B11A-0049
Deposition and Burial Efficiency of Terrestrial Organic Carbon Exported from Small Mountainous Rivers to the Continental Margin, Southwest of Taiwan
Terrestrial organic carbon exported from small mountainous river to the continental margin may play an important role in global carbon cycle and it?|s biogeochemical process. A huge amount of suspended materials from small rivers in southwestern Taiwan (104 million tons per year) could serve as major carbon source to the adjacent ocean. However, little is know concerning fate of this terrigenous organic carbon. The purpose of this study is to calculate flux of terrigenous organic carbon deposited in the continental margin, offshore southwestern Taiwan through investigating spatial variation of organic carbon content, organic carbon isotopic compositions, organic carbon deposition rate and burial efficiency. Results show that organic carbon compositions in sediment are strongly influenced by terrestrial material exported from small rivers in the region, Kaoping River, Tseng-wen River and Er-jan Rver. In addition, a major part of the terrestrial materials exported from the Kaoping River may bypass shelf region and transport directly into the deep sea (South China Sea) through the Kaoping Canyon. Organic carbon isotopic compositions with lighter carbon isotopic values are found near the Kaoping River and Tseng-wen River mouth and rapidly change from heavier to lighter values through shelf to slope. Patches of lighter organic carbon isotopic compositions with high organic carbon content are also found in areas west of Kaoping River mouth, near the Kaoshiung city. Furthermore, terrigenous organic carbons with lighter isotopic values are found in the Kaoping canyon. A total of 0.028 Mt/yr of terrestrial organic carbon was found in the study area, which represented only about 10 percent of all terrestrial organic carbon deposited in the study area. Majority (~90 percent) of the organic carbon exported from the Kaoping River maybe directly transported into the deep sea (South China Sea) and become a major source of organic carbon in the deep sea.
B11A-0050
Effect of Urbanization on River CO2 Emissons
CO2 supersaturation in rivers has been reported for a number of different systems: tropical (e.g. Amazon1), subtropical (e.g. Xijiang River in China2) and temperate (e.g. Hudson3), indicating rivers' role as a source of atmospheric CO2 in regional net carbon budgets. In situ respiration of organic carbon is responsible for the high CO2 concentrations in rivers1. Because this organic carbon primarily originates on land1, land use practices may alter sources and character of this organic carbon significantly, potentially impacting river CO2 emissions. Urbanization is an important, expanding global land use. We are researching the effect of urbanization on river CO2 emissions. In this study, partial pressure of dissolved CO2 (pCO2) and radiocarbon (14C) contents of riverine dissolved inorganic carbon (DIC) are directly measured in time series in Buffalo Bayou and Brays Bayou, two of the main rivers draining Houston, Texas, a developed humid subtropical city. The watersheds of both bayous are entirely unbanized. We will report seasonal trends of pCO2 and 14C of riverine DIC to estimate sources and turnover times of dissolved CO2. For comparison, we are also measuring pCO2 and DIC 14C in Spring Creek, Texas, a nearby river which has a mixed forest/agriculture watershed, as a non-urbanized counterpart to Buffalo and Brays Bayous. References: 1. E. Mayorga et al., Nature 436, 538 (2005). 2. G. Yao et al., Sci. Tot. Environ. 376, 255 (2007). 3. P.A. Raymond, N.F. Caraco, and J.J. Cole, Estuaries 20, 381 (1997).
B11A-0051
Seasonal Variability in Dissolved Organic Matter Quantity and Composition from the Yukon River Basin
The Yukon River basin (YRB) is one of the largest in North America draining an area of 855 x 103 km2 in northwestern Canada and central Alaska and is a major source of terrigenous organic matter to the eastern Bering Sea and Arctic Ocean. The Yukon is also a relatively pristine catchment draining a vast area of taiga that is exceptionally susceptible to climatic change. Dissolved organic matter (DOM) plays a fundamental role in ecosystem biogeochemistry and is ubiquitous in aquatic systems. Samples were collected over a five year period from 2001 to 2005 from a number of locations and at different points in the hydrologic regime throughout the YRB. Sample locations represented different locations on the mainstream of the Yukon River, as well as tributaries ranging from organic rich black waters draining permafrost impacted watersheds to those dominated by glacial melt waters and groundwater. Dissolved organic carbon (DOC) concentrations were observed to vary greatly from 1.5 to 26.1 mgCL-1 depending on source waters and time of year. Specific UV absorbance at 254 nm (SUVA) was also determined and ranged from to 1.3 to 4 highlighting the range in dissolved aromatic carbon content from different sources within the YRB. The hydrophobic acid (HPOA) fraction of the DOM was isolated from samples by XAD-8 resin adsorption for further investigation of DOM composition. The HPOA fraction represented 32 to 57 % of the total DOC for the range of samples studied. SUVA values from the HPOA fraction were higher than the unfractionated water samples (2.5 to 4.4) indicating a higher aromatic content for the HPOA fractions relative to the unfractionated DOM. However, the HPOA SUVA showed a good correlation to the unfractionated water samples SUVA (r2 = 0.84, p<0.01). Dissolved lignin phenols were measured on the HPOA fraction in order to trace vascular plant derived material. The ratios of different lignin phenols (e.g. syringyl to vanillyl; S:V and cinnamyl to vanillyl; C:V) can be used to distinguish between angiosperms and gymnosperms and woody and non-woody vascular plant materials, respectively. In addition, acid to aldehyde ratios of vanillyl and syringyl phenols can indicate the degree of oxidation and have been shown to increase with increased microbial and fungal breakdown. Lignin phenol concentrations varied between 6.7 to 50.5 ug L-1 dependent on source waters and time of year of sampling. The lowest concentrations of dissolved lignin were typically observed in samples taken from under ice prior to the spring melt and in groundwater dominated samples. Most YRB C:V and S:V signatures were consistent with a mixture of traditionally defined angiosperm non-wood tissues and gymnosperm wood sources. Lignin phenol concentrations were also observed to correlate to SUVA on the HPOA fractions (r2 = 0.71, p<0.01) and the whole water samples (r2 = 0.73, p<0.01). To further investigate the sources of DOM in the YRB a number of distinct endmember plant and litter materials were leached for between 194 to 336 hours. The contributions of these source materials using lignin phenol biomarkers of the different leached materials are shown and the potential for sourcing DOM of different origins highlighted.
B11A-0052
Investigating the Sources and Dynamics of Dissolved Organic Matter in an Agricultural Watershed in California (U.S.A.)
Dissolved organic matter (DOM) is ubiquitous and plays critical roles in nutrient cycling, aquatic food webs and numerous other biogeochemical processes. Furthermore, various factors control the quality and quantity of DOM, including land use, soil composition, in situ production, microbial uptake and assimilation and hydrology. As a component of DOM, dissolved organic carbon (DOC) has been recently identified as a drinking water constituent of concern due to its propensity to form EPA-regulated carcinogenic compounds when disinfected for drinking water purposes. Therefore, understanding the sources, cycling and modification of DOC across various landscapes is of direct relevance to a wide range of studies. The Willow Slough watershed is located in the Central Valley of California (U.S.A.) and is characterized by both diverse geomorphology as well as land use. The watershed drains approximately 425 km2 and is bordered by Cache and Putah Creeks to the north and south. The study area in the watershed includes the eastern portion of the foothills of the inner Coast Range and the alluvial plain and encompasses diverse land uses, including orchards, viticulture, dairy, pasture and natural grasslands. The Willow Slough watershed represents a unique opportunity to examine DOC dynamics through multiple land uses and hydrologic flow paths that are common throughout California. Preliminary data show that DOC concentrations at the watershed mouth peak during winter storms and also increase gradually throughout the summer months during the agricultural irrigation season. The increasing DOC concentrations during the summer months may result from agricultural runoff and/or primary production in channel. In addition, initial results using the chromophoric DOM (CDOM) absorption coefficient and spectral slope parameters indicate seasonal differences in the composition of the DOM. Spectral slopes decreased during both the summer irrigation season and winter storms relative to winter base flow, consistent with an increase in terrestrial signature. Biomolecular markers such as lignin phenols provide diagnostic source information on DOM as they are derived uniquely from vascular plants. Lignin can be used to differentiate angiosperm and gymnosperm tissues, but more importantly for this study, carbon-normalized yields can help to constrain the proportions of the increasing DOC during irrigation that come from vascular plants versus in situ production. In addition to supplying useful source information, dissolved lignin phenols undergo rapid photodegradation when exposed to adequate solar radiation, and this process is "imprinted" through increases in the acidic components of lignin and decreases in the syringyl phenols, thus providing insight into DOM cycling in agriculture-dominated watersheds. Data will be presented highlighting the use of a range of analytical and spectrophotometric measurements including lignin phenols, 13C of DOC and CDOM in the Willow Slough watershed for investigating sources and dynamics of DOM throughout the watershed.
B11A-0053
Microbial Origin and Transformation of Dissolved Organic Matter in the Agricultural Willow Slough Watershed, California: Insights From Amino Sugars
Understanding the fundamental processes and land management practices affecting dissolved organic matter (DOM) cycling in agricultural watersheds is essential for managing drinking water quality and maintaining ecosystem health. Although dissolved organic nitrogen (DON) is increasingly recognized as a key component of DOM in disturbed watersheds, our knowledge of its origin and reactivity are limited due to multiple sources, microbial uptake, and secondary production. In particular, the effect of microbial processes on DON dynamics remains poorly understood at the watershed scale. The seasonal and spatial variations of DON concentrations in the surface waters of the Willow Slough watershed, a 425-km2 agriculturally-dominated catchment in the northern Central Valley of California, USA, were monitored weekly at 8 locations since January 2006. Amino sugars are specific microbial biomarkers and their unique distribution among groups of microorganisms such as bacteria, fungi, and algae allows the distinction between different sources of DOM. Although mean annual DON concentrations were lower at the headwaters (0.18 mg/L) than the outlet (0.45 mg/L), DON constituted up to 90% of the total dissolved nitrogen (TDN) at the headwaters, compared to only 15% of the TDN at the watershed outlet. During winter baseflows, DON concentrations at the outlet were low (0.2 mg/L), while they increased to about 1.2 mg/L during winter storms. Remarkably, DON concentrations increased and remained high at 0.6 mg/L during the summer irrigation season. Preliminary data suggests that winter storm runoff and summer irrigation flows are dominated by DON of terrestrial origin, whereas periods of winter baseflow are mainly composed of algal-derived DON. The concentration of total dissolved amino sugars in the Willow Slough surface waters and the contribution of amino sugars to the DON pool (% DON-AS) will be used to evaluate DON composition and degradation state. In addition, molar ratios of four amino sugars monomers; glucosamine, galactosamine, muramic acid and mannosamine, will provide insight on the origin of DON. Microbial processing is at the heart of nutrient and carbon recycling, and as such, the results of this research will have implications beyond the Willow Slough watershed.
B11A-0054
The Erosion of the Terrestrial Biosphere from Mountain Catchments and its Transfer as Particulate Organic Carbon (POC) to the Deep Ocean.
The erosion of particulate organic carbon (POC) from the continents by rivers and its input to the oceans is an important component of the global carbon cycle. A large proportion this material is derived from mountain belts where clastic sediment yields are high. In order to assess the impact of this carbon transfer on global cycles it is extremely important to constrain the source of the POC. If POC sourced from bedrock is oxidised its influence on carbon-cycling is very different from oxidising POC derived from vegetation and soil. The same can be said if a fraction of the POC derived from vegetation and soil is buried in sediment. In addition, rivers are dynamic systems that respond to, amongst other things, climate. How is the POC source and transfer affected by this external variable? We have measured the organic carbon concentration (Corg) of suspended sediment from several rivers draining the vegetated mountain belt of Taiwan. The rivers were sampled frequently across two orders of magnitude of water discharge (Qw) and suspended sediment concentration (SSC) (from low flow conditions and during typhoon-triggered floods). Using Corg, δ13Corg, N and δ15N as geochemical tracers we can determine the source of riverine POC, and differentiate between fossil (bedrock) and non-fossil (vegetation and soil) POC. Measurements of 14C (Fmod) on POC allow us to determine how much non-fossil POC is derived from eroding soil versus vegetation, and give an average soil POC residence time in the catchments. We find that the transfer of non-fossil POC is strongly controlled by climate and that at very high Qw and SSC, non-fossil POC is enriched above the norm. Floods are extremely important in the bulk transfer of non-fossil POC from mountain hillslopes. During these flood events non-fossil and fossil POC are delivered to the ocean in hyperpycnal river plumes (where the density of the river sediment mixture is greater than seawater) which may trigger turbidity currents. The fate of the entrained POC may therefore be to remain associated with sediment for long periods of time.
B11A-0055
Variaitions in Δ14C values of POM in the Tokachi River waters
An important part of global organic carbon cycle is the flux of terrestrial organic carbon from the continents to the oceans. The potential importance of coastal systems in global and regional organic budgets is still unclear because of the inherent complexity and variability of rivers, estuaries and coastal zones. Therefore, it is important to understand the organic matter cycling in estuaries and coastal systems, especially characteristics and dynamics of river particulate organic matter (POM), because the POM is one of end members of terrestrial organic matter. But POM is not homogeneous in terms of particle size or chemical characteristics so that we canft evaluate the linkage of terrestrial and coastal environments. The objective of this study is to understand the transport behavior of particulate organic matter from terrestrial region to ocean. In this study, we selected the Tokachi River in Japan and carried out at a fixed station from 2003 to 2005. Both Delta C-14 and delta C-13 values of POM were used as a tracer of POM, and we discussed the factors controlling variations in these values in a year. The Delta C-14 values range from -101 to -352 permil for the Tokachi River in northeast Hokkaido, Japan. The Delta C-14 vary with season. The values were -154 to -245 permil for the spring snow-melt season, -101 to -160 permil for the normal flow condition, and -235 to -352 permil for the heavy rain event in autumn. These results suggest that the differences in Delta C-14 values may reflect the differences in sources and supply processes of POM from watershed area in each season.
B11A-0056
Relating dissolved organic matter fluorescence to functional properties
The fluorescence excitation emission matrix properties of dissolved organic matter from three rivers and one lake in NW England are analysed. Sites are sampled in duplicate and for some sites seasonally to cover variations in dissolved organic matter composition, river flow, and carbon isotopic (13C, 14C) variability. Results are compared to the functional properties of the dissolved organic matter, the functional assays provide quantitative information on light absorption, fluorescence, photochemical fading, pH buffering, copper binding, benzo[a]pyrene binding, hydrophilicity and adsorption to alumina. Fluorescence characterization of the dissolved organic matter samples demonstrates that peak C fluorescence emission wavelength, the ratio of peak T to peak C fluorescence intensity, and the fluorescence : absorbance ratio best differentiate different dissolved organic matter samples. These parameters correspond to dissolved organic matter aromaticity, the ratio of labile to recalcitrant organic matter, and dissolved organic matter molecular weight. Peak C fluorescence emission wavelength, the ratio of peak T to peak C fluorescence intensity, and the fluorescence : absorbance ratio fluorescence parameters also have strong correlations with several of the functional assays, in particular the extinction coefficients, benzo(a)pyrene binding and alumina adsorption, and buffering capacity. In many cases, regression equations with a correlation coefficient >0.9 are obtained, suggesting that dissolved organic matter functional character can be predicted from DOM fluorescence properties. For one site, the relationship between dissolved organic matter source, fluorescence, function and carbon isotopic composition is discussed.
B11A-0057
Dissolved Inorganic and Spectrophotometrically Characterized Dissolved Organic Carbon From Source to sea: Tyne Catchment, UK
Dissolved organic matter (DOM) fluorescence, absorbance and dissolved organic and inorganic carbon (DIC, DOC) were measured from source to sea in the River Tyne catchment, of c. 2935 km2 and encompassing areas of contrasting land use. The catchment has three major tributaries: the North Tyne which has good water quality, high DOC concentrations and visible water colour from the high proportion of peat in its upper catchment; the South Tyne which has good water quality with typical riverine DOC concentrations and drains from limestone uplands; and the Derwent, a more urbanized catchment which is increasingly impacted by treated sewage effluent discharges towards its mouth. Freshwater and estuarine sampling campaigns yield the following results: (1) High absorbance at 340 nm and DOC concentration identify North Tyne waters due to the peaty headwaters, but no downstream trends in these parameters are observed in any of the tributaries, in contrast to the estuary where a rapid decrease is observed in both. (2) Fluorescence demonstrated downstream trends in both intensity and wavelength, especially in the Derwent as it is increasingly impacted by anthropogenic DOM. Elevated protein- like fluorescence intensity also fingerprints sewage effluent within the estuary. (3) The absorbance coefficient at 340 nm was found to have the strongest correlation to DOC concentration greater than all fluorescence intensity parameters measured. However, fluorescence analysis permits the source of the DOM to be determined. (4) With the exception of peat rich headwaters, DIC concentration is always greater than DOC. DIC is primarily in the form HCO3-, with concentrations highest in highly urbanized catchments, typically greater than those observed in catchments with carbonate bedrock, demonstrating a significant and previously unrecognized anthropogenic DIC. (5) Principal components analyses of estuarine samples showed 63.4% of the variability in DOM can be explained by two sets of components, with the first component correlated to the mixing of terrestrial and marine waters and the second component correlated to sources of pollution such as domestic sewage. http://www.lumin-s.com/pdfs
B11A-0058
A Predictable Terrestrial Signature to Riverine Dissolved Organic Carbon?
In small mountainous watersheds, the majority of dissolved organic carbon (DOC) is derived from terrigenous sources; however, there is much debate over the age and recalcitrance of these organic materials. To determine controls on the age and recalcitrance of DOC found in stream waters, we measured DOC composition in stream and soil water samples, using isotopic (13C and 14C) and spectroscopic (UV and 13C NMR) analyses, in conjunction with soil hydrometric conditions in two first-order watersheds with contrasting vegetation in northern California. In a low-gradient coastal prairie stream, we found low concentrations of old (Δ14C = -200 permil) DOC that most resembled stabilized soil organic matter found deep within the mineral soil during baseflow. In contrast, during storm events where saturation overland flow dominated runoff, we found high concentrations of young (Δ14C = +75 permil) DOC resembling fresher organic matter. These results contrast with observations from a high-gradient coniferous forest where there is a much narrower range in age and chemistry of stream DOC over time. In the forest, runoff generation is dominated by subsurface stormflow with little if any overland flow and there is a much narrower range of stream DOC concentration, age and chemistry DOC, all of which is comparable to that of older, stabilized soil organic matter. At both of these locations DOC in soil water varies with increasing depth: young to old and labile to recalcitrant - due to rapid exchange with surficially-bound organic matter on soil solids. Given this range in soil DOC properties, it appears that the flowpath of water through soils determines the age and composition of DOC as water enters the stream network. During throughflow conditions, the soil acts as a filter for fresh plant-derived DOC, releasing only aged and highly altered DOC to the stream. Shallow flowpaths will largely bypass this filter, resulting in the export of high concentrations of young and labile DOC. In these ecosystems, riverine DOC is not simply terrestrial or aquatic in origin. Within the "terrestrial" signature, we have found nearly as large a range of ages and chemistries as found within the soil profile itself, and the resulting DOC composition is largely predictable with knowledge of runoff generating mechanisms.
B11A-0059
Biochemical composition of organic matter in UK Midlands catchments: implications for drinking water treatment
Insufficient removal of natural organic matter at treatment works can lead to the formation of potentially carcinogenic disinfection by-products (mainly trihalomethanes and haloacetic acids, THMs and HAAs) due to reactions of residual organic matter with chlorine added at the disinfection stage of water treatment process. However, the total organic carbon (TOC) removal efficiency is controlled by the content and character of organic matter in treated water, spatially and temporally dependent (e.g. the ratio of hydrophylic and hydrophobic fractions). Thus, a better understanding of organic matter composition can affect the treatment process strategies, improving the THM formation prediction and the quantification of coagulant and disinfection dosages. Fluorescence analysis of organic matter composition and treatment efficiency has been carried out on raw and partially-treated water samples from catchments in the Midlands region of the UK. The catchments cover an area of different water sources, ranging from upland, peaty-rich subcatchments with coloured, young waters, to agriculturally transformed lowland subcatchments. From the spectrophotometric analysis of raw water it was found that, the abstraction from river with water storage in reservoirs corresponds with a hydrophilic character of organic matter, rather high microbial fraction and high TOC. Opposite properties (hydrophobic, low microbial and variable TOC) are specific for sites with abstraction and storage processes within reservoirs. For direct abstraction from rivers, without water storing in reservoir, a common pattern is intermediate character of organic matter. The fluorescence excitation-emission matrix (EEM) technique was used for the assessment of water treatment works performance (TOC removal) and organic matter characterization. The freshwater organic matter exhibits specific fluorescence properties, with increased intensities of fluorescence in some regions of the EEM, resulting from the water origin. Well-documented relationships of fluorescence properties with aromacity, molecular weight, bioavailability, TOC and biochemical oxygen demand were the basis of discrimination of biochemical organic matter properties, and hence drinking water treatment implications. TOC removal was calculated from the decrease in organic matter peak C fluorescence intensity between raw and clarified water samples. The organic matter character therefore determines the TOC removal at different water treatment works. Low TOC removal appears to correlate with high microbial content and variability of the organic matter characterizing riverine sources, whereas stable, high TOC removal corresponds with small microbial fraction of organic matter of low variability (sites with abstraction from reservoirs).
B11A-0060
Molecular Trickery - is Riverine DOM Really That Degraded?
In the global carbon cycle, less than 1% of the ~60 Pg C fixed by primary production in terrestrial environments each year survives complete remineralization to be exported by rivers to marine environments. Conventional wisdom suggests that this riverine organic matter must therefore be highly degraded, and molecular biomarkers indicate increasing degradation with decreasing size such that dissolved organic matter (DOM) is the most degraded fraction. Conversely, 14C ages of particulate organic matter are significantly older than DOM, and in fact, DOM ages are typically only 10-40 years. Our study of lignin fractionation during litter leaching and sorption of leachates to soils indicates that the degraded lignin signature of riverine DOM may be more an artifact of the processes of leaching and sorption than a true indicator of increased degradation.
B11A-0061
Erosion, Transport and Burial Of Petrogenic Organic Carbon In the Himalayan System: A Closed Loop In The Carbon Cycle?
The burial of terrestrial organic carbon (Corg) in marine sediments represents the second largest atmospheric CO2 sink. Corg exported by rivers is a mix of recent organic carbon (e.g. plant debris and soil Corg) and fossil Corg derived from erosion of carbonaceous material bearing rocks. Burial of petrogenic Corg is a simple recycling of reduced C and does not participate to atmospheric CO2 consumption. Moreover, its oxidation represents a net source of CO2. It is therefore crucial to determine the proportion of fossil Corg in river sediments as well as its fate during transport and burial. Recently, we realised a comprehensive Corg budget for the Himalayan system including source rocks, river sediments and marine sediments buried in the Bengal Fan. We showed that this system is characterised by an extreme burial efficiency of Corg, and represents 10 to 20% of total terrestrial Corg burial. In this study, we present a systematic characterisation of fossil Corg contained in source rocks, river sediments and marine sediments using Raman microspectrometry and High-Resolution Transmitted Electron Microscopy (HRTEM). Fossil Corg has been detected in suspended and bed sediments, as well as in sediments deposited in the Bengal Fan turbiditic system including its more distal part, 3000 km south of the river mouth. Fossil carbonaceous particles are present under 3 main forms: (1) independent, (2) associated with minerals as aggregates, (2) included in minerals. In Himalayan rivers, structural organization of carbonaceous particles is similar to that observed in the source rocks, from highly disorganised C to pure graphite. On the other hand, in the delta and Bengal Fan, sediments contain almost only highly graphitized carbonaceous particles. This suggests that disorganised carbonaceous particles are oxidised during transport in the floodplain, while highly graphitised C is selectively preserved and finally buried in Bengal Fan sediments. This is consistent with an increase of mechanical and chemical resistance during graphitization. Selective preservation of graphitic C forms a closed loop in the long term C cycle since graphitic C may escape to oxidation for several orogenic cycles. Over the geological timescale, the consequence must therefore be an increase of the reduced C reservoir.
B11A-0062
Seasonal changes in the concentration and chemical quality of dissolved organic matter exported from wetland soils to streams in coastal temperate watersheds
The concentration and chemical quality of dissolved organic matter (DOM) fluxes from terrestrial to aquatic ecosystems is an important indicator of watershed-scale hydrologic and biogeochemical processes. Understanding the relative magnitude and chemical character of these DOM fluxes is critical because DOM influences an array of biological, chemical, and physical processes. We used PARAFAC modeling of excitation- emission (EEM) fluorescence spectroscopy and biodegradable dissolved organic carbon (BDOC) incubations to investigate changes in the chemical quality of DOM along a soil-stream gradient in two watersheds in coastal Southeastern Alaska. Within each watershed, two sub-catchments (bog and forested wetland) were selected and soil solution from the sub-catchment soils, sub-catchment outlet streams and the watershed outlet streams were sampled weekly from May to October. Throughout the sampling period, concentrations of dissolved organic carbon (DOC) and BDOC were greatest in the soil solution and generally decreased in both the sub-catchment and watershed outlet streams. DOC concentrations at all sites were lowest during the spring runoff, increased during the summer growing season and decreased gradually with the onset of the fall wet season. In contrast, BDOC at all sites was highest during the spring runoff, decreased during the growing season and increased briefly during the fall wet season. The results from PARAFAC modeling indicate a strong seasonal linkage between soil solution and streams during the spring runoff and fall wet season, as demonstrated by the similar contribution of PARAFAC components in soil solution and the sub-catchment and watershed outlet streams. In particular, the relative contribution of two fluorescent amino acids, which have been attributed to tyrosine and tryptophan-like fluorescence, were very similar in both the soil solution and streams during the spring runoff and fall wet season. However, during the summer growing season, the contribution of both amino acids remained high in soil solution but drastically decreased in streams. Moreover, PARAFAC modeling of fluorescence EEMs revealed that the seasonal and longitudinal changes in the fluorescent amino acids were positively correlated with BDOC for all sites. These findings suggest that wetland soils in southeast, Alaska contribute abundant labile DOM to streams in the spring and fall. However, biological uptake of DOM along the soil-stream gradient appears to alter the character of DOM moving from terrestrial to aquatic ecosystems during the summer growing season. Our findings further suggest that DOM characterization and BDOC measurements are useful tools for evaluating seasonal changes in the biogeochemical coupling between terrestrial and aquatic ecosystems and thus, have the potential to be used as a tracer to evaluate the movement of DOM along soil-stream gradients.
B11A-0063
Mineral-organic Dynamics During Export From Rivers to Oceans: Implications for Organic Matter Source and Diagenetic Alteration
The record of vegetation preserved along continental margins has traditionally been used to assess the contributions of organic matter derived from adjacent watersheds of rivers. Our ability to draw conclusions from these records relies on the fundamental assumption that the processing of these particles is limited, or at least congruent, across different vascular plant biomarkers, thereby allowing direct correlations between vascular plant distributions on land and marine compositions. Ratios of syringyl (S), vanillyl (V) and cinnamyl (C) lignin phenols should provide diagnostic source indicators for angiosperm and gymnosperm woody and nonwoody tissues. We conducted benchtop experiments to test whether lignin phenol-clay particulates prepared in freshwater and exported through a steep geochemical gradient to full marine salinities resulted in distinctly different particulate biomarker compositions. Variations in biomarker compositions highlight the importance of compound- and mineral-specific retention mechanisms as a function of salinity changes. Losses of lignin phenols from mineral surfaces is most pronounced at very low salinities and essentially absent at salinities greater than 2 parts per thousand to full marine salinities. Therefore, sediment processing at slightly elevated salinities, such as in an estuary, may be particularly adept at removing part, but not all lignin phenols sorbed to sediments. Mineral- specific trends indicate that an increase in surface area and reactivity (e.g., cation exchange capacity) slightly increases desorption of particulate-bound lignin phenols. When comparing sediments within and between watersheds, particle history and mineralogy becomes even more important, particularly during the export from riverine to marine settings. For example, preferential loss of syringyl phenols could lead to higher S/V ratios than the areal distribution of angiosperms within the watershed would have indicated. Similarly, the molecular compositions used to infer the extent of diagenetic alteration, and thus the relative age of particulate organic matter, are subject to these desorptive processes. Sediment compositions may appear younger, less diagenetically altered than would be determined for the sediments prior to export. These subtle differences in behavior have significant implications for determining carbon budgets, characterizing vascular plant inputs to marine sediments, and assessing anthropogenic fingerprints from land use change. This work demonstrates a new approach where sorptive-desorptive mechanisms controlling the distribution and composition of vascular biomarkers are accounted for, providing a new lens through which biomarker trends in continental margin sediments should be viewed.
B11A-0064
Abiotic Dissolved Organic Matter-Mineral Interaction in the Karstic Floridan Aquifer
Dissolved organic matter (DOM)-mineral interaction (e.g. adsorption, desorption, mineral dissolution) in groundwater is a significant factor controlling geochemical, environmental and microbial processes and may be helpful in efforts to track groundwater sources or contaminant fate. Despite its importance, the dynamics and consequences of these abiotic interactions remain poorly understood, largely due to the inaccessibility and heterogeneity of the subsurface, as well as the chemical complexity of DOM. This study models the OM-mineral interactions that takes place in the Floridan aquifer through laboratory adsorption-desorption experiments using DOM (groundwater, river water, soil extracts) and carbonate minerals (calcite, dolomite) collected in north Florida. High performance liquid chromatography-size exclusion chromatography (HPLC-SEC) and UV-fluorescence excitation-emission matrix (EEM) spectrophotometry was used to examine the organic compound types exhibiting preferential affinity for carbonate minerals. Our results show that the DOM-carbonate adsorption/desorption isotherms are well described by the Freundlich model. Freundlich exponents (average value: 0.6488) less than one indicated a filling of adsorption sites. Minerals from Ocala tend to have higher adsorption affinity as well as adsorption capacity than those from Suwannee River Basin; however, both were found to have mineral dissolution. Two fluorescent signals, indicative of a fulvic-like (at excitation wavelength 295-310 nm, emission 400-420 nm) and a protein-like (275/345nm) moiety, were detected in DOM. A reduction in the fulvic-like peak intensity occurred following carbonate adsorption while the protein-like peaks remain almost unchanged indicating the preferential adsorption of fulvic acids. HPLC-SEC results (DOM properties as a function of molecular weight) will be discussed. The chemical properties of DOM in environmental groundwater samples will also be presented and evaluated in light of the above experimental results.
B11A-0065
Characterization of Dissolved Organic Matter in Surface, Soil, and Ground Waters of a Small (10 ha) Catchment Using Stable Isotopes (C, N, S) and Chemical Methods
In order to better understand sources of dissolved organic matter (DOM) in streams at the small watershed scale, we initiated a one-year investigation of the chemical and isotopic characteristics of DOM at the HJ Andrews Research Forest in Blue River, OR. These data will be used to test two mechanistic hypotheses to explain observed hysteresis patterns where dissolved organic carbon (DOC) concentrations in surface flow are greatest during the ascending limb of the hydrograph during storms and over the water year, with decreased DOC concentrations in surface flow during the descending limb of the hydrograph: Hypothesis 1) A flushing effect with no change in dominant flowpaths; Stream DOC concentrations directly reflect the DOC concentrations in the soil that are initially high and decrease during the event and throughout the water year due to the flushing of DOC. Hypothesis 2) A change in dominance from near-surface to subsurface hydrologic flowpaths during the event, with high-DOC sources in near-surface flowpaths dominating early and low-DOC sources in groundwater dominating later in the event. In order to address this ambiguity, the characterization of DOM using stable isotopes and other fingerprinting techniques (e.g. SUVA, C:N) was used to identify sources of organic matter to streams throughout an individual storm event and through the water year. If the first hypothesis (flushing effect) is correct, DOM in surface water should carry a similar fingerprint to the DOM in soil waters throughout the rain event and water year. If the second hypothesis (change in flowpaths) is correct, the fingerprint of DOM in the surface water should closely resemble that of soil water early in the event and change to reflect a mix of the two fingerprinted DOM sources groundwater and soil water later in the event. In addition to established chemical characterization methods like SUVA and C:N, a new technique of DOM isolation via solid-phase extraction using C-18 resin was used to isolate DOM in water samples from surface flow, soil water, and groundwater for C, N, and S isotopic analysis. The characterization of DOM from these water sources using stable isotopes, SUVA, and C:N ratios will be applied in an endmember mixing model and compared with a model using d18O to distinguish pre-event and event water.
B11A-0066
Bioavailability, Composition and Fate of Dissolved Organic Matter in the Swan-Canning Catchment, South-Western Australia
Dissolved organic nitrogen (DON) comprises the bulk of the total nitrogen load to the N-limited Swan-Canning river and estuary that bisects Perth, WA, yet its ecological role is largely unknown. Our objective was to assess the bioavailability and composition of dissolved organic matter (DOM), particularly its DON component, and the potential of DOM to supply dissolved inorganic nitrogen (DIN) to the estuary during the summer months when algal blooms are common. We compared water samples from 10 sub-catchments of the Swan-Canning that vary in land-use: eucalypt forests on the Darling Scarp most distant from the estuary, mixed (agriculture/ residential) catchments on the metropolitan perimeter, and urban catchments on the Swan Coastal Plain near Perth CBD. We inoculated water samples with a common bacterial inoculum and measured changes in DOC, DON and DIN over time. We found that 2 to 17 per cent of DOC and 18 to 44 per cent of the DON was consumed during the experiment and DIN was produced in 8 of 10 catchments. DOC and DON consumption were linearly related to concentration across sites and were greatest in the urban catchments. However, DOC and DON consumption were not significantly related, suggesting that C and N are concentrated in different fractions of DOM. Using resin fractionation techniques, we found that DOC was concentrated in the hydrophobic fraction, followed by transphilics, and lesser amounts of charged and neutral hydrophilics. Ongoing analyses will examine the N content of resin fractions and the amino acid composition of streams to determine how N composition relates to DOM decomposition. We are currently examining organic matter leached from native plants (Corymbia, Melaleuca) in coastal plain wetlands in order to characterize allochthonous DOM. Further examination of algal- derived DOM and point sources will enable us to determine the bioavailability and composition of in-stream and anthropogenic sources. These studies provide much needed information to target catchment management and may improve the accuracy of estuarine hydrochemical models by incorporating DOM decomposition as a dynamic parameter.
B11A-0067
Copper Binding Depending on Source and Chemical Quality of DOM in the Colorado Front Range
In alpine and sub-alpine lakes and the Colorado Front Range, the source, concentration and quality of the dissolved organic material (DOM) changes during the spring snowmelt and summer period because of decreasing rates of mountain run-off and increasing algal growth in the lakes. We examined seasonal changes in copper binding properties of DOM in an alpine lake (Green Lake 4) and a subalpine lake (Lake Albion) in Green Lakes Valley by conducting potentiometric titrations of lake water using a cupric ion selective electrode. Depending on the copper-binding characteristics of the DOM, the concentration of bioavailable cupric ion (Cu2+) and other metal ions may be below the toxicity threshold for aquatic biota. The seasonal DOC trend showed the expected decrease throughout the summer months because of the decrease in streamflow and decreasing source of terrestrial DOM. Lake Albion had a greater DOC concentration because of the more extensive surrounding vegetation at the lower elevation. DOM from Green Lake 4 was found to have more Cu binding capacity than DOM from Lake Albion, due to the different quality of DOM. The lesser copper- binding capacity in the summer in both lakes was associated with the decrease in DOC and relative stable level of fulvic acid percentage. The changes in metal binding capacity may also be related to changes in source of DOM and UV induced photodegradation. These data indicate that the seasonal DOM source changes may influence metal binding properties in an ecologically relevant manner.
B11A-0068
Dissolved Organic Matter and Iron Redox Reactions in an Alpine Wetland
The source and chemical character of dissolved organic matter (DOM) in mountain catchments is in part determined by the timing and extent of snowmelt. Another important factor controlling DOM chemistry in mountain catchments is the presence of landscape features such as lakes or wetlands. We studied the impact of a small alpine wetland on the biogeochemistry of DOM and iron in surface waters in the Green Lakes Valley in the Colorado Front Range. Dissolved organic carbon concentrations collected from soil lysimeters (~20 mg/L) in the wetland were 10-20 times greater than DOC concentrations in the surface waters entering and draining the wetland. Characterization of DOM by fluorescence spectroscopy, PARAFAC, and other methods shows that fulvic acid quinones with a microbial contribution (FI~1.5) were processed in the wetland before reaching the outlet; and that the reduced quinones produced in the wetland were transported to the downstream surface waters. Furthermore, high concentrations of dissolved iron in the wetland (1.82 mg/L) resulted in an increase in downstream surface water iron concentrations. However, the iron in the wetland, a more reducing environment, was mostly present as ferric iron; whereas the iron in the surface water samples was predominantly ferrous iron. This trend highlights the potential importance of the role of iron-DOM complexation in the wetland as well as photoreduction of iron in surface waters. These results indicate that the presence of small wetlands in alpine ecosystems can act as biogeochemical hotspots and have a disproportionately large impact on the biogeochemistry of downstream surface waters.
B11A-0069
Hydrologic Controls on Dissolved Organic Matter Mobilization and Transport within Undisturbed Soils
Dissolved organic matter (DOM) in soils plays an important role in the transport of nutrients and contaminants through the terrestrial environment. Subsurface pathways deliver a significant portion of carbon to streams that drain forested and agricultural watersheds. Although the importance of rainfall events to the DOM soil-water flux is well known, the hydrologic factors that govern this flux have not been fully examined. The primary purpose of this study is to investigate the soil and rainfall characteristics controlling the mobilization and transport of DOM in undisturbed soils. Intact soil columns including topsoil and subsoil layers were taken from the Harvard forest in Petersham, MA. Unsaturated flow conditions were maintained by applying suction to the bottom of the soil columns. The columns were irrigated by series of interrupted rainfall events using the same total volume of artificial rain water. Preliminary experiments showed continuous leaching of DOM (measured by dissolved organic carbon) with an initial peak in concentration that coincided with the passage of the wetting front. The leached DOM was also characterized by UV absorbance, fluorescence spectroscopy in the emission mode, and additional spectroscopic derived indexes such as the humification index. Ongoing column experiments are focusing on the effects of rainfall intensity, frequency, and rainfall history on DOM mobilization and transport through natural, structured soils. These investigations can elucidate the influence of factors that are associated with climate change on DOC dynamics. Results of our analyses should also provide insight into the mechanisms that govern DOM mobilization in soils.