Coastal Dune Zone

Posted on Jan 23, 2015


LandResourcesCoastal Dune Zone

Also known as the Perth Coastal Zone, the Coastal Dune Zone is made up of coastal sand dunes and calcarenite. Late Pleistocene to Recent (Quindalup and Spearwood Systems). Calcareous and siliceous sands and calcarenite.

The Coastal Dune Zone includes the youngest dunes being the Quindalup dunes which occur nearest to the coast and then the Spearwood dunes. Limestone occurs as pipes in the profile of the Quindalup dunes and the western margin of the Spearwood dunes, and as limestone rock at the base of both the Quindalup and Spearwood dunes.

The Quindalup dunes are composed of unconsolidated sand (quartz grains) and shell fragments. Sometimes organic matter darkens the surface layers. The shell fragments are mostly calcium carbonate, so the sands are alkaline. As the shell fragments dissolve, calcium moves down the profile and is deposited as lime, initially around plant roots, to form pipes, which are exposed by wind erosion of sand from the surface of dunes at or near the coast (i.e. the Quindalup dunes), or on the western margin of the Spearwood dunes. Eventually, the lime is deposited as limestone at the bottom of the profile of the dunes. The lime at the base of the dunes is dissolved by water to form caves. Good quality water suitable for irrigation is stored in the caves, and is used to water gardens and parks on the Quindalup and Spearwood dunes, or to water vegetable crops grown on the Spearwood dunes.

The Quindalup dunes are not used for agriculture or horticulture for the following reasons. The dunes hold very little water and are only wet when heavy rain is falling. The dunes are also extremely infertile and, when cleared of native vegetation, are very easily eroded by winds. In addition, unlike the native plant species, agricultural and horticultural species are not well adapted to surviving the strong winds and salt spray from the ocean.

Because of their proximity to the ocean, the Quindalup dunes are rapidly being urbanised.

The Spearwood dunes are often higher than either the Quindalup or Bassendean dunes. The Spearwood dune system is believed to have been formed about 40,000 years ago, and comprise red/brown, yellow and pale yellow/grey sands. The sands are coated with both iron and aluminium oxides, with the amount of iron oxide coating the sands largely responsible for the colour of the sands. The greater the amount of iron coating the sand, the darker the colour. The amount of iron and aluminium coating the sand grains increases the capacity of the sands to retain phosphorus (P). The darkest coloured red/brown sands occur farthest to the west of the Spearwood dune system, nearest the Quindalup dunes. These darker coloured sands are closely associated with the limestone pipes or rock, and are exposed by wind erosion of the yellow sand that overlayed the darker sand and limestone.

The eroded sand was blown inland, to expose the darker coloured sand and the limestone. The red/brown sands have been called Cottesloe sands, or terra rosa soils. Most of the Spearwood sands are yellow, and are called Karrakatta sands. The sands become less coloured as they age because the iron (and aluminium) coating the sands is leached. The paler coloured Spearwood sands are farther inland. The red/brown sands are only found near the Quindalup dunes, and are originally deep in the profile, unless exposed by wind erosion, and are coated with the most amount of iron (and aluminium). The yellow sands, the yellow phase of the Karrakatta sands, are to the west of the Spearwood dune system. The paler yellow/grey sands, the grey phase of the Karrakatta sands, occur to the east.

Between the dune systems, inlets, lakes and swamps occur. Inlets (e.g. the Leschenault inlet) occur between the Quindalup and Spearwood dunes. Lakes and swamps occur between all three dune systems. The soils under the swamps and lakes are rich in organic matter, so they are peat swamps, and have often been drained and used for vegetable production. In other places near cities (Perth, Mandurah, Bunbury) or towns (Waroona, Harvey, Pinjarra) the swamps have been used as rubbish tips, or filled in and used for sport and recreation, or as building sites.

Major agricultural and horticultural industries on the dunes

The Cottesloe and Karrakatta sands of the Spearwood dune system frequently have good quality water suitable for irrigation relatively close to the soil surface, consequently these sands have been used for vegetable production. Initially the Cottesloe and yellow phase of the Karrakatta dunes were preferred. However, both the Cottesloe and yellow phase Karrakatta sands are now being urbanised, because they are in popular areas near the coast, forcing vegetable growers onto the grey phase Karrakatta sands and onto the Bassendean dunes.

SWCC Strategic Priority

Threats to be addressed:

  • Wind erosion

DAFWA – Report Card (September 2013) The Coastal Dune Zone, for the purposes of DAFWA’s Report Card, is included in the Agricultural Soil Zone 5. Swan to Scott Coastal Plains (along with the Bassendean Zone, Pinjarra Zone, Scott Coastal Zone and the Donnybrook-Leeuwin Zone). Agricultural Soil Zones are based on repeating patterns of soil and land types. The Ag Soil Zones are used for reporting on the following themes:

  • Soil acidity
  • Wind erosion
  • Water erosion
  • Soil organic carbon
  • Soil compaction
  • Water repellence
  • Nutrient status (phophorus)

Hydrozones are based on grouping areas with similar hydrology and are used for reporting on:

  • Dryland salinity

The Coastal Dune Zone is identified along with the Bassendean and Pinjarra Zones as the hydrozone, Coastal Plain.

Key Findings for this Zone

Soil Acidity

Soil Acidity

Summary – A large proportion of soils are below target, and the trend shows continuing deterioration.

Condition and Trend –Very Poor and Deteriorating (confidence in condition and trend: adequate high-quality evidence and high level of consensus or limited evidence or limited consensus).

Soil acidification and resulting poorer root growth and nutrient use is likely to be more important in coastal zones because of the implications for nutrient leaching and eutrophication of waterways. Increased testing and awareness of subsurface soil acidity is recommended as well as consideration of lime quality when calculating appropriate rates.

This coastal zone is dominated by four main soils accounting for about 70% of the area. Surface soil acidity is extreme. From 70-81% of samples collected had pH below the recommended target layer depending on soil type. Subsurface acidity in the 10-20cm layer is also an issue, although fewer subsurface samples were collected from this region, probably due to the dominance of pasture and decreased need to access deeper soil moisture because of the higher rainfall.

A summary of the percentage of samples below target for depths 0-10 cm, 10-20 cm and 20-30 cm for the Ag Soil Zone 5. Swan Coastal Plain to Scott Coastal Plain (DAFWA Report Card, 2013).

A summary of the percentage of samples below target for depths 0-10 cm, 10-20 cm and 20-30 cm for the Ag Soil Zone 5. Swan Coastal Plain to Scott Coastal Plain (DAFWA Report Card, 2013).

Source: Gazey C, Andrew J and Griffen E (2013). ‘Soil Acidity’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Soil Acidification in the south-west of Western Australia go here.

Wind Erosion

Wind Erosion

Summary – Wind erosion hazard was not monitored for this zone.

Hazard and Trend – Not assessed

Source: Carter D and Laycock J (2013). ‘Wind Erosion’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Wind Erosion in the south-west of Western Australia go here.

Water erosion

Water erosion

Summary –Largely stable. Enterprises in the north are exposed to erosion from flooding of major rivers.

Hazard and Trend – Low and stable (confidence in hazard and trend: limited evidence  or limited consensus in both).

Source: Galloway P and van Gool D (2013). ‘Water Erosion’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Water Erosion in the south-west of Western Australia go here.

Soil organic carbon

Soil organic carbon

Summary – SOC levels related to wide rainfall range. Very high levels often associated with irrigated, fertilised pastures. Decline in SOC under intensively cultivated horticultural systems.

Abundance and Trend – High to very high and unclear trend (confidence in hazard: limited evidence or limited consensus; confidence in trend: evidence and consensus too low to make an assessment).

Source: Griffen E, Hoyle F and Murphy D (2013). ‘Soil Organic Carbon’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Soil Organic Carbon in the south-west of Western Australia go here.

Soil compaction

Soil compaction

Summary – No extensive cropping or use of heavy machinery. Soils not vulnerable.

Hazard and Trend – Low (meaning soil hazard generally low and current land use unlikely to cause compaction) and stable (confidence in hazard and in trend: limited evidence or limited consensus).

Source: Carter D, Davies S and Schoknecht N (2013). ‘Soil Compaction’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Soil Compaction in the south-west of Western Australia go here.

Water repellence

Water repellence

Summary – Most of the aeolian (wind deposited) sandy areas are severely water repellent. No problems where alluvial soils occur.

Condition and Trend – Very poor (meaning water repellence widespread) and stable (confidence in condition: Adequate high-quality evidence and high level of consensus; and in trend: limited evidence or limited consensus).

Source: Carter D, Davies S Blackwell P and Schoknecht N (2013). ‘Water repellence’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

Dryland Salinity

Dryland Salinity

Summary – Extent of salinity very minor; future development possible in the north, but with low impact. Mostly stable trends in groundwater levels.

Risk and Groundwater Trends – Low (Likelihood of occurring: possible; consequence: minor) and stable (confidence in condition and in trend: limited evidence or limited consensus).

Groundwater is shallow over much of the plain but trends are stable, responding to seasonal rainfall. Salinisation on the coastal plain is limited to poorly drained areas on the Pinjarra Plain and coastal swales. The salinity risk is low. Expansion of the area affected is possible but with minor consequences depending on whether high intensity land uses move into poorly drained areas. Increasing salinity is likely in surficial aquifers. Widespread soil salinity occurs in the south-west irrigation areas but is not included in this analysis.

Source: Simons J, George R and Raper P (2013). ‘Dryland Salinity’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Dryland Salinity in the south-west of Western Australia go here.

Nutrient status (phosphorus)

Nutrient status (phosphorus)

Summary – Soil P fertility in excess of optimal range. This could change to well in excess with continued P application; however, ceasing P application would see P levels slowly decrease to optimal levels.

Condition and Trend – Excess (meaning P fertility index > 1.1 – 1.5) and stable (confidence in condition and in trend: limited evidence or limited consensus in both).

Source: Weaver DM and Summers RN (2013). ‘Nutrient status (phosphorus)’. In: Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.

To find out more about Nutrient status (phosphorus) in the south-west of Western Australia go here.

Projects:

SWCC has developed two videos to help you get started with soil health. Part 1 describes a process for investigating soil health and identifying what constraints to manage first. Part 2 answers some common soil health questions, such as how to manage soil organic matter and soil biology, impacts of synthetic fertilisers on soil biology, and organic soil amendments such as compost and biochar.

Source:

  • Department of Agriculture and Food 2013, Report card on sustainable natural resource use in agriculture, Department of Agriculture and Food, Western Australia.
  • N. Schoknecht, P. Tille, B. Purdie (2004). Soil-landscape mapping in south-western Australia. An overview of methodology and outputs.
  • Van Gool, D., Vernon, L. and Runge, W. (2008). Land Resources in the South-West Agricultural Region. A shire-based summary of land degradation and land capability. Department of Agriculture and Food Western Australia.
  • Bolland, M. (1998). Soils of the Swan Coastal Plain. Bulletin 4359. Department of Agriculture, Bunbury.

 

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