Dr John Webb
Associate Professor, College of Science, Health and Engineering
The bulk of my research and teaching is on groundwater, both in terms of resources and chemistry, with current research projects on the influence of climate and land-use change on groundwater funded through the Victorian Department of Primary Industries and the National Centre for Groundwater Research and Training.
Other research projects focus on improving treatment procedures for acid mine drainage and understanding the formation of acid sulphate soils. My geomorphological interests centre on karst, as well as tectonic geomorphology and the interaction between landscape evolution and human settlement.
Acid mine drainage
Acid mine drainage (AMD) is generated when sulphide minerals, usually exposed by mining, are exposed to the atmosphere and oxidise, releasing acidity and dissolved heavy metals. AMD must be neutralised before it can leave a site, and this process generates a sludge which has to be disposed of. Research at La Trobe University on AMD has concentrated on two aspects:
Increasing the chemical stability (resistance to leaching) of neutralisation sludges
Danny McDonald's PhD project (2006) showed that the sludges are readily leached by acid waters, no matter which chemical is used to neutralise the acidity, and should not be disposed of in pit lakes. He also demonstrated that if the iron minerals in the sludge are crystalline, they are much more resistant to acid attack. This project has proceeded in cooperation with several environmental consulting companies, particularly Earth Systems and URS, and has also received financial support from the Australian Synchrotron Research Program.
Neutralisation using limestone, particularly anoxic and open limestone drains
Our studies have looked at natural remediation of AMD in limestone terrains, and Silvana Santomartino's PhD project (2005) investigated ways of minimising the problem of ferrihydrite armouring of the limestone, and made substantial progress in this regard. She developed predictors for the lifetime of the drains, and also determining the role of carbon dioxide exsolution in drain performance. This work has been carried out in collaboration with Charles Cravotta, Water Resources Division of the US Geological Survey, Pennsylvania.
Dryland salinity is one of the most important problems facing Australian agriculture today, as salinisation reduces the productivity of large areas of farmland. Developing management strategies relies on a complete knowledge of the processes that are causing the salinisation; although these are understood at a general level, they vary greatly at a local (paddock) scale.
The Environmental Geoscience group at La Trobe University has been studying dryland salinisation in western and central Victoria for over 8 years, in conjunction with the Glenelg-Hopkins and Wimmera Catchment Management Authorities, Primary Industries Research Victoria (Bendigo) and local landcare groups. The Australian Institute for Nuclear Science and Energy has provided funding for groundwater dating.
Our work has focussed on two aspects: groundwater chemical and isotopic studies, and the effects of land-use (vegetation) and climate on groundwater levels, through very detailed studies of individual sites and medium-long term modelling. There are 3 current and 2 completed PhD projects on these topics, along with 2 MSc and 15 Honours projects, and additional PhD projects are offered. The results have appeared in a number of publications and have been presented at numerous international conferences.
Chemical and isotopic studies
We use chemical and isotopic techniques to determine how groundwater flows through the aquifers and what is causing groundwater to come to the surface in particular locations and develop areas of salinisation. The results of these studies have been used to help manage the groundwater resources of the region.
Our studies demonstrate that soil processes, particularly plant uptake and interactions with clays, quickly change the chemical composition of infiltrating rain water to that of dilute seawater. Salinisation is predominantly due to evaporation where groundwater lies close to the surface, even if the groundwater at depth is fresh. Evaporation may cause salt to build up in low permeability clay-rich soils, but does not necessarily lead to salinisation if the salt lies below the pasture root zone, so productive farmland is frequently underlain by salty soils and saline groundwater.
On the basalt plains of western and central Victoria we have shown that many saline scalds and lakes are related to the geology: edges of basalt lava flows, and upwards groundwater flow from the buried river valley sediments beneath. Recharge to the groundwater in the basalts and underlying sediments occurs mostly through the volcanoes; the thick clayey soils of the plains allow only small amounts of saline recharge. However, the addition of this saline soil water causes the groundwater to progressively increase in salinity down the flow path. Overall, recharge is determined largely by soil texture rather than vegetation cover.
Effects of land-use (vegetation) and climate on groundwater levels
A very detailed study of a farm paddock using data loggers to record hourly groundwater fluctuations showed that drainage lines carrying water only intermittently act as the main recharge area. The drainage line also has very saline soils and groundwater because the watertable is shallow and there is insufficient flow to flush the salt. Thus replanting vegetation along ephemeral drainage lines will intercept runoff and reduce recharge and salinisation.
Tree plantations are believed to reduce recharge to groundwater, but preliminary detailed studies on a plantation, again using data loggers, have shown that there is little difference to nearby farmland. Preferential recharge may be occurring during heavy rainfall events down the tree roots.
Hydrological modelling using a monthly time-step has been carried out on a number of lakes in western and central Victoria, to determine the controls on lake level and salinity. This has shown that groundwater is rarely a significant component of the lake budget, and that saline baseflow is more important than evaporation in increasing salinity in water supply reservoirs. Climatic fluctuations are the primary factor in lake water and salt budgets, although land use changes have an impact in some instances. The models allow prediction of future trends under any likely climatic scenario.
This modelling has been extended to watertables in the basalt plains of western Victoria, by relating infiltration (from local climate data) to watertable fluctuations. Initial progress is promising, and the model is presently being refined by determining the best measure of infiltration and the time lag between infiltration events and watertable response. The results will then be tested against existing catchment models like CAT (Catchment Area Tool) and MIKE SHE, to see how different management strategies (tree planting, level of water usage) will impact on groundwater levels.
- Raiber, M., Webb, J.A., Cendón, D.I., White, P.A., Cox, M.E. and Jacobsen, G.E. 2015. Environmental tracers meet 3D geological modelling: Conceptualising recharge and structurally-controlled aquifer connectivity in the basalt plains of south-western Victoria, Australia. Journal of Hydrology, 527, 262-280.
- Dean, J.F., Webb, J.A., Jacobsen, G., Chisari, R. and Dresel, P.E., 2015. A groundwater recharge perspective on locating tree plantations within low-rainfall catchments to limit water resource losses. Hydrology and Earth System Sciences 19, 1107-1123.
- Adelana, M., Dresel, E., Hekmeijer, P., Zydor, H., Webb, J.A, Reynolds, M. and Ryan, M., 2015. A comparison of streamflow, salt and water balances in adjacent farmland and forest catchments in south-western Victoria, Australia. Hydrological Processes 29, 1630-1643.
- Dean, J.F., Webb, J.A., Jacobsen, G., Chisari, R., and Dresel, P.E., 2014. Biomass uptake and fire as controls on groundwater solute evolution on a Southeast Australian granite: aboriginal land management hypothesis. Biogeosciences, 11, 4099–4114.
- Camporese, M., Daly, E., Dresel, P.E., Webb, J.A., 2014. Simplified modeling of catchment-scale evapotranspiration via boundary condition switching. Advances in Water Resources, 69, 95-105.
- Gill, B.C., Webb, J.A., Wilkinson, R. and Cherry, D., 2014. Irrigator response to groundwater resource management plans in Victoria, Australia. Journal of Hydrology 518, 83–93.
- Yihdego, Y., Webb, J.A., 2013. An empirical water budget model as a tool to identify the impact of land-use change on stream flow in southeastern Australia. Water Resources Management, 27, 4941-4958.
- Yihdego, Y. and Webb, J. A., 2011. Modeling of bore hydrographs to determine the impact of climate and land use change in a temperate subhumid region of southeastern Australia. Hydrogeology Journal, 19, 877-887.
- Raiber, M., Webb, J.A. and Bennetts, D., 2009. Strontium isotopes as tracers to delineate aquifer interactions and groundwater salinisation in the basalt plains of southeastern Australia. Journal of Hydrology, 367, 188-199.
- Edwards, M.D. and Webb, J.A., 2009. The importance of unsaturated zone biogeochemical processes in determining groundwater composition, southeastern Australia. Hydrogeology Journal, 17, 1359-1374
- Bennetts, D.A., Webb, J.A., McCaskill, M. and Zollinger, R., 2007. Dryland salinity processes within the discharge zone of a local groundwater system, Southeastern Australia. Hydrogeology Journal, 15, 1197-1210.
- Tweed, S.O., Leblanc, M., Webb, J.A. and Lubczynski, M.W., 2006. Remote sensing and GIS for mapping groundwater recharge and discharge areas in salinity prone catchments, southeast Australia. Hydrogeology Journal 15, 75-96.
- Bennetts, D.A., Webb, J.A., Stone, D.J.M. and Hill, D.M., 2006. Understanding the salinisation process for groundwater in an area of south-eastern Australia, using hydrochemical and isotopic evidence. Journal of Hydrology, 323, 178-192.
Acid mine drainage and Acid sulphate soils
- Kappen, P. and Webb, J.A., 2013. An EXAFS study of arsenic bonding on amorphous aluminium hydroxide. Applied Geochemistry 31, 79–83.
- Glover, F., Whitworth, K.., Kappen, P., Baldwin, D., Rees, G., Webb, J., Silvester, E., 2011. Acidification and buffering mechanisms in acid sulfate soil (ASS) wetlands of the Murray-Darling Basin, Australia. Environmental Science and Technology, 45, 2591–2597.
- Santomartino, S.L. and Webb, J.A., 2007. Estimating the longevity of limestone drains in treating acid mine drainage containing high concentrations of iron. Applied Geochemistry, 22, 2344-2361.
- McDonald, D. M., Webb, J. A. and Taylor, J. 2006. Chemical stability of acid rock drainage treatment sludge and implications for sludge management. Environmental Science and Technology, 40(6), 1984-1990.
Geomorphology and landscape evolution (including karst)
- Lipar, M., Webb, J.A., White, S.Q. and Grimes, K.G., 2015. The genesis of solution pipes: evidence from the Middle – Late Pleistocene Bridgewater Formation calcarenite, southeastern Australia. Geomorphology, 246, 90–103.
- Lipar, M, and. Webb, J.A., 2015. The formation of the pinnacle karst in Pleistocene aeolian calcarenites (Tamala Limestone) in southwestern Australia. Earth Sciences Reviews, 140, 182–202.
- White, S. and Webb, J., 2015. The influence of tectonics on flank margin cave formation on a passive continental margin: Naracoorte, southeastern Australia. Geomorphology 229, 58-72
- Burnett, S., Webb, J.A. and White, S., 2013. Shallow caves and blowholes on the Nullarbor Plain, Australia - flank margin caves on a low gradient limestone platform. Geomorphology, 201, 246-253.
- Webb, J.A., Gardner, T.W., Kapostasy, D., Bremar, K.A. and Fabel, D., 2011. Mountain building along a passive margin: Late Neogene tectonism in southeastern Victoria, Australia. Geomorphology 125, 253-262.
- Webb, J.A., Grimes, K.G. and Lewis, I., 2010. Volcanogenic origin of cenotes near Mt Gambier, Southeastern Australia. Geomorphology 119, 23–35.
- Gardner, T., Webb, J.A., Pezzia, C., Amborn, T., Tunnell, R., Flanagan, S., Kapostasy, D., Merritts, D., Marshall, J., Fabel, D and Cupper, D., 2009. Episodic intraplate deformation of stable continental margins: evidence from Late Neogene and Quaternary marine terraces, Cape Liptrap, southeastern Australia. Quaternary Science Reviews, 28, 39-53.
- Raiber, M. and Webb, J.A., 2008. Development of the Streatham Deep Lead System in Western Victoria: Implications for Tertiary tectonism and landscape evolution. Australian Journal of Earth Sciences, 55, 493-508.
- Webb, J.A. and James, J.M., 2006. Karst evolution of the Nullarbor Plain, Australia. In Harmon, R.S. and Wicks, C.M. (eds), Karst geomorphology, hydrology and geochemistry - a tribute volume to Derek C. Ford and William B. White. Geological Society of America Special Paper 404, 65-78.
- Gardner, T.W., Webb, J.A., Davis, A.G., Cassell, E.J., Pezzia, C., Merritts, D.J. and Smith, B., 2006. Late Pleistocene landscape response to climate change: eolian and alluvial fan deposition, southeastern Victoria, Australia. Quaternary Science Reviews, 25, 1552-1569.
- Paine, M., Bennetts, D.A., Webb, J.A., and Morand, V., 2004. Nature and extent of Pliocene strandlines in southwestern Victoria and their application to late Neogene tectonics. Australian Journal of Earth Sciences, 51, 407-422.
- Joyce, E.B., Webb, J.A., and others, 2003. Chapter 18 - Geomorphology. In Birch, W. (ed.), Geology of Victoria. Geological Society of Australia Special Publication 23, 533-561.