Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 231-243. / by Susan Margaret Henrichs. / Ph.D.

This work represents an interdisciplinary effort to investigate microbiological and chemical manganese (Mn) cycling in drinking water systems using concepts and tools from civil and environmental engineering, microbiology, chemistry, surface science, geology, and applied physics. Microorganisms were isolated from four geographically diverse drinking water systems using selective Mn-oxidizing and -reducing culture media. 16S rRNA gene sequencing revealed that most are bacteria of the Bacillus spp. (i.e., Bacillus pumilus and Bacillus cereus). These bacteria are capable of performing Mn-oxidation and -reduction under controlled laboratory conditions. Pseudo-first order rate constants obtained for microbiological Mn-oxidation and -reduction (aerobic and anaerobic) of these isolates ranged from 0.02 - 0.66 days⁻¹. It is likely that spores formed by Bacillus spp. protect them from chlorine and other disinfectants applied in drinking water systems, explaining their ubiquitous presence. A new method was developed using X-ray photoelectron spectroscopy (XPS) to identify Mn(II), Mn(III), and Mn(IV) on the surfaces of pure oxide standards and filtration media samples from drinking water treatment plants. A necessary step for the comprehensive analysis of Mn-cycling in drinking water systems is to characterize the chemical properties of filtration media surfaces. Analyses of filtration media samples show that, while Mn(IV) was predominant in most samples, a mixture of Mn(III) and Mn(IV) was also identified in some of the filtration media samples studied. The use of both the XPS Mn 3s multiplet splitting and the position and shape of the Mn 3p photo-line provide added confidence for the determination of the oxidation state of Mn in complex heterogeneous environmental samples. XPS was applied to investigate Mn(II) removal by MnOx(s)-coated media under experimental conditions that closely resemble situations encountered in drinking water treatment plants in the absence and presence of chlorine. Macroscopic and spectroscopic results suggest that Mn(II) removal in the absence of chlorine was mainly due to adsorption, while in the presence of chlorine was due to oxidation. Mn(IV) was predominant in all the XPS analyses while Mn(II) was detected only in samples operated without chlorine. Future research should apply XPS under different experimental conditions to understand the specific mechanisms affecting Mn(II) removal by MnOx(s)-coated media. / Ph. D.

Primary productivity is a fundamental ecological process and an important measure of ecosystem response to environmental change. Currently, there is a considerable lapse in our understanding of primary productivity in hot and cold deserts, due to the difficulty of measuring production in cryptogam vegetation. However, remote sensing can provide long-term, spatially-extensive estimates of primary production and are particularly well suited to remote environments, such as in the McMurdo Dry Valleys (MDV) of Antarctica, where cyanobacterial communities are the main drivers of primary production. These microbial communities form multi-layered sheets (i.e., microbial mats) on top of desert pavement. The cryptic nature of these communities, their often patchy spatial distribution, and their ability to survive desiccation make assessments of productivity challenging. I used field-based surveys of microbial mat biomass and pigment chemistry in conjunction with analyses of multispectral satellite data to examine the distribution and activity of microbial mats. This is the first satellite-derived estimate of microbial mat biomass for Antarctic microbial mat communities. I show strong correlations between multispectral satellite data (i.e., NDVI) and ground based measurements of microbial mats, including ground cover, biomass, and pigment chemistry. Elemental (C, N) and isotopic composition (15N, 13C) of microbial mats show that they have significant effects on biogeochemical cycling in the soil and sediment of this region where they occur. Using these relationships, I developed a statistical model that estimates biomass (kg of C) in selected wetlands in the Lake Fryxell Basin, Antarctica. Overall, this research demonstrates the importance of terrestrial microbial mats on C and N cycling in the McMurdo Dry Valleys, Antarctica. / Master of Science / Primary productivity is an essential ecological process and a useful measure of how ecosystems respond to climate change. Primary production is more difficult to measure in polar desert ecosystems where there is little to no vascular vegetation. Polar regions are also ecosystems where we expect to see significant responses to a changing climate. Remote sensing and image analysis can provide estimates of primary production and are particularly useful in remote environments. For example, in the McMurdo Dry Valleys (MDV) of Antarctica, cyanobacterial communities are the main primary producers. These microbial communities form multi-layered sheets (i.e., microbial mats) on top of rocks and soil. These communities are cryptic, do not cover large areas of ground continuously, and are able to survive desiccation and freezing. All of these characteristics make assessments of productivity especially challenging. For my master’s research, I collected microbial mat samples in conjunction with the acquisition of a satellite image of my study area in the MDV, and I determined biological parameters (e.g., percent ground cover, organic matter, and chlorophyll-a content) through laboratory analyses using these samples. I used this satellite image to extract spectral data and perform a vegetation analysis using the normalized difference vegetation index (i.e., NDVI), which determines areas in the image that contain vegetation (i.e., microbial mats). By linking the spectral data to the biological parameters, I developed a statistical model that estimates biomass (i.e., carbon content) of my study areas. These are the first microbial mat biomass estimates using satellite imagery for this region of Antarctica. Additionally, I researched the importance of microbial mats on nitrogen cycling in Taylor Valley. Using elemental and isotopic analyses, I determined microbial mats have significant effects on the underlying soil and nutrient cycling. Overall, this research demonstrates the importance of terrestrial microbial mats on C and N fixation in Antarctic soil environments.

Microbial community composition plays a vital role in soil biogeochemical cycling. Information that explains the biogeography of microorganisms is consequently necessary for predicting the timing and magnitude of important ecosystem services mediated by soil biota, such as decomposition and nutrient cycling. Theory developed to explain patterns in plant and animal distributions such as the prevalent relationship between ecosystem productivity and diversity may be successfully extended to microbial systems and accelerate an emerging ecological understanding of the "unseen majority." These considerations suggest a need to define the important mechanisms which affect microbial biogeography as well as the sensitivity of community structure/function to changing climatic or environmental conditions. To this end, my dissertation covers three data chapters in which I have 1) examined patterns in bacterial biogeography using gradients of environmental severity and productivity to identify changes in community diversity (e.g. taxonomic richness) and structure (e.g. similarity); 2) detected potential bacterial ecotypes associated with distinct soil habitats such as those of high alkalinity or electrical conductivity and; 3) measured environmental controls over the function (e.g. primary production, exoenzyme activity) of soil organisms in an environment of severe environmental limitations. Sampling was performed in the polar desert of Antarctica's McMurdo Dry Valleys, a model ecosystem which hosts microbially-dominated soil foodwebs and displays heterogeneously distributed soil properties across the landscape. Results for Chapter 2 indicate differential effects of resource availability and geochemical severity on bacterial communities, with a significant productivity-diversity relationship that plateaus near the highest observed concentrations of the limiting resource organic carbon (0.30mg C/g soil). Geochemical severity (e.g. pH, electrical conductivity) primarily affected bacterial community similarity and successfully explained the divergent structure of a subset of samples. 16S rRNA amplicon pyrosequencing further revealed in Chapter 3 the identity of specific phyla that preferentially exist within certain habitats (i.e. Acidobacteria in alkaline soils, Nitrospira in mesic soils) suggesting the presence of niche specialists and spatial heterogeneity of taxa-specific functions (i.e. nitrite oxidation). Additionally, environmental parameters had different explanatory power towards predicting bacterial richness at varying taxonomic scales, from 57% of phylum-level richness with pH to 91% of order- and genus-level richness with moisture. Finally, Chapter 4 details a simultaneous sampling of soil communities and their associated ecosystem functions (primary productivity, enzymatic decomposition) and indicates that the overall organic substrate diversity may be greater in mesic soils where bacterial diversity is also highest, thus a potentially unforeseen driver of community dynamics. I also quantified annual rates of soil production which range between 0.7 - 18.1g C/m2/yr from the more arid to productive soils, respectively. In conclusion, the extension of biogeographical theory for macroorganisms has proven successful and both environmental severity and resource availability have obvious (although different) effects on the diversity and composition of soil microbial communities. / Ph. D.

Thesis advisor: Hilary I. Palevsky / The biological carbon pump in the North Atlantic Ocean is powered by the annual spring phytoplankton bloom. These primary producers use inorganic carbon in the surface oceans and convert it into organic carbon, a fraction of which is exported out of the surface mixed layer and sequestered at depth. Determining the rate of carbon flux below the maximum winter mixed layer depth, driving sequestration on annual or longer timescales, is critical to understanding the North Atlantic carbon cycle.To constrain daily-to-annual scale changes in carbon export in the subpolar North Atlantic, I analyzed seven years of daily optical backscatter depth profiles (200-2600 m) collected from the subsurface profiler mooring at the Ocean Observatories Initiative (OOI)’s Global Irminger Sea Array from September 2014 to May 2021. This is the longest-running time series of daily, year-round optical backscatter profiles that has been collected in this region, providing novel opportunities to assess seasonal and interannual variations in particulate organic carbon (POC) flux to depth. This analysis, focused on large particles and aggregates identified from optical backscatter spikes, shows annual pulses of sinking particles initiating in May to June during each year of our seven-year time series, consistent with these export pulses being driven by organic matter production during the spring phytoplankton bloom. These pulses of particles sink through the water column at rates ranging from 10 and 30 meters per day, and though particle concentration attenuates through the water column due to remineralization, coherent large particle pulses generally extend deeper than 1500 m, the deepest maximum annual mixed layer depth over this period. Although deep winter mixing in this region requires sinking particles to penetrate much deeper than in other parts of the ocean to be sequestered long-term, pulses of large particles consistently penetrate to below even the deepest annual mixed layer depths in the region, highlighting the importance of these large particle pulses to carbon sequestration at depth in the subpolar North Atlantic. / Thesis (MS) — Boston College, 2024. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Master of Science / Department of Biology / John M. Blair / Anthropogenic activities impact ecosystems in numerous direct and indirect ways, affecting the cycling of carbon (C) and nitrogen (N) on local, regional and global scales. North America tallgrass prairie is an ecosystem profoundly altered by anthropogenic activities, with most native prairie converted to alternate land uses or heavily impacted by other environmental changes. While aboveground responses to anthropogenic drivers have received much attention, the responses of belowground biota, ecological processes, and nutrient allocation to land management and environmental change are poorly documented, especially over long timeframes. This research builds upon a long-term experiment (the Belowground Plot Experiment) initiated in 1986 at Konza Prairie Biological Station (Manhattan, KS). I utilized a subset of treatments to address the effects of annual burning vs. fire suppression and/or chronic N additions on soil C and N dynamics and microbial communities in tallgrass prairie. I measured a suite of soil variables related to C and N cycling during the 2012 growing season, including total soil C and N, microbial biomass C and N, in situ net N mineralization, potential N mineralization, in situ CO2 efflux, and potentially mineralizable soil C. I also assessed changes in microbial community composition using microbial phospholipid fatty acids (PLFA) profiles. Annual burning significantly (p≤0.05) increased the soil C:N ratio and in situ CO2 efflux, while decreasing potential ammonification and nitrification rates. Annual burning also increased total PLFA mass and relative abundance of fungi. Chronic N addition (100 kg N ha-1 year-1) significantly reduced the soil C:N ratio, while increasing total soil N and potential nitrification and ammonification rates. Chronic N addition reduced potential C mineralization, microbial biomass C and N, and altered microbial community composition by increasing abundance of bacterial PLFAs and reducing fungal PLFAs. Sampling date also significantly affected many variables. These results indicate that different fire regimes and chronic N enrichment over decades affects soil C and N pools and transformations, as well as microbial biomass and composition. In total, this study highlights the importance of long-term ecological research and identifies likely changes in tallgrass prairie nutrient dynamics and soil microbial communities under increased N and frequent burning.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 51-56). Also available on the World Wide Web.

Biogeochemical carbon dynamics govern the ability of peatlands to storecarbon. The processes controlling the balance between the photosyntheticuptake of C02 and respiration of C02 and CH4 back to the atmosphere remainunclear. A process-based ecosystem biogeochemical study, encompassing tracegas flux measurements, laboratory chemical analyses and field analyses, wasundertaken in order to better understand the carbon dynamics of borealCanadian peatlands.

Nitrogen and sulfur deposition and water table level fluctuations have the potential to influence the C biogeochemistry in peatlands. Processes in peatland mesocosms were examined under steady state and dynamic conditions at different rates of N and S deposition, and water table levels. Net turnover rates were calculated from diffusive-advective mass-balances of pore water constituents. The limitations of the approach were tested with tracer experiments, which showed that diffusive-advective transport adequately described the flow of dissolved substances in peat columns. Incubation experiments quantified potential CO2, CH4, DOC, H2S and Fe 2+ production rates. / The vegetation assimilated most of the deposited nitrogen and sulfate when water table levels were high. Lowered water table levels resulted in seepage of sulfate to the water table, reduced the rates of photosynthesis, and increased the soil respiration rates. The potential for sulfate reduction was fairly large, despite small in situ sulfate concentrations, and the CO2 production could not be fully accounted for by known processes. Potential rates of sulfate reduction were large both in samples taken from the field site and from the controlled experiments. SO42- addition resulted partly in stimulation, partly in reduction of potential CH4 production rates suggesting that the relationship between sulfate reduction and methanogenesis is not exclusively competitive. / Changes of the water table level had in situ effects on CO2 and CH4 production rates not explainable by a distinction in aerobic/anaerobic conditions. Anaerobic in situ rates at greater depths were much lower when the water table was at the surface of the mesocosms than when it was at greater depths. This might have been due to in situ accumulation of CO2 and CH 4 in the deeper peat, which lowers the energy gain of anaerobic C mineralization. Flooding and draining of peat soil resulted in a delayed onset of CH 4 production, in increased anaerobic CO2 production and decreased CH4 production rates, and in the decoupling of gas exchange from production rates. These results document that fluctuations of environmental variables on short time scales have an impact on rates of C turnover in peat soils, and also limit the predictability of fluxes by statistical models.

[Truncated abstract] Most of Australia, and large areas of many other continents, is drained by intermittent rivers and streams, however comparatively few biogeochemical studies have been completed for these systems. Intermittent, dryland streams are highly dynamic environments subject to unpredictable and sporadic flow. Natural disturbance from lengthy drought periods and sudden floods are typical for these systems. Without adequate baselines for natural disturbances, it is difficult to quantify other effects from anthropogenic disturbance such as dewatering, land clearing, and urbanisation, or climate change. This thesis presents work from a four-year study examining the biogeochemistry of nitrogen (N), phosphorus (P) and carbon (C) in soils and sediments of two intermittent streams (Barnett Creek and Pirraburdoo Creek) in the Pilbara region of north-west Australia. The Pilbara is an area of ancient geology and highly weathered environments that is undergoing rapid development yet is poorly understood from an ecological perspective. The principal objectives of this thesis were to determine: i) how flooding affects the spatiotemporal patterns of nutrients in intermittent stream landscapes; ii) the role of flooding in N and C mineralisation and microbial dynamics; and iii) the connections between benthic algae, microbes and nutrient availability in channel sediments. To address these objectives, three field studies and two incubation experiments were conducted. Field studies at Barnett Creek indicated that flooding reduced the spatial heterogeneity of available soil nutrients and microbes in the stream landscape, and that topography (relative elevation) in the stream landscape was of less importance in influencing nutrient and microbial patterns than flooding or landscape position. ... Field studies at Pirraburdoo Creek indicated that microbial biomass and activity increased in benthic algal mats during mat senescent stages, and decreased after flooding when mat biomass peaked. Benthic algae grew rapidly in gravel run environments after flooding, while declining in pools, and demonstrated moderate N limitation and strong P limitation. Pools had two to eight times greater NO3-N, three to five times more total N, and two to three times more labile P, OC and total C than either pools after flooding, or runs before or after flooding. Hence, the pools at Pirraburdoo Creek represented a local, interflood store of nutrients in otherwise nutrient-poor landscape, when connectivity to upstream reaches or upland environments was weak or non-existent. This thesis provides the first detailed analysis of soil and sediment biogeochemical responses to flooding for intermittent streams in the Pilbara region and for semi-arid Australia. Further pressing questions raised by this work include: What is the key pulse size and frequency for maintaining Pilbara riparian communities as well as soil microbial function? How do the spatio-temporal nutrient and microbial patterns observed persist over (i) multi-decadal scales, (ii) mega-spatial (larger landscape to regional) scales, (iii) different flood frequency-magnitude regimes, and (iv) different stream sizes? Stream biogeochemistry is a burgeoning field, and it is therefore reasonable to expect such existing gaps in knowledge may be addressed in the near future.