School of Geography, Earth and Atmospheric Sciences - Research Publications
Now showing items 1-12 of 199
Irrigator relations with water in the Sunraysia region, northwestern Victoria
Irrigated agriculture faces significant challenges under climate change, and may not be feasible in parts of the Murray–Darling Basin beyond 2050. Recent research into the cultural politics of water has paid limited attention to the water cultures and relations of irrigators in Minority World countries. We analyse the water relations of grape farm irrigators in the Sunraysia region of Victoria, using interviews and farm tours undertaken between 2014 and 2016. Findings are summarised under five themes: (1) the sociality of irrigation water, (2) temporal and spatial relations, (3) the risk of rain, (4) the micro-scale of water knowledge, and (5) environment as actor. These themes shed light on the diverse relations that constitute both environmental and irrigation water. Irrigators are embedded in these relations at multiple scales, local and distant, mediated by technology and infrastructure. The scale of our focus makes visible water and other environmental knowledge that often goes unnoticed in broader debates over irrigation. The concept of “the environment”, understood as an embodied actor in policy discourse and by irrigators, is an emergent trend that warrants ongoing research attention.
The indirect response of an aquatic ecosystem to long-term climate-driven terrestrial vegetation in a subalpine temperate lake
Aim To assess whether climate directly influences aquatic ecosystem dynamics in the temperate landscape of Tasmania or whether the effects of long‐term climatic change are mediated through the terrestrial environment (indirect climate influence). Location Paddy's Lake is located at 1065 m a.s.l. in temperate north‐west Tasmania, a continental island south‐east of mainland Australia (41°15–43°25′ S; 145°00–148°15′ E). Methods We developed a new 13,400 year (13.4 kyr) palaeoecological dataset of lake sediment subfossil cladocerans (aquatic grazers), bulk organic sediment carbon (C%) and nitrogen (N%) and δ13C and δ15N stable isotopes. Comparison of this new data was made with a recently published pollen, geochemistry and charcoal records from Paddy's Lake. Results Low cladoceran diversity at Paddy's Lake is consistent with other temperate Southern Hemisphere lakes. The bulk sediment δ15N values demonstrate a significant lagged negative response to pollen accumulation rate (pollen AR). Compositional shifts of dominant cladoceran taxa (Bosmina meridionalis and Alona guttata) occur following changes in both pollen AR and pollen (vegetation) composition throughout the 13.4 kyr record at Paddy's Lake. The δ15N values demonstrate a significant positive lagged relationship to the oligotrophic:eutrophic cladoceran ratio. Main conclusions Long‐term changes in cladoceran composition lag changes in both pollen AR and terrestrial vegetation composition. We interpret pollen AR as reflecting climate‐driven changes in terrestrial vegetation productivity and conclude that climate‐driven shifts in vegetation are the principal driver of the cladoceran community during the last ca. 13.4 kyr. The significant negative lagged relationship between pollen AR and δ15N reflects the primary control of vegetation productivity over within‐lake nutrient status. Thus, we conclude that the effects of long‐term climate change on aquatic ecosystem dynamics at our site are indirect and mediated by the terrestrial environment. Vegetation productivity controls organic soil development and has a direct influence over lake trophic status via changes in the delivery of terrestrial organic matter into the lake.
Exhumed lateral margins and increasing flow confinement of a submarine landslide complex
Submarine landslides, including the basal shear surfaces along which they fail, and their subsequent infill, are commonly observed in modern seabed and seismic reflection data sets; their resultant relief impacts sediment routing and storage patterns on continental margins. Here, three stacked submarine landslides are documented from the Permian Ecca Group, Laingsburg depocentre, Karoo Basin, South Africa, including two superimposed lateral margins. The stratigraphic framework includes measured sections and correlated surfaces along a 3 km long, 150 m high outcrop. Two stacked 2·0 to 4·5 km wide and 90 m and 60 m deep erosion surfaces are recognized, with lateral gradients of 8° and 4°, respectively. The aim of this study was to understand the evolution of a submarine landslide complex, including: evolution of basal shear surfaces/zones; variation of infill confinement; and location of the submarine landslides in the context of basin-scale sedimentation and degradation rates. Three stages of formation are identified: (i) failure of submarine landslide 1, with deposition of unconfined remobilized deposits; (ii) failure of submarine landslide 2, forming basal shear surface/zone 1, with infill of remobilized deposits and weakly confined turbidites; and (iii) failure of submarine landslide 3, forming basal shear surface/zone 2, with infill of remobilized deposits and confined turbidites, transitioning stratigraphically to unconfined deposits. The expression of basal shear varies laterally, from metres thick zones in silt-rich strata to sharp stepped surfaces in sand-rich strata. Faulting and rotation of overlying bedding suggest that the shear surfaces/zones were dynamic. Stacking of landslides resulted from multi-phase slope failure, increasing down-dip topography and confinement of infilling deposits. The failure slope was probably a low supply tilted basin margin evidenced by megaclast entrainment from underlying basin-floor successions and the lack of channel systems. This study develops a generic model of landslide infill, as a function of sedimentation and degradation rates, which can be applied globally.
Pollen-derived biomes in the Eastern Mediterranean-Black Sea-Caspian-Corridor
AIM: To evaluate the biomization technique for reconstructing past vegetation in the Eastern Mediterraneanâ Black Seaâ Caspianâ Corridor using an extensive modern pollen data set and comparing reconstructions to potential vegetation and observed land cover data. LOCATION: The region between 28â 48Â°N and 22â 62Â°E. METHODS: We apply the biomization technique to 1,387 modern pollen samples, representing 1,107 entities, to reconstruct the distribution of 13 broad vegetation categories (biomes). We assess the results using estimates of potential natural vegetation from the European Vegetation Map and the Physicoâ Geographic Atlas of the World. We test whether anthropogenic disturbance affects reconstruction quality using land use information from the Global Land Cover data set. RESULTS: The biomization scheme successfully predicts the broadscale patterns of vegetation across the region, including changes with elevation. The technique discriminates deserts from shrublands, the prevalence of woodlands in moister lowland sites, and the presence of temperate and mixed forests at higher elevations. Quantitative assessment of the reconstructions is less satisfactory: the biome is predicted correctly at 44% of the sites in Europe and 33% of the sites overall. The low success rate is not a reflection of anthropogenic impacts: only 33% of the samples are correctly assigned after the removal of sites in anthropogenically altered environments. Open vegetation is less successfully predicted (33%) than forest types (73%), reflecting the underâ representation of herbaceous taxa in pollen assemblages and the impact of longâ distance pollen transport into open environments. Samples from small basins (<1Â kmÂ²) are more likely to be reconstructed accurately, with 58% of the sites in Europe and 66% of all sites correctly predicted, probably because they sample an appropriate pollen source area to reflect regional vegetation patterns in relatively heterogeneous landscapes. While methodological biases exist, the low confidence of the quantitative comparisons should not be overâ emphasized because the target maps themselves are not accurate representations of vegetation patterns in this region. MAIN CONCLUSIONS: The biomization scheme yields reasonable reconstructions of the broadscale vegetation patterns in the Eastern Mediterraneanâ Black Seaâ Caspianâ Corridor, particularly if appropriateâ sized sampling sites are used. Our results indicate biomization could be used to reconstruct changing patterns of vegetation in response to past climate changes in this region.
Evolution of sandstone peak-forest landscapes - insights from quantifying erosional processes with cosmogenic nuclides
(John Wiley and Sons, 2018-03-15)
The sandstone peak-forest landscape in Zhangjiajie UNESCO Global Geopark of Hunan Province, China, is characterized by >3000 vertical pillars and peak walls of up to 350 m height, representing a spectacular example of sandstone landform variety. Few studies have addressed the mechanisms and timescales of the longer-term evolution of this landscape, and have focused on fluvial incision. We use in situ cosmogenic nuclides combined with GIS analysis to investigate the erosional processes contributing to the formation of pillars and peak-forests, and discuss their relative roles in the formation and decay of the landscape. Model maximum-limiting bedrock erosion rates are the highest along the narrow fluvial channels and valleys at the base of the sandstone pillars (~83–122 mm kyr−1), and lowest on the peak wall tops (~2.5 mm kyr−1). Erosion rates are highly variable and intermediate along vertical sandstone peak walls and pillars (~30 to 84 mm kyr−1). Catchment-wide denudation rates from river sediment vary between ~26 and 96 mm kyr−1 and are generally consistent with vertical wall retreat rates. This highlights the importance of wall retreat for overall erosion in the sandstone peak-forest. In combination with GIS-derived erosional volumes, our results suggest that the peak-forest formation in Zhangjiajie commenced in the Pliocene, and that the general evolution of the landscape followed our sequential refined model: (i) slow lowering rates following initial uplift; (ii) fast plateau dissection by headward knickpoint propagation along joints and faults followed by; (iii) increasing contribution of wall retreat in the well-developed pillars and peak-forests and a gradual decrease in overall denudation rates, leading to; (iv) the final consumption of pillars and peak-forests. Our study provides an approach for quantifying the complex interplay between multiple geomorphic processes as required to assess the evolutionary pathways of other sandstone peak-forest landscapes across the globe.