Thesis (Ph. D.)--University of Hong Kong, 1992.

Thesis (Ph. D.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 253-281).

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Made available in DSpace on 2014-06-11T19:35:43Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-07-02Bitstream added on 2014-06-13T20:07:20Z : No. of bitstreams: 1 loebmann_d_dr_rcla.pdf: 4477659 bytes, checksum: 17d94b5d744cdd36754c31cd3144af79 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / O Planalto da Ibiapaba é um dos mais importantes fragmentos de floresta úmida do Ceará. Localizado do extremo noroeste do estado, essa região é privilegiada não somente pelas áreas de florestas úmidas, mas também por um mosáico de ambientes ao longo de sua extensão. Consequentemente, a fauna de anfíbios e répteis é extremamente rica se comparada as outras áreas do Bioma Caatinga. Durante dois anos a herpetofauna desse refúgio da vida silvestre foi estudada e os resultados obtidos são apresentados nessa tese. As 121 espécies (38 anfíbios e 83 répteis) encontradas no presente estudo revelam um resultado bastante expressivo, não só pelo fato de ser esta a região com maior riqueza de espécies para o Bioma Caatinga conhecidada até o momento, mas também pelo fato de que o Planalto da Ibiabapa abriga espécies consideradas raras e/ou ameaçadas. Padrões reprodutivos de machos e fêmeas em comunidades de anfíbios também foram investigados, tentando compreender melhor os mecanismos adaptativos das espécies para sobreviver às duras condições impostas pelo clima marcadamente sazonal da Caatinga. A presença no Planalto da Ibiapaba de Adelophryne baturitensis, uma espécie considerada ameaçada e até então conhecida somente para a localidade‐tipo, foi também estudada em maior detalhe e dados inéditos de vocalização, descobertas de novas populações e dados moleculares são apresentados. Ampliações de distribuição e atualizações de distribuição de 14 espécies são também apresentadas nessa tese. Os resultados obtidos mostram a necessidade de preservar os fragmentos de floresta úmida e regiões adjacentes do Planalto da Ibiapaba, além do que são importantes para uma melhor compreensão da ecologia, biogeografia e taxonomia dos anfíbios e répteis de florestas úmidas do Nordeste e de áreas abertas do Brasil, em especial do Bioma Caatinga / The Planalto da Ibiapaba is one of the most important fragments of moist forests in the state of Ceará. Located at the Northwestern portion of the state, this region is not only privileged by the presence of moist forest areas, but also by the presence of a mosaic of environments along its extension. Consequently, the fauna of amphibians and reptiles present there is extremely rich if compared to other areas from the Caatinga Biome. During two years the herpetofauna of this wildlife refuge was studied and the results are presented in this thesis. The 121 species (38 amphibians and 83 reptiles) encountered in this study reveal a very expressive result, not only due to the fact that this is the region with the highest species richness for the Caatinga Biome known so far, but also because Planalto da Ibiabapa shelters species considered rare and threatened. Reproductive patterns for males and females in amphibian communities were also investigated, in order to try to understand adaptive mechanisms of the amphibian species to survive the harsh conditions imposed by marked seasonal climate of the Caatinga. The presence in Planalto da Ibiapaba of Adelophryne baturitensis, a species considered endangered and previously known only to its type locality, was also studied in more detail and data from vocalization, discoveries of new populations, and molecular data are here presented. Distribution extensions and upgrades of distribution from 14 species are also presented in this thesis. The results show the need to preserve the moist forest fragments and adjacent areas of the Planalto da Ibiapaba and are also important for the better understanding of ecology, biogeography, and taxonomy of amphibians and reptiles in the moist forests from Northeastern and open areas of Brazil, especially in the Caatinga Biome

The alteration of the global environment by human activities is so widespread that scientists argue we've entered a new geologic epoch known as the Anthropocene. This dissertation examines the impact of human activities on biogeochemical cycling at the land-sea interface. I focus primarily on the role of land use/land cover (LULC) and coastal nutrient enrichment on silicon (Si) cycling in New England rivers and salt marshes. On land, Si is taken up by vegetation, improving plant fitness and protecting plants from a variety of environmental stressors. In aquatic systems, diatoms, the dominant type of phytoplankton in coastal temperate waters, require Si to survive. My research demonstrates that LULC is an important driver of Si export to coastal systems, accounting for 40-70% of the variability of riverine fluxes. Developed watersheds export significantly (p=0.03) more Si than their forested counterparts, which I hypothesize is due to less vegetated cover, a known Si sink, in developed watersheds. Building on this, I calculated the amount of Si fixed by land plants globally (84 Tmol yr-1) and the percent (55%) of global terrestrial net primary production that can be attributed to active Si-accumulating organisms. Next, I created the first complete salt marsh Si budget by quantifying tidal creek fluxes and net Si accumulation in a relatively undisturbed low-nutrient salt marsh. Further, comparing this Si accumulation to that of a high-nutrient marsh revealed that the high-nutrient marsh contained significantly (p<0.05) more Si within the sediments, roots, and porewater. Combining my original data from six New England salt marshes with published values, I quantify the mode of Si accumulation (rejective, passive, or active) by Spartina grasses and the environmental controls on such accumulation. Finally, using radionuclide tracers 137Cs and 210Pb, I calculated vertical accretion rates of five salt marshes and compared these values to historical measurements. I found that accretion rates have slowed and this deceleration is driven, in part, by a decrease in organic matter accumulation. Together, this dissertation improves our knowledge of Si cycling in terrestrial and aquatic ecosystems, and identifies previously unrecognized ways in which humans are perturbing biogeochemical cycles at the land-sea interface.

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Fundação de Amparo a Pesquisa no Estado do Rio Grande do Sul / The role of rice fields in representing alternative refugees for wetland-expelled macroinvertebrates, in various scales, was assessed in southern Brazil. It is expected that rice fields sustain a representative version, although poorer, of wetland s macroinvertebrate fauna. Sampling was carried out in three different areas from the Central Depression in the State of Rio Grande do Sul, away hundreds of kilometers from each other. Wetlands and rice fields were simultaneously sampled. Richness was found to be equivalent in both environments. Macroinvertebrate communities composition and taxonomic structure were different at both environments. In rice fields, active dispersal taxa were more common, suggesting that the maintenance of a dry-phase at growth areas during intercrop season favors colonization by these taxa. In wetlands, regional scale was responsible for the greatest contribution to macroinvertebrate diversity. Though, at intermediate-scale (within-region), rice fields presented higher diversity than wetlands, due to different cultivation systems and growth phases of the culture. Drainage practices together with climatic changes affecting study area, which have caused longer drying periods, held up for differences in communities composition and taxonomic structure at both environments. Yet the influence of study scales was more related to wetland s environmental heterogeneity, opposing to rice field lesscomplex environmental structure. / A capacidade de arrozais irrigados representarem um refúgio alternativo para os macroinvertebrados expulsos de banhados, em diversas escalas de estudo, foi analisada no extremo sul do Brasil. Espera-se que arrozais sustentem uma fauna representativa, porém mais pobre do que a dos banhados. A amostragem foi conduzida em três regiões da Depressão Central do Rio Grande do Sul, distantes centenas de quilômetros umas das outras, onde banhados e arrozais foram amostrados simultaneamente. A riqueza encontrada foi semelhante em ambos os ambientes. A composição e a estrutura taxonômica das comunidades foram distintas nos dois ambientes. Nos arrozais, táxons de dispersão ativa foram mais comuns, o que sugere que a manutenção de fase seca nas áreas de cultivo, durante a entressafra, favorece a colonização por estes tipos de macroinvertebrados. Nos banhados, a escala regional contribuiu para a maior porcentagem da diversidade de macroinvertebrados encontrados. Porém, nos diferentes locais amostrados (escala espacial intermediária) de cada região de estudo, os arrozais apresentaram maior diversidade do que os banhados, o que pode ser creditado aos diferentes sistemas de cultivo e fases de desenvolvimento observadas. A prática de drenagem dos banhados para o plantio de arroz durante o verão, associada às alterações climáticas que têm atingido a região de estudo, causando períodos de estiagem mais prolongados do que o usual, foram responsáveis pelas diferenças de composição e estrutura taxonômica encontradas nos dois ambientes. Já a influência das escalas espaciais esteve mais relacionada à heterogeneidade ambiental dos banhados, em oposição à estrutura mais simplificada dos arrozais.

Salt marshes are some of the most productive ecosystems in the world and have been the centre of attention over the past few decades, due to their decline as a result of global climate change and anthropogenic impacts. The growth of salt marshes is determined by substrate type, soil conductivity and elevation. The permanently open Keurbooms Estuary along the south-east coast of South Africa is subjected to occasional fluvial flooding and its intertidal area lacks well developed salt marshes, with Spartina maritima restricted to the lower reaches of the Bitou tributary and a few sections of the Keurbooms tributary. Presumeably because of fine sediment habitat in the confluence and lower Bitou tributary. The salinity of the estuarine water ranges between 0.1 – 26.9 and 3.2 – 35.3 in the Bitou and Keurbooms tributaries respectively. A typical salt wedge salinity pattern is common in the Keurbooms tributary where saline water often intrudes underneath the freshwater, especially during high river flows. The following hypotheses were developed and tested in this study: The limited spatial distribution of S. maritima in the Keurbooms Estuary is due to limited availability of fine sediment habitat; and the source of the fine sediment in the estuary is the Bitou tributary rather than the Keurbooms tributary or the sea. It was further postulated that after sediment characteristics, floods are the major hydrological driver determining the distribution of S. maritima in the Keurbooms Estuary. The results of the surveys of the estuarine channel bottom sediments showed that the Keurbooms tributary was mostly characterized by the sand-size sediment fraction derived from the feldspathic and sandstone with evidence of fine sediment fractions restricted to the upper reaches at the confluence with Whiskey Creek. The Bitou was almost always composed of coarse sized sediments in the upper reaches, fine sediment deposits in the middle and lower reaches and medium sorted sand with almost no clay or calcium carbonate in the estuarine component below the confluence of the tributaries. These findings were further supported by the surface sediment deposited within the S. maritima intertidal salt marsh, which showed finer sediment deposits in the Bitou marsh compared to the Keurbooms marsh surface. Similar results were also found in the sediment cores, with the Keurbooms marsh sediment becoming finer with increasing depth whereas fine sediments reduced with depth in the Bitou marsh. The results of the sediment mineralogy indicated that the increased concentrations of clay minerals in the S. maritima surface sediments are derived from the Bokkeveld shale, siltstone and clay slate exposed above the N2 Bridge in the Keurbooms Estuary. GIS mapping shows that S. maritima has been declining over the past two decades, with rapid decreases especially evident after big flooding events. The GIS mapping also indicates that the patches of the S. maritima in the Keurbooms tributary are more exposed to big floods than the Bitou marsh. Despite showing an overall decline, S. maritima area coverage remained more consistent in the lower reaches of the Bitou tributary than in the Keurbooms tributary. Despite the larger and more persistent area cover, the S. maritima plants were shorter and less dense than the plants growing in the sandy substrate. The black/grey colouration of soil with increasing depth in the Bitou tributary was an indication of the reduced state of the soil caused by prolonged waterlogged conditions. The roots of S. maritima in both tributaries were mostly restricted to the sub-surface substrate layer (i.e. 0 – 0.25 m), although the Bitou populations showed more vegetative propagation than the Keurbooms populations. This mechanism of reproduction was also demonstrated during the transplant experiment which showed a greater number of new stem production in the fine sediment substrates compared to the sandy silt substrates. Although accretion rates were not determined in this study, the short-term sediment deposition rates revealed that sedimentation is active in the marshes of the Keurbooms Estuary. Therefore, in spite of showing a decline in area cover, the production of viable seed and observed vegetative propagation suggest that the S. maritima is likely to colonize open stable intertidal mudflats / sandflats, thus maintaining its distribution as an intertidal species in the salt marshes of the Keurbooms Estuary.

The Orange River is an important source of freshwater and like many other wetlands in semi-arid regions, supports various social (Spurgeon, 1998), economic (Spurgeon, 1998; Bornman et al., 2005) and ecological functions. The saltmarsh at the Orange River Mouth has become degraded over time following numerous anthropogenic impacts. As a result the Transboundary RAMSAR site was placed on the Montreux record emphasising the importance for rehabilitation. The potential of the marsh for natural rehabilitation was assessed through three physical factors which were considered to have the most influence on the saltmarsh i.e. 1) sediment 2) water 3) wind. Three sampling areas were chosen to investigate the sediment characteristics of the ORM saltmarsh and the suitability for seed germination and adult survival. Site A was representative of the general marsh area, Site B was thought to have favourable sediment conditions for saltmarsh growth because of the large numbers of seedlings and Site C was prone to inundation by wind blown sediment. The sites were sampled in 2005 (dry conditions) and in 2006 after high rainfall and river flooding. Electrical conductivity (EC) of the sediment throughout the marsh was hypersaline in many instances above the tolerance range for S. pillansii (> 80 mS.cm-1) The freshwater event in 2006 lowered salinity significantly in two of the three sites. Differences in sediment characteristics were also compared for three habitats i.e. driftlines, open sites and under vegetation. Driftlines (C. coronopifolia = 872 seedlings m-2; S. pillansii = 1296 seedlings m-2) and the microhabitat associated with adult plants (C. coronopifolia = 803 seedlings m-2; S. pillansii = 721 seedlings m-2) created favourable conditions for seedling growth, however open unvegetated (C. coronopifolia = 56 seedlings m-2; S. pillansii = 49 seedlings m-2) areas had significantly lower seedling density. Due to the marsh currently being in a desertified state this study aimed to establish whether the remaining vegetation could produce enough seed to revegetate the marsh. Laboratory studies indicated that seeds of both species germinated best in freshwater (0 psu). The germination of S. pillansii seeds was 40 percent at 0 psu compared to 5 percent at 35 psu. After storage under hypersaline conditions (35 psu) C. coronopifolia showed 100 percent seed germination when returned to freshwater whereas storage at 70 psu decreased the viability of S. pillansii seeds. The plants are producing adequate seed that will allow for regrowth and rehabilitation if sediment and groundwater characteristics are suitable for seed germination, seedling growth and adult survival. However the increase in bare areas at the Orange River mouth as a result of salt marsh dieback has increased the available sediment source. The wind blown sediment has covered large areas of the remaining adult salt marsh vegetation, particularly in the northern corner at Site C, causing further die-back.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 95-96. / by William Kensett Nuttle. / M.S.