Because of high sedimentation rates in the coastal ocean, particularly along river-dominated ocean margins, estuarine and coastal sediments can be important repositories for organic carbon derived from both allochthonous and autochthonous sources. The overall objective of this research was to investigate the sources of organic carbon and the coupling between organic carbon inputs and deposition on the Mississippi river-dominated Louisiana shelf using pigment and lignin biomarker analyses. During the course of these investigations a further goal was to conduct a comparison of two common methods of lignin analyses -- CuO oxidation and TMAH thermochemolysis Direct comparisons between data yielded from each method were determined to be not comparable. While conventional TMAH analyses can be employed more quickly and efficiently than the CuO method, CuO products appears more consistent and accurate in identifying bulk lignin sources within sediments, and were determined to be more appropriate in systems with low terrestrial organic matter such as the Louisiana shelf The spatial distribution of phytoplankton pigments in surface waters varied by season and appeared strongly influenced by river discharge. Total chlorophyll concentrations ranged up to 31nM in surface waters during the period of high river discharge, and up to 1.71 mg chla 100 mg OC-1 in the sediments during low river discharge. Diatoms made up the most abundant phytoplankton taxa in this system, contributing a substantial amount of the marine-derived organic carbon to surface waters and sediments on the shelf Concentrations of terrigenous organic matter were spatially variable across the shelf, and linked to distinct regions of sediment accumulation. The highest lignin concentrations (up to 4.7 mg lignin 100 mg OC-1 ) were found closest to the river mouth and in the shallow near shore regions of the study area. While there were no discernible seasonal differences in contributions of C3 and C4 terrestrial material to the sediments, the proportions of riverine-derived, marsh-derived, and phytoplankton-derived organic carbon varied according to season and location across the shelf / acase@tulane.edu

In a shallow aquifer underlain by low permeable material, groundwater recharge (R), discharge to rivers or stream as baseflow (BF), and discharge to the atmosphere as evapotranspiration (ET) are related by a simple water balance equation, R - ET - BF = ΔS. Gathering information about these processes is difficult since these processes are hidden from view, yet these processes commingle with one another at the water table surface. The main objective of this dissertation project was to evaluate how main hydrological processes can be inferred from high-resolution water table measurements collected at various sites in Walnut Creek watershed located in southern Iowa. Water table monitoring data available for analysis in the project included three main sites, covering 2573 days between 1996 to 2008 and 61,714 individual water level monitoring points. Water table fluctuations were used to estimate R across an upland-floodplain chronosequence and plant ET under three riparian land covers. High resolution hydraulic head measurements were analyzed with spectral methods to evaluate potential surface and groundwater interaction. Detailed sedimentology and water table monitoring were combined to develop a conceptual model of nitrate leaching to in the near-stream riparian zone of an incised channel. Additional soil moisture and precipitation monitoring are recommended for improved application of methods to other sites. Results from this dissertation indicate that there is a considerable amount of information about key hydrological processes to be gained by measuring water table levels at a high frequency.

Chemical Biomarkers, along with bulk carbon and nitrogen measurements were examined in the lower Mississippi (MR) and Pearl Rivers (PR) (USA) to study seasonal changes in the abundance and composition of organic matter and riverine phytoplankton. Water samples were collected monthly from September 2001 to August 2003. Surveys of spatial variability (225 km downstream in the MR and from Jackson to Stennis Space Center in the PR) in total DOC, DON and amino acids were also conducted in both rivers in June 2003 Higher phytoplankton abundance (dominated by diatoms) was observed in the lower MR than the PR (by chlorophytes), likely the result of decreasing TSS (increased damming in the watershed) and increasing nutrients (enhanced agricultural runoff) over the past few decades. Phytoplankton abundance in the lower MR was high not only in summer low-discharge periods, as observed in the PR, but also during winter and spring, indicating the inputs from reservoirs in primary tributaries Seasonal variations in the abundance and composition of DOM in the PR were highly correlated with water discharge, indicating a coupling between local carbon inputs (soil and wetlands) and regional precipitation events in the PR. Conversely, seasonal variability of bulk composition and chemical biomarkers of DOM in the lower MR was controlled by spatial variability of an integrative signal from watershed inputs and in-situ production from upriver sources. Spatially, very little change in total DOM in the downstream survey of the lower MR, compared to large decreases in the PR, likely suggested that OM has been subject to long-term in-situ processing An increase in the relative importance of phytoplankton biomass in large turbid rivers could have significant effects on the sources, lability of riverine organic matter, and the stoichiometric balance of nutrients delivered to coastal margins. Longer residence time of DOM and POM in large river systems from the drainage basin to the coast is an important difference in the overall processing of organic matter small versus large systems. If we are to better understand the controls of organic matter delivery to the coastal zone from both small and large rivers, sampling strategies need to be adjusted to account for the different scales of hydrologic response time and in-situ processing associated with different residence times / acase@tulane.edu

No description available.

ABSTRACT This work examined the role of micro-organisms in the biogeochemical cycling of selenium within the benthic ecosystem of Lake Macquarie, a coastal lake in New South Wales with a history of anthropogenic heavy metal contamination. Certain micro-organisms possess the ability to oxidise or reduce selenium (Fleming and Alexander, 1973; Doran and Alexander, 1977), and microbial volatilisation of selenium from contaminated sediments and soils utilising naturally-occurring microflora has been shown in overseas research (Thompson-Eagle and Frankenberger, 1992) to be a potentially effective remediation strategy. In examining the impact of micro-organisms upon the oxidation state of selenium in Lake Macquarie sediments, this work also investigated and characterised selenium (and heavy metal) concentrations, speciation and geochemical phase associations (an indicator of potential bioavailability) in the sediments. Seven distinct bacterial species indigenous to Lake Macquarie were identified in this work with the ability to reduce selenium as selenite to elemental selenium, and selenium as selenate to organic forms of selenium, including volatile methylated selenium compounds. Metabolic parameters calculated for these organisms compared favourably with those reported in the literature by other researchers. Mixed populations of sediment micro-organisms were also isolated and studied in this work for their selenite and selenate reduction abilities. Total reduction of added selenite at levels up to 100 mg/L was recorded for a number of the organisms studied in this work. A maximum specific uptake rate for selenite of 3040 mgSe(IV).(gcells)-1.(h)-1 for one isolate (Shewanella putrefaciens) was determined, exceeding rates reported in the literature by other authors. Use of the indigenous micro-organisms from Lake Macquarie for the bioremediation of selenium containing waste streams was also examined in this work and selenium reduction in an immobilised cell reactor was demonstrated with such organisms. Concentrations, speciation, sediment core profiles and geochemical phase associations for selenium were determined for sediment samples collected at a variety of sites throughout Lake Macquarie and from Wyee Creek, a selenium-impacted fluvial input to the lake. The maximum concentration of selenium obtained in this work for the lake proper was 4.04 mg/kg, considerably lower than values reported over a decade ago (Batley, 1987) but consistent with reported reductions of selenium input into the lake from the lead-zinc smelter. Selective extraction methodology (Tessier et al. and BCR methods) studied geochemical phase association of selenium in Lake Macquarie sediments and found up to 44% of selenium was in bioavailable forms. Of interest and environmental concern was levels of selenium found in sediments of Wyee Creek, which previously received overflows from the ash dam associated with the Vales Point Power Station. Sediment selenium levels of up to 300 mg/kg were determined for this creek. These were an order of magnitude or more greater than those recorded for the lake itself and are of concern as to the potential impact on benthic organisms and those animals, including humans, who consume them. While this work can only provide a 'snapshot' of conditions within Lake Macquarie at the time of the sampling events recorded herein, it does make several important contributions to the understanding of selenium biogeochemistry in Lake Macquarie. These include: presentation of the hypothesis that selenium levels in surficial sediments being deposited in the north of the lake have decreased in recent years as a result of selenium reduction measures undertaken by the lead-zinc smelter; determination that up to 44% of selenium in surficial sediments from the lake is associated with sediment phases in which selenium has the potential to become remobilized and hence possibly bioavailable; and documentation of selenium concentrations in Wyee Creek, identifying the area as having selenium concentrations an order of magnitude or more greater than the lake itself. Concerning the role played by microorganisms in the biogeochemical cycling of selenium in Lake Macquarie, this work has: identified individual isolated and mixed cultures of bacteria that can reduce selenium as selenite to lower oxidation states; identified individual isolated and mixed cultures of bacteria that can reduce selenium as selenate to lower oxidation states; identified volatile methylated selenium compounds in the headspace gases of microorganisms reducing selenate; determined Minimum Inhibitory Concentrations for selenate and selenite for organisms isolated from Lake Macquarie; identified casein hydrolysate as a preferred carbon source for selenium reducing microorganisms from Lake Macquarie; and demonstrated that bioremediation of selenium contaminated waste streams using indigenous organisms from Lake Macquarie is feasible on the laboratory scale. Further research areas suggested by this work include: additional investigations of elevated selenium levels in Wyee Creek sediments; determination of the role of microbes in in-situ selenium reduction; and optimisation of selenium biotreatment/bioremediation of selenium-containing waste streams and sediments. In summary, this work, in rejecting the null hypothesis that the oxidation states of selenium in sediments from Lake Macquarie, NSW, are independent of microbial activity and accepting the alternate hypothesis that these oxidation states are not independent of microbial activity, contributes to the understanding of the role of microorganisms in the biogeochemical cycling of selenium, having applicability to both the specific ecosystem of Lake Macquarie, NSW, and also to selenium cycling in the environment in general. In addition, this work has identified selenium contamination in Wyee Creek, one of the fluvial inputs to Lake Macquarie, which was previously been undocumented in the literature and which may pose significant potential risk to humans and the ecosystem due to sediment selenium levels one or more orders of magnitude higher than those recorded in the lake itself. Finally, this work has also identified a number of microorganisms indigenous to Lake Macquarie with the ability to reduce selenium from toxic, mobile forms to less toxic, immobile or volatile forms, and these organisms have been shown to have the potential for use in treatment of selenium contaminated waste streams and also in the bioremediation of selenium-contaminated sediments.

Biogeochemistry has been utilized successfully in Australia as a regional or fellow-up geochemical exploration techniques in the arid terranes of Australia. This Master's study is based on the biogeochemistry approach, which relies on the chemical analysis of plant tissues to obtain information on the geology and geochemistry of the underlying rocks. The project involved the systematic sampling and chemical analysis of plant materials and the supporting soils to establish the suitability of using particular tree species for environmental monitoring and their potential as a sample medium in geochemical exploration in the vicinity of the Temora Gold Mine, NSW, Australia. Working on 168 plant tissues (leaves, twigs and bark) in 54 plants species from 8 families at the three sites of background area, mineralized area and tailings area, and 54 supporting soil samples from three strata of 0-5 cm, 20-30 cm, and 30-40 cm, found that there was a good agreement between soil geochemistry and plant geochemistry on the result of a strong geochemical association between Au and As. The As-Au pattern was suggestive of the presence of the Au-As mineralization. Black cypress pine (Callitris endlicheri) LEAVES show a higher ratio of Asminjn/Aumin in the mineralized area than ASbkg/Aubkg in the background area, up to 7 times. The research finding suggests that the LEAVES of Black cypress pine (Callitris endlicheri) have a potential to be a biogeochemical sample medium as better indicators for Au. Golden wattle (Acacia pycnantha) BARK and Yellow box (E. melliodora) BARK appear to be better indicators for Au but more research is required. The most occurrence of anomalies of As, Au, Sb, Cu and Fe were found in Red box (E. polyanthemos) BARK. Red box (E. polyanthemos) BARK may have the potential to be an Au indicator in the area when Red box (E. polyanthemos) is present. Results on test-tolerant plants show that Eucalyptus species: Red box (E. polyanthemos), Coral gum (E. torquata), and Yellow box (E. melliodora) have a higher rate of uptake trace elements from the tailings soils. Therefore, Eucalyptus family generally adapted to metal-rich soils and can be used as cleaning-up indicators and environmental monitors for the tailings area of metal contaminated soils in the Temora Gold Mine.

<p>Microbes have been suggested to have a strong impact on the transportation of chlorine in soils. There are speculations about environmental factors limiting microbial effect on chlorine movement and retention. For this study, a numerical hydrochemical model was built to describe microbial transformation of chlorine in a laboratory lysimeter experiment. Undisturbed soil cores used to set-up the experiment were collected from a coniferous forest soil in southeast Sweden. The lysimeters were modelled in groups depending on their different water and chloride treatments. Microbial transformation of chlorine was better described under high water residence times and high chloride loads compared to low water residence times and low chloride loads. Microbial activity was also shown to properly account for a sudden shift from net-chlorine retention to net chlorine release in most of the lysimeters. Oxygen proved to be very important in accounting for the short-term shift from chloride retention to release in all the lysimeters. Model outcome revealed that 0.02– 0.10 mg Cl- could be available per day in a coniferous soil depending on season and other soil conditions. This study shows that modeling enable a better understanding of chlorine biogeochemistry. It also confirms the speculated importance of microbial activities on chloride availability in soils.</p>

Carbon and energy fluxes were measured with the eddy covariance technique above two semi-arid ecosystems, ponderosa pine and juniper/sagebrush, located in central Oregon. The two ecosystems have low LAI and a very open canopy structure. The energy closure was ~70-80% at both ecosystems, equivalent to an imbalance of 150-250 W m⁻² on cloudless summer days, when net radiation (R[subscript n]) was ~600-700 W m⁻². The lack of closure cannot be explained by the uncertainty of an estimate of available energy due to a single R[subscript n] sensor location. At the more open juniper/sagebrush ecosystem, a numerical model showed that spatial variation in R[subscript n], even for large differences in surface radiation temperature and reflection coefficient between ecosystem components (soil and vegetation), is less than 10% of measured R[subscript n]. The uncertainty in R[subscript n] at the two-layered ponderosa pine ecosystem with patches of young and old-growth trees is expected to be smaller than at the juniper ecosystem. Net carbon exchange (NEE) at the pine site strongly depends on environmental factors effecting carbon assimilation (A[subscript c]) and ecosystem respiration (R[subscript e]). A more detailed analysis of the carbon budget showed a strong negative response of carbon uptake to large vapor pressure deficits (VPD), whereas water vapor exchange (LE) was less affected. At large VPD the vegetation maintains a sustainable water flow through the soil-plant system by stomatal control of transpiration. The stomatal closure leads to limitation in A[subscript c], but LE is subject to a positive feedback from higher evaporative demand. Annual NEE of the ponderosa pine forest (200-300 gC m⁻²) was in the mid-range of reported NEE of temperate forest ecosystems, though, unusually, much of the annual carbon gain occurred during the fall through spring, because the relatively mild winters allowed carbon assimilation to occur and R[subscript e] rates were low. The information gathered at our ponderosa pine site during two years with contrasting climate suggests that the carbon uptake of the ponderosa pine ecosystem will be more sensitive to global climate change than the water vapor exchange. / Graduation date: 2000

Ryegrass residue consists of three main C fractions: readily available soluble C, intermediately available cellulose and hemicellulose, and slowly available lignin. Changes in chemical composition during decomposition influence rate of degradation as well as composition of the microbial community involved. Use of ����C-labeled plant material coupled with analysis of phospholipid fatty acids (PLEA) by isotope ratio mass spectrometry results in a powerful tool for linking microbial community structure and C cycling processes during decomposition. The objective was to investigate the role of soluble C in the decomposition of ryegrass straw. We wanted to determine (i) if the presence or absence of labile C in straw affects C mineralization by the microbial community, (ii) if community structure would differ based on the presence of labile C, and (iii) if community structure would shift as decomposition progressed. Residue was added to soil microcosms at rates that reflect field loads. Treatments were unleached straw (US), leached straw (LS), and leachate (L), plus an unamended control (C). Added substrates had ������C values between 120% and 180% the native soil signature was 26%. Respiration was measured every 4 to 6 hours for the first 5 d, and weekly thereafter. Destructive sampling took place after 0.6, 1 .6, 1 5, 1 8. 50, and 80 d of incubation and microbial biomass '��C (MBC) and PLFAs were analyzed. The soluble component of ryegrass straw strongly influenced C mineralization and assimilation, as well as microbial community composition and dynamics. CO2 evolution rates and ����C signatures were similar in US and L during the first 3 d of incubation. Most soluble C from leachate was consumed during that time, indicated by the rapid decrease in ������C value of CO2 evolved from L treatment. Substrate-derived C moved quickly into and through the microbial biomass. Distinct temporal shifts occurred in community composition. Early communities in amended soils were dominated by short and branched-chain PLFAs such as 15:Oa. Later samples contained more complex and longer PLFAs. 19:Ocy was an indicator for late succession communities in US and L, and 18:2w6,9 characterized late samples in LS. Soluble C affected when the temporal shift occurred in LS and L, communities shifted earlier than in US. Lipids were differentially enriched with ����C. Fungi, as indicated by 18:2w6,9, were more effective at incorporating substrate C into cellular lipids, as this was the most highly labeled of all PLFAs. / Graduation date: 2004

Graduation date: 2000