Ice Lakes V1.9.4 Game Hack
Edwin Bores
Broadly, depositional environments can be said to be terrestrial, marine, or to reflect a transitional zone between the two. Terrestrial refers to depositional environments on land. These may be depositional environments such as deserts, found on dry land, but they could also be environments such as freshwater lakes or rivers. Marine refers to environments associated with saltwater seas and oceans. Transitional depositional environments include environments such as deltas, where freshwater rivers empty into saltwater seas or oceans.
After making the trek back to our campsite at Lizard Lake, I joined Andy for a lovely evening around a campfire shared with the other groups camping at the lake, cooking our various meals over the fire, swapping stories, and laughing a lot. As dusk approached, we noticed ripples in the water. We'd seen several ducks paddling around the lake, but this time it was definitely something larger - a beaver! He swam back and forth near the shore, warning his friends by slapping the water with his tail several times as I snapped photos. After his show, darkness settled and I headed to the tent for a early bedtime. After the excitement that followed that night, I don't know that I'll return to these lakes soon, but it was certainly a trip we won't soon forget!
Copyright: 2016 Baatar et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the paper and its Supporting Information files. All fastq files are available from the NCBI's Sequence Read Archive database (accession number SRP058905).
The goals of this study were to characterize and compare bacterial communities throughout the water column and determine associations between environmental parameters and bacterial populations among individual layers of these meromictic lakes. Bacterial community composition and biodiversity of the three lakes were determined by 454-pyrosequencing the V1/V2 hyper-variable regions of the 16S rRNA gene. There were clear similarities and differences in bacterial community structure among lakes, as well as unique bacterial profiles in distinct water layers. Furthermore, associations between bacterial community and environmental parameters were explored. Finally, this was the first report to characterize the bacterial community and diversity in Lake Oigon.
Qualified and non-chimeric sequences were analyzed with the UPARSE ( ) to generate operational taxonomic units (OTUs) at 97% similarity level and classified with taxonomic labels from SILVA-ngs pipeline [41]. All singleton OTUs, chloroplasts and unclassified sequences ("No Relative" by SILVA-ngs) were excluded from further analyses as potential noise.
The OTUs from each sample were used for further analyses. The relative abundance of each OTU was log-transformed before being subjected to non-Metric Multidimensional Scaling (nMDS), based on the Bray-Curtis distance matrix using Primer 6 software (PRIMER-E package, Version 6; Plymouth Marine Laboratory, Plymouth, UK).
Transition layers could be crucial in species compositional distribution of PSB among meromictic lakes (S5 Fig). Since some PSB were not only detected in the anoxic layer, but also in the oxic layer, their phylogenetic lineages were further examined. Clearly, there were two broadly classified groups between the oxic and anoxic layers (S5 Fig).
Both statistical and non-statistical methods (i.e., nMDS and clustering/heatmap, respectively) were used to compare similarities among bacterial communities among the three lakes. Based on nMDS plotting, there were clear differences among lakes, as well as significant variation between oxic and anoxic layers within each lake (Fig 5). Bacterial community composition had nearly perfect separation of its two layers in Lake Shunet (as visualized in the nMDS plot). However, bacterial communities in the anoxic layer of Lake Shira were not clearly similar to each other, consistent with bar charts (Fig 4) of its bacterial community structure.
In addition, distributions of the shared OTUs along the vertical gradient in the three lakes were visualized with a clustering-heat map to test the relationship between each sampled layer (Fig 6). Bacterial communities in oxic layers of the lakes differed (P
The CCA analysis was done to determine relationships between environmental variables per sampling layer of the three lakes, as well as associations between abundant bacterial genera (>0.1% of the total community) and physico-chemical parameters. Based on this approach, bacterial communities of the lakes were significantly correlated with temperature, pH, nitrate, nitrite, phosphate, conductivity, dissolved oxygen, H2S and salinity (P < 0.05; Fig 7). Furthermore, some specific bacterial groups correlated closely with particular environmental variables on the CCA plot; for example, Sulfurovum was associated with H2S, phosphate, and NH4+, whereas Psychrobacter and Planococcus were associated with salinity. Moreover, CCA analysis also indicated that bacterial communities in anoxic layers were more closely associated (P
Environmental variables that significantly influenced the bacterial community are represented as vectors; the length of the arrow corresponds to the degree of significance. The genus name is abbreviated as follows. (Thio-Thiocapsa, Rhei-Rheinheimera, Haloch-Halochromatium, Halom-Halomonas, Cy-sb-Cyanobacteria.sp, Cya-Cyanobacteria-FamilyI, Syne-Synechococcus, Acho-Acholeplasma, Algo-Algoriphagus, Pseu-Pseudomonas, Psych-Psychrobacter, Flav-Flavobacterium, Lokt-Loktanella, Nitr-Nitriliruptor, Xiph-Xiphinematobacter, Brev-Brevundimonas, Plan-Planococcus, Gill-Gillisia, Eryt-Erythrobacter, Meri-Merismopedia, Chry-Chryseobacterium, Sulf-Sulfurovum, Lept-Leptolyngbya, Baci-Bacillus, Sphi-Sphingomonas, Sapr-Saprospiraceae-uncultured, Mari-Maritimibacter, Micr-Microbacteriaceae-uncultured, Ali-Aliidiomarina, Clos-Clostridium sensu stricto 17).
This study was a detailed characterization of bacterial diversity and community composition in three high-latitude meromictic lakes near central Asia. Based on high variations and uniqueness of bacterial community in the three lakes, we concluded that meromictic ecosystems were characterized by high diversity and heterogeneity of niches.
Bacterial diversity in the anoxic layer of Lake Oigon was high in this study, with Shannon-Weaver values up to 4.93, which was apparently higher than the 4.36 in Lake Mahoney [18], 3.6 in Lake Pavin [24], 1.8 in Lake Nyos [19], 1.01 in Organic Lake [47], up to 2.5 in lakes of the Monegros Desert [48] and 3.83 in Lake Soap [49]. To the best of our knowledge, this was among the greatest diversity ever reported in a meromictic lake bacterial community. However, we cannot exclude potential bias due to methodology. In that regard, the extreme diversity could have been due, at least in part, to the use of massively parallel pyro-sequencing (although it is a more effective and sensitive approach for detecting bacterial diversity compared to traditional approaches [50]).
Why was bacterial diversity consistently greater in the anoxic versus oxic layer? This phenomenon has been reported in Lake Mahoney [18], Ace Lake [14], Ursu Lake and Fara Fund Lake [8]. Perhaps abundant nutrients in the anoxic layer promote diversity. Furthermore, it has been proposed that the mineralization process (organic compounds becoming impregnated by inorganic compounds in anoxic systems) was a multistep process that needed a diverse and complex bacterial community [14, 51]. Additional explanations for higher diversity in the anoxic layer might be related to a relatively lack of mixing (i.e., homogenization) in the anoxic layer and downward metabolic fluxes [3, 8, 29, 34].
In addition, local bacterial occupants further diversified local environmental characters interactively; ultimately each lake was a unique variation on the meromictic lake theme [13, 16, 53]. Distinct bacterial community compositions in the two layers were attributed to different mixing regimes, as well as disparate physicochemical milieus [8, 20, 54, 55]. Therefore, this may also explain why bacterial communities and physicochemical characteristics frequently differ between oxic and anoxic layers of meromictic lakes, regardless of their similarities in lake profile.
Based on the present and previous reports, we inferred that dominant PSB genera in meromictic lakes were highly variable, as shown by Thiocapsa in Lake Shunet, a novel genus in Lake Shira, Halochromatium in Lake Oigon, Lamprocystis purpurea in Lake Mahoney [18], and Thiodictyon syntrophicum in Lake Cadagno [61]. In the present study, although Lake Shira and Lake Shunet were in close proximity (8 km), dominant PSB species clearly differed between the two lakes. Similar results have been described [15, 29, 32]. For example, dominant species of phototrophic sulfur bacteria differed between Lake Ciso and Lake Vilar, even though those two lakes are only 1 km apart [62]. However, why were no similar dominant PSB species detected among those lakes? Although the causes could be complex, perhaps the uniqueness and consistency of environmental profiles of each meromictic lake could reduce the probability that other foreign PSB species successfully colonized the lake.
In conclusion, this study provided a high-resolution characterization of bacterial diversity and community in three meromictic lakes. Based on comparative analysis of bacterial composition, Lake Shira, Lake Shunet and Lake Oigon clearly had high diversity and uniqueness of bacterial communities between water layers within individual lake and among lake. Several hydrological parameters were significantly correlated with variations in the dominant bacterial groups along the water column; therefore, we speculated that there was an intimate relationship between microenvironments and specific bacterial communities. In addition, abundant unclassified species present in these lakes, particularly Lake Shunet, was evidence that meromictic lakes were hot spots for exploring bacterial diversity, taxonomy and phylogenetics. This study should serve as an initial inventory survey of the bacterial community and diversity of meromictic lakes in central Asia and provide an impetus for further studies, e.g. functional ecology and metagenomics to examine interactions between the bacterial community structure and environmental conditions in meromictic lakes.
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