Lake Coleridge Research Articles

Energy budget for a rock avalanche: fate of fracture-surface energy

A detailed energy budget of a rock avalanche at Lake Coleridge, New Zealand, included fragments as small as 70 nm in diameter in the debris particle-size distribution, and used ultrasonic disaggregation of agglomerates formed during emplacement of the deposit to properly sample the fine fragments created during the rock avalanche. Using the maximum likely value of potential energy released during the debris fall and runout, and minimum values of energy lost to friction and of energy used in creating new rock surface area by fragmentation, the energy budget showed a substantial energy deficit; the available potential energy almost matched the energy lost to friction, leaving very little energy available for creating the new surface. This deficit was much less prominent if sub-micron fragments were ignored as in earlier energy budgets, because about 90% of total fragment surface area occurred on sub-micron fragments. Close examination of possible sources of error in the calculated budget leads to the conclusion, supported by published data, that only a small proportion of the energy used to create new rock surface transforms to surface energy, while a large proportion of it remains available in the form of elastic body-wave energy.

Warming and glacier recession in the Rakaia valley, Southern Alps of New Zealand, during Heinrich Stadial 1

The termination of the last ice age featured a major reconfiguration of Earthʼs climate and cryosphere, yet the underlying causes of these massive changes continue to be debated. Documenting the spatial and temporal variations of atmospheric temperature during deglaciation can help discriminate among potential drivers. Here, we present a 10Be surface-exposure chronology and glaciological reconstruction of ice recession following the Last Glacial Maximum (LGM) in the Rakaia valley, Southern Alps of New Zealand. Innermost LGM moraines at Big Ben have an age of 17,840 ± 240 yrs, whereas ice-marginal moraines or ice-molded bedrock surfaces at distances up-valley from Big Ben of 12.5 km (Lake Coleridge), ∼25 km (Castle Hill), ∼28 km (Double Hill), ∼43 km (Prospect Hill), and ∼58 km (Reischek knob) have ages of 17,020 ± 70 yrs, 17,100 ± 110 yrs, 16,960 ± 370 yrs, 16,250 ± 340 yrs, and 15,660 ± 160 yrs, respectively. These results indicate extensive recession of the Rakaia glacier, which we attribute primarily to the effects of climatic warming. In conjunction with geomorphological maps and a glaciological reconstruction for the Rakaia valley, we use our chronology to infer timing and magnitude of past atmospheric temperature changes. Compared to an overall temperature rise of ∼4.65 °C between the end of the LGM and the start of the Holocene, the glacier recession between ∼17,840 and ∼15,660 yrs ago is attributable to a net temperature increase of ∼4.0 °C (from −6.25 to −2.25 °C), accounting for ∼86% of the overall warming. Approximately 3.75 °C (∼70%) of the warming occurred between ∼17,840 and ∼16,250 yrs ago, with a further 0.75 °C (∼16%) increase between ∼16,250 and ∼15,660 yrs ago. A sustained southward shift of the Subtropical Front (STF) south of Australia between ∼17,800 and ∼16,000 yrs ago coincides with the warming over the Rakaia valley, and suggests a close link between Southern Ocean frontal boundary positions and southern mid-latitude climate. Most of the deglacial warming in the Southern Alps occurred during the early part of Heinrich Stadial 1 (HS1) of the North Atlantic region. Because the STF is associated with the position of the westerly wind belt, our findings support the concept that a southward shift of Earthʼs wind belts accompanied the early part of HS1 cooling in the North Atlantic, leading to warming and deglaciation in southern middle latitudes.

The Little Red Hill Seismic Experimental Study: Topographic Effects on Ground Motion at a Bedrock-Dominated Mountain Edifice

The kinematic response of a bedrock-dominated mountain edifice to seismic shaking near Lake Coleridge in the Southern Alps of New Zealand was examined. A small, elongated, and bedrock-dominated mountain ridge (Little Red Hill) was equipped with a seismic array. Seven EARSS instruments (Mark L-4-3D seismometers) were installed along the ridge crest, the flank, and at the base of the 210 m high, 500 m wide, and 800 m long mountain edifice from February to July 2006. Seismic records of local and regional earthquakes were used to provide information on amplification and deamplification effects, as well as on the frequency response at different parts on the edifice. The ground-motion records were analyzed using three different methods: comparisons of peak ground accelerations, power spectral density analysis, and standard spectral ratio analysis. Time and frequency domain analyses show that site amplification is concentrated along the elongated crest of the edifice where amplifications of up to 1100% were measured relative to the motion at the flat base. The field experiment also highlighted the extreme variations in amplification with regard to closely located sites but at contrasting topographic locations. Theoretical calculations and frequency analyses of field data indicate a maximum response along the ridge crest of Little Red Hill for frequencies of about 5 Hz, which correlate to wavelengths approximately equal to the half-width or height of the edifice. The consequence of amplification effects on the stability and degradation of rock masses can be seen: areas showing high amplification effects overlap with the spatial distribution of seismically generated block fields at Little Red Hill. It is concluded that topography, geometry, and distance to the seismic source play key roles in causing amplification effects of seismic ground motion and supporting dilation and degradation of rock mass across bedrock-dominated mountain edifices.

Successive Holocene rock avalanches at Lake Coleridge, Canterbury, New Zealand

At Lake Coleridge, Canterbury, New Zealand, at least three rock avalanches have been released from a single source area during the Holocene. The first of these was of 107 m3 volume and dates to about 9,750 BP, and two with volumes 5 × 105 and 4 × 104 m3 occurred about 700 BP. All three crossed the course of the Ryton River; the latter two were emplaced within the part of the first that had subsequently been eroded by the Ryton River. All three were most likely triggered by, or related to, seismicity. The first rock avalanche formed a long-lived landslide dam, and no evidence remains to indicate whether its eventual failure was catastrophic. The second formed a correspondingly smaller dam, but there is no evidence that its lake was long-lived; however, a set of anomalously steep outwash terraces downstream of the landslide deposits show that it failed catastrophically. A camping ground is sited about 1 km downstream of the landslide deposits, and proposals to develop it further risk potentially severe hazards from future rock avalanche activity at the site.

Holocene paleoearthquakes on the strike‐slip Porters Pass Fault, Canterbury, New Zealand

The Porters Pass Fault comprises a series of discontinuous Holocene active traces which extend for c. 40 km between the Rakaia and Waimakariri Rivers in the foothills of the Southern Alps. There have been no historical earthquakes on the Porters Pass Fault (i.e., within the last 150 yr), and the purpose of this paper is to establish the timing and magnitudes of displacements on the fault at the ground surface during Holocene paleoearthquakes. Displaced geomorphic features (e.g., relict streams, stream channels, and ridge crests), measured using either tape measure (n = 20) or surveying equipment (n = 5), range from 5.5 to 33 m right lateral strike slip and are consistent with six earthquakes characterised by slip per event of c. 5–7 m. The timing of these earthquakes is constrained by radiocarbon dates from four trenches excavated across the fault and two auger sites from within swamps produced by ponding of drainage along the fault scarp. These data indicate markedly different Holocene earthquake histories along the fault length separated by a behavioural segment boundary near Lake Coleridge. On the eastern segment at least six Holocene earthquakes were identified at 8400–9000, 5700–6700, 4500–6000, 2300–2500, 800–1100, and 500–600 yr BP, producing an average recurrence interval of c. 1500 yr. On the western segment of the fault in the Rakaia River valley, a single surface‐rupturing earthquake displaced Acheron Advance glacial deposits (c. 10 000–14 000 yr in age) and may represent the southward continuation of the 2300–2500 yr event identified on the eastern segment. These data suggest Holocene slip rates of 3.2–4.1 mm/yr and 0.3–0.9 mm/yr on the eastern and western sections of the fault, respectively. Displacement and timing data suggest that earthquakes ruptured the western segment of the fault in no more than one‐sixth of cases and that for a sample period of 10 000 yr the recurrence intervals were not characteristic.

Desmids (Chlorophyta), including two new species and three new varieties, in two swamps, a lake, and a tarn in the South Island of New Zealand

Swamps at Okarito (Westland), Lake Hill (near Lake Coleridge), and Red Tarn and Blue Lake (in Mount Cook National Park) contained 24, 19, 20, and 8 desmid taxa, respectively. Genera represented by the largest number of taxa were Cosmarium with 17 taxa (7 of them in Okarito Swamp), Closterium with 9 taxa (6 of them in Lake Hill Swamp), and Staurastrum with 9 taxa (4 of them in Red Tarn). New species are Closterium okaritoense and Cosmarium paludicola in Okarito Swamp. New varieties are Pleurotaenium ehrenbergii var. contractum and Cosmarium crassipelle var. ornatum (both in Lake Hill Swamp), and Actinotaenium adelochondrum var. parvum (in Red Tarn). New records for the New Zealand flora are Euastrum verrucosum (in Lake Hill Swamp), Micrasterias suboblonga var. tecta (in Okarito Swamp), Cosmarium retusiforme var. incrassatum and Xanthidium smithii var. maius (both in Red Tarn), and Staurastrum neglectum and S. subarmigerum (in Blue Lake). Six other taxa previously recorded in the North Island were found in the South Island, including the endemic Cosmarium subquadratum var. genuosum and Xanthidium intermedium.

Seasonal changes in plankton and nutrient dynamics and carbon flow in the pelagic zone of a large, glacial lake: Effects of suspended solids and physical mixing

The abundance and distribution of phytoplankton and zooplankton were followed from January 1993 to March 1994 in Lake Coleridge, a deep oligotrophic alpine lake in the Canterbury high country of New Zealand. Our data suggest physical processes associated with deep mixing and inputs of suspended sediments combined to limit planktonic biomass, diversity, and determine vertical distribution. The lake was strongly stratified in summer with a surface mixed layer of 20 m gradually extending down to 100 m by May. Over 50 taxa of phytoplankton were recorded. Changes in vertical distribution of most planktonic groups coincided with changes in the depth of vertical mixing. Phytoplankton biomass increased through summer with a diatom‐dominated peak in autumn. Cell numbers however, peaked in spring and were dominated by small chlorophytes. Phytoplankton photosynthetic production was highest in autumn but specific growth rates were highest in summer as a result of greater light availability combined with warmer temperatures. We suggest that large inputs of suspended sediments and glacial silt, may have limited the spring phytoplankton peak which occurs in a number of other temperate lakes. Bacteria and pico‐phytoplankton biomass peaked in winter following the phytoplankton peak suggesting they were relying at least in part on scenescing phytoplankton cells for dissolved organic carbon. Diversity of ciliated protozoa was low (11 taxa), Cladocera were absent, and the only crustacean zooplankton found in significant numbers was Boeckella hamata. Ciliated protozoan abundance was low (maximum 4600 litre 1) and peaked in summer (January‐March). Copepod nauplii peaked in August and peaks in abundance of copepodites and adults followed in September and November‐January respectively. Only two generations occurred during the year. The peak in copepod biomass followed phytoplankton peaks but lagged 1–2 months probably as a result of slow growth rates and the time for response to phytoplankton peaks.

Abundance and daytime vertical distribution of planktonic fish larvae in an oligotrophic South Island lake

The vertical distribution of common bully (Gobiomorphus cotidianus) and koaro (Galaxias brevipinnis) larvae in the limnetic zone of Lake Coleridge were determined using a high-frequency (200 KHz) echosounder. Planktonic bully larvae first appeared in appreciable numbers in January. By February, they formed a scattering layer between depths of 12 to 24 m during the day, where they achieved a maximum density of 0.59 fish m-3. Larger (> 18mm) fish migrated to the littoral zone and densities declined to < 0.01 fish m-3 by July, when remaining larval fish occupied greater daytime depths. Their vertical distribution during the day appeared to be influenced mainly by light levels and water temperatures. Larvae grew more slowly (0.12 mm d-1) than in more productive North Island lakes, and were also present in lower densities for a more restricted period of time. Koaro larvae first appeared in November and December and were found in low numbers (< 0.01 fish m-3) in summer at depths of 10 to 26 m. Salmonid production in the limnetic zone is probably limited by the small size and relative scarcity of forage fish present.

Carbon flow in the littoral food web of an oligotrophic lake

Benthic food web dynamics and carbon flow were examined in the littoral zone of Lake Coleridge, a large deep oligotrophic lake, using radioactive and stable isotope techniques in conjunction with analyses of stomach contents of the fauna. We specifically address two hypotheses: (1) that macrophytes only contribute to the carbon flow to higher trophic levels when they have decayed; and (2) that epiphytic algae is the major source of carbon for macroinvertebrates, and thus fish, with only minor contributions from phytoplankton or terrestrial sources. Epiphytic diatoms were a major component of the stomach contents of the gastropod snail Potamopyrgus antipodarum, and of chironomids. Animal remains were also common in the diet of some chironomids, while amorphous organic matter predominated in the stomachs of oligochaetes. A variety of epiphytic algal taxa was found in trichopteran larvae. Feeding rate of P. antipodarum measured with radioactive tracers increased by 10× on decayed macrophytes (Elodea) compared with live material, while feeding rates on characean algae increased by a factor of 3 when decayed material was presented. However, assimilation rates were less than 20% on decayed material compared with 48–52% on live material. Potential carbon sources were easily distinguished based on their δ13C values, although isotopic ratios showed significant variation among sites. Epiphytic algae showed less variation among sites than macrophytes and were depleted by 4–5‰ compared with macrophytes. Detrital material, organic matter in the sediments and plankton were significantly depleted in δ13C relative to macrophytes and slightly depleted relative to epiphytic algae. Most macroinvertebrate taxa showed a similar pattern among sites to macrophytes and epiphytic algae. P. antipodarum and chironomids were slightly enriched compared with epiphytic algae. Ratios for the common bully (Gobiomorphus cotidianus) were generally consistent with a diet dominated by chironomids, while there was some evidence for terrestrial inputs for koaro (Galaxias brevipinnis) and juvenile brown trout. Epiphytic algae appear to underpin much of the production in the littoral zone of this oligotrophic lake, with trichopteran and chironomid larvae mediating carbon flows from algae to fish. Macrophytes do not make a major contribution directly to carbon flow to higher trophic levels even when decayed. The lack of a direct link between macrophytes and higher trophic levels is due to the faunal composition, including a lack of large herbivores.

External forcing by wind and turbid inflows on a deep glacial lake and implications for primary production

Lake Coleridge is a deep monomictic lake in the Southern Alps of New Zealand which is affected by strong adiabatic winds. It receives significant inputs of inorganic suspended solids from rivers diverted into the lake for hydro‐electric generation. External inputs of wind energy and suspended solids to Lake Coleridge were quantified throughout 1 year and their impacts on hydrodynamics and the light climate were analysed. During stratification, the lake had a deep mixed layer, underlain by a complex metalimnion. High wind energy inputs caused large internal waves which resulted in the upwelling of hypolimnetic water, horizontal density gradients, and significant currents. Calculated vertical diffusivity and exchange coefficients were similar to those of much larger lakes. Analyses indicated that mixing in the metalimnion was often a result of shear stresses arising from vertical gradients in horizontal velocities. Whole lake total suspended solids (TSS) burdens were significantly correlated with the previous 13‐week integrated TSS loading from inflows. A seasonal pattern was observed where TSS from inflows entered either below, within or above the metalimnion. Evidence of effects of sediment resuspension from the marginal lake bottom was observed only when the lake level was low and the resulting impacts on the light climate were minimal. The synergistic effects of climate, thermal structure, and inflows resulted in the apparent light‐limitation of phytoplankton photosynthesis in winter months.

Recruitment and distribution of juvenile salmonids in Lake Coleridge, New Zealand

Rainbow trout (Oncorhynchus mykiss Richardson) and chinook salmon (O. tshawytscha Walbaum) fry and 0+ fingerlings entered Lake Coleridge, a deep, oligotrophic lake in the Southern Alps of New Zealand, in spring and early summer and dispersed throughout the shallow littoral. In contrast, most juvenile brown trout (Salmo trutta Linnaeus) remained in the tributaries for 1–2 years before migrating down stream to the lake. Juvenile salmonids (<35Omm) were more abundant in the shallow littoral (<10 m), especially near tributaries, than in the deep littoral (10–40 m), or the surface layers (0–16 m) of the limnetic zone which were populated by yearling (>150 mm) and adult salmon and rainbow trout (>210 mm). The abundance of 0+ rainbow trout in the littoral zone declined rapidly from February to August and stocks were supplemented by a migration of yearling fish from the tributaries in spring. The shallow littoral zone and tributaries are both important for juvenile trout rearing in this lake.

Mechanisms Underlying the Decline and Recovery of a Characean Community in Fluctuating Light in a Large Oligotrophic Lake

Between July 1993 and September 1994 Lake Coleridge, an oligotrophic New Zealand lake, underwent a period of abnormally low water clarity. Over this time, characean algal biomass in the littoral zone of the lake underwent a dramatic decline. Restoration of the lake’s normal high clarity followed and over the next 2 years there was a recovery of the community to close to pre-decline levels. Experimental and field studies investigated the mechanisms underlying the decline and recovery. The response of Chara corallina Willd. was investigated in detail. This plant responded to exposure to light below the instantaneous compensation point for photosynthesis by reducing rates of photosynthesis and respiration and depletion of storage products. This eventually led to the decay of the basal cells and detachment of plants from the sediment. In the lake, they were subsequently washed out of the littoral zone by wind-generated currents. When C. corallina, acclimated to below-compensating light levels, was returned to favourable light conditions in the laboratory, these trends were reversed. However, once biomass had been lost in the lake, recovery required growth of new plants. The most important methods of regeneration were by down-slope invasion and regrowth of buried shoots.

Macroinvertebrate distribution in the littoral zone of Lake Coleridge, South Island, New Zealand—effects of habitat stability, wind exposure, and macrophytes

The macroinvertebrate community was surveyed at eight littoral zone sites in Lake Coleridge, New Zealand. Sites covered a range of conditions including exposure to prevailing winds, shore‐line topography, and proximity to river inputs—which are a major source of suspended sediment to the lake. The littoral zone contained an abundant and diverse macroinvertebrate fauna (47 taxa). Three communities were identified: a shallow‐water community inhabiting the wave‐break zone, dominated by Trichoptera and chironomid larvae; a middle‐zone community associated with macrophyte beds, with high macroinvertebrate abundance and dominated by gastropods and oligochaetes; and a community in fine sediments below the macrophytes dominated by oligochaetes. The depth distribution of these communities was related to substrate, macrophyte abundance, and shore‐line profile. Superimposed on this pattern were the effects of hillside slope and exposure to prevailing north‐west winds. Greatest abundance was associated with macrophytes on stable shores at 4–7.5 m depth, i.e., below the effective wavebase depth. Sediment deposition had only a localised direct effect close to where river water enters the lake. Indirect effects were mediated through the effects of suspended solids on water clarity, bottom limits, and production of macrophytes and periphyton. Estimates of the proportion of littoral macroinvertebrate biomass to whole‐lake zooplankton biomass was 10:1 and for production was 1.3:1, indicating the potential importance of the littoral zone to whole‐lake production.

Effects of changing water clarity on characean biomass and species composition in a large oligotrophic lake

The biomass and species composition of characean meadows in oligotrophic Lake Coleridge, New Zealand, were monitored over a 2 year period during which water clarity underwent significant fluctuation. Water clarity, measured as vertical attenuation coefficient ( K d), varied between 0.1 and 0.4 m −1 and there was a period of prolonged low clarity in the middle of the study. Characean meadows extended to a maximum depth of over 30 m at the start of the study in April 1993 but were reduced to less than 20 m by July 1995. At depths of 5, 10 and 15 m, where characean meadows persisted through to July 1995, there was a change in species composition, with an upward shift in the proportions of dominant taxa. This change was manifested as an increase in the percentage contribution to biomass of Chara globularis and Chara corallina at the expense of Chara fibrosa. Over the entire study period characean biomass remained maximal at depths of 5 and 10 m at approximately 180 g (dry weight) m −2. At a depth of 5 m, biomass was not affected by changing water clarity and appeared to be limited by exposure to wave action and variable water level. At depths greater than 10 m, biomass declined significantly over the study period of 2 years. Reductions could be related to the underwater light field which plants experienced over the period between each sampling. Total characean biomass declined below maximal when irradiance fell below 1.0 mol m −2 day −1. Despite an increase in water clarity in early 1995, recovery of biomass was not observed within the time scale of this study.

Epiphytes from a deep‐water characean meadow in an oligotrophic New Zealand lake: species composition, biomass and photosynthesis

1. The epiphytic flora of a characean meadow in Lake Coleridge, a deep, oligotrophic lake on the South Island of New Zealand, was dominated by diatoms, particularly Eunotia pectinalis and Achnanthes minutissima. The meadows occupied a depth range from 5 to 30 m. Adnate taxa predominated at all depths below 5 m, while increased taxonomic diversity at 5 m resulted from an increased abundance of erect taxa, including chlorophytes and stalked diatoms.2. Seasonal changes in epiphyte biomass were followed using artificial substrata and by estimating epiphyte chlorophyll a concentration on host plants. The latter required development of a novel technique utilizing the consistent relationship between fucoxanthin and chlorophyll a concentrations in the epiphyton. Epiphyte chlorophyll a on host plants varied with depth and host species between 0.1 and 0.3 mg g–1 dry weight. Maximum epiphyte biomass was at 10–15 m depth. At depths of 15 m and less, epiphyte chlorophyll a reached a maximum of ≈ 200–300 mg m–2 in mid‐summer, while at greater depths maximum biomass was less and coincided with a period of clear water in spring.3. Photosynthetic carbon fixation was estimated from photosynthesis–radiation curves and estimates of radiation flux at sampling depths. At depths greater than 10 m, variability of the vertical extinction coefficient of lake water rather than seasonal fluctuations in incident radiation were responsible for determining the temporal pattern of production. Chlorophyll a‐specific photosynthesis was estimated to peak in summer at 5 m (8 mg mg–1 day–1), and in spring at all other depths.4. Annual epiphyte production was estimated as 27 g C m–2 year–1 at 5 m depth, falling to 15 g C m–2 year–1 at 15 m and 1 g C m–2 year–1 at 30 m. Areal biomass changes tended to be temporally but not quantitatively coupled to estimated in situ photosynthesis, and we hypothesize that epiphyte biomass may have been controlled by grazing gastropod snails.

Modelling surface oscillations in New Zealand lakes

Abstract Lake seiching was modelled using the Finite Element Method combined with eigen‐analysis to calculate the natural modes of oscillation. The model results are compared with analytical solutions for some simple geometrical lakes and are found to be dependent on the grid fineness. The model was then applied to three lakes in the South Island of New Zealand: Lake Ohau, Lake Coleridge, and Lake Te Anau. The resulting periods of oscillation were in reasonable agreement with measured data. The model can be used for selecting new recorder sites, setting the recorder interval, and for removing the effect of seiche.

Determination of the age of brown and rainbow trout in a range of New Zealand lakes

Brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) from eight New Zealand lakes were aged by length-frequency analysis and by examining otoliths, pectoral fin rays and scales. Bimonthly changes in the length frequency of age classes were used to age fish for their first 2 or 3 years of life. Growth rates were highest in spring and summer, when a single wide opaque band was laid down on otoliths and fin rays, followed by a narrow transparent band in winter. Age estimates from otoliths agreed with 94-97% of those from length-frequency methods and with the ages of 21 tagged fish. Otoliths were used to age fish up to 11 years old and were more accurate than fin rays and scales. Although fin rays could be used to age juvenile fish from Lake Coleridge, where there was 78-80% agreement between otolith and fin ray ages, they were of little value for older fish in Lake Alexandrina (28% agreement). Rainbow trout scales from all lakes were difficult to read because of indistinct annuli and the presence of false checks. Mature trout were also difficult to age owing to scale absorption and a cessation of scale growth. The degree of agreement between otolith and scale ages ranged from 83-84% for trout in Lake Coleridge to 32-38% for older rainbow trout in other lakes. This study supports the findings of other researchers that trout scales can provide inaccurate estimates of the age of trout in New Zealand and Australia. It is suggested that otolith examination, supported by length-frequency analysis of juvenile trout, be used to age trout from New Zealand lakes. In many cases, examination of otoliths will be cheaper and quicker than the release and later recapture of fin-clipped or tagged juvenile trout.

Movements and habitat preference of adult rainbow trout (Oncorhynchus mykiss) in a New Zealand montane lake

Abstract Adult rainbow trout (Oncorhynchus mykiss) in Lake Coleridge were tagged with ultrasonic transmitters in 1992, and tracked for up to a year to determine movements, and spatial and temporal changes in habitat preference. Three types of movement were identified: wide‐ranging covering much of the lake, localised within the littoral, and migratory towards river mouths before spawning. Maximum swimming speeds up to 2.27 km h−1 were observed, and speeds of 0.5 km h−1 over several hours were recorded for two fish tracked in the limnetic zone. Adult rainbow trout inhabited littoral areas through winter and spring, with most shifting to a limnetic habitat in summer and early autumn. We suggest that the wide‐ranging limnetic lifestyle is in response to opportunities for feeding on ichthyoplankton, notably larval bullies and galaxiids. Some individuals remained in littoral areas throughout the year, apparently having adopted a benthic/nearshore feeding strategy. As winter approached several fish moved toward...

A macrofossil flora from sediments in a lagoon marginal to Lake Coleridge, Canterbury, New Zealand

Abstract Macrofossils from woody plants and a radiocarbon date (conventional radiocarbon age 7273 ± 104 yr B.P.) from the bottom sediments in a lagoon marginal to Lake Coleridge indicate that mixed podocarp-angiosperm forest was present in the middle Rakaia River basin during most of the Aranuian (post-glacial) period. Among the forest species at Lake Coleridge were some (Prumnopitys taxifolia, Elaeocarpus hookerianus, and Melicope simplex) not present there now and only sparsely represented now anywhere in the middle Rakaia basin. Other aspects of forest history in the region are considered, including changes during the Aranuian and widespread destruction by fire within the last few centuries.

Ground shaking intensity and damage at Lake Coleridge power station in the 18 June 1994 Avoca River earthquake

Apart from highway bridges and embankments, the only major structures close to the epicentre of the 18 June 1994 Avoca River magnitude ML 6.5 were at the Lake Coleridge hydo power scheme. At the power-house location, the peak ground acceleration reached 0.14 g and the felt intensity was estimated as MMI VII.&#x0D; Because most of the buildings and civil structures at the scheme are more than 60 years of age their performance under the moderate level of shaking was of particular interest. Damage to the buildings and other structures was minor and it is thought that the ground shaking intensity was just below the threshold level above which more serious damage might be expected.