Sub-Project 2: Soil Environment Impacts
|
Regional Water and Soil Assessment for Mapping Sustainable Agriculture |
|
Sub-Project 2: Soil Environment Impacts
|
|
|
|
The Soil Environment Impacts Sub-Project will develop soil impact models and contribute information for the tools used in the Water Balance Sub-Project. The applications of this component will be different in the NCP and LP in that the former will focus on salinity and sodicity and the latter on the evaluation of existing indicators involving erosion and nutrients.
For the NCP, related research on salinity, sodicity and soil/water interactions will be reviewed as they relate to the focus catchments and regional areas in China and Australia. These problems include the farm scale problems of producing food efficiently and sustaining the viability and quality of the resource base.
Base data sets will be collected for the selected sites and detailed soil-water process studies will be conducted in representative focus catchments by compiling soil, geological and geomorphological maps after describing and sampling soil profiles down representative toposequences of the focus catchments. These will be analysed to provide the chemical, physical and mineralogical properties of key soil profiles and (through regional accounting) their up-scaling to the catchment scale of the Project.
The base data will be used to establish best choices of conceptual (qualitative) and physical (quantitative) models (e.g. LEACHM and SWIM v2) to predict the processes and fluxes of water and salts within landscapes. The most appropriate physical model to use with the strong base of data being collected will be assessed and selected in the first year of the project. In addition, we will decide which catchments are most suitable and representative for the modeling of salt fluxes. This will ensure that our data sets are comprehensive and fulfil the input requirements for the selected model.
Where instrumentation exists, groundwater levels and throughflow will be monitored. The hydrology and catchment water balance will also be modelled in order to trace pathways, sources and loads of solutes and iron moving through surface and sub-surface soil layers of different porosity and weathering characteristics. Water balance modelling will also be used to understand and quantify solute transport at both focus catchment and regional scales and to establish consistent indicators scaling between farm and region. The indicators will involve interaction with end users and evaluation by all parties using the CSIRO indicator ranking method.
In the LP, the first step is also to review both the base for the existing indicators as they apply to the region and how they relate to the measurements that have been developed in China. The reviews and discussions with the users of the technology will lead to a set of tests using existing data for Morphological Indicators (e.g. Soil organic matter, aggregation, crusting, anti-erodability, shearing stress, infiltration rate) and Biological Indicators (e.g. crop productivity, plant root density, soil microbiology, soil nutrients and chemistry). This will impact directly on Sub-Project 4 where the established set will be validated.
Establish the soil processes involved in the major causes of land degradation in the study sites in China and Australia.
Establish satisfactory approaches for describing and predicting the pathways, mobility, loads and sources of salts and colloids (clays) in the study areas.
Establish candidate physical models for the feedbacks between soil salinity and hydraulic properties of soil profiles that can be used in water balance modelling and based on the base collected at the sites.
Develop soil degradation indicators to assist in catchment planning for achieving environmentally sustainable production.
Year 1 (97/98) Progress - as extracted from the Annual Report
a. Review literature on soil indicators and apply to sites
At a paddock / landscape scale:
At catchment a scale:
List of Published papers
A preliminary study on an ecosystem stability index in the Zhifangguo watershed of Ansai Station(by Liu Guobin and Zheng Fen-li) have finished a draft.
b. Review sites selected in Australia and China
Soils data were collected from the Mt Lofty and Dundas Tablelands sites and added to the existing data base. These data have been published as —
The Upper Murrumbidgee work progressed substantially with the application of an indicator approach to establish the relative health of 13 large catchments and 169 sub- catchments.
The meteorological data base for the Loddon-Campaspe catchments was updated to provide the basis for linking remote sensing with WAVES for the regional water-use efficiency analysis.
Three sites are selected for indicators research in the Loess Plateau.
Vegetation in this area has gradually restored for above 130 years. Before 1886-1872, soil erosion situation in this area is the same as the Ansai Station. Now, Eco-environment is better and soil erosion modulus is less than 100t/km2.y. However, After vegetation land is changed to farmland, soil quality degradation is rapidly accelerated. Soil erosion modulus is 10000-2000t/km2.y.
These three sites are suitable for indicator monitoring and research and they have long term available data for utilization.
Year 2 (98/99) Progress - as extracted from the Annual Report
2. Soil Environment Impacts Sub-Task:
Collected the base data in the Herrmanns (Mt. Lofty Ranges) and Red Barren (Dundas Tableland) focus catchments by:
Preliminary interpretation of metadata suggest that automated monitoring has provided essential temporal data to support integrated spatial models for drainage/waterlogging, salinity and acidity/alkalinity. This information forms the basis of the upscaling approaches and development of specific catchment indicators at the various scales (0.2 km2, 2 km2 and 80 km2 areas). Identical monitoring equipment will be installed in two areas on the North China Plain in October. This information, together with detailed pedological, mineralogical, geochemical and hydrological studies in the focus catchments has led to the construction of several integrated spatial models of surface and groundwater solute movement (22: ADL_10, 23: ADL_13).
Most soils in these medium to high rainfall (>500 mm) catchments in both the Mt Lofty Ranges (22: ADL_10) and Dundas Tablelands (24: ADL_05) are duplex soils and show an abrupt textural boundary between the top soil layers and the subsoil layers (e.g. friable sandy loam over a firm clay). In these catchments, the soils have two distinct water flow systems: (i) a seasonal fresh perched watertable developing between May and October on relatively impermeable subsoil layers, and (ii) a permanent saline sulfatic groundwater table which occurs in the fractured rock geology. Clearance of native vegetation has caused the saline groundwater to rise. The models show where water is moving through the soils; where water movement is being impeded, leading to waterlogging; and where saline and sulfatic groundwaters are causing soils to degrade.
Recognisable soil and vegetation features (indicators) have been identified with varying degrees of waterlogging, salinity, sodicity and acid sulfate soil properties. Farmers are keen observers of their environment and can use this new information to recognise and map waterlogged and salt affected areas. These readily observable soil characteristics can then be used as tools to devise options for management of the problem and for future property planning. The value of this work is currently being enhanced by:
Presentation of an invited paper, "Nature and significance of minerals formed in Australian mediterranean soils during land use changes" at the 6th International Meeting on Soils with Mediterranean Type of Climate (IMSMTC) in Barcelona, Spain in July 99 (Ref 21: ADL_07). The paper gives an overview on how changes in the nature and types of iron oxides, carbonates and salt efflorescences can help distinguish between ancient and recent redox, hydro-geochemical and thermal soil conditions are able to better predict environmental and management options. Because specific types of pedogenic minerals are formed or altered by changes in hydrology, geochemistry (e.g. salinity), fire history, tillage practices and evapotranspiration they can be used to infer where and to what degree Australian soils have been influenced by current landuse changes.
Year 3 (99/00) Progress - as extracted from the Annual Report
Much material has been published this year by the soils environmental impact group located in CSIRO Land and Water in Adelaide. The following headers are used to assist in understanding the partitioning of the 12 publications produced by this group this year. The reporting of soils research by the Chinese groups appears after the summary of the Adelaide groups research outcomes.
2.1 Estimate of hydrologic properties of soils in the Keyneton catchment (ADL_04 to ADL_07)
The duration of waterlogging on the upper slopes and crests in the Keynes catchment in the Mt Lofty Ranges, South Australia is almost as long as lower down on the slope. However, the causes, development and duration of waterlogging on the lower slopes is different to that on the mid and upper slopes which is in turn different to that on the crests. Soil saturation doesn’t always occur on the boundary between the A and B horizons but can form within the B horizon or on the boundary between the B and C horizons. Saturation of the rootzone is also caused by lack of soil water storage capacity due to saturation of the soil profile from below by either saline groundwater or fresh, deep perched water. The management needs of texture-contrast soils with ‘deep throttles’ will be considerably different to those where ponding occurs on the top of the B horizon. These findings have serious ramifications for many agricultural regions with texture-contrast soils. The failure of current management options (drains) to adequately control waterlogging is partly due to the lack of understanding of its causes and the prediction of this variability. Methods used to predict waterlogging at landscape scale in the Mt Lofty Ranges must differentiate between the causes of waterlogging, otherwise they have no practical use in this region.
Ephemeral drainage from the Keynes catchment was predominantly throughflow and groundwater discharge in the years of the study (low to average rainfall years) (ADL_04). The data showed the importance of throughflow in the transport of agricultural contaminants to groundwater (ADL_08) and streams (ADL_06). The stream waters that drain acid sulfate-like soils were highly saline and sulfidic with high phosphorus loads. Particulate materials (clays and attached pollutants) flocculate and sink to the streambed, resulting in most contaminants being transported in solution in low rainfall years. The data suggest that, with the exception of phosphorus, drainage waters from acid sulfate-like soils will only be of environmental concern in high rainfall years when flow is non-saline and there is erosion of the streambed.
Indexes that have been developed to predict the mobility of contaminants through soils, based only on the soil chemical properties (ADL_05), do not adequately predict the movement of these chemicals if the soil has macropores (ADL_07). An index, based on both soil physical and chemical properties, has been developed and published to better predict the movement of contaminants through soils with macropores. The index shows the importance of ‘residence time’ in predicting the mobility of agricultural contaminants through soils.
A new project was commenced with the aim of delineating salinity and waterlogging patterns in the Keynes catchment as predicted by terrain analysis and relating these data to previous data derived from piezometer investigations. Initial results are to be presented at the 10th Australasian Remote Sensing and Photogrammetry Conference in August, 2000.
2.2 Ability to recognise and predict the developing occurrence of waterlogged, saline, acid sulfate and sodic soils within catchment landscapes
2.2.1 Diurnal and seasonal redox changes in waterlogged soils in upland discharge areas in the Herrmanns catchment (ADL_15)
The Herrmann’s perched wetland is a saline discharge area in the Mt Lofty Ranges that is part of the 10% of strongly waterlogged landscape identified by a GIS analysis (see Table 1 in section 3.2 below). The wetland area, 50 m in diameter, was instrumented with a datalogger recording redox (Eh with platinum electrodes) at eight points, temperature probes at two, and rainfall. The sensors were placed along a 25 m transect extending from the marginal area re-vegetated with tall wheatgrass (Agropyron elongtum) to the centre of the wetland. The data records were captured at six hourly intervals since February 17, 1999.
There were pronounced diurnal changes in Eh in the top 5 cm in the wetland, and often at 20 cm, except during winter or when the system was perturbed by rainfall events. These diurnal changes “turned off” in autumn when soil temperature dropped below about 10o C for a period of about 100 days (to day 240) until the minimum soil temperatures rose above 10o C. There is a pronounced decrease in Eh in the late afternoon, often more than 100 mV, due to oxygen removal by the C4 wetland plants or algal mats. Except for the electrode in the sodic soil under tall wheatgrass, all electrodes placed at 20 cm recorded reducing conditions, mostly below 200 mV and commonly between 0 and –200 mV. In the sodic soil, the soil at 20 cm became reducing (about -200 mV) from May until September 1999, the wettest and coldest period. All electrodes, except for the two placed at 5 cm in the wetland, record strongly reducing conditions (0 to –200 mV) that are capable of reducing sulfate to sulfide, and in some instances (below –200 mV) to produce methane. The measurements confirm that the wetland and adjoining soils have conditions capable of reducing NO3-, Mn (IV), Fe (III), SO4-, and to produce methane, or arsine if suitable arsenic containing substrate is present.
The installed automated equipment to monitor soil redox status, moisture, temperature and rainfall at focus sites on the Dundas Tableland (Red Barren) and North China Plain (Nanpi Research station) are providing similar temporal data to support soil process models.
2.2.2 Changes in salinity and development of sodicity (ADL_14)
In the Herrmanns catchment sodic soils have been found to develop from saline soils (ECse >8dS/m) by fresh water leaching. These “secondary sodic soils’ develop from the drainage of saline soils when they are drained following the formation of nearby erosion gullies. These studies have demonstrated the important interrelationships between salinity and sodicity in the context of soil-water-landscape processes and the flocculation and dispersion of clay particles (ADL_14).
2.2.3 Identification and formation of potential acid sulfate soils (ADL_14)
In the Mt. Lofty Ranges and Dundas Tableland catchments the co-dominant anions in saline groundwaters and soils is sulfate and chloride. These saline soils are associated with geological formations that contain sulfur (i.e. pyrites or sulfate salts) and saline sulfate-rich groundwaters (EC 6-13 dS/m). Preferentially flowing through vertical cracks and old root channels, the sulfate-rich groundwaters seep under pressure to the soil surface where ‘potential acid sulfate soils’ (pH>6) develop (ADL_10, ADL_14). These soils have distinctive black coloured blotches because of the presence of sulfidic materials. If the water is evaporated, several types of salt efflorescences and iron oxide gels remain on the soil surface. This can result in a large buildup of minerals including gypsum, halite, thenardite, mirabilite and iron oxides (ferrihydrite and schwertmannite) (ADL_11, ADL_12). These accumulated soluble salt minerals and iron oxyhydroxide minerals are useful indicators of the soil-water processes operating in these catchments and provide possible management strategies for reclaiming such salt-encrusted spots, where only salt-tolerant vegetation will grow (usually sedges and rushes).
2.2.4 Changes in potential acid sulfate soils and development of actual acid sulfate soils
If the waterlogged ‘potential acid sulfate’ soils are disturbed or drained and exposed to the air, sulfuric acid forms and soil pH values can drop below 4 and sometimes below 2 (ADL_10; ADL_14). This process gives rise to different types of ‘actual’ acid sulfate soils, depending on the soil texture, organic matter content and concentration of ions present. The soil pores in these soils often become clogged because of the formation of various iron oxide minerals (natrojarosite, sideronatrite, schwertmannite or goethite). The formation of these minerals is indicative of rapidly changing local environments and variations in pH and rates of Fe, S and Na mineralisation (ADL_11, ADL_12, ADL_13).
Because the soil becomes clogged and less permeable, the sulfate-rich ground water, which is under pressure, moves side ways or upslope with consequent redevelopment of the cycle of formation of potential acid sulfate soils. These soils are unstable and erode easily, leaving cemented soil layers, which are relatively resistant to erosion. The processes give rise to saline scalds, erosion gullies and poor water quality in streams and dams (ADL_14).
2.2.5 Changes in greenhouse gas emissions (ADL_09)
Saturated, saline soils are potential sources of greenhouse gases that have not been adequately researched. High proportions of these soils occur in saline discharge areas and are potential acid sulfate soils. Depending on seasonal conditions, redox status and the nature of groundwaters (sulfidic, sulfatic or oxygenated), greenhouse gases such as CO2, N2O and CH4 may be emitted. Drainage of these sites may decrease production of these greenhouse gases. The acidification process accelerates the decomposition and formation of minerals in the soils and underlying rocks and causes an increase in salinity and carbonate formation (ADL_09).
2.3 Specification of the main processes that lead to degraded landscapes in the Mt Lofty Ranges, Dundas Tableland and North China Plain (ADL_10 to ADL_14)
We have developed new approaches for constructing mechanistic models of soil and water processes that explain and predict the processes giving rise to a range of complex and poorly understood acid sulfate, saline and sodic soils in catchments. We have applied quantitative field and laboratory measurements using hydropedological concepts along toposequences, geochemical and mineralogical analyses and simulation modelling in instrumented catchments. We report, for the first time, the identification of new soil types (inland acid sulfate soils) and iron minerals (e.g. sideronatrite and schwertmannite) that have formed by biomineralization processes. These processes are important because they can to be used to develop biogeochemical dispersion models to describe spatial and temporal changes that lead to degraded landscapes in the regions (ADL_10; ADL_14).
The Adelaide research group has shown that the toposequence is suitable for constructing mechanistic models of spatial and temporal biogeochemical changes in soils, because each of the vertical and lateral changes can be linked to hydrological (seasonal waterlogging), physico-chemical or biomineralogical processes. The toposequence approach provides an effective basis for understanding regolith and hydrological processes because each profile is influenced by, and influences, adjacent profiles, especially those downslope or in the direction of the surface hydraulic gradient. The structural approach provided us with an organisational framework to construct detailed mechanistic biogeochemical models for catchments in the Mt. Lofty Ranges and Dundas Tableland. We have applied the structural approach to describe in detail the vertical and lateral soil morphological and biogeochemical changes that takes place within toposequences. This approach describes the spatial and temporal changes (i.e. direction of expansion) that occurs when soils degrade (e.g. saline, acid sulfate and sodic soils). This is done by identifying and interpreting the major soil and hydrological processes from research involving field monitoring (e.g. salinity, redox potential and piezometers) and laboratory analyses of soils (e.g. chemical and mineralogical). The Adelaide group is currently using this information, together with more detailed biogeochemical data, to refine and develop more comprehensive geochemical dispersion models for each catchment.
In October, 1999 Rob Fitzpatrick and Phil Davies travelled with SIAM staff (Renzhao Mao, Xiaojing Liu and Li Weiqiang) to the North China Plain, where they sampled 6 saline, sodic and acid sulfate soil profiles (68 samples) along a transect from Nanpi/Wangsi research stations to the Bohai sea (Yangcheng reservoir/ Haixing research station). The samples are being used to help assess and predict soil risk on the North China Plain.
In China both groups have produced very important soils environmental research. In SIAM Dr Hu Chunsheng has been involved in research which is using soils data to provide indicators of carry capacity for the North China Plain, see SIAM_06 and SIAM_07. In addition to being involved with research initiated by staff from Adelaide, Renzhao Mao has been instigated research with staff from Adelaide looking at determining the magnetic susceptibility of saline soils (SIAM_09).
For the Loess Plateau there have been several papers addressing the need for soil conservation methods to be incorporated into sustainable agricultural practices. In ISWC_08 Dr Guobin presented a ‘discussion’ paper on this topic which summarised his many years of direct research and experience in this important research topic. To put this ideas into practice data availability is a key issue which often constrains applying methods to large areas. Options for overcoming this problem have been researched by spatial soils staff in Yangling (ISWC_07).
Year 4 (00/01) Progress - as extracted from the Annual Report
Collaborators from Other Organisations
David Machmedt (PIRSA) Soil Survey
John Hutson (Flinders University) Soil Physics, modelling
David Bruce (University of South Australia) Remote sensing,
Lyall Bishop (University of South Australia) GIS
Peter Self (University of South Australia) Mineralogy
Jane Gillooly (Consultant) Climatology
Jodie Pritchard. (Hons. Student, Univ. Adelaide) Modelling
Rob Norton (Melbourne Univ. Horsham) Agronomy, landuse.
Jonathon Fawcett (PhD. Student Melbourne Univ. Horsham) Hydrology, Land use.
Bill Gardner (Consultant) Agronomy, drainage
Richard MacEwan (University of Ballarat) Pedology, land use.
Malcolm McCaskill (Ag. Victoria, Hamilton) Modelling/ pastures
Hugh Brown (Ball State University, USA) Pedology/ modelling
Joost Brouwer (Wageningen, Nth.) Pedology, soil physics
Emmanual Fritsch (ORSTOM - France) Pedology
Jerry Bigham (Ohio State, USA) Mineralogy
Please direct research and general email enquiries to
Rob Fitzpatrick in Australia and Liu Guobin (ISWC) or Yang Yonghui (SIAM) in China
Last updated 7 May 1999 communicator@eoc.csiro.au
Copyright 1998, CSIRO Australia
Use of this web site and information available from it
is subject to one or more of the following leagal notices
CSIRO Legal Notice and Disclaimer