Gley Soils have ‘reductimorphic features’ which are
evidence of oxygen depleted (chemically reduced) conditions that generally extend to at least 90 cm depth. Reductimorphic features are defined as including:
(1) redox depletions, which are pale (low chroma,
2),
predominantly bluish-, greenish-, or whitish-grey, colours, in the soil matrix or on ped faces or pore walls,
signifying long-term water saturation; and/or
(2) redox concentrations which are rust-coloured or orange
mottles and/or small black to brown spots, concretions,
or nodules, in the soil matrix together with dark
Mn-rich or Fe-rich coatings on ped faces or pore walls
signifying short-term water saturation (and oxygen
depletion) interspersed with periods of oxidation.
5.1.2 Areas of Occurrence
Gley Soils are located throughout New Zealand comprising
about 3% of the country (Fig. 5.2). Gley Soils form in the
landscape wherever there is prolonged wetness that has led
to oxygen depletion. Commonly Gley Soils form in
low-lying areas with high groundwater tables, or where
water accumulates in sloping gullies, seepages, or at the base
of slopes (Sect. 5.3). Gley Soils can also occur in elevated
situations (on hills) where upper horizons are slow draining
because water is held up (perched) on an impeding pan or
slowly permeable horizon. Gley Soils are more common in
areas of high rainfall, such as south-Westland. Together with
Fig. 5.1 Gley Soil and associated landscape. Left: Gley Soils often
form in swampy, low lying, areas where there is a high groundwater
table such as this foot slope position. Such areas often have
water-tolerant vegetation such as rushes (Juncus sp.). Right: Gley Soil,
with mottled and grey (low-chroma) colours that indicate that saturation
has occurred intermittently in the topsoil and for prolonged periods at
depths below about 60 cm. The water table is evident at 95 cm depth
Fig. 5.2 Map showing main areas of occurrence of Gley Soils. There
are many small areas of Gley Soil throughout New Zealand that do not
show on a map of this scale
74
5 Gley Soils
evidence of oxygen depleted (chemically reduced) conditions that generally extend to at least 90 cm depth. Reductimorphic features are defined as including:
(1) redox depletions, which are pale (low chroma,
2),
predominantly bluish-, greenish-, or whitish-grey, colours, in the soil matrix or on ped faces or pore walls,
signifying long-term water saturation; and/or
(2) redox concentrations which are rust-coloured or orange
mottles and/or small black to brown spots, concretions,
or nodules, in the soil matrix together with dark
Mn-rich or Fe-rich coatings on ped faces or pore walls
signifying short-term water saturation (and oxygen
depletion) interspersed with periods of oxidation.
5.1.2 Areas of Occurrence
Gley Soils are located throughout New Zealand comprising
about 3% of the country (Fig. 5.2). Gley Soils form in the
landscape wherever there is prolonged wetness that has led
to oxygen depletion. Commonly Gley Soils form in
low-lying areas with high groundwater tables, or where
water accumulates in sloping gullies, seepages, or at the base
of slopes (Sect. 5.3). Gley Soils can also occur in elevated
situations (on hills) where upper horizons are slow draining
because water is held up (perched) on an impeding pan or
slowly permeable horizon. Gley Soils are more common in
areas of high rainfall, such as south-Westland. Together with
Fig. 5.1 Gley Soil and associated landscape. Left: Gley Soils often
form in swampy, low lying, areas where there is a high groundwater
table such as this foot slope position. Such areas often have
water-tolerant vegetation such as rushes (Juncus sp.). Right: Gley Soil,
with mottled and grey (low-chroma) colours that indicate that saturation
has occurred intermittently in the topsoil and for prolonged periods at
depths below about 60 cm. The water table is evident at 95 cm depth
Fig. 5.2 Map showing main areas of occurrence of Gley Soils. There
are many small areas of Gley Soil throughout New Zealand that do not
show on a map of this scale
74
5 Gley Soils