Atun Zawadzki

Atmospheric pollutants in alpine peat bogs record a detailed chronology of industrial and agricultural development on the Australian continent

Two peat bogs from remote alpine sites in Australia were found to contain detailed and coherent histories of atmospheric metal pollution for Pb, Zn, Cu, Mo, Ag, As, Cd, Sb, Zn, In, Cr, Ni, Tl and V. Dramatic increases in metal deposition in the post-1850 AD portion of the cores coincide with the onset of mining in Australia. Using both Pb isotopes and metals, pollutants were ascribed to the main atmospheric pollution emitting sources in Australia, namely mining and smelting, coal combustion and agriculture. Results imply mining and metal production are the major source of atmospheric metal pollution, although coal combustion may account for up to 30% of metal pollutants. A novel finding of this study is the increase in the otherwise near-constant Y/Ho ratio after 1900 AD. We link this change to widespread and increased application of marine phosphate fertiliser in Australias main agricultural area (the Murray Darling Basin).

The hydrological legacy of deforestation on global wetlands

Increased catchment erosion and nutrient loading are commonly recognized impacts of deforestation on global wetlands. In contrast, an increase in water availability in deforested catchments is well known in modern studies but is rarely considered when evaluating past human impacts. We used a Budyko water balance approach, a meta-analysis of global wetland response to deforestation, and paleoecological studies from Australasia to explore this issue. After complete deforestation, we demonstrated that water available to wetlands increases by up to 15% of annual precipitation. This can convert ephemeral swamps to permanent lakes or even create new wetlands. This effect is globally significant, with 9 to 12% of wetlands affected, including 20 to 40% of Ramsar wetlands, but is widely unrecognized because human impact studies rarely test for it. Ancient Australasian deforestations created wetlands where none previously existed. Impacts of deforestation on wetlands Deforestation worldwide may be causing an increase in the extent of wetlands. Using a combination of different approaches, Woodward et al. show that ancient and more recent deforestation has resulted in major changes in global wetland hydrology. For example, in Australia and New Zealand, deforestation has created new wetlands or increased the water level in existing wetlands. Recognition of this effect has implications for landscape management: Reforestation programs in wetland catchments may have unintended consequences for vulnerable wetlands. Science, this issue p. 844

Separation and measurement of thorium, plutonium, americium, uranium and strontium in environmental matrices

A technique for the isolation of thorium (Th), plutonium (Pu), americium (Am), uranium (U) and strontium (Sr) isotopes from various environmental matrices has been adapted from a previously published method specific to water samples (Maxwell, 2006). Separation and isolation of the various elemental fractions from a single sub-sample is possible, thereby eliminating the need for multiple analyses. The technique involves sample dissolution, concentration via calcium phosphate co-precipitation, rapid column extraction using TEVA™, TRU™ and Sr-Spec™ resin cartridges, alpha spectrometry for Th, Pu, U and Am and Cerenkov counting for Sr. Various standard reference materials were analysed and chemical yields are in the range of 70-80% for Th, Am, U and Sr and 50-60% for Pu. Sample sizes of up to 10 L for water, 5 g for dry soil and sediment and 10 g for dry vegetation and seaweed can be processed using this technique.

Unprecedented wind erosion and perturbation of surface geochemistry marks the Anthropocene in Australia

Australia, the last continent to undergo industrial development, is an ideal environment in which to quantify the magnitude of human-induced environmental change during the Anthropocene because its entire agricultural and industrial history has occurred within this period. Analysis of an alpine peat mire showed that rapid industrial and agricultural development (both pastoral and cropping) over the past 200 years has resulted in significant environmental change in Australia. Beginning in the 1880s, rates of wind erosion and metal enrichment were up to 10 and 30 times that of background natural conditions, respectively. Increased dust deposition and an expansion in dust source areas were found to map the progression of European farming across the continent, while dust deposition pulses in the mire matched known land degradation events. After 1990 dust deposition decreased, returning to pre-1880 rates. This was attributed to three factors: net soil loss following more than a century of agricultural activity, increased environmental awareness and soil conservation, and changing windiness. Metal enrichment in the mire reached approximately 2 times natural background accumulation rates by the 1980s as Australias mining industry expanded. However, metal enrichment continued to increase after the 1980s reaching an average of ~5 times background rates by 2006 and reflecting increased mineral resource development in Australia. Collectively, the results show that changes to Australias geochemical and sedimentary systems, as a result of agricultural and industrial development, have profoundly changed the Australian environment during the past two centuries. Key Points The 2.5 up increase in wind erosion since agricultural development Average of 5 times increase in metal enrichment since 1880 Two phases of the Anthropocene are identifiable

Interaction between a river and its wetland: evidence from the Murray River for spatial variability in diatom and radioisotope records

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.

A Holocene record of climate and hydrological changes from Little Llangothlin Lagoon, south eastern Australia

We present a new well dated Holocene record of environmental change from Little Llangothlin Lagoon in eastern Australia derived from aquatic plant macrofossils, macroscopic charcoal flux, and sediment stratigraphy from multiple cores. Little Llangothlin was an ephemeral freshwater wetland exhibiting frequent dry phases between 9800 and 9300 calendar years before present (cal. yr BP). There was a switch to a more positive water balance after 9300 cal. yr BP, and by 8000 cal. yr BP, there was a lake that persisted until 6100 cal. yr BP. The period between 6100 and 1000 cal. yr BP was much drier, and there is no evidence for a permanent lake during this period. The Little Llangothlin record provides evidence for a wet phase during the Early to Middle Holocene (9000–6000 cal. yr BP) from the boundary region between temperate and tropical influences in eastern Australia. We propose that generally enhanced circulation after 9000 cal. yr BP explains the pattern of increasing moisture at the site at this time. The later Holocene climate at the site is consistent with other sites in south east Australia with a switch to generally drier conditions after 6000 cal. yr BP.

Mud, mines and rainforest: a short history of human impact in western Tasmania, using pollen, trace metals and lead-210

Lead-210, pollen and trace-element analyses of a finely sampled 7.5-cm sediment core from a subalpine tarn in western Tasmania have provided a detailed record of post-colonial human impact in the region. Lead-210 analysis indicated that the record extends back to about 1811 AD, with several changes in sediment rates evident. These have been tentatively related to disturbance in the catchment associated with ore prospecting. The regional vegetation has been reconstructed for this period using pollen abundances. Prior to 1860 AD, there appears to have been little disturbance in the regional vegetation, with relatively high taxon diversity and pollen concentrations. Important communities included rainforest dominated by Nothofagus cunninghamii and subdominated by Phyllocladus and Eucryphia, eucalypt-dominated mixed and wet sclerophyll forest and subalpine and/or alpine complexes. From the 1860s, the evidence suggests an overall reduction in the extent of regional forests, particularly rainforest and subalpine woodland. Initially, this appears to have been associated with both elevated charcoal levels and minor increases in concentrations of trace metals, particularly lead, tin, arsenic and copper. By the 1950s, however, significant reductions in taxon diversity and pollen abundance (particularly for rainforest and subalpine woodland) were strongly associated with rapidly increasing concentrations of trace metals. This evidence corresponds with historic records of mineral prospecting and mining in the region, especially around Queenstown where significant deforestation occurred due to logging and pollution from smelters. Interestingly, the evidence for the most significant impacts coincided with the escalation of open-cut mining from the 1950s to the 1970s, rather than earlier phases of smelter-produced pollution.

Unearthing earthquakes and their tsunamis using multiple proxies: the 22 June 1932 event and a probable fourteenth-century predecessor on the Pacific coast of Mexico

Tsunami deposits have been widely studied in temperate latitudes, but the intrinsic difficulties associated with tropical coastal environments, and the intensity of bioturbation in these habitats, limit the possibilities of analysing these formations. Here, we investigate the deposits on the Colima coast of Mexico, which overlies the subducting Rivera and Cocos Plates, in order to reconstruct the tsunami inundation history and related hazard. We developed a multi-proxy study aimed to recognize and date historical and palaeotsunami deposits, including historical data on the effects of a known tsunami, geomorphological mapping, stratigraphic, grain size, organic matter content, diatoms, geochemical composition, magnetic susceptibility, and anisotropy of magnetic susceptibility, together with radiometric dating (210Pb and 14C). We identified two probable tsunami deposits at Palo Verde estuary including a historical event associated with the Mw 6.9 earthquake on 22 June 1932 and a palaeotsunami most likely generated by a similar event in the fourteenth century. This work shows that it is possible to identify both historical and palaeotsunamis in the tropical environment of Mexico’s Pacific coast. These data will serve to enhance our understanding of tsunami deposits in tropical environments and of the regional tsunami hazard.

Determining flow patterns and emplacement dynamics from tsunami deposits with no visible sedimentary structure

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, Spearmans 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. This article is protected by copyright. All rights reserved.

Trench 'bathtubbing' and surface plutonium contamination at a legacy radioactive waste site.

Radioactive waste containing a few grams of plutonium (Pu) was disposed between 1960 and 1968 in trenches at the Little Forest Burial Ground (LFBG), near Sydney, Australia. A water sampling point installed in a former trench has enabled the radionuclide content of trench water and the response of the water level to rainfall to be studied. The trench water contains readily measurable Pu activity (∼12 Bq/L of 239+240Pu in 0.45 μm-filtered water), and there is an associated contamination of Pu in surface soils. The highest 239+240Pu soil activity was 829 Bq/kg in a shallow sample (0–1 cm depth) near the trench sampling point. Away from the trenches, the elevated concentrations of Pu in surface soils extend for tens of meters down-slope. The broader contamination may be partly attributable to dispersion events in the first decade after disposal, after which a layer of soil was added above the trenched area. Since this time, further Pu contamination has occurred near the trench-sampler within this added layer. The water level in the trench-sampler responds quickly to rainfall and intermittently reaches the surface, hence the Pu dispersion is attributed to saturation and overflow of the trenches during extreme rainfall events, referred to as the ‘bathtub’ effect.