Diel patterns of nitrogen (NO₃⁻, NH₄⁺, urea) uptake were investigated in natural assemblages of phytoplankton from neritic and oceanic environments off the coast of British Columbia. This is the first study to report nitrogen uptake rates and extensive measurements of ambient NH₄⁺ and urea concentrations in these waters. Calculated rates of N uptake, 15 based on ¹⁵N incorporation into particulate matter during time course experiments, were maximal during the day and minimal at night. Besides the obvious effects of irradiance, the amplitude of the periodicity in uptake rate was influenced by phytoplankton community composition, ambient nitrogen concentration, forms of nitrogen available, and depth of sampling. Uptake of nitrogen during the night and in artificial darkness were measurable proportions of daytime and light uptake rates, with the importance of dark uptake generally increasing with increasing N limitation. This is the first study of diel urea uptake by marine phytoplankton in the field. The ratios of dark to light urea uptake over a diel cycle were more similar to those of NO₃⁻than those of the other reduced N form, NH₄⁺. Rates of NO₆⁻ and urea uptake by phytoplankton in the shallow and deep chlorophyll layers of the Strait of Georgia were measured over a gradient of irradiances and results of these experiments could be fitted with a hyperbolic function similar to the Michaelis-Menten equation. Half-saturation constants (KLT) for light-dependent uptake of urea and NO₃⁻ ranged from 0 to 14% of the surface irradiance and dark uptake was a variable, but often substantial (> 50%) portion of the total (light + dark) uptake. The uptake response of nitrate-replete and -starved populations of the picoflagellate, Micromonas pusilla (Butch.) Manton et Parke, to urea, NH₄⁺ and NO₃⁻ perturbations was determined by both ¹⁵N accumulation and nutrient disappearance from the culture medium. Maximum specific uptake rates (Vmax) of NH₄⁺ were 0.13 h⁻¹, more than 2 times the Vmax of NO₃⁻ or urea (ca. 0.05 h⁻¹). The half-saturation constants (Ks) for urea, NH₄⁺ and NO₃⁻ were within ± 0.1 µg-at N•L⁻¹ of each other; the average value of 0.41 µg-at. N•L⁻¹ is within the range reported for small, oceanic diatoms. NO₃⁻ uptake was completely inhibited following NH₄⁺ addition (1-10 µg-at. N•L⁻¹), whereas urea addition resulted in only a 28% reduction in NO3- uptake. Starved cultures of M. pusilla exhibited variable uptake of NH₄⁺ and urea as a function of time, with an initial "surge" uptake response. This is the first laboratory study of N uptake by an eucaroyotic picoplankter and demonstrates that many of the transient uptake responses reported for diatoms, with which it competes in the field, are common to this picoplankter. Diel periodicity of nitrogen uptake and assimilation were measured in N-replete batch cultures of M. pusilla and also in N-limited cyclostat cultures (14L:10D) at three growth rates corresponding to ca. 75, 50 and 25% of it's maximal growth rate. Nitrate uptake was continuous and independent of the L:D cycle in the cyclostat cultures at the lowest dilution rate, but NO₃⁻ uptake rates exhibited pronounced periodicity in the batch and higher dilution rate cultures, a response similar to that seen in previous studies of cyclostat cultures of some diatoms. Diel patterns in cell division, mean cell volume, potential uptake rates and internal pools of NO₃⁻ were also observed and are discussed with respect to the nutritional status of the cells. The effect of irradiance on the uptake of NH₄⁺ and NO₃⁻ by M. pusilla was also described by Michaelis-Menten kinetics; with increasing N limitation the importance of light for nitrogen uptake decreased and dark uptake increased from 5-20% to 21-39% of NO₃⁻ and NH₄⁺ uptake rates, respectively, at saturating irradiance. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Respirometric experiments were performed to evaluate the role of nitrogen in aerobic diesel biodegradation. Specific objectives included 1) evaluating the effects of water potential induced by various nitrogen amendments on diesel biodegradation rates in arid region soils, 2) comparing concurrent effects of C:N ratios and soil water potential on diesel degradation rates, and 3), measuring gross rates of nitrogen cycling processes in diesel-contaminated soil to determine duration of fertilizer bioavailability. In all studies, increasing nitrogen fertilization resulted in a decrease in total water potential and correlated with an increase in lag phase and overall reduction in microbial respiration. Highest respiration and estimated diesel degradation was observed in the 250 mg N/kg soil treatments regardless of diesel concentration, nitrogen source, or soil used, suggesting an inhibitory osmotic effect from higher rates of nitrogen application. The depression of water potential resulting in a 50% reduction in respiration was much greater than that observed in humid region soil, suggesting higher salt tolerance by microbial populations of arid region soils. Due to the dependence on contaminant concentrations, use of C:N ratios was problematic in optimizing nitrogen augmentation, leading to over-fertilization in highly contaminated soils. Optimal C:N levels among those tested were 17:1, 34:1, and 68:1 for 5,000, 10,000 and 20,000 mg/kg diesel treatments respectively. Determining nitrogen augmentation on the basis of soil pore water nitrogen (mg N/kg soil H₂0) is independent of hydrocarbon concentration but takes into account soil moisture content. In the soil studied, optimal nitrogen fertilization was observed at an average soil pore water nitrogen level of 1950 mg N/kg H₂0 at all levels of diesel contamination. Based on the nitrogen transformation rates estimated, the duration of fertilizer contribution to the inorganic nitrogen pool at 5,000 mg/kg diesel was estimated at 0.9, 1.9, and 3.2 years in the 250, 500, and 1000 mg/kg nitrogen treatments respectively. The estimation was conservative as ammonium fixation, gross nitrogen immobilization, and nitrification were assumed as losses of fertilizer with only gross mineralization of native organic nitrogen contributing to the most active portion of the nitrogen pool.

Thesis (PhD)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Several genera of cyanobacteria produce a range of toxins. The increased rate of eutrophication of surface fresh waters due to anthropogenic inputs has resulted in more frequent and severe cyanobacterial bloom events. Such bloom events make impoundments unsuitable for recreational use and increase the cost of production of potable water due to the necessity for removal of toxins released from cells during the purification process. Microcystis aeruginosa is the major freshwater bloom-forming toxic cyanobacterium. Concentrations of the hepatotoxin, microcystin, are highly variable in blooms. Published literature on environmental conditions leading to increased microcystin production was often contradictory and in many cases did not consider all relevant parameters. However, environmental nitrogen and phosphorus, temperature and light, and growth rate were implicated in regulation of toxin content. The purpose of this work was therefore to investigate environmental factors (specifically nitrogen and phosphorus) and cellular activities (specifically carbon fixation and nitrogen uptake rates and growth rate) involved in the modulation of microcystin production in M. aeruginosa in order to clarify the role of these parameters, and in an attempt to identify regulatory mechanisms for microcystin production. Environmental nitrogen, phosphorus and growth rate were shown to co-modulate microcystin production in M. aeruginosa. Adequate phosphorus is required for photosynthetic carbon fixation. Phosphorus uptake by M. aeruginosa is strongly correlated with carbon fixation rate. Although microcystin content increased with increasing nitrogen:phosphorus ratios in culture medium, under phosphorus limitation microcystin content was lower irrespective of nitrogen concentrations. This observation and the requirements for fixed carbon for nitrogen assimilation therefore prompted investigation of the effects of cellular carbon fixation and nitrogen uptake in the modulation of microcystin production. Microcystin production was found to be enhanced when nitrogen uptake rate relative to carbon fixation rate was higher than that required for balanced growth. The cellular nitrogen:carbon ratio above which microcystin concentrations increased substantially, corresponded to the Redfield ratio for balanced growth. Investigation of potential regulatory mechanisms involving the cyanobacterial nitrogen regulator, NtcA, yielded putative NtcA binding sites indicative of repression in the microcystin synthetase gene cluster. In culture, the polypeptide synthetase module gene, mcyA, and ntcA were inversely expressed as a function of carbon-fixation:nitrogen-uptake potential. However, no increase or decrease in microcystin production could be linked to either glutamine, glutamate or a-ketoglutarate, metabolites that are involved in regulation of ntcA. The role of NtcA in regulation of microcystin production could therefore not be confirmed. In conclusion, these data suggest that microcystin production is metabolically regulated by cellular C:N balance and specific growth rate. The primary importance of nitrogen and carbon was demonstrated by a simple model where only nitrogen uptake, carbon fixation and growth rate were used to predict microcystin levels. The model also explains results previously described in literature. Similarly, an artificial neural network model was used to show that the carbon fixation dependence on phosphorus allows accurate prediction of microcystin levels based on growth rate and environmental nitrogen and phosphorus. / AFRIKAANSE OPSOMMING: Verskeie genera van sianobakterieë produseer 'n verskeidenheid van toksiene. Die toename in die tempo van eutrofikasie van varswater oppervlaktes as gevolg van antropogeniese insette veroorsaak al hoe meer en al hoe erger sianobakteriële infestasies. Dit veroorsaak probleme vir ontspanninggebruik van hierdie waters en verhoog die koste van produksie van drinkbare water as gevolg van die noodsaak om die toksiene wat deur die selle gedurende die suiweringsproses vrygelaat word te verwyder. Microcystis aeruginosa is die belangrikste varswater bloeisel-vormende toksiese sianobakterium. Die konsentrasie van die hepatotoksien mikrosistien is hoogs varieerbaar in sulke bloeisels. Gepubliseerde literatuur oor die omgewingskondisies wat lei na verhoogde mikrosistienproduksie is dikwels weersprekend en neem in vele gevalle nie al die relevante parameters in ag nie. Desnieteenstaande word omgewingstikstof, fosfor, temperatuur en lig, asook groeisnelheid, geïmpliseer in die regulering van toksieninhoud. Die doel van hierdie navorsing was dus om omgewingsfaktore (spesifiek stikstof en fosfor) en sellulêre aktiwiteite (spesifiek koolstoffiskering en die snelheid van stikstofopname en van groei) betrokke by die modulering van mikrosistienproduksie in M. aeruginosa te ondersoek in 'n poging om die rol van hierdie parameters te verstaan en om regulatoriese meganismes vir mikrosistienproduksie te identifiseer. In hierdie studie is aangetoon dat omgewingstikstof en fosfor sowel as groeisnelheid mikrosistienproduksie in M. aeruginosa ko-moduleer. Genoegsame fosfor word benodig vir fotosintetiese koolstoffiksering. Fosforopname deur M. aeruginosa korreleer sterk met die snelheid van koolstoffiksering. Alhoewel mikrosistieninhoud toegeneem het met 'n toename in die stikstof:fosfor verhouding in die kultuurmedium, was die mikrosistieninhoud onder kondisies van fosforlimitering laer ongeag die stikstofkonsentrasie. Hierdie waarneming, tesame met die noodsaak van gefikseerde koolstof vir stikstofassimilering, het gelei na 'n studie van die effekte van sellulêre koolstoffiksering and stikstofopname op die modulering van mikrosistienproduksie. Dit is gevind dat mikrosistienproduksie verhoog was wanneer die snelheid van stikstofopname relatief tot die snelheid van koolstoffiksering hoër was as die waarde wat benodig word vir gebalanseerde groei. Die sellulêre stikstof:koolstof verhouding waarbo mikrosistienkonsentrasies beduidend verhoog is stem ooreen met die Redfield verhouding vir gebalanseerde groei. 'n Ondersoek na potensiële reguleringsmeganismes waarby die sianobakteriële stikstofreguleerder NtcA betrokke is het gelei na die ontdekking van moontlike NtcA bindingseteis; dit kan dui op die repressie van die mikrosistiensintetase geengroepering. Onder kultuurkondisies is gevind dat die geen vir die polipeptiedsintetase module, mcyA, en ntcA omgekeerd uitgedruk word as 'n funksie van koolstofopname:stikstofopname potensiale. Geen toename of afname in mikrosistienproduksie kon egter gekoppel word aan óf glutamien, óf glutamaat, óf a-ketoglutaraat nie, metaboliete wat betrokke is by die regulering van ntcA. Die rol van NtcA in die regulering van mikrosistienproduksie kon dus nie bevestig word nie. Die gevolgtrekking is dus gemaak dat mikrosistienproduksie metabolies gereguleer word deur die C:N balans en die spesifieke groeisnelheid. Die primêre belang van stikstof en koolstof is gedemonstreer deur 'n eenvoudige model waarin slegs stikstofopname, koolstoffiksering en groeisnelheid gebruik word om mikrosistienvlakke te voorspel. Die model verklaar ook resultate wat tevore in die literatuur beskryf is. Soortgelyk is 'n artifisiële neurale netwerkmodel gebruik om te toon dat die afhanklikheid van koolstoffiksering van fosfor akkurate voorspelling van mikrosistienvlakke gebaseer of groeisnelheid en omgewingstikstof en fosfor moontlik maak.

Nitrogen pollution in marine waters is directly tied to human development – including agricultural runoff, atmospheric deposition, and urban wastewater effluents. After more than a century of urbanization, Hong Kong faces a major challenge in mitigating marine pollution, particularly nitrogen. Indeed, nitrogen pollution may be one of the primary causes of benthic ecosystem decline as evidenced by a contraction in the historical distribution of corals and seagrasses. Such ecosystems provide vital ecosystem services, not limited to nursery grounds for economically important fisheries. While the Hong Kong Government (HK Environmental Protection Department) has established long-term monitoring of marine nitrogen concentrations, the data obtained on the size of the total nitrogen pool does not indicate the proportion of which is derived from human activities. Stable isotope analysis of nitrogen (δ15N) can provide more accurate information on the source of nitrogen not only in the receiving environment but also in the marine and benthic organisms present. This project critically examines Hong Kong’s nitrogen sources from sewage effluents using stable isotope analysis. Objectives were to investigate (1) the δ15N of sewage effluents sampled across Hong Kong, Kowloon, New Territories, Lantau and Outlying Islands (2) the differences in δ15N across sewage treatment type and (3) the differences in δ15N between the wet and dry seasons with the aim of developing a new approach for detecting and mapping sewage impacts in Hong Kong. Through a 6-month sampling effort across 18 sewage treatment facilities, this study shows that 70% of δ15N values obtained from the sewage effluents were characteristically enriched (δ15N values up to 205 ‰) when compared with naturally occurring nitrogen sources in the biosphere (I10‰ < δ15N < 10‰). Overall, δ15N was more variable in plants with preliminary treatment and chemically enhanced primary treatment (CEPT) than in plants with primary, secondary or tertiary treatment. The mean daily flow rate explained 75.7% of the observed variability in δ15N values of preliminary treatment plants and 85% of the variability in primary treatment plants. This was also the case in plants having CEPT with a negative correlation of 46% between mean daily flow rate and sewage effluent δ15N values. This suggests varying models for the quantity and retention time of wastewater versus δ15N signatures for different treatment types that require further study. Microbial activity by aerobic bacteria and protozoa, ammonia volatilization and the amount of nitrogen present in the effluents are possible causes for δ15N enrichment. Enterococcus counts of three sites sampled indicated that that the municipal sewer system and wastewater treatment plant in Stonecutters Island (56,100 CFU 100 mlI1) and preliminary treatment facilities (57,800 CFU 100 mlI1) in Hong Kong Island are insufficient in preventing bacterial contamination in comparison to US EPA standards for recreational use of coastal marine waters (35 CFU 100 mlI1). These findings indicate that enriched δ15N values directly translate to the presence of anthropogenic inputs and that monitoring δ15N of primary producers is a feasible and important tool for monitoring wastewater management in Hong Kong. / published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

published_or_final_version / abstract / toc / Civil Engineering / Master / Master of Philosophy

The focus of this mini-dissertation is the use of riparian buffer zones to manage nitrate pollution of water resources. Riparian buffer zones are vegetated areas adjacent to streams, lakes and rivers, that are managed to enhance and protect aquatic resources from the adverse impacts of agricultural practices. These zones are recognised globally for their function in water quality amelioration. Despite the growing literature, there is little consensus on how to design, assess and manage these riparian buffer zones specifically for nitrate attenuation. For the purpose of this mini-dissertation, a literature review of world-wide research into the nitrate attenuation efficiencies of riparian buffer zones was undertaken. A database was created using the key information from this literature. Two key processes responsible for immobilising and/or removing nitrate from surface and subsurface flows are generally recognised in the available literature, namely: vegetative uptake and the process of denitrification. A comparison of the available riparian studies indicated that there are similar characteristics in riparian buffer zones that may be responsible for enhancing these key mechanisms. Studies where there was shallow lateral subsurface or uniform surface water delivery pathways, vegetation of close structure and composition, high organic matter in the soils and fluctuating soil surface saturation rates showed the most significant nitrate attenuation efficiencies. The mini-dissertation proposes that these similarities can be used to both assess a riparian landscape for its potential to attenuate nitrate, and to size a riparian buffer zone specifically to meet this function. A set of proposed guidelines based on the findings of the dissertation attempt to illustrate how riparian pollution control recommendations can be achieved. These guidelines are an example of how to assist a farmer or similar landowner in achieving good nitrate removal efficiencies from a riparian buffer zone. The guidelines work through three steps, which help to establish and prioritise management zones, assess each zone's potential for nitrate attenuation, and determine adequate riparian buffer widths for each management zone. A case study was used to illustrate the practical application of the guidelines. Full testing of these guidelines was not within the scope of this mini-dissertation, however the guidelines are an indication of how information regarding riparian function can be applied to a system to determine effective management of water resources. / Thesis (M.Env.Dev.)-University of Natal, Pietermaritzburg, 2002

Nitrogen (N) has traditionally been regarded as the primary limiting nutrient to algal growth in marine coastal waters, but recent studies suggest that phosphorus (P) can be limiting in carbonate-rich environments. To better understand the importance of P. alkaline phosphatase activity (APA) was measured in reef macroalgae in seven counties of south Florida ; several significant trends emerged : 1) APA decreased geographically from the highest values in Dada>Monroe>Palm Beach>St. Lucie>Broward>Martin>Lee counties 2) APA varied temporally with increasing nutrient-rich runoff in the wet season 3) APA varied due to taxonomic division Phaeophyta>Rhodophyta>Chlorophyta 4) Nutrient enrichment experiments demonstrated that increased N-enrichment enhanced P-limitation while increased P decreased P-limitation. These results suggest that high APA observed in carbonate-rich waters of Dade County and low APA in Broward County resulted from high nutrient inputs associated with anthropogenic nutrient pollution. / by Courtney Kehler. / Thesis (M.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

Includes bibliographical references (p. 96-102)

Title from PDF of title page. / Document formatted into pages; contains 105 pages. / Thesis (M.S.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Atmospheric deposition of nitrogen has been implicated in the destruction of seagrass beds and in the decline of water quality of Tampa Bay, Florida. The objective of this research was to determine the tendency for air masses of different origins to wet-deposit nitrate and ammonium species to the bay. Precipitation chemistry data was obtained via the NADP AIRMoN Gandy Bridge monitoring site for the period of 1 August 1996 through 31 December 2000. Rainfall events were classified by using the NOAA HYSPLIT trajectory model, precipitation chemistry data, and tropical storm history data. Average nitrate and ammonium concentrations and nitrogen fluxes were calculated based upon the chosen categories. The average annual nitrogen flux for nitrate and ammonium were 2.1 kg/ha/yr and 1.4 kg/ha/yr, respectively. For trajectory-classified data, the lowest nitrate and ammonium nitrogen fluxes were observed with air masses from the west and south, over the Gulf of Mexico. / ABSTRACT: The highest ammonium nitrogen flux was seen from trajectories from the east, while local trajectories demonstrated the highest average nitrate nitrogen flux. For chemically-classified data, the highest nitrate and ammonium fluxes were associated with the local combustion classification. Rainfall from tropical weather systems deposited lower average nitrate nitrogen fluxes than non-tropical events, but ammonium nitrogen fluxes were the same between tropical and non-tropical precipitation. Even the events representing the cleanest air masses contributing precipitation to Tampa Bay had nitrate and ammonium concentrations more than two times the background concentrations associated with the northern hemisphere. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.