Tropical Andean climate variations since the last deglaciation.

Global warming during the Last Glacial Termination was interrupted by millennial-scale cool intervals such as the Younger Dryas and the Antarctic Cold Reversal (ACR). Although these events are well characterized at high latitudes, their impacts at low latitudes are less well known. We present high-resolution temperature and hydroclimate records from the tropical Andes spanning the past ~16,800 y using organic geochemical proxies applied to a sediment core from Laguna Llaviucu, Ecuador. Our hydroclimate record aligns with records from the western Amazon and eastern and central Andes and indicates a dominant long-term influence of changing austral summer insolation on the intensity of the South American Summer Monsoon. Our temperature record indicates a ~4 °C warming during the glacial termination, stable temperatures in the early to mid-Holocene, and slight, gradual warming since ~6,000 y ago. Importantly, we observe a ~1.5 °C cold reversal coincident with the ACR. These data document a temperature change pattern during the deglaciation in the tropical Andes that resembles temperatures at high southern latitudes, which are thought to be controlled by radiative forcing from atmospheric greenhouse gases and changes in ocean heat transport by the Atlantic meridional overturning circulation.

Variations in bacterial community succession and assembly mechanisms with mine age across various habitats in coal mining subsidence water areas.

Microorganisms play a pivotal role as catalysts in the biogeochemical cycles of aquatic ecosystems within coal mining subsidence areas. Despite their importance, the succession of microbial communities with increasing mine age, particularly across different habitats, and variations in phylogenetically-based community assembly mechanisms are not well understood. To address this knowledge gap, we collected 72 samples from lake sediments, water, and surrounding topsoil (0-20 cm) at various mining stages (early: 16 years, middle: 31 years, late: 40 years). We analyzed these samples using 16S rRNA gene sequencing and multivariate statistical methods to explore the dynamics and assembly mechanisms of bacterial communities. Our findings reveal that increases in phosphorus and organic matter in sediments, correlating with mining age, significantly enhance bacterial alpha diversity while reducing species richness (P < 0.001). Homogenizing selection (49.9 %) promotes species asynchrony-complementarity, augmenting the bacterial community's ability to metabolize sulfur, phosphorus, and organic matter, resulting in more complex-stable co-occurrence networks. In soil, elevated nitrogen and organic carbon levels markedly influence bacterial community composition (Adonis R2 = 0.761), yet do not significantly alter richness or diversity (P > 0.05). The lake's high connectivity with surrounding soil leads to substantial species drift and organic matter accumulation, thereby increasing bacterial richness in later stages (P < 0.05) and enhancing the ability to metabolize dissolved organic matter, including humic-like substances, fulvic acids, and protein-like materials. The assembly of soil bacterial communities is largely governed by stochastic processes (79.0 %) with species drift (35.8 %) significantly shaping these communities over a broad spatial scale, also affecting water bacterial communities. However, water bacterial community assembly is primarily driven by stochastic processes (51.2 %), with a substantial influence from habitat quality (47.6 %). This study offers comprehensive insights into the evolution of microbial community diversity within coal mining subsidence water areas, with significant implications for enhancing environmental management and protection strategies for these ecosystems.

Penguin-Driven Dissemination and High Enrichment of Antibiotic Resistance Genes in Lake Sediments across Antarctica.

Numerous penguins can propagate pathogens with antibiotic resistance genes (ARGs) into Antarctica. However, the effects of penguin dissemination on the lake ARGs still have received little attention via guano deposition. Here, we have profiled ARGs in ornithogenic sediments subject to penguin guano (OLS) and nonornithogenic sediments (NOLS) from 16 lakes across Antarctica. A total of 191 ARGs were detected in all sediment samples, with a much higher abundance and diversity in OLS than in NOLS. Surprisingly, highly diverse and abundant ARGs were found in the OLS with a detection frequency of >40% and an absolute abundance of (2.34 × 109)-(4.98 × 109) copies g-1, comparable to those in coastal estuarine sediments and pig farms. The strong correlations of identified resistance genes with penguin guano input amount, environmental factors, mobile genetic elements, and bacterial community, in conjunction with network and redundancy analyses, all indicated that penguins were responsible for the dissemination and high enrichment of ARGs in lake sediments via the guano deposition, which might greatly outweigh local human-activity effects. Our results revealed that ARGs could be carried into lakes across the Antarctica through penguin migration, food chains, and guano deposition, which were closely connected with the widespread pollution of ARGs at the global scale.

Dewatering and valorizing lake sediments by electroosmotic dewatering for lakes restoration.

Dredging eutrophic lake sediments can improve water quality, but it also requires dewatering and valorizing the dredged material to avoid wasting resources like phosphorus. This study experimentally investigated the basic mechanism and performance of electroosmotic dewatering of 1-L dredged sediments using different electric currents (20 mA, 40 mA, and 60 mA) after gravity filtration. The dewatering performance, moisture content and distribution, effect of electrochemical reaction on dewaterability, energy consumption, and changes in metals and phosphorus (P) distribution and pH values were analyzed. The results indicated that electroosmotic dewatering effectively decreased sediment mass by predominantly eliminating free and a portion of interstitial water, with reductions ranging from 7 to 20%. The optimal duration and current should, however, be considered to balance water removal and energy consumption. Higher moisture removal occurred with 40 mA for 24 h and 60 mA for 6 h, while the energy consumption obtained with 60 mA (0.201 kWh/kg water removed) was significantly lower than that of applying 40 mA for 24 h (0.473 kWh/kg water removed), with the assistance of ohmic heating, resulting in reduced viscosity and water release from capillaries. The tested conditions did not significantly extract heavy metals or P from the sediments, which may facilitate the disposal of the removed water back into the lake and the utilization of the treated sediments for different purposes. This technology is easy to operate and suitable for the treatment of dredged sediments, and the dewatering result is comparable to low pressurized filtration but at low energy consumption.

Relationship between human activities and environmental changes in the southern Tibetan Plateau since the Little Ice Age.

The Tibetan Plateau (TP) is one of the most challenging areas for human long-term settlement due to its extreme living environment. Understanding the relationship between human activities and environmental changes in this extreme environment is important and can provide a historical reference for adapting to future climate change. In this study, we took the Angren Basin in the southern TP as a case study to elucidate the relationship since Little Ice Age (LIA). Using fecal stanol in feces, lake and river surface sediments, surface soils, and sediment core, we found that specific indices S1 and S2 from the composition of coprostanol, epicoprostanol, 5ß-ethylcoprostanol and 5ß-ethylepicoprostanol can reflect changes in human population and herbivores, respectively. Through the comparison between environmental changes determined by grain size, elements, sedimentation rate, and other climate records, the relationship between human activities and environmental changes was interpreted. Our results indicate that: (i) during 1480-1820 CE, the fecal stanols in lake sediments mainly originated from livestock, and the human population was low. In contrast, during 1820-2021 CE, the proportion and flux of S1 have been continuously increasing, indicating significant population growth. (ii) During the middle LIA, the cold-dry climate inhibited the development of agriculture and farming. However, the increased precipitation during the late LIA promoted that development, resulting in an increase in human population and livestock in a short term. (iii) Since 1951, people have reclaimed wasteland and developed husbandry, leading to increased soil erosion. (iv) Over the past 40 years, with a warm-humid climate and good policy support, human activities, such as agriculture and husbandry, have rapidly increased, but soil erosion has declined in the recent 20 years due to good soil-water conservation efforts. This study sheds light on the relationship between human activities and environmental changes and provides insights into future climate change responses.

Driver-response relationships in a large shallow lake since the Anthropocene: Short-term abrupt perturbations versus long-term sustainable.

Lakes, as integral social-ecological systems, are hotspots for exploring climatic and anthropogenic impacts, with crucial pathways revealed by continuous sediment records. However, the response of multi-proxies in large shallow lakes to typical abrupt events and sustained drivers since the Anthropocene remains unclear. Here, we explored the driver-identification relationships between multi-proxy peaks and natural and anthropogenic events as well as the attribution of short-term perturbations and long-term pressures. To this end, sediment core records, socio-ecological data, and documented events from official records were integrated into a large shallow lake (Dongting Lake, China). Significant causal cascades and path effects (goodness-of-fit: 0.488; total effect: -1.10; p < .001) were observed among catchment environmental proxies, lake biogenic proxies, and mixed-source proxies. The peak-event identification rate (PEIR) and event-peak driving rate were proposed, and values of 28.57%-46.43% and 50%-81.25% were obtained, respectively. The incomplete accuracy of depicting event perturbations using sediment proxies was caused by various information filters both inside and outside the lake. PEIRs for compound events were 1.41 (±0.72) and 1.09 (±0.46) times greater than those for anthropogenic-dominated and natural-dominated events, respectively. Furthermore, socio-economic activity, hydrologic dynamics, land-use changes, and agriculture exerted significant and persistent pressures, cumulatively contributing 55.3%-80.9% to alterations in sediment proxies. Relatively synergistic or antagonistic trends in temporal contributions of these forces were observed after 2000, which were primarily attributed to the "Grain for Green" project and the Three Gorges Dam. This study represents one of the few investigations to distinguish the driver-response relationship of multiple proxies in large shallow lakes under typical event perturbations and long-term sustained pressures since the Anthropocene. The findings will help policymakers and managers address ecological perturbations triggered by climate change and human activities over long-term periods.

[Distribution Characteristics, Ecological Risk Assessment, and Source Tracing of Heavy Metals in the Sediments of Typical Lakes in the Middle Reaches of the Yangtze River].

In this study, surface sediment samples were collected from Dongting Lake, Honghu Lake, and Chihu Lake, and the concentrations of 10 heavy metals were measured. Then, the potential risk of heavy metal accumulation was evaluated using the cumulative pollution index (Igeo), the enrichment factor (EF), and the potential ecological risk index (RI), and the sources were traced using correlation analysis (Pearson) and principal component analysis (PCA). The results showed that the pollution and potential ecological risk of Cd were the most serious. The mean values of Cd in East Dongting Lake, Honghu Lake, and Chihu Lake were 2.85, 1.59, and 3.57 mg·kg-1, respectively. The concentrations of Cd were 25.87, 11.36, and 37.58 times higher than the soil background values of the corresponding provinces, which exceeded the risk screening value (0.6 mg·kg-1). Particularly, the Cd concentration of Chihu Lake exceeded the risk control value (3.0 mg·kg-1). Besides Cd, the concentration of As in Honghu Lake was also of concern. At the same time, the Cu, As, Zn, and Pb in Chihu Lake should not be neglected. The potential ecological risks of the three lakes were ranked as follows:Chihu Lake (RI=1 127)>East Dongting Lake (RI=831)>Honghu Lake (RI=421). The primary sources of heavy metals were industrial mining, agricultural production, and aquaculture, and some heavy metals (Mn and Cu) were from natural sources. This study was of great significance for the prevention and control of heavy metals in the sediments of typical lakes in the middle reaches of the Yangtze River.

Responses of sediment n-alkanes to climate factors and anthropogenic disturbances from three lakes with different elevations, arid Central Asia.

Biomarkers n-alkanes and pertinent indices in lake sediments are frequently used to infer past changes in climate and environmental conditions in and around lakes. Interpretation of n-alkane records can be confounded by a lack of understanding of the multiple factors that control n-alkanes in sediments. Here, we studied n-alkanes in sediment cores from two alpine lakes, Lakes Son-Kul and Issyk-Kul, and from terminal Lake Balkhash, in arid Central Asia to identify natural and human-mediated influences on sediment n-alkane profiles. Altitudinal differences in climate, as well as in lake trophic status, proved to be important drivers of n-alkane compositional differences in the lake sediments. In the alpine lakes, the distribution of n-alkanes was biased toward long-chain components (n-C29, n-C31, and n-C33), and showed higher carbon preference index (CPIH) values, which come from dense terrestrial plant communities, promoted by greater precipitation. In contrast, n-alkanes in the core from the terminal lake displayed higher proportions of short-chain n-alkanes (n-C17, n-C19, and n-C21) because a greater proportion of the organic matter (OM) input to the sediments was derived from algae, a consequence of higher temperatures and trophic status. In recent decades, increasing nutrient inputs from human activities have caused greater accumulation of short-chain n-alkanes in sediments of alpine, oligotrophic Lake Issyk-Kul. In Lake Balkhash, n-C20 and n-C22 alkanes are exceptionally abundant, suggesting large contributions from microbial reworking of terrestrial OM. In all three study lakes, ∑(n-C29-n-C33) was elevated in sediments that correspond to periods of intense agricultural exploitation. Moreover, expansion of agriculture from low to high altitudes resulted in both synchronous and asynchronous peaks in ∑ (n-C29-n-C33) in the studied cores, suggesting the n-alkanes faithfully record the history of agricultural expansion. These findings provide insights into applications of n-alkane proxies and the response of the lake system to climate and anthropogenic impacts.

Anthropogenic contamination sources drive differences in antimicrobial-resistant Escherichia coli in three urban lakes.

Antimicrobial resistance (AMR) is an ever-present threat to the treatment of infectious diseases. However, the potential relevance of this phenomenon in environmental reservoirs still raises many questions. Detection of antimicrobial-resistant bacteria in the environment is a critical aspect for understanding the prevalence of resistance outside of clinical settings, as detection in the environment indicates that resistance is likely already widespread. We isolated antimicrobial-resistant Escherichia coli from three urban waterbodies over a 15-month time series, determined their antimicrobial susceptibilities, investigated their population structure, and identified genetic determinants of resistance. We found that E. coli populations at each site were composed of different dominant phylotypes and showed distinct patterns of antimicrobial and multidrug resistance, despite close geographic proximity. Many strains that were genome-sequenced belonged to sequence types of international concern, particularly the ST131 clonal complex. We found widespread resistance to clinically important antimicrobials such as amoxicillin, cefotaxime, and ciprofloxacin, but found that all strains were susceptible to amikacin and the last-line antimicrobials meropenem and fosfomycin. Resistance was most often due to acquirable antimicrobial resistance genes, while chromosomal mutations in gyrA, parC, and parE conferred resistance to quinolones. Whole-genome analysis of a subset of strains further revealed the diversity of the population of E. coli present, with a wide array of AMR and virulence genes identified, many of which were present on the chromosome, including blaCTX-M. Finally, we determined that environmental persistence, transmission between sites, most likely mediated by wild birds, and transfer of mobile genetic elements likely contributed significantly to the patterns observed.IMPORTANCEA One Health perspective is crucial to understand the extent of antimicrobial resistance (AMR) globally, and investigation of AMR in the environment has been increasing in recent years. However, most studies have focused on waterways that are directly polluted by sewage, industrial manufacturing, or agricultural activities. Therefore, there remains a lack of knowledge about more natural, less overtly impacted environments. Through phenotypic and genotypic investigation of AMR in Escherichia coli, this study adds to our understanding of the extent and patterns of resistance in these types of environments, including over a time series, and showed that complex biotic and abiotic factors contribute to the patterns observed. Our study further emphasizes the importance of incorporating the surveillance of microbes in freshwater environments in order to better comprehend potential risks for both human and animal health and how the environment may serve as a sentinel for potential future clinical infections.

Network Complexity and Stability of Microbes Enhanced by Microplastic Diversity.

Microplastic mixtures are ubiquitously distributed in global ecosystems and include varying types. However, it remains unknown how microplastic diversity affects the biotic interactions of microbes. Here, we developed novel experiments of 600 microcosms with microplastic diversity ranging from 1 to 6 types and examined ecological networks for microbial communities in lake sediments after 2 months of incubation at 15 and 20 °C. We found that microplastic diversity generally enhanced the complexity of microbial networks at both temperatures, such as increasing network connectance and reducing average path length. This phenomenon was further confirmed by strengthened species interactions toward high microplastic diversity except for the negative interactions at 15 °C. Interestingly, increasing temperatures further exaggerated the effects of microplastic diversity on network structures, resulting in higher network connectivity and species interactions. Consistently, using species extinction simulations, we found that higher microplastic diversity and temperature led to more robust networks, and their effects were additionally and positively mediated by the presence of biodegradable microplastics. Our findings provide the first evidence that increasing microplastic diversity could unexpectedly promote the complexity and stability of microbial networks and that future warming could amplify this effect.

The records of 239+240Pu and 137Cs of global fallout in Lake East Dongting Sediments and Responses to watershed environmental changes.

Plutonium-239 + 240 and 137Cs in the environment can usually be used to track the impact of nuclear activities on the environment, and have become important tools in environmental geochemical studies. In this study, nine sediment cores (E1-E9) in Lake East Dongting were collected and measured for the activity concentration of 239+240Pu, 137Cs and the atomic ratio of 240Pu/239Pu, and then their vertical distribution characteristics were analyzed. The results show that: the activity concentrations of 137Cs and 239+240Pu in Lake East Dongting ranged from 5.26 ± 0.43 to 28.6 ± 2.23 Bq kg-1 and 0.29 ± 0.02 to 1.37 ± 0.09 Bq kg-1, with an average of 7.48 ± 0.68 Bq kg-1 and 0.39 ± 0.03 Bq kg-1, respectively. The atomic ratios of 240Pu/239Pu are 0.168 ± 0.012-0.211 ± 0.015, which are basically consistent with the global atmospheric deposition. The vertical profiles of 137Cs and 239+240Pu in sediment cores show obvious single-peak distribution in E1-E6 and bimodal distribution in E7-E9. The results of sedimentation rates calculated by 137Cs and 239+240Pu method ranged from 0.59 cm y-1 to 1.99 cm y-1 with a mean of 1.18 cm y-1 and 0.61 cm y-1 to 2.18 cm y-1 with a mean of 1.26 cm y-1. The inventories of 137Cs and 239+240Pu in nine sediment cores are 5.87-10.8 kBq m-2 and 307-545 Bq m-2, which are about 8-14 and 9-15 times the inventory in the global average atmospheric deposition at the same latitude respectively. Comparing the results of the sedimentation rates and the inventories from different sampling points indicates that extreme climatic events and human activities have a significant impact on sediment environment of Lake East Dongting.

Vanadium in modern sediments of urban lakes in the North of Russia: natural and anthropogenic sources.

Studies have found that vanadium tends to accumulate in the sediments of lakes located in urban areas where fuel oil thermal power plants or boiler houses are present. The highest concentration of vanadium, amounting to 4785 mg/kg, was found in a lake situated less than a kilometer away from a thermal power plant. In contrast, pristine lakes typically have vanadium levels that are consistent with or below the background levels. In certain regions of Karelia, the elevated concentration of vanadium in lake sediments can be attributed to the presence of uranium­vanadium ores. In urban sediments, vanadium is closely associated with nickel, which can also be released into the environment through the emissions of thermal power plants and boiler houses. It has been observed that vanadium in lakes primarily exists in the solid insoluble fraction, possibly bonded with natural minerals.

Revealing the hidden burden for lake management: the sediment phosphorus storage pools in Eastern Plain Lake Zone, China.

As one of the essential components in ecosystems, lakes play a major role in the global phosphorus (P) cycle. It is helpful for further understanding of the inside lake P geochemical cycle to research P pollution and storage in lakes, which is of positive significance for lake eutrophication restoration. In this study, we investigated the total phosphorus concentrations (TPC) of water and sediments from 37 lakes in the Eastern Plain Lake Zone (EPL) of China, evaluated the P pollution degree of lakes, and estimated P storage in lake sediments with quantitative data of lake area and number. The results indicate that the total phosphorus concentrations of water (TPCW) and total phosphorus concentrations of the surface sediments (0-1 cm, TPCSS) in EPL were high, the mean values were 0.11 mg·L-1 and 869.85 mg·kg-1 respectively, with obvious differences between urban and rural areas, as well as between different river basins. Over half (56.76% and 70.27% respectively) of the lakes reached severe pollution levels in water and surface sediments. There were 16224 lakes (> 0.01 km2) with a total area of 21662.37 km2 in the EPL, and the P storage in the lake sediments (0-30 cm) was about 4.87 ± 2.08 Tg (1 Tg = 1 × 1012 g), accounting for about 2.74% of the basin soil. TPCW and TPCSS of lakes in the EPL were significantly positively correlated, may suggest a close nutrient cycling relationship between the lake water and the sediment. During periods of high winds and waves, the stored P in the top sediments in the EPL may continue to participate in the internal P geochemical cycle and migrate to the overlying water, posing a potential pollution hazard. Therefore, it is crucial to take into account the sediment P pools when formulating effective lake phosphorus management strategies.

Aerobic methanotrophy increases the net iron reduction in methanogenic lake sediments.

In methane (CH4) generating sediments, methane oxidation coupled with iron reduction was suggested to be catalyzed by archaea and bacterial methanotrophs of the order Methylococcales. However, the co-existence of these aerobic and anaerobic microbes, the link between the processes, and the oxygen requirement for the bacterial methanotrophs have remained unclear. Here, we show how stimulation of aerobic methane oxidation at an energetically low experimental environment influences net iron reduction, accompanied by distinct microbial community changes and lipid biomarker patterns. We performed incubation experiments (between 30 and 120 days long) with methane generating lake sediments amended with 13C-labeled methane, following the additions of hematite and different oxygen levels in nitrogen headspace, and monitored methane turnover by 13C-DIC measurements. Increasing oxygen exposure (up to 1%) promoted aerobic methanotrophy, considerable net iron reduction, and the increase of microbes, such as Methylomonas, Geobacter, and Desulfuromonas, with the latter two being likely candidates for iron recycling. Amendments of 13C-labeled methanol as a potential substrate for the methanotrophs under hypoxia instead of methane indicate that this substrate primarily fuels methylotrophic methanogenesis, identified by high methane concentrations, strongly positive δ13CDIC values, and archaeal lipid stable isotope data. In contrast, the inhibition of methanogenesis by 2-bromoethanesulfonate (BES) led to increased methanol turnover, as suggested by similar 13C enrichment in DIC and high amounts of newly produced bacterial fatty acids, probably derived from heterotrophic bacteria. Our experiments show a complex link between aerobic methanotrophy and iron reduction, which indicates iron recycling as a survival mechanism for microbes under hypoxia.

The 3D-Printed (FDM/FFF) Biocomposites Based on Polylactide and Carbonate Lake Sediments-Towards a Circular Economy.

In this study, composites containing polylactide and carbonate lake sediment in concentrations of 2.5, 5, 10, and 15% by weight were prepared by a 3D printing method. The material for 3D printing was obtained by directly diluting the masterbatch on an injection moulder to the desired concentrations, and after granulation, it was extruded into a filament. The material prepared thusly was used to print standardised samples for mechanical testing. To compare the mechanical properties of the composites obtained by 3D printing and injection moulding, two sets of tests were performed, i.e., mechanical tests (tensile strength, flexural strength, and impact strength) and hydrophobic-hydrophilic surface character testing. The degree of composite waste in the 3D printing was also calculated. Mechanical and surface tests were performed for both systems conditioned at room temperature and after accelerated ageing in a weathering chamber. The study showed differences in the properties of composites obtained by 3D printing. Sedimentary fillers improved the hydrophobicity of the systems compared with pure PLA, but it was not a linear relationship. The PLA/CLS sedB composite had higher strength parameters, especially after ageing in a weathering chamber. This is due to its composition, in which, in addition to calcite and silica, there are also aluminosilicates, causing a strengthening of the PLA matrix.

Investigating the impact of climate change on the lake ecosystem during the late Holocene using a sedimentary record from the southern Arabian Desert, Yemen.

Lake systems respond physically, chemically, and biologically to hydro-climatic change and variability, and these responses are documented in the sediments. Individual proxies and lacustrine environments may respond to climate variations in a nonlinear way, making it difficult to determine the direction and extent of a climatic shift. Here we investigate the response of lake ecosystem to climatic and environmental changes using a suite of paleo-proxies including ostracods, chironomids, and n-alkanes distribution from paleolake 'Gayal el Bazal (Yemen)'. A previous study from this site has provided a continuous, and high-resolution dataset providing an understanding of precipitation during the last ca 1200 years, particularly during Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). However, the response of the lake ecosystem to these changing hydro-climate conditions, including water-level, salinity, and productivity, remains unknown. The n-alkanes dataset shows that during pluvial interval such as the MCA, the lake experienced an increase in nutrient input resulting in enhanced aquatic productivity. Concurrently, ostracods assemblage displays an increased abundance of swimmer species (like Bradleytriebella lineata and Fabaeomiscandona cf. breuili), suggesting an indirect response between ostracods and climate shifts. The chironomid community during the MCA interval is dominated by taxa belonging to the subfamilies of Chironomini, suggesting a warm, shallow, productive environment with macrophyte vegetation. The LIA interval is marked by increased abundance of higher-chain length n-alkanes, suggesting increased contribution from higher plants. Furthermore, ostracod distribution revealed increased abundance of non-swimmer species like Vestalenula cylindrica., which thrive under saline conditions in the lake. Changes in abundances of Tanytarsini during the LIA interval, which are associated with higher oxygen levels, suggest changes in lake productivity. As a result, the overall patterns in biological indicators reveal that their individual abundance and species/tribe distribution fluctuates in response to changes in the climate and hydrological conditions.

Variability of sedimentary phosphorus composition across Canadian lakes.

Phosphorus (P) in lake sediments is stored within diverse forms, often associated with metals, minerals, and organic matter. Sediment P can be remobilized to the water column, but the environmental conditions influencing the P retention-release balance depend upon the sediment chemistry and forms of P present. Sequential fractionation approaches can be used to help understand forms of P present in the sediments, and their vulnerability to release. We assessed P composition in surficial sediments (as an assemblage of six P-fractions) and its relationship with watershed, and lake-specific explanatory variables from 236 lakes across Canada. Sediment P composition varied widely across the 12 sampled Canadian ecozones. The dominant P-fractions were the residual-P and the labile organic P, while the loosely bound P corresponded to the smallest proportion of sediment TP. Notable contrasts in sediment P composition were apparent across select regions - with the most significant differences between sediment P in lakes from the mid-West Canada region (Prairies and Boreal Plains ecozones) and both Eastern coastal (Atlantic Maritime and Atlantic Highlands) and Western coastal (Pacific Maritime) ecozones. The ecozone attributes most critical to sediment P speciation across Canadian lakes were related to soil types in the watershed (e.g., podzols, chernozems, and Luvisols) and the chemical composition of lake water and sediments, such as dissolved Ca in lake water, bulk sedimentary Ca, Al, and Fe, dissolved SO4 in lake water, lake pH, and salinity. Understanding predictors of the forms of P stored in surficial sediments helps advance our knowledge of in-lake P retention and remobilization processes across the millions of unstudied lakes and can help our understanding of controls on internal P loading.

Assessment of fungal spores and spore-like diversity in environmental samples by targeted lysis.

At particular stages during their life cycles, fungi use multiple strategies to form specialized structures to survive unfavorable environmental conditions. These strategies encompass sporulation, as well as cell-wall melanization, multicellular tissue formation or even dimorphism. The resulting structures are not only used to disperse to other environments, but also to survive long periods of time awaiting favorable growth conditions. As a result, these specialized fungal structures are part of the microbial seed bank, which is known to influence the microbial community composition and contribute to the maintenance of diversity. Despite the importance of the microbial seed bank in the environment, methods to study the diversity of fungal structures with improved resistance only target spores dispersing in the air, omitting the high diversity of these structures in terms of morphology and environmental distribution. In this study, we applied a separation method based on cell lysis to enrich lysis-resistant fungal structures (for instance, spores, sclerotia, melanized yeast) to obtain a proxy of the composition of the fungal seed bank. This approach was first evaluated in-vitro in selected species. The results obtained showed that DNA from fungal spores and from yeast was only obtained after the application of the enrichment method, while mycelium was always lysed. After validation, we compared the diversity of the total and lysis-resistant fractions in the polyextreme environment of the Salar de Huasco, a high-altitude athalassohaline wetland in the Chilean Altiplano. Environmental samples were collected from the salt flat and from microbial mats in small surrounding ponds. Both the lake sediments and microbial mats were dominated by Ascomycota and Basidiomycota, however, the diversity and composition of each environment differed at lower taxonomic ranks. Members of the phylum Chytridiomycota were enriched in the lysis-resistant fraction, while members of the phylum Rozellomycota were never detected in this fraction. Moreover, we show that the community composition of the lysis-resistant fraction reflects the diversity of life cycles and survival strategies developed by fungi in the environment. To the best of our knowledge this is the first time that the fungal diversity is explored in the Salar de Huasco. In addition, the method presented here provides a simple and culture independent approach to assess the diversity of fungal lysis-resistant cells in the environment.

Anthropogenic atmospheric deposition caused the nutrient and toxic metal enrichment of the enclosed lakes in North China.

Anthropogenic emissions have resulted in increases in the atmospheric fluxes of both nutrient and toxic elements. However, the long-term geochemical impacts on lake sediments of deposition activities have not been clearly clarified. We selected two small enclosed lakes in northern China-Gonghai, strongly influenced by anthropogenic activities, and Yueliang lake, relatively weakly influenced by anthropogenic activities-to reconstruct historical trends of atmospheric deposition on the geochemistry of the recent sediments. The results showed an abrupt rise in the nutrient levels in Gonghai and the enrichment of toxic metal elements from 1950 (the Anthropocene) onwards. While, at Yueliang lake, the rise on TN was from 1990 onwards. These consequences are attributable to the aggravation of anthropogenic atmospheric deposition in N, P and toxic metals, from fertilizer consumption, mining and coal combustion. The intensity of anthropogenic deposition is considerable, which leave a significant stratigraphic signal of the Anthropocene in lake sediments.

Effect of past century mining activities on sediment properties and toxicity to freshwater organisms in northern Sweden.

The release of toxic metals from local mining activities often represents a severe environmental hazard for nearby lake ecosystems. Previous studies on the impact of mining have primarily focused on single lakes, with less emphasis on spatial and temporal recovery patterns of multiple lakes within the same catchment, but with different hydrological connection and distance to the pollutant source. This knowledge gap prevents us from assessing the real environmental risk of abandoned mines and understanding ecosystem recovery. This study explores the intensity and spatial patterns of sediment contamination and the potential for ecosystem recovery in three lakes in close vicinity of a lead (Pb) and zinc (Zn) mine in Sweden that has been inoperative for >20 years. Dated (210Pb and 137Cs) sediment cores from each lake were used to reconstruct temporal patterns in trace element deposition and relate those with past mining activities. Results show that all lakes were affected by mining, indicated by increasing Pb and Zn concentrations and decreasing organic matter content, at the onset of mining. However, the extent and timing of mining impact differed between lakes, which was partly ascribed to differences in the historical use of tailings and settling ponds. Assessment of toxicity levels in sediments, based on normalized Probable Effect Concentration Quotient (PEC-Q) to organic matter content, provided more consistent results with the historical mining than conventional methods, showing a decreasing impact in lakes once the operations ceased. Still, sediment Pb concentrations were > 10 times higher than pre-mining values, evidencing the urgent need for remediation actions in the study lakes. This study highlights the importance of considering spatial heterogeneity in metal deposition, sediment organic matter content, and hydrological connectivity with tailings when risk assessments are performed in mining-impacted lakes. The use of normalized PEC-Q in toxic assessments is also recommended.