Phosphorus (P) is a limiting nutrient regulating productivity in both freshwater and marine ecosystems. A full knowledge of the sources and pathways of the P cycle is essential for understanding aquatic ecosystem function and for managing eutrophication. However, two significant pathways are poorly understood or remain uncharacterized. First, aquatic metazoans represent a significant internal regenerative pathway of P through the mineralization, translocation (i.e., benthic pelagic coupling) and excretion of nutrients. Rates of P excreted are expected to vary across taxa (i.e., zooplankton vs. mussels vs. benthic macroinvertebrates vs. fish), yet the significance of any one group of taxa in supplying P to bacteria and algae is unknown. Therefore, I developed the first comprehensive set of empirical models of nutrient release for aquatic metazoans (zooplankton, mussels, other benthic macroinvertebrates, and detritivorous and non-detritivorous fish) and compared inter-taxonomic differences in P excretion. I demonstrated that detritivorous fish excrete P at rates greater than all other taxa (as a function of individual organism mass); whereas, mussels generally excreted P at rates less than other taxa. Significant differences in the rate of P excretion between zooplankton and non-detritivorous fish were not observed [i.e., the allometry of P excretion was similar between zooplankton and non-detritivorous fish (as a function of individual body mass)]. I subsequently applied the models to assemblage biomass and abundance data to examine and compare the relative contribution of each taxa to the internal supply of P, and to examine the turnover time of P bound in metazoan biomass. I clearly demonstrated a hierarchy in the contribution by different metazoan assemblages to P cycling (zooplankton > benthic macroinvertebrates > mussels > fish) and clarified the significance of different metazoan taxa in P cycling. Moreover, I demonstrated that the slow turnover time of P bound in fish biomass (relative to other metazoans) indicates that fish are important as sinks rather than sources of P. A second potentially significant P pathway is through the influence of ultraviolet radiation (UVR) on P cycling. UVR may alter P cycling abiotically through changes in P availability and biotically through changes in the acquisition and regeneration of dissolved P by plankton. However, the significance of P released from the photodecomposition of dissolved organic P compounds (DOP), and the effect of UVR on the uptake and regeneration of dissolved P, the turnover of particulate P, and on ambient phosphate (PO43-) concentration has not been investigated and remains unknown. Therefore, my initial experiments applied the novel use of radiophosphate uptake assays to quantify the significance of the photodecomposition of DOP to PO43-. I concluded that the liberation of PO43- through the photodecomposition of DOP is not a significant pathway. However, the photochemical liberation of PO43- from suspended sediments was evident and should be an important pathway supplying PO43- to plankton in shallow polymictic lakes. This represents the first study to identify this P pathway in lakes. The turnover time of the PO43- pool increased under UVR irradiance (i.e., uptake of P by plankton decreased), while the regeneration rate of dissolved P and turnover rate of planktonic P were generally not affected. The net effect of UVR was an increase in steady state PO43- concentration (ssPO43-). Alkaline phosphatase activity (APA) in the dissolved and particulate fractions was significantly reduced in UVR treatments, but unrelated to changes in P uptake as proposed in the literature. This is the first study to comprehensively investigate the biotic effects of UVR on P cycling and represents a major advancement in the field of photobiology. In summary, I have characterized several poorly understood pathways in the P cycle of lakes. With the models I have developed, aquatic metazoans can now be integrated into the P cycle of lakes, for example, with other internal and external sources of P (e.g., from inlets, lake sediments and the atmosphere). This will advance our knowledge of P cycling, and will provide researchers with a better understanding of the nutrient pathways supporting primary production.

The photoprotect compound mycosporine-like amino acids ( MAAs ) are a family of secondary metabolites can protect organisms exposed to solar ultraviolet radiation ( UVR ), only produced in the algae. Analyzed by HPLC, only Alexandrium minutum Halim ( Dinophyceae ) produces MAAs among seven marine microalgae species. The strains named AM-2¡BAM-3¡BAM-4 and AM-6 showed the positive results for producing the MAAs, but not AM-5. Researches on the stability the MAAs extracts from algal powder ( AM-3 ) hold at 4¢J, 25¢J and 50¢J for 35 days and light expose. The results showed the MAAs gradually decayed after 35 days at 50¢J, after exposed to UVR but decreased 48 % in one day and disappeared in two days. The growth and the MAAs produced in A. minutum ( AM-4, AM-6 ) under different salinity, nitrate concentration and UVR were analyzed to find their relationships. When the salinity increased ( 15 psu¡B25 psu¡B35 psu¡B45 psu ), the cell densities of both strain decreased significantly, but with similar MAAs composition and contents. In higher nitrate nutrient ( 2 N ), the cells produced more MAAs than those cultivated in lower nitrate ( N / 10¡BN / 2 ). Under the UV treatment with the deficient nitrate nutrient, the concentration of MAAs in A. minutum decreased after exposed to UVR for 14 hours. However, provided enough nitrate nutrient ( 2 N ), UVR can induced A. minutum to produce higher concentration of MAAs. These results showed MAAs may serve as a nitrogenous compound for intracellular storage, and not as a substance for osmotic adjustment. UVR is an important factor which induce MAAs produced in A. minutum.

Thesis--Utrecht. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1942. / Includes bibliographical references (p. 68).

Thesis (Ph. D.)--Institute of Paper Chemistry, 1941. / Bibliography: leaves 91-93.

Thesis (M.S.)--University of North Carolina at Wilmington, 2003. / Includes bibliographical references (leaves : [51]-54).

The "DNA Damage Hypothesis" pertaining to the evolution of sex was tested using Hydra littoralis. DNA damage was produced by irradiating whole live hydra with ultraviolet light. A curve of uv light dosage vs. survival was constructed. Estimations of threshold fluence and LD50 were made from the survival curve. In four separate experiments, using various combinations of environmental temperatures, uv doses, and number of doses, frequencies of asexual and sexual reproduction were observed and compared. The hydra that received uv treatments did not show an increase in the consequent amount of sexual reproduction, and actually showed a decrease. An increase in the amount of sexual reproduction following DNA damage is predicted by the DNA damage hypothesis, therefore these results do not support this theory. The data was also used to make contradictory observations regarding the "stress hypothesis" for the occurrence of sexual reproduction in hydra.

The effect of increased stratospheric dust on the polarization and intensity of sunlight scattered by the terrestrial atmosphere in the spectral region near the ultraviolet transmission cutoff is examined. Particular interest is given to radiation reflected to space or transmitted to the surface in the direction perpendicular to the incident solar beam in a plane containing the sun and the local vertical. Theoretical results are presented from radiative transfer calculations using a simple single scattering model and a four layer model in which ground reflection and multiple scattering were treated. Results show that the polarization state of transmitted radiation of .2975 μ for an incident solar zenith angle of 70° is sensitive to dust loading above 50 mb. The depolarization caused by a moderate increase in stratospheric dust loading is found to be roughly comparable to that caused by ground reflection and tropospheric aerosol. The polarization of light reflected to space is found to be very sensitive to high altitude dust scattering while being much less sensitive to other sources of depolarization. Results show that increasing the amount of stratospheric dust can cause either an increase or a decrease in the daily dosage of ultraviolet radiation at the surface, depending on the altitude profile of the dust, the latitude and the season. Preliminary experimental results or polarization monitoring by a ground-based instrument are presented and discussed. Sky light polarization ratios in the direction normal to the solar beam at .2975 μ and .300 μ based on data collected in the spring and summer of 1980 from the roof of the Physics-Atmospheric Sciences building on the campus of The University of Arizona are presented and discussed. The stratospheric dust problem is considered in terms of stratospheric aerosol enhancement resulting from volcanic activity.

Stratospheric ozone plays an important role in absorbing ultraviolet radiation. The well-known depletion of the ozone layer has raised several concerns in terms of an expected increase in surface ultraviolet radiation. South Africa, situated in the southern mid-latitude regions, has experienced a general downward trend in total column ozone since 1979, As a result of this negative trend in total column ozone, the ultraviolet flux at the earth's surface is expected to increase. Excessive exposure to ultraviolet radiation is known to have acute and chronic effects on human health, including erythema and skin cancer. Numerous studies have acknowledged a relationship between childhood ultraviolet radiation exposure and the risk of contracting skin cancer, namely malignant melanoma, during adulthood. The aim of this study is to investigate the ultraviolet radiation dose and exposure of children and adolescents in Durban, South Africa. Polysulphone film badges were used to quantify the daily erythemal ultraviolet radiation dose of 30 individuals of varying ages and skin types, engaged in different activities, over a one-week period during summer. The results highlight the diversity of childrens' and adolescents' behavioural patterns, with behaviour being found to play an important role in determining an individual's ultraviolet radiation dose. The mean daily erythemal ultraviolet radiation dose of the children and adolescents was 1.03 MED units with a median of 0.57 MED units and a 95% range of 0.22 - 7.22 MED units. The most striking finding was that the median value was below the critical value of 1 MED unit. An explanation for the unexpectedly low erythemal ultraviolet radiation doses recorded in this study was sought in the prevailing climatic conditions. Ambient erythemal ultraviolet radiation levels recorded during the study period were high, ranging between 20.57 - 30.60 MED units. However, high temperatures (>27°C), coupled with high humidity values, may have encouraged the children and adolescents to avoid direct sunlight and find shade while outdoors. The daily erythemal ultraviolet radiation doses of the children and adolescents were also compared to the ambient erythemal ultraviolet radiation levels received on a horizontal surface by a YES UVB-l pyranometer located at the University of Natal (Durban). Children and adolescents in Durban received approximately 4.58% of the total daily ambient erythemal ultraviolet radiation incident upon a horizontal surface. This was found to be similar to a study (5 - 6%) conducted by Diffey et al. (1996) in England, as well as a study (4 - 8%) by Gies et al. (1998) in Brisbane, Australia. The personal ultraviolet radiation exposure journals of the children and adolescents were used to determine the timing of exposures, duration of exposures and nature of outdoor activities and these were then related to their daily ultraviolet radiation doses. Of all the factors considered, the nature of an individual's activity was found to have the strongest influence in determining their ultraviolet radiation dose. An activity model was derived in order to investigate the effect of activity on ultraviolet radiation dose, where three activity factors, namely swimming, walking and tennis, were calculated for a South African context and compared with those from previous international studies. It was found that the activity factors derived in this study were similar to Holman et al. (1983) and Herlihy et al. (1994) and may be used in an activity model to estimate individual erythemal ultraviolet radiation dose for a particular activity. The value of this innovative activity model lies in its ability to predict individual ultraviolet radiation dose and this may help to emphasise the importance of responsible outdoor behaviour. A mannequin was used to quantify the anatomical distribution of erythemal ultraviolet radiation under clear sky and overcast conditions. It was found that the vertex of the head and shoulders received the highest erythemal ultraviolet radiation doses under both conditions. This was then related to the erythemal ultraviolet radiation doses of the children and adolescents as recorded by the polysulphone film badges in order to identify anatomic sites susceptible to high erythemal ultraviolet radiation doses. Behaviour alternatives and ultraviolet radiation protective mechanisms were discussed and recommendations made for children and adolescents residing in Durban. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

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