Biogeochemical Activity Research Articles

Upwelling induced changes in the abundance and community structure of archaea and bacteria in a recurring mud bank along the southwest coast of India

The present study reports the influence of upwelling on the abundance and community structure of archaea and bacteria in a mud bank formed along the coastal waters of Alappuzha, the southwest coast of India. The signatures of upwelling were observed with the onset of southwest monsoon, characterized by a decrease in sea surface temperature and dissolved oxygen in bottom waters and increase in salinity. Nitrite, nitrate, and phosphate showed a significant increase during upwelling compared to pre-upwelling conditions. There were no significant differences in the abundance of archaea across seasons (pre- and during upwelling conditions) and regions (Station S1, inside and Station S2, outside the mud bank), while the bacterial abundance showed a six-fold increase for S1 and four-fold increase for S2 during upwelling. The PCR–DGGE results show the existence of a transient population of archaea and bacteria in the mud bank region during upwelling. The step up multiple regression models could explain 66.5% and 56.3% of the temporal variations in archaeal and 96.5% and 53.63% in bacterial distribution inside and outside of mud bank respectively, at pre-upwelling conditions. About 67% of the temporal variations in the distribution of archaea and 41.4% in bacteria inside and 49.9% in bacteria outside of mud bank during upwelling conditions could be explained by the same model. The temporal variation in the distribution of archaea outside mud bank during upwelling conditions could not be explained by the present regression model. Our studies indicate that the upwelling induces changes in the abundance and community structure of bacteria in the mudbank, which are modulated by the interactive effects of hydrographic variables. Further studies to unravel the interactive effect of hydrographic variables on the biogeochemical activities of microorganisms would be appreciated.

Isotope Channelomics of Chemoautotroph as the Predictor and Regulator of the Metal Deposit formation and the Weathering Factor

Chemoautotrophic and lithotrophic microorganisms are known to participate in the deposit formation and the rock weathering, but the results of such chemoautotroph-mediated biogeochemical activity and mass transfer strongly differ depending on the ionic composition of the medium, the salt conductivity effects and the Pourbaix diagrams of their medium, as well as on some other physico-chemical parameters which are often not considered as the active external factors for the sake of simplicity.

Evaluating the reliability of time series analysis to estimate variable riparian travel times by numerical groundwater modelling

AbstractThe transition zones between rivers and adjacent riparian aquifers are locations of high biogeochemical activities that contribute to a removal of potentially hazardous substances in the aquatic system. The potential of the removal processes depends highly on subsurface water travel times, which can be determined by using the propagation of electrical conductivity (EC) signal from the river into the riparian aquifer. Although this method has been applied and verified in many studies, we observe possible limitations for the usage of EC fluctuation analysis. Our findings are based on EC time series analyses during storm events and artificial hydropeaks induced by watermill operations. Travel times derived by cross‐correlation analysis were compared with travel times calculated based on backward particle tracking of a calibrated transient numerical groundwater flow model. The cross‐correlation method produced only reasonable travel times for the artificial hydropeaks. In contrast, cross‐correlation analysis of the EC data during natural storm events resulted in implausibly negative or unrealistically low travel times for the bulk of the data sets. We conclude that the reason for this behaviour is, first, the low EC contrast between river and groundwater in connection with a strong damping of the infiltrating river EC signal into the subsurface during storm events. Second, the existence of old and less‐mineralized riparian water between the river and the monitoring well resulted in bank‐storage‐driven EC breakthrough curves with earlier arrival times and the subsequent estimation of implausible riparian travel times.

The influence of hyporheic upwelling fluxes on inorganic nitrogen concentrations in the pore water of the Weihe River

Hyporheic zone is an important region of nitrogen removal in river systems. Hyporheic exchange generally leads to heterogeneous redox environments, which are conducive to nitrogen transformation. This study seeks to determine the influence of hyporheic upwelling fluxes on inorganic nitrogen (NH4+, NO3−, and NO2−) concentrations in the sediment pore water of the Weihe River, China. The patterns and magnitudes of hyporheic water exchange on 12 August 2016 were derived by a one-dimensional heat transport model, and inorganic nitrogen concentrations in the pore water, surface water, and groundwater were obtained. The results indicated that hyporheic water exchange was characterized by upwelling at each point during the test period. Moreover, NH4+ dominated the hyporheic zone from 0 to 45 cm, likely due to organic nitrogen mineralization. Additionally, a non-linear relationship was observed between NH4+ concentrations and upwelling fluxes. This relationship was derived by analyzing the effect of upwelling on biogeochemical activity and nitrogen transformation. Notably, increasing upwelling fluxes less than 400 mm/d resulted in high NH4+ concentrations, whereas fluxes exceeding 400 mm/d led to low NH4+ concentrations. Overall, the variations in inorganic nitrogen associated with hyporheic water exchange are of great importance for controlling nitrogen pollution and maintaining sustainable health in river systems.

Evaluation of heavy metal pollution in bogs of Tomsk region on change in biogeochemical activity of ericaceous shrubs

The article discusses the change in biogeochemical activity of plant species in bogs under the influence of various types of human impact (roads, cities, drainage of mires, fire). It has been established that ericaceous shrubs, depending on the species, react with varying degrees of intensity to anthropogenic influences. The biogeochemical activity of species increased by 2.5 to 4.8 times in polluted sites.

Mineralogical and geochemical variation in stream sediments impacted by acid mine drainage is related to hydro-geomorphic setting

Acid mine drainage (AMD) discharge has severe, long lasting impacts on water quality and stream ecology in affected watersheds due in part to the dynamic relationship between toxic metals (e.g. Al, Mn, and Cu) and Fe(III) oxy-hydroxides. Localized areas of biogeochemical activity that can mediate mineralogical transformation changes and cause metal release are potentially linked to stream geomorphology. This relationship has not been previously considered with respect to potential longitudinal variation within an impacted stream. The current work aims to determine how Fe(III) (oxy)-hydroxide speciation and distribution, and pore water chemistry in an AMD-impacted streambed, are affected by the presence of two geomorphic structures (a debris dam and step-pool sequence) in an Ohio watershed impacted by historical coal mining. In terms of solid phase mineralogy and geochemistry, in both the tributary and main stem, goethite was the dominant Fe-bearing phase throughout the AMD deposit depth in cores taken upstream of the geomorphic structures, whereas poorly-crystalline phases dominated downstream of the structures, despite the presence of Fe in the reducible fraction. The concentrations and distribution of extractable Al, Mn, and Cu were also different upstream versus downstream of each structure. Pore water Fe and Mn concentrations were higher downstream of the structures than upstream. Strong downward hydraulic gradients were present above the debris dam and in step-pool 1, whereas weaker upward hydraulic gradients were present below the debris dam and in step-pool 2. This work highlights that AMD deposit speciation and distribution, and pore water chemistry, are not spatially uniform within stream reaches, potentially as a result of groundwater-stream exchange-facilitated interactions in the presence of AMD-derived materials.

The impact of Sumy TPP on the environment of surrounding area

The purpose of the work is to determine the influence of thermal power plant on atmospheric air and soil and the study of heavy metals migration in environmental components.The estimation of the influence of Sumy TPP on the environment condition of the surrounding territories of Sumy during the income of pollutants with gas emissions and filtration from the zone of aeration and ash and slug dump is presented. For studies of the impact of the TPP on the adjacent territory was organized a network of observation points in the zone of influence the Sumy TPP. The assessment of atmospheric air pollution was carried out by studying the snow cover. Complex estimation of the pollution of adjacent territories to the thermal power plant was carried out using the total pollution indexSamples of snow cover, soil and vegetation were sampled, and tested for the content of heavy metals. An assessment was made of the pollution of snow cover and soils by the total pollution index and for the grass pollution by the coefficient of biogeochemical activity. Studies have shown that the level of snow cover pollution in the aeration zone of Sumy TPP is low. The level of soil contamination in the aeration zone of Sumy TPP is low, and the soils in the ash and slug dump zone: for the upper horizon are high, for the lower - medium, indicating the complex impact of atmospheric air pollution and the migration of substances from the body of the ash dip. The study of the most common types of grass Taracxacum officinale and Elytrigia repens showed the ways of migration of heavy metals and allowed to recommend these plants for bioindication of soil contamination by heavy metals. The assessment of the pollution of territories adjacent to the thermal power plant showed that the activity of Sumy TPP leads to increasing of heavy metals concentrations in environment.

Microbial Reduction of Fe(III) and SO42- and Associated Microbial Communities in the Alluvial Aquifer Groundwater and Sediments.

Agricultural demands continuously increased use of groundwater, causing drawdown of water table and need of artificial recharge using adjacent stream waters. River water intrusion into groundwater can alter the geochemical and microbiological characteristics in the aquifer and subsurface. In an effort to investigate the subsurface biogeochemical activities before operation of artificial recharge at the test site, established at the bank of Nakdong River, Changwon, South Korea, organic carbon transported from river water to groundwater was mimicked and the effect on the indigenous microbial communities was investigated with the microcosm incubations of the groundwater and subsurface sediments. Laboratory incubations indicated microbial reduction of Fe(III) and sulfate. Next-generation Illumina MiSeq sequences of V4 region of 16S rRNA gene provided that the shifts of microbial taxa to Fe(III)-reducing and/or sulfate-reducing microorganisms such as Geobacter, Albidiferax, Desulfocapsa, Desulfuromonas, and Desulfovibrio were in good correlation with the sequential flourishment of microbial reduction of Fe(III) and sulfate as the incubations progressed. This suggests the potential role of dissolved organic carbons migrated with the river water into groundwater in the managed aquifer recharge system on the indigenous microbial community composition and following alterations of subsurface biogeochemistry and microbial metabolic activities.

Application of process-based eco-hydrological model to broader northern Eurasia wetlands through coordinate transformation

Wetlands impact on the hydrological cycle, material transport, and biogeochemical processes, and they are indispensable habitats for valuable species. In the present study, the process-based National Integrated Catchment-based Eco-hydrology (NICE) model, which includes complex interactions between hydrologic, geomorphic, and ecological processes, was extended to incorporate coordinate transformation from rectangular coordinate to longitude–latitude coordinate system applicable to continental scale and the higher latitude region by implementing a map factor and a non-uniform grid. This revised model was applied to two different wetlands of northern Eurasia (West Siberian Lowland, and Hokkaido Island in Japan) to evaluate eco-hydrological processes in the higher latitude region. The model reproduced qualitatively the heterogeneous distribution of groundwater level in the flat region of both wetlands, and revealed the connectivity between groundwater and inundated flow in the flat region of the wetlands. This result also indicates the effectiveness of hypothesis that horizontal transport component is predominant as a first approximation. This new simulation system would be effective as one of the methods to expand a grid-based model to a broader area or the higher latitude region, and also would play an important role in the further understanding of biogeochemical activity in the higher latitude region along terrestrial–aquatic continuum in continental scale.

The concurrent use of novel soil surface microclimate measurements to evaluate CO2 pulses in biocrusted interspaces in a cool desert ecosystem

Carbon cycling associated with biological soil crusts, which occupy interspaces between vascular plants in drylands globally, may be an important part of the coupled climate-carbon cycle of the Earth system. A major challenge to understanding CO2 fluxes in these systems is that much of the biotic and biogeochemical activity occurs in the upper few mm of the soil surface layer (i.e., the ‘mantle of fertility’), which exhibits highly dynamic and difficult to measure temperature and moisture fluctuations. Here, we report a multi-sensor approach to simultaneously measuring temperature and moisture of this biocrust surface layer (0–2 mm), and the deeper soil profile, concurrent with automated measurement of surface soil CO2 effluxes. Our results illuminate robust relationships between biocrust water content and field CO2 pulses that have previously been difficult to detect and explain. All observed CO2 pulses over the measurement period corresponded to surface wetting events, including when the wetting events did not penetrate into the soil below the biocrust layer (0–2 mm). The variability of temperature and moisture of the biocrust surface layer was much greater than even in the 0–5 cm layer of the soil beneath the biocrust, or deeper in the soil profile. We therefore suggest that coupling surface measurements of biocrust moisture and temperature to automated CO2 flux measurements may greatly improve our understanding of the climatic sensitivity of carbon cycling in biocrusted interspaces in our study region, and that this method may be globally relevant and applicable.

Arctic shelves as platforms for biogeochemical activity: Nitrogen and carbon transformations in the Chukchi Sea, Alaska

Continental shelves comprise <5% of global ocean area but may account for a disproportionate 30% of primary production, 80% of organic matter burial, and >50% of marine denitrification. The Hanna Shoal region, part of the continental shelf system in the northeast Chukchi Sea, Alaska, is recognized for its high biodiversity and productivity. We investigated the role of sediments in organic matter decomposition and nutrient cycling at five stations on the shallow Hanna Shoal. In particular, we asked (1) how much sediment organic matter is remineralized in the Chukchi Sea, and what factors drive this degradation, (2) do sediments function as a net source for fixed nitrogen (thus fueling primary production in the overlying water), or as a net sink for fixed nitrogen (thereby removing it from the system), and (3) what is the balance between sediment NH4+ uptake and regeneration, and what factors drive NH4+ cycling? We conducted dark sediment core incubations to measure sediment O2 consumption, net N2 and nutrient (NH4+, NO3-, NO2-, PO43-) fluxes, and rates of sediment NH4+ cycling, including uptake and regeneration. Rates of sediment O2 consumption and NH4+ and PO43- efflux suggest that high organic matter remineralization rates occurred in these cold (−2°C) sediments. We estimated that total organic carbon remineralization accounted for 20–57% of summer export production measured on the Chukchi Shelf. Net N2 release was the dominant nitrogen flux, indicating that sediments acted as a net sink for bioavailable nitrogen via denitrification. Organic carbon remineralization via denitrification accounted for 6–12% of summer export production, which made up ~25% of the total organic carbon oxidized in Hanna Shoal sediments. These shallow, productive Arctic shelves are “hotspots” for organic matter remineralization.

An approach for the identification of exemplar sites for scaling up targeted field observations of benthic biogeochemistry in heterogeneous environments

Continental shelf sediments are globally important for biogeochemical activity. Quantification of shelf-scale stocks and fluxes of carbon and nutrients requires the extrapolation of observations made at limited points in space and time. The procedure for selecting exemplar sites to form the basis of this up-scaling is discussed in relation to a UK-funded research programme investigating biogeochemistry in shelf seas. A three-step selection process is proposed in which (1) a target area representative of UK shelf sediment heterogeneity is selected, (2) the target area is assessed for spatial heterogeneity in sediment and habitat type, bed and water column structure and hydrodynamic forcing, and (3) study sites are selected within this target area encompassing the range of spatial heterogeneity required to address key scientific questions regarding shelf scale biogeochemistry, and minimise confounding variables. This led to the selection of four sites within the Celtic Sea that are significantly different in terms of their sediment, bed structure, and macrofaunal, meiofaunal and microbial community structures and diversity, but have minimal variations in water depth, tidal and wave magnitudes and directions, temperature and salinity. They form the basis of a research cruise programme of observation, sampling and experimentation encompassing the spring bloom cycle. Typical variation in key biogeochemical, sediment, biological and hydrodynamic parameters over a pre to post bloom period are presented, with a discussion of anthropogenic influences in the region. This methodology ensures the best likelihood of site-specific work being useful for up-scaling activities, increasing our understanding of benthic biogeochemistry at the UK-shelf scale.

Spatial and seasonal distributions of frontal activity over the French continental shelf in the Bay of Biscay

The frontal activity in coastal regions remains a research field where a large number of open questions needs to be addressed to quantify the potential impact of these processes on dependent systems (e.g. biogeochemical activity). Spatial and seasonal distributions of Sea Surface Temperature (SST) fronts (∼1–100km) in the vicinity of main French rivers, Gironde and Loire, are explored over the continental shelf North of 45°N in the Bay of Biscay. A high resolution (1km spatial and daily temporal resolutions) dataset of 11years' (2003–2013) remotely sensed SST by MODIS sensor onboard Aqua and Terra satellites has been investigated and compared with coastal numerical model experiments. The detection and characterization fronts with fluctuating amplitudes is achieved through the Singularity Analysis (i.e. the process of calculating the degree of regularity or irregularity of a function at each point in a domain). Seasonality of frontal activity in the Bay of Biscay is then described based on the long-term satellite SST archive and coastal operational model simulations. The identified hot spots of higher frontal occurrences correspond on one hand to previously observed features (e.g. tidal fronts) but also reveal new features. These are investigated to identify fine-scale dynamical drivers. In winter, density fronts are prominent in a coastal strip where freshwater influence is important. In spring, this strip diminishes as plumes detach from the coast, while tidal fronts become apparent in other regions. In summer, tidal fronts in Ushant region and internal wave activity along the shelf break dominate. In autumn, coastal density fronts due to freshwater inputs reappear as these inputs increase, and reduced stratification causes a weakening of the Ushant and shelf break fronts. Additional information and an effort to dynamically interpret these fronts, based on a systematic investigation of the whole seasonal cycle and including modeling insights from coastal operational oceanography, complement the description of frontal activity in the Bay of Biscay.

The Role of Organic Matter in the Formation of High-Grade Al Deposits of the Dopolan Karst Type Bauxite, Iran: Mineralogy, Geochemistry, and Sulfur Isotope Data

Mineralogical and geochemical analyses of the Dopolan karstic bauxite ore were performed to identify the characteristics of four bauxite horizons, which comprise from top to bottom, bauxitic kaolinite, diaspore-rich bauxite, clay-rich bauxite, and pyrite-rich bauxite. Diaspore, kaolinite, and pyrite are the main minerals; böhmite, muscovite, rutile, and anatase are the accessory minerals. The main minerals of the Dopolan bauxite deposit indicate slightly acidic to alkaline reducing conditions during bauxitization. Immobile elements (Nb, Ta, Zr, Hf, and rare earth elements) are enriched in the diaspore-rich horizon, which also has the highest alumina content, whereas redox sensitive elements (e.g., Cr, Cu, Ni, Pb, Zn, Ag, U, and V) are enriched in the lowest horizon of pyrite-rich bauxite. The presence of a high content of organic matter was identified in different horizons of bauxitic ore from wet chemistry. The presence of organic matter favored Fe bioleaching, which resulted in Al enrichment and the formation of diaspore-rich bauxite. The leached Fe2+ reacted with the hydrogen sulfur that was produced due to bacterial metabolism, resulting in the formation of the pyrite-rich horizon towards the bottom of the Dopolan bauxite horizons. Biogeochemical activity in the Dopolan bauxitic ore was deduced from the reducing environment of bauxitization, and the deposition of framboidal and cubic or cubic/octahedral pyrite crystals, with large negative values of δ34S of pyrite (−10‰ to −34‰) and preserved fossil cells of microorganisms.

The contribution of component variation and phytoplankton growth to the distribution variation of chromophoric dissolved organic matter content in a mid-latitude subtropical drinking water source reservoir for two different seasons.

The distribution variation in chromophoric dissolved organic matter (CDOM) content in mid-latitude subtropical drinking water source reservoirs (MDWSRs) has great significance in the security of aquatic environments and human health. CDOM distribution is heavily influenced by biogeochemical processes and anthropogenic activity. However, little is known regarding the impact of component variation and phytoplankton growth on CDOM distribution variation in MDWSR. Therefore, samples were collected from a representative MDWSR (the Shanzai Reservoir) for analysis. CDOM absorption and fluorescence coupling with parallel factor analysis were measured and calculated. The results indicated that only two CDOM components were found in the surface water of Shanzai Reservoir, fulvic acid, and high-excitation tryptophan, originating from terrestrial and autochthonous sources, respectively. The types of components did not change with the season. The average molecular weight of CDOM increased in proportion to its fulvic acid content. The distribution variation in CDOM content mainly resulted from the variation in two CDOM components in summer and from high-excitation tryptophan in winter. Phytoplankton growth strongly influenced the distribution variation of CDOM content in summer; the metabolic processes of Cyanobacteria and Bacillariophyta consumed fulvic acid, while that of Cryptophyta produced high-excitation tryptophan.

Response of phytoplankton and enhanced biogeochemical activity to an episodic typhoon event in the coastal waters of Japan

Daily field surveys were conducted at a coastal-shelf station in Sagami Bay, Japan after the passage of typhoon Malou in 2010 to evaluate the after-effect of a typhoon passage on the physical-chemical environment, phytoplankton bloom formation and microbial processes within and below the euphotic layer. The passage of Malou induced an abrupt decrease in salinity and increased loading of nutrients to the euphotic layer. Dinoflagellates dominated the phytoplankton community at the surface, whereas diatoms dominated below the surface just after the passage of Malou. Four days later, the dominant dinoflagellate taxa at the surface changed from Protoperidinium spp. to Prorocentrum spp. and Ceratium spp., indicating a dinoflagellate community succession from heterotrophic to autotrophic functional groups. Five days after passage, the dominant phytoplankton taxa shifted from dinoflagellates to diatom groups of Chaetoceros spp. and Cerataulina spp. throughout the water column. Below the euphotic layer, there were increases in diatom frustules, mainly composed of Chaetoceros spp. and Cerataulina spp., bacterial abundance and NH4+ concentrations. Diatom carbon biomass contributed to approximately half of particulate organic carbon (POC) below the euphotic layer, suggesting a significant contribution of diatoms to POC sinking flux after the passage of a typhoon. Bacterial abundance was positively correlated to both phaeopigment concentrations (p < 0.01) and NH4+ concentrations (p < 0.01), suggesting bacterial growth was associated with zooplankton grazing and remineralization of NH4+. The results suggest that the passage of a typhoon could significantly affect biogeochemical activities within and below the euphotic layer in temperate coastal waters.

Scaled-dependence and seasonal variations of carbon cycle through development of an advanced eco-hydrologic and biogeochemical coupling model

Recent research has shown that inland water may play some role in carbon cycling, although the extent of its contribution has remained uncertain due to the limited amount of reliable data available. In this study, the author developed a new model coupling original eco-hydrology model and five biogeochemical cycle models (NICE-BGC), which incorporates complex coupling of hydrologic-carbon cycle in terrestrial-aquatic linkages and interplay between inorganic and organic carbon during the whole process of carbon cycling. This improved model was applied to Eurasian wetland by using three types of river network data to evaluate scaled-dependence of carbon cycle there. The model improved accuracy of low pH and alkalinity and DOC flux increase in the wetland in the northern part of study area with the finer river network data. The model showed that the difference in the carbon flux between different river network data becomes larger in downstream region, and that this difference is more predominant in the stream channel than in the hillslope, implying the importance of dry watercourses and intermittent rivers. The model was then extended to the global scale to evaluate seasonal variations of carbon cycle both in hillslope and river. The result extended from the previous studies to clarify that; (i) soil temperature has some effect on the carbon transport by biologic process responsible for carbon production in addition to clear relationship between runoff and carbon export, (ii) the high runoff during April to June and the large DOC and POC flux (about 458.38±474.41 TgC/season and 239.25±289.90 TgC/season) during January to March in hillslope, (iii) CO2 evasion becomes maximum about 294.66±93.80 TgC/season during January to June primarily affected by Amazon River, and (iv) sediment storage is larger and takes about 76.80±13.19 TgC/season during July to September particularly in Asian and North American rivers. This scaled-dependence and seasonal variations of carbon cycle helps to bridge the gap between carbon transport to the longitudinal direction and gas emission to the atmosphere in previous researches. This simulation system would also help for the further field observations, remotely-sensed imagery, and satellite datasets, and play important role in improvement in biogeochemical activity in spatio-temporal hot spots.

Deterministic influences exceed dispersal effects on hydrologically-connected microbiomes.

Subsurface groundwater-surface water mixing zones (hyporheic zones) have enhanced biogeochemical activity, but assembly processes governing subsurface microbiomes remain a critical uncertainty in understanding hyporheic biogeochemistry. To address this obstacle, we investigated (a) biogeographical patterns in attached and waterborne microbiomes across three hydrologically-connected, physicochemically-distinct zones (inland hyporheic, nearshore hyporheic and river); (b) assembly processes that generated these patterns; (c) groups of organisms that corresponded to deterministic changes in the environment; and (d) correlations between these groups and hyporheic metabolism. All microbiomes remained dissimilar through time, but consistent presence of similar taxa suggested dispersal and/or common selective pressures among zones. Further, we demonstrated a pronounced impact of deterministic assembly in all microbiomes as well as seasonal shifts from heterotrophic to autotrophic microorganisms associated with increases in groundwater discharge. The abundance of one statistical cluster of organisms increased with active biomass and respiration, revealing organisms that may strongly influence hyporheic biogeochemistry. Based on our results, we propose a conceptualization of hyporheic zone metabolism in which increased organic carbon concentrations during surface water intrusion support heterotrophy, which succumbs to autotrophy under groundwater discharge. These results provide new opportunities to enhance microbially-explicit ecosystem models describing hyporheic zone biogeochemistry and its influence over riverine ecosystem function.

Understanding controls on redox processes in floodplain sediments of the Upper Colorado River Basin

Floodplains, heavily used for water supplies, housing, agriculture, mining, and industry, are important repositories of organic carbon, nutrients, and metal contaminants. The accumulation and release of these species is often mediated by redox processes. Understanding the physicochemical, hydrological, and biogeochemical controls on the distribution and variability of sediment redox conditions is therefore critical to developing conceptual and numerical models of contaminant transport within floodplains. The Upper Colorado River Basin (UCRB) is impacted by former uranium and vanadium ore processing, resulting in contamination by V, Cr, Mn, As, Se, Mo and U. Previous authors have suggested that sediment redox activity occurring within organic carbon-enriched bodies located below the groundwater level may be regionally important to the maintenance and release of contaminant inventories, particularly uranium. To help assess this hypothesis, vertical distributions of Fe and S redox states and sulfide mineralogy were assessed in sediment cores from three floodplain sites spanning a 250km transect of the central UCRB.The results of this study support the hypothesis that organic-enriched reduced sediments are important zones of biogeochemical activity within UCRB floodplains. We found that the presence of organic carbon, together with pore saturation, are the key requirements for maintaining reducing conditions, which were dominated by sulfate-reduction products. Sediment texture was found to be of secondary importance and to moderate the response of the system to external forcing, such as oxidant diffusion. Consequently, fine-grain sediments are relatively resistant to oxidation in comparison to coarser-grained sediments. Exposure to oxidants consumes precipitated sulfides, with a disproportionate loss of mackinawite (FeS) as compared to the more stable pyrite. The accompanying loss of redox buffering capacity creates the potential for release of sequestered radionuclides and metals. Because of their redox reactivity and stores of metals, C, and N, organic-enriched sediments are likely to be important to nutrient and contaminant mobility within UCRB floodplain aquifers.

Accessing the Microbial Diversity of Sugarcane Fields from Gujjarwal Village, Ludhiana and their Molecular Identification

Soil is the richest ecosystem there is, as far as the diversity and populations of microorganisms is concerned. It is known that there could be over ten billion microbes per gram of soil, making soil the ideal ecosystem for mining different genes, ORFs etc. Microbial Diversity forms the lifeline of an ecosystem, interfering, regulating and participating in the biogeochemical activities therein. The present study was conducted to explore and assess the microbial community by culture dependent and independent approach, of sugarcane fields of Gujjarwal Village of Ludhiana. To study microbial diversity in sugarcane fields, a total of nine different colonies were isolated and differentiated based on their cell morphology and size. Biochemical characterizations lead to the identification of Enterobacter cloacae, Proteus mirabilis and Serratia marcescens. Molecular characterization was done by isolating soil DNA (GJSF DNA) and subjected to PCR amplification for identification via 16S rRNA gene analysis. BLAST analysis revealed presence of Serratia sp., uncultured bacterium clones SS-22C07, ep138, K-15-14-19, S127B31, L1A.11C01 and uncultured Enterobacteriaceae bacterium.