Nitrogen fixation is no longer considered to be a minor factor of the nitrogen cycle in oceanic ecosystems. Recent geochemical and biological efforts have led to a significant increase in the estimated input of nitrogen to marine ecosystems by biological fixation, while molecular studies have increased our knowledge of the number and diversity of nitrogen fixers known to be active in the ocean. Although Trichodesmium spp. have long been viewed as the primary marine nitrogen fixers, recent efforts have shown that various members of the picoplankton community are also actively involved in nitrogen fixation. The relative abundance of different nitrogen fixers is an important ecosystem parameter since nitrogen fixers may differ significantly in their physiology, life history and ecology. Here we combine rate measurements and stable isotope natural abundance measurements to constrain the impact of N2 fixation in the waters north of Australia. Samples were collected in the Coral, Arafura, and East Timor Seas, thus spanning three distinct hydrographic regions. Our data show that Trichodesmium has a significant influence on the stable nitrogen isotope ratios of particulate and zooplankton biomass and suggest that Trichodesmium is a significant source of nitrogen for the pelagic ecosystem. Based on stable carbon isotope ratios, it is also likely that the pathways are indirect and nitrogen fixed by Trichodesmium enters the higher trophic levels via decomposition as dissolved organic and inorganic nitrogen. Picocyanobacteria showed high diazotrophic activity at some stations, but unlike Trichodesmium, their N2 fixation rate was not reflected in the stable N isotope ratios of particulate and zooplankton biomass. Our results suggest an important N contribution to biomass by diazotrophs in the Coral Sea, Arafura Sea and East Timor Sea.

Natural abundance of 15N varies greatly and unpredictably within and between environments. The unpredictable nature of 15N limits the use of N isotope natural abundance (d15N) in tracing the flow and fate of N in environments. Recent investigations have, however, revealed consistent and repeatable patterns of 15N in some ecosystem components. These patterns suggest that d15N may yet provide a tool to investigate and illuminate ecosystem N cycling processes. Identifying and quantifying the sources of isotopic variation must precede any significant advance in the application of this technique, and to this end an assessment of isotopic variation associated with major ecosystem components has been carried out in this thesis. d15N patterns have been established, hypotheses proposed and tested, and conclusions about the application of the technique are presented. 15N patterns in surface and groundwater were measured in a variety of different land-use catchments in an attempt to identify distinct isotopic 'fingerprints'. High levels of 15N variation were measured in both stream and groundwaters, resulting in strongly overlapping land-use 'fingerprints'. Environmental 15N variation in streams and groundwaters was found to be too great to differentiate between land-uses based on d15N alone. In contrast, the artificially 15N enriched signature of effluent N was used to trace its flow and fate, following irrigation, in a forested catchment. The effluent d15N signature allowed it to be traced into the major ecosystem components, permitting a first order N budget to be determined for effluent N storage and loss. N sources with significantly different 15N signatures to that of 'background ecosystem N' can therefore be used to trace the flow and fate of N in ecosystems. During the course of this work a number of higher and lower order plants were observed to have highly depleted (lt; -8 ) d15N signatures. Epiphytes and lithophytes, strongly reliant on atmospheric N sources, were consistently depleted in 15N, with signatures as low as -24 , measured in a range of environments. A similar level of depletion was measured in a wide range of plants growing in early primary succession sites (as low as -22.3 ), which could not be accounted for by any abiotic or biotic factor or significantly depleted N source. The absence of any measurable driver of depletion suggested a universal fractionating mechanism which acts in a wide range of environments and vegetation types. Diffusive uptake of atmospheric NH3(g) and the proportional uptake of a supplied N source were two proposed mechanisms that could theoretically account for the level and universal nature of depletion. Diffusive uptake of atmospheric NH3(g) was tested as a primary fractionating mechanism in plants. Strongly N deficient plants were capable of utilising NH3(g) as a nutritional source, but the level of 15N depletion measured in these plants closely approximated that of the inherent NH3(g) d15N signature. No significant additional fractionation is associated with NH3(g) diffusive uptake. Diffusive uptake of atmospheric NH3(g) by plants cannot alone account for the level of depletion measured in early primary succession plant communities. Proportional uptake of a N source as a primary fractionating mechanism was tested by growing plants in various concentrations and rates of applied N. Fractionation attributed to the proportional uptake of a supplied N source, as a consequence of P limitation or rapid flow over roots, resulted in a significant level of 15N depletion in plants. The level of depletion attributed to this mechanism was, however, not sufficient to account for the level measured in early primary succession plant communities. Individual 15N fractionating mechanisms cannot alone explain the level of depletion observed in early primary succession plants, however a combination of fractionating mechanisms can. Fractionation attributed to the proportional uptake of an already depleted N source, i.e., wet deposited N, largely accounts for the level of depletion measured in early succession plant communities. This two-step fractionation model can act on both higher and lower plants, independent of ecosystem biotic and abiotic factors. Additional, and less dramatic fractionations attributed to atmospheric NH3(g) uptake, mycorrhizal associations, internal remobilisation, and taxon-specific N acquisition strategies, will contribute to the level of d15N depletion. This thesis presents the first extensive survey of highly depleted d15N signatures in terrestrial vegetation. Furthermore, thorough testing of theoretically plausible mechanisms has resulted in a full account of the highly depleted d15N signatures measured in a wide range of vegetation types and environments.

Energy demands can be particularly high in arctic-nesting birds that face harsh, unpredictable conditions during the breeding season. Consequences of these demands, particularly energy-partitioning during egg laying and incubation, are fundamentally important for arctic nesters. This study investigated differences in breeding strategies between Long-tailed Duck (<i>Clangula hyemalis</i>) and King Eider (<i>Somateria spectabilis</i>) in the central Canadian arctic. The focus was on ecological variables and influences of variation in nutrient resources used during incubation and egg production. Research was done at Karrak Lake, Nunavut, where both species nest sympatrically at relatively high densities, permitting comparative research about breeding strategies.<p>This study used stable-carbon (d13C) and nitrogen (d15N) isotope analysis to investigate origins and allocation of endogenous (stored) and exogenous (external) nutrients used in egg production. Remote temperature sensors were placed in nests to estimate and compare incubation rhythms and gain insight into capital and income incubating strategies of both species. Results suggest that breeding Long-tailed Ducks and King Eiders used a mixed breeding strategy, that is they relied on both exogenous and endogenous resources for reproduction. Close correspondence between d13C and d15N values of egg components and potential diet items indicated that King Eiders allocated exogenous nutrients for egg production (albumen 98.1%, yolk protein 96.8%, whole yolk 98.4%, and yolk lipids 84%). Female King Eiders relied on endogenous nutrients for incubation, as evidenced by high incubation constancy (96%). Conversely, the range of d13C values in components of Long-tailed Duck eggs and d13C values of diet items suggested that although some females allocated endogenous reserves for egg production, most females allocated exogenous resources for egg production (albumen 98.5%, yolk protein 78.3%, whole yolk 84.9%, and yolk lipids 38.3%). Long-tailed Duck females had an 84% incubation constancy, suggesting less reliance on endogenous nutrients for incubation than was estimated for female King Eiders. Knowledge about the relative importance of endogenous reserves and exogenous nutrients for egg production and incubation may help direct management decisions to specific winter/staging and or breeding areas used by King Eiders and Long-tailed Ducks.

Energy demands can be particularly high in arctic-nesting birds that face harsh, unpredictable conditions during the breeding season. Consequences of these demands, particularly energy-partitioning during egg laying and incubation, are fundamentally important for arctic nesters. This study investigated differences in breeding strategies between Long-tailed Duck (<i>Clangula hyemalis</i>) and King Eider (<i>Somateria spectabilis</i>) in the central Canadian arctic. The focus was on ecological variables and influences of variation in nutrient resources used during incubation and egg production. Research was done at Karrak Lake, Nunavut, where both species nest sympatrically at relatively high densities, permitting comparative research about breeding strategies.<p>This study used stable-carbon (d13C) and nitrogen (d15N) isotope analysis to investigate origins and allocation of endogenous (stored) and exogenous (external) nutrients used in egg production. Remote temperature sensors were placed in nests to estimate and compare incubation rhythms and gain insight into capital and income incubating strategies of both species. Results suggest that breeding Long-tailed Ducks and King Eiders used a mixed breeding strategy, that is they relied on both exogenous and endogenous resources for reproduction. Close correspondence between d13C and d15N values of egg components and potential diet items indicated that King Eiders allocated exogenous nutrients for egg production (albumen 98.1%, yolk protein 96.8%, whole yolk 98.4%, and yolk lipids 84%). Female King Eiders relied on endogenous nutrients for incubation, as evidenced by high incubation constancy (96%). Conversely, the range of d13C values in components of Long-tailed Duck eggs and d13C values of diet items suggested that although some females allocated endogenous reserves for egg production, most females allocated exogenous resources for egg production (albumen 98.5%, yolk protein 78.3%, whole yolk 84.9%, and yolk lipids 38.3%). Long-tailed Duck females had an 84% incubation constancy, suggesting less reliance on endogenous nutrients for incubation than was estimated for female King Eiders. Knowledge about the relative importance of endogenous reserves and exogenous nutrients for egg production and incubation may help direct management decisions to specific winter/staging and or breeding areas used by King Eiders and Long-tailed Ducks.

The following research has focused on the utility of Ulva as an indicator of seawater nitrogen loading. Evaluation was made in three ways: 1) Observation of large-scale geographic variation in nitrogen status in natural populations around New Zealand in summer and winter, 2) Laboratory-based experimental assessment of the biochemical responses of N-indices in Ulva to nitrogen enrichment, and 3) Culturing standardized test-Ulva under low nutrient conditions which could be deployed into a variety of field situations. Seawater inorganic nutrient (nitrate, nitrite, ammonium and phosphate) concentrations and nitrogen (N)-indices (free amino acids, chlorophyll and total tissue nitrogen) in natural Ulva populations from 32 sites around New Zealand were compared. Sites were divided into 6 environmental categories: sheltered rural, exposed rural, rock pools, sheltered urban, exposed urban, and nitrogen-enriched urban sites. Seawater nutrient concentrations were highly variable between all sites in summer and winter. However, in the summer enriched urban sites had the highest mean total inorganic nitrogen concentrations and Ulva with the highest mean levels of all N-indices compared with any other environmental category. In the winter, Ulva contained more nitrogen (reflected in all N-indices) compared with Ulva in the summer, particularly in populations growing in colder southern seawater on more exposed coasts. The increase in Ulva N-status was not explained by increased seawater inorganic nitrogen concentrations. With univariate and multivariate statistical approaches it was shown that there was a significant effect of seawater temperature and site exposure on N-status in Ulva. Compared with other N-indices, stable nitrogen isotopes (δ15N) from Ulva growing in enriched urban sites had the widest range (4.77 ± 0.04 ‰ to 15.16 ± 0.03 ‰) of values compared with all other categories in both summer and winter. Conversely, Ulva from exposed rural sites had the lowest range of δ15N values compared with any other category (6.7 ± 0.1 to 8.8 ± 0.1 ‰) and showed no seasonal change in mean values (7.8 ‰ and 7.6 ‰ for summer and winter, respectively). In addition, δ15N values in Ulva were the only N-index that showed a significant difference between urban and rural categories. To test the relationship between inorganic nitrogen concentration in seawater and the responses of biochemical nitrogen indices in Ulva pertusa, several experiments were conducted in an outdoor, flow-through culture apparatus, in summer and winter. In this apparatus effects of ammonium concentration, nitrogen source (nitrate and ammonium), light and seawater motion were investigated. Of the same three N-indices examined in natural Ulva populations (free amino acids, chlorophyll and total tissue nitrogen), increases in free amino acids, particularly asparagine, provided the strongest indicator of increases in nitrogen availability. In addition, while tissue nitrogen and chlorophyll also increased with seawater nitrogen concentration, it was apparent that these indices were also strongly influenced by light, and probably season. Rates of ammonium assimilation provided no overall measure of the availability of nitrogen in seawater and were clearly affected by season. Similarly, growth rates in Ulva only showed a response to nitrogen addition in summer months. Stable isotopes of nitrogen (δ15N) in Ulva provided a clear distinction between natural and synthetic nitrogen sources, but more importantly, showed only minor fractionation (ranging from 1.3 ‰ to -1.9 ‰) of 15N supplied from synthetic nitrate and ammonium under both light-saturating and light-limiting conditions. To further develop Ulva as a standardized test-organism it was cultured in low-nutrient (non-polluted) seawater to deplete internal storage pools of nitrogen. Each month the resulting test-Ulva was then placed in surface-moored growth enclosures at a range of coastal sites around Auckland and then monitored for one year. In winter there were increases in seawater inorganic nitrogen concentrations and concomitant increases in free amino acid content. However, tissue nitrogen and chlorophyll content in test-Ulva showed similar increases (possibly saturating) across all sites suggesting that seasonal increases in these N-indices were also due to other seasonal factors (e.g., surface irradiance and / or seawater temperature). On the other hand, the total free amino acid pool showed strong differences between a low-nitrogen reference site and the other study sites all year round. It was probable that test-Ulva was integrating differences in tidally-averaged nitrogen loading that were not reliably detected in instantaneous seawater samples. In addition to N-indices in test-Ulva, levels of tissue heavy metals and stable isotopes of nitrogen showed strong differences with higher values of both typically found in urban environments compared with values found in non-polluted reference sites. It is concluded that several abiotic and biotic factors affect nitrogen status in Ulva, but the average nitrogen concentration in seawater, and the physical factors of temperature, light and water motion, appear to be the overarching determinants. It is further suggested that in combination with Ulva tissue δ15N values, tissue nitrogen and the free amino acid pool, as quantitative biochemical measures of nitrogen availability, are likely to provide useful information on both the amount and composition of nitrogen entering coastal environments. / Foundation for Research, Science and Technology. Auckland Regional Council.

The following research has focused on the utility of Ulva as an indicator of seawater nitrogen loading. Evaluation was made in three ways: 1) Observation of large-scale geographic variation in nitrogen status in natural populations around New Zealand in summer and winter, 2) Laboratory-based experimental assessment of the biochemical responses of N-indices in Ulva to nitrogen enrichment, and 3) Culturing standardized test-Ulva under low nutrient conditions which could be deployed into a variety of field situations. Seawater inorganic nutrient (nitrate, nitrite, ammonium and phosphate) concentrations and nitrogen (N)-indices (free amino acids, chlorophyll and total tissue nitrogen) in natural Ulva populations from 32 sites around New Zealand were compared. Sites were divided into 6 environmental categories: sheltered rural, exposed rural, rock pools, sheltered urban, exposed urban, and nitrogen-enriched urban sites. Seawater nutrient concentrations were highly variable between all sites in summer and winter. However, in the summer enriched urban sites had the highest mean total inorganic nitrogen concentrations and Ulva with the highest mean levels of all N-indices compared with any other environmental category. In the winter, Ulva contained more nitrogen (reflected in all N-indices) compared with Ulva in the summer, particularly in populations growing in colder southern seawater on more exposed coasts. The increase in Ulva N-status was not explained by increased seawater inorganic nitrogen concentrations. With univariate and multivariate statistical approaches it was shown that there was a significant effect of seawater temperature and site exposure on N-status in Ulva. Compared with other N-indices, stable nitrogen isotopes (δ15N) from Ulva growing in enriched urban sites had the widest range (4.77 ± 0.04 ‰ to 15.16 ± 0.03 ‰) of values compared with all other categories in both summer and winter. Conversely, Ulva from exposed rural sites had the lowest range of δ15N values compared with any other category (6.7 ± 0.1 to 8.8 ± 0.1 ‰) and showed no seasonal change in mean values (7.8 ‰ and 7.6 ‰ for summer and winter, respectively). In addition, δ15N values in Ulva were the only N-index that showed a significant difference between urban and rural categories. To test the relationship between inorganic nitrogen concentration in seawater and the responses of biochemical nitrogen indices in Ulva pertusa, several experiments were conducted in an outdoor, flow-through culture apparatus, in summer and winter. In this apparatus effects of ammonium concentration, nitrogen source (nitrate and ammonium), light and seawater motion were investigated. Of the same three N-indices examined in natural Ulva populations (free amino acids, chlorophyll and total tissue nitrogen), increases in free amino acids, particularly asparagine, provided the strongest indicator of increases in nitrogen availability. In addition, while tissue nitrogen and chlorophyll also increased with seawater nitrogen concentration, it was apparent that these indices were also strongly influenced by light, and probably season. Rates of ammonium assimilation provided no overall measure of the availability of nitrogen in seawater and were clearly affected by season. Similarly, growth rates in Ulva only showed a response to nitrogen addition in summer months. Stable isotopes of nitrogen (δ15N) in Ulva provided a clear distinction between natural and synthetic nitrogen sources, but more importantly, showed only minor fractionation (ranging from 1.3 ‰ to -1.9 ‰) of 15N supplied from synthetic nitrate and ammonium under both light-saturating and light-limiting conditions. To further develop Ulva as a standardized test-organism it was cultured in low-nutrient (non-polluted) seawater to deplete internal storage pools of nitrogen. Each month the resulting test-Ulva was then placed in surface-moored growth enclosures at a range of coastal sites around Auckland and then monitored for one year. In winter there were increases in seawater inorganic nitrogen concentrations and concomitant increases in free amino acid content. However, tissue nitrogen and chlorophyll content in test-Ulva showed similar increases (possibly saturating) across all sites suggesting that seasonal increases in these N-indices were also due to other seasonal factors (e.g., surface irradiance and / or seawater temperature). On the other hand, the total free amino acid pool showed strong differences between a low-nitrogen reference site and the other study sites all year round. It was probable that test-Ulva was integrating differences in tidally-averaged nitrogen loading that were not reliably detected in instantaneous seawater samples. In addition to N-indices in test-Ulva, levels of tissue heavy metals and stable isotopes of nitrogen showed strong differences with higher values of both typically found in urban environments compared with values found in non-polluted reference sites. It is concluded that several abiotic and biotic factors affect nitrogen status in Ulva, but the average nitrogen concentration in seawater, and the physical factors of temperature, light and water motion, appear to be the overarching determinants. It is further suggested that in combination with Ulva tissue δ15N values, tissue nitrogen and the free amino acid pool, as quantitative biochemical measures of nitrogen availability, are likely to provide useful information on both the amount and composition of nitrogen entering coastal environments. / Foundation for Research, Science and Technology. Auckland Regional Council.

The following research has focused on the utility of Ulva as an indicator of seawater nitrogen loading. Evaluation was made in three ways: 1) Observation of large-scale geographic variation in nitrogen status in natural populations around New Zealand in summer and winter, 2) Laboratory-based experimental assessment of the biochemical responses of N-indices in Ulva to nitrogen enrichment, and 3) Culturing standardized test-Ulva under low nutrient conditions which could be deployed into a variety of field situations. Seawater inorganic nutrient (nitrate, nitrite, ammonium and phosphate) concentrations and nitrogen (N)-indices (free amino acids, chlorophyll and total tissue nitrogen) in natural Ulva populations from 32 sites around New Zealand were compared. Sites were divided into 6 environmental categories: sheltered rural, exposed rural, rock pools, sheltered urban, exposed urban, and nitrogen-enriched urban sites. Seawater nutrient concentrations were highly variable between all sites in summer and winter. However, in the summer enriched urban sites had the highest mean total inorganic nitrogen concentrations and Ulva with the highest mean levels of all N-indices compared with any other environmental category. In the winter, Ulva contained more nitrogen (reflected in all N-indices) compared with Ulva in the summer, particularly in populations growing in colder southern seawater on more exposed coasts. The increase in Ulva N-status was not explained by increased seawater inorganic nitrogen concentrations. With univariate and multivariate statistical approaches it was shown that there was a significant effect of seawater temperature and site exposure on N-status in Ulva. Compared with other N-indices, stable nitrogen isotopes (δ15N) from Ulva growing in enriched urban sites had the widest range (4.77 ± 0.04 ‰ to 15.16 ± 0.03 ‰) of values compared with all other categories in both summer and winter. Conversely, Ulva from exposed rural sites had the lowest range of δ15N values compared with any other category (6.7 ± 0.1 to 8.8 ± 0.1 ‰) and showed no seasonal change in mean values (7.8 ‰ and 7.6 ‰ for summer and winter, respectively). In addition, δ15N values in Ulva were the only N-index that showed a significant difference between urban and rural categories. To test the relationship between inorganic nitrogen concentration in seawater and the responses of biochemical nitrogen indices in Ulva pertusa, several experiments were conducted in an outdoor, flow-through culture apparatus, in summer and winter. In this apparatus effects of ammonium concentration, nitrogen source (nitrate and ammonium), light and seawater motion were investigated. Of the same three N-indices examined in natural Ulva populations (free amino acids, chlorophyll and total tissue nitrogen), increases in free amino acids, particularly asparagine, provided the strongest indicator of increases in nitrogen availability. In addition, while tissue nitrogen and chlorophyll also increased with seawater nitrogen concentration, it was apparent that these indices were also strongly influenced by light, and probably season. Rates of ammonium assimilation provided no overall measure of the availability of nitrogen in seawater and were clearly affected by season. Similarly, growth rates in Ulva only showed a response to nitrogen addition in summer months. Stable isotopes of nitrogen (δ15N) in Ulva provided a clear distinction between natural and synthetic nitrogen sources, but more importantly, showed only minor fractionation (ranging from 1.3 ‰ to -1.9 ‰) of 15N supplied from synthetic nitrate and ammonium under both light-saturating and light-limiting conditions. To further develop Ulva as a standardized test-organism it was cultured in low-nutrient (non-polluted) seawater to deplete internal storage pools of nitrogen. Each month the resulting test-Ulva was then placed in surface-moored growth enclosures at a range of coastal sites around Auckland and then monitored for one year. In winter there were increases in seawater inorganic nitrogen concentrations and concomitant increases in free amino acid content. However, tissue nitrogen and chlorophyll content in test-Ulva showed similar increases (possibly saturating) across all sites suggesting that seasonal increases in these N-indices were also due to other seasonal factors (e.g., surface irradiance and / or seawater temperature). On the other hand, the total free amino acid pool showed strong differences between a low-nitrogen reference site and the other study sites all year round. It was probable that test-Ulva was integrating differences in tidally-averaged nitrogen loading that were not reliably detected in instantaneous seawater samples. In addition to N-indices in test-Ulva, levels of tissue heavy metals and stable isotopes of nitrogen showed strong differences with higher values of both typically found in urban environments compared with values found in non-polluted reference sites. It is concluded that several abiotic and biotic factors affect nitrogen status in Ulva, but the average nitrogen concentration in seawater, and the physical factors of temperature, light and water motion, appear to be the overarching determinants. It is further suggested that in combination with Ulva tissue δ15N values, tissue nitrogen and the free amino acid pool, as quantitative biochemical measures of nitrogen availability, are likely to provide useful information on both the amount and composition of nitrogen entering coastal environments. / Foundation for Research, Science and Technology. Auckland Regional Council.

The following research has focused on the utility of Ulva as an indicator of seawater nitrogen loading. Evaluation was made in three ways: 1) Observation of large-scale geographic variation in nitrogen status in natural populations around New Zealand in summer and winter, 2) Laboratory-based experimental assessment of the biochemical responses of N-indices in Ulva to nitrogen enrichment, and 3) Culturing standardized test-Ulva under low nutrient conditions which could be deployed into a variety of field situations. Seawater inorganic nutrient (nitrate, nitrite, ammonium and phosphate) concentrations and nitrogen (N)-indices (free amino acids, chlorophyll and total tissue nitrogen) in natural Ulva populations from 32 sites around New Zealand were compared. Sites were divided into 6 environmental categories: sheltered rural, exposed rural, rock pools, sheltered urban, exposed urban, and nitrogen-enriched urban sites. Seawater nutrient concentrations were highly variable between all sites in summer and winter. However, in the summer enriched urban sites had the highest mean total inorganic nitrogen concentrations and Ulva with the highest mean levels of all N-indices compared with any other environmental category. In the winter, Ulva contained more nitrogen (reflected in all N-indices) compared with Ulva in the summer, particularly in populations growing in colder southern seawater on more exposed coasts. The increase in Ulva N-status was not explained by increased seawater inorganic nitrogen concentrations. With univariate and multivariate statistical approaches it was shown that there was a significant effect of seawater temperature and site exposure on N-status in Ulva. Compared with other N-indices, stable nitrogen isotopes (δ15N) from Ulva growing in enriched urban sites had the widest range (4.77 ± 0.04 ‰ to 15.16 ± 0.03 ‰) of values compared with all other categories in both summer and winter. Conversely, Ulva from exposed rural sites had the lowest range of δ15N values compared with any other category (6.7 ± 0.1 to 8.8 ± 0.1 ‰) and showed no seasonal change in mean values (7.8 ‰ and 7.6 ‰ for summer and winter, respectively). In addition, δ15N values in Ulva were the only N-index that showed a significant difference between urban and rural categories. To test the relationship between inorganic nitrogen concentration in seawater and the responses of biochemical nitrogen indices in Ulva pertusa, several experiments were conducted in an outdoor, flow-through culture apparatus, in summer and winter. In this apparatus effects of ammonium concentration, nitrogen source (nitrate and ammonium), light and seawater motion were investigated. Of the same three N-indices examined in natural Ulva populations (free amino acids, chlorophyll and total tissue nitrogen), increases in free amino acids, particularly asparagine, provided the strongest indicator of increases in nitrogen availability. In addition, while tissue nitrogen and chlorophyll also increased with seawater nitrogen concentration, it was apparent that these indices were also strongly influenced by light, and probably season. Rates of ammonium assimilation provided no overall measure of the availability of nitrogen in seawater and were clearly affected by season. Similarly, growth rates in Ulva only showed a response to nitrogen addition in summer months. Stable isotopes of nitrogen (δ15N) in Ulva provided a clear distinction between natural and synthetic nitrogen sources, but more importantly, showed only minor fractionation (ranging from 1.3 ‰ to -1.9 ‰) of 15N supplied from synthetic nitrate and ammonium under both light-saturating and light-limiting conditions. To further develop Ulva as a standardized test-organism it was cultured in low-nutrient (non-polluted) seawater to deplete internal storage pools of nitrogen. Each month the resulting test-Ulva was then placed in surface-moored growth enclosures at a range of coastal sites around Auckland and then monitored for one year. In winter there were increases in seawater inorganic nitrogen concentrations and concomitant increases in free amino acid content. However, tissue nitrogen and chlorophyll content in test-Ulva showed similar increases (possibly saturating) across all sites suggesting that seasonal increases in these N-indices were also due to other seasonal factors (e.g., surface irradiance and / or seawater temperature). On the other hand, the total free amino acid pool showed strong differences between a low-nitrogen reference site and the other study sites all year round. It was probable that test-Ulva was integrating differences in tidally-averaged nitrogen loading that were not reliably detected in instantaneous seawater samples. In addition to N-indices in test-Ulva, levels of tissue heavy metals and stable isotopes of nitrogen showed strong differences with higher values of both typically found in urban environments compared with values found in non-polluted reference sites. It is concluded that several abiotic and biotic factors affect nitrogen status in Ulva, but the average nitrogen concentration in seawater, and the physical factors of temperature, light and water motion, appear to be the overarching determinants. It is further suggested that in combination with Ulva tissue δ15N values, tissue nitrogen and the free amino acid pool, as quantitative biochemical measures of nitrogen availability, are likely to provide useful information on both the amount and composition of nitrogen entering coastal environments. / Foundation for Research, Science and Technology. Auckland Regional Council.

Sedimentation rates and compositions of sinking particles were investigated at three sites on the Beaufort slope and one in Canada Basin during the period 1990-1994 using moored sequential sediment traps. A method was developed to identify the terrigenous and biogenic components of the fluxes. The physical context including ice cover, ocean currents, river inputs, winds, air temperature, incident light, and nutrient availability provide essential information to the interpretation of the particle fluxes and to the understanding of shelf-basin sediment transport in this area. Eddies, internal waves, upwelling and downwelling, and the state of the ice cover all played important and overlapping roles in the pattern of observed fluxes. A peak in the flux of highly terrigenous material under complete ice cover in mid-winter to the northwest of Mackenzie Trough was associated with predominantly downwelling conditions and the passage of a series of eddies and internal waves. A prolonged spring diatom bloom occurred in the mid-slope area and was clearly associated with an early opening of the ice on the east side of the shelf. Higher fluxes at the Canada Basin site were associated with a large eddy clearly identifiable from the current-T-S record and also from the composition of the suspended material carried with it. At the base of the slope (2700 m), the composition was highly terrigenous and remarkably consistent. Higher up the slope (700 m), biogenic peaks in the summer diluted the terrigenous material briefly, but it appears that there is a constant background of highly terrigenous material. There was a high degree of variability between sites and over the slope there was not enough data to asses the inter-annual variability. In Canada Basin, the inter-annual variability was closely linked to the extent of open water in the summer period. At all sites, lateral transport is clearly indicated by the increase in flux with depth. The data robustly demonstrate the need for detailed knowledge of physical processes for informed interpretation of particle fluxes and sediment transport in this area.