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9th April 2014Kari Austnes1 Critical limits for acidification of surface waters vs boundary values in the Water Framework Directive (WFD) – a Norwegian.

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Presentation on theme: "9th April 2014Kari Austnes1 Critical limits for acidification of surface waters vs boundary values in the Water Framework Directive (WFD) – a Norwegian."— Presentation transcript:

1 9th April 2014Kari Austnes1 Critical limits for acidification of surface waters vs boundary values in the Water Framework Directive (WFD) – a Norwegian case study 24th CCE workshop and 30 th task force meeting

2 Objective Two sets of management regulations related to acidification of surface waters −LRTAP: Acid deposition below the critical load (CL) for protection of the ecosystems −WFD: Ecological indicators (quality elements) above certain boundary values for achieving good ecological status (with respect to acidification) Both use acid neutralising capacity (ANC) as chemical criterion linking water chemistry to biological effects −Do they set the same requirements? −Not directly comparable – CL calulated based on both criteria for comparison 9th April 2014Kari Austnes 2

3 Critical loads for surface waters SSWC and FAB the commonly used models Both use ANC limit as link chemistry-biology −The criterion we want to compare with the ANC criterion in the WFD SSWC: CL(A) = BC 0 - ANC limit −BC 0 : Flux of (non-marine) base cations from the catchment in pre-acidification times −ANC limit Minimum ANC to avoid harmful effects on selected biota Originally a fixed limit at 20 eq/l  95% probability of no damage 9th April 2014Kari Austnes 3 Lien et al. (1996)

4 The variable ANC limit Less sensitive systems  higher biodiversity  higher ANC limit needed to keep the diversity intact The variable ANC limit varies with the original base cation concentration −[ANC] limit,var = k*CL = k*Q*[BC * ] 0 /(1+k*Q) −ANC-range: 0-50 eq/l Organic acid adjustment −Organic acids contribute to the strong acid anion concentration  larger buffer needed at higher organic acid concentration −[ANC] limit,oaa,var = k*Q*([BC * ] 0 -1/3*m*[TOC])/(1+k*Q) (m=10.2, k=0.2) −CL=Q*([BC * ] 0 - [ANC] limit,oaa,var -3.4*[TOC]) 9th April 2014Kari Austnes 4

5 The WFD and boundary values Ecological status of surface waters based on a set of quality elements −Biological and physicochemical Boundary values set for different quality elements (e.g. ANC) with respect to different pressures (e.g. acidification) −Five status classes from high to bad −Good status environmental target  the good/moderate (G/M) boundary essential −The boundary values represent deviation from a reference status (natural conditions) Different sets of boundary values for different types of water bodies (e.g. small, lowland, humic lakes) 9th April 2014Kari Austnes 5

6 WFD boundary values (Norway) Lake types for acidification classification defined by Ca- and TOC-concentration −Boundary values vary according to buffering capacity and humic acid content  as the ANC limit,oaa,var −Discrete boundary values (ANC limit,oaa,var continuous) 1 st classification manual (2009) −6 types: 2 Ca classes (split at 1 mg/l), 3 TOC classes −Reference value median of reference lakes −G/M boundary Brown trout status vs ANC Benthic invertebrate vs ANC (adj) Expert judgement ANC-range: eq/l 9th April 2014Kari Austnes 6 Hesthagen et al. (2008)

7 WFD boundary values (Norway) cont. 2 nd classification manual (2014) −Revised reference values Pre-industrial ANC from MAGIC  many lakes pre-industrial ANC below G/M boundary  large range within the same lake type Lower Ca-class (<1 mg/l) split into four 9th April 2014Kari Austnes 7 Median of MAGIC-results used −Revised G/M boundary values Re-analysis of brown trout data for new lake types Boundaries adjusted downwards to take delayed biological recovery into account (Wright, 2013) Expert judgement ANC-range: 0-30 eq/l Wright and Cosby (2012) Ca<1, TOC<2

8 Background – variability across Norway 9th April 2014Kari Austnes 8

9 The G/M boundary 9th April 2014Kari Austnes 9 Markedly higher values with the 1 st WFD manual Both reflect the Ca and TOC patterns Not directly comparable to ANC limit,oaa,var  TOC incorporated in the ANC limit,oaa,var value CL calculation used for comparison

10 Critical load: Compare ANC limit,oaa,var and G/M boundary 9th April 2014Kari Austnes 10 Markedly lower CL with G/M boundary based on the 1 st manual Negative CL  aiming for the unachievable

11 Exceedance : Comparison 9th April 2014Kari Austnes 11 Fairly similar results More realistic G/M boundary values in the 2 nd manual Drawing on experience from the LRTAP work WFD requirements slightly lower

12 Differences CLA_oaa and CLA_WFD2 9th April 2014Kari Austnes 12 CLA_oaa mainly lower than CLA_WFD2 Largest differences when CLA_oaa is lower than CLA_WFD2 Largest relevant differences found on the west coast Grid cells with CLA>90 meq/m 2 /yr removed from the analysis – not relevant - no risk of acidification

13 Differences: Humic acid content For both criteria CL decreases with increasing TOC Large range in deviation at low TOC −Different TOC-approach less important At TOC>8 mg/l CLA_oaa is always lower −G/M boundary no differentiation at TOC>5 mg/l (with respect to TOC) −Too low G/M at high TOC? 9th April 2014Kari Austnes 13 Marked changes at class boundaries −Larger differences at the lower end

14 Differences: Buffering capacity 9th April 2014Kari Austnes 14 G/M boundary increases with increasing Ca ANC limit,oaa,var increases with increasing BC 0 Fairly similar pattern  reflect the same effect Lower CLA_WFD2 mainly at Ca mg/l Lower CLA_oaa along the whole range −Majority Ca<0.75 mg/l −Most grid cells with Ca>0.75 mg/l high TOC Marked changes at class boundaries −Larger differences at the lower end

15 Differences: Summary Exceedance −CLA_oaa stricter at very low Ca −CLA_WFD2 stricter at Ca mg/l −Differences in TOC approach mainly relevant at high TOC Discrete G/M boundaries problematic −Artificial trend within classes −High uncertainty around the class boundaries 9th April 2014Kari Austnes 15

16 TOC increases – then what? WFD −Boundaries dynamic for their actual purpose, i.e. to assess ecological status with respect to acidification Increase in TOC  type changes  stricter requirement (higher ANC G/M boundary) But - only three TOC classes: Marked changes needed, and no effect of TOC increase above 5 mg/l LRTAP −In theory critical loads based on ANC limit constant In practice revised as calculations and data improve −Using ANC limit,oaa,var introduces a non-constant factor (TOC)  not taken into account Increasing TOC  lower CL  higher exceedance 9th April 2014Kari Austnes 16

17 TOC increase: Effects on critical loads 9th April 2014Kari Austnes 17 Rough test −TOC increase in line with long-term monitored lakes −Increase from 1995-present −Different factor in different regions: Small changes only −Most pronounced in regions with higher TOC increase

18 TOC increase: Effects on exceedances 9th April 2014Kari Austnes 18 Relatively small differences so far Larger impact in other countries?

19 Conclusions WFD requirements far more in line with the LRTAP requirements in the 2 nd manual for WFD classification Still some differences −WFD requirements somewhat lower overall −The upper TOC class should probably be split −Major differences at very low Ca – difficult to say which criterion is more correct Discrete WFD boundaries give higher uncertainty CLA_oaa decreases with increasing TOC −Small changes so far, but may call for revision if continued TOC increase 9th April 2014Kari Austnes 19


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