Assessing changes in nutrient status in the Richmond River estuary,Australia, using paleolimnological methods   总被引：1，自引：0，他引：1  

Brendan Logan  Kathryn H. Taffs  Bradley D. Eyre  Atun Zawadski 《Journal of Paleolimnology》2011,46(4):597-611

Eutrophication from nutrient over-enrichment is a serious problem for the coastal zone and the estuarine environment globally. Australian estuaries are generally oligotrophic, but assessing whether they are becoming more eutrophic over time is inhibited by a lack of long-term monitoring data. The Richmond River, Australia, provided an ideal example of an estuary under anthropogenic pressure where the use of paleoecological techniques may potentially be used to reconstruct changes in nutrient status over time. Five cores were extracted from depositional areas in the Richmond River, and subjected to paleo-magnetic profiling and loss-on-ignition testing to ensure the core of greatest integrity was selected for further analytical work. Results from diatom and stable isotope analyses combined with ²¹⁰Pb and AMS ¹⁴C dating show a strong indication that the total phosphorus levels in the Richmond River have fluctuated since 1940. Evidence also suggests that these fluctuations are most likely a function of climate. This study has successfully applied paleolimnological techniques to the estuarine environment to produce information that can be used by environmental managers to aid decision making in relation to nutrient control for the Richmond River. Further work using paleolimnological techniques should be aimed at the extraction of a core containing diatoms that pre-date European settlement and include analyses of specific lipids and fatty acid biomarkers.  相似文献   

Book reviews     

G. Kunkel  Gerd Wikan  Richard F. Logan  Viggo Hansen  Barry Floyd  Roland Bono  J. Fernie  E. M. Yates 《GeoJournal》1986,12(2):223-226

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Effects of Docks on Salt Marsh Vegetation: an Evaluation of Ecological Impacts and the Efficacy of Current Design Standards     

John M. Logan  Amanda Davis  Charles Markos  Kathryn H. Ford 《Estuaries and Coasts》2018,41(3):661-675

Private docks are common in estuaries worldwide. Docks in Massachusetts (northeast USA) cumulatively overlie ~ 6 ha of salt marsh. Although regulations are designed to minimize dock impacts to salt marsh vegetation, few data exist to support the efficacy of these policies. To quantify impacts associated with different dock designs, we compared vegetation characteristics and light levels under docks with different heights, widths, orientations, decking types and spacing, pile spacing, and ages relative to adjacent control areas across the Massachusetts coastline (n = 212). We then evaluated proportional changes in stem density and biomass of the dominant vegetation (Spartina alterniflora and Spartina patens) in relation to dock and environmental (marsh zone and nitrogen loading) characteristics. Relative to adjacent, undeveloped habitat, Spartina spp. under docks had ~ 40% stem density, 60% stem biomass, greater stem height and nitrogen content, and a higher proportion of S. alterniflora. Light availability was greater under taller docks and docks set at a north-south orientation but did not differ between decking types. Dock height best predicted vegetation loss, but orientation, pile spacing, decking type, age, and marsh zone also affected marsh production. We combined our proportional biomass and stem elemental composition estimates to calculate a statewide annual loss of ~ 2200 kg dry weight of Spartina biomass (367 kg per ha of dock coverage). Managers can reduce impacts through design modifications that maximize dock height (> 150 cm) and pile spacing while maintaining a north-south orientation, but dock proliferation must also be addressed to limit cumulative impacts.  相似文献   

Ecology of Diloma nov Aezelandiae at Portobello,New Zealand     

Sheila J. Logan 《新西兰海洋与淡水研究杂志》2013,47(4):699-714

Some aspects of the biology of Diloma (Fractarmilla) novaezelandiae (Anton) (= Zediloma subrostrata), a soft‐shore trochid gastropod, were investigated in Latham Bay, Portobello, South Island, New Zealand (45° 50’ 25” S, 170° 38’ 30” E). The distribution of D. novaezelandiae during September 1973 to June 1974 was recorded along three transects; pebble distribution, macroalgal cover, grain‐size distribution and organic carbon content in the sediment, range of water salinity, and length of time of exposure to air were also recorded along the transects.

The greatest population density of D. novaezelandiae occurred between 0.8 m and 1.4 m above Chart Datum. The trochid was found to prefer a hard substratum to a soft substratum, and there was a positive correlation of organic content of the sediment with density of D. novaezelandiae. As the population density decreased towards low water the individual shell size increased. Size: weight relationships were calculated and the results showed that dry flesh weight and dry shell weight were both proportional to the cube of the shell diameter.  相似文献   

On the causes of volcanic action     

J. Logan Lobley 《Proceedings of the Geologists' Association. Geologists' Association》1889,11(1):1-13

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Excursion to Tilgate forest,Cuckfield, and Haywards heath. (Central elevations of the Weald.): Saturday,May 20th, 1882     

J. Logan Lobley 《Proceedings of the Geologists' Association. Geologists' Association》1882,7(6):372-376

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“On the stratigraphical distribution of the British Fossil Brachiopoda”     

J. Logan Lobley 《Proceedings of the Geologists' Association. Geologists' Association》1871,2(2):60

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An isotopic biogeochemical study of Neoproterozoic and Early Cambrian sediments from the Centralian Superbasin, Australia   总被引：4，自引：0，他引：4  

Logan GA  Summons RE  Hayes JM 《Geochimica et cosmochimica acta》1997,61(24):5391-5409

Organic matter from Neoproterozoic and Early Cambrian sediments of the Amadeus and Officer basins of the Centralian Superbasin, Australia, has been studied for biomarker distributions and the carbon isotopic compositions of kerogen and individual hydrocarbons. These sediments represent both shallow and deep water marine facies in the older sections and marine and saline lacustrine carbonate deposits in the Cambrian. Hydrocarbon biomarker patterns were found to be quite consistent with the known sedimentary environments and provide valuable insights into the biogeochemical changes which accompanied the transition from a microbially-dominated ocean to the early stages of metazoan radiation. In particular, carbon isotopic data for n-alkyl and isoprenoid lipids presented here, and in earlier studies, showed a reversal in carbon isotopic ordering between the Proterozoic and Phanerozoic. By comparison with the delta 13C of kerogen, n-alkyl lipids from deep-water Proterozoic sediments were enriched in 13C and appear to be derived mainly from heterotrophs whilst open marine Phanerozoic counterparts are 13C depleted and evidently derived mainly from autotrophs. Data from the samples studied here are consistent with a model invoking a change in the redox structure of the ocean, possibly aided by the innovation of faecal pellets.  相似文献   

Bedform response to flow variability     

J. M. Nelson  B. L. Logan  P. J. Kinzel  Y. Shimizu  S. Giri  R. L. Shreve  S. R. McLean 《地球表面变化过程与地形》2011,36(14):1938-1947

Laboratory observations and computational results for the response of bedform fields to rapid variations in discharge are compared and discussed. The simple case considered here begins with a relatively low discharge over a flat bed on which bedforms are initiated, followed by a short high‐flow period with double the original discharge, during which the morphology of the bedforms adjusts, followed in turn by a relatively long period of the original low discharge. For the grain size and hydraulic conditions selected, the Froude number remains subcritical during the experiment, and sediment moves predominantly as bedload. Observations show rapid development of quasi‐two‐dimensional bedforms during the initial period of low flow with increasing wavelength and height over the initial low‐flow period. When the flow increases, the bedforms rapidly increase in wavelength and height, as expected from other empirical results. When the flow decreases back to the original discharge, the height of the bedforms quickly decreases in response, but the wavelength decreases much more slowly. Computational results using an unsteady two‐dimensional flow model coupled to a disequilibrium bedload transport model for the same conditions simulate the formation and initial growth of the bedforms fairly accurately and also predict an increase in dimensions during the high‐flow period. However, the computational model predicts a much slower rate of wavelength increase, and also performs less accurately during the final low‐flow period, where the wavelength remains essentially constant, rather than decreasing. In addition, the numerical results show less variability in bedform wavelength and height than the measured values; the bedform shape is also somewhat different. Based on observations, these discrepancies may result from the simplified model for sediment particle step lengths used in the computational approach. Experiments show that the particle step length varies spatially and temporally over the bedforms during the evolution process. Assuming a constant value for the step length neglects the role of flow alterations in the bedload sediment‐transport process, which appears to result in predicted bedform wavelength changes smaller than those observed. However, observations also suggest that three‐dimensional effects play at least some role in the decrease of bedform wavelength, so incorporating better models for particle hop lengths alone may not be sufficient to improve model predictions. Published in 2011. This article is a US Government work and is in the public domain in the USA.  相似文献   

The Burrum River estuary: identifying reference sites for Australian sub-tropical estuarine systems using paleolimnological methods   总被引：1，自引：0，他引：1  

Brendan Logan  Kathryn H. Taffs 《Journal of Paleolimnology》2011,46(4):613-622

There is a pressing need to obtain historical information on estuaries so that levels of natural variability and ecosystem thresholds can be identified. Once these factors are known, estuaries that exhibit high conservation value and minimal impact from anthropogenic activity can be acknowledged and protected. In order to understand and quantify the level of change that may have occurred due to human impact, near pristine estuaries that have the potential to act as reference sites need to be identified. However, this is often difficult due to a lack of documented knowledge of estuary variability. This paper retrospectively assesses environmental conditions in the Burrum River, a sub-tropical east Australian estuary on the coast of Queensland, using diatom and stable isotope analyses. These techniques were combined with AMS ¹⁴C dating methods to determine if this system has undergone any natural or anthropogenically induced change. Diatom assemblages have shown very little variation over the past 5,000 years, indicating minimal changes to water quality. Upper and lower limits for δ¹³C and δ¹⁵N stable isotope results also infer that the sources of carbon and nitrogen to the Burrum River estuary have remained constant over this time period. Carbon inputs have been dominated by marine autotrophic production, whilst nitrogen inputs are indicative of terrestrial sources. Hence, the Burrum River has not been altered by anthropogenic activities and is a suitable reference site for benchmarking impacted sub-tropical estuaries. This paper demonstrates that paleolimnological techniques can be applied successfully to identify estuaries that are suitable as reference sites.  相似文献