A dearth of reliably-dated paleolake records from the southern Basin and Range has limited knowledge of past water balance changes there, precluding a more complete understanding of late Pleistocene atmospheric circulation across western North America. Paleoshorelines in closed basins throughout the region can provide accurately dated records of local effective moisture variations, representing a largely untapped source of paleohydrologic information. This dissertation presents paleohydrologic reconstructions from depositional successions in two basins at 32°N, approximately 100 km apart: Willcox basin, in southeastern Arizona, and Playas Valley, in southwestern New Mexico. Also presented are the results of ¹⁴C dating of charcoal samples from the El Fin del Mundo Clovis archaeological site, in northwestern Sonora, Mexico. In depth analysis of these results allowed constraint of the "small sample effect" on the charcoal ages, found to be smaller than 1σ of analytical uncertainty. The magnitude of the problem in ages from miniscule shell samples in the Willcox and Playas chronologies was found to be similar. The successions record moist pluvial conditions from ~20-13 ka in Playas, and>37-11 ka in Willcox, with most dates younger than 19 ka--before which there is no solid evidence for lake transgressions. There is clear evidence for overlapping highstands between ~18.3 and 17.9 ka and a brief highstand of Cochise at ~12.9 ka, coinciding with Heinrich events H1b and H0, respectively. Temporal concordance between wet periods and perturbations in the North Atlantic ocean and/or southern Laurentide ice sheet supports the idea that abrupt paleoclimatic changes in the southwestern U.S. occurred in response to large-scale atmospheric linkages to the northern high latitudes. The H1b highstands fill a hiatus in ¹⁴C dates compiled from paleoshorelines throughout the western U.S., and correspond to the first part of a lowstand in paleo-Lake Estancia (35°N), in north-central New Mexico. Anti-phasing within New Mexico suggests that the newly documented highstands resulted from an increase in southerly-sourced precipitation. This is consistent with paleoenvironmental evidence from southern Arizona and New Mexico that points toward periodic intensification of the summer monsoon during the late Pleistocene.

The aim of this study was to investigate the importance of winter season for the production of carbon dioxide (CO2) and methane (CH4) in humic and clear-water boreal aquatic systems. The study was conducted in 16 experimental ponds in northern Sweden during the winter of 2013. Half of the ponds had a higher concentration of dissolved organic carbon (DOC). CO2, CH4, DOC and dissolved inorganic carbon (DIC) were measured repeatedly under the ice from January to April. The results show that CO2 was accumulated continually during winter. No difference in winter accumulation were found between humic and clear ponds. CH4 was rarely accumulated in neither humic nor clear ponds, and was not an important part of the gas flux at spring ice melt. At ice melt, the flux from humic ponds accounted for 1.6 g C m-2 and 1.7 g C m-2 from clear ponds, which was equivalent for 15.6% respective 100% of the annual gas emissions. On a whole-year basis humic ponds acted as a source of 10.3 g C m-2, while clear ponds acted as a sink of 14.7 g C m-2. 76 mg m-2 d-1 DOC was consumed in humic and 59 mg m-2 d-1 DOC in clear ponds while the DIC accumulation was 125 mg m-2 d-1 in humic and 118 mg m-2 d-1 in clear ponds. This study stresses the importance of ice-covered boreal aquatic systems as a significant parts of the global carbon cycling.

I investigated whether Neogobius melanostomus, an invader of biodiversity “hot-spots” in Ontario facilitates or inhibits unionid mussel recruitment by serving as a host or as a sink for their parasitic larvae (glochidia). Infestation and metamorphosis rates of four mussel Species at Risk (Epioblasma torulosa rangiana, Epioblasma triquetra, Lampsilis fasciola, and Villosa iris) and one common species (Actinonaias ligamentina) on N. melanostomus were compared to rates on known hosts in the laboratory. All species successfully infested N. melanostomus, but only E. triquetra, V. iris, and A. ligamentina successfully metamorphosed, albeit at low rates. Neogobius melanostomus collected from areas of unionid occurrence in the Grand and Sydenham rivers exhibited body burdens of 39.4% and 5.1%, respectively. Analyses indicate that N. melanostomus serves more as a sink for glochidia than as a host for unionids, thereby limiting recruitment, which is a novel way by which N. melanostomus is affecting native mussel species.

In alleviating poverty in Lakes State in general and in the two counties (Yirol East and Wulu) in particular, there is a need to assess the property rights and its effects, identify the livelihoods and production assets of people solely involved in the cultivation of crops and agro-pastoralists, assess the role of land tenure system and how it contributes to land conflicts as well as conduct gender analysis of the impact of land tenure on the vulnerability of women and children in Yirol East and Wulu of Lakes State, South Sudan. Both quantitative and qualitative research methodology were utilized in this study. The qualitative research data consisted of focus group discussion, key informant interviews, and direct observation. Quantitative research data was gathered with the aid of a questionnaire. Two hundred questionnaires were implemented in Yirol East and Wulu County including 100 questionnaires in each county. Furthermore, these primary data sources were supplemented by secondary (or existing) data sources, including the South Sudan Land Act 2009, South Sudan National statistic Bureau, and documents from South Sudan Ministry of Irrigation. The food security is blamed on poor inadequate production assets which include human capital, financial capital, social capital, natural capital, and physical capital. In addition vulnerability factor due to draught, and conflict as well underutilization of the main livelihoods existing in the two communities the agro-pastoral of Yirol East and crop farmers of Wulu counties are the main findings of this research. The author highlighted the need to address the livelihoods and production asset constraints faced by agro-pastoralists of Yirol East Dinka communities and sedentary Beli communities of Wulu County. Dialogues for peace initiatives between rivals should be considered a step forward towards peaceful co-existence. Addressing property rights issues in relation to vulnerable women and children as well as land conflicts due to border demarcation, pastures and water points between communities is essential. / This thesis is an investigation for the use of agriculture and land tenure as a trategy for sustainable livelihoods for rural peoples of Lakes State, South Sudan. Inaddition, it was to access the impact of Sudan civil war on rural lives in the two counties Yirol East and Wulu of Lakes State, South Sudan.

In a climate change perspective, increased air temperatures are already a reality and are expected to increase even more in the future, especially in areas at high latitudes. The present thesis therefore addresses the influence of climate change on the physical properties and the phytoplankton communities of typical small and oligotrophic lakes in northern Sweden (62-64˚N). In the first part of the study, we found a significant trend (10 lakes from 1916 to 2010) of ice break-ups occurring increasingly earlier. The timing of ice break-up was strongly influenced by the April air temperature indicating that expected increases in air temperature in the future will also result in an earlier ice break-up. We also used concentrations of chlorophyll a (chl a) as estimations of phytoplankton biomass and discovered a positive relationship between surface water temperature and concentrations of chl a in Lake Remmaren (from 1991 to 2008). The second part of the thesis focuses on climatic conditions and cyanobacteria abundance in three small, oligotrophic lakes in northern Sweden; Lake Remmaren, Lake S. Bergsjön and Lake Gransjön. The concentration and relative abundance of cyanobacteria differ between 2011 and 2012, with different climatic conditions. The "warm" year of 2011 had higher concentrations and relative abundance of cyanobacteria than the "cold" year of 2012. Trends in increasing surface water temperatures as well as increasing abundance of cyanobacteria in August were found in Lake Remmaren (from 1988 to 2011). The direct or indirect effects of warming had a positive effect on the cyanobacteria abundance, since nutrients (Tot N and Tot P) did not display an increasing trend in Lake Remmaren. An analysis on the composition of phytoplankton species in Lake Remmaren, Lake S. Bergsjön and Lake Gransjön revealed that the cyanobacteria Merismopedia sp. was more common in 2011 than 2012. If different cyanobacteria become more common in oligotrophic lakes in the future, the functioning of lake ecosystems may be impacted. Small zooplankton eats small phytoplankton and if smaller phytoplankton species, e.g. cyanobacteria, increase at the expense of other phytoplankton groups, an extra step in the food chain might be added. Less energy might be transferred to the upper levels because many cyanobacteria contain toxic compounds and are less edible than other phytoplankton groups. An increase of toxic containing cyanobacteria in lakes can also make lakes less attractive for recreational purposes in the future.

No description available.

Bacteria are mediators of biogeochemical cycles and are in this way vital for maintaining life on earth. Their distribution, abundance and functioning are driven by environmental heterogeneity and dynamic change in abiotic and biotic factors. Both, freshwater lakes and oceans play central roles in the global carbon cycle and bacteria in these systems perform many services for the ecosystems, such as the transfer of organic carbon from primary producers to higher trophic levels. With estimated relative abundances up to 50% of the total bacterioplankton, the Alphaproteobacteria lineage SAR11 is the most abundant group of aquatic bacteria. It is globally distributed and can be partitioned into multiple sub-clades, one of which is exclusive to freshwaters. Until recently, the distribution, abundance and ecological role of this freshwater SAR11 named LD12 was unknown. The aim of the thesis was to study the drivers and mechanisms that influence the dynamics of aquatic bacterial communities in general and the SAR11 and LD12 groups in particular. The thesis consists of environmental surveys of a mesotrophic Lake Erken and the western Southern Ocean, an experiment and a data-mining exercise to reveal the phylogenetic structure of the SAR11 lineage on various temporal and spatial scales. The analysis of a long-term bacterioplankton community survey in lake Erken provided insights about the dynamics of the entire bacterial community and the LD12 population over an annual cycle. The results demonstrate that LD12 can be an equally abundant member of freshwater communities as marine SAR11 in oceans. LD12 featured strong seasonality and was positively coupled to environmental conditions indicative for an oligotrophic lifestyle. LD12 as well as other dominant lake bacterioplankton also maintained stable populations throughout spatial and temporal varying environments, but at high phylogenetic resolution, habitat preferences were revealed, particularly in response to oxygen concentrations. The later was not the case in LD12 as a single ribotype dominated. This is in stark contrast to the habitat partitioning with light availability, depth and water masses observed for marine SAR11 subclades in the Southern Ocean. The global data-mining corroborated that LD12 as a group was much less diverse than SAR11 furthermore, suggesting that the marine-freshwater barrier acted as a population bottleneck. My work shows that bacterial populations can respond in very different ways to environmental drivers, highlight the importance of highly resolved temporal and spatial scales as well as the need for high phylogenetic resolutions to target ecologically coherent populations.

No description available.

Global climate change is threatening both our water quality and quantity. Specifically, the influence of climate change on freshwater lakes includes decreased water availability, increased evapotranspiration, changes in nutrient availability, and shifts in species composition. Understanding the changes that are occurring to our freshwater ecosystems is imperative to understanding the full impact of climate change on both the environment and society. This thesis examines a shift in sedimentary diatom assemblages towards increased relative abundances of Discostella species, a phenomenon that has been documented across the Northern Hemisphere. One of the central tenants of this work is that it has been done at the Experimental Lakes Area (ELA) in the boreal region of Canada, a study site that is uniquely devoid of large-scale anthropogenic disturbances. An analysis of the long-term monitoring records at the ELA show that Discostella species are primarily spring bloomers, and recent increases in their abundance is linked to changes in spring thermal conditions. To link the changes recorded in the sedimentary records of eight lakes to climate change, and assess whether Discostella species are in fact showing a response to climate change, a novel approach utilizing the theory of temporal synchrony was applied to eight paleo records. Discostella stelligera was found to be synchronous in all eight lakes studied, suggesting that a broad-scale forcing factor is influencing its abundance. Further, it was significantly correlated with annual and winter temperatures, supporting a link to changes in spring thermal conditions as a possible explanation. To assess the relative sensitivity of the study lakes, particularly in comparison to other boreal and temperate region lakes, an analysis was conducted of the timing of the first change in Discostella species. Several statistical techniques were employed and all approaches showed that the study lakes from ELA responded earlier in comparison to other lakes studied from other boreal and temperate regions (ca. 1900 vs ca. 1970), but later than Arctic and Sub-Arctic lakes. We suggest that this may be due to the lack of local disturbances at the ELA and/or the comparably small size of our study lakes. / Thesis (Ph.D, Biology) -- Queen's University, 2014-06-30 15:03:04.447

The vast majority of Adirondack lakes have been impacted since pre-industrial time through either regional (e.g. acidification) or local (e.g. fish stocking, liming, seepage of road salt, cultural eutrophication) environmental disturbances. Inferring changes related to climate are difficult due to the possible complexities associated with multiple stressors. Thirty minimally-disturbed ‘reference’ lakes were identified from a database of 1469 lakes using the following selection criteria: <5% shoreline development; a circumneutral pH; and no records of introduction of non-native piscivores (protecting against eutrophication, chronic lake acidification and modifications of trophic structure, respectively). As such, these ‘reference’ lakes may be useful for isolating the effects of regional changes, including climate warming, from other anthropogenic influences. A ‘top-bottom’ paleolimnological analysis of diatom assemblages was undertaken to identify changes since pre-industrial times. The uppermost sediment layer was used to represent present-day diatom assemblages, and a sediment sample from a depth of 20cm was used to represent pre-industrial conditions. Discostella stelligera, a planktonic diatom taxon, is presently the dominant species in 50% of the lakes, and showed the greatest change. D. stelligera increased by >10% in 11 of the 30 study lakes. The measured present-day chemical and physical limnological variables in the study lakes could not predict changes in the abundance of D. stelligera, suggesting that unmeasured variables, such as decreased ice cover, and changes in mixing and stratification patterns, are likely driving the observed changes in diatom assemblages. Heavily silicified tychoplanktonic Aulacoseira species declined by an average of 8.3% across the dataset. In three of the relatively deep lakes with higher concentrations of phosphorus, another planktonic diatom, A. formosa, was found to increase in abundance. Additionally, some lakes that were dominated by a high proportion of benthic taxa experienced increases in the relative abundance of benthic taxa over time. Observed changes in the relative abundances since pre-industrial times are significantly higher than the variation between replicate cores, and between two ‘pre-industrial’ sediment intervals. Further studies on the timing of changes in diatom assemblages are necessary to confirm that such changes are consistent with recent changes in climate in the Adirondacks. / Thesis (Master, Biology) -- Queen's University, 2014-05-29 21:33:42.24