1. Soils2Sea – Thresholds for nitrogen in groundwater and streams - a new concept for improved land use regulation and protection of the Baltic Sea and its coastal waters
K. Hinsby, JC Refsgaard, AL Hansen, AL Højberg, R Jakobsen (GEUS, Copenhagen, DK) and
AJ Zurek, P. Wachniew (AGH Univ. S&T, Krakow, PL)
35th CIS Working Group Groundwater meeting , Vienna, 8-9 October, 2018

2. Contents
The nutrient problem / challenge – example: N loads to the Baltic Sea (and gwaae’s in the Baltic Sea Basin)
Achievements, efficiency of solutions and additional requirements
Thresholds as a tool for compliance testing of spatially targeted measures and improved land use regulations – the Norsminde Fjord and Kocinka catchment use cases
Recommendations for WFD implementation and compliance testing

3. THE PROBLEM / CHALLENGE
WATER – FOOD – ENERGY NEXUS

4. THE PROBLEM / CHALLENGE
Steffen et al., Science 347,

5. Hyp- and anoxia in global oceans and the Baltic Sea partly caused by excess nutrients
Breitburg et al., Science 359, eaam7240

6. Water bodies in less than good ecological status in coastal and transitional waters

7. International / European collaboration => signicant reduction in N & P loads to the Baltic Sea, but not enough
Reusch et al., Sci. Adv. 2018;4: eaar8195

8. Soils2sea case studies in the Baltic Sea Basin

9. Thresholds for UZ&SZ, drain pipes, ditches and streams, (Norsminde and Kocinka – two ”end members”)
Groundwater travel or lag times to streams = hours to days
Travel or lag times to streams = decades

10. Two strategies for N regulation monitoring and compliance testing in Norsminde, DK
Equal N-leaching per ha throughout the Norsminde catchment, is close to the commonly used uniform regulation strategy, where all farmers are treated the same way with respect to requirements to agricultural practice and N-leaching.
Equal or compensated N-load per ha throughout the Norsminde catchment, exploits the spatial differences in the natural N-reduction in groundwater and surface water. This is a spatial differentiation strategy aiming at a more cost-effective mitigation, where farmers in subcatchment with a large removal of nitrate by dilution and attenuation in the subsurface may use more fertilizers that farmers in subcatchments with little or no removal of nitrate in the subsurface .

11. Spatial variation in nitrate reduction in groundwater in Denmark and Norsminde fjord
Højberg et al J. Hydrol. Reg Stud. And
Hinsby et al Soils2Sea D6.1:

12. Procedure of threshold derivation and WFD compliance testing

13. Compliance testing by comparing flow-weighted concentratIons in drain pipes and streams to threshold loads (flow-weighted mean concentrations)
Monitoring stations in drain pipes, ditches and streams
Protected GWAAE
European Commission, Technical report – 093. Modified after Hinsby et al. 2008, Sci Total Environ, 401, and Hinsby et al., Hydrol. Earth Syst Sci., 1,

14. Monitoring strategies and compliance testing in catchments considering dilution and attenuation
LEGEND:
TV / ‘TMDL’ in stream for compliance testing of strategy with equal leakage from all farm lands
threshold load in streams for compliance testing of effect of strategy utilizing varying dilution and attenuation factors in catchment
threshold load in drain pipes and ditches for compliance testing of effect of strategy utilizing dilution and attenuation varying dilution and attenuation factors in catchment and possible monitoring by farmers
Threshold for Submarine Groundwater Discharge at bottom of estuary with or without N

15. General recommendations (1)
#1: The findings and before they are adopted as part of WFD and GWD policy and implerecommendations from our study should be tested against conditions in other case areas
#2: The WFD and GWD guidances presently focussing on concentrations as thresholds should be extended to include annual, daily and monthly loads (fluxes) and corresponding flow-weighted average concentrations of nitrate in drain pipes, ditches and streams as possible thresholds.

16. General recommendations (2)
#3: The WFD and GWD guidances should emphasize that analysis of the groundwater body and its interaction with … ecosystems should be carried out through joint use of monitoring and spatially distributed coupled groundwater/surface water modelling, when threshold values for total loads of nutrients and other contaminants have to be assessed and established.
#4: The WFD and GWD guidances should emphasize that use of TVs for spatially differentiated regulation cannot be done entirely from scientific principles, but is conditioned on associated political decisions.

17. CONCLUSION
Total N / Nitrate already constitute a major problem of many European aquifers, which will be difficult to mitigate before climate change will enhance the problems for ecosystems and call for more efficient nitrogen reduction measures
A general quality standard for nitrate in groundwater of 50 mg/l does not provide sufficient protection of many ecosystems. targeted thresholds are required to protect specific ecosystems – dilution and attenuation factors should be taken into account to improve cost-efficiency
Targeted measures utilizing detailed knowledge about subsurface geochemical processes seem to be a promising option for some groundwater bodies and catchments
Monitoring of groundwater quality in drain pipes, ditches and streams for WFD compliance tests is more cost-efficient in drained catchments than monitoring of wells

18. You can find all Soils2Sea deliverables and published papers etc at:
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