Crater Lake Research Articles

Mastigodiaptomus galapagoensis n. sp. (Crustacea: Copepoda: Diaptomidae), a possibly extinct copepod from a crater lake of the Galápagos archipelago.

A new species of a Neotropical diaptomid copepod is described based on individuals recovered from a small, almost forgotten collection of unique plankton samples from El Junco, a crater lake in San Cristóbal island, Galápagos archipelago. This copepod was regularly reported (1966-2004) as an abundant zooplankter in the lake, but it was not found in subsequent plankton surveys (2007-2018), and its specific identity remained unknown. In 2020, it was declared extinct because of introduced fish predation, rotenone treatment, and other major disturbances. The taxonomic examination of these invaluable specimens allowed us to recognize them as representing an undescribed species of the freshwater diaptomid genus Mastigodiaptomus Light, 1939. Here, we describe the new species from El Junco crater lake, located in the San Cristóbal island a part of the Galápagos archipelago, collected with plankton nets. The description is based on detailed morphology, based on SEM and light microscopy. The taxonomic examination of these invaluable specimens allowed us to recognize them as representing an undescribed species of the freshwater diaptomid genus Mastigodiaptomus Light, 1939. The new species was readily assigned to this genus and is distinguished from its known congeners by details of (1) the male right fifth leg terminal claw and aculeus, (2) spiniform processes pattern of the right geniculate antennule segments 10-16, (3) length and structure of the spiniform process of the antepenultimate segment of the male right antennule, and (4) details of the dorsal process on the female fourth pediger. This finding represents the first report of this Neotropical copepod genus outside its original biogeographic region, the third species of a diaptomid copepod reported from insular freshwater systems, the southernmost record of Mastigodiaptomus, and the only freshwater calanoid in the Galápagos. The intriguing presence of this chiefly Neotropical copepod genus here could be related either to (1) human agency linked to pirate activities, commercial travelling by Spaniard ships, whaling activities, and intense tortoise hunting in San Cristóbal island. In the past, El Junco was the only freshwater source 600 nautical miles around, or (2) zoochory of resistant dormant stages passively transported by more than 65 migrating bird species known to settle in San Cristóbal. These two hypotheses cannot be properly tested at this time, so the explanation of the presence of this copepod will remain as a new open question in the fascinating natural history of the Galápagos.

Phenotypic rate and state are decoupled in response to river-to-lake transitions in cichlid fishes.

Geographic access to isolated ecosystems is an important catalyst of adaptive radiation. Cichlid fishes repeatedly colonized rift, crater, and volcanic lakes from surrounding rivers. We test the "lake effect" on the phenotypic rate and state across 253 cichlid species. The rate of evolution was consistently higher (~10-fold) in lakes, and consistent across different dimensions of the phenotype. Rate shifts tended to occur coincident with or immediately following river-to-lake transitions, generally resulting in 2- to 5-fold faster rates than in the founding riverine lineage. By contrast, river- and lake-dwelling cichlids exhibit considerable overlap in phenotypes, generally with less disparity in lakes, but often different evolutionary optima. Taken together, these results suggest that lake radiations rapidly expand into niches largely already represented by ancestral riverine lineages, albeit in different frequencies. Lakes may provide ecological opportunity via ecological release (e.g., from predators/competitors) but need not be coupled with access to novel ecological niches.

Challenges and Opportunities of Community Based Ecotourism: The Case of Wonchi Crater Lake, South-west Shoa, Oromia Regional State, Ethiopia

Challenges and Opportunities of Community Based Ecotourism: The Case of Wonchi Crater Lake, South-west Shoa, Oromia Regional State, Ethiopia

Innovative receiving phase for Chemcatcher® passive sampler for phosphorus in the water environment: Calibration of sampling rate by water temperature and pH

Passive sampling is a technique for monitoring orthophosphate (PO4-P) in the water environment. Compared with traditional grab sampling followed by PO4-P quantification, kinetic-type passive samplers such as Chemcatcher® express representative concentrations of PO4-P as time-weighted average concentrations (CTWA). They can also potentially evaluate much lower PO4-P concentrations, but the available receiving phases of Chemcatcher® used for PO4-P were extremely limited. We developed a new receiving phase, the PSfZS sheet, comprising a zirconium sulfate–surfactant micelle mesostructure and polysulfone matrix. We examined its performance in terms of PO4-P sorption characteristics, PO4-P selectivity, and PO4-P sampling rate (Rs). Its capacity was adequate (12.0 μg-P/cm2) and selectivity for PO4-P uptake was good. The Rs for PO4-P increased with increasing water temperature (8.1–29.1 °C) and decreasing pH (4.1–9.7) in a laboratory calibration, and ranged from 5.27 × 10−2 L/d to 1.66 × 10−1 L/d. We placed the samplers in a municipal wastewater treatment plant, a shallow eutrophic lake, and an oligotrophic caldera lake. The Rs in the deployment sites was calibrated by monitored water temperature and pH. The estimated CTWA of PO4-P in the municipal wastewater treatment plant was similar to the averaged concentration of soluble reactive phosphorus determined by multiple grab samplings. In the lake deployments, we found that the new sampler can quantify CTWA values of PO4-P below 10 μg/L, and thus it provides more technical monitoring options and contributes to the conservation and management of the water environment.

Characterizing lithological, weathering, and hydrothermal alteration influences on volcanic rock properties via spectroscopy and laboratory testing: a case study of Mount Ruapehu volcano, New Zealand

The geomechanical characterization of volcanic material has important implications for geothermal and mineral exploration, engineering design, geophysical signals of volcano unrest, and models of instability and mass flows. Chemical weathering and hydrothermal systems can alter the host rock, leading to changes in mechanical behavior and failure mode. Here, we compare the physical and mechanical properties of lava, autoclastic breccia, and pyroclastic (scoria) rocks from Mount Ruapehu volcano (Ruapehu) in New Zealand to mineralogical composition determined via infrared spectroscopy and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). We use correlation matrices, principal component analysis, and parametric analysis to determine which parameters can be used to predict physical and mechanical properties and form the basis for transfer functions. Laboratory-based spectroscopy shows that the samples contain absorption features indicative of Al- and Mg-rich hydrous phyllosilicates (e.g., kaolinite, halloysite, montmorillonite), Fe- oxides (e.g., goethite), and sulfates attributed to surface weathering, supergene, and steam-heated alteration. We find that porosity and primary lithology are the predominant control on physical and mechanical properties, followed by the pervasiveness of weathering/alteration, and then mineralogical composition. Several properties, such as porosity, uniaxial compressive strength, P-wave seismic velocity, density, and Young’s modulus, show strong correlations with other properties, indicating the potential for transfer functions between these properties. Hydrothermally altered rocks near the vent complex (up to ~ 400 m depth beneath the crater lake) with high-intensity hydrothermal alteration do not follow typical physical and mechanical property trends due to high clay content, low permeability, and low strength. The presence of these rocks within the edifice at Ruapehu implies local barriers to fluid flow and subsequent pore pressure variations. Additionally, they may have less than half the strength than would be dictated by typical porosity-strength trends for surface rocks, increasing the likelihood of structural failure. Trends in the pervasiveness of weathering with physical and mechanical properties, along with shifts in the position of spectral absorption peaks as hydrothermal/weathering alteration increases, suggest that it may be possible to extrapolate properties from imaging spectroscopy.

Runoff required to drive postimpact gully development on the walls of Meteor Crater (Arizona, USA)

Since the impact ∼50,000 yr ago, surface runoff has entrained and transported sediment from the walls to the floor of Meteor Crater (Arizona, USA). Previous work interpreted this erosion and deposition to be due to predominantly fluvial (i.e., dilute water transport) processes. However, light detection and ranging (LiDAR)−derived topographic data and field observations indicate that debris flows dominated, which were likely generated by runoff that entrained the talus that borders bedrock cliffs high on the crater walls. The low gradient of the crater floor caused debris flows to stop, leaving lobate deposits, while fluvial processes delivered sediment toward the center of the crater. Cosmogenic radionuclide dating of levee deposits suggests that debris-flow activity ceased in the late Pleistocene, synchronous with regional drying. Assuming a rock-to-water ratio of 0.3 at the time of transport by mass flows, it would have taken ∼2 × 106 m3 of water to transport the estimated ∼6.8 × 106 m3 of debris-flow deposits found at the surface of the crater floor. This extensive erosion would require ∼6 m of total runoff over the 0.35 km2 upslope source area of the crater, or ∼18 mm of runoff per debris-flow event. Much more runoff did occur, as evidenced by crater lake deposits, Holocene fluvial activity (which produced little erosion), and contemporary rainfall rates. Rarely on Earth is the total amount of water that creates and runs through a landscape estimated, yet such calculations are commonly done on Mars. Our analysis suggests that erosional and depositional landforms may record only a small fraction of the total runoff.

Ebeko Volcano Activity in 2022: Mechanism and Products of Eruption

The paper provides information about the eruptive activity of the Ebeko volcano in 2022. From January 22 to June 13, phreatic explosions occurred in the crater lake caused by water seeping through the plug formed in the upper part of the magma channel and its boiling. On June 14, Vulcanian explosions began, destroying the lake. The granulometric composition of the ashes has changed in the direction of reducing the particle size. Petrographic and mineralogical-geochemical studies of tephra allow us to define this period as a phreatomagmatic eruption by the presence of fresh juvenile material. It is established that the interaction of magma with the waters of the hydrothermal system of the Ebeko volcano leads to its depletion with alkali metals and enrichment with silica. It is suggested that the formation of amorphous water-containing silica in the form of numerous separations and its subsequent dehydration may contribute to the explosive activity of the volcano.

Isolation and Identification of Arsenic-Resistant Extremophilic Bacteria from the Crater-Lake Volcano "El Chichon", Mexico.

The crater lake at "El Chichón" volcano is an extreme acid-thermal environment with high concentrations of heavy metals. In this study, two bacterial strains with the ability to resist high concentrations of arsenic (As) were isolated from water samples from the crater lake. Staphylococcus ARSC1-P and Stenotrophomonas ARSC2-V isolates were identified by use of the 16S rDNA gene. Staphylococcus ARSC1-P was able to grow in 400mM of arsenate [As(V)] under oxic and anoxic conditions. The IC50 values were 36 and 382mM for oxic and anoxic conditions, respectively. For its part, Stenotrophomonas ARSC2-V showed IC50 values of 110mM and 2.15 for As(V) and arsenite [As(III)], respectively. Arsenic accumulated intracellularly in both species [11-25nmol As × mg cellular prot-1 in cells cultured in 50mM As(V)]. The present study shows evidence of microbes that can potentially be a resource for the bio-treatment of arsenic in contaminated sites, which highlights the importance of the "El Chichón" volcano as a source of bacterial strains that are adaptable to extreme conditions.

Hydroclimate changes since the last glacial maximum from sedimentary biomarkers in a crater lake in the Great Khingan Mountains, Northeast China

The scarcity of well-dated, highly temporally resolved, paleoclimate records since the last glacial maximum (LGM) in Northeast China limits our understanding of past climatic variations and the prediction of future hydrological changes in the context of anthropogenic global warming. A high-resolution n-alkane record covering the past ∼25 kyr was retrieved from Lake Tuofengling, a hydrologically closed crater lake in the central Great Khingan Mountains. The sediments contained a suite of mid- and long-chain n-alkanes with a strong odd-to even-carbon number predominance. The relative proportion of mid-to long-chain n-alkane homologues (Paq) was proposed to evaluate the input of submerged/floating plants into lake sediments relative to that from emergent/terrestrial plants, which could be a useful indicator of lake level in lacustrine settings. The Paq proxy demonstrated that lake level increased stably from the shallowest level during the LGM to a maximum depth at 7.5–3.0 cal ka BP, with a minor decreasing trend during the late Holocene. The asynchronous changes in effective moisture in the East Asian summer monsoon (EASM) region since the LGM might be directly or indirectly mediated by the shift in the rainfall belt, the position and intensity of the Western Pacific Subtropical High and Okhotsk High at different timescales. Our study provides new insights into climatic evolution in Northeast China, where the main climate pattern may not always be similar to the typical EASM pattern.

The hidden role of dissolved organic carbon in the biogeochemical cycle of carbon in modern redox-stratified lakes

Abstract. The dissolved organic carbon (DOC) reservoir plays a critical role in the C cycle of marine and freshwater environments because of its size and implication in many biogeochemical reactions. Although it is poorly constrained, its importance in ancient Earth's C cycles is also commonly invoked. Yet DOC is rarely quantified and characterized in modern stratified analogues. In this study, we investigated the DOC reservoirs of four redox-stratified alkaline crater lakes in Mexico. We analyzed the concentrations and isotopic compositions of DOC throughout the four water columns and compared them with existing data on dissolved inorganic and particulate organic C reservoirs (DIC and POC). The four lakes have high DOC concentrations with great variability between and within the lakes (averaging 2 ± 4 mM; 1 SD, n=28; i.e., from ∼ 15 to 160 times the amount of POC). The δ13CDOC signatures also span a broad range of values from −29.3 ‰ to −8.7 ‰ (with as much as 12.5 ‰ variation within a single lake). The prominent DOC peaks (up to 21 mM), together with their associated isotopic variability, are interpreted as reflecting oxygenic and/or anoxygenic primary productivity through the release of excess fixed carbon in three of the lakes (Alberca de los Espinos, La Preciosa, and Atexcac). By contrast, the variability of [DOC] and δ13CDOC in the case of Lake Alchichica is mainly explained by the partial degradation of organic matter and the accumulation of DOC in anoxic waters. The DOC records detailed metabolic functions such as active DIC-uptake and DIC-concentrating mechanisms, which cannot be inferred from DIC and POC analyses alone but which are critical to the understanding of carbon fluxes from the environment to the biomass. Extrapolating our results to the geological record, we suggest that anaerobic oxidation of DOC may have caused the very negative C isotope excursions in the Neoproterozoic. It is, however, unlikely that a large oceanic DOC reservoir could overweigh the entire oceanic DIC reservoir. This study demonstrates how the analysis of DOC in modern systems deepens our understanding of the C cycle in stratified environments and helps to set boundary conditions for the Earth's past oceans.

Mongolian Dust Activity Over the Last 25 Kyr Predominantly Driven by the East Asian Winter Monsoon: Insights From the Geochemistry of Lake Tuofengling Sediments

AbstractDust deposition in northeastern Asia since the Last Glacial Maximum has previously been studied using a variety of archives. However, the mechanisms driving variability in dust are less well constrained. Here, we present records of the Nd‐Sr isotope and major element composition of sediments from Lake Tuofengling, a crater lake located in northeastern China, over the past ∼25 thousand years. The results indicate that the lithogenic fractions of the sediments are a mixture between aeolian dust and local volcanic detritus. Our provenance data suggest that the aeolian dust component is predominantly from the Mongolia Plateau, likely carried by the East Asian Winter Monsoon. Our isotope and calculated dust flux records exhibit similar changing patterns to proxies of global ice volume and the strength of Atlantic meridional overturning circulation, potentially implicating ice sheets and ocean circulation as the dominant drivers of the East Asian Winter Monsoon over this time interval.

Hydrogeochemistry of trace and rare earth elements in the Caviahue-Copahue Volcanic Complex

The Caviahue-Copahue Volcanic Complex is one of the most studied active volcanic systems in the South American Andean range, and yet little research has focused on trace and rare-earth elements of waters, especially during an eruptive cycle. In this study, we sampled and investigated natural waters from 23 sites (involving the crater lake, hot springs, streams, rivers, and bubbling pools) in two campaigns in 2017 and 2018, using physicochemical parameters, major, trace and rare-earth elements concentrations. With this novel dataset, it was possible to identify, characterize and compare three groups of waters with distinctive hydrofacies. Indeed, the normalization of water compositions against host rock concentrations showed a particular trace element pattern for each group of waters. Although the absolute concentrations of the elements in each sampling site changed from 2017 to 2018, the normalized patterns did not. Boron, As, Cd, Tl, Se, and Te, commonly recognized as volatile, are the main trace elements that magmatic gases supply to the system headwaters, whereas elements such as Ca, K, and Ba are affected by precipitation of secondary minerals (gypsum, anhydrite, barite, jarosite, and alunite). Furthermore, the main river draining the summit volcano shows a steep decrease in As, Cr, and V concentrations correlated to the precipitation of Fe and Al hydroxysulfates (schwertmannite and basaluminite, respectively). Moreover, it is the first time that a comparison between the different water groups is made using the patterns of the rare-earth elements, allowing us to identify and separate depletion patterns due to dilution processes from those due to precipitation processes.

Climate-vegetation-erosion interactions revealed by the sediments of Huguangyan Maar Lake, southern China

Soil erosion is a serious environmental problem in the red soil region of southern China, yet little is known about the factors responsible and their specific effects on long-term soil erosion dynamics in this region. We addressed this issue via a study of the sediments of Huguangyan Maar Lake (HML), a crater lake in southern China. Our results confirm that the sediments in HML are mainly derived from the erosional input of weathering products of wall rocks, via catchment runoff. Having established the provenance of the HML sediments, the sediment accumulation rate, mass accumulation rate, and geochemical element fluxes were used to reconstruct soil erosion processes in the HML catchment over the past ∼1400 years. The potential drivers of soil erosion were explored, and regional comparisons were made to evaluate the representativeness of this study. The results show that: 1) Higher precipitation before ∼830 CE, coupled with a lower level of human activity, promoted increased vegetation coverage which reduced the rate of soil erosion. 2) Lower precipitation during 830 CE–1390 CE reduced the rate of soil loss. 3) Abundant precipitation was the main cause of the more intense soil erosion during 1390 CE–1878 CE, which may have been exacerbated by the reduced vegetation cover caused by intensive human activity. 4) During 1878 CE–2019 CE, the vegetation cover gradually recovered under the combined effects of vegetation restoration and higher precipitation, which reduced the rate of soil erosion within the HML catchment. Compared to the Chinese Loess Plateau, the erosion level in the HML catchment was relatively low during the period of intensive human activities. Overall, our results contribute to an improving understanding of the driving mechanisms of soil erosion, and they provide a guide for soil conservation measures in southern China.

Risk of invasiveness of non-native fishes can dramatically increase in a changing climate: The case of a tropical caldera lake of conservation value (Lake Taal, Philippines)

Risk of invasiveness of non-native fishes can dramatically increase in a changing climate: The case of a tropical caldera lake of conservation value (Lake Taal, Philippines)

Benthic macroinvertebrates community to response environmental factors in a crater lake (Case study: Lake Menjer, Indonesia)

Lake Menjer is one of the crater lakes located in the highland of Central Java, Indonesia, which has received multiple stressors from anthropogenic activities. Benthic macroinvertebrates as a key indicator for water quality were little known there. Thus, this present research aimed to identify benthic macroinvertebrate structures and to understand the response of this community to water quality in Lake Menjer. Samplings were conducted twice, one week each in August and October 2019 at five sites. Sampling in August represented the condition of the dry season, while in October represented the rainy season. Some groups were identified into the family and others into the genus level. Water quality variables were measured directly on the site, including water clarity, pH, dissolved oxygen (DO), conductivity, total dissolved solids (TDS), and oxidation-reduction potential (ORP). Meanwhile, the level of total nitrate (TN), total phosphate (TP), nitrite, and chlorophyll-a were analyzed separately. A total of 4312 benthic macroinvertebrates composed of eleven taxa belonging to eight families were recorded, namely Chironomidae (22.85%), Tubificidae (73.50%), Lumbricullidae (0.68%), Thiariidae (0.21%), Planorbidae (0.45%), Lymnaeidae (0.21%), Unionidae (0.92%), and Corbiculidae (1.13%). The number of taxa varied between 1 to 3 in each station. Mollusk was the best-represented group with five families. Meanwhile, Tubificidae was shown as the predominant family in abundance both in August (3879 ind/m2) and October (2008 ind/m2). Shannon-Wiener index ranged nearly similar between the two seasons, 0.17 to 0.91 in August and 0.0 to 0.91 in October. ANOSIM CAP6 result illustrated that there was an insignificant difference in benthic macroinvertebrates abundance (P below 0.05) among sampling sites in Lake Menjer. This community was mostly homogenous. Bray-Curtis analysis using MVSP shows similarities in the taxa compositions between the sites. The analysis between water quality and macroinvertebrates which was performed by Canonical Correspondence Analysis shows that nine taxa tended to correlate with the level of TN, DO, and conductivity. Meanwhile, the other two taxa had a relationship with water clarity, temperature, level of TP, nitrite, and chlorophyll-a.

Optimization of Rock Salt Washing Process to Remove Selected Chemical Impurities in Lake Katwe Rock Salt

Rich deposits of mineral salts, present in substantial economic quantities, characterize the geological bounty of Uganda. The primary location of this wealth is lake Katwe, a saline crater lake southwest of the country. However, all grades of rock salt extracted from Lake Katwe remain contaminated with chemical impurities such as calcium, magnesium, heavy metals and sulphate ions, even after solar evaporation process from the salt pans. There is a need to conduct research into possible contaminant removal methods which could increase the market value of the extracted salt, and add to the body of knowledge for future salt processing and chlor-alkali industries in Uganda. This study examined the effect of varying water volumes and temperature on the levels of Calcium, Magnesium and Sulphate ions in rock salt samples from Lake Katwe. The samples were methodically crushed and washed. The salt was then dissolved, crystallized, dried and meticulous analysis to determine the concentration of these impurities was carried out. The data was analysed and represented in Microsoft Excel and MATLAB. Results obtained revealed that a temperature of 40°C and salt-water ratio of 1:2 are the optimal parameters for maximum reduction of calcium, magnesium and sulphate impurities in rock salt. This analysis enhances the purity of salt harvested from Lake Katwe’s solar evaporation process and offers optimal washing parameters to reduce impurities in brine, thereby improving plant yield and reducing production costs across various salt grades. It also provides new information to the mining communities at Lake Katwe on how to affordably improve the percentage purity of their rock salt. The study will also contribute novel industry-tailored data for future prospective salt processing and chlor-alkali industrial plants near the Lake while also filling a knowledge gap for further research on rock salt purification.

Sedimentary ancient DNA of rotifers reveals responses to 200 years of climate change in two Kenyan crater lakes

Abstract Sedimentary ancient DNA (sedaDNA) has proven to be a useful tool for palaeoenvironmental studies, but only a handful of studies exist so far for tropical regions. In this study we used sedaDNA to study the temporal succession of Brachionus spp. rotifer mitochondrial DNA haplotypes using two sediment cores from two climatically different alkaline‐saline crater lakes from the Kenyan Rift Valley. Data were retrieved from a sediment core (dating back to AD 1800) from Lake Kageinya, located in the remote, hot and hyper‐arid Suguta Valley. sedaDNA was used to study the temporal succession of mitochondrial DNA haplotypes of Brachionus spp. rotifers. The results were compared to previously published data from Lake Sonachi, a well‐studied lake in the humid and colder mountainous region of Kenya near the town of Naivasha, now supported by a 210Pb age chronology. Both records extend back before the onset of substantial anthropogenic impact in these regions. The results revealed that climate—rather than anthropogenic impact—was most strongly correlated with haplotype changes in both lakes. During prolonged dry periods (such as from AD 1910 to the late AD 1960s), certain haplotypes persisted. Sudden changes and the emergence of alter native haplotypes were observed when climate became more humid or during episodes of highly variable climate (before AD 1910 and from AD 1960s onwards). Progressive changes in prevailing haplotypes during periods with variable climate could reflect local adaptation and/or be the result of immigration of new haplotypes after the eradication of previous populations during extreme environmental conditions (high temperatures, UV irradiation, pH and salinity). The results indicate that, despite adverse chemical conditions, sedaDNA in tropical lake sediments is preserved for at least a few hundred years. Therefore, its analysis provides a useful complementary palaeoenvironmental proxy for palaeolimnological reconstructions and novel insights on changes in rotifer populations through time.

Valley morphology and Quaternary seismic stratigraphy of the Manicouagan impact crater lake (Eastern Canada)

ABSTRACTLakes in formerly glaciated regions can provide valuable paleoclimate archives. Lake Manicouagan (Manikuakan, according to Innu toponymy), formed in the basin of the ~214‐Ma Manicouagan impact crater of eastern Québec, is a key area for reconstructing long‐term environmental change, as it was directly affected by the Pleistocene glaciations and the waxing and waning of the Laurentide Ice Sheet. Here, we present high‐resolution seismic data revealing an overdeepened bedrock valley filled with a sedimentary sequence. We assess its potential to serve as a paleoclimate archive. The varying shape of the overdeepened valley indicates complex erosional processes. A lower narrow V‐shaped gorge is indicative of either pressurized subglacial meltwater or pre‐Quaternary fluvial erosion, or a combination of both. Three scenarios are discussed regarding deposition of the sedimentary sequence: (i) deposition only during and after retreat of the last glacial episode; (ii) deposition during multiple glacial–interglacial cycles; and (iii) deposition mainly during a subglacial lake stage. We suggest subglacial followed by proglacial sedimentation as the most probable scenario for deposition of the sedimentary succession. We recommend considering the sediments of Lake Manicouagan as a paleoclimate archive reaching back at least to 7.5 ka, but the lake also probably contains sediments deposited before the last deglacial period.

Deterioration of the Littoral–Benthic Ecosystem Following Recent Expansion of Signal Crayfish (Pacifastacus leniusculus) in the World’s Clearest Large Lake

Some biological invasions can result in algae blooms in the nearshore of clear lakes. We studied if an invasive crayfish (Pacifastacus leniusculus) modified the biomass and community composition of benthic macroinvertebrates and therefore led to a trophic cascade resulting in increased periphyton biomass, elevated littoral primary productivity, and benthic algae bloom in a lake with remarkable transparency [Crater Lake, Oregon, USA]. After quantifying the changes in the spatial distribution of invasive crayfish over a 13-year period, we compared biomass and community composition of littoral–benthic macroinvertebrates, periphyton biovolume, community composition, nutrient limitation, and the development of benthic algae bloom in locations with high and low crayfish density. In addition, we determined if the alteration in community structure resulted in directional changes to gross primary production and ecosystem respiration. The extent of crayfish distribution along the shoreline of Crater Lake doubled over a 13-year period, leaving less than 20% of the shoreline free from crayfish. At high crayfish density sites, benthic macroinvertebrate biomass was 99% lower, and taxa richness was 50% lower than at low crayfish areas. High crayfish sites show tenfold greater periphyton biovolume, sixfold higher periphyton biomass (chlorophyll a), twofold higher metabolic productivity, and the presence of large filamentous algae (Cladophora sp.). The invasion of crayfish had negative consequences for a lake protected under the management of the USA National Park Service, with direct impacts on many levels of ecological organization.

Depositional and Diagenetic Processes of Martian Lacustrine Sediments as Revealed at Pahrump Hills by the Mars Hand Lens Imager, Gale Crater, Mars

AbstractThe Murray formation represents fine‐grained sedimentary deposition in lacustrine environments within Gale crater, Mars. Both the overall thickness of the Murray formation and its broad uniformity in sedimentary character suggest the potential for a long‐lived, groundwater‐supported lake system. Rock textures were imaged by the Mars Hand Lens Imager camera at the Pahrump Hills location, which represents the lowermost Murray formation. We analyze data from Pahrump Hills to refine earlier estimates of grain size and grain size distribution, as well as to make detailed observations of diagenetic features and modification of primary sedimentological features. These observations and resulting interpretations provide a detailed look at the dynamic behavior of lake systems on Mars. The lower portions of this exposure are characterized by planar laminated, fine‐grained material; the predominant grain size in this region is smaller than that of very fine sand. Diagenetic mineral precipitation is also prominent in these lower layers, evidenced by likely in situ precipitation of lenticular crystals, preferential cementation of laminae in several layers, precipitation of late‐diagenetic crystal clusters, and secondary modification of previously deposited crystals. The upper portions of this locality are coarser‐grained, varicolored, and contain cross‐stratified features. The variation of these features over a relatively thin stratigraphic interval indicates rapid fluctuation in the hydrodynamic behavior of Gale crater lake, similar to that observed in the shallow‐water regions of terrestrial closed basin lakes.