Lake Tekapo Research Articles

생육환경이 주요 목초의 뿌리발육에 미치는 영향 II. 생육환경에 따른 뿌리 분포

비교되는 포장조건에 따라 부리 분포 양상을 조사하기 위하여 Rhizotron법을 사용하였다. Lincoln 지역에서 토양 깊이에 따른 뿌리의 분포는 15∼30 cm 깊이에 대부분의 뿌리가 분포되어 있고, 0∼15 cm와 30 cm 이하에서는 분포가 적었다. 반면, Winchmore에서는 토양 깊이가 깊어질 수록 뿌리 수가 많아졌다. Mt John에서는 표토에 가까울 수록 뿌리 분포도가 더 높았으며, 시비량이 높고 관개를 한 곳이 부리 분포가 더 높았다. 모든 지역에서 토양 깊이에 따른 뿌리 수의 분포는 뿌리 길이와 같은 경향을 보여주었다. Tube법이 같은 장소에서 뿌리의 비교 연구와 장기간 무리 생장 연구를 하는데 좋은 방법임이 입증되었다. Rhizotron technique was used to determine the zone of active root growth in contrasting field situations. The distribution of roots with depth showed most root in the 15∼30 cm layer with fewer in the 0∼15 cm and below 30 cm layer at Lincoln Farm, while root density increased with depth at Winchmore. At Mt Johm (Lake Tekapo) roots were more distributed near soil surface. Root density was increased with fertilizer and irrigation at Mt John. Root number showed the same trends as root length at all lesions. Tube method was good for comparative purposes, and for long-term root growth studies at the same place.

The Lake Tekapo Experiment (LTEX): An Investigation of Atmospheric Boundary Layer Processes in Complex Terrain

A research program on atmospheric boundary layer processes and local wind regimes in complex terrain was conducted in the vicinity of Lake Tekapo in the southern Alps of New Zealand, during two 1-month field campaigns in 1997 and 1999. The effects of the interaction of thermal and dynamic forcing were of specific interest, with a particular focus on the interaction of thermal forcing of differing scales. The rationale and objectives of the field and modeling program are described, along with the methodology used to achieve them. Specific research aims include improved knowledge of the role of surface forcing associated with varying energy balances across heterogeneous terrain, thermal influences on boundary layer and local wind development, and dynamic influences of the terrain through channeling effects. Data were collected using a network of surface meteorological and energy balance stations, radiosonde and pilot balloon soundings, tethered balloon and kite-based systems, sodar, and an instrumented light aircraft. These data are being used to investigate the energetics of surface heat fluxes, the effects of localized heating/cooling and advective processes on atmospheric boundary layer development, and dynamic channeling. A complementary program of numerical modeling includes application of the Regional Atmospheric Modeling System (RAMS) to case studies characterizing typical boundary layer structures and airflow patterns observed around Lake Tekapo. Some initial results derived from the special observation periods are used to illustrate progress made to date. In spite of the difficulties involved in obtaining good data and undertaking modeling experiments in such complex terrain, initial results show that surface thermal heterogeneity has a significant influence on local atmospheric structure and wind fields in the vicinity of the lake. This influence occurs particularly in the morning. However, dynamic channeling effects and the larger-scale thermal effect of the mountain region frequently override these more local features later in the day.

Supplement to the Lake Tekapo Experiment (LTEX): An Investigation of Atmospheric Boundary Layer Processes in Complex Terrain

Supplement to the Lake Tekapo Experiment (LTEX): An Investigation of Atmospheric Boundary Layer Processes in Complex Terrain

Analysis of the wind field and heat budget in an alpine lake basin during summertime fair weather conditions

¶Observational data collected in the Lake Tekapo hydro catchment of the Southern Alps in New Zealand are used to analyse the wind and temperature fields in the alpine lake basin during summertime fair weather conditions. Measurements from surface stations, pilot balloon and tethersonde soundings, Doppler sodar and an instrumented light aircraft provide evidence of multi-scale interacting wind systems, ranging from microscale slope winds to mesoscale coast-to-basin flows. Thermal forcing of the winds occurred due to differential heating as a consequence of orography and heterogeneous surface features, which is quantified by heat budget and pressure field analysis.

Characteristics of aeolian grain transport over a fluvio-glacial lacustrine braid delta, Lake Tekapo, New Zealand

This paper presents results from one of the few scientific studies to examine the physical characteristics of aeolian sediment transport in an alpine area, where topographically reinforced foehn winds initiate dust storm events. The major objective of this study is to improve knowledge of aeolian processes in mid-latitude alpine regions experiencing extreme wind speeds. Of particular interest is the role of surface characteristics in contributing to the unusually deep saltation layer which is seen to form over fluvio-glacial deposits in the Southern Alps of New Zealand. Sediment was collected at several heights (0ċ5, 1, 2 and 4 m) and locations over a large alpine braided river delta, and standard laboratory techniques used to examine grain size characteristics. An image processing technique was also used to evaluate grain roundness. Grains filtered from the airstream at 0ċ5 m and 1 m above such surfaces were found to display a mean grain size of approximately 300 to 435 μm, resembling grain size characteristics of saltation clouds previously observed in high latitude, cold climate locations, in contrast to desert and prairie environments. Samples collected at 2 and 4 m above the surface were found to consist of 60 to 65 per cent sand-sized material, with some grains exceeding 1–1ċ5 mm in diameter. Grain shape analysis conducted on silt- and clay-sized grains filtered from the airstream above mixed sand and gravel surfaces showed such grains to display an increase in grain roundness with height. This characteristic is thought to reflect the airstream's shape-sorting ability and has important implications with respect to the often observed increase in grain roundness in aeolian deposits with increasing distance from source areas. Namely, if more rounded grains are preferentially carried higher into the airstream and therefore into regions of higher wind speed, they should theoretically be transported further from the entrainment zone before being deposited. The high wind speeds observed, often exceeding 30 m s−1, are seen to transport significantly larger sediment than reported in the literature for desert and prairie environments. In addition, the mixture of grain sizes, and especially the pebble- and cobble-sized clasts that dominate the fluvio-glacial deposits associated with the braided rivers in this mountain region, also appear to increase significantly the trajectory height of saltating sand grains. As a result of these two factors, the depth of the saltation cloud often exceeds 1 m. Observations made in this study therefore highlight the need for field and laboratory aeolian process studies to be extended to examine grain transport over coarse-grained beds during much higher wind velocities than typically reported in the literature. Such studies would provide a valuable insight into aeolian processes in high latitude/altitude environments, such as loess genesis. © 1997 by John Wiley & Sons, Ltd.

Characteristics of aeolian grain transport over a fluvio‐glacial lacustrine braid delta, Lake Tekapo, New Zealand

This paper presents results from one of the few scientific studies to examine the physical characteristics of aeolian sediment transport in an alpine area, where topographically reinforced foehn winds initiate dust storm events. The major objective of this study is to improve knowledge of aeolian processes in mid-latitude alpine regions experiencing extreme wind speeds. Of particular interest is the role of surface characteristics in contributing to the unusually deep saltation layer which is seen to form over fluvio-glacial deposits in the Southern Alps of New Zealand. Sediment was collected at several heights (0ċ5, 1, 2 and 4 m) and locations over a large alpine braided river delta, and standard laboratory techniques used to examine grain size characteristics. An image processing technique was also used to evaluate grain roundness. Grains filtered from the airstream at 0ċ5 m and 1 m above such surfaces were found to display a mean grain size of approximately 300 to 435 μm, resembling grain size characteristics of saltation clouds previously observed in high latitude, cold climate locations, in contrast to desert and prairie environments. Samples collected at 2 and 4 m above the surface were found to consist of 60 to 65 per cent sand-sized material, with some grains exceeding 1–1ċ5 mm in diameter. Grain shape analysis conducted on silt- and clay-sized grains filtered from the airstream above mixed sand and gravel surfaces showed such grains to display an increase in grain roundness with height. This characteristic is thought to reflect the airstream's shape-sorting ability and has important implications with respect to the often observed increase in grain roundness in aeolian deposits with increasing distance from source areas. Namely, if more rounded grains are preferentially carried higher into the airstream and therefore into regions of higher wind speed, they should theoretically be transported further from the entrainment zone before being deposited. The high wind speeds observed, often exceeding 30 m s−1, are seen to transport significantly larger sediment than reported in the literature for desert and prairie environments. In addition, the mixture of grain sizes, and especially the pebble- and cobble-sized clasts that dominate the fluvio-glacial deposits associated with the braided rivers in this mountain region, also appear to increase significantly the trajectory height of saltating sand grains. As a result of these two factors, the depth of the saltation cloud often exceeds 1 m. Observations made in this study therefore highlight the need for field and laboratory aeolian process studies to be extended to examine grain transport over coarse-grained beds during much higher wind velocities than typically reported in the literature. Such studies would provide a valuable insight into aeolian processes in high latitude/altitude environments, such as loess genesis. © 1997 by John Wiley & Sons, Ltd.

Free aluminium and related parameters in soil solution from a South Island (New Zealand) high country site under contrasting S and P fertilisation

Soil solution samples were taken from 7 plots of varying Hieracium infestation at the AgResearch (NZ) Mt John trial site, Lake Tekapo. The soils, which had been fertilised, oversown, and grazed, were analysed for free (reactive) Al, total Al, pH, NOM (natural organic matter), and phosphate. The plots had received annual fertiliser combinations of 0–100 kg P and 0–20 kg S/ha·year. Soil solution pH was in the range 4·33-5·76 and total Al concentrations were in the range 13–68 µM. Free Al concentrations were in the range 0·48–4·8 µM. The pH dependence of log (free[Al]) (slope: –0·69±0·37) indicated control of soluble Al by NOM rather than Al(OH)3 solubility. Soil solution phosphate concentrations depended strongly on P application rate, reaching over 100 mM. At high P concentrations, the product [Al3+][PO3-4] indicated approximate saturation with respect to variscite. One comparison indicated that effects on pH and NOM in the upper 5 cm were due to the presence or absence of grazing.

Aeolian dust transport and deposition by foehn winds in an alpine environment, Lake Tekapo, New Zealand

Observations from an automatic weather station and anemograph network are used in conjunction with recorded dust deposition rates to identify principle sources of wind blown dust within an alpine lake basin. Meteorological observations made throughout the study indicate that foehn windstorms provide ideal conditions for the initiation of aeolian processes, including dust storm genesis. A mean wind speed during foehn windstorms of 7.5 m s −1 at 2.65 m above the surface was observed to initiate entrainment of dust particles from geomorphically active areas within the lake basin, particularly from the dry braid channels of glacier fed rivers, exposed lacustrine deltas and degraded tussock grasslands. This threshold entrainment velocity is similar to others presented within the international literature for such surface types. A diurnal modulation of meteorological parameters monitored during foehn wind events suggests that aeolian processes, such as dust entrainment, are most likely to occur from late morning to early evening. However, where topography enhances wind speeds, for example by channelling airflow down river valleys, favourable conditions for dust entrainment may prevail throughout the night in the absence of precipitation. Potential dust roses were determined for two sites within the lake basin. The dust roses supported anecdotal and observational evidence of principle dust sources within the study area, and appear to be an effective tool for identifying the potential hazard to a particular location from blowing dust, once the physical trigger conditions for dust entrainment are known. This requires detailed and concurrent monitoring of meterological variables in association with dust transportation and deposition rates, especially in complex terrain where many micro-climates often exist.

Earth-bound observations of asteroid 19 Fortuna as support to HST imaging: lightcurves, pole direction and shape

To support the 19 Fortuna imaging work performed by the Hubble Space Telescope, this asteroid was photoelectrically observed in September 1993 at Mt. John, Lake Tekapo and Serra la Nave observatories, covering a complete rotational cycle. These observations and the unpublished ones, collected in November 1986 at Torino Observatory, allowed us to compute the value of the synodic rotational period, which results in accordance with that already known. The spin axis direction and the shape of 19 Fortuna were determined by applying the amplitude-magnitude method (Zappalà et al., in Asteroids, Comets, Meteors (edited by C.-I. Lagerkvist and H. Rickman), pp. 73–76. Uppsala Univeritet, Reprocentralen, HSC, Uppsala, 1983) to our data and to those reported in the literature. The values of the pole coordinates are in agreement with the previous determinations, while the ratio between the semi-axes a and b is larger than about 0.1.

Interacting multi-scale wind systems within an Alpine basin, Lake Tekapo, New Zealand

The wind regime of the Lake Tekapo Basin is examined with reference to the interaction of multi-scale local, regional and synoptic circulations. Analysis of the historical wind direction record from Mt John identifies airflow from three principal directions to most frequently affect the study area. Both seasonal and diurnal trends in the frequency of each directional category are identified, which reflect the influence of local thermal forcings and seasonal changes in synoptic circulation on the Lake Tekapo windfield. Meteorological observations from a network of automatic weather stations and anemographs within the study area identified Lake Tekapo to generate its own circulation system, a lake/land breeze. This combines with the larger scale valley wind, which during ideal conditions continues after sunset in the upper reaches of the lake catchment. During light to moderate foehn northwesterly conditions, the combined lake breeze/valley wind system remains decoupled from the prevailing synoptic airstream. Towards evening when local thermal circulations weakened, a channelised foehn airstream often becomes dominant over the entire field area. Observations made during this investigation have a number of applied implications with respect to air pollution dispersion modelling and forecasting within alpine lake basins.

Timothy cultivars in a New Zealand high country environment

Herbage yields of 12 timothy cultivars and 4 control grasses were compared over 4 years under 50 250 and 500 (with irrigation) kg N/ha/year in the South Island high country near Lake Tekapo. Timolhy produced high yields (10.9-12.2 t/ha/year) of quality herbagc under high nitrogen and irrigation. Mean yields at 50 and 250 kg N/ha/year were 4.8 and 7.1 t/ha/year respectively under dryland conditions. Differences between the timothy cultivars were small but Grasslands Kahu was the top- or near the top-performing of the 12 cultivars tested at all times. Keywords: cultivars, high country, Phleum pratense

Regional and local scale characteristics of foehn wind events over the South Island of New Zealand

Regional and local scale windfield and air mass characteristics during two distinct synoptic foehn wind events over southern New Zealand are examined. The Southern Alps were observed to effectively block low level onshore gradient northwesterly airflow and to channel it through both Cook and Foveaux Straits. Blocking of the onshore synoptic northwesterly airstream also resulted in barrier jet formation along the western slopes of the Southern Alps. This feature of the regional windfield has not previously been documented and develops during favourable conditions to a height of between 1500 to 1800 m above sea level. In the immediate lee of the Southern Alps at Lake Tekapo, classic foehn conditions such as warm ambient air temperatures, low relative humidities and gusty winds were monitored throughout both foehn events examined. Differences in the local windfield were however observed, which reflect the importance of local topography on lee side windfield dynamics during foehn events. Spillover of precipitation to the lee of the mountains was monitored in the latter stages of each case study and appeared to be associated with the passage of the cold front over the Southern Alps. Observations made by this investigation have a number of applied and theoretical implications with respect to meso-scale modelling, orographic rainfall distribution and forecasting.

Thermal and dynamic characteristics of alpine lake breezes, Lake Tekapo, New Zealand

Thermodynamic characteristics and temporal variation of alpine lake breezes in the eastern Southern Alps are examined. Research was conducted in a large glacially excavated basin dominated by an 87 square kilometre melt-water lake as part of a study of windblown dust dispersion. The surrounding mountain ranges were found to shelter the lake basin from most synoptic winds, thereby allowing local and regional thermally generated circulations to develop to ridge height, approximately 1300m above the surrounding landscape. During favourable synoptic conditions the local lake breeze becomes embedded within the regional valley wind forming an extended lake breeze. Tethersonde flights during these conditions made using a kite based sounding system identified both stable internal (SIBL) and thermal internal boundary layer (TIBL) conditions over the down wind shoreline. Two equations for estimating the height of both boundary-layer types were tested against observations and found to provide good first order predictive estimates of boundary-layer height.

A seismic velocity profile across the central South Island, New Zealand, from explosion data

Abstract Data from a seismic experiment across the central South Island, New Zealand, were used to model the crustal structure of the Australia‐Pacific plate continent‐continent boundary to a depth of c. 40 km. Large explosions were detonated off each coast and in Lake Tekapo and recorded on 19 seismographs deployed in a line from Timaru to just south of Fox Glacier, and on the Pukaki Seismograph Network. In the upper crust, a clear difference was found between the seismic velocities in Permian and younger rocks, in agreement with findings from other studies. Within the Permian schists and greywackes, the P‐wave velocity is 5.8 km/s to 2.7 km depth and 6.0 km/s below, contrasting with 5.4 km/s in the Triassic greywackes which form the basement near Lakes Pukaki and Tekapo in the central part of the survey area. Strong second arrivals from a layer 24 km deep at the east coast, and dipping inland at 3.4°, were seen from both offshore shots. The true velocity of the arrivals was determined to be 7.2 km/s. Ar...

Relative sheep liveweight gain on perennial lupin, red clover and alsike

Young Merino wethers set stocked from November to April, over 5 years, on developed high country legume pastures, at Lake Tekapo at 50 kglhafyr superphosphate, showed daily liveweight gain on perennial lupin and alsike clover that were 53% and 70%; respectively, of that on Pawera red clover (110 g/day). Keywords: high country, Lupinus polyphyllus, Trifolium hybridum, T. pratense, sheep weight gains

CCD Photometry of the Eclipsing Binary HV 2274 in the Large Magellanic Cloud

B, V and Ic photometry of the eclipsing binary HV 2274, located in the LMC, was obtained with the CCD system at the Mount John University Observatory, Lake Tekapo, New Zealand during 1990. Over 100 data points were acquired in each filter to an estimated precision of 0.02 mag. The flat maxima evident in the light curves suggest that the system, which is currently classed as an interacting candidate, should probably be considered as a detached one. A revised orbital period based on the inclusion of current data is presented. Eclipse timings indicate an eccentric orbit. An apsidal period in the vicinity of 120 yr is likely.

Two-channel Photometry of Cataclysmic Variables

AbstractHigh-speed photometry of two cataclysmic variables is presented. The observations were made using a two-channel photometric system and the Mt John 0.6 or 1-m telescopes at Lake Tekapo in New Zealand. Both objects have only recently been identified as cataclysmic variables. One of the objects is a high inclination system featuring a deep eclipse in the light curve and a 5.5 hour period, while the other object, despite being relatively faint, clearly exhibits a 2.5 hour period and out of eclipse variability. Simultaneous monitoring of a nearby comparison star for this latter object was particularly beneficial, even during good photometric conditions.

SPECIES, AND FERTILISER EFFICIENCY - A HIGH COUNTRY EXAMPLE

Species dominance and sheep grazing days relative to fertiliser costs are given for the first 6 years of 2 trials at Lake Tekapo. Both were sown in a multiple species mixture. Trial I examined 27 different annual P and S levels; Trial II examined 30 combinations of 5 superphosphate levels, 3 sheep grazing intensities and 2 stocking methods. Pastures were mostly legume dominant, and species differences were related to P fertiliser and stocking method. Perennial (Russell) lupin (Lupinus poflyphyllus) dominated at all low to medium fertiliser rates, alsike clover (Trifolium hybridum) at intermediate rates, and cocksfoot (Dactylis glomerata) and white clover (T repens) at high ferttliser rates. The stocking rate achieved was related to both S and P rates. Greatest fertiliser efficiency (returns v. costs) was at low annual rates of 4-5 kg P plus 16-25 kg S/ha. Keywords: lupin, cost-benefit, cocksfoot, alsike clover, phosphate, sulphur, sheep grazing management, fertiltser efficiency.

Temporal variations of some trace organics (HCB, HCH, PCB and PAH) in rainfall, runoff and in lake sediments in remote sites of New Zealand

The concentrations of some PAH (fluoranthene, 3.4-benzopyrene), α - and γ - HCH, HCB and PCB in rainfall, runoff and near-surface groundwater were measured in two small experimental river basins and in an alpine river basin in remote areas of Westland and Fiordland resp., New Zealand. Because of very low concentrations, the trace organics were concentrated from water samples on XAD-resins. The temporal variation of concentrations and fluxes in the New Zealand rivers depends on the physicochemical properties of the trace organics, first of all the partition coefficients and the transport of their dominant carriers, e.g. humic substances. Thus, the temporal pattern resembles that found in rivers without point sources of these trace organics in northeastern Bavaria. However, the concentrations in the New Zealand rainfall and runoff are generally one to two orders of magnitude below those in northeastern Bavaria. In contrast to Bavarian fog, that of New Zealand is not more polluted by trace organics than the rainfall. The pattern of the temporal variation of trace organics in runoff is generated by the characteristic adsorption isotherms in the river water/suspended sediment system of the trace organics under investigation. We could not show an increase of concentration of chlorinated hydrocarbons in varved sediment cores of Lake Tekapo during the last twenty years. However, the PAH revealed a clear increase of concentration at the top of the column. This might equally be explained by an increase of PAH-pollution in recent years or by degradation of hydrocarbons in oxidized sediments or both, since the pevalues show oxidized conditions within the upper 20 cm of the cores.

Phytoplankton periodicity of the Waitaki lakes, New Zealand

The Waitaki River system in the South Island of New Zealand includes three large glacially-formed headwater lakes, Tekapo, Pukaki and Ohau, which drain into the manmade Lake Benmore. Phytoplankton periodicity was followed from December 1975 to January 1980 as part of a study investigating possible changes in these lakes as a consequence of hydroelectric development. The phytoplankton was highly dominated by diatoms, e.g., Diatoma elongatum, Cyclotella stelligera, Asterionella formosa, and Synedra acus, but in lakes Ohau and Benmore populations of green algae occasionally developed. In all four lakes seasonal phytoplankton periodicity was observed with maximum biomass in spring and summer. In Lake Tekapo, the first lake in the chain, maximum biomass did not exceed 300 mg m-3, but in the very turbid Lake Pukaki the maximum summer biomass ranged between 300 and 800 mg m-3. In Lake Ohau, the least turbid lake, maximum biomass was around 1 000 mg m-3. In the newly created Lake Benmore periodicity was less evident and summer maxima reached over 1 500 mg m-3. The phytoplankton periodicity in these lakes is greatly influenced by seasonal patterns of turbidity from inflowing glacial silt.