Bacteria are highly important for the cycling of organic and inorganic matter in freshwater environments; however, little is known about the diversity of bacterioplankton in tropical systems. Studies ...on carbon and nutrient cycling in tropical lakes suggest a very different seasonality from that of temperate climates. Here, we used 16S rRNA gene next-generation sequencing (NGS) to investigate seasonal changes in bacterioplankton communities of two tropical lakes, which differed in trophic status and mixing regime. Our findings revealed seasonally and depth-wise highly dynamic bacterioplankton communities. Differences in richness and structure appeared strongly related to the physicochemical characteristics of the water column, especially phosphate, pH and oxygen. Bacterioplankton communities were dominated by common taxonomic groups, such as Synechococcus and Actinobacteria acI, as well as rare and poorly characterized taxa such as 'Candidatus Methylacidiphilum' (Verrucomicrobia). Stratification and oxygen depletion during the rainy season promoted the occurrence of anoxygenic phototrophic and methanotrophic bacteria important for carbon and nutrient cycling. Differences in lake mixing regime were associated with seasonal beta diversity. Our study is the first attempt to use NGS for cataloging the diversity of bacterioplankton communities in Brazilian lakes and thus contributes to the ongoing worldwide endeavor to characterize freshwater lake bacterioplankton signatures.
The capacity of a lake to remove reactive nitrogen (N) through denitrification has important implications both for the lake and for downstream ecosystems. In large oligotropic lakes such as Lake ...Superior, where nitrate (NO₃ ⁻) concentrations have increased steadily over the past century, deep oxygen penetration into sediments may limit the denitrification rates. We tested the hypothesis that the position of the redox gradient in lake sediments affects denitrification by measuring net N-fluxes across the sediment–water interface for intact sediment cores collected across a range of sediment oxycline values from nearshore and offshore sites in Lake Superior, as well as sites in Lake Huron and Lake Erie. Across this redox gradient, as the thickness of the oxygenated sediment layer increased from Lake Erie to Lake Superior, fluxes of NH₄ ⁺ and N₂ out of the sediment decreased, and sediments shifted from a net sink to a net source of NO₃ ⁻. Denitrification of NO₃ ⁻ from overlying water decreased with thickness of the oxygenated sediment layer. Our results indicate that, unlike sediments from Lake Erie and Lake Huron, Lake Superior sediments do not remove significant amounts of water column NO₃ ⁻ through denitrification, likely as a result of the thick oxygenated sediment layer.
In North America, land use practices of the last two centuries have strongly influenced aquatic communities and freshwater quality, but the impacts of prehistoric land use on freshwater resources ...remain poorly documented. Here we investigate the influence of prehistoric and historical land use on Horseshoe Lake, Illinois, USA, an oxbow lake in a floodplain of the Mississippi River that is adjacent to Cahokia, the largest prehistoric indigenous population center north of Mexico. Diatom assemblages from Horseshoe Lake’s sedimentary record track shifts in aquatic environmental conditions over the last ca. 1600 years. During the period of prehistoric population growth and agricultural intensification associated with Cahokia’s emergence (ca. 600–1200 CE), the relative abundance of
Aulacoseira granulata
—a planktonic diatom associated with shallow eutrophic lakes—increased. Following the abandonment of Cahokia in the 14th century CE, the diatom flora of the lake shifted from planktonic
Aulacoseira
taxa to the epiphytic taxa
Cocconeis
and
Gomphonema
. This shift in diatom assemblages is consistent with a reduction of nutrient inputs to the lake and/or reduced fishing pressure as prehistoric populations abandoned the area. Following the intensification of historic settlement after 1800 CE, diatom assemblages shift to epipelic species of small
Staurosira
and
Fragilaria
, indicating a reduction in aquatic macrophytes and increased turbidity. Our results document prehistoric indigenous impacts on a freshwater system beginning nearly 1000 years before European colonization of the Americas and demonstrate the antiquity of human impacts on freshwater resources in North America.
The Great Lakes have been the focus of extensive environmental research, but recent data on the aquatic concentrations of emerging compounds, such as flame retardants, are scarce. Water samples from ...18 stations on the five Great Lakes were collected in 2011 and 2012 using XAD-2 resin adsorption and analyzed for PCBs, organochlorine pesticides, PAHs, polybrominated diphenyl ethers (PBDEs), and emerging flame retardants, including organophosphate flame retardants (OPEs). Total PCB concentrations ranged from 117 ± 18 pg/L in Lake Superior to 623 ± 113 pg/L in Lake Ontario. Among the organochlorine pesticides, the most abundant was dieldrin, with the highest average concentration of 99 ± 26 pg/L in Lake Erie, followed by p,p′-DDD with an average concentration of 37 ± 8 pg/L in Lake Ontario. Total PAH concentrations were higher in Lakes Erie and Ontario than in Lakes Michigan, Huron, and Superior. Total PBDE concentrations were highest in Lake Ontario (227 ± 75 pg/L), and the most abundant congeners were BDE-47, BDE-99, and BDE-209. Total OPE concentrations ranged between 7.3 ± 4.5 ng/L in Lake Huron to 96 ± 43 ng/L in Lake Erie.
Lakes and reservoirs (LaR) are important parts of water resources and their rapid and accurate monitoring is an essential guarantee for maintaining ecological health and social development. The ...existing waterbody extraction methods are mostly targeted at local water bodies, with little attention on the national scale. In this letter, an improved U-Net method is proposed for LaR extraction from GF-1 satellite imagery. First, 21 scenes of GF-1 images are evenly selected across China, and the training set and validation set are produced by image processing, cropping, and augmentation. Second, a deep learning network is constructed by modifying the U-Net, deepening the network and introducing multiple skip connections, which is suitable for extracting LaR China-wide. Experiments on the GF-1 imagery demonstrate that the superiority of the improved U-Net when compared with other deep learning methods (U-Net, UNet++, FastFCN, DeepLabv3+) and traditional methods the normalized difference water index (NDWI), maximum likelihood method (MLM). In addition, 20 LaR are selected for further evaluation of the model, and all of them achieve good extraction results, showing excellent generalization of the model.
Abstract
David Schindler and his colleagues pioneered studies in the 1970s on the role of phosphorus in stimulating cyanobacterial blooms in North American lakes. Our understanding of the nuances of ...phosphorus utilization by cyanobacteria has evolved since that time. We review the phosphorus utilization strategies used by cyanobacteria, such as use of organic forms, alternation between passive and active uptake, and luxury storage. While many aspects of physiological responses to phosphorus of cyanobacteria have been measured, our understanding of the critical processes that drive species diversity, adaptation and competition remains limited. We identify persistent critical knowledge gaps, particularly on the adaptation of cyanobacteria to low nutrient concentrations. We propose that traditional discipline-specific studies be adapted and expanded to encompass innovative new methodologies and take advantage of interdisciplinary opportunities among physiologists, molecular biologists, and modellers, to advance our understanding and prediction of toxic cyanobacteria, and ultimately to mitigate the occurrence of blooms.
This review advocates for interdisciplinary research on cell physiology, molecular biology, and ecological modelling to improve predictions of cyanobacterial blooms in response to variability in phosphorus supply rates in situ.
Lakes are one of the most important parts of the terrestrial hydrosphere. The long-term series of lake area dynamic data with high spatial-temporal resolution is of great significance to the study of ...global change of the water environment. Satellite observations (such as Landsat) have provided images since the 1970s, but there were challenges for the construction of long-term sequences of lake area on a monthly temporal scale. We proposed a temporal-spatial interpolation and rule-based (TSIRB) approach on the Google Earth Engine, which aims to achieve automatic water extraction and bimonthly sequence construction of lake area. There are three main steps of this method which include bimonthly image sequence construction, automatic water extraction, and anomaly rectification. We applied the TSIRB method to five typical lakes (covering salt lakes, river lagoons, and plateau alpine lakes), and constructed the bimonthly surface water dataset (BSWD) from 1987 to 2020. The accuracy assessment that was based on a confusion matrix and random sampling showed that the average overall accuracy (OA) of water extraction was 96.6%, and the average Kappa was 0.90. The BSWD sequence was compared with the lake water level observation data, and the results show that the BSWD data is closely correlated with the water level observation sequence, with correlation coefficient greater than 0.87. The BSWD improves the hollows in the global surface water (GSW) monthly data and has advantages in the temporal continuity of surface water data. The BSWD can provide a 30-m-scale and bimonthly series of surface water for more than 30 years, which shows good value for the long-term dynamic monitoring of lakes, especially in areas that are lacking in situ surveying data.
Oxbow lakes generated from meandering river cutoffs are an indispensable component of riparian ecosystem. This study aimed to examine whether predictable patterns in water properties arise relative ...to oxbow lake geometry and lake-channel connectivity. We selected 24 oxbow lakes along a meandering river belt in Zoige Basin, the Tibetan Plateau, to conduct field work at the beginning (May) and the end (September) of the flood season, 2019. Six parameters (pH, dissolved oxygen (DO), conductivity, total dissolved organic carbon, nitrogen and phosphorus) were measured to represent water property. Lake surface area, length, width, length/width ratio, distance to active channel, and curvature were measured to represent lake geometry. Shrinkage ratio, defined as current lake length/initial lake length, was measured to represent lake-channel connectivity between oxbow lakes and active channel. We found an environmental gradient relative to connectivity. As oxbow lakes aged and gradually disconnected from the channel, increased DO and nutrients drove the lakes towards eutrophication. This trend however was disturbed by (i) flood pulses that diluted nutrient concentrations in oxbow lakes and narrowed the differences among different types of lakes and the channel through altering lake-channel connectivity, and (ii) lateral meander migration passed through older lakes such that regulated water properties by reconnecting older lakes to newly formed lakes. Maintenance or restoration of connectivity thus should be of great importance to prevent oxbow lakes from eutrophication in meandering river belts in Zoige Basin.
The Atacama Desert has extreme environmental conditions that allow the development of unique microbial communities. The present paper reports the bacterial diversity of microbial mats and sediments ...and its mineralogical components. Some physicochemical conditions of the water surrounding these ecosystems have also been studied trying to determine their influence on the diversity of these communities. In that way, mats and sediments distributed among different hypersaline lakes located in salt flats of the Atacama Desert were subjected to massive parallel sequencing of the V4 region of the 16S rRNA genes of Bacteria. A higher diversity in sediment than in mat samples have been found. Lakes that harbor microbial mats have higher salinity than lakes where mats are absent. Proteobacteria and/or Bacteroidetes are the major phyla represented in all samples. An interesting item is the finding of a low proportion or absence of Cyanobacteria sequences in the ecosystems studied, suggesting the possibility that other groups may be playing an essential role as primary producers in these extreme environments. Additionally, the large proportion of 16S rRNA gene sequences that could not be classified at the level of phylum indicates potential new phyla present in these ecosystems.
Soil salinization is one of the most important causes for land degradation and desertification and is an important threat to land management, farming activities, water quality, and sustainable ...development in arid and semi-arid areas. Soil salinization is often characterized with significant spatiotemporal dynamics. The salt-affected soil is predominant in the Ebinur Lake region in the Northwestern China. However, detailed local soil salinity information is ambiguous at the best due to limited monitoring techniques. Nowadays, the availability of Multi-Spectral Instrument (MSI) onboard Sentinel-2, offers unprecedented perspectives for the monitoring and mapping of soil salinity. The use of MSI data is an innovative attempt for salinity detection in arid land. We hypothesize that field observations and MSI data and MSI data-derived spectral indices using the partial least square regression (PLSR) approach will yield fairly accurate regional salinity map. Based on electrical conductivity of 1:5 soil:water extract (EC) of 72 ground-truth measurements (out of 116 sample sites) and various spectral parameters, such as satellite band reflectance, published satellite salinity indices, red-edge indices, newly constructed two-band indices, and three-band indices from MSI data, we built a few inversion models in an attempt to produce the regional salinity maps. Different algorithms including Pearson correlation coefficient method (PCC), variable importance in projection (VIP), Gray relational analysis (GRA), and random forest (RF) were applied for variable selection. The results suggest that both the newly proposed normalized difference index (NDI) (B12 − B7) / (B12 + B7) and three-band index (TBI4) (B12 − B3) / (B3 − B11) show a better correlation with validation data and could be applied to estimate the soil salinity in the Ebinur Lake region. The established models were validated using the remaining 44 independent ground-based measurements. The RF-PLSR model performed the best across the five models with R2V, RMSEV, and RPD of 0.92, 7.58 dS m−1, and 2.36, respectively. The result from this model was then used to map the soil salinity over the study area. Our analyses suggest that soil salinization changes quite significantly in different seasons. Specifically, soil salinity in the dry season was higher than in the wet season, mostly in the lake area and nearby shores. We contend that the results from the study will be useful for soil salinization monitoring and land reclamation in arid or semi-arid regions outside the current study area.
•The introduction of red-edge bands can enhance the sensitivities of the indices to soil salinity.•Three-band index (B12 − B3) / (B3 − B11) shows a best correlation (r = 0.544) with measured EC.•RF-PLSR model was proved a suitable method for soil salinity estimating and mapping.•The study shows a large variability in soil salinity in dry and wet seasons.
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