, which implies that the groundwater recharge lake was dominated by the intensity of groundwater recharge from monsoon margin area, especially the northeastern of Tibetan Plateau. As a record from groundwater recharge lake without runoff, our study provides the groundwater output quantity record from northeastern of Tibetan Plateau and would benefit the environment change research and regional water resources allocation around the Tibetan Plateau.

Tracing natural groundwater recharge to the Thiaroye aquifer of Dakar, Senegal

Urban groundwater in Sub-Saharan Africa provides vital freshwater to rapidly growing cities. In the Thiaroye aquifer of Dakar (Senegal), groundwater within Quaternary unconsolidated sands provided nearly half of the city’s water supply into the 1980s. Rising nitrate concentrations traced to faecal contamination sharply curtailed groundwater withdrawals, which now contribute just 5% to Dakar’s water supply. To understand the attenuation capacity of this urban aquifer under a monsoonal semi-arid climate, stable-isotope ratios of O and H and radioactive tritium (3H), compiled over several studies, are used together with piezometric data to trace the origin of groundwater recharge and groundwater flowpaths. Shallow groundwaters derive predominantly from modern rainfall (tritium >2 TU in 85% of sampled wells). δ18O and δ2H values in groundwater vary by >4 and 20‰, respectively, reflecting substantial variability in evaporative enrichment prior to recharge. These signatures in groundwater regress to a value on the local meteoric water line that is depleted in heavy isotopes relative to the weighted-mean average composition of local rainfall, a bias that suggests recharge derives preferentially from isotopically depleted rainfall observed during the latter part of the monsoon (September). The distribution of tritium in groundwater is consistent with groundwater flowpaths to seasonal lakes and wetlands, defined by piezometric records. Piezometric data further confirm the diffuse nature and seasonality of rain-fed recharge. The conceptual understanding of groundwater recharge and flow provides a context to evaluate attenuation of anthropogenic recharge that is effectively diffuse and constant from the vast network of sanitation facilities that drain to this aquifer.

Modeling of Seasonal Lake Level Fluctuations of Titan's Seas/Lakes

AbstractSeasonal variations in lake levels of Titan's hydrocarbon seas/lakes are predicted by an ocean circulation model in an effort to understand the observed temporal changes in lake size or lack thereof. Three different ground permeabilities are assumed so as to change the relative importance of precipitation, evaporation, river runoff, and groundwater seepage for the lake methane budget. The lake level generally rises in the rainy season around the summer solstice and falls or stagnates during long dry periods in autumn and winter. The annual lake level range in the northern hemisphere amounts to 50–120 cm depending on geographic location and size of the lakes and ground permeability. If the hydraulic connection between Punga Mare and Kraken Mare is weak, the lake level range of Punga Mare amplifies at the expense of other seas and also establishes a large lake level difference between these two seas, which is not compatible with the observation by the Cassini spacecraft. On‐lake precipitation would cause the lake level of Ontario Lacus to vary seasonally by merely 15 cm, yet river runoff from the huge catchment area can increase the annual lake level range to several meters. The shrinkage of Ontario Lacus observed by Cassini is more likely to be caused by lakebed seepage than by evaporation. The ultimate cause of the difference in the seasonal behavior between northern and southern lakes may be the hemispheric asymmetry in precipitation, be it caused astronomically or topographically.

Hydrodynamic investigation of surface hydrological connectivity and its effects on the water quality of seasonal lakes: Insights from a complex floodplain setting (Poyang Lake, China)

Small, seasonal lakes that exist in floodplains are rarely investigated, and yet they play an important role in the protection of biodiversity and are highly susceptible to modification due to human activities. This study presents a first attempt to combine hydrodynamic modeling and statistical methods to investigate hydrological connectivity and its relationship with the water quality of nine seasonal lakes within the floodplains of Poyang Lake (China). The hydrodynamic model reproduced reasonably well the hydrological regime of the lake and surrounding floodplains, based on field measurements and remote sensing data. Floodplain lakes exhibit similar water-level dynamics to the main lake during connected periods of flooding, while they decouple from the main lake during recession periods. Geostatistical results reveal that although the north-south hydrological connectivity extends over a longer pathway than the west-east connectivity, the rapid reduction in the west-east connectivity indicates a more sensitive response. The west-east connectivity tends to play a dominant role in affecting the interactions between the main lake and floodplains, as expected. Statistical methods indicate that surface hydrological connectivity across the floodplain results in an enhanced spatial similarity in the water quality of the floodplain lakes, in terms of a multitude of water quality parameters (TN, TP, NH4+-N, NO3−-N, NO2−-N, PO43−, CODMn, and Chl a), while surface hydrological isolation was observed to increase the water quality differences between the seasonal lakes. Additionally, enhanced hydrological connectivity may lead to improved water quality of the seasonal lakes from low connectivity to high connectivity condition. Hydrological connectivity may be a key factor controlling the dynamics in water quality between seasonal lakes. The findings of this study support the management of both Poyang Lake and the floodplain wetlands by providing important information on both water resource and water quality, and proposals to better manage the impacts of intensive human activities.

Arapaima Fish Scale: One of the Toughest Flexible Biological Materials

In order for fish scales to provide protection from predators without significantly compromising mobility, they have to be lightweight, flexible and tough. The Arapaima fish scale is a superb example of these properties, which enable survival in piranha-infested seasonal lakes of the Amazon. These elasmoid scales are composed of two layers: a laminate composite of parallel collagen fibrils arranged in a Bouligand-like pattern, and a hard, highly mineralized surface layer that prevents initial penetration damage. We measure here the J-integral based fracture toughness of the scale and find that the crack-growth toughness as high as ~200 kJ⋅m-2, representing a very high fracture resistance for a flexible biological material. This toughness is primarily the result of multiple mechanisms of deformation acting in concert in the twisted plywood structure of the scale, involving the collagen lamellae at varying orientations controlling crack advance through stretching, rotation, delamination and shear, and finally fracture. These toughening mechanisms operate in sequence at the crack tip, retarding its advance in a most effective manner. The toughness values obtained for the Arapaima scales indicate that they are among the toughest of nature’s flexible biological materials.

Water Regime Evolution of Large Seasonal Lakes: Indicators for Characterization and an Application in Poyang Lake, China

Impacted by ongoing climate change and anthropogenic activities, large seasonal lakes experience water regime evolution, which raises challenges for the management of water resources and environment. The water regime evolution refers to the spatial and temporal alterations in the hydrological features of lakes. Characterizing the lake water regime and its alteration may help policymakers design effective adaption strategies. Therefore, total 47 hydrological indicators were proposed, considering intra-annual fluctuations, flood and drought features, and rate and frequency of water level variations. Combined with Mann-Kendall algorithm and Sen’s slope, the indicators were applied in Poyang Lake, a typically large seasonal lake in China, as a case study. The results revealed temporal and spatial variations in different hydrological indicators. The most dramatic alteration was the water level decline in October and November over the entire study phase, especially over the past 30 years. This was an urgent environmental problem that Poyang Lake faced, partially caused by the increased hydraulic gradient between southern and northern lake. It could trigger the drought occurring earlier, prolong the drought duration, and impair the wetland ecosystem. Environmental water requirements of both Poyang Lake and Yangtze River were suggested for regional sustainable development. The application in Poyang Lake showed the practicability and reliability of the indicators, which are applicable in international seasonal lakes. The series of indicators can be used in whole or in part, determined by the ecohydrological characters of a specific lake and the research objectives.

A wide window of migration phenology captures inter‐annual variability of favourable conditions: Results of a whole‐lake experiment with juvenile Pacific salmon

Abstract Survival of post‐larval and juvenile organisms can depend on multiple seasonally‐fluctuating features, including thermal conditions and food availability. Alterations in the phenology of either consumers or their prey might decouple trophic relationships and reduce consumer growth and survival, and this potential for mismatches is especially pronounced in migratory organisms that change habitats. Juvenile sockeye salmon (Oncorhynchus nerka) migrate from natal streams to lake habitats, and we hypothesised that their in‐lake growth and survival depends on whether timing of migration matches suitable lake conditions. We used mixed effects models to test the hypotheses that: (a) the most successful entry times correspond to favourable prey densities and lake thermal conditions; and (b) a mismatch in fish entry time and seasonal lake dynamics can reduce fish growth and survival. These models were applied to an 11‐year time series of migration timing, capture rate and size at smolting for juvenile sockeye salmon in Lake Washington, WA, USA. Juvenile sockeye salmon entering Lake Washington later in the season encountered higher zooplankton abundance and warmer water, and experienced higher average rates of growth and survival, but the optimal date for lake entry ranged across years by up to a month. Zooplankton abundance and bloom timing affected fish growth and relative survival more than lake temperature, and survival was most influenced by zooplankton abundance in the spring when fish entered the lake. In contrast, fish size at seaward migration from the lake depended primarily on zooplankton abundance in the spring as they left the lake rather than the previous spring when they entered. These results suggest that maintaining a wide window of lake entry dates allows this population to capture the annually‐varying period of favourable conditions, minimising mismatches between juvenile fish and their resources and thereby enabling successful recruitment in an unpredictable environment.

The genesis and evolution of carbonate minerals in shale oil formations from Dongying depression, Bohai Bay Basin, China

Shale oil is attracting increasing attention in the petroleum industry as an essential target of unconventional oil and gas exploration. Recent exploration efforts have indicated that laminar carbonates are closely related to the favorable depositional strata of shale oil. This research focused on inter-bedded layers of laminar carbonates as well as mudstone and shale in the Dongying depression of the Bohai Bay Basin in eastern China, and attempted to reveal the genesis and evolution of the carbonates by means of drill core observations, thin sections, high resolution scanning electron microscopic observations, and fluorometric, cathodoluminescence and geochemical analyses. The results demonstrated that: (1) the carbonates could be categorized into two groups, crystalline carbonates and micritic carbonates; (2) the crystalline carbonates were well crystallized and greenish under fluorescent light; and (3) the micritic carbonates were not well crystallized and had biotic textures. It was discovered that the crystalline carbonates were mainly developed in the shale layer and were formed from the late-filling effects of the diagenetic cracks along the shale fissility planes; shale layers with crystalline carbonates are usually favorable for shale oil reserves. The micritic carbonates were formed from direct deposition controlled by biological effects in the stratified flows of the seasonal lake basins and are unfavorable for shale oil reserves.

Influence of rewetting process on distribution and release of phosphorus in sediments of East Lake Dongting

研究干燥覆水后低流速条件下东洞庭湖沉积物中磷的形态变化及释放量，可以为轻度富营养化湖泊中磷的生物地球化学循环提供基础数据，为季节性湖泊內源营养盐的迁移转化规律研究、內源营养盐的释放风险评价提供理论依据.本文采集处于干湿交替状态的东洞庭湖表层沉积物，利用室内模拟装置，研究风干沉积物低流速条件下覆水后沉积物及上覆水中磷的形态变化.结果表明，低流速覆水后东洞庭湖沉积物中的磷向上覆水及大气中迁移释放，上覆水中磷的释放量随覆水时长增大，释放速率随覆水时长减小，上覆水流速和磷释放量相关性显著.上覆水循环过程中释放到上覆水中的溶解态有机磷比溶解态活性磷更容易吸附于颗粒物而转化为颗粒态磷.覆水后沉积物中各形态有机磷、无机磷及磷的生物有效性均发生转变，覆水初期沉积物中无机磷向有机磷转化，磷的生物可利用性增大；上覆水循环过程中有机磷向无机磷转化，磷的生物可利用性减小；覆水后沉积物的无机磷的主要组分由铝磷转变为铁磷，有机磷的主要组分有从中活性有机磷向活性有机磷转变的趋势.;Fractions and release amount of phosphorus in sediment from East Lake Dongting were analyzed in the process of rewetting with low flow velocities, to provide evidence for phosphorus biogeochemical recycle, risk assessment of endogenous phosphorus release and eutrophication control scheme in seasonal lakes. In this paper, sediments collected in Eastern Dongting were air dried before rewetted. Phosphorus fractions in sediments and water were analyzed and indicated that phosphorus in sediments transported into water and air during rewetting process. Release amount of phosphorus in sediments increased and release rate decreased during the rewetting process. Significant positive correlation was observed between phosphorus release amount and water velocity. Dissolved organic phosphorus had relatively stronger absorption ability onto suspended particulate matter, thus they transformed into particle phosphorus more quickly than dissolved reactive phosphorus. Inorganic phosphorus in sediments transformed into organic phosphorus, and bioavailable phosphorus in sediments increased in the beginning of rewetting process. However, in the following stage of rewetting process, organic phosphorus in sediments transformed to inorganic phosphorus, and bioavailable phosphorus decreased. The dominate component of inorganic phosphorus in sediments transformed from aluminum-bound phosphate to iron-bound phosphorus. And the dominate component of organic phosphorus transformed from moderately labile organic phosphorus to labile organic phosphorus in rewetting process.

The hydrogeology of the Gort Lowlands

The Gort Lowlands is an extensively karstified lowland limestone catchment located in Co. Galway, on the western coast of Ireland. The hydrogeomorphological history of the Gort Lowlands is complex; recurrent karstification and glaciation of the Carboniferous limestone formations has created an extensive conduit and cave system that dominates groundwater flow. Variations in the lithology, stratigraphy, fracturing and faulting of the limestone bedrock have all played a role in shaping this subterranean system. So too has the nature of catchment recharge, with just over half of annual recharge supplied by rivers from the adjacent non-carbonate Slieve Aughty Mountains. Surface flow in the lowlands is intermittent and drainage is via the karst network which discharges at a series of intertidal and submarine springs in Kinvara Bay. The catchment is also interspersed with seasonal lakes known as turloughs, which provide storage for excess recharge that cannot be accommodated by the groundwater system. The complex regional hydrogeology poses significant water resource and land management challenges. This paper contributes towards addressing these challenges by presenting the accumulated hydrogeological knowledge, including the genesis, behaviour and principal features of the catchment.

Paleoenvironments and human occupation in the El Bolsón Valley of northwest Argentina (province of Catamarca, dept. of Belén)

Using an interdisciplinary perspective that integrates archaeological, geomorphological, and palynological data, this work analyzes the relationship between environmental changes and cultural landscapes in the El Bolsón Valley in the province of Catamarca, Argentina. The palynological and sedimentological studies took place using a sediment core extracted from a seasonal lake, while the geomorphological studies made use of stratified fluvial deposits. The palynological sequence indicates that wetter conditions existed at 6400calBP, but that this wetness decreased to create the current more arid conditions along with increases in anthropogenic disturbance. There is also evidence for intense processes of sediment accumulation and erosion, including changes in the uses of space by human populations as recorded for the last 2000years in fine deposits from the valley floor. The present work also makes an effort to insert this local history into its broader context, in order to contribute to existing knowledge regarding late Holocene changes at the regional level.

Microbial community diversity patterns are related to physical and chemical differences among temperate lakes near Beaver Island, MI.

Lakes are dynamic and complex ecosystems that can be influenced by physical, chemical, and biological processes. Additionally, individual lakes are often chemically and physically distinct, even within the same geographic region. Here we show that differences in physicochemical conditions among freshwater lakes located on (and around) the same island, as well as within the water column of each lake, are significantly related to aquatic microbial community diversity. Water samples were collected over time from the surface and bottom-water within four freshwater lakes located around Beaver Island, MI within the Laurentian Great Lakes region. Three of the sampled lakes experienced seasonal lake mixing events, impacting either O2, pH, temperature, or a combination of the three. Microbial community alpha and beta diversity were assessed and individual microbial taxa were identified via high-throughput sequencing of the 16S rRNA gene. Results demonstrated that physical and chemical variability (temperature, dissolved oxygen, and pH) were significantly related to divergence in the beta diversity of surface and bottom-water microbial communities. Despite its correlation to microbial community structure in unconstrained analyses, constrained analyses demonstrated that dissolved organic carbon (DOC) concentration was not strongly related to microbial community structure among or within lakes. Additionally, several taxa were correlated (either positively or negatively) to environmental variables, which could be related to aerobic and anaerobic metabolisms. This study highlights the measurable relationships between environmental conditions and microbial communities within freshwater temperate lakes around the same island.

Understanding and Predicting the Fate of Semivolatile Organic Pesticides in a Glacier-Fed Lake Using a Multimedia Chemical Fate Model

Melting glaciers release previously ice-entrapped chemicals to the surrounding environment. As glacier melting accelerates under future climate warming, chemical release may also increase. This study investigated the behavior of semivolatile pesticides over the course of one year and predicted their behavior under two future climate change scenarios. Pesticides were quantified in air, lake water, glacial meltwater, and streamwater in the catchment of Lake Brewster, an alpine glacier-fed lake located in the Southern Alps of New Zealand. Two historic-use pesticides (endosulfan I and hexachlorobenzene) and three current-use pesticides (dacthal, triallate, and chlorpyrifos) were frequently found in both air and water samples from the catchment. Regression analysis indicated that the pesticide concentrations in glacial meltwater and lake water were strongly correlated. A multimedia environmental fate model was developed for these five chemicals in Brewster Lake. Modeling results indicated that seasonal lake ice cover melt, and varying contributions of input from glacial melt and streamwater, created pulses in pesticide concentrations in lake water. Under future climate scenarios, the concentration pulse was altered and glacial melt made a greater contribution (as mass flux) to pesticide input in the lake water.

FACIES, ENVIRONMENTS, AND FOSSIL PRESERVATION IN THE BARSTOW FORMATION, MOJAVE DESERT, CALIFORNIA

Continental deposits of the middle Miocene Barstow Formation formed in an extensional basin of the Mojave region. Mammalian faunas of the type section in the Mud Hills, California, are the basis for defining the Barstovian North American Land Mammal Age. Prior mapping, lithostratigraphy, geochronology, and fossil collecting have established a structural, chronostratigraphic, and biostratigraphic framework for the Barstow Formation. Here, we analyze the sedimentary facies of the lithostratigraphic sequence, infer the major depositional environments, and assess controls on fossil preservation in relation to major facies. We recognize six major facies associations that represent alluvial fans, shallow or seasonal lakes, and channels and floodplains. The transition from older, fan-dominated to younger, floodplain-dominated environments reflects changes in tectonics, accommodation, drainage, and depositional settings during the formation and filling of the basin. Fossil-mammal concentrations are common in four facies associations. Body fossils are abundant in two facies associations that represent well-drained floodplains and spring-fed wetlands. Fossil concentrations are moderately abundant in facies associations that represent floodplains and channel deposits, and fossils are rare in facies associations that represent alluvial fans and lake margins. The highest frequency of fossil localities occurs in the facies associations representing both suitable life habitats and high preservation potential for terrestrial mammals.

Satellite microwave assessment of Northern Hemisphere lake ice phenology from 2002 to 2015

Abstract. A new automated method enabling consistent satellite assessment of seasonal lake ice phenology at 5 km resolution was developed for all lake pixels (water coverage ≥ 90 %) in the Northern Hemisphere using 36.5 GHz H-polarized brightness temperature (Tb) observations from the Advanced Microwave Scanning Radiometer for EOS and Advanced Microwave Scanning Radiometer 2 (AMSR-E/2) sensors. The lake phenology metrics include seasonal timing and duration of annual ice cover. A moving t test (MTT) algorithm allows for automated lake ice retrievals with daily temporal fidelity and 5 km resolution gridding. The resulting ice phenology record shows strong agreement with available ground-based observations from the Global Lake and River Ice Phenology Database (95.4 % temporal agreement) and favorable correlations (R) with alternative ice phenology records from the Interactive Multisensor Snow and Ice Mapping System (R = 0.84 for water clear of ice (WCI) dates; R = 0.41 for complete freeze over (CFO) dates) and Canadian Ice Service (R = 0.86 for WCI dates; R = 0.69 for CFO dates). Analysis of the resulting 12-year (2002–2015) AMSR-E/2 ice record indicates increasingly shorter ice cover duration for 43 out of 71 (60.6 %) Northern Hemisphere lakes examined, with significant (p < 0.05) regional trends toward earlier ice melting for only five lakes. Higher-latitude lakes reveal more widespread and larger trends toward shorter ice cover duration than lower-latitude lakes, consistent with enhanced polar warming. This study documents a new satellite-based approach for rapid assessment and regional monitoring of seasonal ice cover changes over large lakes, with resulting accuracy suitable for global change studies.

The spatial distribution of turloughs

Preliminary observations are made on the distribution of turloughs (seasonal lakes) on the Irish Carboniferous Limestone. The majority of turloughs are located on well-bedded, pure, grey calcarenite, lithologically similar to the Burren Limestone. In contrast, turloughs are not found on impure, shaly Calp limestone, or on the massive Waulsortian bank limestone. The purity and well-developed bedding of the Burren-type limestone may render it particularly susceptible to karstification, favouring the development of turloughs. Structural geology is not thought to play an important role in the siting and orientation of turloughs.Turloughs tend to occur in glacial depositional landscapes with gently undulating relief. The area surrounding a turlough is usually soil-covered, but limited evidence suggests that the glacial drift is relatively thin and permeable. Thus the absence of turloughs from some areas of suitable bedrock is thought to be due to thick glacial drift (e.g. east of Portlaoise), or impermeable drift (e.g. in the northern drumlin belt).

The impact of meteorological conditions on snow and ice thickness in an Arctic lake

Inter-annual variation of meteorological conditions and their effects on snow and ice thickness in an Arctic lake Unari (67.14° N, 25.73° E) were investigated for winters 1980/1981–2012/2013. The lake snow and ice thicknesses were modelled applying a thermodynamic model, and the results were compared with observations. Regression equations were derived for the relationships between meteorological parameters and modelled snow and ice properties. The composite differences of large-scale atmospheric circulation patterns between seasons of thin and thick ice were analysed. The air temperature had an increasing trend (statistical significance p<0.05) during the freezing season (1.0° C/decade), associated with an increasing trend of liquid precipitation (p<0.05) in winter. Both observed and modelled average and maximum ice thicknesses showed a decreasing trend (p<0.05). The model results were statistically more reliable (1) for lake ice than snow and (2) for seasonal means than maxima. Low temperature with less precipitation prompted the formation of columnar ice, whereas strong winds and heavy snowfall were in favour of granular ice formation. The granular (columnar) ice thickness was positively (negatively) correlated with precipitation. The seasonal mean and maximum modelled lake ice and snow thicknesses were controlled by precipitation and temperature history, with 58–86 % of the inter-annual variance explained. Using regression equations derived from data from 1980 to 2013, snow and ice thickness for the following winter seasons was statistically forecasted, yielding errors of 9–12 %. Among large-scale climate indices, the Pacific Decadal Oscillation was the only one that correlated with inter-annual variations in the seasonal average ice thickness in Lake Unari.