How Protection Zones and Land Management Restored Nitrate Contaminated Groundwater on the Island of Tunø, DK

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1 How Protection Zones and Land Management Restored Nitrate Contaminated Groundwater on the Island of Tunø, DK Senior geochemist, Lærke Thorling Chef Consultant & Richard Thomsen Geological Survey of Denmark and Greenland Ministry of Climate and Energy

2 Lessons learnt Groundwater restoration is time consuming Only lasting measures are relevant Cooperation with local famers prerequisite Monitoring is crucial for evaluation of measures Expect changes in politics and ownership A credible forecast is vital for planning and acceptance.

3 Tunø waterworks: A Story of success: Protection by action plans and monitoring page 3 Tunø

4 Setting the scene: The microcosmos, Tunø 120 inhabitants, 1water works Many tourists Vegetables are the primary crop (leeks, cabbage, onions etc.) > 100 mg/l nitrate in the aquifer Saltwater risk Very limited groundwater resource Low precipitation 500 mm/y Import of water unrealistic expensive Need for both clean water and income from efficient farming page 4 Geological cross section, height 6 m Till over sand,

5 Nitrate mg/l The rise and fall of nitrate at Tunø water works Sustainable solution in place Nitrate in abstractionwells Tunø Waterworks Grass established in protection zone Well 1 Well Well 1 stopped page 5 Constant abstraction approx m 3 /year

6 Selecting the solution, Cost of choice Partners: Municipality, County, Agricultural advisors. Århus County responsible for action plan and measures page 6 Costs in

7 Initial Protection strategy, ha permanent grass land in inner zone near wells. Outer zone with Good agricultural practises in the cultivated areas (30 acres) Extra agricultural advisory services in outer zone Intensive monitoring of soil water and groundwater. Adjustments if monitoring showed so after 3-5 years. page 7

8 Water quality: Monitoring activities Monitored in both the unsaturated and the saturated zone Monitoring within and outside the protection zone Monitoring of nitrate and main components. Groundwater dating with CFC to give a time frame. Recharge : Monitoring in lysimeters. Very important information about the variations in the size of the groundwater recharge. Data were used to establish the size of the protection zone necessary for the actual water abstraction Soundings: Wells around the coast and in the protection zone Sensitivity to saltwater intrusion and climate changes page 8

9 Nitrate leaching in protection zones Results from unsaturated zone 1 m.b.s page 9

10 Nitrate leaching from cultivated areas Results from unsaturated zone 1 m.b.s page 10

11 Final Protection Strategy 1992 ff. Increased (6,5 ha) inner protection zone with very low nitrate leaching from Permanent grass where the areas are bought by the waterwork, exchange of fields between farmers to secure productive areas. Long term ( )set a side with clover+grass (EU-support) in area (7 ha) owned by older farmer Best practise implemented in market garden crops Improving of nitrogen efficiency with fertilizer plans Improving tools to place fertilizer Soil quality improvement (solve soil compaction etc.)

12 Map of the abstraction area and final protection zones

13 National regulation on nitrate in cultivated zones, Skrives ind page 13

14 The art of forecasting. Age distribution in aquifer gives timeframe for expectations 200 Nitrate in abstractionwells Tunø Waterworks page 14

15 Nitrate in groundwater below protection zone Nitrate in upper groundwater GW-table 6 m.b.s m.b.w.t. 4-5 m.b.w.t

16 Nitrate mg/l Nitrate in groundwater below the arable fields Nitrate in groundwater, below crops P1 P page 16

17 mm- netprecipitation Measurement of recharge 1,25 m.b. surface Recharge measurements- Tunø A B

18 Nitrate concentrations at the waterworks as a function of abstraction volume and recharge Conditions: Present size of protection zone 200 mg/l nitrate outside 0 mg/l nitrate within the zone Nitrate content in abstracted water Larger abstraction demands a larger protection zone Lower nitrate leaching from agriculture gives smaller protection zone Climate change may influence recharge and thus area of protection zone page 18

19 Challenges Adoptive planning necessary. Monitoring helps keeping staying on track. The cooperation with the farmers, from scepticism to partnership. Don t rush things through. The need of patience, also by the administrative system Changing political organisation and staff The water work was privatised, farms are sold. Changes in agricultural regulation, possible measures change New knowledge can change conceptual understanding. To let go, when mission accomplished

20 Green Grass gives good groundwater Conclusions Measures must be lasting and found in agreement with the local farmers interests. Monitoring of effect is a necessary part of adaptive groundwater protection Things take their time. Be patient and steady. page 20