Recent drought over West Africa (1970s-present) has been a global concern, and the ability to predict the frequency and severity of future droughts is important to mitigate the devastating socio-economic effects of drought. The Sahel region, situated at 10-20°N just south of the arid Sahara Desert and north of the forested Guinea Coast, is particularly vulnerable to drought periodicity because rainfall is already low at 400 mm yr-1. The ability to predict future climate variability depends on adequate knowledge of fluctuations in the past. In West Africa, meteorological records are too sparse and too short in duration to characterize the drought frequency. Consequently, climate reconstructions from lacustrine sediment records are increasingly recognized as an important source of information on past climate variability. Lake Bosomtwe, Ghana (6o30N and 1o25W) was formed over one million years ago by a meteorite impact crater in the Guinea Coast region, just south of the Sahel region. Lake Bosomtwe has a closed-drainage hydrology and lake levels are known to fluctuate with the net flux in rainfall inputs relative to evaporative outputs. In 2004, the International Continental Scientific Drilling Program recovered the complete sediment record for paleoclimatic reconstructions. However, very little has been studied of the limnological conditions that lead to the formation of laminated sediments in Lake Bosomtwe. This thesis has set out to understand the influence climate has on the physical, chemical and biological in-lake processes that generate sedimenting materials, which are preserved as laminated sediment layers. Two years of water column sampling of temperature, oxygen and nutrients at a central deep-water site (78 m water depth maximum) found that this quiescent crater lake is thermally stratified during much of the year, with anoxia persisting below 35 m water depth. During the short dry season of July and August, the monsoon rains that are associated with the intertropical convergence zone (ITCZ) are displaced northwards over the Sahel region (and away from lake Bosomtwe), and cool air temperatures and clear night skies lead to the disruption of the thermocline and circulation of dissolved nutrients nitrogen (N) and phosphorus (P) in Lake Bosomtwe. Phytoplankton primary productivity, as measured by particulate carbon and chlorophyll a concentrations, was found to increase markedly following the nutrient upwelling event in August. Sediment trap samplers deployed at 20 and 30 m water depth captured the pattern of organic matter deposition and a high flux of organic sediment was deposited shortly after the nutrient upwelling episode in August. The composition of these organic-rich sediments was distinguished by a marked depletion in δ13C and enrichment of δ15N, as compared to sediments deposited before and after this event. Spatial assessment of sediment cores identified that presently, visible laminations were preserved at and below 35 m water depth, but, not at shallower depths. Water depth was also positively correlated with the organic matter content in sediment records and could be used to reconstruct pre-historic lake levels down core. The relationship between lake level and organic content in sediments predicted that water levels were likely 22 m lower than present levels during the period ~1425-1610 CE, which corresponds with a climatic periods known as the Little Ice Age (LIA). The spatial sediment trends also revealed that inorganic sedimentation rates had increased since the onset of recent land clearance and road construction in the catchment, particularly to the north, near the town of Abono. For this reason, two cores from the central deep-water region of Lake Bosomtwe were analysed for organic and carbonate content, δ13C and δ15N, nutrients (C, N, P), magnetic susceptibility, greyscale imagery of the x-radiograph and micro-X-ray analysis of elemental constituents. Paleoenvironmental reconstructions during the past 550 years found that climate-driven lake level change was a prominent factor contributing to the organic content of sediments. High inorganic content, iron concentrations and depleted δ13C distinguished a low stand during the LIA (~1425-1610) when pelagic sediments were likely exposed to periodic oxygenation. High concentrations of organic matter, calcium (Ca) and strontium (Sr), enrichment of δ13C and low C:N ratios were indicative of wet years that likely increased lake levels and the depth of water column mixing. However, sediments with high organic content, depleted δ13C signatures and reduced Ca and Sr concentrations were suggestive of drought years that restricted the depth of seasonal water column mixing and nutrient circulation and did not necessarily result in pronounced lake-level change. During the past century, δ13C of bulk matter was positively correlated with the rainfall anomalies (r2 = 0.45, P < 0.002), indicating that droughts can result in reduced primary productivity, which may ultimately lower fishery yields. The communities living within the crater are dependent on subsistence fishing and farming, and predicting the drought frequency and magnitude in this region is essential to protecting both the ecosystem and the human population. Long-range climate forecasts for West Africa predict greater drought and increasing air temperature. However, with a detailed long-term paleoclimatic reconstruction from Lake Bosomtwe sediment records, potentially the accuracy of these predictions can be improved and better equip policy makers to enact a viable action plan in the best interests of the people.

Cumulative effects, often minor individually but collectively significant, are continually being grappled with by researchers, policy makers and practitioners. Despite this the Canadian approach to cumulative effects assessment is thought by many to be ineffective. In this thesis I investigate the literature that surrounds cumulative effects and uncovered three distinct themes that occur chronologically: genesis, project-based approach and integration. During the genesis phase cumulative effects nomenclature, ideas and frameworks was created. The main theme of this era was to asses these effects at a large scale and to have a strong understanding of a systems ecology prior to the assessment. This approach was found to be too complex and so a more narrow project-based approach was implemented and still remains today. This approach is heavily criticized and as such researchers are now trying to find an approach that integrates these two divergent themes into a regional level assessment. I have found there to be several frameworks but an absence of effective regional methodologies. There is a need for regional metrics if this approach is to ever be institutionally supported. Food web structure can be evaluated at multiple scales and has been shown to be responsive to environmental variation; thus, it has potential for application as a metric for cumulative effects. Here, using stable isotope analysis, I field test integrative measures of food web structure (food chain length, habitat coupling, trophic omnivory) at sites of varying degrees of anthropogenic stressors in Georgian Bay, Ontario to evaluate the use of food webs as a metric for cumulative effects assessment. I found that food web structure varied significantly among sites. Sites with high levels of stress displayed structural characteristics reflective of human activities such as shorter food chain lengths, increased trophic omnivory, and reduced habitat coupling relative to the non-stressed sites. These results indicate that food web structure as an ecosystem level metric may provide insight into anthropogenic activities, and may be applied routinely as a metric for doing Cumulative Effects Assessment. / University of Guelph, Saugeen Ojibway Nation, Georgian Bay Forever

Šiame darbe eksperimentiniais ir modeliavimo metodais buvo nagrinėjami skirtingose hidrogeologinėse sąlygose esančių branduolinių objektų aikštelių aeracijos zonos gruntuose vystantys drėgmės (ir priemaišų) pernašos procesai. Aeracijos zonos profiliai buvo palyginti atlikus eksperimentinius tyrimus ir apibendrinus duomenis apie gruntų hidraulines savybes, drėgnį ir izotopinę sudėtį. Krituliuose ir aeracijos zonos grunto profilių drėgmėje buvo nustatyti globaliai paplitusio radionuklido tričio bei vandens molekulės izotopinių traserių pasiskirstymo ypatumai. Nustatyta, kad krituliuose pasireiškiančios stabiliųjų izotopų sezoninės variacijos aeracijos zonoje ir ypač gruntiniame vandenyje beveik išnyksta, tačiau išlieka nežymūs sezoninių smailių pėdsakai, kurie Maišiagalos aikštelėje yra šiek tiek kontrastiškesni nei Stabatiškės aikštelėje, kadangi Maišiagalos aikštelėje drėgmės tranzito aeracijos zonoje laikas trumpesnis. Priėmus hipotetines žemės paviršiaus užtvindymo sąlygas esant žemam, vidutiniškam ir aukštam slėgiui, momentiniam ir pastoviam priemaišų įvedimui, palyginimui buvo išnagrinėti šeši scenarijai. Sudarytas tričio pernašos aeracijos zonoje modelis parodė, kad paros įvesties parametrų suvidurkinimas atskiram mėnesiui gali riboti tričio koncentracijos aeracijos zonos profilyje ir vandens balanso elementų pasiskirstymo atkūrimą. / Two nuclear waste disposal sites (Maišiagala radioactive waste storage facility site and Stabatiškė near surface repository site) were compared in terms of the contaminant movement through the unsaturated zone. Extensive data sets of the hydraulic properties, water content and isotope composition have been collected and summarized. Distribution features of globally widespread radionuclide tritium and the water molecule tracer isotopes in precipitation, unsaturated zone soil moisture profiles and groundwater were determined. Stable isotopes seasonal variation occurring in precipitation almost disappears in the unsaturated zone soil moisture and especially in shallow groundwater, but in both sites slight seasonal peak traces remain, which at the Maišiagala site are a bit more contrasting in comparison with the Stabatiškė site. Both sites were modelled by using unsaturated flow and transport models. Six scenarios have been developed to simulate the water and solute movement under low, moderate, and high water input, and instantaneous and continuous solute input conditions. In order to validate the representativeness of the hydraulic parameters, the model has been used to estimate the tritium distribution in the unsaturated zone, which properly represents the dynamics of the unsaturated zone. The uniformity of the daily input in each month should be kept in mind in the evaluation of the smooth changes of the tritium profile and water budget elements.

Šiame darbe eksperimentiniais ir modeliavimo metodais buvo nagrinėjami skirtingose hidrogeologinėse sąlygose esančių branduolinių objektų aikštelių aeracijos zonos gruntuose vystantys drėgmės (ir priemaišų) pernašos procesai. Aeracijos zonos profiliai buvo palyginti atlikus eksperimentinius tyrimus ir apibendrinus duomenis apie gruntų hidraulines savybes, drėgnį ir izotopinę sudėtį. Krituliuose ir aeracijos zonos grunto profilių drėgmėje buvo nustatyti globaliai paplitusio radionuklido tričio bei vandens molekulės izotopinių traserių pasiskirstymo ypatumai. Nustatyta, kad krituliuose pasireiškiančios stabiliųjų izotopų sezoninės variacijos aeracijos zonoje ir ypač gruntiniame vandenyje beveik išnyksta, tačiau išlieka nežymūs sezoninių smailių pėdsakai, kurie Maišiagalos aikštelėje yra šiek tiek kontrastiškesni nei Stabatiškės aikštelėje, kadangi Maišiagalos aikštelėje drėgmės tranzito aeracijos zonoje laikas trumpesnis. Priėmus hipotetines žemės paviršiaus užtvindymo sąlygas esant žemam, vidutiniškam ir aukštam slėgiui, momentiniam ir pastoviam priemaišų įvedimui, palyginimui buvo išnagrinėti šeši scenarijai. Sudarytas tričio pernašos aeracijos zonoje modelis parodė, kad paros įvesties parametrų suvidurkinimas atskiram mėnesiui gali riboti tričio koncentracijos aeracijos zonos profilyje ir vandens balanso elementų pasiskirstymo atkūrimą. / Two nuclear waste disposal sites (Maišiagala radioactive waste storage facility site and Stabatiškė near surface repository site) were compared in terms of the contaminant movement through the unsaturated zone. Extensive data sets of the hydraulic properties, water content and isotope composition have been collected and summarized. Distribution features of globally widespread radionuclide tritium and the water molecule tracer isotopes in precipitation, unsaturated zone soil moisture profiles and groundwater were determined. Stable isotopes seasonal variation occurring in precipitation almost disappears in the unsaturated zone soil moisture and especially in shallow groundwater, but in both sites slight seasonal peak traces remain, which at the Maišiagala site are a bit more contrasting in comparison with the Stabatiškė site. Both sites were modelled by using unsaturated flow and transport models. Six scenarios have been developed to simulate the water and solute movement under low, moderate, and high water input, and instantaneous and continuous solute input conditions. In order to validate the representativeness of the hydraulic parameters, the model has been used to estimate the tritium distribution in the unsaturated zone, which properly represents the dynamics of the unsaturated zone. The uniformity of the daily input in each month should be kept in mind in the evaluation of the smooth changes of the tritium profile and water budget elements.

Ecosystem changes from grassland to shrubland in the Rio Grande Plains are thought to have negative effects on the hydrology of the region. The increase in woody plants, known as woody encroachment, may alter the amount of water moving beyond the root zone of plants. Water moving beyond the root zone is referred to as deep drainage, and has potential to become aquifer recharge. A vegetation manipulation project was designed to understand the effects of woody vegetation removal on soil water dynamics in the recharge zone of the Carrizo-Wilcox aquifer of south Texas. The primary objective of the project was to determine the potential to increase groundwater recharge through woody vegetation removal. To understand the effects of vegetation removal on various soil textures we studied changes in soil water, rooting depth, and the role of water redistribution by woody vegetation. Woody vegetation was removed using common methods of cut-stump and roller chop across three soil types. Soil water contents and changes were measured using neutron moisture meter to a depth of 180 cm. Average rooting depth was determined across three soil types. Soil and stem water stable isotopes were used to understand soil water movement. Rooting depth was determined to between 140 and 160 cm for all soil textures. Soil water content and changes were analyzed at three depth increments: 0-60, 60-120 and 120-180 cm. ANOVA analysis showed that there was no treatment response in average soil profile water in the sandy or sandy loam soils. There was a significant decrease in soil profile water for clay loam soil in response to roller chopping. Changes in soil profile water were the greatest in the sandy roller chopped soils. Below 120 cm, three months had significant differences in change in soil water in the sandy roller chop plot. During dry conditions, Honey mesquite shifts water use to deeper in the soil profile. In clay loam soils under dry conditions there is evidence of water being moved up from below 2 m soil depth to drier shallow soils. Roller chopping in sandy soils is the vegetation removal treatment and soil type most likely to result in water moving beyond the root zone. Although treatments had significant effects on soil moisture dynamics that interacted with soil type, we did not find support for deep drainage effects over the Carrizo-Wilcox aquifer from woody vegetation removal.

No description available.

No description available.

This study aims to investigate the stable isotopic characteristics of meteoric and ground waters, and to obtain spring flow rates in the Coronet Peak Skifield, Queenstown. Spring flows were gathered during the winters of 2008 and 2009, whilst water samples were collected from precipitation, springs, reservoirs and groundwater during July, August and September 2009. The spring flows were examined and the water samples were analysed for δD and δ¹⁸O values using the CF-IRMS at the University of Canterbury. A database has been gathered from all natural water sources to give a local meteoric water line (LMWL) for the area that fits clearly with the global meteoric water line. The LMWL has an R2 value of 0.97 and the equation is δD = 8 δ¹⁸O +10. An understanding of evaporation as it occurs in the water storage reservoirs of the mountain has also been obtained, giving rise to a local evaporation line. The stable isotope ratios of hydrogen and oxygen within precipitation have been used extensively to characterise the hydrogeology with emphasis on altitude effects, storm duration and variations in storm track trajectories. Of these three phenomena, it is the trajectory of the storm track that is best shown to affect the composition of precipitation in this area. The air masses advancing on the study area from the north being more depleted in their isotopic signatures, with approximate δD and δ¹⁸O values of –130‰ and -16‰. The air masses approaching from a southerly direction are more positive in comparison, having approximate δD and δ¹⁸O values of –65‰ and -9‰. The altitude effect in precipitation on the Skifield has led to an altitude gradient being found: for every 100-metre increase in elevation, δ¹⁸O decreases by 0.71‰. However there were some inconsistencies. The influence on precipitation from storm duration is also inconsistent in this area. The R2 values range from 0.14 to 0.99, but this method does not take into account the position of the individual samples. Some samples did not plot in the expected order that is governed by a decrease in stable isotopic ratios with storm duration. The stable isotopic compositions within meteoric waters can be used as tracers of water sources. The isotope date of the springs also infers an altitude effect. The springs gave an altitude gradient of a decrease –0.43‰ with each 100-metre increase in elevation. This indicates that precipitation is the main influence on the stable isotopic composition of the springs in this area. However, data shows differences between the current precipitation and the groundwater compositions, indicating that present precipitation is not flowing from the springs, past precipitation is. The stable isotopic compositions of the springs have also been correlated with groundwater isotope data and suggest the sources of the springs are groundwater dominated. Although some springs compositions indicate an influence by current precipitation. This is shown by a negative stable isotopic trend in the precipitation sampled in August, corresponding with a relatively negative stable isotopic composition in some springs during this time period. Monitoring of spring flows on Coronet Peak have led to an average winter flow rate being established of 26.5 litres per second. Spring flow rates range from 0.25 – 6 litres per second. This monitoring has indicated the springs of the greatest yield that are not already being utilised on the Skifield. It is these springs that should be further investigated as to whether they would provide a sustainable source of water on the mountain. This locally derived water would then be utilised for the purposes of artificial snowmaking and other activities and amenities that are currently operated by NZ Ski on Coronet Peak.

The Ngatamariki Geothermal Field is located 20 km north of Taupo in the Taupo Volcanic Zone and has a boundary of 12 km² as delineated by magneto-telluric surveys (Urzua 2008). Rhyolitic deposits, derived from the Maroa Volcanic Centre, dominate the geology of the area with the 186 AD (Wilson et al. 2009) Taupo pumice mantling stream valleys in the area. The majority of thermal features at Ngatamariki are located along the Orakonui Stream on the western boundary of the field; the stream area is dominated by a 50x30 m geothermal pool filling a hydrothermal eruption crater. This crater was formed during a hydrothermal eruption in 1948, with a subsequent eruption in April 2005. Orakei Korako is located 7 km north of Ngatamariki and has one of the largest collections of thermal features in New Zealand. The geology at Orakei Korako is similar to Ngatamariki, but the area is dominated by a series of south-west trending normal faults which create sinter terraces on the eastern bank of Lake Ohakuri. Water samples from springs and wells at Ngatamariki and Orakei Korako were taken to assess the nature of both fields. Spring waters at Ngatamariki have chloride contents of 56 to 647 mg/l with deep waters from wells ranging from 1183 to 1574 mg/l. This variation is caused by mixing of deep waters with a steam heated groundwater, above clay caps within the reservoir. Stable isotopic results (δ¹⁸O and δD) suggest that reservoir waters are meteoric waters mixed with magmatic (andesitic) water at Ngatamariki. Reservoir water chemistry at Orakei Korako exhibits low chloride contents, which is anomalous in the Taupo Volcanic Zone. Chloride content in well and spring waters is similar ranging from 546 to 147 mg/l, due to mixing of reservoir fluids with a ‘hot water’ diluent at depth. Isotopic compositions of spring waters suggest that they are meteoric waters which mix with magmatic (rhyolitic) water, more enriched in δ¹⁸O and δD than ‘andesitic’ water. Relationships between major ion concentrations and known subsurface geology suggest there is no hydraulic connection between the two fields.

The North Bank area lies on the north side of the Wairau River, Marlborough, New Zealand, bounded by the Richmond Ranges to the north and the Wairau River to the south. The North Bank is an interactive zone where groundwaters and surface waters from North Bank tributary valleys mix with waters of the Wairau River. This investigation aimed to define the nature and origin of groundwaters of the North Bank area. Stable isotopes of oxygen and hydrogen, along with hydrogeochemistry, were utilised in order to define the spatial extent of the North Bank riparian margin and delineate the Wairau River-groundwater interface. Distinct stable isotopic signatures differentiate ground and surface waters that come from high mountain catchments versus those that arrive more locally at lower altitude. The results gathered by this study demonstrated stable isotopes to be the most powerful forensic tool capable of distinguishing Wairau River water from North Bank tributary groundwater sources. In contrast, hydrogeochemical characteristics of the waters of the North Bank were young and chemically dilute in nature, which made them chemically indistinguishable from waters of the Wairau River. Geomorphological mapping was conducted in order to investigate the relationship between groundwater flow patterns and geomorphology upon the North Bank. Geomorphology, in the form of prominent fluvial terraces, was found to play a role in limiting the extent of Wairau River influence to groundwater to either low-lying Q2 Speargrass Formation, Q1 Rapaura Formation alluvium or the Wairau River channel itself. Aquifer pump testing and water level observation carried out in the Waikakaho Valley revealed a plentiful groundwater resource in the local context. Like other tributary valleys within the North Bank study area, surface water and groundwater were found to be chemically and isotopically linked to one another which points to an interconnected ground and surface water resource, larger than first thought. Driven by recharge by the Waikakaho River, the groundwater resource has development potential, and continued monitoring will further define the hydrogeological system and ensure long term sustainable use.