scholarly journals Effects of Ice Freeze-Thaw Processes on U Isotope Compositions in Saline Lakes and Their Potential Environmental Implications

2021 ◽  
Vol 9 ◽  
Author(s):  
Pu Zhang ◽  
Chenyang Cao ◽  
Xiangzhong Li ◽  
Xuezheng Pei ◽  
Chi Chen ◽  
...  
Keyword(s):  
Lake Sediments ◽  
Water Column ◽  
Water Samples ◽  
Saline Lakes ◽  
Saline Lake ◽  
Qinghai Lake ◽  
Environmental Implications ◽  
Freeze Thaw ◽  
Absolute Dating ◽  
Lake Waters

The dissolved uranium (U) content in the water column of saline lakes varies little between ice-free seasons throughout the whole water column. Such uniformity allows for the potential absolute dating and/or paleohydrologic interpretations of lake sediments and biogenic shell materials using U isotopes. Before using these methods in cold regions, however, it is necessary to evaluate the effects that ice freeze-thaw processes have on the distribution of U isotopes in saline lake waters, and to determine the amount of variation in U isotopic values when such processes occur. In this paper, we collected ice and dissolved water samples from six lakes with variable salinity in February 2021. Five groundwater and three water samples from rivers into Qinghai Lake were sampled in November 2020. The sampled water was analyzed for dissolved concentrations of 238U and the activity ratio of 234U/238U ([234U/238U]AR). The results show that the 238U concentration of ice samples was less than that of the underlying water. The [234U/238U]AR of ice in the five saline lakes was similar to that of the underlying water with less than a 10‰ variation, suggesting no observable fractionation between ice and dissolved water. Thus, the ice freeze-thaw processes have almost no effect on the uranium content and [234U/238U]AR of the sampled saline lakes, which were characterized by a limited recharge volume from surface runoff, groundwater, and ice volume, namely the close saline lake in arid alpine background. The results from the indoor freeze-thaw experiments also showed that the U isotopic composition of Qinghai Lake waters and ice were similar with the 238U concentration of the ice was about 40% of that of the dissolved lake water, supporting the data obtained from natural saline lakes. The above results provide important insights into whether it is feasible to use U isotopes for absolute dating and/or paleohydrologic analysis of lake sediments or biogenic shell materials. In addition, the results are important for evaluating the [234U/238U]AR and uranium concentrations in seawater when there exists a process of melting polar ice, and for determining the initial delta 234U variations needed for dating of coral and other fossil materials.

Sedimentation of Pb-210 in Laurentian Shield Lakes

1984 ◽  
Vol 19 (2) ◽  
pp. 97-109 ◽  
Author(s):  
R.J. Cornett ◽  
L. Chant ◽  
D. Link
Keyword(s):  
Lake Sediments ◽  
Water Column ◽  
Rate Constant ◽  
Bottom Sediments ◽  
Atmospheric Fallout ◽  
Small Lakes ◽  
Fractional Rate ◽  
Total Input ◽  
Shield Lakes ◽  
Annual Flux

Abstract The average annual flux of Pb-210 from the atmosphere to lake surfaces and to the bottom sediments was measured in seven small lakes located on the Laurentian Shield. Direct atmospheric fallout of Pb-210 was 136 ± 16 Bq m-2 a-1 Streams from the lakes' catchments input an additional 5 to 473 Bq m-2 a-1. Only 16 to 80 percent of the total input was found in the lake sediments. The fractional rate constant for Pb-210 sedimentation from the water column ranged from 0.25 to 5.3 per annum.

CARBONATE MINERALOGY OF LAKE SEDIMENTS AND SURROUNDING SOILS. 2. THE QU’APPELLE LAKES

1983 ◽  
Vol 63 (2) ◽  
pp. 259-269 ◽  
Author(s):  
K. GHEBRE-EGZIABHIER ◽  
R. J. ST. ARNAUD
Keyword(s):  
Lake Sediments ◽  
Particle Size Analysis ◽  
Parent Material ◽  
Size Analysis ◽  
Carbonate Content ◽  
Mineral Contents ◽  
Ionic Activity ◽  
South Central ◽  
Direct Precipitation ◽  
Lake Waters

The nature and distribution of carbonate minerals in the upper Qu’Appelle basin in south-central Saskatchewan were investigated. The equivalent carbonate content and calcite:dolomite ratios of the deposits reflect the mechanisms of glacial deposition and some differences in the sources of the original parent material. The particle size analysis shows that the Qu’Appelle Lake sediments are more clayey than the surrounding soils and till deposits. Mg-bearing calcites occur only in the fine-sized fraction of the carbonate accumulation horizons. However, most of the upper Qu’Appelle Lake sediments contain appreciable amounts of sand-sized Mg-bearing calcites. The marked increase in carbonate content of the sediments relative to the adjacent soils and deposits is partially due to direct precipitation of calcite from the supersaturated lake waters. In this respect, a good correlation exists between the lake water ionic activity products for CaCO3 and the relative equivalent carbonatic mineral contents of the sediments. Key words: Mg-bearing calcite, dolomite, IAP, erosion

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

2020 ◽  
Vol 12 (24) ◽  
pp. 4098
Author(s):  
Weixiao Han ◽  
Chunlin Huang ◽  
Hongtao Duan ◽  
Juan Gu ◽  
Jinliang Hou
Keyword(s):  
Surface Water ◽  
Random Forest ◽  
Surface Temperature ◽  
Land Surface Temperature ◽  
Land Surface ◽  
Qinghai Lake ◽  
Water Index ◽  
Freeze Thaw ◽  
Normalized Difference Water Index ◽  
Break Up

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.

Active hematite concretion formation in modern acid saline lake sediments, Lake Brown, Western Australia

2008 ◽  
Vol 268 (1-2) ◽  
pp. 52-63 ◽  
Author(s):  
Brenda Beitler Bowen ◽  
K.C. Benison ◽  
F.E. Oboh-Ikuenobe ◽  
S. Story ◽  
M.R. Mormile
Keyword(s):  
Lake Sediments ◽  
Western Australia ◽  
Saline Lake

Geochemical behavior of rare elements in Paleogene saline lake sediments of the Qaidam Basin, NE Tibetan Plateau

2017 ◽  
Vol 34 (2) ◽  
pp. 359-372 ◽  
Author(s):  
Pei Guo ◽  
Chiyang Liu ◽  
Peng Wang ◽  
Ke Wang ◽  
Haili Yuan ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Lake Sediments ◽  
Saline Lake ◽  
Qaidam Basin ◽  
Geochemical Behavior ◽  
Rare Elements ◽  
Ne Tibetan Plateau

Field evaluation of plaster-based temephos pellets for residual control of midge larvae (Diptera: Chironomidae) in establishing rice crops

1994 ◽  
Vol 34 (5) ◽  
pp. 659 ◽  
Author(s):  
MM Stevens ◽  
GN Warren
Keyword(s):  
Water Column ◽  
Water Samples ◽  
Field Evaluation ◽  
Application Rate ◽  
Control Agent ◽  
Fourth Instar ◽  
Soil Core ◽  
Potential Control ◽  
Core Samples ◽  
Application Rates

A pelletised formulation of temephos (5% a.i.) was evaluated as a potential control agent for chironomid midge larvae in establishing rice crops. Four application rates between 0.03 and 0.53 mg a.i./L (42-732 g a.i./ha) were applied to 80 m2 experimental rice bays immediately after flooding. Water samples and soil core samples were taken at regular intervals until 29 days post-treatment. Larvae were extracted from core samples using magnesium sulfate (MgSO4) flotation, whilst laboratory-reared fourth instar Chironomus tepperi Skuse larvae were used in bioassays with field-collected water samples to determine pesticide activity in the water column. All treatments significantly suppressed C. tepperi-type larvae in the field for at least 13 days. Some suppression of non-C. tepperi-type larvae was obtained at 0.27 mg a.i./L, whilst at 0.53 mg a.i./L all chironomids were reduced to negligible levels for the full period of the trial. In bioassays, significant levels of water column toxicity to fourth instar C. tepperi larvae were only recorded for 2 days after treatment at the highest application rate. Our results indicate that plaster-based temephos pellets have the potential to provide effective, single application control of chironomid larvae in establishing rice crops without the risk of spray drift inherent in the aerial application of liquid insecticides.

scholarly journals Distribution Characteristics and Influencing Factors of Uranium Isotopes in Saline Lake Waters in the Northeast of Qaidam Basin

Minerals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 74
Author(s):  
Chen Zhao ◽  
Pu Zhang ◽  
Xiangzhong Li ◽  
Youfeng Ning ◽  
Liangcheng Tan ◽  
...  
Keyword(s):  
Influencing Factors ◽  
Saline Lakes ◽  
Natural Waters ◽  
Qaidam Basin ◽  
Influencing Factor ◽  
Dominant Factor ◽  
Uranium Isotopes ◽  
Distribution Characteristics ◽  
Total Dissolved Solid ◽  
Lake Waters

Four saline lakes in the northeast of Qaidam Basin were selected to explore the distribution characteristics and influencing factors of uranium isotopes in lake waters with high evaporation background. The 238U concentration and the activity ratios of 234U/238U ([234U/238U]AR) showed that there was no significant change in the same lake, but there was a certain degree of difference in the distribution between different lakes. We found that aqueous 238U concentration within a certain range increased with an increase in TDS (total dissolved solid) and salinity, as was also the case with pH. As in natural waters, the pH affects the speciation of 238U, but TDS and salinity affect the adsorption process of aqueous 238U. Further, the replenishment of water will also affect the uranium isotope concentration for lakes, but it is not the main influencing factor for saline lakes. Therefore, we suggest that pH is the dominant factor affecting changes in aqueous 238U concentration of the sampled saline lakes. The [234U/238U]AR in these saline lakes are closely related to the input water and the associated water–rock interactions involving sediments, atmosphere dust, and organic material, etc. during the evolution stage, metamorphous degree, and hydrochemistry of the saline lakes. Lake water samples collected in the maximum and minimum discharge water period, were used to evaluate the seasonal distribution characteristics of aqueous 238U, and we found that 238U concentration did not show an evident change with the seasons in these saline lakes. If the 238U concentration and [234U/238U]AR can remain consistent during a period of time, then the sediment ages and/or sedimentation rates could be determined by lake sediment and/or biogenic carbonate in future, thus allowing for the accurate reconstruction of the paleoclimate and paleoenvironment.

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