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

• 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

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.

Dryland salinities result from:

Anthropogenic Salinisation (cont.)

Salinisation common in semi-arid regions of annual rainfall of 25-500 mm

43-47 % of all irrigated land has been effected by salinisation

Potential to cause irreversible damage to arid land rivers and wetlands

In Australia lost agricultural production is $ 50 mil/yr U.S. and degradation of infrastructure is an additional $ 90 mil/yr. U. S.

Vegetation death is caused by toxic levels of bicarbonate, magnesium, sulphate, sodium, and chloride

Loss of species and species diversity

Waters become unusable for irrigation or drinking

Copper Lode Gold Bauxite Tin

Nickel Uranium

Figure 1 – Known Mineral Resources

Removal of native vegetation causes increased recharge to groundwater

Water table rises with increased groundwater mobilization

Low Permeability layer

Saline Seeps

Dry land Crops

and Grazing

Hydraulic Pressure and upward groundwater movements in aquifers Saline soil develops

where water table rises to less than 2 meters from surface

Saline groundwater in drains

Saline lake size increases as water table rises

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 NaCl Cations

• Removed Cl ions by washing• Mix clay with sand for permeable layer• Flow solution of CaCl2 through clay/sand • Remove excess Ca cations and Cl ions by

washing• Extract Ca cations with LaMotte Extraction

Solution• Precipitate Ca cations with LaMotte Sodium

Oxalate• Compare sample precipitate with LaMotte

sample strip

RESULTS: Visually compare test tube results with PPM chart

Background Ca Na Exchanged 130 mg/L Ca Na Exchanged in Sat. Ca

Figure 3. Dryland Salinity Hazard

Tree clearing in upper part of catchment

Winter rains with low evapotranspiration

Fractured rock deep groundwater aquifer

Hydraulic head beneath clay floor Kaolinite, illite, and semectite in debris-

flow allows cation-exchange releasing sodium

Clays decrease hydraulic conductivity under saturated conditions

Australian rising groundwater salinity – sequence of events & dryland salinity hazard mapping using GIS

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

Reference List

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