摘要:

Lagarosiphon majorhas successfully out‐competed native species wherever it has colonised New Zealand lakes in the depth zone 2–6 m—normally occupied by native milfoils(Myriophyllumspp.) and pondweeds(Potamogetonspp.). In this investigation we examined the early growth stages ofL. majorandM. triphyllum. Both species showed an initial lag in shoot growth when grown from vegetative shoot propagules in situ. During this lag in shoot growth, the development of a functional root system was apparent. The length of the lag in shoot growth appeared dependent on the ability to utilise internal nutrient stores and on the water nutrient availability. However, irrespective of nutrient status,L. majoralways grew better thanM. triphyllum. In laboratory experiments investigating this lag phase,L. majornot only produced roots faster, it also grew faster, both in length and biomass, than the nativeM. triphyllum. This suggests thatL. majorhas an early competitive advantage which may explain the dominance this species now has in the littoral zones of many New Zealand lakes.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516611

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Underwater census and single‐pass electrofishing were compared for estimating relative abundance of juvenile brown trout in the Kakanui River, South Island, NZ. Mean sampling efficiency was lower, and the variability of sampling efficiency was much greater, for underwater census (0+ trout: x = 0.38,s =0.368; 1+ trout: x = 0.62,s= 0.822) than for single‐pass electrofishing (0+ trout: x = 0.61,s= 0.143; 1+ trout: x = 0.74, s = 0.171). Sampling efficiency of both methods was dependent on temperature. Electrofishing became less efficient at higher temperatures whereas underwater census became less efficient at colder temperatures. The low, and highly variable, sampling efficiency for underwater census of 0+ brown trout was related to substrate hiding behaviour which is dependent on temperature. A ratio method for comparing relative abundance estimates is presented. Minimum significance values for the ratio (R) were derived for 0+ trout using temperature adjusted sampling efficiencies. To be statistically significant, relative abundance estimates made by underwater census had to differ by a factor of 6–7 times, whereas those made by single‐pass electrofishing had to differ only by about 2 times, depending on the number of fish counted. By confining comparisons of relative abundance estimates made by underwater census to the summer period, differences of about 3.5–4 times could be detected statistically. It was concluded that single‐pass electrofishing is superior to underwater census for estimating the relative abundance of juvenile brown trout in shallow (< 1 m) river habitat, especially when temperature varies widely as with season and time of day.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516612

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The distribution of fish and benthic invertebrates in relation to riparian willow(Salixspp.) concentrations was investigated in three New Zealand streams. In each of the streams, representative sites were sampled quantitatively in willowed and non‐willowed sections. The abundance (m‐2) and biomass (g m‐2) of brown trout(Salmo truttaL.) were significantly greater in the willowed than in the non‐willowed sections in two streams; the third stream showed the same trend but any differences were not significant. Mean size of trout was greater in the willowed than in the non‐willowed sections, but size of fish varied greatly and the differences were not significant. Eels(Anguillaspp.) showed no consistent pattern in population characteristics between streams; however, their abundance in one river and biomass in another were significantly greater in the willowed than in the non‐willowed sections. Distribution of other fish (e.g.,Galaxiasspp. andGobiomorphusspp.) appeared not related to riparian willows. The abundance and biomass of several benthic invertebrate taxa (e.g., Ephemeroptera, Trichoptera, Diptera) differed significantly in relation to riparian willow concentrations. In all three streams, species richness and diversity of the benthic invertebrates were greater in the willowed than the non‐willowed sections, with moderate degrees of similarity between the communities. Moderately‐willowed riparian zones are beneficial to trout and food organisms in streams and small rivers.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516613

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The effects of an introduced willow tree species(Salix fragilis)on the densities of macroinvertebrates were examined in two Central Otago, New Zealand, streams during 1991. Significantly lower invertebrate densities and biomass were observed in willow‐lined sections of the streams than in nearby open sections in summer, autumn, and winter. This result was observed in riffles and pools, for most dominant species and nearly all functional feeding groups. The effect was not associated with differences in the amount of fine paniculate organic matter (< 1 mm), stone surface organic layer biomass, or chlorophyllaconcentration, which were similar it open and willow‐shaded sites. Amounts of coarse paniculate organic matter (> 5 mm) were significantly higher in willow‐shaded riffles, but this did not result in increased abundance or biomass of shredders. Willow trees reduced incident stream illumination by as much as 80%, but did not appear to influence water chemistry between open and willow‐shaded sites. The decreased invertebrate densities probably result from a decrease in average substrate size and/or a lowering of food production through shading effects.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516614

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A survey of benthic invertebrates and associated environmental factors was carried out in three Southland streams in relation to developed and undeveloped pasture over 15 months in 1985— 1987. In all three streams the invertebrate community changed in the sections within developed pasture in such a way as to suggest pollution, although no point sources were present. Numbers ofDeleatidiumspp.,Pycnocentrodes aureola, Olingaferedayi, Archichauliodes diversus, Aoteapsyche colonica, and Plecoptera tended to decrease in the developed pasture area, whereas numbers ofPotamopyrgus antipodarum, Physastra variabilis, Gyraulus corinnaand Oligochaeta tended to increase. Stepwise regression was carried out on six environmental variables vs seven of the more numerous taxa. Significant regressions atP <0.01 were obtained for 7 out of 21 instances, but little consistency was apparent across streams or taxa. The significant regressions that were obtained did not explain readily the tendency towards a pollution‐type community, and it is suggested that dips and drenches used on sheep in the developed pastures could be partly responsible for some of the changes.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516615

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

DDT, DDE, and DDD (up to 0.5 ng g‐1per compound) and traces of dieldrin (< 0.1 ng g‐1), were detected in surficial sediments collected from four sites in the greater Tauranga Harbour. An elevated level of PCBs (19.9 ng g‐1) was identified in a Waikareao Estuary sample. PCB and DDT levels of up to 24.1 ng g‐1and 5.38 ng g‐1,respectively, were subsequently detected in other eastern shore Waikareao Estuary sediment samples. Higher levels of PCBs (68.6 and 73.8 ng g‐1) and DDTs (total 7.52 and 19.2 ng g‐1) were detected in sediments from two eastern shore stormwater drains identified as the likely sources of the PCB and DDT burden entering the Waikareao Estuary. Black, carbonaceous, coal‐ and asphalt‐like, paniculate material (98% loss of organic carbon on ignition), isolated by sieving a representative sediment sample, exhibited DDT and PCB levels which were respectively 85 and 6 times higher than was the case for other sieved fractions.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516616

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The distribution of the picophytoplankton community of the West Coast region of South Island, New Zealand, was investigated during a period of thermal stratification in February 1989. The < 2 urn size fraction was found to account for a significant proportion of the plankton biomass, with up to 73% of the particulate nitrogen and phosphorus occurring in this size class. The spatial variability of the picophytoplankton community was high with cell concentrations in the range 1.5–10.7 × 107cells I‐1. The vertical distribution of cell numbers was highly variable, although the maximum cell concentrations occurred in the mixed layer in all but two of the 15 stations sampled. At these two stations the maximum cell concentration coincided with the deep chlorophyllamaxima in the region of the pycnocline. The composition of the picophytoplankton community was highly variable with the P:E ratio ranging from 5.7 to 162 within the mixed layer. Maximum concentration of eukaryotic cells occurred either just below or just above the pycnocline where NO3concentrations were elevated. This study has illustrated the high degree of spatial variability in the composition of the picophytoplankton population of the West Coast region. Some of this variation can be attributed to physico‐chemical environmental factors such as nutrient supply impacting on growth rates.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516617

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

New Zealand isolates ofVibrio anguillarumfrom water, sediments and healthy salmon were tested for their ability to grow under iron‐limiting conditions and to produce sidero‐phores. Their growth in the presence of the iron chelator ethylenediamine‐di(o‐hydroxyphenyl‐acetic acid) (EDDA) suggested they could withstand conditions of iron limitation, with a 200 μM EDDA MIC recorded for the majority of strains. A positive reaction in the chrome azurol sulphate assay after growth in a low iron‐containing medium, which was negated when the medium was supplemented with 10 μM iron, indicated they could produce siderophores. The siderophores were of the phenolate class and their biological activities indicated they were related to enterobactin.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516618

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A turbulent eddy viscosity model based on analytical expressions for the energy dissipation in a bore is presented to predict wave conditions in the surf zone. The computational model, based on the Boussinesq equations, has been tested for a bar‐trough beach in random waves, and the results are compared with wave flume measurements. The root‐mean‐square (rms) values of the wave heights in the breaker zone are well predicted, but detailed features of the setup are not accurately presented by the model.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516619

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516620

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor