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Figure 1. Changes in soil stability between 2007 – 2012
60.4% of the Waikato region's point sample in 2012 currently have no soil disturbance and are therefore intact and currently well-vegetated. Soil disturbance (natural through erosion/deposition or as a result of land use disturbance) which exposes bare soil can lead to land degradation and loss of soil.
Soil disturbance in the region accounts for 32.3% of the region's point sample in 2012. The actual measure of bare soil amounts to 1.93% or 48,250 hectares of the region’s area.
The main pressure from land use disturbance in 2012 (Figure 2.) is from tracking which accounts for 0.89% of the total 1.31% of bare soil. There has been no change in bare soil relating to tracking between the two survey dates. The one class where there was a significant change is cultivation down from 0.81% in 2007 to 0.16% in 2012. There has been a small decrease in all other categories.
Figure 2. Change in bare soil by land use disturbance 2007 – 2012
Natural disturbance accounts for 9.1% of the region in 2012. Although natural disturbance as a percentage of the region is up from 7.5% in 2007, the area of bare soil by region is down, from 0.52% in 2007 to 0.38% in 2012. There has been a significant change between dates in the category surface erosion, which is made up of sandblows, sheetwash, rock fall or bare rock and geothermal classes (Figure 3).
Figure 3. Change in bare soil by natural process disturbance between 2007 – 2012
Surfaces where the soil has been partly or completely removed by rural buildings, roads, urban areas or waterbodies are categorised as extensively disturbed. The number of points recorded across the region has increased slightly from 7.0% in 2007 to 7.3% in 2012 and the area of bare soil has slightly increased from 0.23% to 0.24% in 2012. The changes is attributed to an increase in bare soil in the waterbodies class.
Overall bare soil has reduced significantly from 2.85% in 2007 to 1.93% in 2012. Most of this decrease is related to a decrease in land use disturbance from 2.27% in 2007 to 1.44% in 2012. The decrease in bare soil from natural processes went from 0.57 % in 2007 to 0.48 % in 2012.
Figure 4 shows that there have been significant decreases in bare soil associated with land use disturbance under horticulture and cropping, dairying, dry stock, and forestry.
Figure 4. Changes in bare soil through land use disturbance between 2007 – 2012
The results indicate that although there has been increase in the percentage of eroding surfaces in 2012, the actual amount of bare soil generated through natural processes on these surfaces has decreased. The eroding surfaces are subjected to natural processes and will need to be stabilised and re-vegetation of these surfaces as soon as possible will prevent further exposure and release of sediment.
There has been a sharp decline in the area of bare soil under the commercial land uses of horticulture and cropping, dairying, dry stock, and forestry going from 2.27% in 2007 to 1.44% in 2012. The change will help avoid soil loss and potentials sediment generation.