Thesis (Ph.D.)--University of Alberta, 2010. / Title from PDF file main screen (viewed on July 13, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Soil Science, Department of Renewable Resources, University of Alberta. Includes bibliographical references.

Thesis (Ph.D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 139-149). Also available on the World Wide Web.

Thesis (M.S.)--Washington State University, August 2006. / Includes bibliographical references (p. 29-31).

Thesis (Ph.D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

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The biogeochemical cycling of oceanic dissolved cadmium (dCd) has been an active area of research for the past ~40 years, due in part to the close correlation with phosphate (PO4). The global Cd:PO4 relationship has led to the use of microfossil Cd/Ca as a paleoproxy for ocean circulation and nutrient utilization; however considerable spatial and temporal variability in the relationship - particularly in surface waters - limits the utility of the proxy. Understanding the global biogeochemical cycling of Cd is an active area of research; however the Arctic Ocean is largely omitted from global models due to lack of data. This work presents depth profiles of dCd and Cd/PO4 ratios from 18 individual stations in the Canadian Arctic, collected during the Canadian GEOTRACES cruises GN02 and GN03, which connect the Arctic Ocean to the North Atlantic through the Canadian Arctic Archipelago (CAA). Salinity-driven water mass stratification exerts a primary control on the spatial distribution of Cd in the region, with elevated dCd and high Cd/PO4 ratios (~0.37 pM/μM) associated with waters of Pacific-origin. The elevated dCd and Cd/PO4 ratios are used as a tracer of Pacific-origin waters, identifying the presence of Pacific-origin water through the CAA and into Baffin Bay. High surface Cd/PO4 ratios were observed across the transect, consistent with a general global increase in surface water Cd/PO4 with increasing latitude. The analysis of Cd and other bioactive trace metals (Mn, Fe, Ni, Cu, Zn and Pb) still presents considerable analytical challenges due to the high-risks of contamination, low concentrations and complex matrices. I present a novel multi-element analytical method, which combines the commercially-available seaFAST pico preconcentration system with ICP-MS/MS analysis. In this work, we demonstrate that ICP-MS/MS, which combines two mass-selecting quadrupoles separated by an octopole collision/reaction cell, effectively removes common interferences (ArO+ on 56Fe and MoO+ on Cd) when pressurized with O2 gas. Accurate and precise measurements of iv the consensus references standards SAFe S and SAFe D and the certified reference material NASS-6 are presented as validation of the method. This thesis presents a novel method for the analysis of trace / Graduate

Over sixty years of oceanographic observations from Ocean Station Papa (OSP) in the northeast Pacific indicate the region is losing dissolved oxygen faster than the average global rate. The greatest negative trends in oxygen concentration occur on isopycnals in the upper water column (σθ = 26.1–26.8 kg m−3) but have considerable uncertainty due to natural variability near the surface. In this thesis, I use eight Argo profiling floats equipped with oxygen optode sensors to assess the 2008—2016 interannual variability of subsurface dissolved oxygen near OSP. I developed a method to implement a time-lag correction to the optode profiles using high frequency CTD data and used reference profiles from the OSP time series to calibrate the dissolved oxygen observations. The time-lag correction markedly improves subsurface bias caused by slow optode response time. The analysis of isopycnal properties indicates that episodic shoaling of the isopycnals can cause rapid reduction of the dissolved oxygen concentration. Changes in ventilation, horizontal mixing, and water mass age were assessed and deemed unlikely drivers for the rapid O2 loss events examined. The dissolved oxygen loss during shoaling events is linked to organic matter export, due to higher concentrations of organic matter and greater respiration rates at shallower depths. Reduced net community production during the “Blob” marine heatwave may have reduced the impact of the second shoaling event examined. Studying the natural variability of dissolved oxygen in these layers can provide context for the uncertainty in the long-term trends, as well as provide insight towards the future potential for extreme oxygen minima from the combined impacts of the long-term trend and natural variability. / Graduate / 2022-09-13

Watersheds within northwestern Mississippi, a productive agricultural region referred to as the Delta, were recently identified as contributors of total nitrogen and phosphorus fluxes to the Gulf of Mexico. Water withdrawals for irrigation in the Delta have altered flow paths between surface-water and groundwater systems, allowing for more surface-water losses to the underlying alluvial aquifer. In order to understand how to manage nitrogen in a watershed, it is necessary to identify and quantify hydrologic flow paths and biogeochemical conditions along these flow paths, which ultimately combine to determine transport and fate. In order to evaluate the extent and role of surface-water losses to the alluvial aquifer on the transport of nitrate, a two-dimensional groundwater/surface-water exchange model was developed for a site within the Delta. Results from this model determined that groundwater/surface-water exchange at the site occurred regularly and recharge was laterally extensive into the alluvial aquifer. Nitrate was consistently reported in surface-water samples (n= 52, median concentration = 39.8 micromol/L), although never detected in samples collected from instream or near stream piezometers (n=46). Coupled model and water-quality results support the case for denitrification/ nitrate loss from surface water moving through an anoxic streambed. At larger scale, recent results from two Spatially Referenced Regressions on Watershed attributes (SPARROW) models imply that nitrogen is transported relatively conservatively once it enters the main channel of the Big Sunflower River Basin, which contributes much of the water discharging from the Yazoo River Basin to the Mississippi River. Net loss of nitrogen was assessed by comparing total nitrogen data from Lagrangian sampling events to chloride, drainage area, and predicted total nitrogen flux results from the SPARROW models. Results indicated relatively conservative instream transport of nitrogen at the scale of the Big Sunflower River Basin; however, two potential nitrogen loss mechanisms were identified: (1) transport and transformation of nitrogen through the streambed, and (2) sequestration and transformation of nitrogen above the drainage control structures downstream of Anguilla.

<p dir="ltr">Physical traits and the hydrologic setting of lake and wetland environments strongly affect the biogeochemical signature of aquatic ecosystems and their structure and function in the landscape. Natural freshwater ecosystems have a high propensity for carbon capture and storage through aerobic production, sedimentation, and sequestration, yet differing physical characteristics including water depth, lake surface area, and watershed size likely influence the extent to which these processes occur. Anthropogenically modified ecosystems also demonstrate complex function regarding carbon cycles, where the influence of human disturbance heightens nutrients and carbon loads into aquatic systems and leads to unique biochemical regimes. Across Indiana, agricultural practices currently affect around 65 percent of the state’s landscape, while urban development and population growth are expected to expand throughout the state. This trend is modeled throughout the midwestern United States, where the impacts of urban development on aquatic environments is further heightened by expected changes in climate, as storm intensity strengthens, and rainfall increases during certain times of the year. While understudied, there is good reason to believe that Indiana’s lakes and wetlands have incredible variability in carbon processing and carbon quality within and between systems. This variation is influenced by the wide variety of drivers including hydrology, geomorphology, water chemistry, metabolic processes, and redox conditions. The interactive influence of each of these drivers, however, is poorly understood across wide scale gradients. Predicting ecosystem productivity and its relationship with carbon dynamics is therefore an important tool for understanding freshwater ecosystems’ contributions to global fluxes of carbon. The variability within and across midwestern ecosystems creates a challenging, yet critical paradigm to understand the complexities of carbon dynamics in aquatic ecosystems, emphasizing the importance for direct data collection across a stratified gradient of ecosystems. This research shows that 1) human-assigned classifications of system type, including lake, reservoir, and wetland, are useful tools in classifying the metabolic and nutrient regimes of lentic systems, and 2) morphological features including lake depth and watershed area influence the structure of carbon quality throughout the water column. Findings provide valuable information to watershed and lake managers on the importance of different physical drivers in determining water quality across a range of lentic systems.</p>