Browsing by Author "Willgoose, GR"
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- ItemCharacterisation of the hydrology of an estuarine wetland(Elsevier, 1998-11) Hughes, CE; Binning, P; Willgoose, GRThe intertidal zone of estuarine wetlands is characterised by a transition from a saline marine environment to a freshwater environment with increasing distance from tidal streams. An experimental site has been established in an area of mangrove and salt marsh wetland in the Hunter River estuary, Australia, to characterise and provide data for a model of intertidal zone hydrology. The experimental site is designed to monitor water fluxes at a small scale (36 m). A weather station and groundwater monitoring wells have been installed and hydraulic head and tidal levels are monitored over a 10-week period along a short one-dimensional transect covering the transition between the tidal and freshwater systems. Soil properties have been determined in the laboratory and the field. A two-dimensional finite element model of the site was developed using SEEP/W to analyse saturated and unsaturated pore water movement. Modification of the water retention function to model crab hole macropores was found necessary to reproduce the observed aquifer response. Groundwater response to tidal fluctuations was observed to be almost uniform beyond the intertidal zone, due to the presence of highly permeable subsurface sediments below the less permeable surface sediments. Over the 36 m transect, tidal forcing was found to generate incoming fluxes in the order of 0.22 m3/day per metre width of creek bank during dry periods, partially balanced by evaporative fluxes of about 0.13 m3/day per metre width. During heavy rainfall periods, rainfall fluxes were about 0.61 m3/day per metre width, dominating the water balance. Evapotranspiration rates were greater for the salt marsh dominated intertidal zone than the non-tidal zone. Hypersalinity and salt encrustation observed show that evapotranspiration fluxes are very important during non-rainfall periods and are believed to significantly influence salt concentration both in the surface soil matrix and the underlying aquifer. © 1998 Elsevier Science B.V.
- ItemComparing the stability and chemistry of soil organic carbon protected via pyrogenesis, aggregation and mineral-association(International Union of Soil Science, 2014-06-23) Hobley, E; Willgoose, GR; Frisia, S; Jacobsen, GEWe investigated the influence of soil texture and mineralogy on soil organic carbon (SOC) stability in two native soils of different texture and mineralogy from the Southern Highlands of NSW, Australia. To do this, a heavy-textured (clayey) soil and coarse-textured (sandy) soil were sampled at various depths to bedrock. The bulk samples were then fractionated into different particle-sizes and SOC content and stability measured using elemental analysis and radiocarbon analysis. Diffuse-reflectance infrared Fourier Transform spectroscopy was applied to infer molecular chemistry and variability in the soils, and investigate to SOC chemical structures associated with shifts in radiocarbon content of the soils. In both soils, the highest SOC content was found in the finest fraction, indicating that particle-size is a dominant control on SOC retention, independent of soil texture. In contrast, the mechanisms of SOC stabilization varied between the two soils, which we attribute to the differences in mineralogy and texture. In the coarse-textured soil, the chemical recalcitrance of charcoal was found to be the dominant stabilization mechanism in most of the soil profile, and the chemical recalcitrance of other aromatic structures may have contributed to SOC stability in subsoils. In the clayey soil, the most important stabilization mechanism throughout the soil profile was aggregation, which was centuries older than the mineral-associated organic matter in the soil. SOC was highly correlated with radiocarbon content and depth in both soils, so that SOC turnover may be limited by substrate availability at depths near bedrock in the soils. Comparing the radiocarbon ages of the two soils, the most stable carbon was (1) C stored in charcoal, followed by (2) C occluded within aggregates consisting of highly-charged clay minerals, (3) C associated with highly-charged clay minerals and Fe/Mn oxides, and (4) C associated with lowly-charged silicates or sandy aggregates. Our results indicate that there is a disconnect between SOC storage and SOC stability. Our findings have implications for SOC sequestration schemes, namely that trade-offs exist between enhancing SOC storage and enhancing SOC stability, and that texture and mineralogy should be considered when tailoring these schemes within an ecosystem.
- ItemEstimating evapotranspiration for a temperate salt marsh, Newcastle, Australia(John Wiley & Sons, Ltd., 2001-04-18) Hughes, CE; Kalma, JD; Binning, P; Willgoose, GR; Vertzonis, MEvapotranspiration was studied at a salt marsh site in the Hunter River estuary, NSW, Australia, during 1996–8. Estimates of actual evapotranspiration (Ea) were obtained for three sites using the eddy correlation method. These values were compared with results obtained with the Penman and Penman–Monteith equations, and with pan evaporation. The Penman–Monteith method was found to be most reliable in estimating daily and hourly evapotranspiration. Surface resistance values averaging 12 s m−1 were derived from the eddy correlation estimates. Recent tidal flooding and rainfall were found to decrease surface resistance and increase Ea/Ep ratios. Estimates of evapotranspiration obtained using the Penman–Monteith method were shown to be sensitive to changes in surface resistance, canopy height and the method used to estimate net radiation from incoming solar radiation. These results underline the importance of accurately estimating such parameters based on site‐specific data rather than relying on empirical equations, which are derived primarily for crops and forests. © 2001 John Wiley & Sons, Ltd.
- ItemStability and storage of soil organic carbon in a heavy-textured Karst soil from south-eastern Australia(CSIRO publishing, 2014-05-09) Hobley, E; Willgoose, GR; Frisia, S; Jacobsen, GEBoth aggregation and mineral association have been previously found to enhance soil organic carbon (SOC) storage (the amount of organic C retained in a soil), and stability (the length of time organic C is retained in a soil). These mechanisms are therefore attractive targets for soil C sequestration. In this study, we investigate and compare SOC storage and stability of SOC associated with fine minerals and stored within aggregates using a combination of particle-size fractionation, elemental analysis and radiocarbon dating. In this heavy-textured, highly aggregated soil, SOC was found to be preferentially associated with fine minerals throughout the soil profile. By contrast, the oldest SOC was located in the coarsest, most highly aggregated fraction. In the topsoil, radiocarbon ages of the aggregate-associated SOC indicate retention times in the order of centuries. Below the topsoil, retention times of aggregate-SOC are in the order of millennia. Throughout the soil profile, radiocarbon dates indicate an enhanced stability in the order of centuries compared with the fine mineral fraction. Despite this, the radiocarbon ages of the mineral-associated SOC were in the order of centuries to millennia in the subsoil (30–100 cm), indicating that mineral-association is also an effective stabilisation mechanism in this subsoil. Our results indicate that enhanced SOC storage does not equate to enhanced SOC stability, which is an important consideration for sequestration schemes targeting both the amount and longevity of soil carbon. © 2014 CSIRO Publishing
- ItemVertical distribution of charcoal in a sandy soil: evidence from DRIFT spectra and field emission scanning electron microscopy(Wiley Online Library, 2014-09-12) Hobley, E; Willgoose, GR; Frisia, S; Jacobsen, GEThis study uses diffuse reflectance infrared Fourier Transform (DRIFT) spectrometry and field emission scanning electron microscopy to investigate the vertical distribution of charcoal in a sandy soil from SE Australia. The soil was sampled to bedrock (120 cm) at varying depths and bulk samples were fractionated into three particle-sizes: macro- (2000–200 µm), micro- (200–60 µm) and mineral-associated organic matter (MAOM, < 60 µm). Charcoal was isolated from 0–30 and 30–60-cm depths. Soil charcoal was detected by using a DRIFT band centred at 1590 cm−1 and scanning electron microscopy combined with energy dispersive spectroscopy. Charcoal content as a proportion of soil organic carbon (SOC) was estimated with linear regressions of cumulative DRIFT bands. At 0–30 cm, charcoal content as a portion of SOC did not differ significantly between particle-size fractions, constituting 5–26% of SOC. At a depth of 30–60 cm, charcoal constituted 19–39% of SOC in the fractions. At 60–100 cm, charcoal was only detectable in the mid-sized fraction, where it constituted about 17% of SOC. These results support our previous hypothesis of charcoal enrichment in the micro-fraction inducing a greater SOC stability in this fraction as inferred from radiocarbon ages (Hobley et al., 2013). Our findings indicate that DRIFT spectra can be used to detect the presence and amount of charcoal in soil, which may prove to be a simple and low-cost alternative to more laborious and costly detection methods.© 2014, British Society of Soil Science.