Browsing by Subject "Dissolved organic matter"

Now showing 1 - 3 of 3
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    Effect of topography and glaciation history on the movement of carbon and nitrogen within arctic hillsides.
    (2010-04) Whittinghill, Kyle A.
    The transport of dissolved organic matter (DOM) down hillslopes to aquatic ecosystems has important implications for both terrestrial and aquatic primary productivity. DOM is an important energy and nutrient source for both terrestrial and aquatic microbes. Within watersheds, physical, chemical, and biological processes transform DOM, but it not well known how landscape heterogeneity may affect these processes in arctic watersheds. In the northern foothills of the Brooks Range, expansion and contraction of mountain glaciers over the last several ice ages have created a mosaic of landscape ages with similar climate and vegetation. My research indicates that younger landscapes (<50,000yrs) have significantly lower pH, 10x higher exchangeable base cation concentrations, and significantly lower rates of DOM production and microbial respiration than older landscapes, which could significantly affect fluxes of carbon and nutrients across the landscape. At the watershed scale, I examined patterns in soil and stream water concentrations of DOM within hillslopes across the chronosequence. I found that while concentrations of dissolved organic carbon decreased significantly moving downslope from the hilltop to the stream; dissolved organic nitrogen concentrations remain similar within the hillslope, but are significantly different among landscape ages. I also used a variety of indices to examine spatial patterns in the biodegradability of DOM within hillslopes and among landscape ages in northern Alaska. My results suggest the low biodegradability of DOM found in streams and rivers in the region is not due to microbial processing of labile DOM in terrestrial ecosystems, but rather to production of recalcitrant DOM throughout the landscape.
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    Photochemical Production of Reactive Intermediates in Inland Surface Waters
    (2017-09) McCabe, Andrew
    Reactive intermediates form when dissolved natural organic matter (DOM) absorbs sunlight in surface waters. These reactive intermediates include triplet excited states of dissolved organic matter (T*), reactive oxygen species, carbonate radical, and halide radicals. They are associated with a variety of physicochemical processes, including carbon and metal cycling, pathogen inactivation, and reactions with trace organic contaminants. T* is particularly important in these processes because it can react either through electron or energy transfer mechanisms and it is responsible for the formation of secondary reactive intermediates, such as singlet oxygen and radicals. The quantity and composition of DOM are key variables that control the rate and efficiency of T* formation, defined as the ratio of the rate of T* formation to the total rate of light absorption. As DOM is transported through aquatic environments, its composition is altered by natural and anthropogenically-influenced biogeochemical processes. Here, DOM composition is related to the reactivity of T* in stormwater and in temperate wetlands, two important aquatic systems involved in the production and transport of DOM. The rate and efficiency of T* formation were measured with two chemical probes, 2,4,6-trimethylphenol and trans,trans-2,4-hexadienoic acid, that quantify rates of T* electron transfer and energy transfer, respectively. DOM composition was characterized using absorption spectrophotometry, fluorescence spectroscopy, and Fourier transform ion cyclotron mass spectrometry. Within our sample set, the observed range in the efficiency of T* formation is <1%–14%, and shows a distinct dependence on watershed vegetative land cover and open water extent. The rate of T* formation increases with the concentration of dissolved organic carbon (DOC) while the efficiency of T* formation is independent of DOC. The data reported here suggests that DOM derived from vascular plants has a dual role, controlling both the rate of light absorption and the efficiency of T* formation.
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    Photodegradation of Natural Organic Matter in Plume Versus Non-plume Waters in Lake Superior
    (2021-08) Edge, Devin
    Natural organic matter (NOM) undergoes direct and indirect photodegradation under ultraviolet (UV) light exposure, is an important source of energy for the aquatic food web and affects how much light can penetrate a water column. Photodegradation of NOM can lead to photobleaching of colored dissolved organic matter (CDOM), the release of low-molecular weight (LMW) organic species and the release of bioavailable nitrogen and phosphorus species . Photomineralization of NOM can produce carbon dioxide and carbon monoxide, removing organic carbon from the system. Recent storm events of greater intensities and frequencies have caused increased amounts of runoff, including dissolved and particulate natural organic matter, in the Laurentian Great Lakes region. This increased runoff may change the extent and types photochemistry happening in surface waters of these large lakes. The differences between the photodegradation of natural organic matter from plume-impacted water versus open lake water in Lake Superior were studied by performing irradiations under natural sunlight at 47°N latitude in August and September 2020. Terrestrially impacted samples (both before and after a storm), as well as open water samples were exposed to three days of natural sunlight. Autoclaved whole-water and filtered-water samples from before, during, and after the irradiations, along with matching dark controls, were analyzed for total and dissolved organic carbon, total and dissolved nitrogen, total and dissolved phosphorus, soluble reactive phosphorus, ammonia, and UV-Visible spectroscopy proxies (spectral slope ratios, CDOM absorbance, and SUVA254). Irradiated filtered water samples from the terrestrially impacted and storm-impacted sites exhibited larger percent and overall changes in spectral slope ratios and greater losses of colored dissolved organic matter (CDOM) absorbance relative to open water samples. This differed from the whole water samples, where the storm-impacted site experienced the smallest percent change in UV-Vis measurements, most likely because the particulates in this sample limited its light exposure. Except for this site, filtered water irradiations generally experienced lower percent changes and overall changes in UV-Vis measurements compared to whole water samples. An increase in DOC concentration was found in the dark sample for the whole water irradiation of the terrestrially-impacted site taken before a storm occurred, indicating potential desorption occurring when POM is included. Finally, there was also an increase in ammonium concentration in the same aforementioned whole water sample upon light exposure. The photodegradation of organic matter in Lake Superior was mainly affected by site location and whole vs. filtered treatment, and resulted in some ammonium release in whole, terrestrially-impacted samples.