The aims of this thesis were to characterize the molecular ecology of the hyporheic zone – between dissolved organic matter (DOM) and microbes – and to test whether seasonal and spatial patterns existed in correlation with seasonal ecosystem processes. The hyporheic zone is an area of vertical integration between groundwater and surface water, and lateral integration between terrestrial and stream ecosystems. Colonization corers were used to collect in situ DOM and bacterial communities from the hyporheic sediments of two streams that varied in hydroperiod (i.e., permanent vs. intermittent). DOM was collected using passive samplers and analyzed using 1H NMR and fluorescence spectroscopy; bacteria were characterized using terminal-restriction fragment length polymorphism. At the permanent site, bacteria correlated significantly with seasonal environmental factors including: fall communities with DOM concentration; spring and winter communities with nitrate concentrations; and summer communities with temperature. Bacterial communities at the intermittent site were significantly correlated with flooding as a function of hydrologic connectivity. Sediment communities were discriminated between hyporheic sediments and interstitial porewaters, and shared several operational taxonomic units (OTUs). Sediment communities were more distinct when hydrologic connectivity was low, and porewater communities changed dramatically upon flooding. Fifteen out of 259 OTUs were shared across aquatic sediments, interstitial porewater and watershed soil samples. DOM was spatially and seasonally dynamic in both sites. Five key DOM groups described using 1H NMR spectroscopy revealed spatial differences between the permanent and intermittent sites. EEM-PARAFAC models confirmed that despite significantly different molecular components, the relative sources of DOM at both sites were similar, including humic-like terrestrial sources and tyrosine (microbial) sources. This study provides new knowledge on both organic matter dynamics and bacterial communities in a dynamic aquatic ecotone, and also confirmed the hypothesis that bacterial communities correlated significantly with ecosystem processes within a watershed.

The aims of this thesis were to characterize the molecular ecology of the hyporheic zone – between dissolved organic matter (DOM) and microbes – and to test whether seasonal and spatial patterns existed in correlation with seasonal ecosystem processes. The hyporheic zone is an area of vertical integration between groundwater and surface water, and lateral integration between terrestrial and stream ecosystems. Colonization corers were used to collect in situ DOM and bacterial communities from the hyporheic sediments of two streams that varied in hydroperiod (i.e., permanent vs. intermittent). DOM was collected using passive samplers and analyzed using 1H NMR and fluorescence spectroscopy; bacteria were characterized using terminal-restriction fragment length polymorphism. At the permanent site, bacteria correlated significantly with seasonal environmental factors including: fall communities with DOM concentration; spring and winter communities with nitrate concentrations; and summer communities with temperature. Bacterial communities at the intermittent site were significantly correlated with flooding as a function of hydrologic connectivity. Sediment communities were discriminated between hyporheic sediments and interstitial porewaters, and shared several operational taxonomic units (OTUs). Sediment communities were more distinct when hydrologic connectivity was low, and porewater communities changed dramatically upon flooding. Fifteen out of 259 OTUs were shared across aquatic sediments, interstitial porewater and watershed soil samples. DOM was spatially and seasonally dynamic in both sites. Five key DOM groups described using 1H NMR spectroscopy revealed spatial differences between the permanent and intermittent sites. EEM-PARAFAC models confirmed that despite significantly different molecular components, the relative sources of DOM at both sites were similar, including humic-like terrestrial sources and tyrosine (microbial) sources. This study provides new knowledge on both organic matter dynamics and bacterial communities in a dynamic aquatic ecotone, and also confirmed the hypothesis that bacterial communities correlated significantly with ecosystem processes within a watershed.

Anaerobic oxidation of methane (AOM) in peatlands was investigated using 13carbon isotope tracers. Existence of AOM in marine and freshwater ecosystems is well known, but only recently has solid evidence for this process been demonstrated in northern peat accumulating wetland ecosystems. The primary objective of this thesis research was to characterize rates of AOM in peatlands across site types (bogs and fens with varying physicochemical properties) and latitudinal gradients. It was found that AOM was ubiquitous process across North American sites and dominant in fens over bogs, however carbon derived from methane was similar in both types of peatlands. Though, none of the proposed electron acceptors hypothesized stimulated AOM. AOM had a combined, average rate of 2.9 nmol methane kg-1s-1, which would translate to an approximate global consumption of 24 Tg methane annually. This mass of methane is equivalent to almost 7% of all annual anthropogenic carbon dioxide emissions.

Anaerobic oxidation of methane (AOM) in peatlands was investigated using 13carbon isotope tracers. Existence of AOM in marine and freshwater ecosystems is well known, but only recently has solid evidence for this process been demonstrated in northern peat accumulating wetland ecosystems. The primary objective of this thesis research was to characterize rates of AOM in peatlands across site types (bogs and fens with varying physicochemical properties) and latitudinal gradients. It was found that AOM was ubiquitous process across North American sites and dominant in fens over bogs, however carbon derived from methane was similar in both types of peatlands. Though, none of the proposed electron acceptors hypothesized stimulated AOM. AOM had a combined, average rate of 2.9 nmol methane kg-1s-1, which would translate to an approximate global consumption of 24 Tg methane annually. This mass of methane is equivalent to almost 7% of all annual anthropogenic carbon dioxide emissions.

Mercury (Hg)-contaminated freshwater fisheries are a global toxicological concern. Previous research suggests that the slow release of Hg in runoff from upland soils may delay the recovery of Hg-contaminated aquatic systems. Four complementary studies were undertaken in a small boreal Shield headwater catchment as part of the Mercury Experiment to Assess Atmospheric Loading in Canada and the U.S. (METAALICUS) to assess the controls on the retention and release of historically-deposited Hg (ambient Hg) and newly-deposited (spike Hg) in the soil landscape. In the first study, hydrometric and GIS-based methods were used to quantify thresholds in terrestrial water storage and their relationship to observed rainfall-runoff response. It was found that event-scale hydrologic response displayed a threshold relationship with antecedent storage in the terminal depression and predictions of event runoff improved when storage excesses from upslope depressions were explicitly routed through the catchment. In the second study, it was shown that the dominant source of ambient Hg to the lake was likely derived from shallow soil-water flowing through the lower, well-humified organic soil horizon. Throughout the catchment, ambient Hg to soil organic carbon (SOC) ratios increased with depth and the experimentally-applied spike Hg was concentrated in the surface litter layer, suggesting that the vertical redistribution of Hg in the soil profile is a function of the rate of decomposition of SOC. In the third study, canopy type was found to be a good predictor of ambient Hg and spike Hg stocks in the lower organic horizon, while drainage conditions were not, suggesting that vertical fluxes of Hg dominate over lateral fluxes in topographically-complex landscapes. Lastly, it was shown that catchment discharge, antecedent depression storage and antecedent precipitation were the best predictors of dissolved organic carbon (DOC), ambient Hg and spike Hg concentrations in catchment runoff. A comparison of DOC, ambient Hg and spike Hg dynamics for two storm events showed that distinct shifts occurred in the concentration-discharge relationship as a result of differences in antecedent moisture conditions. Combined, the results of the four studies demonstrate the need to incorporate hydrological, biogeochemical and landscape controls into predictive models of terrestrial-aquatic Hg export.

The first project is focused on kinetic analysis of two enzymes: Rsc1362 (Ralstonia solanacearum GMI1000) and PA0810 (Pseudomonas aeruginosa PA01). Rsc1362 had a kcat of 504±66 min-1 and a KM of 0.06±0.02 mM, PA0810 had a kcat of 2.6±0.6 min-1 and a KM of 0.44±0.2 mM. A lack of environmental context for a chloroacetate dehalogenase was noted in Pseudomonas aeruginosa PA01. The second project focuses on kinetic and stable isotope fractionation of 1,2- dichloroethane by DhlA (Xanthobacter autotrophicus GJ10), and Jann2620 (Jannaschia CCS1). Although both enzymes had different kinetics (DhlA: KM = 4.8±0.6 mM and kcat = 133±8 min-1, Jann2620: KM = 25.9±2.3 mM and kcat = ~1.7 min-1), they fractionated similarly (ε values of -33.9‰ and -32.9‰ for DhlA and Jann2620, respectively). As calculated AKIE values were similar to the expected values of an abiotic reaction, it was determined that neither enzyme masks the intrinsic fractionation.

Mercury (Hg)-contaminated freshwater fisheries are a global toxicological concern. Previous research suggests that the slow release of Hg in runoff from upland soils may delay the recovery of Hg-contaminated aquatic systems. Four complementary studies were undertaken in a small boreal Shield headwater catchment as part of the Mercury Experiment to Assess Atmospheric Loading in Canada and the U.S. (METAALICUS) to assess the controls on the retention and release of historically-deposited Hg (ambient Hg) and newly-deposited (spike Hg) in the soil landscape. In the first study, hydrometric and GIS-based methods were used to quantify thresholds in terrestrial water storage and their relationship to observed rainfall-runoff response. It was found that event-scale hydrologic response displayed a threshold relationship with antecedent storage in the terminal depression and predictions of event runoff improved when storage excesses from upslope depressions were explicitly routed through the catchment. In the second study, it was shown that the dominant source of ambient Hg to the lake was likely derived from shallow soil-water flowing through the lower, well-humified organic soil horizon. Throughout the catchment, ambient Hg to soil organic carbon (SOC) ratios increased with depth and the experimentally-applied spike Hg was concentrated in the surface litter layer, suggesting that the vertical redistribution of Hg in the soil profile is a function of the rate of decomposition of SOC. In the third study, canopy type was found to be a good predictor of ambient Hg and spike Hg stocks in the lower organic horizon, while drainage conditions were not, suggesting that vertical fluxes of Hg dominate over lateral fluxes in topographically-complex landscapes. Lastly, it was shown that catchment discharge, antecedent depression storage and antecedent precipitation were the best predictors of dissolved organic carbon (DOC), ambient Hg and spike Hg concentrations in catchment runoff. A comparison of DOC, ambient Hg and spike Hg dynamics for two storm events showed that distinct shifts occurred in the concentration-discharge relationship as a result of differences in antecedent moisture conditions. Combined, the results of the four studies demonstrate the need to incorporate hydrological, biogeochemical and landscape controls into predictive models of terrestrial-aquatic Hg export.

The first project is focused on kinetic analysis of two enzymes: Rsc1362 (Ralstonia solanacearum GMI1000) and PA0810 (Pseudomonas aeruginosa PA01). Rsc1362 had a kcat of 504±66 min-1 and a KM of 0.06±0.02 mM, PA0810 had a kcat of 2.6±0.6 min-1 and a KM of 0.44±0.2 mM. A lack of environmental context for a chloroacetate dehalogenase was noted in Pseudomonas aeruginosa PA01. The second project focuses on kinetic and stable isotope fractionation of 1,2- dichloroethane by DhlA (Xanthobacter autotrophicus GJ10), and Jann2620 (Jannaschia CCS1). Although both enzymes had different kinetics (DhlA: KM = 4.8±0.6 mM and kcat = 133±8 min-1, Jann2620: KM = 25.9±2.3 mM and kcat = ~1.7 min-1), they fractionated similarly (ε values of -33.9‰ and -32.9‰ for DhlA and Jann2620, respectively). As calculated AKIE values were similar to the expected values of an abiotic reaction, it was determined that neither enzyme masks the intrinsic fractionation.

Microbial activity occurs year-round in Arctic soils, including during the winter when soils are frozen. From 2004 to 2008 I monitored soil microbial and nutrient dynamics in low Arctic wet and dry sedge meadows near Churchill, Manitoba. I documented a consistent annual pattern in which soil microbial biomass (MB) and soil nutrients peak in late winter, and decrease during the early stages of spring thaw, remaining in low abundance during the summer. Based on a series of experiments, resource shortages do not appear to be the cause of the microbial decline, as has been hypothesized. Observations and theoretical considerations regarding soil physical properties indicate that this decrease is driven by the influx of liquid water at thaw that brings about a rapid change in the chemical potential of water, leading to cell lysis. I have used 15N isotope tracing to show that inorganic nitrogen is taken up very quickly at thaw by the roots of the dominant plant, Carex aquatilis. This represents a critical window of opportunity for these plants, as nitrogen remains abundant only for a short time. The described annual pattern was pronounced in wet sedge sites, but some inter-annual variation is evident, for example a post-thaw soil nitrogen pulse in 2006, and low winter MB in 2008. In the dry sedge meadow, fluctuations in MB and nutrients were dampened relative to wet sites, and the annual pattern was variable, particularly after 2006. Over four years, peak winter values of soil MB and nutrient variables declined in both wet and dry sites, and this could be related to a drying trend. This work improves our understanding of the controls on decomposition and primary productivity in a system that is experiencing climate warming and increased precipitation. Changes to hydrology, carbon and nitrogen cycling, and primary productivity will have further effects on vegetation communities and higher trophic levels, including several species of migratory birds.

Presently within the scientific literature no terrestrial biogenic silica models exist that compare by magnitude, processes transporting silica. Change in vegetation type has the potential to alter dissolved concentrations of Si in rivers and ultimately the oceans. Diatoms greatly depend on Si concentrations for growth, and as a result land cover change may have influenced onset diatom radiation during the Cenozoic. To expand our understanding of this cycle, a terrestrial biogenic silica model is proposed. This model accounts for biogenic silica production, dissolution and leaching through soils, as well as providing estimates for annual silica soil storage. A case study performed using the constructed biogenic silica model, showed an increase in oceanic DSi concentration during the Miocene (period of diatom diversification). However, this increase does not appear to have been sufficient to trigger global diatom radiation, suggesting multiple geographically isolated locations for this diversification.