Land use intensification on the Canterbury Plains:

1. Land use intensification on the Canterbury Plains: What are the implications for water quality? Ken Taylor Environment Canterbury

2. “The vast majority of studies on cause effect relationships…conclude that agriculture, as typically practiced in New Zealand, has a detrimental effect on water quality. These studies have shown that high levels of sediments, nutrients, and bacteria are generally found in waterways in agricultural areas, and water quality guidelines are often compromised, particularly where farming activity is intensive” NIWA report April 2002

3. Land use intensification contents • Potential effects • Indicators of change • Groundwater quality • Nitrate contamination - state & trends • Surface water quality • Nitrate loads to spring-fed streams • Phosphorus • Microbial contamination • Sedimentation • Habitat loss • Loss of flow • Managing nutrient leaching to groundwater – ECan approach

4. Land use intensification - potential effects • Groundwater • Leaching of nutrients and micro-organisms - impacts on drinking water quality and “down-stream” effects

5. Land use intensification - potential effects • Surface waters • Nutrient loads to spring-fed streams • Nitrate toxicity • Excessive plant growth • Coastal lagoons • Marine waters • Microbial contamination • Recreational water quality • Drinking water supply • Sedimentation • Habitat change • Natural character • Wetland loss • Loss of shading • Loss of flow • Habitat loss • Water quality effects

6. Land use intensification – what’s happening out there?

7. Tonnes of urea applied to Canterbury farmland 1992-2004 Indicators of land use intensification…

8. Indicators of land use intensification… 1995

9. Indicators of land use intensification… 2005

10. Canterbury Groundwater • 75% of the region in some form of agricultural production • Agriculture is the largest user of gw (84%). est. 350,000 ha is irrigated • Untreated groundwater principal source of drinking water for communities, dwellings, & businesses (13%)

12. Schematic cross-section of the Canterbury Plains

13. Groundwater vulnerability

14. Canterbury Groundwater • Deep unconfined aquifers & confined aquifers – water quality generally high • Shallow unconfined aquifers & spring fed streams – water quality affected by human activities

15. What is the problem with nitrate? • In groundwater • “universal” drinking water standard 11.3 mg NO3-N/L • In surface water • Range of adverse effects • Nitrate toxicity – ANZECC guidelines • Excessive plant growth • Coastal lagoons – e.g., Opihi • Coastal waters

16. Coastal issues • Increasing N loads to coastal waters • shift to ocean outfalls • community sewerage schemese.g. Christchurch City, Waimakariri District, Timaru District • industrial discharges • rivers, coastal streams, springs • e.g. Ashburton Dist. - 2,500 tonnes N exported / yr under base flows, or 830 kg/km2 • cf. Chesapeake Bay – 130 million tonnes N per yr , or 740 kg/km2

17. What about phosphorus? • Not a problem for groundwater • Tends to move with sediment in surface water • Most Canterbury streams P-limited • What happens when P gets into surface water?

18. Sedimentation • Is a consequence of the way land is managed • Intermittent inputs • Stock in or adjacent to streams • Drain-clearing • Is a particular issue for streams that do not get flushed