INTERNATIONAL ASSOCIATION OF HYDROGEOLOGISTS the worldwide groundwater organisation

1. INTERNATIONAL ASSOCIATION OF HYDROGEOLOGISTS the worldwide groundwater organisation THE AGRICULTURAL INTERFACE critical to groundwater resource status in the EU and beyond Prof Dr Stephen Foster (IAH Past President 2004-08) World Bank – Groundwater Management Team Director University College London – Visiting Professor of Groundwater Science IUGS Affiliate UN-Water Partner WWC Member GWP Member

2. AGRICULTURE & GROUNDWATER an intimate relationship BECAUSE agricultural activity occupies large proportion of most aquifer recharge areas CONSEQUENCES • predominant influence on groundwater quality • affects mechanisms/rates of aquifer recharge • also the major consumer of (ground)water resources must understand and control relationship to conserve/protect groundwater resources

3. AGRICULTURE & GROUNDWATER Scope of Presentation • focused at science-policy interface • in each facet start with the scientific realities • then concentrate on the policy implications • conscious of climate-change dimensions • groundwater often key to adaptive management • subtle long-term (but significant) impacts on groundwater recharge rates and quality likely • increased irrigation demand more immediate • biofuel cultivation could give rise to concern

4. AGRICULTURE & GROUNDWATER FACETS CONSIDERED : • Effects of Agricultural Land-Use on Groundwater Quality • Groundwater Use for Irrigated Agriculture • Conjunctive Use of Groundwater & Surface Water Resources

5. EFFECT OF AGRICULTURAL LAND-USE ON GROUNDWATER QUALITY‘As the Land – So the Water’ • cultivation of permeable soils is a ‘leaky activity’ – thus farmers cultivating land also (accidentally) harvest (and pollute) groundwater • agricultural land use practices thus markedly influence groundwater quality (especially N compounds + some pesticides leached) • diagnostic/prognostic capability as regards ‘groundwater quality risks’ now improved - but confirmatory monitoring always needed

6. DIFFUSE POLLUTION FROM AGRICULTURAL LAND-USE nutrient leaching pesticide mobility Cryptosporidium hazard saline returns

7. AGRICULTURAL LAND-USE & GROUNDWATERwidespread nutrient leaching • well established and often dominant influence (especially intensive monocultures on permeable soils) • principally NO3 (and in some cases NH4, PO4) • subsurface denitrification can reduce impact, but only in some hydrogeological conditions • technical control measures (plant husbandry, fertiliser regimes, livestock density, irrigation scheduling) very important – but for vulnerable aquifers may not be sufficient to protect drinking water and ecosystem interests

8. DIFFUSE GROUNDWATER POLLUTION FROM AGRICULTURAL LAND USElong term nitrate trends related to intensification

9. NO3(mg/l) EXCESS N APPLICATIONS TO SOIL GROUNDWATERNO3 CONCENTRATIONS kgN/ha/a Groundwater Nitrate Trend Data for Valencia Plain - Spain

10. AGRICULTURAL LAND-USE & GROUNDWATER the question of pesticide mobility • pesticides are designed to be (to some degree) biotoxic • more localised basis problem than nitrate (usually related to preferential flow in vadose zone, shallow water table, thin low storage aquifers) • main concern focuses on persistence in subsurface environment of soluble/mobile pesticides and their metabolites used in : • pest/weed control in horticulture/fruit production • weed control on arable/pasture land

11. GROUNDWATERPESTICIDES CONTAMINATION problem of analytical complexity and spatial + temporal variability in vulnerable aquifers(South Yorkshire Triassic Sandstone, England –compounds detected during Jan 2002 –June 2003) • 14 other compounds detected occasionally, almost all at <0.1 g/l) • pesticide metabolites and derivatives not included (Goody et al, 2005)

12. IMPACT OF GROUNDWATER POLLUTION IN BRITAIN problems requiring water utility action CAPITAL COST – E 950million (plus operational costs) MAIN CAUSES- groundwater quality deterioration- tighter drinking-water standards M/ld various causes - incl. cryptosporidium largely pesticides,arsenic and solvents mainly nitrates

13. CONTROL OF DIFFUSE AGRICULTURAL POLLUTION approaches and their limitations for protecting groundwater quality • Guidelines of ‘Best Agricultural Practice’ • Groundwater Special Protected Areas • Drinking Water Safeguard Zones • Private Agreements on Modified Cropping • Groundwater-Friendly Farming Regimes (with CAP financial support)

14. BEST AGRICULTURAL PRACTICE integration of groundwater quality considerations much welcomed BUT for some crops and soils not capable of reducing average nutrient and/or pesticide losses to below drinking-water guidelines

15. CONTROL OF DIFFUSE AGRICULTURAL POLLUTION approaches and their limitations for protecting groundwater quality • Guidelines of ‘Best Agricultural Practice’ • Groundwater Special Protected Areas • Drinking Water Safeguard Zones • Private Agreements on Modified Cropping • Groundwater-Friendly Farming Regimes (with CAP financial support)

16. GROUNDWATER SUPPLY PROTECTION ZONES focus for land-use controls

17. GROUNDWATER PROTECTED AREASspecific measures needed for quality protection

18. GROUNDWATER PROTECTED AREAS legal basis and limitations • declaration of ‘protected areas’ with special powers to constrain/prohibit activities in public interest feasible in most national legal codes • but legal powers may require a level of land-owner • compensation that is difficult to administer – and • private agreements may be more practicable • participation of stakeholders always needed with • major implications for monitoring and data provision

19. IMPACT OF BRITISH ‘NITRATE SENSITIVE AREA’ POLICYin fast response aquifer required tight control of N applications and limited conversion of arable land to unfertilised pasture and deciduous woodland – with payment of some compensation to farmers Old Chalford - Oxford(Jurassic Limestone) NO3 Concentration (mg/l) 1960 1980 2000 2020 1940 measured data model output Silgram et al, 2005

20. CONTROL OF DIFFUSE AGRICULTURAL POLLUTION approaches and their limitations for protecting groundwater quality • Guidelines of ‘Best Agricultural Practice’ • Groundwater Special Protected Areas • Drinking Water Safeguard Zones • Private Agreements on Modified Cropping • Groundwater-Friendly Farming Regimes (with CAP financial support)

21. GROUNDWATER QUALITY MONITORINGDo we really know what is going on under our feet ? substantial investment widely needed with much more emphasis on impact monitoring in recharge zones

22. AGRICULTURE & GROUNDWATER FACETS CONSIDERED : • Effects of Agricultural Land-Use on Groundwater Quality • Groundwater Use for Irrigated Agriculture • Conjunctive Use of Groundwater & Surface Water Resources

23. BENEFITS OF GROUNDWATER USE FOR IRRIGATED AGRICULTURE‘The Silent Revolution’ • massive growth of waterwells for agricultural irrigation – especially in more arid and/or drought-prone regions • mainly private investment but frequently stimulated by government waterwell grants, electrical energy subsidies, crop guarantee prices, etc • initially investment returns are very good both for : • staple crops (groundwater development fuelling ‘green revolution’) • cash crops with improvements in rural livelihoods and high water productivity

24. GROUNDWATER FOR AGRICULTURAL IRRIGATION controlling demand versus regulating use • many areas with good aquifers showing signs of excessive groundwater abstraction with question of sustainability over 10-50 year time-base • more consistent enforcement of controls over illegal waterwell drilling/deepening + installation of larger-capacity well pumps • ‘irrigation water demand management’ critical to sustainable groundwater resources in such areas (especially in aquifers susceptible to irreversible degradation) – with blend of agronomic, participatory, regulatory and economic measures required

25. GROUNDWATER FOR AGRICULTURAL IRRIGATION understanding the ‘use drivers’ • clear that ‘irrigation demand’ is strongly driven by economic subsidies for irrigation infrastructure, pumping energy and crop prices/risks – which reduce effectiveness of auto-regulation of abstraction through increasing costs in situations of falling water-table • solution of agricultural sector is invariably so-called ‘irrigation water-use efficiency’ improvements – but unless nature of real water-losses versus recirculation returns well understood and respected this is not effective and can be positively misleading

26. IRRIGATION WATER ORIGIN & APPLICATION TECHNIQUE major influence on groundwater recharge rates and scope for ‘real water resource saving’

27. REAL GROUNDWATER RESOURCE SAVINGSfrom improved irrigation techniques only reductions in non-beneficial evaporation are real groundwater savings

28. rh5 Carrizal Valley Mendoza- Argentina

29. MENDOZA CARRIZAL AQUIFER growing problem of groundwater salinisation

30. MENDOZA CARRIZAL AQUIFERcharacteristics of groundwater flow regime

31. GROUNDWATER RESOURCES MANAGEMENT approach in Mendoza – Carrizal Aquifer • declare ‘area of restriction’ to prevent further growth in numbers of irrigation waterwells • constrain spatial transfer of groundwater use rights from ‘down-gradient’ areas to ‘terrenos chacra’ • intensify monitoring of groundwater levels, use and salinity – as basis to ensure continued aquifer drainage • caution about cumulative effects of improving irrigation efficiency (widespread adoption of ‘drip technology’) since total groundwater resource consumption increasing (even if licensed abstraction fixed)

32. AGRICULTURE & GROUNDWATER FACETS CONSIDERED : • Effects of Agricultural Land-Use on Groundwater Quality • Groundwater Use for Irrigated Agriculture • Conjunctive Use of Groundwater & Surface Water Resources

34. CHALLENGE OF CONJUNCTIVE USE OF GROUNDWATER & SURFACE WATER RESOURCES the ‘dismal reality’ in many areas • informal/spontaneous conjunctive use widely practised in tail zones of major canal commands as ‘coping strategy’ – response of farmers to inadequate canal-water supply (poor maintenance related) • simultaneously some head-canal zones are experiencing soil waterlogging/salinisation and loss of valuable agricultural land – due to excessive seepage from canals and over-irrigation of fields • overall cropping intensity thus reduced to < 150%

36. HYDROGEOLOGICAL CONDITIONS OF GANGETIC PLAIN interfluve canals as recharge mounds and rivers as discharge sumps

37. CHALLENGE OF CONJUNCTIVE USE OF GROUNDWATER & SURFACE WATER RESOURCES scientific logic frustrated by social barriers • integrated modelling for tropical climates often demonstrates that cropping intensity for entire command area could be increased to 200-250% with ‘planned conjunctive use’ and better crop choices could further enhance ‘irrigation water productivity’ • but how to overcome social and economic obstacles to rationalising conjunctive use (political power of head-canal land owners, comparative water cost to users and initial capital investment requirements) ?

38. AGRICULTURE & GROUNDWATERGeneral Conclusion • need very widely to move from ‘opportunistic water engineering and agricultural development to integrated land and water management including full consideration of groundwater ‘ (long overdue even in EC) • in our overall long-term interest and especially so facing the need to adapt to accelerated climate change

39. INTERNATIONAL ASSOCIATION OF HYDROGEOLOGISTS the worldwide groundwater organisation www.iah.org www.worldbank.org/gwmate