Causes impacts and sustainability issues of dryland salinity
Causes, impacts, and sustainability issues of dryland salinity on wetlands in Australia SWES 574 W. J. Ward 12/09/2003
Mining and Agriculture Anthropogenic Salinisation ØDryland salinities result from: • Diverted inflows for irrigation and other uses • Excessive clearance of natural, deep rooted vegetation from catchments • Discharge of saline agricultural wastewater • Rising saline groundwater • Mining and discharge of brine waters Ø Salinity rising in: Mono Lake, CA. , Pyramid Lake, NV. , Aral Sea, Asia, Qinghai Hu, China, Lake Qarum, Egypt, Lake Corangamite, AUS. and rivers Syr, Amu darya, Asia, Blackwood, AUS.
Anthropogenic Salinisation (cont. ) Ø Salinisation common in semi-arid regions of annual rainfall of 25 -500 mm Ø 43 -47 % of all irrigated land has been effected by salinisation Ø Potential to cause irreversible damage to arid land rivers and wetlands Ø In Australia lost agricultural production is $ 50 mil/yr U. S. and degradation of infrastructure is an additional $ 90 mil/yr. U. S. Ø Vegetation death is caused by toxic levels of bicarbonate, magnesium, sulphate, sodium, and chloride Ø Loss of species and species diversity Ø Waters become unusable for irrigation or drinking
Copper Lode Gold Nickel Bauxite Tin Uranium Figure 1 – Known Mineral Resources
Water table rises with increased groundwater mobilization Removal of native vegetation causes increased recharge to groundwater s ep Se e n ali S Low P erme ability s rop C nd ing a l z Dry Gra d an layer Hydraulic Pressure and upward groundwater movements in aquifers Saline soil develops where water table rises to less than 2 meters from surface Saline lake size increases as water table rises Saline groundwater in drains Figure 2. Clearing deep rooted vegetation leads to salinity of rivers and lakes
CEC = total amount of exchangeable cations that can be held by a given mass of soil
Exchangeable Ca / Na Cation Experiment • Saturate Arizona White House Bt horizon clay with Na. Cl Cations • Removed Cl ions by washing • Mix clay with sand for permeable layer • Flow solution of Ca. Cl 2 through clay/sand • Remove excess Ca cations and Cl ions by washing • Extract Ca cations with La. Motte Extraction Solution • Precipitate Ca cations with La. Motte Sodium Oxalate • Compare sample precipitate with La. Motte sample strip
RESULTS: Visually compare test tube results with PPM chart Background Ca Na Exchanged 130 mg/L Ca Na Exchanged in Sat. Ca
Australian rising groundwater salinity – sequence of events & dryland salinity hazard mapping using GIS Ø Tree clearing in upper part of catchment Ø Winter rains with low evapotranspiration Ø Fractured rock deep groundwater aquifer Ø Hydraulic head beneath clay floor Ø Kaolinite, illite, and semectite in debrisflow allows cation-exchange releasing sodium Ø Clays decrease hydraulic conductivity under saturated conditions Figure 3. Dryland Salinity Hazard
Summary • Early mining timber use and early settlement and agriculture land clearing degraded long term sustainability • Increased recharge creates valley area groundwater discharge through clay debris flow. • Discharge cation exchange causes increased salinity of surface waters negatively impacting lakes and wetlands
Summary (cont. ) • Column experiment simulated the cation exchange between Ca & Na in high CEC clays • Cation exchange occurring in Yass River Catchment, New South Wales, Australia causing rising salinity in rivers, lakes, and wetlands • Mapping salinity and remediation to prevent excess infiltration is key to further damage
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