Browsing by Author "Findlay, Robert H."

Now showing 1 - 6 of 6
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    Direct and Indirect Influence of Parental Bedrock on Streambed Microbial Community Structure in Forested Streams
    (American Society of Microbiology, 2011) Mosher, Jennifer J.; Findlay, Robert H.; University of Alabama Tuscaloosa
    A correlative study was performed to determine if variation in streambed microbial community structure in low-order forested streams can be directly or indirectly linked to the chemical nature of the parental bedrock of the environments through which the streams flow. Total microbial and photosynthetic biomass (phospholipid phosphate [PLP] and chlorophyll a), community structure (phospholipid fatty acid analysis), and physical and chemical parameters were measured in six streams, three located in sandstone and three in limestone regions of the Bankhead National Forest in northern Alabama. Although stream water flowing through the two different bedrock types differed significantly in chemical composition, there were no significant differences in total microbial and photosynthetic biomass in the sediments. In contrast, sedimentary microbial community structure differed between the bedrock types and was significantly correlated with stream water ion concentrations. A pattern of seasonal variation in microbial community structure was also observed. Further statistical analysis indicated dissolved organic matter (DOM) quality, which was previously shown to be influenced by geological variation, correlated with variation in bacterial community structure. These results indicate that the geology of underlying bedrock influences benthic microbial communities directly via changes in water chemistry and also indirectly via stream water DOM quality.
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    High resolution molecular characterization of photochemical and microbial transformation of dissolved organic matter in temperate streams of different watershed land use
    (University of Alabama Libraries, 2014) Li, Xiaping; Lu, Yuehan; Zheng, Chunmiao; University of Alabama Tuscaloosa
    The objective of the present study was to provide better understanding of the effects of watershed land use on molecular composition of streamwater DOM and molecular transformations associated with photochemical and microbial processing of DOM. We compared DOM from headwater streams draining forest-dominated watersheds (FW) and pasture-dominated watersheds (PW) in the lower Chesapeake Bay region (Virginia, USA). Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry analysis was conducted on streamwater DOM prior to and after laboratory incubations: 1) bacteria-only incubations; 2) light-only incubations; and 3) combined light+bacterial incubations. Results showed that DOM in FW streams and PW streams differed in molecular characteristics--the former was characterized by greater structural complexity and aromaticity, higher proportions of condensed aromatic molecules and black carbon-like components, while the latter was higher in the proportions of lipid-like components, protein-like components and aliphatic compounds. Relative to DOM from FW streams, DOM from PW streams was more reactive to bacterial transformation. Protein-like components, lipid-like components and unsaturated hydrocarbon-like components are primarily responsible for the changes associated with bacterial transformation of DOM. However, similar behavior was also observed for DOM in FW streams and PW streams under the influence of bacterial and photochemical processes. Bacterial transformation reduced the proportions of lipid-like components but increased the proportions of lignin-like components and carboxyl-rich alicyclic molecule-like components, indicating that lipid-like components was a bioreactive class while lignin-like components and carboxyl-rich alicyclic were resistant to bacterial processing. Photochemical processes, alone or combined with microbial alterations, increased the proportions of protein-like components, which may be due to the light stimulation of autochthonous production of protein-like components, and increased the relative abundance of carboxyl-rich alicyclic molecule-like components, which indicates the refractory nature of these molecules. Photochemical processes also significantly reduced the amount of dissolved black carbon-like components, which suggests dissolved black carbon was a photoreactive class, countering the conventional view that black carbon was an inter group in carbon cycle. Collectively, these findings suggest that human land use in upstream watersheds may lead to alterations to the molecular composition of streamwater DOM as well as to its behavior to photochemical and microbial processing.
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    Laboratory incubations of Macondo oil-derived hydrocarbons in Alabama salt marsh sediments and water
    (University of Alabama Libraries, 2013) Fields, Daniel; Lu, Yuehan; University of Alabama Tuscaloosa
    In order to better understand the impact of the BP Deepwater Horizon and future oil spills on the Gulf of Mexico coast this study assesses the variation of alkanes and polycyclic aromatic hydrocarbons (PAH) in coastal sediments and water. 500g of Sediment and water from Bayou La Batre, Alabama was spiked with 10g Macondo oil for a time series experiment with sampling points at 0, 6, 12, 24, 48, 168, and 336 hours. Sediment and water were also spiked with 0.2g, 2g, 10g, 20g and 50g Macondo oil and were incubated for 21 days for a concentration variation experiment. The composition and concentrations of alkanes and PAHs in the sediments and the concentrations of dissolved inorganic nitrogen and phosphorous and dissolved organic carbon were characterized. Results from the time series experiment show 54.6% total alkanes in sediments were lost within the first six hours and 71.5% were lost after 14 days. Total PAHs decreased by 90.1% within the first six hours and did not show apparent decreases afterwards. The loss of hydrocarbons in the sediments may be attributed to microbial degradation. Low molecular weight (≤ C17) alkanes were preferentially degraded over high molecular weight (> C17) alkanes during the first 24 hours, whereas normal alkanes were not preferentially degraded over isoprenoid alkanes. The high degradation rates of hydrocarbons in the first 12 hours were attributed to aerobic microbial degradation rates of hydrocarbons; the decreases in the loss rates after hour 12 were perhaps due to oxygen depletion in the microcosms. The oxygen depletion was supported by the elevated iron concentration in seawater after 168 hours that indicated anaerobic microbial respiration using Fe (III) as an electron acceptor. However, the concentration of dissolved nitrate and ammonium did not show evident patterns over the course of the incubation, providing no evidence that nitrate was used by microbes as an electron acceptor during anaerobic microbial respiration. Dissolved organic carbon (DOC) concentration continuously decreased until reaching the ambient seawater concentration, indicating an active microbial degradation of oil-derived hydrocarbons that were dissolved in the seawater. In the concentration variation experiment, sterilized controls with 0.2g and 20g of oil treatment had much higher concentrations of saturated alkanes in the sediments than corresponding non-sterilized microcosms with in situ microbial community left intact. However, the microcosms with 10g and 50g of oil treatment did not show reduced concentration of hydrocarbons in the sediments relative to their non-sterilized counterparts. Similarly, variable patterns appeared from the comparison of the dissolved organic carbon concentrations between non-sterilized microcosms vs. sterile microcosms treated with the same amount of oil. Therefore, data from the concentration variation experiment provided inconclusive evidence that the in situ microbial community degraded oil-derived alkanes in sediments and seawater of the microcosms.
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    Periphytic algae decouple fungal activity from leaf litter decomposition via negative priming
    (Wiley, 2019) Halvorson, Halvor M.; Barry, Jacob R.; Lodato, Matthew B.; Findlay, Robert H.; Francoeur, Steven N.; Kuehn, Kevin A.; University of Southern Mississippi; University of Alabama Tuscaloosa; Eastern Michigan University
    Well-documented in terrestrial settings, priming effects describe stimulated heterotrophic microbial activity and decomposition of recalcitrant carbon by additions of labile carbon. In aquatic settings, algae produce labile exudates which may elicit priming during organic matter decomposition, yet the directions and mechanisms of aquatic priming effects remain poorly tested. We tested algal-induced priming during decomposition of two leaf species of contrasting recalcitrance, Liriodendron tulipifera and Quercus nigra, in experimental streams under light or dark conditions. We measured litter-associated algal, bacterial, and fungal biomass and activity, stoichiometry, and litter decomposition rates over 43 days. Light increased algal biomass and production rates, in turn increasing bacterial abundance 141%-733% and fungal production rates 20%-157%. Incubations with a photosynthesis inhibitor established that algal activity directly stimulated fungal production rates in the short term. Algal-stimulated fungal production rates on both leaf species were not coupled to long-term increases in fungal biomass accrual or litter decomposition rates, which were 154%-157% and 164%-455% greater in the dark, respectively. The similar patterns on fast- vs. slow-decomposing L. tulipifera and Q. nigra, respectively, indicated that substrate recalcitrance may not mediate priming strength or direction. In this example of negative priming, periphytic algae decoupled fungal activity from decomposition, likely by providing labile carbon invested towards greater fungal growth and reproduction instead of recalcitrant carbon degradation. If common, algal-induced negative priming could stimulate heterotrophy reliant on labile carbon yet suppress decomposition of recalcitrant carbon, modifying energy and nutrients available to upper trophic levels and enhancing organic carbon storage or export in well-lit aquatic habitats.
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    Spatial Variability in Streambed Microbial Community Structure across Two Watersheds
    (American Society of Microbiology, 2021) Akinwole, Philips O.; Kan, Jinjun; Kaplan, Louis A.; Findlay, Robert H.; DePauw University; University of Alabama Tuscaloosa
    Both spatial and temporal variability are key attributes of sedimentary microbial communities, and while spatial effects on beta-diversity appear to dominate at larger distances, the character of spatial variability at finer scales remains poorly understood, especially for headwater stream communities. We investigated patterns of microbial community structure (MCS) in biofilms attached to streambed sediments from two watersheds across spatial scales spanning <1 m within a single stream to several hundred kilometers between watersheds. Analyses of phospholipid fatty acid (PLFA) profiles indicated that the variations in MCS were driven by increases in the relative abundance of microeukaryotic photoautotrophs and their contribution to total microbial biomass. Furthermore, streams within watersheds had similar MCS, underscoring watershed-level controls of microbial communities. Moreover, bacterial community structure assayed as either PCR-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprints or PLFA profiles edited to remove microeukaryotes indicated a distinct watershed-level biogeography. No distinct stream order-level distributions were identified, although DGGE analyses clearly indicated that there was greater variability in community structure among 1st-order streams than among 2nd- and 3rd-order streams. Longitudinal gradients in microbial biomass and structure showed that the greatest variations were associated with 1st-order streams within a watershed, and 68% of the variation in total microbial biomass was explained by sediment atomic carbon-to-nitrogen ratio (C:N ratio), percent carbon, sediment surface area, and percent water content. This study confirms a distinct microbial biogeography for headwater stream communities driven by environmental heterogeneity across distant watersheds and suggests that eukaryotic photoautotrophs play a key role in structuring bacterial communities on streambed sediments. IMPORTANCE Microorganisms in streams drive many biogeochemical reactions of global significance, including nutrient cycling and energy flow; yet, the mechanisms responsible for the distribution and composition of streambed microbial communities are not well known. We sampled sediments from multiple streams in two watersheds (Neversink River [New York] and White Clay Creek [WCC; Pennsylvania] watersheds) and measured microbial biomass and total microbial and bacterial community structures using phospholipid and molecular methods. Microbial and bacterial community structures displayed a distinct watershed-level biogeography. The smallest headwater streams within a watershed showed the greatest variation in microbial biomass, and 68% of that variation was explained by the atomic carbon-to-nitrogen ratio (C:N ratio), percent carbon, sediment surface area, and percent water content. Our study revealed a nonrandom distribution of microbial communities in streambeds, and showed that microeukaryotic photoautotrophs, environmental heterogeneity, and geographical distance influence microbial composition and spatial distribution.
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    U(VI) Reduction in Sulfate-Reducing Subsurface Sediments Amended with Ethanol or Acetate
    (American Society of Microbiology, 2013) Converse, Brandon J.; Wu, Tao; Findlay, Robert H.; Rodena, Eric E.; University of Wisconsin Madison; University of Alabama Tuscaloosa
    An experiment was conducted with subsurface sediments from Oak Ridge National Laboratory to determine the potential for reduction of U(VI) under sulfate-reducing conditions with either ethanol or acetate as the electron donor. The results showed extensive U(VI) reduction in sediments supplied with either electron donor, where geochemical and microbiological analyses demonstrated active sulfate reduction.