This study looks at characterizing the terrigenous OC sources, like permafrost, of POC and DOC through 17 rivers and six soils of the Hudson Bay (HB) using lignin biomarkers, and Δ14C. Our findings show the dominance of the OC flux (89%) from the southwest Hudson Bay Rivers, especially from DOC (93%), shedding light on the sources and fate of OC in HB sediments. With warming, organic cryosols, with high OC content in the Cz horizon, have the potential to release as much as 1.5 gOC/m2 for every cm increase in active layer depth. The [Ad/Al] ratios, when combined with 14C ages of DOM, show that older SOC is being released in some rivers and is fresher than expected due to its preservation within permafrost. S/V and C/V ratios, are well correlated to latitude in DOM, reflecting the vegetation in their drainage basins and can be used to indicate OC sources.

Water quality is of great importance for ecosystems and society. This thesis characterized and modeled the variation in several key constituents of Swedish surface waters, with particular consideration given to intra-annual variability and sensitivity to climate change. Cyanobacterial data from 29 lakes and basins as well as total organic carbon (TOC) from 215 watercourses were used. Extensive data on catchment characteristics, morphometry, discharge, temperature and other water chemistry data were also analyzed. Models characterizing the seasonality in cyanobacterial concentration and relative cyanobacterial abundance were developed with common lake variables. Concentrations of TOC, iron and absorbance were simulated using discharge, seasonality and long-term trend terms in the Fluxmaster modeling system. Spatial patterns in these model terms were investigated, and the sensitivity of cyanobacteria and TOC to future climate was explored. Nutrients were the major control on cyanobacterial concentration seasonality, while temperature was more important for relative cyanobacterial abundance. No cyanobacterial blooms occurred below a total phosphorus threshold of 20 µg l-1. Discharge and seasonality explained much of the intra-annual variability in TOC, but catchment characteristics could only explain a limited amount of the spatial patterns in the sensitivity to these influences. North of Limes Norrlandicus the discharge term had a larger impact on the TOC concentration in large catchments than in small catchments, while south of Limes Norrlandicus the seasonality had a larger impact in small catchments than in larger catchments. According to the climate change scenarios, both TOC and cyanobacterial concentrations will be higher in the future. The cyanobacterial dominance will start earlier and persist longer. The spring TOC concentration peak will come earlier. The changes in TOC loads are more uncertain due to predicted declines in discharge. Parsimonious statistical regression models could explain observed variability in cyanobacteria and TOC. For predictions, these models assume that future aquatic ecosystems will exhibit the same sensitivity to major drivers as in the past. If this proves not to be the case, the modeling can serve as a sentinel for changing catchment function as indicated by degradation in model performance when calibrations on older data are used to model later observations.

Overall soil productivity is declining in the U.S. due to loss of soil organic matter (SOM). Decreased SOM lowers soil water storage, reduces water infiltration, slows aggregate formation, and depletes soil of nutrients. In many systems, crop nutrients are replaced by expensive synthetic fertilizers that can lead to environmental concerns. This practice is not economically or environmentally sustainable in the long term. To secure future soil use and crop production, sustainable management practices are needed to prevent further SOM depletion. Incorporating legumes into cropping systems is one alternative that can bolster soil organic C (SOC) (key indicator of SOM) and reduce N fertilizer applications through symbiotic legume N fixation. Three studies were conducted over multiple years at the Texas A&M AgriLife Research and Extension Center near Overton, TX. Annual cool- and warm-season legumes were evaluated as potential green manure crops and intercrops under grain sorghum [Sorghum bicolor (L.) Moench], high-biomass sorghum [Sorghum bicolor (L.) Moench], and annual forage cropping systems. These studies quantified legume soil moisture usage and C and N contributions to the soil and subsequent crop yields in East Texas. Primary project objectives were to maintain or maximize primary crop yields at reduced N fertilizer rates and to build SOC through the integration of legume green manures and intercrops. Green manuring cool-season legumes showed the most beneficial effect on SOC, soil total N, and crop yields; however, significant increases in yield were only detected after three years in rotation. Intercropping Iron-and-Clay cowpea (Vigna unguiculata L. [Walp]) decreased yield of both high-biomass sorghum and grain sorghum due to competitive vegetative growth. Iron-and-Clay did however improve biomass yields of high-biomass sorghum in two subsequent years when implemented as a green manure. Despite large N yields as high as 310 kg ha-1, impacts of legumes on annual forage crops was limited. Poor response was likely a result of previous field history in which a permanent warm-season grass pasture was cultivated for site preparation and mineralized SOC released substantial amounts of available N. Under low soil N conditions, legume green manures produce enough N to likely reduce N fertilizer requirements cost-effectively for subsequent crops in East Texas.

Chromium (VI) is a pervasive groundwater contaminant that poses a considerable threat to human health. Remediation techniques have focused on the reduction of the highly mobile Cr(VI) to the sparingly soluble, and less toxic, Cr(III) species. Traditionally, remediation performance has been evaluated through the measurement of Cr(VI) concentrations; however, this method is both costly and time-consuming, and provides little information regarding the mechanism of Cr(VI) removal. More recently, Cr isotope analysis has been proposed as a tool for tracking Cr(VI) migration in groundwater. Redox processes have been shown to produce significant Cr isotope fractionation, where enrichment in the ⁵³Cr/⁵²Cr ratio in the remaining Cr(VI) pool is indicative of a mass-transfer process. This thesis describes laboratory batch and column experiments that evaluate the Cr isotope fractionation associated with the reduction of Cr(VI) by various materials and under various conditions. Laboratory batch experiments were conducted to characterize the isotope fractionation during Cr(VI) reduction by granular zero-valent iron (ZVI) and organic carbon (OC). A decrease in Cr(VI) concentrations was accompanied by an increase in δ⁵³Cr values for the ZVI experiments. Data were fitted to a Rayleigh-type curve, which produced a fractionation factor α = 0.9994, suggesting a sorption-dominated removal mechanism. Scanning electron microscopy (SEM), X-ray absorption near-edge structure (XANES) spectroscopy, and X-ray photoelectron spectroscopy (XPS) indicated the presence of Cr(III) on the solid material, suggesting that reduction of Cr(VI) occurred. A series of batch experiments determined that reaction rate, experimental design, and pre-treatment of the ZVI had little to no effect on the Cr isotope fractionation. The interpretation of isotope results for the organic carbon experiments was complicated by the presence of both Cr(VI) and Cr(III) co-existing in solution, suggesting that further testing is required. A laboratory column experiment was conducted to evaluate isotopic fractionation of Cr during Cr(VI) reduction by OC under saturated flow conditions. Although decreasing dissolved Cr(VI) concentrations also were accompanied by an increase in δ⁵³Cr values, the isotope ratio values did not fit a Rayleigh-type fractionation curve. Instead, the data followed a linear regression equation yielding α = 0.9979. Solid-phase analysis indicated the presence of Cr(III) on the surface of the OC. Both the results of the solid-phase Cr and isotope analyses suggest a combination of Cr(VI) reduction mechanisms, including reduction in solution, and sorption prior to reduction. The linear characteristic of the δ⁵³Cr data may reflect the contribution of transport on Cr isotope fractionation.

Upland environments are important sources of mercury (Hg) to downstream wetlands and water bodies. Hydrology is instrumental in facilitating Hg transport within, and export from watersheds. Two complementary studies were conducted to assess the role hydrological processes play in controlling Hg mobility and transport in forested uplands. A field study compared runoff and Hg fluxes from three, replicate hillslope plots during two contrasting spring snowmelt periods, in terms of snowpack depth and timing. Hillslope Hg fluxes were predominately flow-driven. The melting of soil frost significantly delayed a large portion of the Hg flux later into the spring following a winter with minimal snow accumulation. A microcosm laboratory study using a stable Hg isotope tracer applied to intact soil cores investigated the relative controls of soil moisture and precipitation on Hg mobility. Both hydrologic factors control the mobility of contemporary Hg; with greatest Hg flushing from dry soils under high-flow conditions.

Thesis (M.S.)--Indiana University, 2007. / Department of Earth Sciences, Indiana University-Purdue University Indianapolis (IUPUI). Advisor(s): Philippe G. Vidon, Lenore P. Tedesco, Kathy J. Licht. Includes vitae. Includes bibliographical references (leaves 110-114).

Arctic regions are expected to be highly sensitive to climate change regarding the prediction of disproportionately large increases in surface temperatures and their related influence over the hydrological cycle and permafrost thaw. These modifications have the potential to impact biogeochemical cycles in these regions and in particular the mobilization of organic carbon into rivers. The most crucial period in arctic rivers hydrological cycle is the spring freshet that can account for most of the annual organic carbon transfers to the ocean in a very short window of time. The focus of this thesis was to monitor the dynamic of DOM in terms of quantity and quality along the hydrological cycle of the Yenisei river, through DOM characterization approaches to reveal seasonal variations in its composition, sources, age and degradation state. The first step was to make a review of the full range of existing DOM characterization approaches in worldwide river systems to identify the most widely used, the most relevant and reliable ones. Through the development of a DOM quality measurements database, we have been able to evaluate the geographical coverage of DOM characterization studies, to give estimates and ranges of values of the main reported DOM characterization variables and to observe global trends of DOM quality across latitudinal gradient. Second stage was to investigate DOC dynamic in the Yenisei river with regard to quantity and links with water chemistry and hydrology. We conducted sampling campaigns during three consecutive years (2014 to 2016), covering with a high sampling frequency the spring flood period to capture its very dynamic evolution. We reported DOC concentrations that followed the hydrograph with highest concentrations observed a few days before peak discharge. DOC concentration also responded to discharge variation (increase, likely due to higher precipitation) in early autumn. We reported average DOC flux over the three sampling years of about 4.53 Tg yr-1 which is within the range of values reported in the literature. We observed interannual variability with annual export estimates ranging from 5.45 Tg yr-1 in 2014 to 3.57 Tg yr-1 in 2016, likely driven by discharge amplitude. We confirmed the important role of spring freshet in DOC export with on average more than 65% occurring during this period (roughly May/June). Third point was to determine DOM quality combining characterization techniques. Combination of approaches helped to strengthen observations and cross validate interpretations. Most of the variables reported from the different characterization techniques confirmed one each other. The use of lignin biomarkers, optical properties and radiocarbon age of DOM allowed us to trace DOM main sources has primarily deriving from recently produced organic matter leached from boreal forest litter and top soil horizon during the spring flood and older organic matter derived from deeper soil horizons during low flow period.

Northern peatlands are a globally important soil carbon (C) store, and aquatic systems draining peatland catchments receive a high loading of dissolved and particulate forms of C from the surrounding terrestrial environment. Once incorporated into the aquatic environment, internal processes occur to modify the C pool. Of these, photo-processing preferentially targets terrestrially derived C and therefore might have a significant effect on the C budget of peatland draining aquatic systems. The overarching aim of this study was to investigate photochemical processing of C in Scottish peatland draining aquatic systems in order to determine the importance of this pathway in aquatic biogeochemical cycles. For initial laboratory experiments, water samples from a peatland headwater stream (Auchencorth Moss, SE Scotland) were collected. Laboratory based irradiation experiments were conducted at a range of temperatures, and different filtration treatments, including unfiltered samples, were employed to understand the fraction of C most susceptible to photo-processing. UV irradiation and temperature had a significant effect on DOC and gas headspace concentrations, with Q10 values of ~1.42 and ~1.65 derived for CO2 and CO photoproduction in unfiltered samples, respectively. However, filtration treatment did not induce significant changes in gaseous C production between light and dark samples, indicating that the experimental conditions favoured breakdown of DOC rather than POC to CO2 and CO. In all light treatments a small but significant increase in CH4 concentration was detected. These data were compared to results from experiments conducted in ambient light and temperature conditions. DOC normalised CO2 photoproduction was an order of magnitude lower than in laboratory conditions, although relative abundances of C species within overall budgets were similar and these experiments demonstrated that ambient exposure is sufficient to generate photo-processing of aquatic peatland C. Overall these data show that peatland C, particularly the < 0.2 μm fraction, is highly photoreactive and that this process is temperature sensitive. Further laboratory irradiation experiments were conducted on filtered water samples collected over a 13-month period from two contrasting aquatic systems. The first was the headwater stream draining Auchencorth Moss peatland with high DOC concentrations. The second was a low DOC reservoir (Loch Katrine, C Scotland) situated in a catchment with a high percentage peat cover. Samples were collected monthly from May 2014 to May 2015 and from the stream system during two rainfall events. Significant variation was seen in the photochemical reactivity of DOC between the two systems, with total irradiation induced change typically two orders of magnitude greater and DOC normalised CO2 production a factor of two higher in the headwater stream samples. This is attributed to longer water residence times in the reservoir rendering a higher proportion of the DOC recalcitrant to photo-processing. Overall the magnitude of photo-induced C losses was significantly positively correlated with DOC concentration in the headwater stream, which varied seasonally with highest concentrations detected in late autumn and winter. Rainfall events were identified as important in replenishing the stream system with photoreactive material, with lignin phenol data indicating mobilisation of fresh DOC from woody vegetation in the upper catchment during a winter rainfall event. Whilst these data clearly demonstrate that peatland catchments generate significant volumes of photoreactive DOC, the degree to which it is processed in the aquatic environment is unclear. Field investigations were undertaken to address this uncertainty. In-situ experiments with unfiltered water samples in light and dark conditions were conducted in two contrasting open water peatland pool systems. At the high DOC site (Red Moss of Balerno, SE Scotland), DOC concentrations in surface light exposed samples decreased by 18% compared to dark controls over 9 days and light treatments were enriched in CO2 and CH4. Photochemical processing was evident in δ13C-DOC and δ13C-DIC signatures of light exposed samples, which were enriched and depleted, respectively, relative to dark controls (+0.23 ‰ and -0.38 ‰) after 9 days of surface exposure. At the low DOC site (Cross Lochs, Forsinard, N Scotland) net production of DOC occurred in both light and dark samples over the experiment duration, in part due to POC breakdown. δ13C-DIC signatures indicated photolysis had occurred in light exposed samples (-1.98 ‰), whilst δ13C-DOC data suggest an absence of photo-processing, as the signatures in both treatments were similar. Accounting for light attenuation through the water column, 46 ± 4.9 and 8.7 ± 0.5 g C-CO2 eq m−2 yr−1 was processed by photochemical and microbial activity in peatland pools within the catchments at the high and low DOC sites, respectively. At both sites, light driven processing was responsible for a considerable percentage (34 and 51%) of gaseous C production when compared to equivalent estimates of microbial C processing and thus should be considered a key driver of peatland pool biogeochemical cycles. It is clear from this study that temperature, seasonal cycles, rainfall events and water residence time provide strong controls on the photoreactivity of aquatic C in Scottish peatland systems. The photo-processing pathway has the potential to alter the C balance of peatland catchments with a high percentage coverage of aquatic systems. Under climate change scenarios where light, temperature and rainfall conditions are expected to change, this process may become increasingly important in aquatic C cycling, particularly if the upward trend in DOC concentrations in northern aquatic systems continues.

abstract: Atmospheric particulate matter has a substantial impact on global climate due to its ability to absorb/scatter solar radiation and act as cloud condensation nuclei (CCN). Yet, little is known about marine aerosol, in particular, the carbonaceous fraction. In the present work, particulate matter was collected, using High Volume (HiVol) samplers, onto quartz fiber substrates during a series of research cruises on the Atlantic Ocean. Samples were collected on board the R/V Endeavor on West&ndash;East (March&ndash;April, 2006) and East&ndash;West (June&ndash;July, 2006) transects in the North Atlantic, as well as on the R/V Polarstern during a North&ndash;South (October&ndash;November, 2005) transect along the western coast of Europe and Africa. The aerosol total carbon (TC) concentrations for the West&ndash;East (Narragansett, RI, USA to Nice, France) and East&ndash;West (Heraklion, Crete, Greece to Narragansett, RI, USA) transects were generally low over the open ocean (0.36&plusmn;0.14 &mu;g C/m3) and increased as the ship approached coastal areas (2.18&plusmn;1.37 &mu;g C/m3), due to increased terrestrial/anthropogenic aerosol inputs. The TC for the North&ndash;South transect samples decreased in the southern hemisphere with the exception of samples collected near the 15th parallel where calculations indicate the air mass back trajectories originated from the continent. Seasonal variation in organic carbon (OC) was seen in the northern hemisphere open ocean samples with average values of 0.45 &mu;g/m3 and 0.26 &mu;g/m3 for spring and summer, respectively. These low summer time values are consistent with SeaWiFS satellite images that show decreasing chlorophyll a concentration (a proxy for phytoplankton biomass) in the summer. There is also a statistically significant (p<0.05) decline in surface water fluorescence in the summer. Moreover, examination of water&ndash;soluble organic carbon (WSOC) shows that the summer aerosol samples appear to have a higher fraction of the lower molecular weight material, indicating that the samples may be more oxidized (aged). The seasonal variation in aerosol content seen during the two 2006 cruises is evidence that a primary biological marine source is a significant contributor to the carbonaceous particulate in the marine atmosphere and is consistent with previous studies of clean marine air masses. / Dissertation/Thesis / M.S. Chemistry 2011

The importance of dissolved organic carbon (DOC) to aquatic environments is well established in the scientific community. In boreal landscapes, small streams receive water from headwater lakes, mires, and discrete flow paths that drain riparian soils. The goal of this study was to investigate the importance of these discrete riparian inputs (DRIPs) as sources of DOC and to explore whether quantity and quality of DOC from DRIPs differs from other sources in the landscape, including groundwaters that are not as hydrologically connected to streams. To do this, I collected water from already established riparian groundwater wells installed at the Krycklan Catchment Study (KCS) in northern Sweden, as well as from an adjacent lake, stream, and mire. Microbial activity (respiration) was analyzed in 24-hour laboratory incubations using a metabolically active dye, resazurin (Raz) which in the presence of aerobic respiration transforms into resorufin (Rru). Rru is easily measured in the lab, and its production can serve as a proxy for rates of microbial respiration. DOC concentration was also measured at each location, along with specific absorbance at 254 nm (SUVA254) and the absorbance ratio (254/365 nm) as indices of DOC quality. The results show a large variation in DOC concentration among potential water sources to the stream. Furthermore, there was a strong correlation (R2=0.96) between Rru production and DOC concentration among these sources, but no significant difference (p=0.067) in median Rru production between DRIPs and non-DRIPs. Overall, these results highlight important spatial variability in DOC from different water sources in the landscape, which likely have important consequences for patterns of microbial respiration in streams.