Volcanic Lake Research Articles

Present sedimentation in the volcanic lakes of the Kurile-Kamchatka region (Russia) as a basis for paleoreconstructions

Abstract. The results of modern processes observations of the sedimentation in the volcanic lakes of the region are summarized with the use of material from other regions of the world. The available data on the drained volcanic lakes deposits, Uzon-Geysernaya caldera as example, was analysed. The main sources of material (volcanic and post-volcanic activity, gravitational displacements on slopes, and erosion-denudation processes) and the mechanisms of its entry into volcanic lakes, as well as the features of the subsequent deposits transformation as a result of hydrothermal, seismic, and volcano-tectonic activity, are identified. The results of the studies carried out allow us to conclude that the volcanic lakes deposits are complexly constructed polyfacial complexes with alternating fine-grained lacustrine and lacustrine-swamp deposits with pyroclastic horizons and interlayers of untreated or poorly processed coarse clastic material coming as a result of volcano-tectonic activity, gravitational and erosion processes. The irregularity of horizons along strike is typical; and is characterized by the large-scale sediments deformation under the influence of seismic activity, growth of effusive and extrusive domes, phreatic explosions, etc. Hydrothermal activity contributes to the weathering and cementation of the lake sediments. Lava outpourings and the high-temperature pyroclastic flows provokes sintering of contacting horizons sediments.

Hydrochemical and Hydroacoustic Investigation of the Yugama Acid Crater Lake, Kusatsu-Shirane, Japan

The gases dissolved in the waters of volcanic lakes can present a serious hazard if the physical-chemical conditions change due to variations in the supply of magmatic gases. The monitoring of gases such as CO2 and He help us understand the degassing process and their connection with magmatic/hydrothermal system. One of the most acidic volcanic lakes on the planet is the Yugama, on Kusatsu Shirane volcano (Japan). We report the results of an interdisciplinary study carried out in August 2013 at Yugama consisting of the first estimation of rate of diffuse CO2 emission, the chemical and isotopic analysis of water and dissolved gases in samples from vertical lake profiles, and an echo-sounding survey. The lake water has an average temperature of 24-25°C, pH 1.01, concentrations of SO42- between 1,227 and 1,654 mgL−1 and Cl− between 1,506 and 2,562 mgL−1, with gas bubbling at several locations and floating sulfur globules with sulfide inclusions. A total of 66 CO2 efflux measurements were taken at the lake surface by means of the floating accumulation chamber method to estimate the diffuse CO2 output from the studied area. CO2 efflux values ranged from 82 up to 25,800 g m−2 d−1. Estimation of the diffuse CO2 emission at Yaguma Crater Lake was 30 ± 12 t d−1. Normalized CO2 emission rate (assuming an area of 0.066 km2) was 454 t km−2 d−1, a value within the range of acid volcanic lakes. Vertical profiles of major ions and dissolved gases showed variations with increases in ion content and dissolved CO2 and He with depth. Acoustic imaging shows the presence of intense bubbling and provides important information on the bathymetry of the lake. The 50–200 kHz echograms exhibit frequent vertical plumes of rising gas bubbles. Within the crater-lake, three circular submarine vents have been identified showing flares due to a significant activity of sublacustrine emissions. This work shows the first data of diffuse CO2 degassing, dissolved gases in water and echosounding (ES) from Yugama Crater Lake. Periodic hydrogeochemical and hydroacoustic surveys at Yugama Crater Lakemay thus help to document changes in the state of activity of this high-risk volcanic area.

Geochemistry of Water and Gas Emissions From Cuicocha and Quilotoa Volcanic Lakes, Ecuador

There are hundreds of volcanic lakes around the world that represent an important hazard due to the potential occurrence of phreatomagmatic or limnic eruptions. Variations in geochemical and geophysical parameters could help to identify potential risks for these events. Cuicocha and Quilota volcanic lakes, located at the North Andean Volcanic Zone of Ecuador, are geologically young, with gas emissions manifested mainly as CO2via bubbling gases. Both lakes present a limited monitoring record. Therefore, volcanic monitoring is a priority task due to the potential hazard they represent by the possibility of water stratification and CO2accumulation. During 2012-2018 period, geochemical investigation based mainly on diffuse CO2surveys and analyzing the chemical and isotopic composition of bubbling gases has been carried out at Cuicocha and Quilotoa lakes. Additionally, vertical profiles of water columns were conducted in both lakes to investigate the possibility of water stratification and CO2accumulation in the lakes. A bathymetric study was also carried out in Quilotoa in 2017, giving further information about the degasification processes and the morphology of the lake bottom. The computed diffuse CO2output for Cuicocha volcanic lake (3.95 km2) showed a range from 53 to 652 t d−1for the period 2006–2018, with a maximum value in 2012, coinciding with a maximum of the3He/4He ratio measured at the bubbling gases and an increase in the seismic activity with an episode of long-period seismicity recorded in 2011–2012. For Quilotoa volcanic lake (3.50 km2) diffuse CO2output was estimated between 141 and 536 t d−1for the period 2014–2018. The chemical and isotopic data show that Cuicocha has a chemical composition typical of worldwide superficial shallow waters and aquifers, while Quilotoa shows a chemical composition typical of crater lakes in active volcanic systems. The distribution of the dissolved gas composition along the vertical profiles shows the existence of different water masses in both lakes, with an increase in the concentration of dissolved gases with depth. The carbon isotopic signature indicates an endogenous origin of the CO2, with a greater contribution in the stratification zone in both lakes. This study shows methods applicable to other volcanic lakes of the world to monitor their activity and potential risks.

The dynamics and temperature regime of the crater lakes in the Nevado de Toluca volcano, Mexico

Volcanic lakes are unique ecosystems with complex relationships between atmospheric variables and crater lake dynamics. In two adjacent tropical, high mountain lakes, spectral analysis of coupled in situ meteorological and hydrodynamic measurements revealed strong diurnal fluctuations in water temperature due to wind-forced internal gravity waves and free seiche oscillations. Although the amplitudes of these internal motions were small, they contribute to the transfer of momentum and mixing, with large potential impacts on lake productivity. During daytime heating, in both lakes, a thermocline formed in the near-surface layer (2−3 m depth) but eroded at night. The heat penetration into each lake within the crater differed significantly, even though they were ∼ 500 m apart, driven by differences in water transparency and algal growth. Analyses of coupling between local meteorology and lake hydrodynamics revealed complex forcing of small-scale patterns which are important to incorporate into future studies to understand how ecosystem productivity is modulated.

Microbial Contamination Survey of Environmental Fresh and Saltwater Resources of Upolu Island, Samoa

Analysis of microbe diversity in freshwater resources and nearshore seawater samples of Upolu Island was performed to investigate the distribution of harmful bacteria. For this, 124 samples were collected from 23 river systems, two volcanic lakes, and 45 locations inside and outside the barrier reef of Upolu Island, Samoa. Physicochemical parameters for general water quality, detection of coliform bacteria and 16S rRNA amplicon sequencing were performed on all samples. Fecal indicator bacteria (FIB) testing indicated a wide distribution of coliform bacteria in all sampled freshwater sites with evidence of fecal coliform in most locations. Importantly, evidence of coliform bacteria was found in most seawater samples inside and along the reef, apart from those samples taken ~20 km offshore. Illumina 16S rRNA amplicon sequencing of the V4 hypervariable region confirmed the presence of various types of harmful bacterial species, namely from the Enterobacteriaceae, Enterococcae, Streptococcaceae, and Vibrionacea families. By combining the sensitivity of FIB testing and next-generation sequencing, we were able to show the extent of potential contaminations in fresh and seawater samples and simultaneously identify the potential pathogenic bacterial genera present. The wide distribution of potential harmful bacteria from river runoff or direct sewage dumping has an impact on human health, leading to many skin and intestinal diseases, and is potentially detrimental to coral reef community health.

Volcanic Lakes in Africa: The VOLADA_Africa 2.0 Database, and Implications for Volcanic Hazard

Volcanic lakes pose specific hazards inherent to the presence of water: phreatic and phreatomagmatic eruptions, lahars, limnic gas bursts and dispersion of brines in the hydrological network. Here we introduce the updated, interactive and open-access database for African volcanic lakes, country by country. The previous database VOLADA (VOlcanic LAke DAta Base, Rouwet et al., Journal of Volcanology and Geothermal Research, 2014, 272, 78–97) reported 96 volcanic lakes for Africa. This number is now revised and established at 220, converting VOLADA_Africa 2.0 in the most comprehensive resource for African volcanic lakes: 81 in Uganda, 37 in Kenya, 33 in Cameroon, 28 in Madagascar, 19 in Ethiopia, 6 in Tanzania, 2 in Rwanda, 2 in Sudan, 2 in D.R. Congo, 1 in Libya, and 9 on the minor islands around Africa. We present the current state-of-the-art of arguably all the African volcanic lakes that the global experts and regional research teams are aware of, and provide hints for future research directions, with a special focus on the volcanic hazard assessment. All lakes in the updated database are classified for their genetic origin and their physical and chemical characteristics, and level of study. The predominant rift-related volcanism in Africa favors basaltic eruptive products, leading to volcanoes with highly permeable edifices, and hence less-developed hydrothermal systems. Basal aquifers accumulate under large volcanoes and in rift depressions providing a potential scenario for phreatomagmatic volcanism. This hypothesis, based on a morphometric analysis and volcanological research from literature, conveys the predominance of maar lakes in large monogenetic fields in Africa (e.g. Uganda, Cameroon, Ethiopia), and the absence of peak-activity crater lakes, generally found at polygenetic arc-volcanoes. Considering the large number of maar lakes in Africa (172), within similar geotectonic settings and meteoric conditions as in Cameroon, it is somewhat surprising that “only” from Lake Monoun and Lake Nyos fatal CO2 bursts have been recorded. Explaining why other maars did not experience limnic gas bursts is a question that can only be answered by enhancing insights into physical limnology and fluid geochemistry of the so far poorly studied lakes. From a hazard perspective, there is an urgent need to tackle this task as a community.

Iron and total organic carbon shape the spatial distribution pattern of sediment Fe(III) reducing bacteria in a volcanic lake, NE China.

Fe(III) reducing bacteria (FeRB) play a vital role in the biogeochemical cycle of Fe, C and N in nature. The volcanic lake can be considered as an ideal habitat for FeRB. Here, we investigated the diversity and spatial distribution of FeRB in sediments of Wenbo lake in Wudalianchi volcano based on culture-dependent and independent methods. A total of 28 isolates affiliated with the genera of Enterobacter, Bacillus, Pseudomonas and Clostridium were obtained from 18 sediment samples. We detected 783 operational taxonomic units (OTUs) belonged to FeRB using high high-throughput sequencing, and the dominant phyla were Proteobacteria (3.65%), Acidobacteria (0.29%), Firmicutes (10.78%). The representative FeRB genera such as Geobacter, Pseudomonas, Thiobacillus and Acinetobacter distributed widely in Wenbo lake. Results showed that the diversity and abundance of FeRB declined along the water-flow direction from Libo to Jingbo. In contrast, the FeRB diversity decreased and the FeRB abundance increased along with depth transect of sediments. It was found that the dominant phylum changed from Firmicutes to Proteobacteria along the water-flow direction, while changed from Proteobacteria to Firmicutes along with the depth of sediments. RDA indicated that the FeRB distribution were driven by soluble total iron, total organic carbon, Fe(II) and Fe(III). These will provide information for understanding the role of FeRB in the elements geochemical cycles in the volcanic environment.

Microbiological quality of the water of the Quilotoa volcanic lake. Cotopaxi-Ecuador

El agua de los lagos volcánicos no es estéril, en ella se ha adaptado a través de milenios una microbiota con diversas capacidades metabólicas. Los microorganismos de los lagos volcánicos en Ecuador han sido poco estudiados y aún se desconoce su cantidad y su diversidad. Objetivo del trabajo fue conocer la calidad microbiológica del agua del lago Quilotoa, situado en la Provincia de Cotopaxi-Ecuador. Metodología: Se realizaron dos muestreos durante el año 2019, recolectando un total 32 muestras. La calidad microbiológica se cuantifico utilizando la técnica de filtración por membrana en agar R2A para bacterias heterótrofas, agar eosina azul de metileno para coliformes, agar manitol salado para Staphylococcus, agar cetrimide para Pseudomonas y agar Sabouraud con cloranfenicol para hongos. Resultados: Resultados promedios fueron para bacterias heterótrofas de 2,00 x 102 UFC/mL; Pseudomonas 7,00 x 10 UFC/mL, Staphylococcus 3,80 x 10 UFC/mL y hongos 1,40 x 10 UFC/mL. No se detectó la presencia de bacterias coliformes. Discusión: Los grupos microbianos presentes en bajo número son indicativos de una microbiota característica adaptada a las condiciones fisicoquímicas de este lago Se concluye que se trata de un lago con una población microbiana escasa lo que indicaría una buena calidad microbiológica.

Isoëtes sabatina (Isoëtaceae, Lycopodiopsida): Taxonomic distinctness and preliminary ecological insights

Abstract Isoëtes sabatina is the rarest aquatic quillwort in Europe. Although recently found (2013) in Lake Bracciano (central Italy), the species is just one step away from extinction with an estimated population not exceeding 400 individuals and a spatial range of a few hundred square metres. Lake Bracciano is a deep, oligo‐mesotrophic Mediterranean volcanic lake that has been subjected to human activities. From January to October 2017, the lake experienced a dramatic water level decrease (up to −1.50 m), which significantly affected the littoral zone and the habitat of I. sabatina. To improve the chances of survival of I. sabatina, the first eco‐taxonomic investigation on this species was carried out to describe its genetic distinctness, physical and chemical requirements and companion species. The phylogenetic position of I. sabatina was investigated by applying standard DNA barcoding methods. Simultaneously, during summer 2019, the physical and chemical features of water and sediments of the I. sabatina population and five small Alpine lakes colonized by Isoëtes echinospora – a supposed close relative – were characterized. These data were then compared with the available data on the trophic requirements of the target obligate aquatic Isoëtes, together with Isoëtes lacustris and Isoëtes malinverniana. The present survey confirmed the taxonomic and ecological distinctness of I. sabatina – providing the first evidence of genetic differentiation from I. echinospora. Isoëtes sabatina grows in waters with temperature, conductivity and total alkalinity up to 30°C, 561 μS cm−1 and 3.45 meq L−1, respectively. The edaphic requirements of I. sabatina confirm its outstanding conservation value, and this study offers a basic understanding of how to prevent its extinction. Now, all possible actions must be taken immediately to save this species.

Carbon Dioxide in Lake Nyos, Cameroon, Estimated Quantitatively From Sound Speed Measurements

Gases dissolved in the deep water of lakes can pose a hazard when extreme concentrations are reached. A sudden release of large amounts of gas can cost the lives of humans living in the neighbourhood, as happened at Lake Nyos in 1986. Since 2001, the gas risk at Lake Nyos has been mitigated by induced degassing, but the lake continues to be supplied by CO2, and a regular survey needs to be implemented to guarantee safe conditions. Frequent sampling of this remote lake requires an enormous effort, and many analytical techniques are very difficult to run at the lake site. In this contribution, we combined a commercially available sound speed sensor with a CTD (electrical conductivity, temperature, depth) probe to obtain an indirect but quantitative estimate of carbon dioxide concentrations with fine depth resolution (decimetre scale). Dissolved carbon dioxide increases sound speed but does not contribute to electrical conductivity. Hence the difference between measured and calculated (on the base of electrical conductivity, temperature and pressure) sound speed gives a quantitative indication of dissolved carbon dioxide. We infer the vertical distribution of dissolved CO2 and hence continue the survey of the progress of the intended degassing. In conclusion, we present an easy to implement method for very high CO2 concentrations in deep lakes, and we highly recommend the implementation of the sound speed-CTD probe combination at Lake Nyos and at other gas-laden volcanic lakes, as such an approach could safeguard the people living in the area with acceptable cost and effort for the operators. In this manner, alarming CO2 concentrations in deep parts of lakes can be detected in a timely fashion.

Ianula (1970) revisited. Lessons from a pioneering study

More than fifty years ago, G.E. Hutchinson published “Ianula: an account of the history and development of the Lago di Monterosi, Latium, Italy”, a detailed report of one of the first multi-disciplinary palaeolimnological studies. The main result of that study was that the last Glacial climate in peninsular Italy was not only cold but also dry, in contrast with the assumption prevalent at that time of wet "pluvials" in Glacial stages of the northern Mediterranean. These finding were confirmed by more recent studies on other volcanic lakes in Italy. Furthermore, the authors found a major change in ecosystem structure and concluded that it was caused by the building of a road in Roman time. Comparing Monterosi pollen profile with those obtained from cores in other lakes in Central Italy and in the Adriatic Sea, I suggest an alternative hypothesis linking the dramatic environmental change recorded to soil development during forest onset at the beginning of the Holocene. The original report made available a large share of the data set, as a pioneering example of Open Data, allowing a re-examination of the results and the formulation of new hypotheses, underlying the importance of open data in environmental science.

On the Capability of the Epigeous Organs of Phragmites australis to Act as Metal Accumulators in Biomonitoring Studies

With a view of shedding light on the accumulation capability of the epigeous organs of common reed (Phragmites australis), employed worldwide in metal biomonitoring, an accumulation study of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn was performed, focusing on leaves belonging to different whorls and culms. To this end, in five sampling sites on the littoral zone of the volcanic Lake Averno (Italy), and in one occasion (autumn) before plant senescence, leaves of different ages and culms were collected and analyzed for metal concentrations. In terms of the suitability for biomonitoring, culms demonstrated poor performances in relation to the low metal accumulation and the difficulties in sampling and processing, whereas leaves proved their effectiveness in highlighting whole plant exposure. Since the accumulation degree of Cr, Cu, Fe and Zn is unaffected by leaf age, the pooling of leaves from different whorls is advisable to improve the representativeness of samplings. This strategy becomes mandatory in the case of Ni, the non-monotonic age-dependent variations of which would affect the derivation of contamination gradients otherwise. For Mn, Cd and Pb, the accumulation patterns strictly dependent on age can instead be exploited in selecting the sensitivity of biomonitoring by focusing on the organs where they are preferentially accumulated: old leaves for Mn and young leaves for Cd and Pb.

Water Mixing Conditions Influence Sentinel-2 Monitoring of Chlorophyll Content in Monomictic Lakes

Prompt estimation of phytoplankton biomass is critical in determining the ecological quality of freshwaters. Remote Sensing (RS) may provide new opportunities to integrate with situ traditional monitoring techniques. Nonetheless, wide regional and temporal variability in freshwater optical constituents makes it difficult to design universally applicable RS protocols. Here, we assessed the potential of two neural networks-based models, namely the Case 2 Regional CoastColour (C2RCC) processor and the Mixture Density Network (MDN), applied to MSI Sentinel-2 data for monitoring Chlorophyll (Chl) content in three monomictic volcanic lakes while accounting for the effect of their specific water circulation pattern on the remotely-sensed and in situ data relation. Linear mixed models were used to test the relationship between the remote sensing indices calculated through C2RCC (INN) and MDN (IMDN), and in situ Chl concentration. Both indices proved to explain a large portion of the variability in the field data and exhibited a positive and significant relationship between Chl concentration and satellite data, but only during the mixing phase. The significant effect of the water circulation period can be explained by the low responsiveness of the RS approaches applied here to the low phytoplankton biomass, typical of the stratification phase. Sentinel-2 data proved their valuable potential for the remote sensing of phytoplankton in small inland water bodies, otherwise challenging with previous sensors. However, caution should be taken, since the applicability of such an approach on certain water bodies may depend on hydrological and ecological parameters (e.g., thermal stratification and seasonal nutrient availability) potentially altering RS chlorophyll detection by neural networks-based models, despite their alleged global validity.

Global carbon dioxide output of volcanic lakes in the Azores archipelago, Portugal

The Azores archipelago (Portugal) contains 88 lakes, two located inside caves spread across six of the nine volcanic islands of the archipelago; the formation of the lakes is associated with various types of volcanic structures. Surveys were performed on 45 water bodies corresponding to a representative data set and omitting only small ephemeral ponds to extensively research CO2 emissions from the volcanic lakes.The modified accumulation chamber method was used to measure the CO2 flux at the surface of the lakes; 16,119 measurements were performed with flux values ranging from 0 to 20,960 g m−2 d−1. Graphical statistical approaches identified different geochemical populations from the CO2 flux data. Multiple populations associated with limnological and biogenic processes or volcanic/hydrothermal sources were identified in some cases. The influence of these sources was also confirmed by the determined δ13C content of the lakes.The lakes of the Azores emit approximately ~171 × 103 t yr−1 of CO2 into the atmosphere; much of this is released by the Furnas and Furna do Enxofre lakes, both showing mantle-derived CO2 origin. Deep-seated CO2 accounts for approximately 42% of the total degassing.

Modeling approach to determine priority sub-catchment for volcanic lake restoration

Catchment restoration is one of important aspects taken into account when planning lake restoration. The initial step to this is identifying the location and characteristics of the problem areas for further analysis in deciding suitable restoration measures. The objective of this study is to identify and characterize priority sub-catchment to be managed in order to promote Lake Maninjau restoration by using calibrated and validated 2-dimensional multilayers hydrodynamics and water quality model. Results showed that small sub-catchments which are significantly occupied by settlements in the verge of the lake should be prioritized since they provide higher immediate nutrient which lead to eutrophication near the lakeshore area. While large sub-catchments may not cause immediate eutrophication in the lakeshore area, they must also be managed wisely to increase water quality in the much wider part of the lake.

Length-weight relationship, condition factor, and distribution of spotted barb (Barbodes binotatus Valenciennes, 1842) in Lake Tamblingan Bali

Tamblingan Lake is a volcanic lake located in the caldera of Mount Lesung a rain-fed lake in a confined endorheic basin and there is no inflow or outflow. Nyalian is a type of fish from the Cyprinidae family that is quite common compared to other fish in its class in Tamblingan Lake. Information on the growth and distribution of these fish parameters in Tamblingan Lake does not exist. This study aims to analyze and explain the growth patterns of Barbodes binotatus, especially the length-weight relationship, condition factor, and their distribution in the waters of Tamblingan Lake. The research was conducted in Tamblingan Lake from January to June 2019 using a modify gill nets with the mesh size 0.5; 1.0; 1.5; 2.0; 2.5; 3.0 in centimeter. The sampling done in five locations. The length-weight relationship analysis used the power regression. The fish sample found was 204 individuals during the study with a range of total length was 5.2 – 15.0 cm. The equation of length-weight relationship is W = 0.0051 L3.387. The value of b formed based on this equation is 3.387 with a positive allometric growth pattern.The condition factor values ranged from 0.587 to 1.246. Barbodes binotatus spread in the litoral area where there are many aquatic plants. This information of nyalian fish could use as the basis for fish resource management in Tamblingan Lake.

Astronomical Tide and Storm Surge Signals Observed in an Isolated Inland Maar Lake Near the Coast

Aimed at the explanation of clear tidal signal and storm surge signals in a closed inland lake near the coast (the Huguangyan Lake), this work uses a combined approach with observations and model experiments. Huguangyan Lake is a closed inland freshwater coneless volcanic crater lake near the coast in tropical southern China, less than 5 km from an estuary. It has a diameter of about 1.5 km and relatively deep water of up to 20 m. Bottom pressure was measured from an acoustic Doppler current profiler (ADCP) for 10 days in September 2018 and 10 days in January 2019. The observations encompass the period of Typhoon Mangkhut, which passed the region when it made its landfall. The time series demonstrate clear tidal and subtidal signals. The tidal signal remains even if we exclude the barometric pressure effect. Interestingly, the lake has no surface connection with the ocean. The astronomical tide has an amplitude of about 2 cm. The major tidal signals include the principal solar semidiurnal (S2) and lunisolar (K1) constituents. During the passage of Typhoon Mangkhut, the water level variability inside the lake increased by an order of magnitude (>0.3 m). To examine whether the lake water level change was due to the natural oscillations inside the lake (or seiche), a numerical wind-driven hydrodynamics model was designed using the 3-D Finite Volume Community Ocean Model (FVCOM). The results show that a small first-order seiche can be generated, but only with a time scale of minutes and with a magnitude much smaller than the observed surface elevation changes. This excludes any measurable seiche and the observed surface elevation change inside the lake cannot be wind-driven. Moreover, tides inside the lake are not generated by tidal potential, as the lake is too small for having a locally generated tide. The main result of our study has therefore excluded the local tidal-generating force, wind-driven seiche, and barometric effect, as possible causes of the lake oscillation which has tidal and subtidal signals. The subtidal variation is at least one order of magnitude greater than tides inside the lake and is caused by weather-induced overall coastal ocean water level oscillations transmitted into the lake through groundwater connection. All these lead to the major conclusion that the lake is connected to the coastal ocean through groundwater.

Fluid pathways identified beneath Narl\u0131 Lake (Central Anatolia) show the geothermal potential of former volcanoes

We investigated the volcanic Narlı Lake in Central Anatolia combining high-resolution bathymetry and geochemical measurements. In this study, we present it as proof of a new concept to verify fluid pathways beneath lakes integrating the structure of the geothermal reservoir into the surrounding tectonic frame. We recognized dextral faults fracturing inherited volcanic formations and thus generating highly permeable zones beneath the lake. At intersection points of faults, reservoir fluids discharge from deep holes as imaged by the high-resolution bathymetry at the bottom of the Narlı Lake. Onshore, the tectonic setting also generates both extensional and compressional structures. Extensional structures result in extensive fluid discharge through hot springs while compressional structures do not discharge any fluid. The water of the lake as well as in the hot springs is highly saline and has relatively high concentrations of Cl, HCO3, SO4, Na, Ca, Mg, and Si. In several hot springs, we observed mixtures of high-saline fluids having a deep origin and low-saline shallow groundwater. We observed discharge into the lake by gas bubbles, which contain probably CO2 or H2S. Mineral precipitation indicates a carbonatic source at the lake bottom and along the shoreline. Extensive travertine precipitation also occurs near hot springs along the nearby extensional zone of Ihlara Valley. In summary, the composition of fluids and minerals is controlled by water–rock interaction through the volcanic and carbonatic rocks beneath this volcanic lake.

Phylogenetic diversity contributes more to sediment magnetism than abundance during incubation of iron-reducing sediment from a non-active volcanic lake in Northeast China.

This study aimed to analyse bacterial community and biomineralization products from Wudalianchi non-active volcanic field and the relationship between magnetization and bacterial community. Eighteen sediment samples obtained from Wenbo Lake, high-throughput sequencing and quantitative PCR (qPCR) were separately employed to investigate the bacterial community composition dynamics and abundance variation of the sediment sample with the highest iron-reducing capacity during incubation. The mineralization products were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction (XRD), Raman spectroscopy, vibrating sample magnetometer (VSM) and variable-temperature magnetism analyses. The results showed that the highest iron reduction rate was 98·06%. Seven phyla were identified as dominant bacterial phyla during the incubation process. Iron-reducing bacteria (FeRB) including Geobacter, Desulfosporosinus and Clostridium were involved in the iron mineralization process. The 16S rDNA copy numbers of sediment decreased quickly and then stayed steady during the incubation. Bacteria with rod-shaped and spheroid species were involved in extracellular iron reduction to produce magnetic particles with massive aggregation and columnar structures on the mineral surface morphologies. The materials produced by the microbial community over the incubation period were sequentially identified as siderite, magnetite and maghemite. The magnetism of the mineral samples gradually increased from 0·31748 to 33·58423emug-1 with increased incubation time. The final products showed relatively stable magnetism under 0-400K. Meanwhile, the saturation magnetization (MS ) of the mineralized substance was tightly associated with bacterial diversity (P<0·05). Bacterial community varied during incubation of iron-reducing sediment of volcanic lake. Various iron mineral crystals were in turn formed extracellularly by FeRB. The magnetism of mineralized products was tightly associated with bacterial community. These results not only help us to better understand the iron mineralization of FeRB in the volcanic lake sediments but also provide basic information for the future application of FeRB in environmental bioremediation.

Volcanic carbon cycling in East Lake, Newberry Volcano, Oregon, USA

Abstract The carbon cycle in East Lake (Newberry Volcano, Oregon, USA) is fueled by volcanic CO2 inputs with traces of Hg and H2S. The CO2 dissolves in deep lake waters and is removed in shallow waters through largely diffusive surface degassing and photosynthesis. Escaping gas and photosynthate have low δ13C values, leading to δ13C(DIC) (DIC—dissolved inorganic carbon) as high as +5.7‰ in surface waters, well above the common global lake range. A steep δ13C depth gradient is further established by respiration and absorption of light volcanic CO2 in bottom waters. The seasonal CO2 degassing starts at &amp;gt;100 t CO2/day after ice melting in the spring and declines to ∼40 t/day in late summer, degassing ∼11,700 t CO2/yr. Thus, volcano monitoring through gas fluxes from crater lakes should consider lacustrine processes that modulate the volcanic gas output over time. The flux contribution of a bubbling CO2 “hotspot” increased from 20% to &amp;gt;90% of the lake-wide CO2 flux from 2015 to 2019 CE, followed by a “toxic gas alert” in July 2020. East Lake is an active volcanic lake with a “geogenic” ecosystem driven primarily by hydrothermal inputs.