Monitoring lake ice phenology from CYGNSS: Algorithm development and assessment using Qinghai Lake, Tibet Plateau, as a case study

This study introduces the first use of Global Navigation Satellite System Reflectometry (GNSS-R) for monitoring lake ice phenology. This is demonstrated using Qinghai Lake, Tibetan Plateau, as a case study. Signal-to-Noise Ratio (SNR) values obtained from the Cyclone GNSS (CYGNSS) constellation over four ice seasons (2018 to 2022) were used to examine the impact of lake surface conditions on reflected GNSS signals during open water and ice cover seasons. A moving t-test (MTT) algorithm was applied to time-varying SNR values allowing for the detection of lake ice at daily temporal resolution. Strong agreement is observed between ice phenology records derived from CYGNSS and Moderate Resolution Imaging Spectroradiometer (MODIS) imagery. Differences during freeze-up (i.e., the period starting with the first appearance of ice on the lake until the lake becomes fully ice covered) ranged from 3 to 21 days with a mean bias error (MBE) and mean absolute error (MAE) of 10 days, while those during breakup (i.e., the period beginning with the first pixel of open water and ending when the whole lake becomes ice-free) ranged from 3 to 18 days (MBE and MAE: 6 and 7 days, respectively). Observations during the breakup period revealed the sensitivity of GNSS reflected signals to the onset of surface (snow and ice) melt before the appearance of open water conditions as determined from MODIS. While the CYGNSS constellation is limited to the coverage of lakes between 38° S and 38° N, the approach presented herein will be applicable to data from other GNSS-R missions that provide opportunities for the monitoring of ice phenology from large lakes globally (e.g., Spire constellation of satellites).This research was undertaken thanks, in part, with support from the Global Water Futures Program funded by the Canada First Research Excellence Fund (CFREF)

Petrography, geochemistry and mechanism of dolomitization of late Precambrin succession in Chopoghlu Section, South East of Zanjan

Introduction      Dolomite is mainly composed of internal structures and geochemical properties that usually indicate the conditions of formation environments and can be formed through the different mechanisms. For all these mechanisms, fluid flow and suitable amount of the magnesium in the fluid are required. During recent years, studies of dolomites have been one of the most important issues in the international sediment researches. Most of the Precambrian carbonate sequences are affected by dolomitization. Due to the spread amount of dolomites in the late Precambrian rocks of the Alborz Basin, carbonate systems of Chopoghlu section which are located in the southeast of Zanjan into the Soltanieh Mountains have been discussed in this research. Despite the significant presence of dolomite in the late Precambrian carbonate platforms of the Chopoghlu section, no work has been done up to now related to the texture, geochemical properties and also the origin of the late Precambrian dolomitization in this section. Therefore, this study was carried out to determinate the textural, mineralogical and geochemical characteristics of the late Precambrian dolomites in Chopoghlu section to determinate its dolomitization mechanism and the nature of dolomite fluids. Material & Methods     Different fieldwork and laboratory methods were used in this research. During the fieldwork studies, 50 rock samples from carbonate deposits (limestone and dolomite) have been taken for petrography and geochemical studies of these dolomites to determinate dolomitization mechanisms. The thickness of the layers is measured and the stratigraphic column of this section drowns. For the petrography study, 18 thin sections of these dolomites have been prepared. After petrography studies, 14 samples of these dolomites were selected for geochemical analysis to determinate the mechanisms of dolomitization by ICP-OES method. Also, 4 samples were analyzed for mineralogy studies and the determination of major and minor minerals by XRD method. Discussion of Results & Conclusions     The study of dolomite in the Chopoghlu section identified five types of dolomite including: very fine-crystalline, fine-crystalline, medium-crystalline, medium to coarse-crystalline and also dolomitic cement. It should be noted that the fine-crystalline dolomites is the most abundant type of dolomite in the region. In this section, dolomite cements which filled the vugs and fractures have been distinguished into the some of the studied samples. XRD results from dolomite samples in the region indicate that the most abundant mineral is dolomite, and calcite, quartz and muscovite minerals are present as minor and trace minerals in the studied rocks.   The results of this study clearly show that the very fine-crystalline dolomite is related to primary diagenesis and is formed under a sabkha dolomitization model in a shallow and saline environment (average of sodium is around 478 ppm). The low amount of the strontium content into the coarse-crystalline dolomite in this section (average of 43 ppm) relative to sea water and the present-day dolomites, and even related to the very fine-crystalline dolomites, clearly shows that the coarse crystalline dolomites are formed during greater burial depths. Second type of dolomite or fine-crystalline dolomite is formed under shallow burial depth. These dolomites are formed via marine fluids with normal salinity and are interpreted from the progressive recrystallization of previous dolomite. The presence of stylolite is the main characteristic of this type of dolomite into the studied section. Third to fifth type dolomites formed during the last stages of diagenesis and are related to deep burial and impact of hypersaline interstitial fluids. The higher amount of iron and manganese into the chopoghlu late Precambrian dolomites in comparison with modern dolomites and seawater probably indicate that the formation of these kinds of dolomites may be associated with reduction conditions and the presence of sulfate-reducing bacteria. In general, the dolomitization mechanism for the first-type of dolomite is related to Sabkha model, for the second-type of dolomite is related to shallow burial dolomitization and finally for the third to fifth-types of studied dolomites are related to deep burial dolomitization

Sedimentary records of polycyclic aromatic hydrocarbons (PAHs) in remote lakes across the Tibetan Plateau

Sediment cores from five lakes across the Tibetan Plateau were used as natural archives to study the time trends of polycyclic aromatic hydrocarbons (PAHs). The depositional flux of PAHs generally showed an increasing trend from the deeper layers towards the upper layer sediments. The fluxes of PAHs were low with little variability before the 1950s, and then gradually increased to the late 1980s, with a faster increasing rate after the 1990s. This temporal pattern is clearly different compared with those remote lakes across the European mountains when PAHs started to decrease during the period 1960s-1980s. The difference of the temporal trend was attributed to differences in the economic development stages and energy structure between these regions. PAHs are dominated by the lighter 2&3-ring homologues with the averaged percentage over 87%, while it is notable that the percentage of heavier 4-6 ring PAHs generally increased in recent years, which suggests the contribution of local high-temperature combustion sources becoming more predominant

MICP and Advances towards Eco-Friendly and Economical Applications

Biomineralization is a natural process aided by living organisms. Due to its applicability in ground improvement and bioremediation, Microbially Induced Calcite Precipitation (MICP) is an interdisciplinary field of study combining engineering, chemistry and microbiology. Bioremediation has been applied widely for contamination containment or removal, in this case it will be containment. MICP can also be applied to improve the efficiency of insitu bioremediation. Urease is an enzyme which can facilitate increased calcite precipitation. However the production of urease by bacteria and thus the resulting carbonate precipitation are inhibited by environmental factors including calcium concentration, bacterial concentration, pH and temperature. Under good conditions MICP can be used for heavy metal and radionuclide immobilization. However technologies such as bioconsolidation and biocementation require improvement such as time and cost. This paper highlights the application of MICP in addition to suggested improvements to make it more eco-friendly and sustainable.XJTL

Precipitation of high Mg-calcite and protodolomite using dead biomass of aerobic halophilic bacteria

The microbial dolomite model has been used to interpret the origin of sedimentary dolomite. In this model， the formation of low-temperature protodolomite， an important precursor to sedimentary dolomite， can be facilitated either by actively metabolizing cells of anaerobic microbes and aerobic halophilicarchaea or by their inactive biomass. Aerobic halophilic bacteria are widely distributed in （proto-）dolomite-depositing evaporitic environments and their biomass might serve as a template for the crystallization of protodolomite. To test this hypothesis， carbonation experiments were conducted using dead biomass of an aerobic halophilic bacterium （Exiguobacterium sp. strain JBHLT-3）. Our results show that dead biomass of JBHLT-3 can accelerate Mg2+ uptake in carbonate mineral precipitates. In addition， the amount of Mg incorporated into Ca-Mg carbonates is proportional to the concentration of biomass. High Mg-calcite is produced with 0.25 or 0.5 g/L biomass， whereasprotodolomite forms with 1 g/L biomass. This is confirmed by the main Raman peak of Ca-Mg carbonates， which shifts towards higher wavenumbers with increased Mg substitution. Microbial cells and their imprints are preserved on the surface of high Mg-calcite and protodolomite. Hence， this study furthers our understanding of the dolomitization within buried and dead microbial mats， which provides useful insights into the origin of ancient dolomite

Precipitation Of Synthetic Dolomite At Low Tempearures With The Influence Of Microbes

New approaches in carbonate geochemistry are aiding geoscientists in understanding dolomite formation. Dolomite is largely absent in modern depositional environments but is present in ancient rocks. The current problem is the inability to synthesize it under low-temperature conditions in the laboratory. Until recently laboratory preparation of dolomite required elevated temperatures (\u3c100oC) to overcome kinetic barriers. One novel approach involves using bacteria to overcome the kinetic barriers that have frustrated efforts to synthesize dolomite at near surface temperatures. This study presents preliminary results of experiments in which three strains of bacteria were used to inoculate a magnesium deficient amorphous calcium carbonate (Mg-ACC) medium (CO3 2-: Mg2+: Ca2+ in 2:1:1 ratio). The bacteria used include an aerobic strain, Virgibacillus marismortui (ATCCÎ 700626™) and two anaerobic strains, Desulfovibrio desulfuricans subsp. deslufuricans (ATCCβ9577™) and Escherichia coli. All the experiments were conducted at 30oC and 37˚C for 40 days. Preliminary XRD results are consistent with the precipitation of a carbonate phase with a dolomite-like XRD peak near 31˚ 2θ, Cu kα radiation. Similar peaks were not apparent for the experiments using the aerobic strain nor the bacteria free control. These results indicate that the two strains of anaerobic bacteria may aid in the formation of a magnesium-rich carbonate phase similar to dolomite at low temperature, within short periods of time

Relationships between potentially toxic elements in intertidal sediments and their bioaccumulation by benthic invertebrates

The bioaccumulation of Potentially Toxic Elements (PTEs) by benthic invertebrates in estuarine sediments is poorly understood. We sampled and analysed PTEs in sediments and benthic invertebrates from five sites in the Skeena Estuary (British Columbia, Canada), including sites adjacent to an abandoned cannery and a decommissioned papermill. Our aim was to elucidate baseline levels of PTE concentrations at sites that may be recovering from disturbance associated with prior industrial development and identify organisms that could be used to biomonitor the impact of future industrial developments. There was no indication that sediments of the salmon cannery were polluted, but acidic sediments adjacent to the papermill contained elevated concentrations of Cd, Cr, Hg and Pb. Benthic invertebrate community assemblages confirm that sediments have mostly recovered from prior industrial development associated with discharge of papermill sludge. Overall, we did not observe any relationship between PTE concentrations in the sediment and PTE concentrations in invertebrate tissues. However, we did observe a negative relationship between sediment pH and the Biota-Sediment Accumulation Factor (BSAF) of most PTEs for Oregon pill bugs (Gnorimosphaeroma oregonensis). G. oregonensis, observed at all sites, feeds on the fibers associated with the papermill discharge. Thus, G. oregonensis is a useful biomonitors for quantifying the impact of the decommissioned papermill, and are candidate biomonitors for assessing the impact of similar industrial development projects on intertidal ecosystems

Phanerozoic variation in dolomite abundance linked to oceanic anoxia

The abundance of dolomitic strata in the geological record contrasts with the general rarity of locations where dolomite forms today, a discrepancy that has long posed a problem for their interpretation. Recent culture experiments show that dolomite can precipitate at room temperature, raising the possibility that many ancient dolomites may be of syngenetic origin. We compiled a large geodata set of secular variations in dolomite abundance in the Phanerozoic, coupled with compilations of genus richness of marine benthic invertebrates and sulfur-isotope variations in marine carbonates. These data show that dolomite abundance is negatively correlated to genus diversity, with four dolomite peaks occurring during mass extinctions. Dolomite peaks also correspond to the rapid increase in sulfur-isotope composition (δ³⁴S), an indicator of enhanced sulfate reduction, in anoxic oceans. These results confirm that variations in dolomite abundance during the Phanerozoic were closely linked with changes in marine benthic diversity, with both in turn related to oceanic redox conditions

Fate and Transport of Polycyclic Aromatic Hydrocarbons in Upland Irish Headwater Lake Catchments

Polycyclic aromatic hydrocarbons (PAHs) are a concern due to their carcinogenicity and propensity for transboundary atmospheric transport. Ireland is located on the western periphery of Europe and assumed to receive clean Atlantic air. As such, it has been used as an atmospheric reference for comparison to other regions. Nonetheless, few studies have evaluated concentrations of PAHs within the Irish environment. In the current study, PAHs were measured at five upland (500–800 masl) headwater lake catchments in coastal regions around Ireland, remote from industrial point source emissions. Semipermeable membrane devices were deployed in lakes for a 6-month period in July 2009, and topsoils were sampled from each catchment during October 2010. The concentrations of PAHs were low at most study sites with respect to other temperate regions. Homologue groups partitioned between lake and soil compartments based on their molecular weight were: “lighter” substances, such as Phenanthrene and Fluorene, were found in higher proportions in lakes, whereas “heavier” compounds, such as Chrysene and Benz[a]anthracene, were more prominent in soils. Concentrations of PAHs were highest at the east coast sites, potentially due to contributions from historical transboundary and regional combustion sources

Catalytic effect of microbially-derived carboxylic acids on the precipitation of Mg-calcite and disordered dolomite: Implications for sedimentary dolomite formation

The genesis of dolomite is a contentious issue partly due to the difficulty in its synthesis at ambient temperature. Certain types of microorganisms have been demonstrated to be effective in promoting the precipitation of disordered dolomite, an important precursor of sedimentary ordered dolomite. In contrast to a growing body of research on the catalytic role of microbial exopolymers in the crystallization of disordered dolomite, the role of other microbial exudates (e.g., carboxylic acids) remains unknown. To fill in this knowledge gap, precipitation experiments, mimicking the carbonation process within microbial mats, were conducted in saline solutions containing 0-30 mM succinic acid or citric acid, which are commonly produced by microbes. The starting salinities of experiment solutions were set to 35‰ and 70‰, in order to evaluate the effect of solution salinity on dolomite formation. Our results showed that both succinic acid and citric acid enhanced the incorporation of Mg2+ into growing Ca-Mg carbonates. Solution salinity also played a positive role in enhancing Mg signature in Ca-Mg carbonates. Disordered dolomite with 40.92 mol% MgCO3 was detected under the conditions of 30 mM succinic acid and 70‰ salinity, whereas in other reactors with succinic acid, Mg-calcites formed. Citric acid was more effective in loading Mg2+ into Ca-Mg carbonates compared with succinic acid, as evidenced by the predominant occurrence of disordered dolomite with MgCO3 content ranging from 40.91 mol% to 46.75 mol% in most conditions tested. The results of this study have implications for the formation mechanism of sedimentary dolomite