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102 records were found.

Over the last few decades, anthropogenic eutrophication has become a significant problem in New Zealand and other parts of the world. Lake Rotorua is located in the central North Island, New Zealand. It is a lake with significant historical, cultural and recreational values that has undergone anthropogenic eutrophication. Lake Rotorua has been exposed to anthropogenic impacts through conversion of forested land to agricultural use within its catchment, and the discharge of domestic sewage into the lake. Cyanobacterial blooms have become a common occurrence in the lake each summer. These blooms not only reduce aesthetic appeal but also have potential to affect human health. Lake stratification and physical mixing events are the most important factors influencing nutrient availability and phytoplankton growth in Lake Rotorua. The main ...
The objective of this study was to apply a coupled hydrodynamic-ecological model to a peat-stained and shallow (~4 m maximum depth) eutrophic lake whose catchment is likely to be subject to urban expansion associated with the development of Hamilton city, Waikato, New Zealand. The in-lake modelling was designed to increase understanding of the lake ecosystem and potentially to influence planning and management decisions associated with the prospective urban development project being undertaken by the Hamilton City Council (HCC). The overarching goal of the development is to accommodate urban expansion whilst retaining and enhancing the existing natural resources of Lake Rotokauri and Waiwhakareke Lake, and to restore the ecological value of the Rotokauri catchment. The main objective of this study was to understand the relationship bet...
Globally, the accelerated eutrophication of lake ecosystems due to excess inputs of nitrogen (N) and phosphorus (P) is a significant problem. The rate of loading of N and P to lakes varies both in space and time; consequently, developing good understanding of such spatial and temporal variability is critical for developing integrated approaches to managing lake water quality. This study aimed to improve understanding of spatial and temporal variations in N and P loading to lakes, and, to examine how this variability affects water quality. The topic was considered at global, national and catchment scales. Analysis of an extensive global dataset was undertaken to examine relationships between N, P and chlorophyll a (chl a) in lakes along a gradient of latitude inclusive of tropical, temperate and polar regions. The ratio of total nitro...
The Te Arawa/Rotorua lakes located in the central North Island of New Zealand have significant cultural, historic, social and economic value. Anthropogenic changes in land use have led to a decline in water quality in some lakes. A number of lakes have accelerated eutrophication with recurring cyanobacterial blooms and periods of bottom-water anoxia. Whilst there has been extensive research undertaken on phytoplankton dynamics in freshwater lakes there is little information on the abundance and activity of viral-like particles (VLPs) and bacteria. VLPs are the most abundant biological entities in aquatic environments and play an important role in carbon and nutrient cycling, reproducing either by cell lysis or replication in the host cell. Bacterial community structure is thought to be closely linked to the viral community and bacteria...
This thesis was a comparative study of a natural and a recently re-constructed (artificial) side-arm in the lower Waikato River. A twelve monthly temporal investigation into (i) the physico-chemical variables, nutrient and suspended solid dynamics; and (ii) phytoplankton and zooplankton abundance and community composition was carried out in order to compare each side-arm with the river, and any patterns occurring within the side-arm longitudinally. The study was based on three observed phases of connectivity of the side-arms with the river flow: Phase 1 - side-arms connected with the river (late spring-summer); Phase 2 - side-arms disconnected from the river (autumn); Phase 3 - side-arms re-connected with the river (winter). Functional roles described for side-arms in the literature were used to assess whether the natural and artificia...
Spatial and temporal variations in the physical, chemical and biological composition of Lake Ōkaro were measured over 16 months. Lake Ōkaro is a small (0.32 km2) hypertrophic, monomictic lake located in the Central Volcanic Zone of the North Island, New Zealand. Vertical profiles of temperature, chlorophyll fluorescence, dissolved oxygen concentration (DO), pH, specific conductance, photosynthetically active radiation (PAR) and nutrient species, including ammonium-nitrogen (NH4-N), nitrite-nitrogen (NO2-N), nitrate-nitrogen (NO3-N) and phosphate-phosphorus (PO4-P), were collected at up to nine stations at weekly to monthly frequencies. High-frequency variability was assessed during two separate 24-hour monitoring periods, coinciding with an Anabaena spiroides-dominated surface bloom, and a Ceratium hirundinella-dominated deep chlorophy...
The Taupo Volcanic Zone (TVZ) is in the Waikato and the Bay of Plenty regions of North Island of New Zealand and contains many volcanic lakes of diverse history, physiography, and limnology. The lakes vary in size (0.2 to 620 km2), mixing regime (monomictic and polymictic), and trophic status (oligotrophic to supertrophic). The purpose of this study is to develop an understanding of the sediment-pore water interactions over a range of trophic conditions and how the biogeochemical cycles influence the lake ecosystem and the implications that this has for management of the TVZ lakes. The monthly changes in composition of lake water, pore water, sediments and stable isotopes of dinitrogen gas were monitored in five monomictic TVZ lakes (Taupo, Tarawera, Okataina, Rotoiti and Ngapouri) of widely varying trophic state, in order to evaluate ...
Deterioration of water quality is a common problem for aquatic systems globally, which is accelerated by factors such as urban settlement, farming, forestry and recreation. Spatial variability of water quality in these systems hinders a more advanced understanding of their dynamics, to better enable strategies to be developed to combat their deterioration. Understanding the drivers for spatial variability is fundamentally important for predicting how lake ecosystems will respond to management scenarios and which management actions are most likely to be successful to improve lake health. Through a field study in a morphologically diverse lake in New Zealand, and the application of a lake ecosystem model, this study examined the spatial and temporal variability of phytoplankton biomass and made a detailed consideration of the performance...
During this study, the effect of different processing methods on the microcystin quota (microcystins per cell) was investigated. Microcystins from two Microcystis strains and one Planktothrix strain were quantified using liquid chromatography-mass spectrometry (LC-MS) after processing via; (1) direct freezing (no prior cell concentration) and extraction by freeze-thaw cycles, (2) cell concentration by centrifugation and extraction in methanol and (3) cell concentration by filtration and extraction in methanol. Microcystin quotas were lower for samples concentrated by filtration compared with the other two methods. In order to distinguish between extracellular microcystins actively exported from cells and those that are present as a result of cell lysis, a comparative microcystin export (CME) assay was developed using LC-MS to com...
This thesis describes an investigation into the impacts on charophytes of four selected aquatic herbicide and a mycoherbicide products currently used or under development in New Zealand for alien invasive aquatic plant management. Of particular interest was the charophyte response with respect to oospore germination, germling susceptibility and species response. In New Zealand, charophytes are native submerged aquatic plants which are recognized as beneficial components of lake ecosystems. They form dense meadows on the lake sediment and are rapid colonisers as they are the first plant to recolonise a lake after a disturbance event. Charophytes produce oospores (seeds) which can remain dormant in seed banks until suitable germination conditions are met. New Zealand lake sediments contain a seed bank which is dominated by charophyte oos...
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