Upstream Freshwater and Terrestrial Sources Are Differentially Reflected in the Bacterial Community Structure along a Small Arctic River and Its Estuary.
ABSTRACT: Glacier melting and altered precipitation patterns influence Arctic freshwater and coastal ecosystems. Arctic rivers are central to Arctic water ecosystems by linking glacier meltwaters and precipitation with the ocean through transport of particulate matter and microorganisms. However, the impact of different water sources on the microbial communities in Arctic rivers and estuaries remains unknown. In this study we used 16S rRNA gene amplicon sequencing to assess a small river and its estuary on the Disko Island, West Greenland (69°N). Samples were taken in August when there is maximum precipitation and temperatures are high in the Disko Bay area. We describe the bacterial community through a river into the estuary, including communities originating in a glacier and a proglacial lake. Our results show that water from the glacier and lake transports distinct communities into the river in terms of diversity and community composition. Bacteria of terrestrial origin were among the dominating OTUs in the main river, while the glacier and lake supplied the river with water containing fewer terrestrial organisms. Also, more psychrophilic taxa were found in the community supplied by the lake. At the river mouth, the presence of dominant bacterial taxa from the lake and glacier was unnoticeable, but these taxa increased their abundances again further into the estuary. On average 23% of the estuary community consisted of indicator OTUs from different sites along the river. Environmental variables showed only weak correlations with community composition, suggesting that hydrology largely influences the observed patterns.
Project description:The Arctic is experiencing dramatic changes including increases in precipitation, glacial melt, and permafrost thaw, resulting in increasing freshwater runoff to coastal waters. During the melt season, terrestrial runoff delivers carbon- and nutrient-rich freshwater to Arctic coastal waters, with unknown consequences for the microbial communities that play a key role in determining the cycling and fate of terrestrial matter at the land-ocean interface. To determine the impacts of runoff on coastal microbial (bacteria and archaea) communities, we investigated changes in pelagic microbial community structure between the early (June) and late (August) melt season in 2018 in the Isfjorden system (Svalbard). Amplicon sequences of the 16S rRNA gene were generated from water column, river and sediment samples collected in Isfjorden along fjord transects from shallow river estuaries and glacier fronts to the outer fjord. Community shifts were investigated in relation to environmental gradients, and compared to river and marine sediment microbial communities. We identified strong temporal and spatial reorganizations in the structure and composition of microbial communities during the summer months in relation to environmental conditions. Microbial diversity patterns highlighted a reorganization from rich communities in June toward more even and less rich communities in August. In June, waters enriched in dissolved organic carbon (DOC) provided a niche for copiotrophic taxa including <i>Sulfitobacter</i> and <i>Octadecabacter</i>. In August, lower DOC concentrations and Atlantic water inflow coincided with a shift toward more cosmopolitan taxa usually associated with summer stratified periods (e.g., SAR11 Clade Ia), and prevalent oligotrophic marine clades (OM60, SAR92). Higher riverine inputs of dissolved inorganic nutrients and suspended particulate matter also contributed to spatial reorganizations of communities in August. Sentinel taxa of this late summer fjord environment included taxa from the class Verrucomicrobiae (<i>Roseibacillus</i>, <i>Luteolibacter</i>), potentially indicative of a higher fraction of particle-attached bacteria. This study highlights the ecological relevance of terrestrial runoff for Arctic coastal microbial communities and how its impacts on biogeochemical conditions may make these communities susceptible to climate change.
Project description:Sediment microbial communities from plain river networks exert different effects on pollutant transformation and migration in lake basins. In this study, we examined millions of Illumina reads (16S rRNA gene amplicons) to compare lake, lake wetland, and estuary bacterial communities through a technically consistent approach. Results showed that bacterial communities in the sampled lake sediments had the highest alpha-diversity (Group B), than in sampled lake wetland sediments and estuary sediments. Proteobacteria was the most abundant (more than 30%) phyla in all the sediments. The lake sediments had more Nitrospirae (1.63%-11.75%) and Acidobacteria (3.46%-10.21%) than the lake wetland and estuary sediments, and estuary sediments had a greater abundance of the phylum Firmicutes (mean of 22.30%). Statistical analysis (LEfSe) revealed that lake wetland sediments contained greater abundances of the class Anaerolineaceae, orders Xanthomonadales, Pseudomonadales, and genera Flavobacterium, Acinetobacter. The lake sediments had a distinct community of diverse primary producers, such as phylum Acidobacteria, order Ignavibacteriales, and families Nitrospiraceae, Hydrogenophilaceae. Total phosphorus and organic matter were the main factors influencing the bacterial communities in sediments from several parts of the lake wetland and river estuary (p < .05). The novel insights into basin pollution control in plain river networks may be obtained from microbial distribution in sediments from different basin regions.
Project description:The Maumee River is the primary source for nutrients fueling seasonal <i>Microcystis</i>-dominated blooms in western Lake Erie's open waters though such blooms in the river are infrequent. The river also serves as source water for multiple public water systems and a large food services facility in northwest Ohio, USA. On 20 September 2017, an unprecedented bloom was reported in the Maumee River estuary within the Toledo metropolitan area, which triggered a recreational water advisory. Here we (1) explore physical drivers likely contributing to the bloom's occurrence, and (2) describe the toxin concentration and bacterioplankton taxonomic composition. A historical analysis using ten-years of seasonal river discharge, water level, and local wind data identified two instances when high-retention conditions occurred over ≥10 days in the Maumee River estuary: in 2016 and during the 2017 bloom. Observation by remote sensing imagery supported the advection of cyanobacterial cells into the estuary from the lake during 2017 and the lack of an estuary bloom in 2016 due to a weak cyanobacterial bloom in the lake. A rapid-response survey during the 2017 bloom determined levels of the cyanotoxins, specifically microcystins, in excess of recreational contact limits at sites within the lower 20 km of the river while amplicon sequencing found these sites were dominated by <i>Microcystis</i>. These results highlight the need to broaden our understanding of physical drivers of cyanobacterial blooms within the interface between riverine and lacustrine systems, particularly as such blooms are expected to become more prominent in response to a changing climate.
Project description:Future increases in the intensity of hurricanes and El Niño periods predicted by climate change models have focused attention on their role in stimulating harmful algal blooms (HABs). A series of hurricanes that recently impacted Florida (USA) provided a unique opportunity to explore the relationships between hurricanes, El Niño and HABs in two Florida estuaries subject to repeated intense ecosystem disruptive HABs, the Indian River Lagoon and the St. Lucie Estuary. The roles that hurricanes and El Niño play in contributing to HAB events are examined in the context of key structural and functional features of each estuary and their watersheds, including morphology, water residence time and hydrology, such as the influence of Lake Okeechobee discharges into the St. Lucie Estuary. The most direct impact was the increase in rainfall associated with hurricanes and El Niño, resulting in enhanced nutrient loads which drive HABs in the Indian River Lagoon and Lake Okeechobee. Major HABs in Lake Okeechobee also present an indirect threat of freshwater HAB blooms in the St. Lucie Estuary via mandated discharges from the lake into the estuary during high rainfall periods. Conversely, during the absence of HABs in Lake Okeechobee, short water residence times produced by discharges into the St. Lucie Estuary can result in lower bloom intensities.
Project description:Sediment bacterial communities are critical for the circulation of nutrients in lake ecosystems. However, the bacterial community function and co-occurrence models of lakes have not been studied in depth. In this study, we observed significant seasonal changes and non-significant spatial changes in the beta diversity and community structure of sediment bacteria in Lake Chaohu. Through linear discriminant analysis effect size (LEfSe), we observed that certain taxa (from phylum to genus) have consistent enrichment between seasons. The sudden appearance of a Firmicutes population in spring samples from the Zhaohe River, an estuary of Lake Chaohu, and the dominance of Firmicutes populations in other regions suggested that exogenous pollution and environmental induction strongly impacted the assembly of bacterial communities in the sediments. Several taxa that serve as intermediate centers in Co-occurrence network analysis (i.e., Pedosphaeraceae, Phycisphaeraceae, Anaerolineaceae, and Geobacteraceae) may play an important role in sediments. Furthermore, compared with previous studies of plants and animals, the results of our study suggest that various organisms, including microorganisms, are resistant to environmental changes and/or exogenous invasions, allowing them to maintain their community structure.
Project description:Global climate change is causing a wastage of glaciers and threatening biodiversity in glacier-fed ecosystems. The high turbidity typically found in those ecosystems, which is caused by inorganic particles and result of the erosive activity of glaciers is a key environmental factor influencing temperature and light availability, as well as other factors in the water column. Once these lakes loose hydrological connectivity to glaciers and turn clear, the accompanying environmental changes could represent a potential bottleneck for the established local diversity with yet unknown functional consequences. Here, we study three lakes situated along a turbidity gradient as well as one clear unconnected lake and evaluate seasonal changes in their bacterial community composition and diversity. Further, we assess potential consequences for community functioning. Glacier runoff represented a diverse source community for the lakes and several taxa were able to colonize downstream turbid habitats, although they were not found in the clear lake. Operational taxonomic unit-based alpha diversity and phylogenetic diversity decreased along the turbidity gradient, but metabolic functional diversity was negatively related to turbidity. No evidence for multifunctional redundancy, which may allow communities to maintain functioning upon alterations in diversity, was found. Our study gives a first view on how glacier-fed lake bacterial communities are affected by the melting of glaciers and indicates that diversity and community composition significantly change when hydrological connectivity to the glacier is lost and lakes turn clear.
Project description:The examination and statistical analysis of loricate choanoflagellate material collected from Greenland waters during the period 1988-1998 represents a de facto baseline study of heterotrophic nanoflagellates from the Atlantic Arctic Region. The geographic sites sampled are Disko Bay (West Greenland) and the high-arctic North-East Water (NEW) and North Water (NOW) polynya. The analyses encompass close to 50 taxa. Some of these are described as new species, i.e. Acanthocorbis glacialis, A. reticulata and Diaphanoeca dilatanda. Two distinct clusters of species that are separated in time and space occur at all three sampling sites. A PCA analysis of NEW and NOW data points to that one community is linked to e.g. an early season high nutrient and low phytoplankton biomass scenario, whereas the other is predominant when nutrient levels are exhausted and the phytoplankton biomass high or declining. The material additionally allows for a comprehensive examination of e.g. the Cosmoeca ventricosa morphological variability encountered, as well as puts on record bimodal size variability within a number of species.
Project description:Bacterioplankton communities are deeply diverse and highly variable across space and time, but several recent studies demonstrate repeatable and predictable patterns in this diversity. We expanded on previous studies by determining patterns of variability in both individual taxa and bacterial communities across coastal environmental gradients. We surveyed bacterioplankton diversity across the Columbia River coastal margin, USA, using amplicon pyrosequencing of 16S rRNA genes from 596 water samples collected from 2007 to 2010. Our results showed seasonal shifts and annual reassembly of bacterioplankton communities in the freshwater-influenced Columbia River, estuary, and plume, and identified indicator taxa, including species from freshwater SAR11, Oceanospirillales, and Flavobacteria groups, that characterize the changing seasonal conditions in these environments. In the river and estuary, Actinobacteria and Betaproteobacteria indicator taxa correlated strongly with seasonal fluctuations in particulate organic carbon (?=-0.664) and residence time (?=0.512), respectively. In contrast, seasonal change in communities was not detected in the coastal ocean and varied more with the spatial variability of environmental factors including temperature and dissolved oxygen. Indicator taxa of coastal ocean environments included SAR406 and SUP05 taxa from the deep ocean, and Prochlorococcus and SAR11 taxa from the upper water column. We found that in the Columbia River coastal margin, freshwater-influenced environments were consistent and predictable, whereas coastal ocean community variability was difficult to interpret due to complex physical conditions. This study moves beyond beta-diversity patterns to focus on the occurrence of specific taxa and lends insight into the potential ecological roles these taxa have in coastal ocean environments.
Project description:Glacier retreat as a consequence of climate change influences freshwater ecosystems in manifold ways, yet the physical and chemical bases of these effects are poorly studied. Here, we characterize how water temperature differs between alpine lakes with and without direct glacier influence on seasonal and diurnal timescales. Using high temporal resolution monitoring of temperature in 4 lakes located in a catchment influenced by glacier retreat, we reported unexpectedly high surface temperatures, even in proglacial lakes located 2600 m a.s.l. Cold glacier meltwater and low nighttime air temperatures caused a distinct diurnal pattern of water temperature in the water column of glacier-influenced lakes. Precipitation onto glacier surfaces apparently leads to rapid cooling of the glacier-fed lakes and disrupts the thermal stratification with several mixing events during the summer. Taken together, these mechanisms contribute to the unique seasonal and diurnal dynamics of glacier-influenced lakes that contrast with the typical dimictic pattern of clear alpine lakes and represent an example of discontinuous cold polymictic lake type. This work contributes to the basic description of how climate and meteorology affect the physical properties of an increasingly common lake type.
Project description:Water quality is impacted significantly by urbanization. The delivery of increased nutrient loads to waterways is a primary characteristic of this land use change. Despite the recognized effects of nutrient loading on aquatic systems, the influence of urbanization on the bacterial community composition of these systems is not understood. We used massively-parallel sequencing of bacterial 16S rRNA genes to examine the bacterial assemblages in transect samples spanning the heavily urbanized estuary of Milwaukee, WI to the relatively un-impacted waters of Lake Michigan. With this approach, we found that genera and lineages common to freshwater lake epilimnia were common and abundant in both the high nutrient, urban-impacted waterways, and the low nutrient Lake Michigan. Although the two environments harbored many taxa in common, we identified a significant change in the community assemblage across the urban-influence gradient, and three distinct community features drove this change. First, we found the urban-influenced waterways harbored significantly greater bacterial richness and diversity than Lake Michigan (i.e., taxa augmentation). Second, we identified a shift in the relative abundance among common freshwater lineages, where acI, acTH1, Algoriphagus and LD12, had decreased representation and Limnohabitans, Polynucleobacter, and Rhodobacter had increased representation in the urban estuary. Third, by oligotyping 18 common freshwater genera/lineages, we found that oligotypes (highly resolved sequence clusters) within many of these genera/lineages had opposite preferences for the two environments. With these data, we suggest many of the defined cosmopolitan freshwater genera/lineages contain both oligotroph and more copiotroph species or populations, promoting the idea that within-genus lifestyle specialization, in addition to shifts in the dominance among core taxa and taxa augmentation, drive bacterial community change in urbanized waters.