Добірка наукової літератури з теми "Estuarine hydrology New Zealand"

Climate change is increasingly affecting the water cycle and as freshwater plays a vital role in countries’ societal and environmental well-being it is important to develop national assessments of potential climate change impacts. Focussing on New Zealand, a climate-hydrology model cascade is used to project hydrological impacts of late 21st century climate change at 43,862 river locations across the country for seven hydrological metrics. Mean annual and seasonal river flows validate well across the whole model cascade, and the mean annual floods to a lesser extent, while low flows exhibit a large positive bias. Model projections show large swathes of non-significant effects across the country due to interannual variability and climate model uncertainty. Where changes are significant, mean annual, autumn, and spring flows increase along the west and south and decrease in the north and east. The largest and most extensive increases occur during winter, while during summer decreasing flows outnumber increasing. The mean annual flood increases more in the south, while mean annual low flows show both increases and decreases. These hydrological changes are likely to have important long-term implications for New Zealand’s societal, cultural, economic, and environmental well-being.

Physical geographers in New Zealand have a tradition of applied research in a variety of contexts, including environmental management as well as soil, vegetation and landform systems conservation. In recent years this work has been given new impetus (with the promise of even greater involvement) as a result of economic restructuring at the national level, restructuring of government departments and agencies dealing with environmental and resource management and conservation, the introduction of new statutes relating to environmental and resource management, and major changes in the funding and management of science research in the public sector. This article provides an overview of the institutional environment within which New Zealand physical geographers now carry out applied work. The contemporary resource management and legislative contexts are described and structural changes that have taken place in New Zealand science over the last decade are reviewed. Research undertaken by the authors or their research students provides examples of the different types of work now being undertaken by physical geographers in New Zealand under the new legislative and funding regimes. Two examples are described in detail. The first is drawn from research dealing with catchment hydrology and water supply and has been undertaken by a physical geographer employed by Landcare Research, a Crown-owned research company. The second comes from work carried out by two university-based physical geographers into the environmental effects on coasts of a new mode of marine passenger transport (`fast ferries'), to meet the requirements of new environmental legislation.

Coastal lagoon systems are complex and dynamic environments that respond rapidly to the changes of fluvial, marine, climatic and anthropogenic influences. The purpose of this research was to investigate the morphology and dynamics of the New River Lagoon before and after the implementation of engineering outlet management using a methodological framework to analyse active process environments. This information was then used to determine the functional effectiveness of engineering management at reducing the risk of flooding and erosion to the local community and imposing minimal impacts on the environmental integrity of the lagoon system. This investigation used a multidisciplinary approach to investigate the morphology and dynamics of the New River Lagoon in relation to active process environments. Outlet dynamics, lagoon channel structure and adjacent shoreline stability were assessed over a decadal timescale prior to engineering management by analysing temporal aerial photographs. Following engineering management, the hydrology of the lagoon was investigated, along with the relationship between morphological changes to the artificial lagoon outlet and changes in lagoon hydrology, local wave climate and local precipitation levels. Water depth, conductivity and temperature records were used to explain lagoon hydrology and Global Navigation Satellite Surveying (GNSS) and weekly oblique photographs were used to explain and document changes in outlet morphology. Wave and rainfall data were used to explain the balances between marine and fluvial environments and their affects on outlet dynamics. Significant changes in lagoon morphology and dynamics were observed at the New River Lagoon between pre- and post-management periods, with the former considered more stable in terms of outlet migration patterns and hydrodynamics. The lagoon outlet prior to engineering management showed morphological characteristics similar to hapua-type systems, migrating along the coastline and forming shore-parallel outlet channels in response to the dominance of a strong longshore drift of sediment. Current outlet dynamics are restricted by artificial outlet management and typically cycle intermittently between open/closed phases in response to variable levels of rainfall and marine sediment supply; characteristics similar to Intermittently Open/Closed Lagoons (ICOLs) found in areas of Australia and South Africa. Hydrologically, the lagoon is considered to be located on a continuum between hapua and estuaries during pre- and post-management periods due to intermittent tidal influences. However, artificial outlet management has significantly increased the frequency and duration of tidal exchange, which now classifies the New River lagoon closer to an estuarine environment. The artificial lagoon outlet and associated breakwater were effective at flushing high flows of water during the study period. However, the outlet was prone to blockage and migration; two morphological states capable of causing flooding. Currently, the greatest risks to flooding at the lagoon are flash floods, following dry periods where marine sediment has established a solid barrier across the outlet, during which water levels are already elevated. Increases in tidal influences, lower lagoon water levels and an increase in lagoon salinity are a direct result of engineering management intervention. An increase in freshwater flushing through the lagoon outlet and deepened of the outlet channel to below sea level, allows for pronounced tidal influences during outlet opening. Restriction of the lagoon outlet from forming a natural migration outlet channel in the direction of littoral drift has meant the outlet is most often oriented perpendicular to the sea, as appose to at an angle away from the direction of incoming waves and currents, further increasing tidal influences. In order to make sustainable management decisions, future management of the lagoon system must weight-up the effects of a high energy coastline to the integrity of the engineering structure, the impact of the structure on the lagoons environmental integrity and the outlets ability to become unstable and cause a flood risk. The findings of this research have improved the understanding of the New River Lagoon system, and its response to engineering management intervention, while adding to the understanding of river-mouth lagoon systems both nationally and internationally.

The research presented in this thesis was undertaken in order to develop an understanding of the biology of Perna canaliculus sufficient to allow for commercial hatchery based production of Greenshell™ mussel spat. Hatchery production is an alternative to unreliable and inconsistent wild spat collection. In a Perna canaliculus population followed for one year spawning occurred in early spring and late summer. Three quantitative histological measures of gonad maturity utilising image analysis technology and a qualitative classification system were compared. Measuring the relative surface area comprised of gametes on histological sections was found to be the most reliable method. A practical gonad visual index to determine the reproductive condition of adults for the selection of broodstock was developed and found to be highly effective as a means of predicting induced spawning success. Serotonin was not effective for inducing spawning of Perna canaliculus. Temperature shock and the use of stripped gametes was however found to be a reliable spawning induction method. Relative gamete concentration, gamete age, temperature, sperm half life and gamete contact times were all found to have effects on fertilisation success for Perna canaliculus. Sperm concentration and the conditions of sperm aging were particularly important. Fertilisation kinetics of Perna canaliculus gametes modelled using the Vogel-Czihak-Chang-Wolf method suggested that 5% of sperm-egg contacts lead to successful fertilisation. Broodstock management protocols that could be used to condition the adult of Perna canaliculus were investigated in order to enhance and prolong the natural reproductive season. Research suggested that for successful broodstock conditioning animals should already have begun gametogenesis at the time conditioning is commenced. Successful conditioning of Perna canaliculus was achieved at temperatures between l0 and 16°C over a period of about 50 days. A diet ration above 2-3% of the dry meat mass per day is suggested. A trial examining non-algal diet supplements suggest a mixture of yeast and lipid emulsion may have some potential value. Photoperiod manipulation did not effect the reproductive condition of Perna canaliculus. The yield of veliger larvae was significantly enhanced if embryo culture water was treated with 1.0 mg/l EDTA. Veliger yield was not significantly affected at densities below 50 embryos/ml. Perna canaliculus larvae grew most rapidly and survived well at the salinity of 35 ppt. Larvae grew most rapidly when cultured at low densities. Experiments suggest that early larvae can be cultured at 5-10/ml, however late stage larvae grew most rapidly when cultured at l/ml. Perna canaliculus larvae displayed best growth and good survival if fed a mixed flagellate-diatom diet comprising Isochrysis galbana (T-Iso) and Chaetoceros calcitrans. The optimal diet ration, as a function of larval size, increased from about 20 cells/μl Isochrysis galbana (T-Iso) to around 150 cells/μl through the larval development period. Thyroxine between the concentrations of l0-5 and l0-8 M did not have an observable effect on larval developmental rate or eye spot development. Down welling settlement systems were found to be generally successful for Perna canaliculus lanrae. L-DOPA was also demonstrated to enhance the settlement and metamorphosis of Perna canaliculus pediveligers.

Worldwide, estuaries are under increasing pressure from numerous contaminants. There is a need to develop reliable bioassay methodologies to assess the effects of these stressors on estuary health. This thesis aimed to develop and validate toxicity tests in a New Zealand marine harpacticoid copepod species for use in monitoring and evaluating the effects of estuarine pollution. A survey and toxicological assessment of a range of native copepod species resulted in the selection of Quinquelaophonte sp. as the ideal bioassay species. This selection was based on a broad regional distribution, ease of culture and high reproductive rate in the laboratory, sexual dimorphism, and sensitivity to contaminants. To validate the bioassay, spiked sediments were used to expose Quinquelaophonte sp. to three reference compounds representing important categories of estuarine chemical stressors: zinc (a metal), atrazine (a pesticide), and phenanthrene (a polyaromatic hydrocarbon). A method for spiking sediments that Quinquelaophonte sp. inhabit was developed to ensure even contaminant distribution in sediments. Two sediment bioassays using lethal and sublethal endpoints were validated, one acute (96 h) and one chronic (14 d). These assays incorporated both lethal and sublethal endpoints, which included reproductive output and mobility. Acute-to-chronic ratios were calculated for use in environmental risk assessment and to provide insight into the mode of action of the reference contaminants. The chronic sediment bioassay was used to assess sediment quality in three estuaries across New Zealand: Napier, Christchurch and Invercargill. This validated the bioassay for use with naturally-contaminated field sediments with varying mixtures of pollutants and sediment types (coarse sandy to fine silty organic rich sediments). Quinquelaophonte sp. was also tested to assess whether it can be used to characterise multi–generation impacts. After four generations of exposure to zinc, there were changes in acute sensitivity, indicating this species possesses mechanisms for acclimating or adapting to toxic stressors. Sediment bioassays in Quinquelaophonte sp. were successfully developed and validated, offering significant promise as a tool for monitoring effects of pollution in New Zealand estuaries.

Interactions among large brown macroalgae, sea urchins, and fishes were investigated in northeastern New Zealand during the period 1988 - 1993. The Cape Rodney to Okakari Point Marine Reserve was the site of many of these investigations. The patterns of abundance of large brown macroalgae and urchins down depth gradients over a wide geographic range were compared with those reported from earlier studies, and 3 major trends were identified. First, the fucoid alga Carpophyllum flexuosum now occurs at many sites which are exposed to wave action, in contrast to earlier studies. This alga occurred most abundantly on urchin-grazed coralline flat areas. Second, at four sites in the Marine Reserve, the densities of the echinometrid urchin Evechinus chloroticus decreased with increasing depth, rather than reaching maximal densities at mid-depths, as had previously been described. Finally, at sites of decreased exposure to wave action, the coralline flats habitat did not occur at all, and dense stands of. C. flexuosum occurred, in conjunction with the ubiquitous laminarian alga, Ecklonia radiata. Following the discovery of this new algal component to exposed rocky reefs, a more detailed study of its population characteristics was initiated. The population size structure of C. flexuosum on coralline flat areas was markedly different from that of the same species in sites sheltered from wave action. These differences occurred at both offshore islands and sites near Leigh, suggesting that it was a general pattern. C. flexuosum plants on coralline flats were smaller than those from sheltered sites, and had a greater number of smaller laminae, heavier stipes, and a greater degree of branching. There was some evidence of temporal change in the morphology of C. flexuosum from coralline flats. Comparisons between a site with C. flexuosum and a site with coralline flats suggested that the activity of fish was 75% lower in the vegetated than in the unvegetated site, and the feeding rate in the vegetated site was less than 50% that in the unvegetated site. I speculate that future effects on fish activity of the invasion of C. flexuosum into a habitat which previously lacked macroalgal vegetation may depend on changes in the morphology of plants. An investigation of many aspects of the biology of E. chloroticus in different habitats was undertaken. Analysis of the body dimensions of E. chloroticus suggested that this species was relatively tall compared to other echinometrids (average ratio of test height: test diameter = 0.54), Comparisons among habitats with differing amounts of vegetation revealed only small differences in the relationship between test diameter and test height. Small E. chloroticus (<40 mm test diameter) lived in crevices, while larger individuals grazed freely over the substratum. In vegetated habitats, the crevice-dwelling habit was maintained at test diameters about l0 mm greater than in unvegetated habitats. Very small (<20 mm test diameter) E. chloroticus frequently covered themselves with shell. Population size structures of E. chloroticus within the Cape Rodney to Okakari Point Marine Reserve were bimodal; other localities had unimodal populations. Modal sizes varied among localities, with smallest modes (50-60 mm TD) being found at Inner Hauraki Gulf sites, and largest modes at the offshore Mokohinau Islands (70-80 mm TD). Habitat did not predictably affect population size structure. A bimodal population structure was maintained at Waterfall Reef rock flats throughout the 5-year study period. Gonad size showed seasonal fluctuations at several sites, being greatest in summer. There were few consistent differences in gonad size between biological habitats. Gonad colour varied among sites and habitats, with orange gonads generally being more prevalent in vegetated habitats, and black gonads being represented more in unvegetated habitats. Smaller urchins had greater proportions of orange gonads, while larger urchins had greater proportions of brown and black gonads. Although highly variable among individual urchins, movement of E. chloroticus was greater at unvegetated sites (0.7 m per 5 days) than at vegetated sites (0.4 m per 5 days), in the Marine Reserve. Feeding of E. chloroticus was studied at a number of sites in the Marine Reserve. Urchins frequently consumed drift algae, particularly E. radiata. C. flexuosum was consumed at less than half the rate of other macroalgae in several laboratory feeding experiments, and was chosen least frequently in a field assay of feeding preferences among 8 species of macroalgae. Boosting densities of E. chloroticus in stands of E. radiata to 60 m-2 led to destructive grazing of plants over a 2 month period - at lower densities, the urchins dispersed. Densities of C. flexuosum were effectively unchanged when urchin densities were increased to these elevated levels. As a result of these observations I speculate that feeding preferences of E. chloroticus may have a role in allowing C. flexuosum to survive on coralline flats. In a laboratory experiment, urchins from a feeding aggregation did not graze algae at higher rates than individuals from outside aggregations. Diets of both E. radiata and C. flexuosum consistently produced similar gonad volumes in urchins held in the laboratory, although gonad volumes produced were low. A preliminary experiment suggested that C. flexuosum from exposed sites was consumed at lower rates than C. flexuosum from sites which were sheltered from wave action. These differences in palatability are mirrored in the formation of stable borders between coralline flats and C. flexuosum of the sheltered morphology, and the ability of C. flexuosum of the exposed morphology to survive in the coralline flats habitat. The fish fauna of the Cape Rodney to Okakari Point Marine Reserve was shown to be different from that of a nearby area. A number of species were more abundant within the Marine Reserve. Subsequent surveys showed that there were differences in abundances of 3 large carnivorous fishes among sites within the Marine Reserve, and that population size structure and the distance within which divers could approach one species, (Pagrus auratus), clearly varied between areas within the Marine Reserve. Mean standard length of P. auratus in the central marine reserve was 40% larger than that of P. auratus outside the central marine reserve, and the average minimum approach distance was 70% less in the central marine reserve. Feeding of fish by humans in the central part of the Marine Reserve was suggested to be the main cause of the differences in responses to divers. Population size structure of, and crevice occupancy by, E. chloroticus, clearly differed between the Marine Reserve and an adjacent area, with bimodal population size structures and a 10 mm greater size of crevice occupancy occurring in the Marine Reserve. The implications of these findings for extrapolating from experiments done in one area to other areas are discussed. The major biological components of rocky reef habitats identified in this study were broadly similar to those identified in previous studies in northeastern New Zealand, and have parallels in overseas studies. Long term changes to the flora of rocky reefs in northeastern New Zealand have occurred, and appear to persist by a mechanism which had previously been discounted. Similar processes to those observed in overseas studies appear to maintain habitats (consistent recruitment of algae or urchins to habitats which they dominate), or cause them to change from one habitat state to another (e.g. grazing outbreaks by urchins). However, the predictability of the persistence of these habitats at a particular site appears to be low. Further, the precise mechanisms whereby habitats may change from one to another may also be unpredictable. I argue that there is little scope for general statements concerning the spatial and temporal occurrence, or mode, of habitat transitions on temperate subtidal reefs. This study emphasises the value of repeated descriptions of patterns of abundance, and highlights problems of extrapolation and generalisation in marine ecology. Insufficient information exists at present to comment adequately on the persistence of subtidal habitat types. This may in part stem from the types of information which have been collected in the past. Methodological problems with the use of quadrats to sample densities of organisms in areas of differing topography are therefore addressed. In conclusion, it is suggested that sampling protocols which incorporate a variety of information, gathered over as wide an area, and as intensively as possible, should be used in future research of this type.

The eggs and larvae of the New Zealand snapper Pagrus auratus are pelagic with early buoyancy provided by dilute body fluids. The swimbladder begins to develop on the third day after hatch from a dorsal evagination of the gut tube. Communication w1h the gut is lost on about the tenth day following pneumatic inflation at around day eight. At this age the gas gland system appears fully functional and capable of secreting gas. By the age of settlement at around 30 days the swimbladder is a fully functional replica of the adult form except for the lack of a resorbent capillary system which does not develop until later in juvenile life. The swimbladder of the adult is of the euphysoclist form with a dorsally located resorbent oval area and sits high in the pleural cavity. The ventral tunica externa is firmly attached to the connective tissue lining the pleural space. The adult swimbladder displaces 5.6% of the volume of the body and its volume is regulated to provide near neutral buoyancy. The connective tissue integument provides almost no restriction to volume changes brought about by vertical movements of the fish and the swimbladder obeys Boyle's Law for physiological pressure changes. The ability of the connective tissue of the tunica externa to accommodate large tissue strains is due to massive regular crimping of otherwise straight collagen fibrils allowing reversible extensions up to 130%. In all other respects however the tissue structure of the tunica externa is consistent with a tissue providing an active mechanical role. The fibrillar morphology and physicochemical properties of swimbladder collagen is consistent with the vertebrate type I form however there are interesting variations in collagen form distributed throughout the swimbladder. Fibrillar morphology of the highly extensible tunica interna is significantly different to that of the tunica externa and appears to play very little mechanical rote. The extensibilty of the tunica externa appears to be regulated by physiological stress and related to the past history of tissue strain.

The management of New Zealand’s freshwater resources has come under increasing pressure from different industrial and environmental stakeholders. Land use change and the pressure it can put on water resources has been a significant issue regarding resource management in New Zealand. A significant mechanism driving land use change has been the growth of forestry, dairy farming, and other agricultural industries. Improvements in agricultural and forestry science and irrigation techniques have allowed new, previously less arable areas of New Zealand to be subject to land use change, such as the conversion of tussock grassland to pasture in steep, mountainous regions in the South Island. Studies regarding the effects of land use change in such catchments, especially with focus on flood hydrology, appear to be limited, despite the importance of managing catchment headwaters to minimise flood risk downstream. The TopNet model was used in this research project to evaluate the potential effects of land use change on flood hydrology in mountain catchments. It is a semi-distributed continuous rainfall-runoff model developed by the National Institute of Water and Atmospheric Research (NIWA). It has been widely used in New Zealand, and applications have included modelling water yield and the effect of climate change in catchment networks. However, it was not developed specifically for predicting flood flows. Hence, testing the model for flood peak prediction in mountainous catchments was also performed, and may show that TopNet can be a useful tool in resource management in New Zealand. The Ahuriri and Pelorus River catchments were used in this investigation. Both are steep catchments located in the South Island. The Ahuriri River catchment, in the Waitaki Basin on the eastern side of the Southern Alps, is a semi-arid catchment dominated by tussock grassland. The surrounding catchments are heavily influenced by infrastructure for hydroelectric power (HEP) generation and more recently irrigation for dairy farming. The Pelorus River catchment is located at the northern end of the South Island. It is primarily covered in native forest, but adjacent catchments are subject to agricultural and forestry development. The ability of the TopNet model for each catchment to predict flood flows were tested using a selection of historical flood events. Rainfall input to the model was at a daily timestep from the virtual climate station network (VCSN), and the method of disaggregating the daily estimate into an hourly rainfall series to be used by the model was found to have a significant influence on flood prediction. Where an accurate historical rainfall record was provided from a rainfall gauge station within the catchments, the disaggregation of the daily rainfall estimate based on the station data produced a significantly more accurate flood prediction when compared to predictions made using a stochastic disaggregation of the daily rainfall estimate. The TopNet models were modified to reflect land use change scenarios: the conversion of tussock grassland to pasture and the afforestation of tussock in the Ahuriri River catchment, and the conversion of forested land to pasture and the harvest of plantation forestry in the Pelorus River catchment. Following a past study into modelling the effects of land use change using TopNet, three key model parameters were modified to reflect each land use scenario: saturated hydraulic conductivity KS, canopy storage capacity, and the canopy enhancement factor. Past studies suggested a wide range of suitable values for KS, although also acknowledged that KS depends heavily on the specific catchment characteristics. A sensitivity analysis showed that KS had a significant influence on flood peak prediction in TopNet. It is recommended that further investigation be conducted into suitable values for KS. TopNet appeared to predict the effect of land use change on flood magnitude in mountainous catchments conservatively. Past studies of land use change suggested that the effect on flood flows should be significant, whereas TopNet generally predicted small changes in flood peaks for the scenarios in each catchment. However, this may suggest that the topography, geology, and soil properties of steep catchments are more important to flood hydrology than land cover. Further investigation into the effect of such catchment characteristics is recommended. Nevertheless, TopNet was shown to have the potential to be a useful tool for evaluating and managing the effects of land use change on the flood hydrology of mountainous catchments in New Zealand.

In the Heretaunga Plains area, New Zealand, parts of the low lying land adjacent to the Awanui Stream are flooded annually. The purpose of the study was to find out if the flooding water trapped in the field gets sealed off from infiltrating the soils in any way (and hence is unavailable to replenish the stream flow). What would be the effects on stream base flow if pumping of the flooding water would occur direct to the stream after wet periods and heavy rains? The method of this project was to investigate the infiltration, soil type and ground water conditions in the field. The infiltration was investigated with the help of a double ring infiltration test, a disc permeameter that measures hydraulic conductivity, and pvc-pipes with core samples were saturated for an extended period of time to find out if there was any kind of seal forming during saturated conditions. The soil in field was sampled and a soil fraction test was performed. The potential evaporation was measured with an evaporation pan and calculated with data from a climate station in field. With flow records from the outgoing drain, potential evaporation and precipitation data a rough water balance model could be created. The results showed that there is no seal formed in the top part of the soil profile preventing the water from infiltrating. The flooding water is the result of a rising groundwater table, on top of a thick clay layer seven meters down in the ground. Once the flooding water has drained and evaporated away there is nothing wrong with the infiltration rate in field. There are very fine particles of silt and clay in the top soil that decreases the infiltration rate and can cause a separation of the ground water and the water above land surface. When the project was finished two recommendations could be given to the landowner to solve the problem with the flooding. The recommendations were to either re-level the field to get the surface water to runoff towards the drains instead of being trapped in the current low parts of the field. Or to dig drains from Horonui Drain and Cambell Drain into the field's low parts and in that way drain the flooding water away.
I området Heretaunga Plain, Nya Zeeland, översvämmas årligen delar av det låglänta området kring floden Awanui Stream. Syftet med den här studien var att ta reda på om översvämningsvattnet i fält hindras från infiltration i jorden på något sätt (och kan där med inte bidra till basflödet till floden). Vad skulle effekterna på basflödet i floden bli om översvämningsvattnet pumpades direkt ut i floden efter våtare perioder och större regn? Metoden för att svara på detta var att undersöka infiltrationen, jordtyperna och grundvattenförhållandena i fält. Infiltrationen undersöktes med hjälp av dubbelring infiltrationstest, en s.k. disc permeameter användes för att undersöka den hydrauliska konduktiviteten och PVC-rör med borrkärnor ställdes under vattenmättadeförhållanden en längre tid för att ta reda på om infiltrationen då skulle förändras. Jorden i fält provtogs och ett kornstorlekstest utfördes. Den potentiella avdunstningen mättes med en evaporationspanna och beräknades med data från en klimatstation i fält. Med flödesdata från diket med utgående vatten, potentiell avdunstning och nederbördsdata kunde en grov uppskattning av vattenbalansen i fält göras. Resultaten visade att det inte bildas någon hinna som hindrar infiltrationen av vatten i den övre delen av jordprofilen. Översvämningen är ett resultat av en stigande grundvattenyta, som stiger från ett tjockt lager av lera 7 meter ner i marken. När vattnet har dräneras och avdunstat bort är det ingenting som hindrar infiltrationen i fält. Det är dock väldigt fina partiklar av silt och lera i den översta torvjorden som minskar infiltrationshastigheten och kan orsaka en separation av grundvatten över och under markytan. När projektet var avslutat kunde två rekommendationer ges till landägaren om hur man kan lösa problemet med översvämningen. Rekommendationerna var att antingen skulle landägaren kunna göra om marknivån i fält för att få ytvattnet att rinna av mot dikena istället för att vara fast i de lägre partierna av fältet. Eller att gräva diken in i fältet från Horonui Drain och Cambell Drain in till de lägre översvämmade områdena i fält för att dränera bort översvämningsvattnet.

The New Zealand (NZ) sea lion Phocarctos hookeri is the only pinniped endemic to NZ with a population of approximately 12,000 individuals. Its breeding range is currently restricted to NZ sub-Antarctic islands, and it has failed to recolonise its pristine distribution around the NZ main islands despite its protection since 1881. The current hypothesis is that the population growth of this pinniped is limited by the distribution of suitable prey on the Auckland Islands (50°30'S, 166°E) shelf, and by the direct and indirect pressure exerted by the arrow squid Nototodarus sloani fishery. However, this hypothesis has not been fully tested to date as there has been limited information on the diet of the NZ sea lion and their potential prey. The objective of this thesis is to analyse the diet of NZ sea lions over several years with particular emphasis on the most reproductively important segment of the population: lactating females. This thesis provides the first quantification by percentage mass of the diet of NZ sea lion using a combination of stomach content analysis, qualitative fatty acid (FA) analysis, and quantitative FA signature analysis (QFASA). Stomach contents and blubber FAs were analysed from 121 individuals incidentally caught (by-caught) in the southern arrow squid fishery from the years 1997 to 2006. The blubber FAs of 78 freeranging lactating females captured at Enderby Island, Auckland Islands, were also examined during January and February of 2000 to 2005. Data obtained from both stomach analysis and QFASA indicate that arrow squid, rattails Macrouridae, hoki Macruronus novaezelandiae and red cod Pseudophycis bachus are key prey species for NZ sea lions in the Auckland Islands region. Because these prey species live mostly at depths greater than 200 m, lactating females must undertake long foraging trips and dive regularly to greater depths than other sea lion species. Data from QFASA indicates that this foraging pattern is conducted over an extended period through the summer and autumn. The daily food requirement of a lactating female was estimated by a simple energetic model to be greater than 20% of its body mass. During years of low arrow squid recruitment such as 1999 and 2001, the amounts of squid required by the NZ sea lion population may have been similar to the amount harvested by the fishery, suggesting that resource competition is likely to occur between the arrow squid fishery and NZ sea lions in years of low squid abundance. Half of the fishing activity of the southern squid fishery occurs in the north of the Auckland Islands shelf where NZ sea lions forage, leading to incidental captures every year. This research emphasises that management of the NZ sea lion must not only consider the direct interactions with the arrow squid fishery, but also the likelihood of food resource competition between the fishery and NZ sea lions.

The potential impact of sea level rise on Lake Ellesmere - Te Wiahora and the subsequent effect on the efficiency and performance of the L2 Drainage network was investigated in relation to the operation of the L2 Drainage scheme. Lake Ellesmere is currently manually opened for drainage to the sea when the lake levels reach 1.05 m above mean sea level (asl) in summer and 1.13 m asl in winter. With a rise in sea level, the lake opening levels for both summer and winter would have to increase in order to maintain the current hydraulic gradient. Higher lake levels would impact drainage schemes such as the L2 drainage network. An integral research approach was used to study this potential impact, including fieldwork, analysis of data, hydrologic and hydraulic modelling. Both the hydrologic and hydraulic response of the L2 catchment and river were reproduced with reasonable accuracy by the use of computational models. Simulations of 2, 10 and 20 year annual recurrence intervals (ARI) rainstorm events coupled with higher lake levels show increase flooding along the length of the river. An increase in the lake opening levels, coupled with south-easterly wind was shown to have increased the degree of flooding on adjacent farmlands, but only a 3.50 per cent increase of water level (for all conditions simulated) 3.5 km upstream of the L2 River. The study clearly shows that weed growth within the L2 River plays an important part in controlling the water level within the channel. Results show it was responsible for an observed water level rise of 0.30 m from the winter to summer season. The combined use of hydraulic and hydrological models provides an effective tool to study future impacts on the drainage efficiency and performance of the L2 drainage scheme and other similar systems. The potential for both models to be used as a predictive tool for improving the operation of the L2 scheme and Lake Ellesmere was only limited by the difficulty in estimating model parameters especially for the hydrologic model.