摘要:

Juveniles of giant kokopu(Galaxias argenteus(Gmelin)) that had newly entered fresh water were captured, primarily from the Buller and Hokitika Rivers, New Zealand, between 5 November and 15 December (when sampling ceased). Age at migration estimated from otolith daily growth rings was mostly c. 104–140 days. There is a positive relationship between fish length and number of otolith growth rings at migration, though variation is broad. Back calculation to hatch indicated that hatching occurred 185–245 days after 1 January (4 July‐2 September); allowing 28 days for development, these data suggest that giant kokopu spawn between early June and early August.

ISSN:0028-8330    

DOI:10.1080/00288330.1999.9516875

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper describes studies on the settlement of the abaloneHaliotis australisGmelin. Ten‐day‐oldH. australislarvae had a slower rate of settlement than 5‐day‐old larvae. A high proportion of veliger larvae had the ability to prolong the searching phase of settlement and delay metamorphosis, even over prepared settlement surfaces but radula development continued at a similar rate in both settled and swimming larvae. In any one batch of larvae settlement was slow and asynchronous and post‐settlement survival was low. Light was shown to influence the swimming behaviour of larvae in settlement tanks, with more larvae swimming in the dark than in the light. The implications of these behaviours are discussed in relation to larval and post‐larval energetics and feeding.

ISSN:0028-8330    

DOI:10.1080/00288330.1999.9516876

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A natural‐gradient tracer experiment and laboratory batch tests were conducted to study attenuation and transport of atrazine and picloram in an alluvial gravel aquifer. An analytical transport model, AT123D, was used to analyse the field data. Data analysis suggests that there was no retardation and degradation of atrazine and picloram in the aquifer over a distance of 90 m within a period of 49 h. In the batch tests with a much longer time duration (194 days), atrazine concentrations significantly decreased and picloram concentrations showed a small decrease. It is considered that the rapid decrease in atrazine levels in the first 2 days was sorption‐dominated and the slow decrease subsequently was mainly because of degradation and partially the result of slow sorption. If it is assumed that the decrease in the first 2 days was all the result of sorption and it had reached equilibrium, the estimatedKdvalues are 0.04 ml/g for atrazine, and 0.02 ml/g for picloram. Rates of atrazine degradation estimated from the data after 2 days (slow rate of decrease) are 3.4 × 10‐3per day (equivalent half‐life 204 days), and 3.0 × 10‐3per day (equivalent half‐life 231 days), for total and chemical degradation, respectively, assuming that there was no adsorption after 2 days. No degradation rate could be determined from the picloram data of the batch tests because of its highly noisy data and insignificant decrease in concentrations. The significantly higher attenuation parameters derived from the batch tests compared to those derived from the field data suggests that attenuation of pesticides in the field is affected by other factors, such as aquifer heterogeneity and preferential flow, and flow hydrodynamics etc., which should be taken into account when applying laboratory‐derived values to the field conditions.

ISSN:0028-8330    

DOI:10.1080/00288330.1999.9516877

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Three first‐order, hill country, pasture streams in Waikato, New Zealand, were chosen to investigate the effects of patches of late‐succession indigenous riparian forest on water quality, epilithon, stream morphology, and aquatic macro‐invertebrates. Sites were situated in open pasture and at two distances (c. 50 and 300 m) into a forest remnant on each stream. Shade, channel width, and epilithon biomass were restored to conditions similar to a native forest control site within 300 m of the streams entering the native forest remnants, whereas water chemistry and levels of surficial fine sediment changed more slowly. Invertebrate community composition showed shifts towards the native forest condition just 50 m into the forest remnants, and full recovery had occurred within 300 m. Results from this study suggest that discontinuous restoration of riparian margins could mitigate some changes associated with pastoral land use, but sediment and water quality problems may not be solved.

ISSN:0028-8330    

DOI:10.1080/00288330.1999.9516878

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

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.

ISSN:0028-8330    

DOI:10.1080/00288330.1999.9516879

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor