Acidic Lakes Research Articles

Mid- to Late-Miocene hypogene speleogenesis tied to the tectonic history of the central Basin and Range province, USA

Twenty-five caves displaying evidence of hypogene speleogenesis in White Pine County, Nevada, were studied between May 2022 and October 2023. Results demonstrate that the central Basin and Range Province is a major hypogenic cave region with speleogenesis dating back to the Middle Miocene. The U-Pb radiometric dates of cave mammillaries obtained so far cover a wide span of time, ranging between 14 Ma to 2 Ma. Tectonic shearing along the Snake Range Décollement up to about 22 Ma probably brackets the maximum age of speleogenesis. Thus, speleogenesis began between 22-14 Ma, which predates most of the Basin and Range extensional tectonism of the Late Miocene. Robust dates for the common mammillaries in the region have been hard to obtain mostly due to Pb contamination. There are elevated levels of Pb throughout the area, likely due to mineralized fluids associated with the décollement. While 11 mammillary samples (from 10 caves) have been assessed for U-Pb dating viability, five contained too much Pb for analysis. Hypogenic features in these caves include mammillaries, tilted folia, bubble trails, cupolas, ceiling vents/tubes, floor vents, acid lake basins, pseudoscallops (cusps), and boneyard (megacusps). A common and newly identified feature of these caves is extensive secondary deposits of a complex mixture with silt-sized calcite and quartz grains. Some quartz grains have calcite overgrowths, suggesting authigenic growth. We named these lithified, and very porous, deposits “calc-siltite”. Sulfuric acid speleogenesis (SAS) has been clearly demonstrated in only one cave, Lehman Caves, but is strongly suspected in at least four other study sites (Old Mans, Cathedral, #041709-NS-012, and #LC01 caves). However, the great antiquity of these hypogenic caves means that they have probably experienced climatic and surface geomorphologic changes resulting in extensive alterations by epigenic groundwater. The evidence specific to demonstrating SAS processes may have been removed or covered by later epigenic activities.

The influence of atmospheric deposition and climate change driven catchment internal processes on the recovery from acidification of high-altitude Alpine lakes

The impact of atmospheric deposition and environmental factors on catchment processes and water chemistry of 20 high-altitude Alpine lakes in Southern Switzerland was investigated over four decades. Through the analysis of input-output budgets of sulphur (S), nitrogen (N), base cations and alkalinity significant trends emerged. Notably, S and N input concentrations significantly declined since the 1980s, by approximately 78 % and 22 %, respectively, with N primarily declining after 2000. Recovery from acidification was slightly delayed, likely due to the increased release of S, possibly originating from legacy S pools, alongside the simultaneous reduction in leaching of base cations from exchange sites. Catchments heavily impacted by thawing cryospheric features increasingly released S and base cations due to enhanced weathering processes, with hardly any impact on the recovery process, as evidenced by the balanced releases of S and base cations. N output concentrations followed the decrease of N input concentrations, while the relative N retention in the catchments remained relatively stable. Recently, both input concentrations of S and N have stabilised, while output concentrations of base cations began to increase across all catchments. The trend likely arises from the stabilisation of S and N input concentrations and/or the ongoing increase in weathering rates induced by climate change. Consequently, there was a consistent rise in alkalinity output concentrations even after the stabilisation of the S and N input concentrations. Ion ratio analysis suggests that carbonation primarily drives weathering processes in catchment areas unaffected by thawing cryosphere, while in areas impacted by thawing cryosphere, sulphide oxidation (or sulphate dissolution) is the dominant process. Further recovery depends on future N deposition and the effects of climate change.

Nutrient structure dynamics and microbial communities at the water-sediment interface in an extremely acidic lake in northern Patagonia.

Lake Caviahue (37° 50 'S and 71° 06' W; Patagonia, Argentina) is an extreme case of a glacial, naturally acidic, aquatic environment (pH ~ 3). Knowledge of the bacterial communities in the water column of this lake, is incipient, with a basal quantification of the bacterioplankton abundance distribution in the North and South Basins of Lake Caviahue, and the described the presence of sulfur and iron oxidizing bacteria in the lake sediments. The role that bacterioplankton plays in nutrient utilization and recycling in this environment, especially in the phosphorus cycle, has not been studied. In this work, we explore this aspect in further depth by assessing the diversity of pelagic, littoral and sediment bacteria, using state of the art molecular methods and identifying the differences and commonalties in the composition of the cognate communities. Also, we investigate the interactions between the sediments of Lake Caviahue and the microbial communities present in both sediments, pore water and the water column, to comprehend the ecological relationships driving nutrient structure and fluxes, with a special focus on carbon, nitrogen, and phosphorus. Two major environmental patterns were observed: (a) one distinguishing the surface water samples due to temperature, Fe2+, and electrical conductivity, and (b) another distinguishing winter and summer samples due to the high pH and increasing concentrations of N-NH4+, DOC and SO42-, from autumn and spring samples with high soluble reactive phosphorus (SRP) and iron concentrations. The largest bacterial abundance was found in autumn, alongside higher levels of dissolved phosphorus, iron forms, and increased conductivity. The highest values of bacterial biomass were found in the bottom strata of the lake, which is also where the greatest diversity in microbial communities was found. The experiments using continuous flow column microcosms showed that microbial growth over time, in both the test and control columns, was accompanied by a decrease in the concentration of dissolved nutrients (SRP and N-NH4+), providing proof that sediment microorganisms are active and contribute significantly to nutrient utilization/mobilization.

Comparing microbial populations from diverse hydrothermal features in Yellowstone National Park: hot springs and mud volcanoes.

Geothermal features, such as hot springs and mud volcanoes, host diverse microbial life, including many extremophile organisms. The physicochemical parameters of the geothermal feature, such as temperature, pH, and heavy metal concentration, can influence the alpha and beta diversity of microbial life in these environments, as can spatiotemporal differences between sites and sampling. In this study, water and sediment samples were collected and analyzed from eight geothermal sites at Yellowstone National Park, including six hot springs, a mud volcano, and an acidic lake within the same week in July 2019, and these geothermal sites varied greatly in their temperature, pH, and chemical composition. All samples were processed and analyzed with the same methodology and taxonomic profiles and alpha and beta diversity metrics determined with 16S rRNA sequencing. These microbial diversity results were then analyzed with respect to pH, temperature, and chemical composition of the geothermal features. Results indicated that predominant microbial species varied greatly depending on the physicochemical composition of the geothermal site, with decreases in pH and increases in dissolved heavy metals in the water corresponding to decreases in alpha diversity, especially in the sediment samples. Similarly, sites with acidic pH values had more similar microbial populations (beta diversity) to one another than to relatively neutral or alkaline pH geothermal sites. This study suggests that pH and/or heavy metal concentration is a more important driver for microbial diversity and population profile than the temperature for these sites and is also the first reported microbial diversity study for multiple geothermal sites in Yellowstone National Park, including the relatively new mud volcano Black Dragon's Caldron, which erupted in 1948.

Pike Mercury Concentration in Small Boreal Headwater Lakes During Four Decades of Regional and Local Changes

We measured the total mercury (THg) concentration in the muscle of northern pike (Esox lucius L.) from 12 boreal headwater lakes once per decade during the 1980s to 2010s. Relations of pike THg to regional environmental changes, such as reduction of acid deposition and increase in water colour (i.e. browning), were examined as well as the effects of local lake-specific changes caused by introduced beavers (Castor canadensis) and intensive fishing of pike. No consistent decrease in pike THg took place during 1983–2013 despite the reductions in mercury emissions from European sources since the 1990s and the associated decreased mercury deposition in Finland. In most of the lakes, individual pike exceeded the recommended limit for human consumption (1 mg kg−1, wet weight). The highest THg levels were recorded in 2002 following intensive browning of the lakes in the 1990s in connection with decreased sulphate deposition. The effects of acid deposition were only seen as the highest pike THg in the two most acidic lakes in the early 1980s. After taking length effects into account, pike THg had a negative relationship with growth (i.e. growth dilution), but a positive relationship with water colour, iron, nutrients and maximum lake depth. Females grew faster and had lower THg than males. Pike THg was elevated in beaver-impacted lakes. Experimental removal of pike from three study lakes during 2005–2013 resulted in a decrease of pike THg. These findings emphasize the significance of local abiotic and biotic drivers when interpreting the regional long-term trends in pike THg.

Evolution of shallow volcanic seismicity in the hydrothermal system of La Soufrière de Guadeloupe following the April 2018 Mlv 4.1 earthquake

La Soufrière de Guadeloupe volcano is characterized by seismo-volcanic activity dominantly linked to an active hydrothermal system. This microseismicity is shallow, mainly triggered in swarms and characterized by repeating earthquakes. Four recurrent families of Volcano-Tectonic (VT) repeaters have been identified and the main repeater accounts for 80% of detections. Stacking repeating seismic waveforms produces MASTER events with a high Signal-to-Noise Ratio (SNR) and thanks to the deployment of a temporary seismic nodal array, their absolute locations can be better constrained. Because we observe systematic positive residuals of P-wave arrival times at almost all stations, we investigate potential bias in the velocity model in the shallow part of the dome. By increasing the P-wave velocity and decreasing the VP/VS ratio from 1.8 to 1.69, we reduce these residuals and improve the local velocity model. We use this new velocity model to locate each VT event relatively to is own MASTER hypocenter. This procedure offers a new image of the hydrothermal seismic activity that we locate under the acid lake of the summit Tarissan crater, along a sub-vertical conduit. We also define a linear relationship between the logarithm of the peak amplitude of seismic events and their duration to obtain a pseudo local magnitude. The approach enables to accurately and automatically estimate the magnitude during the event detection. We show that after the occurrence in April 2018 of the largest earthquake (Mlv 4.1) since the last phreatic eruption in 1976–1977, the swarm frequency and amplitude increased significantly, and a new family of VT repeater emerges, accounting for up to 14% of detections. We show a quiescence in the main repeaters activity in the month following the April 2018 earthquake, suggesting a significant stress release within the volcanic system, which is likely related to dynamic stress changes rather than static stress variations caused by the earthquake. Moreover, we detect the emergence of a new family of repeaters 3 months after the event, located ∼100 m above the main repeater family, that could be related to a fluid pressure increase induced by the regional hydrological cycle, superimposed to the internal forcing driven by the hydrothermal system. Finally, using a statistical approach, we highlight seasonal periodicities in the number of events and the released seismic moment at La Soufrière de Guadeloupe, with a dominant peak of seismic activity in October–November and a second, less significant, peak of in April.

Trace elements in the water column of high-altitude Pyrenean lakes: Impact of local weathering and long-range atmospheric input

High altitude (alpine) lakes are efficient sentinels of environmental processes, including local pollution and long-range atmospheric transfer, because these lakes are highly vulnerable to ongoing climate changes and increasing anthropogenic pressure. Towards improving the knowledge of trace element geochemistry in the water column of alpine lakes, we assessed 64 physico-chemical parameters, including macro- and micronutrients, major and trace element concentrations in the water column of 18 lakes in the Pyrenees, located along the border between France and Spain.Lake depth, morphology, retention time and watershed rock lithology did not exhibit sizable impact on major and trace element concentrations in the water column. However, acidic (pH = 4.7 ± 0.2) lakes were distinctly different from circumneutral lakes (pH = 6.8 ± 0.5) as they exhibited >10 times higher concentrations of SO42− and trace metals (Fe, Mn, Zn, Cd, Pb, Co, Ni, Be, Al, Ga and REEs). While some of these elements clearly mark the presence of sulphide-rich minerals within the watershed (Fe, Zn, Cd and Pb), the increased mobility of lithogenic elements (Be, Al, Ga and REEs) in acidic lakes may reflect the leaching of these elements from silicate dust derived from atmospheric deposits or surrounding granites. At the same time, compared to circumneutral lakes, acidic lake water displayed lower concentrations of dissolved oxyanions (As, Mo, V, B and W) and elevated SO42− concentrations. The latter could lead to efficient Ba removal from the water column. The exploitation of metal ores within the watershed of three lakes clearly impacted high Zn and Cd concentrations observed in their water column, despite two of these lakes not being acidic. We conclude that local impacts have a greater effect on the water column than long-range atmospheric inputs and that dissolved trace element concentration measurements can be used for revealing sulphide-rich minerals or acid mine drainage within the lakes’ watershed.

Metagenomic insight into the acidophilic functional communities driving elemental geochemical cycles in an acid mine drainage lake

Acidophiles play a key role in the generation, evolution and attenuation of acid mine drainage (AMD), which is characterized by strong acidity (pH<3.5) and high metal concentrations. In this study, the seasonal changes of acidophilic communities and their roles in elemental cycling in an AMD lake (pH∼3.0) in China were analyzed through metagenomics. The results showed eukaryotic algae thrived in the lake, and Coccomyxa was dominant in January (38.1%) and May (33.9%), while Chlorella in July (9.5%). The extensive growth of Chlamydomonas in December (22.7%) resulted in an ultrahigh chlorophyll a concentration (587 μg/L), providing abundant organic carbon for the ecosystem. In addition, the iron-oxidizing and nitrogen-fixing bacterium Ferrovum contributed to carbon fixation. Ammonia oxidation likely occurred in the acidic lake, as was revealed by archaea Ca. Nitrosotalea. To gain a competitive advantage in the nutrient-poor environment, some acidophiles exhibited facultative characteristics, e.g. the most abundant bacterium Acidiphilium utilized both organic and inorganic carbon, and obtained energy from organic matter, inorganic sulfur, and sunlight simultaneously. It was suggested that sunlight, rather than chemical energy of reduced iron-sulfur was the major driver of elemental cycling in the AMD lake. The results are beneficial to the development of bioremediation strategies for AMD.

Acidification of freshwater lakes in Scandinavia: impacts and recovery of chironomid communities under accelerating environmental changes

We re-examined the effects of acidification on Scandinavian freshwater lakes using paleolimnological reconstructions focused on subfossil chironomids. Our study showed a widespread shift in chironomid community composition occurring at around 1960 and corresponding with the maximum fallout of anthropogenic SO42− deposition. Results also showed that taxonomic turn-over was higher in chironomid records from nitrogen-limited lakes, likely due to the cumulative effects of acidification and eutrophication driven by atmospheric nitrogen deposition. Despite strong evidence of chemical recovery from acidification, all lake records failed to show a return to pre-acidified community compositions and most chironomid communities instead continue to follow the trajectories triggered by acidification. We hypothesized that when SO42− deposition started to decrease after 1980, a period also marked by rapid environmental and climatic changes, the influence of pH and/or other acidification-related variables in structuring chironomid community became less important, thus, giving more relative importance to other drivers, such as brownification and climatic processes. Results, therefore, suggest the key role of acidification in shaping the response of chironomid communities to future environmental changes. Future paleolimnological studies will contribute to better manage aquatic ecosystems recovering from acidification worldwide by allowing managers to quantify the efficacy of different management actions taken to mitigate acidification as well as to redefine appropriate restoration targets.

Freshwater diatom evidence for Southern Westerly Wind evolution since ∼18 ka in northwestern Patagonia

We report a fossil diatom record from small closed-basin Lago Lepué (43°S) to examine past changes in freshwater ecosystems and hydrologic balance in northwestern Patagonia since ∼18 ka. The record starts with abundant staurosiroids and the heavily silicified Aulacoseira granulata suggesting deep turbulent mixing during a low lake level stand between ∼18- 16.4 ka. A. distans increased shortly after ∼16.4 ka and achieved maximum abundance between ∼15.4-13.6 ka, while A. granulata disappeared at ∼15.8 ka and A. alpigena rose at ∼14.9 ka to its maximum between ∼13-12 ka. We infer turbulent, cold, and circumneutral to slightly acid lake conditions contemporaneous with a steady lake level rise that started at ∼16.4 ka and culminated between ∼13-12 ka. These trends reversed between ∼11-7.8 ka with the dominance of Discostella stelligera and staurosiroids, suggesting warmer lake conditions and shallower mixing. Subsequent changes include increases of A. distans with D. stelligera between ∼7.8-5.8 ka, dominance of the former between ∼5.8-3.3 ka, a rapid increase in A. perglabra at ∼3.3 ka, and ensuing diversification of benthic acidophilous species. We infer a rapid lake-level decline between ∼11-7.8 ka, with subsequent rising pulses at ∼7.8 ka and ∼5.8 ka, a multimillennial-scale lake acidification trend, and overall high lake levels with centennial-scale reversals between ∼6-0 ka. Coherent variations in terrestrial and aquatic ecosystem changes recorded in the same core suggest negative hydrologic balance between ∼18-16.4 ka and ∼11–7.8 ka, positive balance between ∼14.9-12 ka and ∼6–0 ka, with transitional conditions in the interim, overprinted by millennial-scale changes and enhanced variability since ∼6 ka. Covariation with paleoclimate records at regional, pan-Patagonian, and hemispheric scale suggests millennial to centennial-scale variability superimposed upon a multi-millennial pacing of Southern Westerly Wind evolution since ∼18 ka.

High-resolution structural imaging of volcanoes using improved muon tracking

SUMMARY Muography is increasingly used to image the density distribution of volcanic edifices, complementing traditional geophysical tomographies. Here, we present a new muon data processing algorithm, and apply it to a new generation of scintillator-based muon detectors, to image the relative density distribution in La Soufrière de Guadeloupe volcano (Lesser Antilles, France). Our processing method iteratively searches for the best fit of each muon trajectory, accounting for all the hits registered by the detector related to the particular muon event. We test the performance of our algorithm numerically, simulating the interaction of muons with our detector and accounting for its exact assemblage including the scintillator bars and lead shielding. We find that our new data processing mitigates the impact of spurious signals coming from secondary particles, and improves the amount of successfully reconstructed events. The resulting 2-D muon images at La Soufrière have higher angular resolution than previous ones and capture the heterogeneous structure of the dome. They show density anomalies located on the summit southern region, which includes a boiling acid lake and degassing fractures, where the rock is the most porous and fumarolic activity is ongoing. This work shows the importance of combining numerical simulations of muon propagation with precise raw data processing to obtain high-quality results. It is also a first step towards fully assessing the noise contamination sources when performing muon tomography, and their correction, prior to geophysical interpretations.

Relationship of Modern Diatoms with Lake Acidification and Water Quality in Nsonji Lake of Nagaland, North-East India

Understanding the relationship of diatoms and water quality is of paramount importance to link it to Holocene Climate Change. Since diatoms are extremely sensitive to environmental changes, they are the obvious choice to study diatom inferred water quality and climate changes. Therefore, sediment samples along with water samples were collected during pre monsoon seasons from the Nsonji Lake of the Nagaland, India to establish the relationship between the diatom and water quality. The Nsonji Lake has circum-neutral pH (around 7) indicating gradual degradation of organic matter leading to acidification of the lake. The surface sediments of the Nsonji Lake revealed the dominance of Discostella stelligera, Achnanthidium sp., Navicula cryptocephala, Navicula radiosa and Nitzschia palea. These diatom species could be used to unravel the acidification history of lake caused by natural and anthropogenic activities. Understanding the past climate dynamics need modern analogue in order to evaluate the important processes relative to Earth's history and built future scenario. Keywords: Diatoms, Water Quality, Acidification, pH, Organic Matter, Nsonji Lake, Nagaland

Relationship of Modern Diatoms with Lake Acidification and Water Quality in Nsonji Lake of Nagaland, North-East India

Understanding the relationship of diatoms and water quality is of paramount importance to link it to Holocene Climate Change. Since diatoms are extremely sensitive to environmental changes, they are the obvious choice to study diatom inferred water quality and climate changes. Therefore, sediment samples along with water samples were collected during pre monsoon seasons from the Nsonji Lake of the Nagaland, India to establish the relationship between the diatom and water quality. The Nsonji Lake has circum-neutral pH (around 7) indicating gradual degradation of organic matter leading to acidification of the lake. The surface sediments of the Nsonji Lake revealed the dominance of Discostella stelligera, Achnanthidium sp., Navicula cryptocephala, Navicula radiosa and Nitzschia palea. These diatom species could be used to unravel the acidification history of lake caused by natural and anthropogenic activities. Understanding the past climate dynamics need modern analogue in order to evaluate the important processes relative to Earth's history and built future scenario. Keywords: Diatoms, Water Quality, Acidification, pH, Organic Matter, Nsonji Lake, Nagaland

Comammox Nitrospira and Ammonia-Oxidizing Archaea Are Dominant Ammonia Oxidizers in Sediments of an Acid Mine Lake Containing High Ammonium Concentrations.

Exploring nitrifiers in extreme environments is vital to expanding our understanding of nitrogen cycle and microbial diversity. This study presents that complete ammonia oxidation (comammox) Nitrospira, together with acidophilic ammonia-oxidizing archaea (AOA), dominate in the nitrifying guild in sediments of an acid mine lake (AML). The lake water was characterized by acidic pH below 5 with a high ammonium concentration of 175 mg-N/liter, which is rare on the earth. Nitrification was active in sediments with a maximum nitrate production potential of 70.5 μg-N/(g-dry weight [dw] day) for mixed sediments. Quantitative PCR assays determined that in AML sediments, comammox Nitrospira and AOA amoA genes had relative abundances of 52% and 41%, respectively, among the total amoA genes. Further assays with 16S rRNA and amoA gene amplicon sequencing and metagenomics confirmed their dominance and revealed that the comammox Nitrospira found in sediments belonged to comammox Nitrospira clade A.2. Metagenomic binning retrieved a metagenome-assembled genome (MAG) of the comammox Nitrospira from sediments (completeness = 96.76%), and phylogenomic analysis suggested that it was a novel comammox Nitrospira. Comparative genomic investigation revealed that this comammox Nitrospira contained diverse metal resistance genes and an acidophile-affiliated F-type ATPase. Moreover, it had a more diverse genomic characteristic on nitrogen metabolism than the AOA in sediments and canonical AOB did. The results suggest that comammox Nitrospira is a versatile nitrifier that can adapt to acidic environments even with high ammonium concentrations. IMPORTANCE Ammonia-oxidizing archaea (AOA) was previously considered the sole dominant ammonia oxidizer in acidic environments. This study, however, found that complete ammonia oxidation (comammox) Nitrospira was also a dominant ammonia oxidizer in the sediments of an acidic mine lake, which had an acidic pH < 5 and a high ammonium concentration of 175 mg-N/liter. In combination with average nucleotide identity analysis, phylogenomic analysis suggested it is a novel strain of comammox Nitrospira. Moreover, the adaption of comammox Nitrospira to the acidic lake had been comprehensively investigated based on genome-centric metagenomic approaches. The outcomes of this study significantly expand our understanding of the diversity and adaptability of ammonia oxidizers in the acidic environments.

Brachysira heteropolaris, a new diatom (Brachysiraceae, Bacillariophyta) species observed in an historic Weissflog slide from Scotland (UK)

During the analysis of an historic slide of Loch Canmor, Aberdeenshire (Scotland, UK) prepared by Eugene Weissflog and conserved in the Van Heurck collection (BR, Belgium), an unknown, heteropolar Brachysira taxon was observed that could not be identified using the currently available literature. The new species, described as Brachysira heteropolaris sp. nov., is characterised in having a strictly heteropolar, broadly lanceolate valve outline with non-protracted, acutely rounded apices. The new species was observed in a dystrophic-oligotrophic, weakly acidic lake, based on the analysis of the composing diatom flora, dominated by several Brachysira species, Gomphonema coronatum and Encyonopsis cesatii var. geitleri.

γ-Al2O3 supported silver nanoparticle applied in C3H8-SCR: Nanosphere and nanoflake

The γ-Al2O3 support (nanosphere and nanoflake) was used to support Ag nanoparticles and applied in C3H8-SCR to remove NOx. Ag/Al2O3-flake exhibited superior catalytic activity than Ag/Al2O3-sphere in C3H8-SCR. It is found that Al2O3-flake rich in Al octacoordinated ions promoted more Agnδ+ species to disperse on Ag/Al2O3-flake than Ag/Al2O3-sphere. Agnδ+ species could strengthen the low-temperature catalytic activity for HC-SCR while Ag metal particles were unbeneficial since they could promote complete oxidation of hydrocarbon. This was the first time to explore the remarkable effect of Al2O3 intrinsic properties on catalytic activity of alumina-supported catalyst for HC-SCR from the perspective of uniform morphology. Environmental implicationThe number of transport vehicles has increased dramatically during the past decades due to global economic growth. The accompanying concern is the huge consumption of fossil fuels, for example, gasoline and diesel, which speeds up global warming. Internal combustion engines produce toxic emissions, where NOx forms nitric acid in the atmosphere, reacts with HCs to form which causes acidification of land and lakes. Currently, it is urgent to develop a leading deNOx technique for the after-treatment of commercial engine-powered vehicles to meet stringent emission legislations.

Using a multi-proxy paleolimnological approach to track the effects of multiple stressors on a naturally acidic lake from Killarney Provincial Park (Ontario, Canada)

Ruth-Roy Lake (Killarney Provincial Park, Ontario, Canada) is an ultra-oligotrophic, naturally acidic waterbody. Lakes in Killarney Provincial Park were impacted by long-range transportation of contaminants from copper-nickel smelting operations in nearby Sudbury, but recent lake monitoring indicates that Ruth-Roy Lake has been less acidic than inferred pre-industrial pH conditions. We assessed the effects of pH change, reduced sulphur emissions, and drivers of reduced acidity using biological and geochemical paleolimnological techniques. Ruth-Roy Lake experienced notable biological and chemical change over the past ~150 years. All examined proxies supported that Ruth-Roy Lake was naturally acidic but further acidified as early as ca. 1920s, with the strongest acidification signal apparent in ca. 1940s. Biological recovery in diatom and cladoceran assemblages, however, is modest. We highlight the importance of understanding reference conditions to assess ecosystem recovery and climate-mediated change in clear acidic lakes located in industrial landscapes.

A century of diatom monitoring in acidified and warmed Dutch moorland pools

Diatoms are well-known indicators for acidification and recovery of lakes, as mainly with paleolimnological methods. However, from the last few decades, such studies are scarce, especially in Europe, and there is a poor insight into the interaction between the impact of the recovery from acidification and drought periods on diatoms. The surface water chemistry of Dutch moorland pools has shown strong signs of chemical recovery as a response to declines in sulphur and nitrogen deposition between 1978 and 2018. We expected that changes in water chemistry were associated with changes in diatom assemblages and that the diatom assemblages at the end of the monitoring period would be dissimilar to pre-acidification diatom assemblages due to the changed biogeochemical processes in the pools. To monitor the recovery from acidification, diatoms from plants and surficial sediments were sampled in 11 Dutch moorland pools from 1978 to 2018. As far as we know, this is the longest series of semi-annual diatom records in stagnant shallow waters recovering from acidification. Early 20th-century samples were retrieved from collections. Changes in the diatom assemblages were assessed by analyses of traits (including pH-preference) and ecological groups. Direct correspondence analysis revealed high correlations between the species composition and environmental variables (pH, sulphate, ammonium, dissolved organic carbon, calcium, and aluminium). Between 1916 and 1978, the greatest species composition changes occurred in pools with relatively flat banks exposed to the air in extremely dry summers. After the dry summer of 1921, the changes were insignificant, but after the extremely dry summer of 1976, the changes were dramatic due to acidification by oxidation of the reduced sulphur and nitrogen compounds stored in the moorland pool bottom. After 1980, the changes were consistent with chemical recovery from acidification. However, there was a significant interaction with climatic factors: drought episodes in the short term and temperature increase in the long term. Some species in the samples from the last decades indicate an acid, but eutrophic environment, due to internal eutrophication. The species composition did not return to the historical composition (1920 s), as the chemical dynamics due to the large stock of sulphur and nitrogen compounds are now entirely different from those a century ago.

Drone monitoring of volcanic lakes in Costa Rica: a new approach

For the first time ever, samples were collected from volcanic lake waters in Costa Rica using an unmanned aerial vehicle (drone), which represents a major achievement in human–machine interaction and innovation in the technology sector. A Matrice 600 Pro drone was used for remote sampling in the hyperacid crater lake of the Poás volcano, the mildly acidic Lake Botos, and the nearly neutral Lake Hule. A bailer bottle of 250 mL and a HOBO temperature probe, mounted on the drone, were deployed using a specially designed delivery retrieval system. A comparison was carried out relating to the geochemistry of lake water collected by drone as opposed to the hand-collected samples. The SO4−2/Cl ratios of the two samples at Poás hyperacid crater lake were similar, (1.1 ± 0.2) on average, an indication of a lake with homogenous water composition. The Lake Hule showed a similar composition to that registered 20 years ago. The waters from Lake Botos showed some differences, which may be explained by the influence of springs at the bottom of the lake, but the Wilcoxon's signed-rank test showed a good exhibit of a satisfactory level of similarity. Autonomous navigation proves to be very useful for faster, more efficient, reliable, and less hazardous sampling of volcanic lakes.

Non-charismatic waterbodies and ecosystem disservices: Mine pit lakes are underrepresented in the literature.

Pit lakes are one of the greatest legacies of open-cut mining. Despite the potential hazards of these lakes, they represent newly formed ecosystems with great scientific and ecological potential. Although thousands of pit lakes occur on every inhabited continent, with more being created, the microbial ecology of pit lakes is relatively under-researched. We evaluated the current state of microbial research in pit lakes by performing a Web of Science search and creating a literature database. Study lakes were categorized according to location and water quality (pH and conductivity) which is a key community and environmental concern. Research technology employed in the study was also categorized. We compared research effort in lakes, rivers, and streams which are the more "charismatic" inland aquatic ecosystems. Pit lake publications on microbes from 1987 to 2022 (n = 128) were underrepresented in the literature relative to rivers and streams (n = 321) and natural lakes (n = 948). Of the 128 pit lake publications, 28 were within the field of geochemistry using indirect measures of microbial activity. Most pit lake microbial research was conducted in a few acidic lakes in Germany due to social pressure for remediation and government initiative. Relatively few studies have capitalized on emerging technology. Pit lake microbial research likely lags other more charismatic ecosystems given that they are viewed as performing "ecosystem disservices," but this is socially complex and requires further research. Improving understanding of microbial dynamics in pit lakes will allow scientists to deliver safer pit lakes to communities.