Diss. (sammanfattning). Uppsala : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2002. / Härtill 4 uppsatser.

Diss. (sammanfattning). Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 5 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2000. / Härtill 4 uppsatser.

The habitability of Earth is dependent upon the global recycling of elements essential for life, such as nitrogen, sulfur and carbon. Nutrient-cycling by micro-organisms is vital to these biogeochemical cycles because many key steps are mediated primarily, or exclusively, by microbial life. The dynamics of these cycles are highly complex, and environmental perturbations (such as changes in the oceanic oxygen concentration) can have unexpected or catastrophic effects; often causing abrupt switches between chemical states. Despite the importance of these environmental perturbations however, few theoretical models have addressed how they affect the dynamical behaviour of nutrient-cycling microbial ecosystems. In this work, we investigate the effect of environmental perturbations on microbially-mediated nutrient cycles and assess the likelihood of "sudden transitions" between chemical states of the ecosystem occurring in a variety of ecological contexts. To do this, we first use computational modelling of microbial nutrient-cycling, using a "box model" approach. We then move on to an experimental study using the microbial sulfur cycle as a model ecosystem, with freshwater pond sediment/water microcosms. These microcosms have the advantage of retaining many of the features of the real ecosystem (such as microbial diversity, spatial structure, and abiotic interactions) while allowing the controlled manipulation of environmental perturbations. We study these microcosms using a combination of chemical measurements and high-throughput sequencing of the microbial community. Finally, we return to the computational side, and attempt to reproduce chemical data from our experiments in a mathematical model containing realistic abiotic chemical interactions.

Magister Scientiae - MSc / The research was driven by a need to increase the knowledge base concerning wetland ecological responses, as well as to identify and evaluate the factors driving the functioning of the Franschhoek Trust Wetland. An ecohydrological study was undertaken in which vegetation cover, depth to groundwater, water and soil chemistry were monitored at 14 sites along three transects for a 12 month period. The parameters used include temperature, pH, electrical conductivity (EC), sodium, potassium, magnesium, calcium, iron, chloride, bicarbonate, sulphate, total nitrogen, ammonia, nitrate, nitrite and phosphorus. T-tests and Principal Component Analysis (PCA) were used to analyze trends and to express the relationship between abiotic factors and vegetation. / South Africa

>Magister Scientiae - MSc / The research was driven by a need to increase the knowledge base concerning wetland ecological responses, as well as to identify and evaluate the factors driving the functioning of the Franschhoek Trust Wetland. An ecohydrological study was undertaken in which vegetation cover, depth to groundwater, water and soil chemistry were monitored at 14 sites along three transects for a 12 month period. The parameters used include temperature, pH, electrical conductivity (EC), sodium, potassium, magnesium, calcium, iron, chloride, bicarbonate, sulphate, total nitrogen, ammonia, nitrate, nitrite and phosphorus. T-tests and Principal Component Analysis (PCA) were used to analyze trends and to express the relationship between abiotic factors and vegetation. Results reflect the strong influence of hydrology, microtopography and nutrient availability in structuring vegetation composition in the wetland. The wetland has been classified as a palustrine valley bottom with channel wetland, which is predominantly groundwater-fed (phreatrotropic), but receives surface water inputs as well. Small scale gradients of microtopography allow for differences in flooding frequency and duration resulting in hydrologically distinct sites which differ chemically. Three zones were distinguished in the wetland. Hollows or low sites were characterized by intermittent flooding and drying and higher nutrient concentrations in soil and groundwater. High sites which were rarely or never flooded exhibited higher groundwater temperature and ammonia as well as iron in soils and groundwater. The inundated sites remained flooded throughout the year and were characterized by high nitrate and nitrite in soil as well as high EC, magnesium, bicarbonate, sulphate and phosphorus in groundwater. The limited availability of nitrogen in the wetland favoured plant types Typha capensis, Paspalum urvillei and Juncus .kraussii which are able to either fix nitrogen or store nitrogen during more favorable conditions. The main chemical concentration changes take place between summer and winter. The Principal Component Analyses suggest that sodium, chloride, potassium, ammonia and phosphorus are the dominant ions determining the chemistry of groundwater. Increased abstraction from the table mountain aquifer to supplement human demand may put the wetland at risk of degradation. Intensified agriculture and other land use in the area are likely to increase pollution loads into the wetland causing shifts in nutrient availability and vegetation composition. Continued and long term monitoring is essential to ensure effective management of the wetland and is highly recommended. Closer partnerships between wetland managers and scientists as well as community awareness and involvement through a volunteer monitoring programme should be encouraged

Soil nutrient availability is a key component to understanding the boreal ecosystems, as it directly relates to plant productivity and ecosystem diversity. There is however little known about how the nutrient availability changes seasonally in the boreal forest. This study aimed to understand how soil temperature and nutrient availability changed seasonally as well as with or without reindeer grazing. This was done through measuring NH4, NO3, PO4, total N, and C:N ratio in soil samples taken in- and outside a reindeer exclosure in northern Sweden and then analyzing for differences over sampling time, grazing treatment, and the interaction of both. Differences in soil temperature were more extreme in the grazed areas, giving higher summer temperatures and lower winter temperatures, due to a decreased layer of insulating lichens. Increased soil temperatures also resulted in lowering the C:N ratio, possibly by enhancing the microbial activity leading to larger amounts of CO2 being released. No nutrients differed by grazing treatments, possibly due to the system being complex enough to contain contradicting effects. No systematical differences in seasonal nutrient levels could be found, which was deemed as surprising, but opens for the possibility of sampling one time being sufficient to have an approximation of nutrient levels all year round

Southern Appalachian wetlands have yet to be studied in terms of net primary production (NPP), thus few studies have been conducted to examine what environmental factors have relationships with NPP. To that end, this research investigates several facets of southern Appalachian wetland production. The research was divided into three studies. The first study was conducted to answer the question of what environmental factors have relationships with NPP. It appears that stream discharge and annual precipitation had the strongest relationships with NPP (r = 0.91, p <0.05 and r = 0.81, p <0.05, respectively), yet both factors showed multicolinearity (r = 0.97, p <0.05). The strong relationships between hydrologic factors and NPP is similar to montane wetlands in the western United States. The second study was conducted to examine the relationship between water chemistry and NPP. Calcium (Ca), Magnesium (Mg), and pH were examined in order to determine if any of the aforementioned factors had a relationship with NPP. Neither Ca (r = -0.34, p = 0.0835) nor Mg (r =-0.38, p = 0.0535) had strong relationships with NPP, though pH (r = -0.66, p <0.05) had a strong negative relationship with NPP. The acidity of the stream water, driven by the acid rain in the southern Appalachians, creates enhanced conditions for wetland plants to grow. The third study was conducted to establish which vegetation index was best for estimating NPP from proximally and remotely sensed data. The findings suggest that VARIRed Edge was best for examining NPP at the in situ level, NDVI was best for examining NPP at the airborne level, and the DVI was the best for examining NPP at the satellite level. NPP in southern Appalachian wetlands is driven by the chemistry, specifically the pH, of stream discharge and annual precipitation and can be monitored by NDVI using NAIP data or DVI using Landsat data. The examination of NPP in southern Appalachians in response to environmental factors and water chemistry along with the examination of vegetation indices at three levels of platforms will help to monitor and manage these rare and unique ecosystems in the future.