Convergency and Stability Responses of Bacterial Communities to Salinization in Arid and Semiarid Areas: Implications for Global Climate Change in Lake Ecosystems

Climate change has given rise to salinization and nutrient enrichment in lake ecosystems of arid and semiarid areas, which have posed the bacterial communities not only into an ecotone in lake ecosystems but also into an assemblage of its own unique biomes. However, responses of bacterial communities to climate-related salinization and nutrient enrichment remain unclear. In September 2019, this study scrutinized the turnover of bacterial communities along gradients of increasing salinity and nutrient by a space-for-time substitution in Xinjiang Uyghur Autonomous Region, China. We find that salinization rather than nutrient enrichment primarily alters bacterial communities. The homogenous selection of salinization leads to convergent response of bacterial communities, which is revealed by the combination of a decreasing β-nearest taxon index (βNTI) and a pronounced negative correlation between niche breadth and salinity. Furthermore, interspecific interactions within bacterial communities significantly differed among distinct salinity levels. Specifically, mutualistic interactions showed an increase along the salinization. In contrast, topological parameters show hump-shaped curves (average degree and density) and sunken curves (modularity, density, and average path distance), the extremums of which all appear in the high-brackish environment, hinting that bacterial communities are comparatively stable at freshwater and brine environments but are unstable in moderately high-brackish lake.

National natural heritage at risk: The Seven Rila Lakes

The area of the Seven Rila Lakes is situated in the North-West part of the Rila Mountain at an altitude between 2100 and 2500 m a.s.l. within the borders of Rila National Park. There are 140 glacial lakes in Rila Mountain but the area of the Seven Rila Lakes is the most visited and famous with its natural beauty and sacred significance. It is a valuable part of the national natural heritage. The popularity of this area grows constantly with the number of visitors from the country and abroad. This process leads to the deterioration of the natural conditions in the site. At the same time, it is not clear what is the effect of climate change on the environment in the lake’s area. There are many factors that contribute to the degradation of ecosystems in the protected area of the Seven Rila Lakes and pose risk to this valuable natural heritage. These factors are natural (mainly climate change-related), anthropogenic (associated with the excessive tourist pressures on the ecosystems in the protected area), and management (stemming from the ongoing conservation policy over the years). This study explores to what extent climate change may put at risk the ecosystems of Seven Rila Lakes. Mean monthly data from The European Center for Medium-Range Weather Forecasts (ECMWF) ERA5-Land reanalysis were used in this study. The resolution of these data is 0.1 x 0.1 (9 x 9 km) and their period is 1981-2020. Reanalysis data include air temperature, precipitation, evaporation, snow depth, etc. Based on data from various sources such as reanalysis data, in situ measurements, and statistical modeling, a scenario, based on current trends in different climatic elements, has been developed in order to project future changes and their impact on lake ecosystems. The results of the modelling of climate change show that in the coming decades an increase in temperature is expected in the high mountain regions of South-western Bulgaria and in particular in the Seven Rila Lakes area. This, combined with the ever-increasing flow of tourists, and high demand for the provided cultural ecosystem services, and insufficient management practices, put at risk the state of the lakes and their capacity to provide the same quality of cultural ecosystem services in the future, which attracts tourists in the area now. Recommendations have been made for the optimization of the management of the protected area in accordance with the observed trends.

Variations in δ13CDIC and influencing factors in a shallow macrophytic lake on the Qinghai-Tibetan Plateau: implications for the lake carbon cycle

The primary sources of dissolved inorganic carbon (DIC) in water are carbonate materials and CO produced during the biological processing of organic matter. The application of carbon isotope techniques to terrestrial and aquatic ecosystems can accurately elucidate carbon fluxes and other carbon cycle processes in these systems. Lake ecosystems on the Qinghai-Tibetan Plateau are fragile and sensitive to changes in climate and environment. This study explored the relationship between the carbon isotopic composition (δC) of the DIC (δC) in the Genggahai Lake, the lake environment, and the climate of the watershed based on the observed physicochemical parameters of water in areas with different types of submerged macrophyte communities, combined with changes in the temperature and precipitation during the same period. Overall, the δC of the Genggahai Basin exhibited a large range of values, with an average δC for inflowing spring water (δC) of –11.1 ‰, which was the most negative, followed by an average δC value of –10.8 ‰ for that from the Shazhuyu River (δC) and an averageδC value of –6.91 ‰ for lake water (δC). Variations in the photosynthetic activity intensity of different aquatic plants yield significantly changing δC values in areas with varied aquatic plant communities. Hydrochemical observations revealed that δC and aquatic plant photosynthesis primarily affected the differences in the δC values of the Genggahai Lake, thereby identifying them as the key components of the lake carbon cycle.

On the parameterization of phytoplankton primary production in water ecosystem models

Parametrization of the formation of organic matter in ecological models is traditionally carried out by using the dependence of the Michaelis – Menten – Monod type [Monod, 1942], which describes the growth rate of algal biomass depending on the factor limiting their development. One of the biggest drawbacks of these dependences is the presence of empirical parameters in them, which in a complex way depend on environmental factors and are an individual characteristic of various types of algae. These parameters in the models actually become fitting coefficients that provide the best fit between observational data and modeling results, which does not allow for effective diagnostics and forecasting of the state of aquatic ecosystems. In this work, on the basis of dimensional analysis, a parametrization was obtained that describes the photosynthesis of algae depending on the parameters relatively easily measured in natural conditions - total solar radiation, phytoplankton biomass, and water transparency. Parametrization has been verified according to observations on more than 30 different types of lakes located in different regions of the world. The calculated data are in satisfactory agreement with the data of field observations, both qualitatively and quantitatively. Discrepancies in field and calculated data may be due to the fact that the species composition of algae in lakes of different trophic status is not taken into account, which can lead to errors in assessing the efficiency of using solar radiation. Discrepancies may also be related to the total solar radiation, rather than photosynthetic active radiation, which varies in different geographic and atmospheric conditions. The proposed parametrization can be used in the development of mathematical models of lake ecosystems, as well as to determine the trophic status of poorly studied water bodies.

Compound hot temperature and high chlorophyll extreme events in global lakes

An emerging concern for lake ecosystems is the occurrence of compound extreme events i.e., situations where multiple within-lake extremes occur simultaneously. Of particular concern are the co-occurrence of lake heatwaves (anomalously warm temperatures) and high chlorophyll-a extremes, two important variables that influence the functioning of aquatic ecosystems. Here, using satellite observations, we provide the first assessment of univariate and compound extreme events in lakes worldwide. Our analysis suggests that the intensity of lake heatwaves and high chlorophyll-a extremes differ across lakes and are influenced primarily by the annual range in surface water temperature and chlorophyll-a concentrations. The intensity of lake heatwaves is even greater in smaller lakes and in those that are shallow and experience cooler average temperatures. Our analysis also suggests that, in most of the studied lakes, compound extremes occur more often than would be assumed from the product of their independent probabilities. We anticipate compound extreme events to have more severe impacts on lake ecosystems than those previously reported due to the occurrence of univariate extremes.

Space and Species Interactions in Welfare Estimates for Invasive Species Policy

Aquatic invasive species (AIS) can cause catastrophic damages to lake ecosystems. Bigheaded carp are one such species that pose a current threat to Lake Michigan. Bigheaded carp are expected to have spatially differentiated impacts on other aquatic species in the metapopulation. Policymakers must decide how much to invest in mitigation or conservation policies, if at all, by understanding how invasions impact social welfare or social wellbeing. Estimates of social welfare implications, however, may be biased if important interactions between species and space are overly simplified or aggregated out of the model. In this analysis, a bioeconomic model that links an ecological model with an economic model of recreational fishing behavior is used to complete a comparative analysis of the social welfare implications across several different ecological specifications to demonstrate what biases exist if species interactions are neglected or if ecological characteristics are assumed to be homogenous across space. Results of the bigheaded carp case study suggest that social welfare losses from the invasion vary substantially if species interactions are excluded and vary less if space is treated homogeneously.

Predictive Model of Lake Photic Zone Temperature Across the Conterminous United States

As the average global air temperature increases, lake surface temperatures are also increasing globally. The influence of this increased temperature is known to impact lake ecosystems across local to broad scales. Warming lake temperature is linked to disruptions in trophic linkages, changes in thermal stratification, and cyanobacteria bloom dynamics. Thus, comprehending broad trends in lake temperature is important to understanding the changing ecology of lakes and the potential human health impacts of these changes. To help address this, we developed a simple yet robust random forest model of lake photic zone temperature using the 2007 and 2012 United States Environmental Protection Agency’s National Lakes Assessment data for the conterminous United States. The final model has a root mean square error of 1.48°C and an adjusted R2 of 0.88; the final model included 2,282 total samples. The sampling date, that day’s average ambient air temperature and longitude are the most important variables impacting the final model’s accuracy. The final model also included 30-days average temperature, elevation, latitude, lake area, and lake shoreline length. Given the importance of temperature to a lake ecosystem, this model can be a valuable tool for researchers and lake resource managers. Daily predicted lake photic zone temperature for all lakes in the conterminous US can now be estimated based on basic ambient temperature and location information.

Stratification in Microbial Communities with Depth and Redox Status in a Eutrophic Lake Across Two Years

Bacteria have a profound impact on many key biogeochemical cycles in freshwater lake ecosystems; in turn, the composition of bacteria in the lake is contingent on the chemistry of the water. Many parameters that affect bacterial growth in freshwater ecosystems, such as water temperature, nutrient levels, and redox status, exhibit notable inter-annual differences in addition to seasonal changes. However, little is known about the impact of these inter- and intra-annual differences on the freshwater microbiome, especially in anoxic bottom waters. In this study, we paired biogeochemical field data with 16S rRNA gene amplicon sequencing of depth-discrete samples from a dimictic lake across two open-water seasons to observe variation in the microbiome relative to differences in water chemistry between two years. We found differences in the timing anoxia onset and the redox status in the water column across the two years. Changes in redox status led to major shifts in the microbial community composition. While there was little variation between years in the microbial taxonomic composition at the phyla level, there was substantial interannual variation at more resolved taxonomic levels. Some interannual differences can be explained by links between the predicted metabolic potential of those lineages and the different redox conditions between the two years. These results emphasize the need for repeated monitoring to deduce long-term trends in microbial communities in natural ecosystems and the importance of a comprehensive evaluation of environmental conditions contemporary with any microbiome analysis.

Limnochemistry and Plankton Diversity in Some High Altitude Lakes of Kashmir Himalaya

High altitude lakes (HALs) of Kashmir Himalaya are the important ecosystems in the mountain ecology of the broader Hindukush Himalayan region. This article provides a comprehensive information about the plankton (phytoplankton and periphyton) assemblages, water quality (WQ), bathymetry, morphometry, and land use land cover (LULC) of some select high altitude mountain lakes of Kashmir Himalaya. LULC analysis revealed that the catchment of the lakes spread over an area of about 16179 ha, is covered by different land cover types dominated by pastures (50.8%), followed by barren rocky (32.6%), snow and glaciers (11.9%), lakes (2.5%), forest (2%), and streams (0.2%). Bathymetric and morphometric analysis revealed that the Gangbal Lake is the deepest (84 m) and largest (162.4 ha) among the investigated lakes. The water quality index revealed that all the HALs have the excellent water quality category. Statistical analysis (Wilk’s λ) depicted that nitrate-nitrogen (NO3−-N), nitrite nitrogen (NO2−-N), ammoniacal nitrogen (NH3-N), total phosphorus (TP), and magnesium hardness (Mg-H) are responsible for major variability between all HALs sites. The cations followed the order of Ca2+ > Mg2+ > Na+ > K+ while as anions followed the order as HCO3− > Cl− > SO42−. Algal composition (phytoplankton and periphyton) assessment revealed the presence of 61 taxa belonging to Bacillariophyceae (45), Chlorophyceae (14), Cyanophyceae (1), and Xanthophyceae (1). The higher dominance of Bacillariophyceae indicates oligotrophic nature of the lakes. Canonical correspondence analysis (CCA) highlighted the role of various water quality parameters like pH, EC, and TDS on the composition of phytoplankton and periphyton species among the lakes. The present study therefore generated a baseline database for some of the HALs of Kashmir Himalaya that can act as a precursor for more research on future changes in the lake ecosystems of the region.

Spatio-temporal dynamics of bacterial communities in the shoreline of Laurentian great Lake Erie and Lake St. Clair’s large freshwater ecosystems

Background Long-term trends in freshwater bacterial community composition (BCC) and dynamics are not yet well characterized, particularly in large lake ecosystems. We addressed this gap by temporally (15 months) and spatially (6 sampling locations) characterizing BCC variation in lakes Erie and St. Clair; two connected ecosystems in the Laurentian Great Lakes. Results We found a spatial variation of the BCC between the two lakes and among the sampling locations (significant changes in the relative abundance of 16% of the identified OTUs at the sampling location level). We observed five distinct temporal clusters (UPGMA broad-scale temporal variation) corresponding to seasonal variation over the 15 months of sampling. Temporal variation among months was high, with significant variation in the relative abundance of 69% of the OTUs. We identified significant differences in taxonomic composition between summer months of 2016 and 2017, with a corresponding significant reduction in the diversity of BCC in summer 2017. Conclusions As bacteria play a key role in biogeochemical cycling, and hence in healthy ecosystem function our study defines the scope for temporal and spatial variation in large lake ecosystems. Our data also show that freshwater BCC could serve as an effective proxy and monitoring tool to access large lake health.