Does one size fit all? An evaluation of length–weight relationships for New Zealand's freshwater fish species     

PG Jellyman  DJ Booker  SK Crow  ML Bonnett  DJ Jellyman 《新西兰海洋与淡水研究杂志》2013,47(4):450-468

Length–weight relationships are a fundamental tool for assessing populations and communities in fisheries science. Many researchers have collected length–weight data throughout New Zealand, yet parameters describing these relationships remain unpublished for many species of freshwater fish. We compiled 285,124 fish records from researchers and institutions across New Zealand to parameterise length–weight equations, using both power and quadratic models, for 53 freshwater species belonging to 13 families. The influence of location and sex on length–weight relationships was also assessed. Location, in particular, generated different length–weight relationships for 65% of the species examined. Length–weight equations were validated by comparing predicted weights against independently measured weights from 25 electrofished sites across New Zealand and the equations were highly accurate (R²>0.99). Recommendations are made about how to robustly apply this new resource which should assist freshwater fisheries researchers throughout New Zealand.  相似文献   

Estimating periphyton standing crop in streams: a comparison of chlorophyll a sampling and visual assessments     

C Kilroy  DJ Booker  L Drummond  JA Wech  TH Snelder 《新西兰海洋与淡水研究杂志》2013,47(2):208-224

Periphyton standing crop is often measured as chlorophyll a but there is increasing interest in using visual assessments of periphyton cover. Visual methods are rapid and require no sample analysis, but can be regarded as subjective with high inter-operator variability. We investigated variability in periphyton standing crop across operators, rivers and time, as determined visually and from chlorophyll a measurements. We found that visual assessments (comprising percentage cover estimates of up to eight periphyton categories) distinguished sites and occasions as effectively as chlorophyll a. Furthermore, an estimate of chlorophyll a could be derived from the visual assessments. Because our surveys were conducted in only three rivers, general applicability of the derivation of estimated chlorophyll a from the visual assessments warrants further investigation. The current recommendation of 20 views was sufficient for realistic visual assessments of average cover. Overall, our results indicated that inter-operator variability in visual assessments need not be a major concern, given adequate training.  相似文献   

Late Holocene Marsh Expansion in Southern San Francisco Bay, California     

Elizabeth Burke Watson  Roger Byrne 《Estuaries and Coasts》2013,36(3):643-653

Currently, the largest tidal wetlands restoration project on the US Pacific Coast is being planned and implemented in southern San Francisco Bay; however, knowledge of baseline conditions of salt marsh extent in the region prior to European settlement is limited. Here, analysis of 24 sediment cores collected from ten intact southern San Francisco Bay tidal marshes were used to reconstruct spatio-temporal patterns of marsh expansion to provide historic context for current restoration efforts. A process-based marsh elevation simulation model was used to identify interactions between sediment supply, sea-level rise, and marsh formation rates. A distinct age gradient was found: expansion of marshes in the central portion of southern San Francisco Bay dated to 500 to 1500 calendar years before present, while expansion of marshes in southernmost San Francisco Bay dated to 200 to 700 calendar years before present. Thus, much of the tidal marsh area mapped by US Coast Survey during the 1853–1857 period were in fact not primeval tidal marshes that had persisted for millennia but were recently formed landscapes. Marsh expansion increased during the Little Ice Age, when freshwater inflow and sediment influx were higher than during the previous millennium, and also during settlement, when land use changes, such as introduction of livestock, increased watershed erosion, and sediment delivery.  相似文献   

Finding a “Disappearing” Nontimber Forest Resource: Using Grounded Visualization to Explore Urbanization Impacts on Sweetgrass Basketmaking in Greater Mt. Pleasant,South Carolina∗     

Patrick T. Hurley  Angela C. Halfacre  Norm S. Levine  Marianne K. Burke 《The Professional geographer》2013,65(4):556-578

Despite growing interest in urbanization and its social and ecological impacts on formerly rural areas, empirical research remains limited. Extant studies largely focus either on issues of social exclusion and enclosure or ecological change. This article uses the case of sweetgrass basketmaking in Mt. Pleasant, South Carolina, to explore the implications of urbanization, including gentrification, for the distribution and accessibility of sweetgrass, an economically important nontimber forest product (NTFP) for historically African American communities, in this rapidly growing area. We explore the usefulness of grounded visualization for research efforts that are examining the existence of “fringe ecologies” associated with NTFP. Our findings highlight the importance of integrated qualitative and quantitative analyses for revealing the complex social and ecological changes that accompany both urbanization and rural gentrification.  相似文献   

Effect of groundwater pH and ionic strength on strontium sorption in aquifer sediments: Implications for Sr mobility at contaminated nuclear sites     

Sarah H. Wallace  Samuel Shaw  Katherine Morris  Joe S. Small  Adam J. Fuller  Ian T. Burke 《Applied Geochemistry》2012

Strontium-90 is a beta emitting radionuclide produced during nuclear fission, and is a problem contaminant at many nuclear facilities. Transport of ⁹⁰Sr in groundwaters is primarily controlled by sorption reactions with aquifer sediments. The extent of sorption is controlled by the geochemistry of the groundwater and sediment mineralogy. Here, batch sorption experiments were used to examine the sorption behaviour of ⁹⁰Sr in sediment–water systems representative of the UK Sellafield nuclear site based on groundwater and contaminant fluid compositions. In experiments with low ionic strength groundwaters (<0.01 mol L⁻¹), pH variation is the main control on sorption. The sorption edge for ⁹⁰Sr was observed between pH 4 and 6 with maximum sorption occurring (K_d ∼ 10³ L kg⁻¹) at pH 6–8. At ionic strengths above 10 mmol L⁻¹, and at pH values between 6 and 8, cation exchange processes reduced ⁹⁰Sr uptake to the sediment. This exchange process explains the lower ⁹⁰Sr sorption (K_d ∼ 40 L kg⁻¹) in the presence of artificial Magnox tank liquor (IS = 29 mmol L⁻¹). Strontium K-edge EXAFS spectra collected from sediments incubated with Sr²⁺ in either HCO₃-buffered groundwater or artificial Magnox tank liquor, revealed a coordination environment of ∼9 O atoms at 2.58–2.61 Å after 10 days. This is equivalent to the Sr²⁺ hydration sphere for the aqueous ion and indicates that Sr occurs primarily in outer sphere sorption complexes. No change was observed in the Sr sorption environment with EXAFS analysis after 365 days incubation. Sequential extractions performed on sediments after 365 days also found that ∼80% of solid associated ⁹⁰Sr was exchangeable with 1 M MgCl₂ in all experiments. These results suggest that over long periods, ⁹⁰Sr in contaminated sediments will remain primarily in weakly bound surface complexes. Therefore, if groundwater ionic strength increases (e.g. by saline intrusion related to sea level rise or by design during site remediation) then substantial remobilisation of ⁹⁰Sr is to be expected.  相似文献   

The intensity variations of solar and galactic cosmic rays with azimuthal angle in the polar region     

DJ. Heristchi  J.-P. Legrand 《Planetary and Space Science》1976,24(3):281-285

A balloon-born multidirectional detector is used to measure the intensity variation of galactic and solar cosmic rays with the azimuthal angle, the zenith angle being maintained at 60°. In polar regions, the intensity towards the north is found to be 20% larger than that towards the south. It is shown that this anisotropy does not originate in interplanetary space and is not produced by a magnetospheric source. It is suggested that the effect is due to propagation effects within the magnetosphere.  相似文献   

Planetary systems: Formation,evolution, and detection - introduction     

Bernard F. Burke 《Astrophysics and Space Science》1994,212(1-2):xi-xii

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Imaging the Sun at 21 cm: Budgetting the S-component     

I. E. Burke  K. F. Tapping 《Solar physics》1995,157(1-2):295-314

On fourteen days in July and August 1992 and June 1993, we used the 7-element synthesis radio telescope at the Dominion Radio Astrophysical Observatory to make full-disc, arc-min resolution images of the Sun at 21 cm, with the objective of budgetting the contributions to the slowly-varying component of solar radio emission. This instrument has the advantage that the mapping field at this wavelength is about 2.5° wide. However, it has also the severe disadvantage that with only 12 hours to record each image, the brightness distribution is severely undersampled. This difficulty, along with solar rotation and declination motion during each observation, required development of special image correction procedures.The two observing sessions spanned about 25% of the activity range over a solar cycle. Over this range, comparable contributions to the slowly-varying component came from active region sources and a weak emission, widely-distributed over the solar disk. Both these contributions are correlated with the total photospheric magnetic flux and with the 10.7 cm flux.  相似文献   

Changing elevation,accretion, and tidal marsh plant assemblages in a South San Francisco Bay tidal marsh     

Elizabeth?Burke?WatsonEmail author 《Estuaries and Coasts》2004,27(4):684-698

Analyses of organic content, pollen, and the carbon-isotopic composition of a 3.5-m sediment core collected from a subsided tidal marsh located in South San Francisco Bay, California, have provided a 500-yr record of sediment accretion and vegetation change before, during, and after a rapid 1 m increase in sea level. Core chronology was established using¹⁴C dating of fossil plant material, the first appearance of pollen types produced by plants not native to California, and changes in lead concentrations coincident with anthropogenic contamination. Prior to the mid 19th century, rates of sediment accretion were between 1 and 4 mm yr⁻¹; sediment accretion accelerated to an average of 22 mm yr⁻¹ following the initiation of subsidence. Changes in tidal marsh vegetation also accompanied this depositional change. Vegetation shifted from a high to low marsh assemblage, as indicated by a larger percentage of grass pollen, rhizomes ofSpartina foliosa, and a strong C₄ signal. Between 1980 and 2001, Triangle marsh again developed high marsh vegetation, as indicated by higher percentages of the Amaranthaceane pollen type, seed deposition, includingSalicornia spp., and more negative carbon isotopic ratios.  相似文献   

The Annual Meeting of Political Geographers     

Terence Burke 《The Professional geographer》1967,19(5):282-283

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