Operative Waikato Regional Policy Statement (October 2000)

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3  Significant Resource Management Issues, Objectives, Policies and Methods

3.3  Land and Soil

3.3.6 Significant Resource Management Issues

This section briefly sets out the significant land and soil resource management issues for the Waikato Region.

Erosion is a natural phenomenon which constantly acts to reduce landscapes and lower slope angles. New Zealand is geologically young and active and, as a result, the natural level of erosion is high by international standards. Changes to the vegetative cover of the land brought about by activities such as farming, burning, forestry, road construction or urban development, frequently disturb the balance by reducing protection against erosive forces and leads to accelerated erosion. Land uses can be undertaken with management practices that avoid degradation of land and water resources. It is accelerated erosion (erosion that is accelerated or caused by human activity) that is the focus of section 3.3.7 of the regional policy statement.

Although much of the Waikato Region is stable, the National Land Resource Inventory Worksheets identified over one million hectares affected by erosion with almost 36,000 hectares ranked as severe to extreme. In the Waikato Region accelerated erosion occurs in different forms depending on the locality as described in sections 3.2-3.5.

The effects of accelerated erosion include:

1. long term irreversible impacts which have potential to constrain future land uses
   
2. water quality is affected both in terms of clarity and nutrient status. This has effects on biological communities living in freshwater and estuarine water bodies as well as on aesthetic and recreational values (Refer to section 3.4 Water)
   
3. the occurrence and severity of natural hazards may be exacerbated (Refer to section 3.8 Natural hazards).

Many land based activities make use of material which, if discharged or deposited in or on the land, has the potential to significantly alter the physical, chemical or biological condition of the soil. In the past, soils in parts of the Region have been contaminated by discharges of contaminants onto or into land. For example, the fungicide pentachlorophenol (PCP) (used as a timber preservative) has contaminated soils at numerous old timber treatment sites.

Existing contaminated sites¹ are addressed in section 3.10.3. However, there is a need to ensure that soil contamination does not occur in the future. Soil contamination can occur either from:

1. Discrete Contamination - where chemicals are spilt or disposed of incorrectly. Methods of avoiding this sort of contamination are addressed in section 3.10 Hazardous Substances.
   
2. Diffuse Contamination -where the soil is contaminated as a side effect of the use of materials in land based activities. The substances involved may include fertilisers, pesticides, herbicides, some wastes etc.

The effects of soil contamination depend upon the chemical involved, but they can include reduced soil versatility and productivity. Some contaminants are bioaccumulative and may, even in low concentrations, pose an environmental health hazard. The presence of these contaminants may restrict future uses of the soil resource.

Contaminants in the soil can be leached from the soils and contaminate surface and ground water resources. Issues associated with water quality are addressed in section 3.4 Water.

The term soil health encompasses soil physical and chemical conditions and biological activities which make soil a dynamic, productive ecosystem, as distinct from an accumulation of weathered rock.

A survey of commercial soil test results in the Waikato Region shows that 50 percent of dairy land, and 70 to 75 percent of drystock land is below optimum phosphate levels. The implications of these low levels are less vigorous pasture growth, greater erosion risk and reduced income.

Soil compaction due to stock treading, reduced infiltration capacity, horticulture and cropping can have significant effects in the Waikato Region. Hydraulic conductivity may be reduced by 65 to 80 percent leading to ponding and/or increased runoff. Root penetration and aeration in the rooting zone are also reduced.

Poor moisture management within productive soils is indicated by ground water levels that are either too high, resulting in a loss of productivity, or too low so that over drainage occurs with a consequent damage to soil structure.

The Waikato Region contains large areas of agricultural land that rely on drainage to maintain production. This production is economically important to the Region and the nation. The proper management of drained soils is important to ensure that agricultural production from this land is sustainable.

Land drainage activities within the Region are concentrated mainly in the valleys of the Lower Waikato, Waipa and Mangawara rivers, the Hamilton Basin and the Hauraki plains. Approximately 45 percent of the drained land within the Region is former peat swamp. Peat soils are susceptible to irreversible damage due to poor soil moisture management.

Drainage of peat for agricultural production requires achieving a balance between the conflicting requirements for maintaining the water table at a low enough level to maximise agricultural production and maintaining the water table high enough to minimise long term damage. Varying land uses within land drainage areas may result in conflicts over the optimum drainage standard.

Destabilisation of the beds of rivers and lakes may have adverse effects on water quality through increased transport of sediment, and erosion and deposition causing damage to aquatic habitat. Destabilisation may also cause changes in the course of rivers and streams resulting in loss of land, damage to property and damage to infrastructural assets such as roads, bridges and flood protection and drainage works.

Activities within or adjacent to the beds of rivers, streams or lakes can cause damage to the beds and banks, or result in changes in the hydraulic regime which can cause destabilisation. Structures located within the beds of rivers and streams may alter flow characteristics, water levels, or sediment transport patterns, or cause or contribute to erosion and/or deposition resulting in bed destabilisation. Structures in the beds or on the shores of lakes which interfere with either littoral currents or off-shore currents, or reflect or refract wave energy, may cause instability. Some structures may also have visual impacts and could limit access to the beds and banks of lakes and rivers. Section 3.3.11 addresses destabilisation within or adjacent to river and lake beds which may result in the adverse effects listed above.

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Footnotes

1. See Glossary for definition of contaminated sites.