排序方式: 共有9条查询结果,搜索用时 15 毫秒
1
1.
The Northland region of New Zealand includes numerous high-value, macrophyte-dominated dune lakes. Recent water policy reforms offer limited guidance on managing for aquatic macrophytes. In addition, dune lake histories are poorly known as regular monitoring dates to 2005 AD. Here, ca. 4000 years of lake functional behaviour is reconstructed from sedimentary archives in two Northland dune lakes (Humuhumu and Rotokawau). Results demonstrated that macrophyte dominance is sensitive to catchment erosion and hydrological drawdown. Degradation of macrophyte communities occurred in the nineteenth and twentieth centuries, earlier at Lake Humuhumu than Lake Rotokawau (post-1880 AD and post-1930 AD, respectively). In both lakes, increased erosional influx reduced macrophyte productivity, before later increases to wider trophic state (post-1970 AD). Lake-level decline is linked to increased nutrient loading at Lake Rotokawau but less so, Lake Humuhumu which is more strongly groundwater-fed. In Northland dune lakes, water-level reduction and erosional influx from land use have driven macrophyte degradation. 相似文献
2.
Emily?LeydenEmail author John?Tibby Adriana?García Atun?Zawadzki 《Journal of Paleolimnology》2011,46(4):637-647
Bombah Broadwater is a shallow coastal lake within the Ramsar-listed Myall Lakes system on the mid-north coast of New South
Wales, Australia. Increased nutrient and sediment loads resulting from catchment modification are thought to have instigated
the loss of aquatic plants in the lake, causing it to “switch” from a clear, macrophyte dominated system (similar to the conditions
in present day Myall Lake) to a turbid, phytoplankton dominated system. To assess this hypothesis, charophytes, foraminifera
and aquatic fauna remains from an 800 year sediment record were examined. The sediment chronology was established using 14C, 210Pb and 137Cs radiometric dating and sediment composition. Interestingly, a clear increase in charophytes since European arrival conflicted
with the hypothesised aquatic plant loss. Hence, it appears Bombah Broadwater has not undergone a change in stable state since
European arrival. An additional and unexpected finding in the patterns of the foraminifera and testate amoeba suggest that
Bombah Broadwater has freshened substantially since European arrival. This freshening may have resulted from increased catchment
run off as a result of the clearance of catchment vegetation. Since catchment vegetation clearance is widespread in Australia,
this finding raises the possibility that post-settlement freshening of coastal lakes may be a common occurrence. 相似文献
3.
Paul Augustinus Charles E. Barton Atun Zawadzki Kate Harle 《Environmental Earth Sciences》2010,61(3):625-639
Macquarie Harbour in southwest Tasmania, Australia, has been affected severely by the establishment of mines in nearby Queenstown
in the 1890s. As well as heavy metal-laden acid rock drainage from the Mount Lyell mine area, over 100 Mt of mine tailings
and slag were discharged into the Queen and Ring Rivers, with an estimated 10 Mt of mine tailings building a delta of ca.
2.5 km2 and ca. 10 Mt of fine tailings in the harbour beyond the delta. Coring of sediments throughout Macquarie Harbour indicated
that mine tailings accreted most rapidly close to the King River delta source with a significant reduction in thickness of
tailings and heavy metal contamination with increasing distance from the King River source. Close to the King River delta
the mine tailings are readily discriminated from the background estuarine sediments on the basis of visual logging of the
core (laminations, colour), sediment grain size, sediment magnetic susceptibility and elemental geochemistry, especially concentrations
of the heavy metals Cu, Zn and Pb. The high heavy metal concentrations are demonstrated by the very high contamination factors
(CF > 6) for Cu and Zn, with CF values mostly >50 for Cu for the mine-impacted sediments. Although the addition of mine waste
into the King River catchment has ceased, the catchment continues to be a source of these heavy metals due to acid rock drainage
and remobilisation of mine waste in storage in the river banks, river bed and delta. The addition of heavy metals to the harbour
sourced from the Mount Lyell mines preceded the advent of direct tailings disposal into the Queen River in 1915 with the metals
probably provided by acid rock drainage from the Mount Lyell mining area. 相似文献
4.
Suzanne?E.?HollinsEmail author Jennifer?J.?Harrison Brian?G.?Jones Atun?Zawadzki Henk?Heijnis Stuart?Hankin 《Journal of Paleolimnology》2011,46(4):579-596
In this study, we combined grain size and geochemical analyses with radioisotope analysis of lead-210 (210Pb), caesium-137 (137Cs) and radiocarbon (14C) ages to reconstruct the sedimentation history of two urbanised coastal lagoons in south-east Australia. Towradgi and Fairy
Lagoons were both found to exhibit slow initial sedimentation of less than 1 mm year−1 prior to anthropogenic influences. Land clearing in the catchments increased runoff and erosion in the creeks feeding into
the estuaries, and has resulted in progradation of fluvial material into the estuarine systems with a marked increase in sedimentation
to between 2 and 7 mm year−1. The upper 20–50 cm of the sediment column in both lagoons contained elevated concentrations of heavy metals such as Pb,
Cu, Ni and Zn. This pollution trend was found to be consistent with the history of industrialisation and urbanisation in the
region, which expanded rapidly post World War 2. The total metal concentrations were consistent with other urbanised/industrialised
estuaries around the world. Despite the fairly disturbed nature of these coastal lagoons, the use of 210Pb, 137Cs and 14C dating in combination with bulk geochemical analyses allowed detailed reconstruction of sedimentation history. 相似文献
5.
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
6.
7.
Determining flow patterns and emplacement dynamics from tsunami deposits with no visible sedimentary structure 下载免费PDF全文
Claire Kain Patrick Wassmer James Goff Catherine Chagué‐Goff Christopher Gomez Deidre Hart Daniela Fierro Geraldine Jacobsen Atun Zawadzki 《地球表面变化过程与地形》2017,42(5):763-780
In the absence of eyewitness reports or clear sedimentary structures, it can be difficult to interpret tsunami deposits or reconstruct tsunami inundation patterns. The emplacement dynamics of two historical tsunami deposits were investigated at seven transects in Okains Bay, New Zealand, using a combined geospatial, geomagnetic and sedimentological approach. The tsunami deposits are present as layers of sand and silt intercalated between soils and become finer and thinner with distance inland. The deposits are attributed to the 1960 and possibly the 1868 tsunamis, based on radiometric dating and correlation with historical records. Measurements of Magnetic Fabric (MF: Anisotropy of Magnetic Susceptibility) and particle size were used to reconstruct the evolution of flow dynamics laterally and vertically. A combination of statistical methods, including spatial autocorrelation testing, Spearman's rank order correlation, Principal Component Analysis (PCA) and K‐means cluster analysis, was applied to examine relationships between MF parameters and sediment texture, and infer depositional hydrodynamics. Flow patterns deduced from MF show the estuary channel acted as a conduit for inundation, with flow commonly aligned sub‐perpendicular to the estuary bed. MF and sediment data suggest deposition occurred from settling during laminar flow. Evidence of both uprush and backwash deposition, as well as wave reflection from infrastructure, was found. Statistical analysis of data showed significant relationships between grain size parameters and MF parameters associated with flow speed and magnetic fabric type. PCA and cluster analysis differentiated samples into two primary hydrodynamic groups: (1) samples deposited from laminar flow; and (2) samples deposited close to the limit of inundation, which includes samples deposited further inland, those affected by flow convergence, and those in the upper part of tsunami deposits. This approach has potential as a tool for reconstructing hydrodynamic conditions for palaeotsunamis and by combining spatial and statistical analyses, large‐scale investigations can be more easily performed. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
8.
Interaction between a river and its wetland: evidence from the Murray River for spatial variability in diatom and radioisotope records 总被引:1,自引:1,他引:0
Sinclair Flat is small wetland, located within the gorge section of the Murray River floodplain. situated near Blanchetown,
South Australia, the wetland is closely linked to the River and, since regulation, has become permanently inundated. High
summer evaporation rates deplete the volume of water within the wetland. However, this is compensated by perennial inflow
via a permanent inlet from the River. This site provides an opportunity to explore the relative contribution of river and
wetland diatom flora to the sediment record, and the fluvial and aerial contribution of radiometric isotopes to the system.
The geochronological and biostratigraphic data provide an insight into the history of the water quality of Sinclair Flat.
Evidence exists for the River being a source of sediments and isotopes and of diatom species typical of the main river channel.
Prior to 1950, Sinclair Flat was an oligotrophic, oligosaline, clear-water wetland. The wetland shifted gradually to an environment
that favoured clear-water benthic species, most likely as a consequence of changes following river regulation in the 1920s,
although the capacity to date these sediments is limited. During the 1950s, the wetland became plankton dominated. Peaks in
epiphytic diatoms during the 1960s suggest increased emergent macrophyte cover. The contemporary condition is of a connected,
turbid, eutrophic and mesosaline lagoon. The ecological condition of Sinclair Flat has diverged considerably from its historical
range of condition. This record supports evidence from upstream of widespread state switches in the Murray–Darling Basin floodplain
wetlands. This record also lends considerable weight to modern studies attesting to the degraded state of the waterways of
the Murray–Darling Basin and the impact of river regulation practices on the water quality of these ecosystems. 相似文献
9.
Craig Woodward Jie Chang Atun Zawadzki James Shulmeister Robert Haworth Sasha Collecutt Geraldine Jacobsen 《Quaternary Science Reviews》2011,30(27-28):3743-3747
Paleoenvironmental reconstructions from Little Llangothlin Lagoon have been used to argue for early European impact on the eastern Australian landscape. In particular, these studies have argued for European arrival on the New England Tablelands at about 1800 AD, with significant impacts including the clearance of one species of Casuarina before 1820 AD and significant erosion by 1836 AD (Gale et al., 1995; Gale and Pisanu, 2001; Gale and Haworth, 2002, 2005). We have re-cored the lagoon, dated the cores using 210Pb and radiocarbon, and counted pollen and other proxies. Our 210Pb results indicate that 210Pb background was achieved stratigraphically later than the erosion event and we have three early Holocene radiocarbon ages in the erosion event interval. We conclude that the ‘erosion event’ predates European settlement. The 210Pb results indicate much less erosion in response to European settlement than suggested by these earlier studies. We also find no notable decline in Casuarina in the pollen record spanning the time of initial European impact, and in fact we find very little Casuarina in the record. Instead of a Casuarina dominated vegetation we conclude that the area was dominated by open Eucalypt forest prior to European settlement. Rather than changes in the regional vegetation in the early 19th century, we attribute changes in the palynoflora spanning the ‘erosion event’ to changes within the lake/wetland and in particular to changes in the dominance of different species of Myriophyllum; most likely due to water depth fluctuation. This site has stood out as indicating an earlier European impact than other localities in eastern Australia, beyond the original limits of settlement near Sydney. Our findings suggest that a more traditional interpretation of this site is warranted and that no very early impact is discernable. 相似文献
1