Human activities such as urban settlement, farming, forestry and recreation, have caused deterioration of water quality in many freshwater lakes worldwide. Apart from anthropogenic impacts, it is also recognized that climate has a direct influence on lake water temperature, nutrient loads, phytoplankton abundance and chemistry. However, little is known about the potential effects of future climate change on lake water quality. Understanding the dynamics, abundance and availability of nutrient pools in lake bottom sediments is fundamentally important for predicting how, and over what time-scales, lake ecosystems will respond to future scenarios such as climate change, in-lake restoration or altered external nutrient loading. Through a sediment field study on 14 different lakes, and applications of complex lake ecosystem models to three New Zealand lakes, this study examined the spatial and temporal dynamics of sediment nutrient concentrations, and made considerations of the effects of restoration measures and future climate change on lake water quality. To gain insight into processes influencing the dynamics of horizontal and vertical gradients of sediment nutrient concentrations, intact sediment cores were collected from twelve lakes within the Bay of Plenty province, North Island of New Zealand. In addition, intact sediment cores were collected from shallow Lake Te Waihora (Ellesmere) in the Canterbury province, South Island of New Zealand and shallow Lake Taihu in the Jaingsu province, China. The observed vertical concentration profiles of total phosphorus (TP) in the sediments revealed that the shape of these profiles can be similar across gradients of widely differing trophic status. Empirical and mechanistic steady state profile models were derived to describe the vertical distribution of total carbon (TC), total nitrogen (TN) and TP concentrations in the sediments. These models revealed that density-driven burial and biodiffusive mixing, which in the models also includes effects of redox-driven gradients, are strongly correlated with vertical gradients of sediment TC, TN and TP content, whereas lake trophic status was not. Despite enhancing knowledge of the processes influencing vertical gradients of sediment nutrient concentrations, little is known about the rates at which sediment nutrient concentrations may change as a response to changes in external loading or climate. Studies into the composition of bottom sediments have been undertaken intermittently over the past three decades for the 12 lakes in the Bay of Plenty. These studies, together with the data collected in this study, were used to quantify temporal changes in sediment chemistry across the lakes. Comparison of the data collected in this study with results from a survey in 1995 showed that surficial sediment (0-2 cm) TP concentrations have increased in three of the 12 lakes, at rates ranging from 27.5 to 114.4 mg P kg-1 dry wt yr-1. TN concentrations in surficial sediments have increased in nine of the 12 lakes at rates ranging from 51.8 to 869.2 mg N kg-1 dry wt yr-1. A correlation analysis revealed that temporal changes in sediment TP and TN concentrations were not significantly linearly related (pgt0.05) to catchment area or temporal changes of different water column indices considered to reflect lake trophic state, including annual mean water column concentrations of TP, TN or chlorophyll a (Chl a). While vertical profiles of sediment nutrient concentrations can be used to provide information about historical changes of trophic status in lakes, little is known about horizontal variability of sediment nutrient concentrations, including possibly relationships with horizontal variations in water column variables. In the large, shallow and eutrophic Lake Taihu, China, there are distinct horizontal water column concentration gradients of nutrients and Chl a. Concentrations are generally high in the north, where some of the major polluted tributaries enter the lake, and relatively low in the south, where macrophytes generally are abundant. To test whether these water column concentration gradients are similarly reflected in spatial heterogeneity of nutrient concentrations within the bottom sediments of Lake Taihu, I examined correlations between concentrations of TP and TN in surficial sediments (0-2 cm) and TP, TN and Chl a concentrations in water column samples determined for 32 sites in 2005. Linear correlation analysis revealed that surficial sediment TP concentrations across the 32 stations were related significantly, though weakly, to annual mean water column concentrations of TP and TN as well as Chl a. Correlations of surficial sediment TN with water column variables were, however, not significant (p gt 0.05). To better understand the effects of future climate change on lakes of different trophic status, I applied the one-dimensional lake ecosystem model, DYRESM-CAEDYM, to oligo-mesotrophic Lake Okareka, eutrophic Lake Rotoehu and highly eutrophic Lake Te Waihora. All three models were calibrated based on a three-year period (July 2002 - June 2005) and validated on a separate two-year period (July 2005 - June 2007). The model simulations generally showed good agreement with observed data for temperature, dissolved oxygen (DO), and total nutrient and Chl a concentrations. To represent a possible future climate of 2100, temperature predictions were derived from the regional climate model, DARLAM, based on the Intergovernmental Panel on Climate Change (IPCC) A2 scenario, which suggests that air temperatures by the year 2100 will increase by an average of 2.5 'C and 2.7 'C for the Bay of Plenty and the Canterbury province, respectively, relative to the base scenario (years 2002-2007). Model simulations of the future climate scenarios indicate that climatic changes generally will lead to a degradation of lake water quality in all three lakes, especially during summer months, and further suggest that the effects on annual mean surface concentrations of TP, TN and Chl a will be equivalent to an increase in external TN and TP loading by 25-50%. Simulations for Lake Rotoehu, where diatoms and cyanophytes were represented in the conceptual model, further suggest that cyanophytes will be more abundant in the future, increasing by gt15% in annual mean biomass. Although the effects of climate change may be delayed or slightly mediated by the chemical resilience of the sediment nutrient pools, the effects of climate change on lake water quality in the New Zealand lakes will be of a magnitude that should be considered as management strategies are planned and implemented, thus increasing the probability of successful preservation or improvement in water quality in future decades.

During the 1990s a large-scale study of Port Phillip Bay, Australia, was undertaken by the CSIRO (the Commonwealth Scientific and Industrial Research Organisation, Australia's national research body). A major outcome of the study was a complex ecosystem model intended to provide scientific input into management decisions concerning the nutrient load to the bay. However, its development was costly and time-consuming. Given this effort, it is natural to seek smaller models (reduced models) that reproduce the performance measures of the large model (the full model) that are of interest to decision makers. This thesis is concerned with identifying such models. More generally, this thesis is concerned with developing methods for identifying these smaller models. Several methods are developed for this purpose, each simplifying the full model in different ways. In particular, methods are proposed for aggregating state variables, setting state variables to constants, simplifying links in the ecological network, and eliminating rates from the full model. Moreover, the methods can be implemented automatically, so that they are transferable to other ecological modelling situations, and so that the reduced models are obtained objectively. In the case of the Port Phillip Bay model, significant reduction in model complexity is possible even when estimates of all the performance measures are of interest. Thus, this model is unnecessarily complex. Furthermore, the most significant reductions in complexity occur when the methods are combined. With this in mind, a procedure for combining the methods is proposed that can be implemented for any ecological model with a large number of components. Aside from generating reduced models, the process of applying the methods reveals insights into the mechanisms built into the system. Such insights highlight the extent to which the model simplification process can be applied. Given the effectiveness of the model simplification process developed here, it is concluded that this process should be more routinely applied to large ecosystem models. In some cases, the full sequence of methods might prove too computationally expensive to justify its purpose. However, it is shown that even the application of a subset of the methods can yield both simpler models and insight into the structure and behaviour of the system being modelled.

<p>This Bachelor‟s thesis aims at explaining the relationship between forests and climate change, a subject that has been given a lot of attention in environmental discussions in recent years, particularly because forests are a source of carbon dioxide emissions and in the same time have the potential to mitigate climate change through carbon sequestration. However, with the importance of mitigation as a background, the focus of this study is on adaptation. The purpose is to identify mutual benefits from the diverse forest ecosystems, and examine the possible benefits from forests to the rural poor population in Tanzania, in a future scenario of increased vulnerability to climate change. The methodology for the study can be divided into two parts, one qualitative literature study and one field study in Babati District northern Tanzania, limited to interviews and excursions. This thesis gives details about the scientific projections and local perceptions of climate change and the effects of climate change. The results of the thesis highlights the importance of sustainably managed forests and agroforestry systems, which have been successful in Babati through local participation; economic incentives such as carbon credit and other payments for ecosystem services, which is a possible future extension of forestry activities; and increased integration between sectors, which make sure that adaptation within different sectors can be done simultaneously.</p>

Thesis (Ph.D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (April 26, 2007) Vita. Includes bibliographical references.

The Eastern stock of Atlantic bluefin tuna (Thunnus thynnus thynnus) has experienced a steep decline, 74.2%, in recent decades, mainly driven by large unreported catches and growth of the capture-based aquaculture of this species in the Mediterranean. This study addresses the potential food-web effects on trophic linkages in the ecosystem through the removal of both small pelagic fish species and wild bluefin tuna (BFT) for capture-based aquaculture operations. An Ecopath model of the Southern Catalan Sea (Western Mediterranean) was modified to include a BFT farm supplied entirely by the area modeled (Coll et al, 2006). Six scenarios were developed to simulate possible changes to the system using Ecosim, including the continued growth of aquaculture operations, as well as changes to the total allowable catch for BFT as set by ICCAT. Species not directly connected with the production of BFT showed large fluctuations in biomass and yield as a result of these simulations. Using these models, increases in biomass of lower trophic level functional groups were observed with reductions in biomass from other top trophic level predators. Jellyfish and benthopelagic fish exhibited an increase in biomass, the largest being 8.76% for jellyfish and 69.76% for benthopelagic fish, while wild BFT biomass decreased 87.26%. Atlantic bonito and swordfish showed similar rates of decline in biomass levels. These outcomes stress that fishing at top trophic levels can have unforeseen outcomes on the structure of the ecosystem, due to the complexity of the food web. Capture-based aquaculture of Atlantic bluefin tuna can be expected to increase along the proposed scenario levels, due to the decision not to place this species on Appendix I of CITES during the CITES meeting of 2010. This study suggests that farming activity has additional impacts on the ecosystems that should be taken into account when evaluating the suitability of this industry and projecting the trends towards the future. Results suggest that, in the case of the Western Mediterranean Sea, increasing BFT farming activities will likely contribute towards further degradation of an already highly exploited marine ecosystem. The development of hatchery technology to close the life cycle and produce juvenile BFT for stocking cages as well as using artificial diets during the grow out stage are required to minimize long-term impacts and support industry expansion.

Thesis (M.S.)--Oregon State University, 1973. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

This Bachelor‟s thesis aims at explaining the relationship between forests and climate change, a subject that has been given a lot of attention in environmental discussions in recent years, particularly because forests are a source of carbon dioxide emissions and in the same time have the potential to mitigate climate change through carbon sequestration. However, with the importance of mitigation as a background, the focus of this study is on adaptation. The purpose is to identify mutual benefits from the diverse forest ecosystems, and examine the possible benefits from forests to the rural poor population in Tanzania, in a future scenario of increased vulnerability to climate change. The methodology for the study can be divided into two parts, one qualitative literature study and one field study in Babati District northern Tanzania, limited to interviews and excursions. This thesis gives details about the scientific projections and local perceptions of climate change and the effects of climate change. The results of the thesis highlights the importance of sustainably managed forests and agroforestry systems, which have been successful in Babati through local participation; economic incentives such as carbon credit and other payments for ecosystem services, which is a possible future extension of forestry activities; and increased integration between sectors, which make sure that adaptation within different sectors can be done simultaneously.

No description available.

The purpose of the study was to investigate possible environmental impacts of a reduced catchment area (~25 %) for Kaunisjärvi lake and Patojoki river due to establishment of a iron ore mine in Kaunisvaara, Pajala municipality. To accomplish this, two methods were used; first a literary study was inducted to establish impacts of reduced inflow to lakes and reduced flow in rivers. Secondly, the state of the waters was determined by collecting background data from the mining company (Northland Resources SA) which included chemical- and biological parameters. The result showed that a reduced inflow can affect a lake by either eutrophication or oligotrophication, depending on the lakes condition and the character of the inflow, which in turn has impacts on the entire food-web. Reduced flow in rivers also has impacts on the entire food-web by increased water temperature, decreased dissolved oxygen levels, decreased inundation (witch effects nutrient and organic material exchange), decreased biodiversity in phytoplankton, benthos and fish and inhibiting migration, studies differed in effects on pH and alkalinity. The result also showed that both Kaunisjärvi and Patojoki are affected by nutrient load and organic matter, which impacts the entire ecosystem of the waters. Possible consequences for Kaunisjärvi and Patojoki of reduced inflow and reduced flow are discussed. The report concluded that the reduced catchment area will have impacts on environmental goals set by EU and also on national level, but that the interest of exploitation weighs higher.

The relative contribution of allochthonous and autochthonous production in zooplankton nutrition has been of interest since the net heterotrophy of lakes was recognised to be common. I measured the 13C signature of epilimnetic CO2, particulate organic carbon (POC), and zooplankton in 27 north-temperate lakes in late summer and used the relationships between the POC and zooplankton 13C signatures and the CO2 signature to estimate the autochthonous contribution to these fractions of the plankton. My hypothesis was that POC and zooplankton signature would reflect the 13CO2 signature if they were autochthonous. Conversely, increasing allochthonous C would result in a 13C signature of POC or zooplankton that is increasingly influenced by the allochthonous 13C signature (δ-28‰) and decreasingly dependent on the CO2 signature. The average autochthonous contribution to epilimnetic POC was estimated to be between 62 and 75%. Epilimnetic zooplankton were, on average, between 77 and 91% autochthonous, indicating that zooplankton bias their feeding towards the autochthonous fraction of POC. On average, zooplankton were 1.2‰ enriched in 13C relative to POC, but their biased feeding on phytoplankton means that they can be depleted relative to POC in lakes where POC is highly depleted in 13C. The relationship between 13C POC and 13CO2 allowed us to estimate average photosynthetic fraction as -15.9‰. This estimate is independent of how much allochthonous C contributes to POC. Variation in photosynthetic fractionation was not a major contributor to differences among lakes in POC and zooplankton 13C signature. Allochthonous C is an important, although clearly secondary, source of C to zooplankton of these lakes in late summer. I expanded the above analysis by culling the literature for 13C stable isotope data of lake CO2, POC, and zooplankton. I found that, similar to the lakes that I had sampled, POC signature showed a strong influence of allochthonous C, and inferred that it was close to 50% allochthonous on average. I calculated an autochthonous fractionation of -14.1‰ for the metadata, which was similar to that of the lakes I sampled. While POC had a considerable allochthonous contribution, zooplankton signatures were strongly related to the CO2 signatures, suggesting that their carbon was mostly autochthonous. Therefore, while terrestrial inputs form a major portion of POC, zooplankton C, on average, was largely autochthonous. I also examined the differences in 13C/15N among zooplankton taxa, and differences in 13CO2, 13C/15N of POM, and 13C/15N of zooplankton with depth. There were small differences among the 15N of various taxa, and I did not detect differences in 13C amongst taxa. I found vertical heterogeneity was most marked in 13CO2 signatures, which generally depleted appreciably with increasing lake depth. The signatures of 13C POM and 13C zooplankton also generally depleted with depth, but much less so than did 13CO2. I interpret this as indicating that a large portion of POM and zooplankton C in the metalimnia and hypolimnia of these lakes is derived from C fixed in the epilimnia.