- 2.1 Survey of Regional Officials
- 2.2 Agricultural Impacts on Water Quality
- 2.3 Sedimentation of Water Bodies
- 2.4 Nutrient Loading
- 2.5 Alterations in Physical Characteristics of Waterways
- 2.6 Faecal Contamination
- 2.7 Pesticides and Water Quality
- 2.8 Nitrate Contamination of Groundwater
- 2.9 Increased Oxygen Demand and Ammonia Toxicity in Streams
- 2.10 Reduced Flow in Streams and Rivers
- 2.11 Summary
2.0 THE NATURE AND EXTENT OF AGRICULTURAL IMPACTS ON WATER QUALITY
There is a large body of literature in New Zealand regarding agricultural impacts on water quality, largely consisting of technical descriptions of site-specific situations. As a result, we have a growing appreciation of the physical processes of runoff and groundwater flows, including how sediment, nutrients, and contaminants are transported. Some of these findings are summarized below.
The National Institute of Water and Atmospheric Research (NIWAR)3 monitors drinking water supplies for a variety of contaminants on behalf of the Department of Health (Mattingly, 1991). In 1989, NIWAR scientists began national monitoring of a full range of water quality criteria in 77 major rivers. The study is designed primarily to monitor long term trends, rather than specific impacts, but should also provide useful comparisons between sites (Smith and Quinn, 1991). The dataset has also been matched with land use data, enabling analyses of the relationship between land use and water quality (Smith and Quinn, 1992).
2.1 Survey of Regional Officials
It remains difficult, however, to obtain an overall assessment of agricultural impacts on water quality. In an attempt to partially overcome this problem, MAF surveyed regional councils in June 1991 to get their assessment of impacts on water quality. Regional councils were chosen due to their working knowledge of water quality issues stemming from statutory responsibilities.
Among other things, the survey revealed that all fourteen regional councils collect water quality data4. Some councils collect a considerable amount of data; others are increasing their efforts. For instance, the Otago Regional Council has initiated an annual survey to complement the NIWR national monitoring programme, and monitors faecal coliforms, plant nutrients, pH, dissolved oxygen, conductivity, and other parameters at a series of river and lake sites. In addition to systematic monitoring, councils collect data in the course of monitoring water rights, investigating complaints, and studying particular problems (e.g. see Huser, 1990).
This report does not attempt to summarise the data collected by the fourteen councils, but rather to provide a general description of the nature and extent of impacts based on published data and MAF's survey of regional officials. This report, therefore, should be seen as a first step. The need for further work is discussed in the final section of this paper.
In the survey, regional officials ranked primary agriculture and human sewage as causing the most damage to water quality of nine major sources, with the average values being 4.9 and 4.8, respectively, on a scale from 0 to 10. Three respondents gave primary agriculture ratings of 8, indicating serious damage. When impacts from agricultural processing are included, the agricultural sector is seen by regional officials as being the most significant source of water quality problems. See the first column of Table 1.
Table 1: Sources of impacts on water quality, as ranked by regional officials
0 = no damage
10 = severe damage
Simple |
Weighted Average |
Weighted Average |
|
Average |
(Population)1 |
(Area)2 |
|
| Primary agriculture | 4.9 |
5.4 |
4.8 |
| Human sewage | 4.8 |
4.3 |
4.3 |
| Urban storm run-off | 3.9 |
4.1 |
4.2 |
| Industry (excl agric.) | 3.8 |
4.4 |
3.5 |
| Agric. processing | 3.7 |
3.7 |
4.2 |
| Mining | 2.6 |
2.1 |
3.0 |
| Forestry | 2.6 |
2.7 |
2.7 |
| Other | 0.7 |
1.6 |
0.3 |
| Native vegetation | 0.5 |
0.2 |
0.7 |
1 The ranking provided by each region was weighted by the region's proportion of the total population of New Zealand.
2 The ranking provided by each region was weighted by the region's proportion of the total area of New Zealand.
Other major sources of water quality problems identified in the survey were urban runoff and industry. Mining and forestry were also cited as significant but, overall, less serious sources of water quality problems.
The survey responses were also weighted by population of each region. This increases the weight given to responses from heavily populated regions on the premise that more people are affected and therefore the water quality problems are in that sense more serious. This weighting system increases the amount by which primary agriculture exceeds the second-ranked source, but the only other difference is that industry (excluding agricultural processing) replaces human sewage as the second-ranked problem.
Total land area was used as an alternative weighting scheme on the premise that, because larger areas are likely to include more total water, a stated water quality problem probably affects more water and is therefore more serious than a problem assigned a similar value in a small region. Again, this weighting increases the prominence of primary agriculture as a source of water quality problems. Other results of this weighting are that agricultural processing and urban storm runoff appear somewhat more serious, and non-agricultural industry somewhat less serious, though relative rankings are only marginally affected.
Neither of the alternative weighting schemes sufficiently alters the conclusion that agriculture is a major source of impacts on water quality.
2.2 Agricultural Impacts on Water Quality
The survey also asked respondents for indications of the severity of specific agricultural impacts on water quality, the sources of those impacts, and the relative damage done to other users of the water resources.
Of nine major agricultural impacts on water quality, regional officials identified sedimentation and nutrient loading of surface water bodies as the most serious. Changes to physical characteristics of surface waters and faecal contamination of surface waters were ranked as slightly less serious impacts, followed closely by nitrate contamination of groundwater. See Table 2. One council noted that some impacts are not well documented, which may lead to erroneously low rankings compared to impacts that are well documented. The various impacts are discussed separately below.
Responses on the severity of specific water quality problems were weighted by population and area, respectively. Neither alternative weighting had a significant effect on the ranking or magnitude of the various impacts.
Table 2: Specific agricultural impacts on water quality
Main Sources |
Severity |
Main Sources |
Effects |
| Sedimentation | 6.4 |
1 non-ag activity |
1 scenic |
2 crops (all) |
2 fishing | ||
| Nutrient contamination | 6.2 |
1 dairy sheds |
1 fishing |
2 dairy pasture |
2 scenic | ||
| Alteration of | 5.6 |
1 dairy grazing |
1 habitat |
| physical characteristics | 2 other activity |
2 scenic | |
| Faecal contamination | 5.4 |
1 dairy sheds |
1 Maori |
| of surface water | 2 dairy pasture |
2 Recr'n | |
| Nitrate contamination | 4.6 |
1 stock urine |
1 drink'g |
| of groundwater | 2 fertiliser |
||
| Pesticide contamination | 2.8 |
-insufficient data |
|
| of surface water | |||
| Faecal contamination | 2.8 |
1 sheds |
1 drink'g |
| of groundwater | 2 other |
2 stock | |
| Pesticide contamination | 1.6 |
-insufficient data |
|
| of groundwater | |||
2.3 Sedimentation of Water Bodies
Over the past 150 years, vast areas of New Zealand have been cleared of native vegetation for farming. As a result, soils have been exposed to surface erosion by wind and water, as well as land slips. This adds to New Zealand's high natural rate of erosion, which is related to the country's active tectonic setting, soil types and wet climate (Blaschke
In the survey, regional officials rated non-agricultural sources of sediment as more serious than agricultural sources, though this may reflect a bias toward identifiable point sources. Major sources of sediment run-off include: mining, quarries, forestry, earthworks and roadworks, and natural geological processes. Among agricultural sources, cropping uses, including market gardening, were rated, on average, as slightly more serious sources of sediment than pastoral uses.
Eroded particles usually end up in lakes, rivers, and streams, to be deposited downstream or in the coastal environment. Rates of erosion generally increase as slope of land and intensity of rainfall increase, and as amount of vegetative cover decreases. Trampling by livestock reduces infiltration to the soil and therefore increases surface runoff and erosion. Certain soils are also more vulnerable to erosion than others.
Sediment generated by agricultural activity causes a number of problems, in addition to the direct effects on the land resource. 'Me most immediate impact on water bodies is reduced clarity, which reduces the penetration of light to aquatic plants and may otherwise inhibit native flora and fauna. Sediment also covers rocky stream bottoms, reducing spawning habitat for fish, and can also scour the stream bed of small plants as particles are transported by stream flow. These changes in the ecological community structure diminish the quality and quantity of food supply for fish.
There may be differences in how different Maori perceive muddy water. Waters affected by sedimentation may be favoured by highly valued native species such as eels, while non-commercial native species prefer water with higher clarity (Davenport, pers comm).
Sediment and rocks eroded due to agriculture also raise the level of river beds. As a result, channels can carry less water, increasing the likelihood of flooding. Sedimentation reduces the life span of reservoirs, and suspended sediment also increases treatment costs for drinking water and diminishes aesthetic, recreational and cultural values of the water. The Department of Health has found that 25% of New Zealand drinking water supplies have undesirable levels of turbidity, of which suspended sediment is an important component (Mattingly, 1992). In June 1992, a meatworks at Taumarunui was temporarily closed due to discolouration of the water supply from sediment. No health concerns were raised, but the discoloured water did not meet European Community standards for water used in meatworks (Atkinson, 1992).
A number of practices are available to reduce loss of sediment from agricultural land. These include:
- management of crop residues and tillage practices to limit exposure of bare soil in arable and horticultural systems;
- traditional soil conservation practices such as planting trees in gullies and contour ploughing;
- improved riparian management, such as maintaining grass or tree buffers to trap sediments, or restricting grazing along streambanks;
- lower stocking rates or improved fertiliser management to maintain adequate vegetative cover;
- transition to forestry on unstable lands.
Prior to enactment of the Resource Management Act 1991, most councils used section 34 of Soil Conservation and Rivers Control Act 1941 as the basis for controlling activities which cause loss of sediment to natural water. Some use was also made of water right conditions and water classification under the Water and Soil Conservation Act 1967, but all these policy options had limited capability to deal with non-point sources of sediment.
Soil conservation measures, often subsidised by government, have been the main policy instrument for dealing with sediment. In MAF's survey, Southland Regional Council noted that land management guidelines are needed for soil conservation and drainage, as many non-standard practices are having deleterious effects on the quality of receiving waters. This may focus on extreme "non-standard" cases, however, whereas attention to "standard" practices may be merited as well.
The Wellington Regional Council indicated that, in addition to soil conservation measures, it has been restricting grazing along stream banks to combat sediment problems. Taranaki Regional Council said it is considering moving to standards and regulations and has recently issued a policy discussion paper on management of riparian margins.
If more councils move in this direction, they could set standards and take action against those who violate the standard by discharging too much sediment into local waters, though monitoring and enforcement would be difficult. They could also encourage soil conservation as they have done in the past. It is not clear to what extent regional councils could require improved land management practices under the Resource Management Act. The RMA is discussed further in section 3 of this paper.
2.4 Nutrient Loading
Agricultural nutrients such as nitrogen and phosphorus frequently find their way into local streams, rivers, and lakes.5 Nutrients attached to soil particles can be carried into waterways by erosion (McColl 1983), but also can be leached directly by water. Dairy and piggery sheds also contribute significantly to nutrient loads in waterways. Nutrients from faeces and urine, which contain significant amounts of nitrogen and phosphorus, may enter waterways directly from livestock or from pasture via surface or subsurface flows. Apart from agriculture, human sewage disposal systems contribute significantly to nutrient loads in some waterways.
Reviewing other New Zealand studies, Wilcock (1986) noted that, after storms, concentrations of phosphorus and nitrate-nitrogen are generally well above levels known to cause growth of nuisance organisms downstream. Pasture and disturbed forest contribute significantly higher nutrient loads than does native vegetation. Based on average stocking rates and fertiliser application, Wilcock concluded that 30% of New Zealand's total area in grassland, lucerne and tussock in New Zealand can be described as intensively grazed. This pasture, he says, "would be expected to contribute a significant pollutant load to streams and lakes in their catchments."
Waters which are "eutrophic", ie have excessive nutrients, typically have higher than normal plant growth, which upsets aquatic ecosystems. A report by Otago Regional Council (1991) cited 0.05 g/m3 total phosphorus and 0.3 g/m3 nitrate nitrogen as desirable limits for preventing excessive growth of nuisance plants. River sampling by the Council in 1990/91 ound that roughly one-fourth of the sites regularly exceeded these levels, though some of the sites probably reflected urban sources of nutrients. Nutrient loading could be expected to be worse in regions with intensive pastoral use, such as Waikato, Manawatu, and Taranaki.
Growth of algae is a common problem caused by nutrient loading, and the nightly respiration of algae and other plant growth can cause fish kills by using all the available oxygen. Aquatic weeds such as water net interfere with recreation and other uses. Excessive plant growth also reduces water clarity, affecting scenic, recreational and cultural values (see Vant and Davies-Colley, 1986).
Regional officials ranked dairy sheds and piggeries as the most serious source of nutrient loading of waterways, followed by dairy pasture. They ranked fishing and other types of recreation as the uses most affected. It is doubtful whether many regional councils have investigated the relative contributions of point and non-point source nutrients to waterways. The potential significance of runoff from agricultural land as a source of instream nutrient loading should not be overlooked.
For point sources of nutrients, such as dairy sheds and piggeries, conditions on water discharge permits can be used to require treatment prior to discharge. Even with treatment by oxidation ponds, Hickey et al (1989) estimated that a dilution factor6 of 2700 may be needed to prevent nuisance algal growth in 95% of dairy shed discharges, based on nitrogen discharged. The range of dilution factors for the roughly 7000 oxidation ponds in New Zealand is not known.
For non-point sources, practices which reduce sediment runoff will also reduce nutrient loading, since nutrients are often attached to sediment. Restoring wetlands and riparian vegetation will help to trap and absorb nutrients before they enter waterways. In many cases, diversification to include farm forestry will reduce soil and nutrient runoff.
In most problem cases, improved management of fertiliser would probably help. In many cases, the amount of fertiliser applied could be reduced. However, an increase in fertiliser could be suggested where a shortage of fertiliser is causing degradation of pasture and increased erosion, because it is primarily eroded soil particles which transport nutrients into waterways (Syers 1974). Improved pasture management, in the broad sense of using appropriate grasses and grazing regimes as well as better fertiliser management, would reduce nutrient runoff.
2.5 Alterations in Physical Characteristics of Waterways
Agricultural development has led to the removal of a large amount of riparian vegetation. Reduced shading leads to increased light and greater temperature extremes in waterways, especially small streams, which can disrupt aquatic ecosystems. In addition, removal of vegetation increases streambank erosion, especially where grazing livestock enter streams.
Apart from adding more sediment, altering the stream bank can also change the flow characteristics of the waterway, causing potential problems for flood protection works.
Removal of riparian vegetation also affects the water retention capacity of streamside wetlands and "seeps," or miniature wetlands, especially if these areas are deliberately drained. These wetlands and associated vegetation slow the movement of water into streams and rivers, and thus help to moderate storm flows. Wetland plants also absorb nutrients in runoff, removing over 90% of nitrates according to one study (Cooper, 1990), though some of these nutrients will be later released as plant matter decomposes. Thus, loss of wetlands and riparian vegetation increases flow variability and flooding and increases nutrient loading of waterways.
Drainage of wetlands may also affect water quality by allowing anaerobic drainage water to come into contact with other surface water, thereby creating localised shortages of dissolved oxygen. Darkly coloured water from wetlands, especially peat, can affect clarity and colour of water as well.
Regional officials ranked dairy grazing as having the highest impact on physical characteristics of waterways, followed by "other activities," primarily non-agricultural activities such as river works and urban development. Habitat for native flora and fauna was considered to suffer the most damage, followed by scenic values. The Waikato Regional Council has noted that the destruction of aquatic habitat is as much a concern as degradation of the water resource, and that the causes, effects and remedies are often very similar.
To restrict alteration of the physical characteristics of waterways, many councils require a landowner to have a permit to drain wetlands or to carry out any significant river control works. It is more difficult, however, to control the removal of streamside vegetation, the drainage of seeps, or the entry of livestock into streams. More intensive riparian management to protect vegetation may be the only way to protect the physical characteristics of waterways where this is deemed necessary.
2.6 Faecal Contamination
Animal faeces enter waterways directly from dairy sheds and piggeries, sheep and beef feedlots, from stock access to streams, and from pasture run-off. Of these, regional officials rate sheds and dairy pasture as the main sources. Again, because there is little data on diffuse sources of faecal contamination, one should be aware of the potential for bias towards the point sources and under-estimation of diffuse sources. Respondents rate degradation of Maori values as the most serious impact, followed by reduced value of water for recreation.
Faecal contamination can be a vector for disease, potentially causing illness if water is used for swimming or other contact recreation, for drinking by humans or livestock, or for food processing. Water treatment costs may also be increased. Faecal contamination of coastal waters can render shellfish unfit to cat.
Animal faeces also contaminate groundwater on occasion, though regional officials indicate this is not a widespread problem. Domestic septic tanks are cited as a source by several survey respondents. Contamination can also occur where dairy shed or piggery effluent is spread on land and is transported down to aquifers by percolating rainfall. Intensely grazed pasture might contaminate groundwater in the same way.
As noted, the primary sources of faecal contamination are daily sheds and piggeries. Oxidation ponds can achieve significant reductions in contaminants discharged to waterways, though some faecal coliforms are still discharged. Spraying effluent on land can achieve virtually 100% control if properly managed, depending on land forms.
Most councils have used conditions on water rights to require some control practices, but in some areas these conditions have not been strictly enforced. This is changing as councils devote more resources to the problem. Water rights can only be used to control point discharges, however. Diffuse sources, such as runoff from pastures, are more difficult to deal with. As for non-point sources of other contaminants, improved riparian management is one means of reducing diffuse discharge of faecal contaminants.
2.7 Pesticides and Water Quality
There is only scattered information on contamination of surface and groundwater supplies by pesticides in New Zealand. Regional councils report only sporadic monitoring, owing largely to the complexity and expense of the analysis required. The Department of Health monitors for pesticides and other contaminants in its surveys of drinking water. In a report on sampling done in the five years leading up to 1991, four out of 236 samples had detectable levels of 2,4,5-T, while 2,4-D was detected in two samples. Acute exposure to either of these organochlorine herbicides, especially 2,4-D, can cause health problems. When the samples were analysed some weeks after collection, residues detected were well below guideline levels. The chemicals degrade rapidly, however, and the levels at the time of sampling are not known (Nokes 1992).
Run-off from cropland, market gardens, and orchards would be expected to be the main sources of pesticides found in waterways. To date no widespread sampling has been done. Disposal of sheep dip may also be a source, though again, little is known. Ryder (1992) reported an incident of sheep dip discharged to a Otago stream, with severe impacts on invertebrate organisms over several kilometres of the stream. The disappearance of invertebrates allowed additional algal growths, extending recovery time up to a year.
Now that multi-residue testing for pesticides is possible, a separate test is no longer required for each active ingredient suspected. This recent development should lower the cost of monitoring and hopefully allow more to be done.
A limited number of sampling programmes have been carried out to assess the risk that pesticides present to water quality. Freeman and Baxter (1988) sampled drainage water from an orchard in Canterbury and tested for insecticides, fungicides and herbicides. Two herbicides were found in the samples, Simazine and Amitrole. The high concentration of Simazine indicated a strong possibility of impacts on aquatic life if other orchards had similar residues in field drains. Orchard managers agreed to stop using Simazine.
The main uses of water potentially affected by pesticides are drinking water for humans and livestock, fishing, habitat for native flora and fauna, and Maori values. A study in Southland (Scott, 1985) sampled streams and rivers for key indicator invertebrates. The report cited possible correlations between the absence of key invertebrates and 1) intensively grazed flat land and 2) animal health practices, such as drenching and dipping. An update in 1987 found conditions in the rivers of Southland Central Plain had not improved.
Groundwater contamination can be a particularly serious form of pollution if treatment is expensive or impossible. Close (1992) reported findings of pesticides in groundwater in Poverty Bay, Te Puke, Pukekohe, and Motueka. Of these findings, atrazine was found at over 10 times the health advisory limit of the United States Environmental Protection Agency. Tests at the same site six and twelve months later found residues below the USEPA limit on one occasion and no detectable residues on another occasion.
Practices to reduce the possibility of pesticides entering surface waters include better management of pesticides, including timing and quantities applied, planting buffer strips along streams, and using organic and biological control of pests. Discharge of pesticides into water was an offence under previous legislation, as well as the Resource Management Act, but it is difficult to control these non-point sources.
2.8 Nitrate Contamination of Groundwater
Nitrogen fertilisers, animal faeces and urine, and nitrogen fixing plants all contribute indirectly to nitrate levels in soils. Water percolating down through the soil picks up nitrate ions and eventually transports them to groundwater or to surface water via subsurface runoff. According to research from the UK, freshly ploughed clover may be especially vulnerable to leaching of nitrates (Cameron and Wild, 1984). These nitrate losses represent significant losses of nutrients to farmers as well as an environmental problem.
Nitrate is of concern primarily because it reduces to nitrite in human digestion. Nitrite can cause anaemia in infants, known as "blue-baby syndrome," and high levels of nitrate are therefore considered unhealthy. The World Health Organisation has set a limit of 10 mg/litre of nitrate for public water supplies, though the EC standard is 50 mg/litre (MAFF/UK, 1991). DSIR's monitoring of drinking water during 1983-1989 found nitrate levels above 10 mg/litre in about 1% of samples tested (Mattingly 1991).
Regional officials cited nitrate in groundwater as a moderately serious problem, and identified stock urine and fertiliser as the main sources. Contamination of drinking water was cited as the most serious impact.
Probably the most feasible way to prevent groundwater contamination is to control land use practices in sensitive areas. Monitoring against a set quality standard is unlikely to be effective because of the cost, and even if discovered, violations are difficult if not impossible to remedy. In such a case, it would probably be less costly to find alternative water supplies.
In Hawke's Bay, strict regulations have been imposed on land use over the unconfined aquifer, enforced under the district scheme. In Otago, Taranaki, and other regions, disposal of effluent and other waste onto land has been controlled by conditions on water rights.
2.9 Increased Oxygen Demand and Ammonia Toxicity in Streams
There are other significant agricultural impacts on water quality which were not explicitly canvassed in the survey of regional councils. Oxidation ponds associated with dairy sheds and piggeries also contribute nutrients and suspended sediment to streams, as mentioned earlier. The decay of the organic sediment consumes oxygen, as does the nighttime respiration of plants, which are fed by the nutrients. This increases the biochemical oxygen demand (BOD) in the receiving water, and lowers the availability of dissolved oxygen. In severe cases, high BOD can cause fish kills.
Background levels of BOD are typically below 1 g/m3; waters with BOD greater than 5 g/m3 would be considered to be of doubtful quality, according to Otago Regional Council (1991). Of fifteen river sites sampled by that Council in 1990-91, one reading of 2 g/m3 was recorded at an urban site; all others were 1 g/m3 or below. Despite these favourable results, there may be locally high BOD levels at points immediately downstream of oxidation pond discharges.
Farm oxidation ponds also discharge ammonia (NH4-N), which may also enter streams directly from the urine of animals in or near waterways. Ammonia is toxic to fish and invertebrates at certain concentrations. It also consumes a considerable amount of oxygen as it is trarisformed into nitrate (N03-N) in the stream, a process not measured by BOD tests. This oxygen demand may be three to four times the demand from the decay of organic material from the ponds (Hickey et al, 1989).
Hickey et al estimated that, based on the variable performance of farm oxidation ponds, the volume of receiving water would need to be 250 times the volume of the discharge to dilute ammonia sufficiently to avoid toxicity to fish in 95% of discharge situations. If a lower degree of protection were accepted, including adverse effects over a certain length of the stream (the "mixing zone"), the dilution could be less.
2.10 Reduced Flow in Streams and Rivers
Although the survey of regional officials did not ask about agricultural impacts on quantities of water, several respondents noted that flow volumes directly affect water quality. A given amount of contamination, whether it be nutrients, pesticides, sediment, or faecal coliforms, will have a greater impact on water quality when there is reduced flow (McColl, 1983; Hickey et al, 1989). The fact that flows tend to be lowest in summer, when agricultural activity is greatest, further exacerbates the problem.
Agriculture directly affects flows by extracting water for irrigation and stock watering. Removal of riparian vegetation and wetlands increases flow variability, exacerbating both peak and low flows and therefore reducing the volume of water available to process or dilute contaminants during critical low-flow periods.
In addition to magnifying the range of impacts discussed above, with consequent impacts on other uses of water, extraction of water for agricultural purposes has other direct impacts on other uses, namely by reducing the volume available for recreation, electricity generation, human drinking water, flora and fauna, etc. Maori and other cultural values may be affected if low flows are extreme.
2.11 Summary
Agriculture causes a range of impacts on water quality, adversely affecting a range of other uses of water. In many cases, measures taken to address one problem will also have beneficial effects on other problems. Improved riparian management is one measure that can help to resolve a number of problems.
Individual water quality problems, and the means of addressing them, should not be considered in isolation. Rather, we should look at a farming system as a whole and analyse how to adjust the system to address all adverse effects on the environment.
For instance, when considering sediment problems associated with pastoral farms, we should also keep in mind other potential environmental impacts from that farm: soil degradation, pesticide and nutrient run-off impacts on the physical characteristics of waterways, etc. The social and cultural values of the local community will also need to be considered, as well as the ability of land managers to provide for their own wellbeing.
Hopefully, the planning process now established under the Resource Management Act will encourage this integrated approach, as councils will be expected to describe the full range of desired outcomes. Mechanisms considered to achieve one outcome should be scrutinised for positive or negative effects on other outcomes. Similarly, the consent procedures in the new Act, which require environmental impact assessments in many cases, should make it easier for land managers and regional officials to look at the farming system as a whole when considering how to address any adverse effects on the environment.
3 Formerly part of the Department of Scientific and
Industrial Research (DSIR) and MAF Technology.
4 This study was done before the dissolution of the
Nelson-Marlborough Regional Council, whose functions have now been passed to Tasman
District, Marlborough District, and Nelson City Councils.
5 See Rutherford et al, 1987; Sharpley
and Syers, 1981; C Smith, 1987; C Smith, 1989; Steele and Judd, 1984.
6 Dilution is the volume of receiving waters compared to
the volume of the discharge. E.g. for a discharge of .2 litres/sec, a dilution factor of
2700 would require stream flow of 540 litres/sec.
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