Fuerzas de corte

Leaching of one kg of nitrate N (NO3N) from soil will contaminate about 88.5 m3 of water from 0 mg NO3N/L to 11.3 mg NO3N/L18: the MAV (Maximum Allowable Value) for drinking water standards. Dairy leaching rates per hectare can be used to estimate the volume of water that dairy farming could contaminate from having zero nitrate concentrations. To reduce nitrate concentrations by 85 to 95% in water costs at a minimum between $0.30 and $1.80 per 1000 litres (Jensen et al., 2012); however, costs vary considerably depending on the system type used and can be much higher.

To estimate the amount of water that could exceed nitrate drinking water standards caused by dairy farming in New Zealand, leaching rates of 12, 28, 130 and 200 kg N/ha/yr were used (Table 9.1) based on leaching ranges measured throughout New Zealand (detailed in Chapter 5). The average dairy leaching rate of 28 kg N/ha/yr may be heavily conservative for some regions, particularly irrigated dairy land, and it is likely that some dairy land leaches more than this. The volume of water contaminated was estimated for one hectare, the average dairy

18 _{Based on the following calculations: 1 kg NO}

3N = 1,000,000 mg NO3N; 1,000,000/11.3 = 88496 L = 88.5

Valuation of Impacts 133 farm size (140 ha19), and the total land area in dairy farming nationally (about 2.4 million ha)

(Table 9.1). Although leaching rates up to 200 kg N/ha/yr are unrealistic for all dairy land, they could indicate possible future scenarios under continued dairy intensification. Scenarios estimate the cost to treat all water contaminated from dairy farming that would exceed nitrate drinking water standards. In reality, all of the contaminated water would not be used for drinking. Nevertheless, it represents a degraded natural resource and an externality from dairy farming. Additionally, estimates of nitrate contamination are based on water initially containing no nitrate; however, many groundwater reservoirs already contain nitrate with some areas currently exceeding drinking water standards. For example, 11% of monitored wells in the Canterbury region exceeded nitrate drinking water standards in 2012 (Environment Canterbury, 2013b). Therefore, some estimates in Table 9.1 are likely to be more conservative than reality. For instance, if water previously contained 50% of the nitrate levels for drinking water standards, then 1 hectare would contaminate between 2,124 and 35,400 m3 of water per year depending on N leaching rates (compared to 1,062 to 17,700 m3).

Table 9.1: Estimations of water exceeding nitrate drinking water standards from various dairy farm leaching rates for one hectare, the average farm size, and national dairy land.

Leaching rates (kg N/ha/yr)

12 28 130 200

1 ha dairy land

Nitrate leached (kg) 12 28 130 200

Water polluted (cubic

metres - m3) 1,062 2,478 11,505 17,700

Cost to remediate ($/ha) $319 – $1,912 $743 - $4,460 $3,452 - $20,709 $5,310 - $31,860

Average farm size – 140 ha

Nitrate leached (kg) 1,680 3,920 18,200 28,000 Water polluted (m3) 148,680 346,920 1,610,700 2,478,000 Cost to remediate $44,604 - $267,624 $104,076 - $624,456 $483,210 – $2.9 million $743,400 – $4.46 million

National dairy land – 2.4 million ha

Nitrate leached (kg) 28,800,000 67,200,000 312,000,000 480,000,000

Water polluted (Mm3) 2,549 5,947 27,612 42,480

Cost to remediate ($

billion) $0.76 - $4.59 $1.78 - $10.70 $8.28 - $49.70 $12.74 - $76.46

Notes: Mm3 = Million cubic metres. Costs are based on a range of $0.30 - $1.80 per 1000 litres.

19 _{Average effective hectares on dairy farms; however, this does not include wintering areas (LIC &}

Valuation of Impacts 134 Water contaminated with nitrate above drinking water standards in three predominant

dairying catchments (Waikakahi, Canterbury; Bog Burn, Southland; and Toenepi, Waikato) were estimated using measured leaching rates from dairy farms in these respective catchments (estimates are outlined in Appendix K). The volume of water that could reach nitrate drinking water standards from proposed irrigation schemes in Canterbury was also estimated (Appendix K). Proposed irrigation schemes were estimated to equip an additional 270,000 hectares of land with irrigation in Canterbury (Kaye-Blake et al., 2010). Associated with this is an expected 180,000 hectares of dairy support land, estimated to leach 70 kg N/ha/yr (personal communication with Angus Robson, 11 June 2013). This projection assumes all newly irrigated land would be converted to dairy, leaching around 130 kg N/ha/yr; however, other land-use sectors may also use the irrigated land.

Waikakahi catchment, Canterbury

The Waikakahi catchment has attracted considerable attention regarding the impacts of intensive irrigated dairy farming on stream water quality (Monaghan et al., 2009). About 40% of the catchment is occupied by dairy farming and irrigation is required to maintain farm production20 (Monaghan et al., 2009). Around 2000 ha was reported to be in dairy farming. Monaghan et al. (2009) determined leaching rates by soil type, with 52 kg N/ha/yr on free draining soil and 27 kg N/ha/yr on poorly drained soil (Appendix K). In addition, Power et al. (2002) measured average leaching rates in the catchment and estimated leaching would almost double if dairying intensity was to increase by 23%, from an average leaching rate of 39 kg N/ha/yr to 64 kg N/ha/yr.

Bog Burn catchment, Southland

About 37% of the Bog Burn catchment is in dairy farming with dry stock farming and forestry predominant in the headwaters (Monaghan et al., 2007). Monaghan et al. (2007) differentiated between leaching rates from dairy milking areas (16 kg N/ha/yr) and dairy wintering areas (55 kg N/ha/yr) (Appendix K). Power et al. (2002) reported average current leaching rates (18 kg N/ha/yr) from dairy farms in the catchment and estimated leaching rates from increased dairying intensity (23 kg N/ha/yr) (Appendix K).

20

Border dyke irrigation is used in the catchment, where “water is applied to the top of an irrigation bay at flow rates that exceed soil infiltration rates” (Monaghan et al., 2009, p. 201). Excess water flows down the bay into drainage channels where captured water may be re-applied for irrigation elsewhere or discharged to a stream.

Valuation of Impacts 135

Toenepi catchment, Waikato

Nearly 90% of the Toenepi catchment is under dairying with no irrigation used on farms (Power et al., 2002). Average leaching from dairy land was 41 kg N/ha and scenarios estimate leaching associated with a 20% and 50% increase in intensity (Appendix K). Nitrate contamination from the average farm and total dairy land in the catchment are estimated (Appendix K).

Conclusion

To remedy water polluted with nitrate associated with leaching from one hectare of dairy land is estimated to cost between $319 and $31,860, depending on leaching rates and the treatment system used (Table 9.1). For an average sized dairy farm of 140 ha, costs range between $44,600 and $4.5 million. National water remediation costs for average leaching of 28 kg N/ha/yr are estimated between $1.78 billion and $10.70 billion (Figure 9.1 and Table 9.1). On the one hand, estimates are conservative because they assume contaminated water initially has zero nitrate levels. On the other, not all water would be used for drinking so would not require treatment. Therefore, it may be more realistic to only value the amount of water that is used for drinking water in New Zealand, estimated at 1832 Mm3/year (Rajanayaka et al., 2010). To treat this amount of water for nitrate contamination would cost between $549 million - $3.30 billion. It is important to realise that this is not an actual fee that the dairy industry has to, or may have to, pay in the future. Rather, these costs represent an externality that dairy farming is not compensating, by being allowed to discharge nitrate to water generally unrestricted.

To remediate contaminated water from dairy land for the three dairy catchments would cost between $500,000 and almost $14 million per catchment (Appendix K). At estimated increased intensity scenarios, remediation would cost up to $25 million for one of the catchments (Toenepi) for a 50% increase in intensity. For an average sized farm in the Toenepi catchment, remediation would cost between $82,000 and $496,000, but if intensity were to increase by 50% the costs would increase to between $200,000 and $1.2 million per farm (Appendix K). Even more deplorable is that proposed irrigation areas in Canterbury have the potential to cost up to $8.2 billion for water remediation.

Valuation of Impacts 136 Figure 9.1: Variation of costs to remove nitrate in water that exceeds nitrate drinking water standards

(11.3 mg N/L) estimated to leach from New Zealand’s national dairy land under various leaching rates.