The energetic situation of terminal fermentations in methanogenesis was analyzed by pool size determinations in sediment cores taken in the oligotrophic Lake Constance, Germany. Distribution profiles ...of fermentation intermediates and products were measured at three different water depths (2, 10, and 80 m). Methane concentrations were constant below 10 cm of sediment depth. Within the methanogenic zone, concentrations of formate, acetate, propionate, and butyrate varied between 1 and 40 μM, and hydrogen was between 0.5 and 5 Pa. From the distribution profiles of the fermentation intermediates, Gibbs free energy changes for their interconversion were calculated. Pool sizes of formate and hydrogen were energetically nearly equivalent, with -5 ± 5 kJ per mol difference of free energy change (ΔG) for a hypothetical conversion of formate to hydrogen plus CO
The ΔG values for conversion of fatty acids to methanogenic substrates and their further conversion to methane and CO
were calculated with hydrogen and with formate as intermediates. Syntrophic propionate oxidation reached energetic equilibrium with formate as the sole electron carrier but was sufficiently exergonic if at least some of the electrons were transferred via hydrogen. The energetic consequences of formate versus hydrogen transfer in secondary and methanogenic fermentations indicate that both carrier systems are probably used simultaneously to optimize the energy yields for the partners involved.
In the terminal steps of methane formation in freshwater lake sediments, fermenting bacteria cooperate syntrophically with methanogens and homoacetogens at minimum energy increments via interspecies electron transfer. The energy yields of the partner organisms in these cooperations have so far been calculated based mainly on
hydrogen partial pressures. In the present study, we also analyzed pools of formate as an alternative electron carrier in sediment cores of an oligotrophic lake. The formate and hydrogen pools appeared to be energetically nearly equivalent and are likely to be used simultaneously for interspecies electron transfer. Calculations of reaction energies of the partners involved suggest that propionate degradation may also proceed through the
pathway, which converts propionate via butyrate and acetate to three acetate residues, thus circumventing one energetically difficult fatty acid oxidation step.
As one of the world's great natural treasures, the Great Lakes have also served in recent decades as an early warning system for many emerging environmental problems. In the early twenty-first ...century, as the Lakes face unprecedented challenges, we need to revisit both the wonder of the Lakes and the perils plaguing them, and to take action to protect this majestic ecosystem.Dave Dempsey weaves the natural character and phenomena of the Great Lakes and stories of the schemes, calamities, and unusual human residents of the Basin with the history of their environmental exploitation and recovery. Contrasting the incomparable beauty and complexity of the Lakes, and the poetry, folklore, and citizen action they have inspired, with the disasters that short-sighted human folly has inflicted on the ecosystem, Dempsey makes this history both engaging and relevant to today's debates and decisions.Underlying the neglectful treatment of the Lakes are two irreconcilable and faulty human assumptions: that the Lakes are a system so big that human beings cannot do great harm to it, and that the Lakes are a resource that can be bent to the will of humankind. Dempsey finds evidence that, despite great changes in the laws governing the Lakes and public attitudes toward them in the last fifty years, government policy and institutions are still dominated by these dangerous attitudes.A central theme ofOn the Brinkis that citizens, who have displayed an increasing sense of commitment to the Lakes and a growing sense of place, must challenge their leaders to reform Great Lakes institutions. While everything from large-scale water exports to global climate change looms in the future of the Lakes, single-purpose solutions do not suffice-no more than a Band- aid would on a gaping wound. Dempsey shows that it is necessary to create a governing system that reflects the realities of life "on the ground" in communities and that taps into the passion and determination of citizens to protect these treasures.
Lake eutrophication is a serious environmental problem worldwide, caused by both natural processes and anthropogenic influences. For effective lake eutrophication management, a variety of models have ...been designed to investigate the complex interrelationship between physical, chemical and biological factors and processes in lakes. However, these models are inconvenient for predictions of lake eutrophication in practical application. To date, very few studies have focused on lake eutrophication in terms of anthropogenic influences (such as sewage emissions and agricultural practices), which are more readily regulated than natural processes. Effective lake eutrophication prediction models should base primarily on facile controlled or predictable indicators. Therefore, to meet this requirement, we designed simple predictive models to determine the interrelationship between the trophic states of lakes and nutrient inputs, which is a direct measurement to characterize anthropogenic influences. Lake Taihu (China) was used as a representative eutrophic water body to assess the accuracy of the proposed predictive models. Firstly, to comprehensively understand the role of nutrient input indicators (NIIs) during eutrophication, Pearson correlation coefficient analysis was conducted on 7 NIIs and 38 types of algae. Secondly, based on the NIIs identified with high correlation coefficients, we modified three commonly used growth models (Gompertz, logistic and Richards) to describe the lake's trophic state. A particle swarm optimization algorithm (PSOA) was used to optimize model variables. Results showed that the mean absolute percentage errors of the optimized Gompertz, logistic and the Richards models were 2.95%, 2.88% and 2.17%, respectively. Finally, these optimized models were used to predict lake eutrophication under several different nutrient input scenarios. Two adjustment scenarios revealed remarkably satisfied trophic states (including roughly oligotrophic and even ultra-oligotrophic) by the 2030s. Our results show that these established models are a simple way to support lake restoration projects by setting realistic and effective targets.
Glacial and kettle lakes in the high-altitude Himalayas are unique habitats with significant scope for microbial ecology. The present study provides insights into bacterial community structure and ...function of the sediments of two high-altitude lakes using 16S amplicon and whole-genome shotgun (WGS) metagenomics. Microbial communities in the sediments of Parvati kund (glacial lake) and Bhoot ground (kettle lake) majorly consist of bacteria and a small fraction of archaea and eukaryota. The bacterial population has an abundance of phyla Proteobacteria, Bacteroidetes, Acidobacteria, Actinobacteria, Firmicutes, and Verrucomicrobia. Despite the common phyla, the sediments from each lake have a distinct distribution of bacterial and archaeal taxa. The analysis of the WGS metagenomes at the functional level provides a broad picture of microbial community metabolism of key elements and suggested chemotrophs as the major primary producers. In addition, the findings also revealed that polyhydroxyalkanoates (PHA) are a crucial stress adaptation molecule. The abundance of PHA metabolism in Alpha- and Betaproteobacteria and less representation in other bacterial and archaeal classes in both metagenomes was disclosed. The metagenomic insights provided an incisive view of the microbiome from Himalayan lake's sediments. It has also opened the scope for further bioprospection from virgin Himalayan niches.
Geochemical investigations of volatiles in hydrothermal systems are used to understand heat sources and subsurface processes occurring at volcanic-tectonic settings. This study reports new results of ...gas chemistry and isotopes (O, H, N, C, and He) of thermal spring samples (T=36.8–83.5°C; pH=8.5–10.3) from the Magadi and Natron basin (MNB) in the East African Rift (EAR). Although a number of thermal springs are shown to ascend along normal faults and feed into major lakes (Magadi, Little Magadi, and Natron), volatile sources and fluxes of these fluids are poorly constrained. CO2 is the most abundant phase (up to 996.325mmol/mol), and the N2-He-Ar abundances show a mixture of dissolved gases from deep (mantle-derived) and shallow (air/air saturated water) sources. The H2-Ar-CH4-CO2 geothermometers indicate that equilibrium temperatures range from ~100 to ~150°C. δ18O (−4.4 to −0.2‰) and δD (−28.9 to −3.9‰) values of the MNB thermal waters still lie slightly to the right of the local meteoric water lines, reflecting minor evaporation. Each mixing relationship of N2 (δ15N=−1.5 to 0.4‰; N2/3He=3.92×106–1.33×109, except for an anomalous biogenic sample (δ15N=5.9‰)) and CO2 (δ13C=−5.7 to 1.6‰; CO2/3He=7.24×108–1.81×1011) suggests that the predominant mantle component of the MNB volatiles is Subcontinental Lithospheric Mantle (SCLM). However, N2 is mostly atmospheric, and minor CO2 is contributed by the limestone end-member. 3He/4He ratios (0.64–4.00 Ra) also indicate a contribution of SCLM (R/Ra=6.1±0.9), with radiogenic 4He derived from a crustal source (R/Ra=0.02). The MNB 4He flux rates (3.64×1011 to 3.34×1014atoms/m2s) are significantly greater than the reported mean of global continental flux values (4.18×1010atoms/m2s), implying that magma intrusions could supply mantle 4He, and related heating and fracturing release crustal 4He from the Tanzanian craton and Mozambique belt. Total flux values (mol/yr) of 3He, N2, and CO2 are 8.18, 4.07×107, and 5.31×109, which are 1.28%, 2.04%, and 0.24% of global fluxes, respectively. Our results suggest that the primary source of magmatic volatiles in the MNB is SCLM, with additional crustal contributions, which is different from the KRV volatiles that have more asthenospheric mantle components. Volatiles from SCLM in magmas stall in the crust to heat and fracture country rock, with accompanying crustal volatile release. These volatile signatures reveal that MORB-type mantle replaces a relatively small volume of SCLM during incipient rifting (<10Ma) in the EAR.
•Equilibrium temperatures ranging from ~100 to ~150°C.•Volatiles from SCLM with crustal and atmospheric contributions.•A smaller volume of SCLM replaced by the asthenosphere.
Organic compounds used in agriculture, industry, and households make their way into surface waters through runoff, leaking septic-conveyance systems, regulated and unregulated discharges, and ...combined sewer overflows, among other sources. Concentrations of these organic waste compounds (OWCs) in some Great Lakes tributaries indicate a high potential for adverse impacts on aquatic organisms. During 2010–13, 709 water samples were collected at 57 tributaries, together representing approximately 41% of the total inflow to the lakes. Samples were collected during runoff and low-flow conditions and analyzed for 69 OWCs, including herbicides, insecticides, polycyclic aromatic hydrocarbons, plasticizers, antioxidants, detergent metabolites, fire retardants, non-prescription human drugs, flavors/fragrances, and dyes. Urban-related land cover characteristics were the most important explanatory variables of concentrations of many OWCs. Compared to samples from nonurban watersheds (<15% urban land cover) samples from urban watersheds (>15% urban land cover) had nearly four times the number of detected compounds and four times the total sample concentration, on average. Concentration differences between runoff and low-flow conditions were not observed, but seasonal differences were observed in atrazine, metolachlor, DEET, and HHCB concentrations. Water quality benchmarks for individual OWCs were exceeded at 20 sites, and at 7 sites benchmarks were exceeded by a factor of 10 or more. The compounds with the most frequent water quality benchmark exceedances were the PAHs benzoapyrene, pyrene, fluoranthene, and anthracene, the detergent metabolite 4-nonylphenol, and the herbicide atrazine. Computed estradiol equivalency quotients (EEQs) using only nonsteroidal endocrine-active compounds indicated medium to high risk of estrogenic effects (intersex or vitellogenin induction) at 10 sites. EEQs at 3 sites were comparable to values reported in effluent. This multifaceted study is the largest, most comprehensive assessment of the occurrence and potential effects of OWCs in the Great Lakes Basin to date.
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•709 samples were collected from 57 tributaries and analyzed for 69 compounds.•Compounds commonly occurred as complex mixtures of 10 or more.•Water-quality benchmarks were exceeded at 35% of the sampled sites.•Estrogenic effects from nonsteroidal compounds alone were estimated at 18% of sites.•Urban-related land use characteristics were important predictors of concentrations.
Summary
Located on the shore of Kandalaksha Bay (the White Sea, Russia) and previously separated from it, Trekhtzvetnoe Lake (average depth 3.5 m) is one of the shallowest meromictic lakes known. ...Despite its shallowness, it features completely developed water column stratification with high‐density microbial chemocline community (bacterial plate) and high rates of major biogeochemical processes. A sharp halocline stabilizes the stratification. Chlorobium phaeovibrioides dominated the bacterial plate, which reached a density of 2 × 108 cell ml−1 and almost completely intercepts H2S diffusion from the anoxic monimolimnion. The resulting anoxygenic photosynthesis rate reached 240 μmol C l−1 day−1, exceeding the oxygenic photosynthesis rate in the mixolimnion. The rates of other processes are also high, reaching 4.5 μmol CH4 l−1 day−1 for methane oxidation and 35 μmol S l−1 day−1 for sulfate reduction. Metagenomic analysis demonstrated that the Chl. phaeovibrioides population in the bacterial plate layer had nearly clonal homogeneity, although some fraction of these cells harbour a plasmid. The Chlorobium population was associated with bacteriophages that share homology with CRISPR spacers in the host. These features make the ecosystem of the Trekhtzvetnoe Lake a valuable model for studying regulation and evolution processes in natural high‐density microbial systems.
This work presents the first assessment of temporal trends (2005–2016) for perfluoroalkyl acids (PFAAs) in top predator fish of the Laurentian Great Lakes except Lake Ontario, for which we provide a ...post-2008 update. Lake trout (Salvelinus namaycush) or walleye (Sander vitreus; Lake Erie only) collected annually from 2005 to 2016 were analyzed for 12 perfluoroalkyl carboxylic acids (PFCAs) and 4 perfluoroalkyl sulfonic acids (PFSAs) with carbon chain lengths between 4 and 16 (C4-C16). Individual analyte concentrations generally decreased in fish basin-wide between 2005 and 2016, including Lake Ontario lake trout previously found to lack declining PFAA concentrations up until 2008. Declining fish PFAA burden reflects a positive response to the industrial phase-outs of these chemicals. Notable exceptions to this general decline included most analytes in lake trout collected from Lake Superior near Keweenaw Point and C6 and C8 PFSAs and C9 PFCAs in Lake Erie lake trout and walleye, which exhibited constant or increasing concentrations in recent years. Recent increases in Lake Superior shoreline development and mobilization from increased sediment resuspension and contamination from biosolids-amended agricultural soils in the Lake Erie watershed are plausible explanations for these cases. However, data scarcity prohibits confirmation of these suspected causes. The lingering lack of declining concentrations noted in this study together with the ongoing evolution of the fluorinated chemical industry emphasize the vigilance needed to better understand how past and future emissions will affect the Great Lakes and global ecosystems.
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•First basin-wide temporal assessment of perfluoroalkyl acids in Great Lakes fish•Fish used to assess biosphere/hydrosphere for industrial phase-outs' effectiveness•Generally declining fish PFAA concentrations reflects prior industrial phase-outs.•Lakes Superior and Erie exhibited the most stable or increasing concentrations.•Shoreline development and biosolids amendment likely cause PFAA persistence in fish.
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