To assess the relative contribution of phosphorus release from sediment in Cootes Paradise Marsh, I first examined spatial and temporal variability of laboratory-measured release rates from sediment samples collected from 12 sites within the wetland (Chapter 1 ). The microbial communities from these 12 sites were characterized on the basis of sole-carbon-source utilization using BIOLOG GN plates containing 95 substrates. Results from these experiments were entered into a principal component analysis and the release rates for all sites were regressed against corresponding PC 1 and PC2 scores (Chapter 2). Differences in microbial physiology as defined by PC 1 and PC2 scores accounted for 49% and 53%, respectively of the variation in phosphorus release rates. Using stepwise multiple regression, I concluded that the key determinants of laboratory-derived release rates from West Pond sediment (a highly eutrophic site within Cootes Paradise Marsh) are oxic state, ambient temperature and time of sediment collection (Chapter 3). Using this information I developed a multivariate model to predict release rates. This model, along with 2 alternative approaches, was used to estimate the extent of internal loading (kg d-1) in Cootes Paradise Marsh (Chapter 4). Method 1 was a highly controlled, static approach and resulted in an internal load of 11 .6 kg d-1, which was attributed to diffusion. The remaining two methods were more dynamic in nature as they took into account temporal variation, ambient temperature and the development of anoxia. Using Method 2, I estimated an internal load of 7.8 to 8.5 kgd-1, which was based on empirically-derived laboratory release rates. Method 3 consisted of the predictive model from which I estimated an internal load of 6.7 kgd-1• I attributed the release from the latter two methods to microbial mineralization processes. Based on this work and a previous estimate of internal loading in Cootes Paradise Marsh (Prescott & Tsanis 1997), I concluded that mineralization accounts for 22.3% of total phosphorus loading to the system, preceded only by urban runoff ( 41% ). / Thesis / Master of Science (MS)

Indiana University-Purdue University Indianapolis (IUPUI) / Phosphorus (P) is essential for aquatic life; cycling between both inorganic and organic forms to maintain an ecological balance. Its addition into P-scarce freshwaters, either through terrestrial (external) or sedimentary (internal) loading, may disrupt this balance causing blooms of phytoplankton to flourish, often resulting in harmful environmental and anthropogenic consequences. Accordingly, reduction of external P loading has been commonly implemented with a recent focus on sediment-bound legacy P that is mobilized into the water column during dynamic redox conditions. Mobile P species have been identified as both inorganic and organic, with the former representing the most bioavailable fraction, and the latter serving as a source for labile P in freshwaters when in high demand, particularly during blooms. Missisquoi Bay in Lake Champlain, VT experiences harmful cyanobacterial blooms driven by internal P loading and has been the target of numerous geochemical and hydrological studies. This thesis describes a high-resolution investigation of both the organic P and organic matter compositions of the bay with respect to mobility, reactivity, and bioavailability using Fourier Transform-Ion Cyclotron Mass Spectrometry (FT-ICR MS). Sediment from Missisquoi Bay was extracted with a diverse set of reagents, resulting in fractionation of both organic matter and organic P, and illustrating the distribution of various labile and recalcitrant compounds. Many of these molecules are associated with porewater or easily extractable mineral surfaces providing a link to the benthic organic matter and phosphorus fractions available to microorganisms. Additionally, the organic chemistry of the bay was investigated seasonally from May 2017 to January 2018 revealing biological processing from the spring runoff season through the post-bloom summer season. The transition from late summer to under ice conditions in winter was less severe with a higher commonality between both organic matter and organic P compounds, suggesting reduced biological and abiotic degradation. Moreover, short-term anoxic incubations of sediment cores from each season revealed the presence of diverse organic signatures from sorption processes, and a significant contribution of benthic microbial activity to the benthic organic geochemistry.

Eutrophication is an increasing global concern as human effluent saturates lakes with an over abundance of nutrients. Phosphorus, generally being the limiting nutrient, is often the most impactful, allowing cyanobacteria populations to grow out of control leading to harmful blooms that can produce cyanotoxins, anoxic lake conditions, and mass fish kills. Utah Lake, a shallow highly eutrophic fresh water lake located in central Utah Valley, has experienced these harmful algal blooms for the last several years. The internal phosphorus cycle is a significant driver in Utah Lake's eutrophication, as the sediments act as both a sink and a source for phosphorus. Most of the phosphorus originates from external sources, gets captured by the sediment, and then through several physiochemical and biological process, gets released back into the surface water as a self sustaining eutrophication system. To determine the effects of the different physiochemical processes that drive the internal phosphorus system, we incubated 72 total sediment cores taken from two locations, chosen to best represent the lake's chemical and spatial variability, under aerobic, anaerobic, pH=9.5 and pH=7 conditions with various P concentrations (ambient, 0.5X, 2X, 4X) taking water samples at 0, 12, 24, and 72 hours. Dissolved oxygen (DO), pH, soluble reactive phosphorus (SRP), total dissolved phosphorus (TDP), and other major ions were measured for each sample. The highest P sediment release occurred under aerobic conditions, while the highest P sediment uptake occurred under anaerobic conditions. While pH did appear to have a mild effect on P flux, our study showed the lake has a remarkably stable bicarbonate buffer system making it unlikely that pH would contribute significantly under natural settings. Under all conditions the 2X and 4X cores experienced the highest P uptake, but final elevated P concentrations were still higher than initial ambient concentrations, indicating a probable delayed recovery time after external reductions occur.

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