The isotopic composition of the organic components of an animal's body, with respect to carbon and nitrogen, reflect the weighted average of the isotopic compositions of the animal's food sources, with a certain degree of enrichment in the heavier isotopes. Thus, by comparing the isotopic compositions of the animal and all the potential food sources, it is possible to ascertain the relative proportions of each availible food source in its diet, if the various food sources are sufficiently isotopically distinct. This approach is particularly usefull in estuarine communities where food-webs tend to be complex and where there are several sources of primary productivity. In this study it was used on two types of claw in an arctic and a temperate estuarine tidal flat in order to assess the importance of terrestrially fixed organic matter to each community. The results indicated that while marine and terrestrial organics were important food sources in the arctic tidal flat, the clams in the temperate site depended mostly on marine organics. / Thesis / Bachelor of Science (BSc)

Forests ecosystems cover about 30% of the Earth’s land surface, corresponding to an area of roughly 42 million km2 globally. Forests play an important role in the global carbon cycle by exchanging carbon dioxide (CO2) with the atmosphere. Annually, forests act to effectively sequester large amounts of anthropogenically-emitted CO2 from the atmosphere through photosynthetic processes. Through the unparalleled increase of CO2 emissions over the past century and the subsequent climatic inconsistencies due to global climate change, the carbon sink-capacity of the world’s forests remains uncertain. Furthermore, since increasing temperatures have been shown to extend the vegetative growing season in forests, phenological responses to this change are of particular interest. In an effort to effectively assess the future carbon sequestration potential of forests, a better understanding of the climatic controls on phenology, and its influence on carbon processes, is needed. The eddy covariance (EC) technique is a stand-level, in-situ, method used widely to assess the net CO2 exchange across the canopy-atmosphere interface. Together with meteorological data, the sequestration of CO2 and the subsequent ecosystem productivity can be quantified over various time scales (half-hours to decades). This dissertation reports results from field observations of EC measured fluxes that were used to study the climatic impacts on forest phenology and the resulting carbon dynamics in southern Ontario, Canada. The study sites, part of the Turkey Point Observatory, consisted of two similarly-aged, temperate, North American forests growing under similar climatic and edaphic conditions: the 80-year old (in 2019) white pine plantation (coniferous evergreen) and 90+ year-old, naturally-regenerated, white oak (deciduous broadleaf) forest. These forests were studied from 2012 to 2017, using the EC technique, digital phenological cameras, and remote-sensing measurements. At the deciduous broadleaf forest, mid-summer (July and August) meteorological conditions were the key period in determining the annual carbon sink-strength of the site, acting to regulate the interannual variability in carbon uptake. The forest experienced higher net ecosystem productivity (+NEP; carbon sink) when soil temperatures ranged from 15 to 20°C and vapor pressure deficit was 0.7 and 1.2 kPa. From 2012 to 2016, the forest remained a net annual sink, with mean NEP of 206 ± 92 g C m-2 yr-1, similar to that of other North American deciduous forests. Spring and autumn phenological transition dates were calculated for each year (2012 to 2017) from measured EC data and digital camera greenness indices. The timing of spring and autumn transition dates were impacted by seasonal changes in air temperature and other meteorological variables. Contrary to past studies, an earlier growing season start did not equate to increased annual carbon uptake. In autumn, a later end to the deciduous forest growing season negatively impacted the net carbon uptake of the forest, as ecosystem respiration (RE) outweighed the gains of photosynthesis. The digital camera indices failed to capture the peak dates of photosynthesis, but accurately measured the spring and autumn transition dates, which may be useful in future remote sensing applications. A comparison of the two forests from 2012 to 2017 found the coniferous forest to have higher but more variable annual NEP (218 ± 109 g C m-2 yr-1) compared to that of the deciduous broadleaf forest (200 ± 83 g C m-2 yr-1). Similarly, the mean annual evapotranspiration (ET) was higher (442 ± 33 mm yr-1) at the coniferous forest compared to that of the broadleaf forest (388 ± 34 mm yr-1). The greatest difference between years resulted from the response to heat and drought. During drought years, deciduous carbon and water fluxes were less sensitive to changes in temperature or water availability compared to the evergreen forest. Carotenoid sensitive vegetative indices and the red-edge chlorophyll index were shown to effectively capture seasonal changes in photosynthesis phenology within both forests via proximal remote sensing measurements during the 2016 growing season. Satellite vegetative indices were highly correlated to EC photosynthesis, but significant interannual variability resulted from either meteorological inputs or the heterogeneous landscapes of the agriculturally-dominated study area. This dissertation improved our understanding of the dynamics of carbon exchange within the northeastern North American deciduous forest ecozone, through the examination of climatic variability and its impact on carbon and phenology. This dissertation also contributed to efforts being made to better evaluate the impact of species composition on carbon dynamics in geographically similar forests. Moreover, the use of the digital phenological camera observations and remote sensing techniques to complement and better understand the fluxes observed with the EC method was innovative and may help other researchers in future studies. / Dissertation / Doctor of Philosophy (PhD)

The environmental and human health benefits of urban forests have been well documented. In the United States, volunteers conduct 5% of municipal tree care-related activities in urban forests. A literature review related to urban forestry volunteers in the United States was conducted and it was concluded that urban forestry volunteers are often organized via a committee or non-governmental organization (NGO) and that there is limited understanding around many of these entities. Following Dillman’s methods, an electronic qualitative survey with a primary objective of better understanding their characteristics was disseminated to urban forestry NGOs throughout the temperate forest region of the United States. Private citizens are significant partners that are essential in forming and funding urban forestry NGOs. More than 40% of organizations were established to extend limited municipal resources and improve urban tree canopy cover. Nearly 80% of responding NGOs had helped develop, shape, or implement local urban forestry-related policy in their community.

In this dissertation I describe how coupled internal cycling and external forcing from the atmosphere and climate can regulate the dynamics of nitrogen (N) loss from forest watersheds. I address three major gaps in our understanding of the global N cycle: 1) the role of dissolved organic N (DON) in internal N cycling in low-N ecosystems; 2) The influence of atmospheric pollution on DON production and loss from forests; and 3) the inherent climate sensitivity of forest N cycling and loss. In chapter 2, I present the results of a study of DON spiraling that showed enormous capacity for stream microorganisms to immobilize and transform organic nutrients. Although most DON in surface waters is highly refractory products of SOM dissolution, this study revealed very tight internal cycling of DON at the sediment interface and suggested significant production of DON in the hyporheic zone. Most remarkably, this DON was not expressed in stream waters, supporting the idea that watershed DON losses would have been higher in the absence of pronounced benthic demand. The experiments also suggested that coupled dynamics between DOC and DON spiraling may be altered under conditions of elevated N supply. Chapter 3 challenges the idea that soil organic matter (SOM) and its dissolved products are stoichiometrically static as N pools accumulate. Using a broad geographic survey of forest streams, I show that DON losses increase as a consequence of N pollution and that this occurs through a disproportionate enrichment of N on dissolved organic matter rather than alteration of soil and dissolved carbon dynamics. These results have implications for N limitation in forests and aquatic systems. In particular, DOC: DON ratios of DOM draining N-saturated forests were strikingly low suggesting possible increases in DOM bioavailability with increasing N supply. Chapter 4 provides insight into how local forest nutrient cycles may be organized by synchronous global-scale climate-atmosphere dynamics. This study of long term (30 yr) hydro-chemistry from reference forest watersheds provides an integrated example of the overall climate sensitivity of N cycling and underscores the importance of complex synergies between simultaneous vectors of global change. Results from this study argue that the combined influence of N pollution and warming are likely to have pronounced long-term effects on ecosystems globally. / Ph. D.

Despite significant vector control advancements in the past years, the current malaria trends suggest that new control strategies are urgently required. These new approaches should address the current frontline intervention challenges like increasing insecticide resistance in mosquitoes and residual transmission issues. Insecticide-treated livestock (ITL) is one of the novel potential strategies to overcome the above challenges. ITL involves treating livestock near humans with an insecticide like ivermectin (IVM) to kill zoophagic malaria vectors. However, ivermectin pharmacokinetics data suggests that most IVM-administered drugs remain intact, and more than 90 % of this drug is eliminated in feces. Biological metabolites: 3′′-O-demethylivermectin (3DI) and 24-hydroxymethyl ivermectin (24OHI) are also excreted in feces. Therefore, using manure from treated cattle as fertilizers contaminates the soil, ground, and surface water with IVM or its metabolites through leaching and hydraulic water flow affecting the soil and aquatic ecosystems. Contemplating the contamination impacts, these drugs' environmental fate and effects could be regarded before massive IVM applications. Many researchers have tried to address this subject in temperate regions compared to the tropics, where IVM is urgently needed. Regional discrepancies such as soil types and climate can independently and dependently determine the fate and impact of ivermectin. Our research investigates the environmental fate of IVM and its primary biological metabolites. Laboratory and field studies in Tanzania and Virginia were conducted to simulate the difference between tropical and temperate climates. Soil and soil-manure mixture spiked with IVM were layered into two 5 mm layers in columns exposed to natural sunlight. The remaining IVM and its primary metabolite were quantified using Liquid Chromatography with a tandem mass spectrometry detector (LC-MS/MS. These compounds degraded up to 1.5 times faster in Tanzania than in Virginia, depending on temperature, soil depths and type, organic matter, and soil moisture. When IVM is subcutaneously injected into cattle, drug residues and metabolites: 3DI and 24OHI are excreted in feces following a positive skewed Poisson distribution profile. IVM, 3DI, and 24OH were found to degrade rapidly when cattle pats when exposed to the field. Since we conducted our study in the Summer, no IVM or its metabolites leached into the soil beneath. The obtained half-lives suggest that ivermectin's massive drug administration has little to worry about, primarily when the dung from treated cattle is spread into the field in thin layers in the Summer before farm application. / Doctor of Philosophy / Despite significant vector control advancements in the past years, the current malaria trends suggest that new control strategies are urgently required. These new approaches should address the current frontline intervention challenges like increasing drug resistance in mosquitoes and residual transmission issues. Treating cattle with ivermectin is one of the novel potential strategies to overcome the above challenges. This strategy is effective because the amount of ivermectin (IVM) found in the blood of treated cattle is enough to kill malaria vectors feeding on them. However, the literature suggests that most IVM-administered drugs remain intact, and more than 90 % of this drug is eliminated in feces. Metabolite bioproducts: 3″-O-demethylivermectin (3DI) and 24-hydroxymethyl ivermectin (24OHI) are also excreted in feces. Therefore, using manure from treated cattle as fertilizers contaminates the soil, ground, and surface water with IVM or its metabolites through leaching and hydraulic water flow affecting the soil and aqua ecosystems. Contemplating the contamination impacts, these drugs' environmental fate and effects could be regarded before massive IVM applications. Many researchers have tried to address this subject in temperate regions compared to the tropics, where IVM is more needed. Regional discrepancies such as soil types and climate can independently and dependently determine the fate and impact of ivermectin. Our research investigates the environmental fate of IVM and its primary bioproducts. Laboratory and field studies in Tanzania and Virginia were conducted to simulate the difference between tropical and temperate climates. Soil and soil-manure mixture spiked with IVM were layered into two 5 mm layers in columns exposed to natural sunlight. The remaining IVM and its primary metabolite were quantified on the appropriate instrument. These compounds degraded up to 1.5 times faster in Tanzania than in Virginia, depending on temperature, soil depths and type, organic matter, and soil moisture. When IVM drug is injected into cattle, the intact drug and its bioproducts: 3DI and 24OHI, are eliminated in feces following a favorable skewed normal distribution profile. IVM, 3DI, and 24OH were found to degrade rapidly when cattle pats when exposed to the field. Since we conducted our study in the Summer, no IVM or its bioproducts leached into the soil beneath. The obtained data suggest that ivermectin's massive drug administration has little to worry about, primarily when the dung from treated cattle is spread into the field in thin layers in the Summer before farm application.

The expansion and proliferation of reactive nitrogen (N) sources, predominantly fertilizer application and fossil fuel combustion, has enriched the earth with N and acidified ecosystems. Acid rain is a primary vector of both N fertilization and acidification, initiating a cascade of consequences that alter biogeochemical cycling and global biological structure and function. Studies on N and acid influences are however rarely linked despite their common source. We used a wide, chronic gradient of N deposition (5.5 – 31 kg N ha⁻¹ yr-1) to explore patterns in carbon (C) and N cycling in light of recognized biogeochemical responses to acidic deposition. Specifically, we examined the response of key controls on dissolved C and N stability because soluble pools are involved in decomposition and nutrient recycling, the formation of soil organic matter (SOM), and the translation of elements through the biogeochemical continuum from atmospheric to soil to water. Results suggest that N deposition led to reduced organic matter C/N, enhanced net nitrification, and greater DON generation; and, these patterns were associated with changes in C composition. Conversely, physiochemical processes in the mineral soil seemed to control organic matter dynamics, with effects on N processing. Moreover, pH dependent controls on DOC stability were evidenced by changes in DOC concentration, chemical complexity and recalcitrance. These horizon-specific, differential responses to acid rain indicate that changes in the forest floor N economy were responsible for increased surface water NO3-N concentrations, whereas enhanced organomineral stability of DOC caused a significant increase in DOM concentrations in export. / Master of Science

No description available.

Much of the current research into the processing and storage of carbon (C) in small lakes has focused on arctic and boreal lake systems, due to their global abundance. However this has led to an imbalance in the interpretation of lake functioning. Oligotrophic lakes are prevalent in the arctic and boreal zone, but are typically net heterotrophic due to loading of catchment-derived dissolved organic carbon (DOC) which alters their metabolic balance. In comparison, temperate lake systems tend to be more nutrient rich, typically due to anthropogenic activity, and would therefore be expected to exhibit the signs of net autotrophy, as a result of higher rates of gross primary production (GPP) and lower rates of catchment-derived DOC potentially subsidising respiration (R). In order to test the hypothesis that temperate, eutrophic lakes are net autotrophic (GPP > R) on an annual basis the C-dynamics of Rostherne Mere (maximum depth, zm, 31 m) and Tatton Mere (zm = 11 m), two monomictic Cheshire-Shropshire meres, were quantified over an 18 months period from 2010 2012. This monitoring study used high-resolution (hourly) oxygen (O2) sonde measurements, combined with high-resolution data from an automated on-lake monitoring buoy at Rostherne Mere (as part of the national UKLEON lake network) to calculate rates of epilimnion C-fixation. For both lakes, sediment traps were also used to determine water column C-flux and sediment core data to establish C-burial efficiency of these strongly stratifying lakes. Water column profiles of dissolved O2 and CO2 was also measured at 2 4 weekly intervals across both lakes. Particular attention was focused on: i) the long term C-storage of eutrophic, monomictic lakes; ii) up-scaling C-accumulation estimates from these two meres to the Cheshire-Shropshire meres region and all UK eutrophic waters; and iii) methodological sensitivity for estimating C-fixation, flux and burial efficiency and upscaling C-accumulation estimates. The results show that both lakes are net autotrophic on an annual basis, on average fixing 121 ± 2 g C m-2 yr-1 and sequestering 68 ± 4 g C m-2 yr-1, a C-burial efficiency of ~60%. If up-scaled to the Cheshire-Shropshire meres region, annual C-accumulation was estimated to be 506 ± 32 t C yr-1 or 0.05 ± 0.001 Mt C since 1900. From this, it was estimated that UK eutrophic waters could be sequestering 0.12 ± 0.01 Mt C yr-1 or 13.3 ± 0.2 Mt C since 1900. Annual UK CO2 emissions are ~128.85 Mt C yr-1, therefore UK eutrophic waters currently offset 0.09% of yearly UK CO2 emissions. Despite the finding that eutrophic, stratifying lakes have high C-fixation and sequestration values, lakes in other areas of the globe such as the arctic and boreal zones are typically a more important long term C-sink as they are far more abundant within the landscape and local soils are typically very poor within low C retention rates. Further investigation is needed into how lakes function on a regional and national scale, the importance of lake type and number when up-scaling C accumulation estimates and the potential impact on future C accumulation as a result of a changing environment and supra-regional policies in areas such as Europe.

Ten ring-width based chronologies from Nepal are described and the prospects for further dendroclimatic work there reviewed briefly. The initial results are encouraging, and more intensive subregional sampling is called for. All the cores examined showed distinct annual rings, and there was little evidence of double or missing rings, except juniper at some sites and in some Pinus roxburghii trees. Difficulty was encountered in dating Pinus wallichiana and Cupressus dumosa. Individual site chronologies of Cedros deodora, P. roxburghii and P. wallichiana were particularly promising, and of high elevation Abies spectabilis moderately so. Densitometric data are likely to be more useful for this species. The paucity of meteorological data in Nepal represents an obstacle to further dendroclimatic work there.

No description available.