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<p> Nitrification is a prokaryote-mediated oxygen consumptive process of the oxidation of ammonia to nitrite/nitrate that traditionally has been only viewed as a nutrient transformation process. Renewed concern about hypoxia in the shallow hypolimnion of the Central Basin of Lake Erie provides impetus for examining whether nitrification has a significant impact on oxygen dynamics. To evaluate the contribution of nitrification to oxygen demand, water column and sediment samples were collected during the summers of 2008-2010 in Lake Erie and the oxygen consumption due to nitrification and the abundance and distribution of potential bacterial (AOB) and archaeal (AOA) that oxidize ammonia to nitrite was characterized in water column and sediment samples by qPCR of a portion of the ammonia monooxygenase (amoA) gene. Environmental variables and nitrification rates were examined for correlations to understand factors that may control nitrification rates and/or the distribution of nitrifiers. The nitrification rate in the epilimnion and hypolimnion was 3.1 &plusmn; 3.2 micromole N/L/day and 3.7 &plusmn; 2.9 (mean &plusmn; 1 SD) micromole oxygen/L/day respectively. Nitrification accounted for 28.2 &plusmn; 23.1% of the total oxygen consumption in the epilimnion and 32.6 &plusmn; 22.2% in the hypolimnion. Oxygen consumption by nitrification in sediment slurries and intact sediment cores was 7.1 &plusmn; 5.8 micromole oxygen/gram/day and 682 &plusmn; 61.1 micromole oxygen/square m/day respectively. Nitrification accounted for 27.0 &plusmn; 19.2% of the total oxygen consumption in sediment slurries and 30.4 &plusmn; 10.7% in intact sediment cores. AOA and AOB were present in all samples, with a distribution that was variable over time and space. Highlighting the potential importance of archaeal nitrifiers, the AOA/AOB ratio in the epilimnion, hypolimnion, and sediments was 1.02, 1.08, and 5.25. The nitrification rate or nitrifier numbers did not strongly correlate with environmental factors such as oxygen, nitrate or ammonium. In the water column, respiration and the percentage of oxygen used due to nitrification were negatively correlated. While nitrification is unlikely to be the dominant oxygen consumptive process, the rates observed in Lake Erie were sufficient to theoretically deplete a large portion of the hypolimnetic oxygen pool during the stratified period. </p>

<p> While environmental controllers of decomposition have been extensively studied, organic matter quality and biotic controllers of decomposition, such as detritivore preference and manipulation of detritus, are largely understudied. In the studies described in this dissertation, a range of biotic controllers of detrital dynamics in aquatic ecosystems are presented. Crayfish, as model shredders, produce a diverse pool of fine particulate organic matter (FPOM) through fragmentation of coarse particulate organic matter (CPOM) and fecal production in the laboratory. Crayfish process maple leaves at a greater rate than oak leaves, and produced a greater amount of FPOM from maple compared to oak. Crayfish-generated FPOM had lower C:N ratios and increased bacterial abundances compared to original CPOM. Further, hydropsychid caddisfly and simuliid blackfly larvae confer greater growth efficiency when reared on crayfish-generated FPOM compared to mechanically ground FPOM in the laboratory, indicating that crayfish increase bioavailability of FPOM. No differences in growth or metamorphosis of simuliid larvae were observed when larvae were lab-reared on crayfish-generated FPOM from CPOM of different tree species (<i>i.e.</i>, sugar maple, sycamore, or white oak) or different stream conditioning times (<i>i.e. </i>, 30 or 150 d). This suggests that crayfish processing reduces organic matter origin effects on bioavailability. Changes in macrophyte abundance in a tropical wetland due to competition and ecosystem management can affect litter availability and litter quality. In two field-based, replacement series experiments with floating-mat macrophytes (<i>Eichhornia crassipes</i> and <i>Neptunia oleracea</i>), no interspecific competition was detected. However, <i>E. crassipes</i> dominated experimental enclosure biomass through attrition. Decomposition rates were faster for <i>E. crassipes</i> litter compared to <i>N. oleracea</i> litter within enclosures, but no differences in decomposition rates were detected by floating-mat species composition. Both synergistic and antagonistic diversity effects were observed on decomposition dynamics in an experiment varying litter richness from one to five species. Additionally, cattail (<i>Typha domingensis </i>) eradication efforts lead to changes in the decomposition landscape within the wetland, as <i>E. crassipes</i> colonizes managed areas, and decomposition rates were slower for litter of <i>T. domingensis</i> compared to <i>E. crassipes</i>. The compounding effects of litter species, detritivore interactions, and anthropogenic impacts on organic matter dynamics illustrate that it is critical to consider ecosystem function in ecosystem management. </p>

<p> HIV associated neurocognitive disorders (HAND) encompass a spectrum of cognitive deficits that affect 40-70% of HIV-infected individuals, despite antiretroviral therapy. Monocytes are among the first cells infected by HIV and are critical mediators of HAND as they facilitate viral seeding of the central nervous system (CNS) upon their transmigration across the blood brain barrier (BBB). Monocyte subpopulations exist with differing levels of maturation and functions. Monocytes that express CD14, the LPS receptor, and CD16, the Fcylll receptor, are a mature population of cells that are highly susceptible to HIV. While CD14⁺CD16⁺ monazites are believed to mediate the neuropathogenesis of HIV, little is known about the mechanisms that contribute to their diapedesis across the BBB. As the CD14⁺CD16⁺ monocyte represents a small percentage of monocytes in healthy individuals, we developed a tissue culture model to enrich for this population. We found that there was a selective transmigration of CD14⁺CD16⁺ monocytes across our BBB model, with little migration of other monocyte populations. HIV infection resulted in the increased transmigration of CD14⁺CD16⁺ monocytes in response to CCL2 relative to uninfected cells, which was due to increased CCR2 and a heightened sensitivity to the chemokine. The junctional proteins JAM-A and ALCAM were also critical for this transmigration as antibody blockade reduced the number of migrating monocytes. These CD14+CD16+ monocytes were present in significantly greater numbers in HIV-infected people, despite viral suppression, in contrast to individuals without HIV. CCR2 was increased on CD14⁺CD16⁺ monocytes in HIV-infected individuals with HAND compared to those with normal cognition and was predictive of fluctuations in cognitive impairment upon longitudinal study. ALCAM and JAM-A were increased on CD14⁺CD16⁺ monocytes in those with HIV compared to HIV seronegative people. Blocking antibodies to ALCAM and JAM-A inhibited the transmigration of CD14⁺CD16⁺ monocytes, but not of T cells, suggesting their importance in specifically facilitating monocyte transmigration across the BBB. Our findings indicate therapeutic strategies to monitor HAND, and that may decrease the entry of CD14⁺CD16⁺ monocytes into the CNS of HIV-infected individuals, contributing to the eradication of neuroinflammation, HAND, and CNS viral reservoirs.</p>

In response to the likely future change in the Canadian Guidelines regulating the maximum allowable concentration of trihalomethanes (THM) in potable water, an investigation into the possible causes and variability of THM precursors was conducted during the summers of 1990 and 1991 at Lake Memphremagog in south-eastern Quebec. A number of associated parameters were correlated with THM formation potential (THMFP) with respect to season, depth and position on the lake. The THMFP was quantified indirectly by measuring the THM concentration present after chlorination under standard conditions. / THM concentrations in the samples were found to exceed the US EPA standard of 100 $ mu$g/L, sometimes considerably. There did not appear to be any statistically significant contribution to THMFP from human activity. No close agreement was observed between THMFP and any of the associated parameters for the lake as a whole. A few correlations were found between THMFP and nutrient concentrations at individual sites.

Thesis (Ph.D.)--The University of Toledo, 2006. / (UnM)AAI3218587. Adviser: Daryl L. Moorhead. Source: Dissertation Abstracts International, Volume: 67-05, Section: B, page: 2328.

Greatly condensed portion of Thesis--University of Michigan. / Reprinted from Transactions of the American Microscopical Society, vol. LXIV, no. 1, January, 1945. Literature cited: p. 18-20.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 0824. Adviser: Carol A. Shearer. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Small temperate lakes are under increasing pressure from a number of anthropogenic sources, including but not limited to: habitat alteration, invasive species, climate change, and pollution. In Gatineau Park, Quebec, Canada small temperate lakes have been demonstrated to be under threat from introduced piscivores, among other potential stressors. Here, I assessed the historical impact of four introduced piscivores on minnow, small fish and total fish species richness for a set of small Gatineau Park lakes. Fish community data were obtained from two previously published studies and a lake survey conducted in the summers of 2006 and 2007. I used a modified Control/Impact study design and repeated measures analysis of variance to test the hypothesis that introduced piscivores negatively affect species richness over time. My results strongly demonstrate that piscivores have had a negative effect on minnow and small fish species richness over time, whereas total fish species richness was unaffected. Assuming that these introduced piscivores pose a risk to the parks small temeprate lakes, I then assessed what lake characteristics best predict piscivore invasion risk. To do this, I estimated invasion risk employing two different analytical approaches for a total of 42 small lakes located in Gatineau Park using current and historical data collected in 1971, 1981, 1991 and 2006. Bootstrapped logistic regression was used to predict historical occurrence, and whether or not a lake was invaded/not invaded over time using predictor variables that included lake anthropogenic, spatial-isolation, and morphometric factors. For both logistic regression analyses, lake area and small fish species richness were found to be excellent predictors of piscivore invasion risk and historical occurrence, while lake spatial-isolation factors were also found to be excellent predictors of piscivore historical occurrence. The bootstrapped models with the most support based on Akaike's Information Criterion corrected for small sample size (AICc) were then used to identify lakes at greatest risk for future invasion. My results support the contention that introducing top predators into novel aquatic environments has detrimental impacts on native fish communities, and that these impacts are not always immediately obvious, but are indeed discernable over time. In conclusion, I make specific recommendations to guide the conservation and management of small temperate lake ecosystems.

Photodegradation rates of methylmercury (MeHg) were measured in water samples from several lakes in the Lake Berthelot region in Quebec in order to investigate the impact of drainage basin logging and associated changes in dissolved organic carbon (DOC) concentrations on MeHg levels in lake water. The lakes were selected on the basis of the amount of logging that had previously taken place in the drainage basin, and on DOC levels which were correspondingly higher in logged lakes due to increased runoff. Lakes DA9 and DF9 had DOC concentrations of 12.3 and 20.9 ppm, respectively and were designated as high DOC for the purposes of this study. Lakes N55 and N70 had DOC concentrations of 6.9 and 6.8 ppm, respectively and were designated as low DOC lakes. Experiments were conducted with both ambient and 2 ppt spiked MeHg levels in the high and low DOC lakes to determine whether the spiked levels reflect photodegradation patterns occurring in nature. The effect of different sized DOC fractions on photodegradation rates were also examined. Upon spiking, the binding of added MeHg reached equilibrium virtually immediately (within minutes) for all size fractions. It was hypothesized that less photodegradation of MeHg would be found in high DOC lakes than in low DOC lakes. In contrast to expected results, no photodegradation was observed in the two lower DOC lakes, but there was photodegradation in the two higher DOC lakes. Hypothesizing that larger size fractions of DOC would result in lower methylmercury (MeHg) photodegradation rates, water samples were fractionated into three DOC size fractions (300 kDa, 30 kDa, and 5 kDa). In the two high DOC lakes in which photodegradation was detected, DOC size fractions had an effect on photodegradation rates, though this effect varied. Average k values (hr-1) for DA9 were -1.25 x 10-1 for the 5 kDa fraction, -1.16 x 10 -1 for the 30 kDa fraction, and -9.21 x 10-2 for the 300 kDa fraction, indicating a decrease in photodegradation rates with larger fractions. For DF9, average k values were -1.69 x 10-1 for the 5 kDa fraction, -6.38 x 10-2 for the 30 kDa fraction, and -1.34 x 10-1 for the 300 kDa fraction, which does not indicate a clear trend in photodegradation rates with respect to DOC size fraction. A comparison of samples from a wetland outflow using ambient MeHg levels demonstrated that 300 kDa DOC fractions showed no photodegradation while 5 kDa DOC showed photodegradation with a k value of -9.12 x 10-2 (hr-1). Overall, watershed logging status was found not to affect MeHg photodegradation rates in the lakes studied. A possible contributor to the variation in photodegradation rates between lakes was postulated to be pH, with H+ ions displacing MeHg from binding sites on DOC and rendering it available for photodegradation. To study the relationship between rates of photodegradation and pH, water samples were adjusted to pH values of approximately 4.5, 6.5, and 7.5 and incubated in sunlight. Rates of photodegradation increased with decreasing pH conditions in all lakes, except for one lake (N55) which also had no detectable photodegradation during the initial field trials. In the remaining three lakes studied, however, lower pH values (4.1-4.6) resulted in greater photodegradation than higher pH values that resulted in little or no photodegradation. It appears that this effect only occurs in lakes with a potential for photodegradation. As results suggested that the size of DOC controls rates of photodegradation, samples were analyzed for the size of DOC and corresponding MeHg content using tangential flow ultrafiltration (TFUF). The efficacy of the TFUF system as a means of both removing microbes as well as fractionating DOC into differing size fractions was evaluated. Results indicated that this is an effective field-portable method. Mass balances for MeHg recovery after filtering large volumes of water were found to be 96% for the 5 kDa filter, 81% for the 30 kDa filter, and 109% for the 300 kDa filter, while flow rates decreased by 26%, 17%, and 50% respectively. Potential artifacts of DOC fractionation using the TFUF were investigated. The amount of DOC passing through the filter was found to decrease with increasing volume of filtrate that passed through the membrane.