Partial denitrification anammox (PdNA) is an emerging wastewater treatment technology with the potential to increase process capacity and save on energy and carbon. PdNA circumvents potential issues with stability of the more familiar mainstream partial nitritation anammox (PNA) process. The PdNA process can be used to effectively remove ammonia, nitrate, and nitrite from mainstream municipal waste streams. To retain slow growing anammox, some sort of retention system is needed with media being a common solution to this problem. PdNA has been successfully implemented in mainstream full-scale systems in sand filters and with moving media. The goal of this study was to assess the denitrifying capabilities, anammox treatment capacity, and effective surface area to volume of two types of fixed media. A nitrifying pilot was set up to assess the effective surface area to volume. To assess the nitrifying and anammox ammonia removal capabilities of the fixed media, a fixed media PdNA system was installed in the second anoxic zone of a full-scale municipal wastewater treatment plant. The fixed media system consisted of three modules of sheets modified to mimic a plug flow system. After accounting for the estimated nitrate removal from mixed liquor, denitrification rates normalized to media surface area were 0.52 +/- 1.9 g/m2-day in the first module, 0.62 +/- 0.91 g/m2-day for the second module, and 0.56 +/- 0.90 g/m2-day for the third module. In ex situ batch testing it was found that maximum ex-situ anammox ammonia removal rates for the / Master of Science / Urban population growth has created a two-pronged problem for wastewater treatment plants. Plants in populated areas are seeing increases in flow along with growing space restrictions that limit new infrastructure construction. Additionally, rising environmental awareness from the public has spurred regulatory agencies to impose tighter limits on the quality of water leaving plants and entering sensitive watersheds. These factors have driven a need for treatment techniques that allow plants to operate better with their existing equipment. Overall, this concept is known as process intensification. One such method that treatment plants are using to intensify wastewater treatment is the addition of plastic media into their existing tanks. This media provides additional surfaces for the microorganisms that biodegrade the pollutants in the wastewater to grow and allows waste to be treated faster in the same area. It also allows slow growing organisms to be retained in the system that would otherwise not have time to grow. Such slow-growing microbes are especially critical for the removal of ammonia, a toxic form of nitrogen that occurs in high concentrations in wastewater. The partial denitrification-anammox process is an intensification process that leverages microbial metabolisms to convert nitrate to nitrite instead of denitrifying the nitrate all the way to nitrogen gas. Plants then let more ammonia pass through the aeration zone, where ammonia is converted to nitrate. The bleed through ammonia and the nitrite generated from partial denitrification is used by microbes called anammox, which denitrify without the addition of carbon. The full denitrification process requires externally added carbon, which is energy intensive to produce and expensive, and aeration requires energy to run the aeration blowers. Bypassing the full denitrification process using PdNA results in two-fold cost and energy savings. The plastic media help slow-growing anammox bacteria attach and grow to achieve this aim. Most of the plants that use plastic media use media that is free floating in the tank. However, certain plants cannot use this floating plastic media because it can either plug up the system, or flow to the end of the treatment tank and have no way to get back to the front. In instances such as these it could be beneficial to use a type of media that is fixed in place. One potential use of fixed media that has never been tried before is with partial denitrification with anammox. This research sets out to evaluate the effectiveness of fixed media with use in a partial denitrification anammox process and compare it to a treatment tank of moving media that is present at the same plant to find out whether it may be a viable option for retrofitting plants that cannot use moving media.

The CE-QUAL-W2 model has been selected as a tool for use in water quality management studies of the Occoquan Reservoir. In order for the model to achieve its best possible predictive capability, additional quantitative information on denitrification rates in the reservoir was required. A microcosm operating protocol was developed to obtain such information and also to enhance the understanding of complex nitrate-sediment-phosphorus interactions. The microcosm system developed was a biphasic system, consisting of a single continuous stirred tank reactor (CSTR), or a series of CSTRs containing representative sediment and water samples from the reservoir. The system was configured to simulate the bottom waters in the upper reaches of the reservoir during anoxic conditions. Nitrate concentrations in the microcosm system were monitored, and first-order denitrification-rate constants calculated to be used as an input to the reservoir water quality model CE-QUAL-W2. Other water chemistries were also monitored to investigate the nitrate effects on water quality. From the investigation results, it appears that the first-order denitrification-rate constant of the model should be set at 0.22 day-1 instead of the model default value. Nitrate was also observed to be removed by chemical and/or biologically mediated reduction by reduced forms of manganese. Once the nitrate was depleted, soluble manganese was released from the sediment first, followed by soluble iron. The release of phosphorus was not observed in this study after the depletion of nitrate, but nevertheless, was believed to occur. The absence of the release was attributed to phosphorus adsorption to the Plexiglas reactor walls. / Master of Science

An alternative on-site wastewater treatment and disposal system (OSWTDS) consisting of a soil infiltrator with low pressure distribution was evaluated in a soil that was unsuitable for a conventional OSWTDS under current Commonwealth of Virginia Sewage Handling and Disposal Regulations, due to a shallow seasonally perched water table and low hydraulic conductivity. The absorption field consisted of two subsystems numbered as 1 and 2 with effluent design loading rates of 5.1 and 10.2 Lpd/m2, respectively (actual loading rates of 2.4 and 4.9 Lpd/m2, respectively). Soil matric potentials compared seasonally for each subsystem and indicated that both provided similar hydraulic performance. Background water quality was generally improved by subsurface movement through the absorption fields. A bacterial tracer was found in shallow (45.7 cm) and deep (213.4 cm) sampling wells within 24 h in the two subsystems (but in low numbers) over both summer and winter sampling periods. A viral tracer was detected within 48 h in both shallow and deep wells, but only in subsystem 2 in the winter. In evaluating denitrification potential, the addition of glucose to soil core samples did increase quantitatively, although not significantly, nitrous oxide production in each subsystem, at each depth, during each season. Overall, the performance of both subsystems was very similar. The soil infiltrator functioned very well, as designed for the site and soil limitations. It appears to be a potential alternative OSWTDS for use in problem soils. / Master of Science

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 114-131). Also available on the World Wide Web.

Decreasing the nitrogen transport from land to surrounding seas is a major task throughout the world to limit eutrophication of the coastal areas. Several approaches are currently used, including the establishment of wetlands, to decrease the transport of nitrogen. Wetlands represent ecosystems where the nitrogen removal from water can be efficient given that they are appropriately designed. The aim of this thesis was to investigate and quantify the effect of critical factors that regulate the nitrogen removal in wetlands, and to develop better guidelines for wetland design. Studies were performed at different scales, from microcosms to full scale wetlands, and methods included modelling, mass balance calculations and process studies. A first order rate model was used to simulate the nitrogen transformations in two large wetlands treating wastewater containing both ammonium and nitrate nitrogen. It was found that the dynamics of the main itrogen transformation processes could not be satisfactorily described using this approach. Large wetlands containing vegetation are complex ecosystems, and the process rates vary in both time and space. The great diversity of microenvironments favours different nitrogen processes, and large differences in potential nitrification and denitrification rates were found between different surface structures within a wetland. The results from microcosms measurements showed that the highest potential for nitrification was on surfaces in the water column, while the denitrification capacity was highest in the sediment. For the sediment denitrification capacity, the plant community composition was shown to be of major importance primarily by supplying litter serving as a carbon and energy source, and/or attachment surfaces, for denitrifying bacteria. Denitrification rates may be affected more than three fold by different types of litter and detritus in the sediments. Intact sediment cores from stands of the emergent plants Glyceria maxima and Typha latifolia had higher denitrification potential than sediment cores from stands of the submersed plant Potamogeton pectinatus. However, the quality of the organic material for the denitrifying bacteria was highest in G. maxima and P. pectinatus stands. All sediment cores from the wetland were limited by carbon, and the lower denitrification capacity of the submersed plant, P. pectinatus, was likely due to lower amounts of organic matter. However, in another wetland, intact cores from stands of the submersed plant Elodea canadensis had a higher denitrification capacity than the cores from stands of T. latifolia and Phragmites australis. This was possibly due to a larger biomass, and better quality, of the organic matter from that submersed specie, or to epiphytic biofilms on the living plants. Those microcosms studies showed that both the quality of the organic matter as a substrate for the microbial communities, and the amount of organic material produced were important for the denitrification capacity. In pilot scale wetlands, the composition of the plant community was also a more important factor for high nitrate removal than the differences in hydraulic loads (equivalent of 1 or 3 d retention time), despite the cold climate. The greatest removal was found in wetlands with emergent vegetation dominated by P. australis and G. maxima, rather than in wetlands with submersed vegetation. In brief, the results presented in this thesis emphasize the importance of dense emergent vegetation for high annual nitrate removal in treatment wetlands.

Nitrogen and phosphorus are involved in many processes on the Planet Earth. Especially in agricultural areas water is contaminated by nutrients, which can cause the eutrophication of surface waters, and other problems. The solution could be use of denitrifying bioreactors, which are used for the reduction of high nitrate concentrations in shallow groundwaters. The subject of the thesis was the study of phosphorus removal in the denitrification bioreactor by steel turnings, which are constituent part of the organic load of the bioreactor. Steel turnings release Fe, which causes the precipitation and adsorption of P. Eight bioreactors were filled with poplar woodchips. To these columns just above the surface were added model water enriched with nitrate nitrogen, phosphate phosphate was added to 4 columns, where two of them were enhanced by the addition of steel turnings upstream of the wood medium. Sampling and the analyses of the samples were determined weekly, determination of the phosphorus, iron and other substances necessary for the detection of processes in the bioreactor was performed. The dependence of phosphorus removal on the bioreactor operating conditions was evaluated based on measured data, and the effect of iron on the biological denitrification process was also assessed. Steel turnings have been found to be effective in removing TP, but it is necessary to solve iron leaching in the future. The concentration of phosphorus was reduced up to 0 mg/l on the effluent from the denitrification bioreactors, efficiency of phosphorus removal reached 100 %. The presence of steel chips had no effect on denitrification speed. The denitrification process was also successful in the phosphorus removal columns. From the point of view of leaching of substances and iron, the removal of N and P seems to be preferable in dry period during stoppage with no water fillings. Shutdown of bioreactors with flooded filling caused high concentrations of leached iron up to 149 mg/l

<p>More than 50% of wastewater biosolids are applied to agricultural fields as fertilizer in the U.S. This technique has been used for decades as a widely accepted beneficial reclamation method for biosolids, which meet the established regulatory levels for nutrients, metals, and pathogens. A major drawback to land application is the potential environmental release of non-regulated organic contaminants, which accumulate in biosolids during the wastewater treatment process. Recent studies have been performed to identify and quantify the presence of emerging contaminants in biosolids, and others have investigated the effects of compounds already identified as `priority pollutants' and whose use is waning. However, there is limited research on the effect of emerging organic contaminants on soil microbial ecology and nutrient cycling. Because many of the compounds found in biosolids are specifically designed to elicit biological modifications (e.g., antimicrobials), there is a risk that these compounds will disrupt microbial soil functions, decrease soil productivity, and ultimately affect the long term viability of these ecosystems, resulting in unforeseen economic and social costs. Therefore, there is a clear need to characterize the effects of novel contaminants on soil health.</p><p>This dissertation was divided into three distinct parts examining the impacts of emerging organic contaminants on soil microbial ecology with increasing complexity to better reflect environmental conditions. To assess the ecological impacts, the functional endpoint of denitrification was selected because it provides a vital indication of soil health. Denitrifying bacteria play a critical role in this process, and thus, were used as indicator organisms for determining contaminant ecotoxicological potential. Furthermore, antimicrobial agents (a.k.a., bactericides or biocides) were selected as model contaminants because they are designed specifically to deactivate microorganisms, are heavily used in the U.S with over $1 billion in yearly sales, and have been measured in biosolids.</p><p>Overall, the objectives of this dissertation were to: 1) develop a rapid, high-throughput functional assay that measured denitrification inhibition for screening potential ecological impacts of biosolids-derived antimicrobial agents, 2) determine the potential effects of common and emerging biosolids-derived antimicrobial agents on denitrification by a model soil denitrifier, Paracoccus denitrificans PD1222, 3) examine the impacts of the most commonly used antimicrobial, triclosan (TCS), on wastewater treatment efficiency in bench scale sequencing batch reactors (SBRs) coupled with anaerobic digesters, 4) examine the impacts of biosolids aged and spiked with TCS on denitrification under simulated agricultural soil conditions, and 5) evaluate potential impacts of TCS in `traditional' biosolids on denitrification in agricultural soil under field conditions.</p><p>The first phase of research pertaining to Objectives 1 and 2 examined the baseline interactions between biosolids-derived antimicrobial agents and soil microbial ecology. However, to isolate the effect of an individual contaminant from the myriad of contaminants found in biosolids, there was a need for developing a rapid, high-throughput method to evaluate general ecotoxicity. In the first part of this dissertation, we developed a novel assay that measured denitrification inhibition in a model soil denitrifier, Paracoccus denitrificans Pd1222. Two common (TCS and triclocarban) and four emerging (2,4,5 trichlorophenol, 2-benzyl-4-chlorophenol, 2-chloro-4-phenylphenol, and bis(5-chloro-2-hydroxyphenyl)methane) antimicrobial agents found in biosolids were analyzed as model contaminants. Overall, the assay was reproducible and measured impacts on denitrification over three orders of magnitude exposure. The lowest observable adverse effect concentrations (LOAECs) were 1.04 &mu;M for TCS, 3.17 &mu;M for triclocarban, 0.372 &mu;M for bis-(5-chloro-2-hydroxyphenyl)methane, 4.89 &mu;M for 2-chloro-4-phenyl phenol, 45.7 &mu;M for 2-benzyl-4-chorophenol, and 50.6 &mu;M for 2,4,5-trichlorophenol. Compared with gene expression and cell viability based methods, the denitrification assay was more sensitive and resulted in lower LOAECs. Of the six compounds examined, four resulted in LOAECs that were below or within an order of magnitude of concentrations that were measured in the environment, indicating potential ecological impacts.</p><p>In the second part of the dissertation, the impacts of emerging contaminants were examined first under laboratory conditions mimicking wastewater treatment processes (Objective 3) and then agricultural fields (Objective 4). For this phase, TCS, which is the most widely used antimicrobial agent and identified in the first phase for potential ecological impacts, was used as the model contaminant. To mimic wastewater treatment processes, bench scale SBRs coupled with anaerobic digesters were set up and operated. The SBRS and digesters were seeded with activated and anaerobically digested sludge from the North Durham Water Reclamation Facility (NDWRF, Durham, NC). Reactors were fed synthetic wastewater with or without 0.73 &muM of TCS. Samples were taken periodically to monitor chemical oxygen demand (COD), ammonium (NH₄<super>+</super>), nitrate (NO₃<super>-</super>), nitrite (NO<sub>2</super>-</super>), total suspended solids (TSS), volatile suspended solids (VSS), dissolved oxygen (DO), and phosphate (PO₄<super>3-</super>) and pH. In addition, biomass samples were collected for DNA extraction and microbial community analysis using terminal restriction fragment length polymorphism (T-RFLP) of 16S SSU rDNA. Methane production was also monitored for the anaerobic digesters. In addition, the final digested biosolids that were generated from the SBRs fed with and without TCS were analyzed for TCS concentration, TSS, VSS, TKN, phosphorus (as P₂O₅), potassium (as K₂O), and pH. Overall, biological processes associated with nitrogen removal (nitrification and denitrification), were impacted by TCS entering the SBRs regardless of the starting microbial community. Both of the SBRs that were not receiving TCS reached steady-state at greater than 92% NH₄<super>+</super>, removal within the first week of operation, whereas the SBRs receiving TCS took 42 and 63 days to reach steady-state removal at that level. However, while NH₄<super>+</super> removal was temporarily inhibited, elevated levels of NO₃<super>-</super> and NO₂<super>-</super> in the effluent of the TCS fed SBRs, suggested longer-term impacts on nitrite oxidizing bacteria (NOB) and denitrifiers. After Day 58, the NO₃<super>-</super> effluent concentration for the SBRs receiving TCS was 3.9 ± 0.16 mg/L, which was 2.4 times greater than the NO₃<super>-</super> effluent of the SBRs not receiving TCS (1.7 ± 0.08 mg/L). Similarly, after Day 58, the NO₂<super>-</super> effluent of the SBRs receiving TCS reached a steady-state concentration of 8.7 ± 0.75 mg/L. The mean NO₂<super>-</super> concentration in the controls after Day 58 was 7.7 times lower at 1.1 ± 0.78 mg/L, but was still trending towards 0 when the reactors were stopped. No inhibition was observed for COD and PO₄<super>3-</super> removal. In addition, non-metric multidimensional scaling (NMS) ordination analysis showed that the microbial communities between SBRS fed with and without TCS were similar on Day 0, but increased in difference to Day 41, around when the major changes in nitrification were observed. After a slight increase in similarity between the control and TCS SBR microbial communities on Day 41, the communities increased in difference to Day 63.</p><p>To mimic agricultural field conditions, containers of soil were amended with the biosolids generated from the SBRs. The containers were maintained in a growth-chamber to simulate field lighting and watering conditions. Three biosolids treatments were examined: 1) biosolids generated from the SBRs not fed TCS, but that still had low backgrounds of TCS (a.k.a., Control Biosolids); 2) biosolids generated from the SBRs fed with TCS (a.k.a., Aged TCS Biosolids); and 3) biosolids that were generated by the SBRs not fed TCS, but spiked with TCS 24 h before application (a.k.a., Spiked TCS Biosolids). Alfalfa was planted in half of the containers receiving the Control and Aged TCS Biosolids to assess differences due to vegetation. To assess the overall ecotoxicity of biosolids aged and spiked with TCS, the function, abundance, and diversity of the soil denitrifying communities were examined. The impacts on total bacteria abundance and diversity were also examined for comparison. Specifically, the denitrifying enzyme activity (DEA) assay was used to measure functional impacts, quantitative polymerase chain reaction (qPCR) was used to measure impacts on abundance, and T-RFLP was used to measure impacts on diversity. Correlations between these methods were also examined for possible interactions between denitrifier function and community structure and to provide insight into targets of inhibition. Lastly, a denitrification inhibition score was developed to quantify global impacts of TCS on denitrification. The containers with plants that received biosolids aged with and spiked with TCS showed potential long-term inhibition based on measurement of soil denitrification at 26.9 ± 4.6 &mu;g/kg and 68.6 ± 26.9 &mu;g/kg of TCS, respectively. Denitrifier abundance and diversity, however, were more sensitive to TCS in biosolids and inhibition was observed throughout the experiment, with maximum inhibition on Days 7 and 28. Inhibition of denitrifier abundance and diversity was observed at TCS concentrations as low as 17.9 ± 1.93 &mu;g/L, which was about 10 to 3000 times lower than concentrations reported by other studies that showed impacts on other functional endpoints (i.e., respiration, phosphatase activity, NO₃<super>-</super> and NO₂<super>-</super> production, and Cy17 stress biomarker abundance), even after taking pH into account. Five significant correlations were developed, three of which related qPCR and the DEA assay, or abundance and activity. However, the analyses that were correlated did not yield the same results as far as significant inhibition in the presence of TCS. Thus, while the results suggested some relatedness between activity, abundance, and diversity, the results generally support the use of multiple methods to determine the ecotoxicity of biosolids-derived organic contaminants. As a result, a denitrification inhibition score was developed that took into account all three methods to determine the overall ecotoxicity of TCS in biosolids. Overall, the denitrification inhibition score showed that denitrification was inhibited by both biosolids that were aged and spiked with TCS over the extent of the 84 day experiment, but maximum inhibition occurred after a week to about a month. While the denitrification inhibition score indicated that the TCS in the biosolids aged with TCS was less bioavailable than in the spiked biosolids, the impacts of the aged and spiked biosolids could have also been due to differences in TCS concentrations.</p><p>Objective 5 consisted of a long-term soil sampling campaign on four agricultural fields receiving Class B municipal biosolids. Soil samples were taken before and after biosolids application and were analyzed to elucidate potential impacts of TCS in the biosolids on denitrification. Again, to assess the overall impacts of TCS on the soil denitrifying community, the DEA assay, qPCR, and T-RFLP were used to measure impacts on function, abundance, and diversity, respectively. Similar to Objective 4, the analysis included an examination of potential correlations between denitrifying community structure and function, and quantification of global impacts using the denitrification inhibition score. As expected, the results in this pilot-study reflected the complexity of the system that was analyzed and many more samples, which account for variables including, but not limited to soil characteristics, biosolids characteristics, biosolids application rates, and chemical composition and quantities, would be needed to show any statistically significant differences. Nevertheless, several key results were obtained. Again potential long-term inhibition of denitrification was observed using the DEA assay, however the effects of exhaustion of resources, such as NO₃<super>-</super>, or significant changes in the local environment were suspected, but could not be verified. Inhibition was also observed for denitrifier abundance, but little to no inhibition was observed when examining the relative number of denitrifying species. Thus, while the abundance of denitrifiers was reduced, and denitrification was eventually depressed, the number of species in the soil remained constant. When looking at the denitrification inhibition score, which took all three measurements into account, increased inhibition over time was observed with the exception of the measurements on Days 30 and 103, which indicated overall, but weak inhibition of denitrification by the application of biosolids. NMS ordinations showed no correlation between the shift in denitrifying microbial community and TCS. Because of the complexity of the soil and biosolids and because of the myriad of contaminants likely in the biosolids, the results may not be significant and a more in-depth study was recommended.</p><p>Overall, the results presented in this dissertation provide a systematic evaluation of the effects of biosolids-derived TCS on agricultural soil microbial ecology. First, it was demonstrated that statistically significant inhibition of denitrification could be used as a potential indicator of biosolids-derived emerging organic contaminant ecotoxicity. The denitrification assay that was developed was then used to analyze ecotoxicological potential of six emerging biosolids-derived antimicrobial agents, and found inhibition of denitrification at environmentally relevant concentrations. The most widely used antimicrobial agent, TCS, was further shown to inhibit wastewater treatment processes, as well as, denitrification in simulated agricultural conditions after being aged with and spiked into biosolids. In addition, evidence showing potential inhibition of denitrification by TCS in `traditional' biosolids under field conditions was also obtained. Based on these results, this dissertation asserts that biosolids-derived emerging organic contaminants pose a potential risk to agricultural soil microbial ecology and overall soil health. Future studies, however, are needed to examine the impacts of other contaminants that might be flagged with the assay developed in this dissertation under more complex conditions mimicking the environment. Furthermore, other research is needed to examine the role microbial communities play in the bioavailability of emerging contaminants, especially TCS, and a more extensive, in-depth study is needed to characterize the individual impacts of emerging contaminants on soil microbial communities under field conditions.</p> / Dissertation

published_or_final_version / abstract / Civil Engineering / Master / Master of Philosophy

The remarkable synchrony between changes in temperature recorded in Greenland ice cores and variations in N isotope records from sedimentary cores recovered from the Arabian Sea and the Eastern Tropical North Pacific (ETNP) has provided evidence for teleconnections between changes in marine denitrification in the tropics and climate variations in the northern high latitudes. Changes in tropical denitrification have been attributed to changes in productivity, changes in the source of intermediate waters and the flux of dissolved oxygen to suboxic zones. Variations in marine denitrification and anammox occurring at intermediate depths in proximity to productive continental margins have had profound effects on the N:P ratio of upwelled waters between stadials and interstadials, and may have indirectly affected carbon sequestration in the ocean by changing the balance of nutrients available to primary productivity. Competitive equilibrium, the changing stoichiometric balance of elements available as nutrients and the shorter residence time of N compared to P are factors that are believed to favour diazotrophs (N2-fixing organisms) during interstadials and shift the competitive advantage to non-N2-fixing ecosystems during stadials. This study presents a very high-resolution analysis of sedimentary nitrogen isotope records, phosphorus concentrations and bulk detrital element concentrations from two cores collected along the Pacific Mexican Margin. The results show that the oxygen minimum zone (OMZ) bathing intermediate waters in ETNP is modulated by the interaction of a Northern Hemisphere climate component with the “leakage” of heavy nitrate believed to derive from the Eastern South Pacific (ESP). This southerly component has a more “Antarctic” timing and is similar to records from the Peru-Chile margin. The sedimentary core recovered from the Mazatlan margin shows a “Greenland” timing of millennial-scale events, with reduced upwelling and reduced primary productivity, a less intense OMZ leading to reduced denitrification and a more southerly position of the mid-tropospheric subtropical ridge during stadials. This would have increased the onshore flow of moist air, ultimately leading to increased precipitation along the western Mexican Margin. Interstadials show a reversal of these conditions. In contrast to the Mazatlan core, the N isotope record from the core recovered from the Gulf of Tehuantepec records an element of “Antarctic” timing superimposed on local, millennial-scale variations in denitrification that are more similar in timing to Greenland temperature changes. In addition, the interpretation of observed variations in detrital elements from the Gulf of Tehuantepec highlights latitudinal displacements of the ITCZ that are consistent with those observed in the Cariaco Basin in Venezuela. Bulk P concentrations from both cores suggest that although phosphorite formation in the ETNP during interstadials is not as widespread as previously thought, the very high accumulation rates in the Gulf of Tehuantepec and Mazatlan Margin lead to total Holocene phosphorus burial rates that are up to 4-5 times higher than had been estimated in previous studies. These observations lead to the argument that the ETNP may play a more important role in regulating global P budgets than was previously thought and call for an improved appreciation of the benthic microbial communities that modulate biomes at tropical latitudes.

The occurrence of large scale and rapid climate shifts at millennial time-scales (suborbital) remains an enigma between records from high and low latitudes spanning the Late Quaternary. This thesis studies such variations in the eastern tropical North Pacific (ETNP) using marine sediment cores retrieved from Mexico and Nicaragua. The main goals are to understand the nature of millennial timescale climate-changes in the Pacific low latitudes, to identify the atmospheric and oceanic teleconnections involved, to document the impacts on the biogeochemical cycles of carbon, nitrogen and silicon, and their potential to regulate Greenhouse Gas (GHG) concentrations during the last two glacial cycles (the last 240,000 years before present). In this thesis, we use a suite of multi-proxy records from the Core MD02-2519, which are compared to others records from adjoining regions to study the climatic history of the ETNP at millennial timescales. The Core MD02-2519, was retrieved from 955 mbsl off NW Mexico. It is strategically located within the North Pacific Intermediate Water (NPIW), underlying the coastal upwelling and denitrification zones of the ETNP. The paleoceanography of the region is studied using proxy records of productivity, denitrification, intermediate water circulation and radiocarbon activity, which are discussed in 5 separated chapters. In Chapter 1, we use records of organic carbon (%OC) and diffuse spectral reflectivity (DSRa*) to document changes in productivity, which are shown in phase with Northern Hemisphere (NH) timing at millennial scale, suggesting a direct atmospheric teleconnection with higher northern latitudes. In Chapter 2, reconstruction of nitrogen isotope records (δ15N) show that abrupt changes in denitrification are in phase with NH timing over the last glacial period; however, the advection of heavy nitrate from southern sources is also documented, possibly from the denitrification zone off Peru-Chile. Records of opal (%opal – Chapter 3) and carbon isotopes from benthic foraminifera (δ13C-Uvigerina – Chapter 4) support the inference of oceanic teleconnections between the ETNP and the South Pacific via subthermocline circulation. In Chapter 4, the δ13C records also suggest that intermediate water circulation changed over glacial periods and terminations, being the result of intrusion of southern component waters. In Chapter 5, the reconstruction of radiocarbon activity (Δ14C) records from surface (planktonic foraminifera) and intermediate water (benthic foraminifera) suggest oceanic degassing of old-carbon from the deep ocean during the last termination. In this way, the ETNP upwelling system could be an important locus of CO2 release at millennial timescales.