1 Trends and patterns of DON and DOC/DON in deposition and soil solution in Flanders, Northern Belgium Arne Verstraeten Meeting of the ICP Forests Expert Panel on Deposition 23 April 2015, Göttingen, Germany

2 Introduction Hypotheses Results - DON trends and patterns - DOC/DON trends and patterns - Dependence of DOC/DON on variables: forest type soil texture hydrological conditions NO 3 - concentration N stock soil C/N ratio Conclusions Overview

3 Acidifying depositions (N and S) decreased (1994–2010) Soil solution concentrations (NO 3 -, SO 4 2-, Al, Ca 2+, K +, Mg 2+ ) and ionic strength decreased, pH increased (1994–2010) DOC concentrations and fluxes increased in soil solution (2002–2012) (Verstraeten et al. 2012, 2014) Introduction Knowledge gap Do concentrations and fluxes of DON follow trends and patterns of DOC? We analyzed data trends and patterns of DON and DOC/DON (2005–2013) collected at the 5 Level II plots in Flanders National data evaluation Initial recovery in five Level II plots in Flanders

4 1) DON concentrations and fluxes increased (like DOC) 2) DOC/DON remained stable 3) Soil solution DOC/DON depended on the forest type, soil texture, soil C/N, soil organic N stock, soil solution NO 3 – concentration and hydrological conditions Hypotheses

5 Results

6 Open field precipitation - moderate to high levels - slightly higher during the growing season Stand precipitation conspicuous peak in May in deciduous plots => bud burst + bud scales, water brown color effect of the forest type spring > autumn phenology Soil solution peak was mirrored, but later towards the season DON concentrations (Seasonal) patterns

7 Results open field precipitation similar to concentrations stand precipitation coniferous > deciduous Soil solution - highest in organic layer - decline with depth - 1.2–3.7 kg ha –1 yr –1 leaching (<0.1% of N stock) - higher peak during winter (more abundant rainfall) DON fluxes (Seasonal) patterns Precipitation

8 Results Open field precipitation - 6.6–7.2 (quite low) - higher during the growing season Stand precipitation - coniferous > deciduous 15.8– – higher during the autumn Soil solution - higher during the autumn - silty–loamy < sandy soils effect of soil texture (sorption capacity) DOC/DON (Seasonal) patterns

9 Soil type, depth, genetic horizons, C/N, pH, CEC, base saturation (BS) and texture

10 Results Trends DON concentrations Open field precipitation stable Stand precipitation increase Soil solution - increase, particularly in O and A horizon - downward peak in 2007, increase (peak) in 2008, then more or less stable ns(5) +(2) ++(1) +++(2) +++(5) +(1) ++(1) +++(3) ns(2) +(1) ++(1) +++(1) ns(3) ++(1) +++(1)

11 Results Trends DON fluxes Similar as concentrations, but less significant (variability water fluxes) ns(5)ns(3) ++(1) +++(1) ns(1) +(1) ++(2) +++(1) ns(2) +(3) ns(3) +(2) ns(4) ++(1)

12 Results Trends DOC/DON Open field precipitation stable Stand precipitation decrease Soil solution - decrease in O and A horizon, stable in B and C horizon - conspicuous peak in 2007, downward peak in 2008, then more or less stable => effect drying and rewetting April–May 2007: drought (36–37d no rain) June–August: up to 400 mm rain ns(4) -(1) ns(1) -(1) - -(3) - -(1) (4) -(3) - -(1) (1) ns(4) -(1) ns(5)

13 DOC/DON was positively related to NO 3 – concentration in the A horizon (p<0.05), but not in the O, B and C horizon In the O horizon, DOC/DON was negatively correlated with litter input rate (g m –2 d –1 ) (p<0.05), suggesting an effect of the forest type DOC/DON showed no relationship with soil C/N ratio or soil organic N stock Results Dependence of DOC/DON on other factors

14 Conclusions DON increased (2005–2013), particularly in stand deposition, O and A horizons DOC/DON decreased in stand deposition, O and A horizons, because DON increased faster than DOC DOC/DON depended on the forest type, soil texture and hydrological conditions, but not on soil C/N ratio and soil organic N stock, while results were inconclusive with regard to NO 3 – concentration It would be interesting to check whether results are valid on a European scale, using aggregated data from deposition and soil solution

15 Thank you for your attention!

16 Precipitation

17 Quality control water fluxes Fig. Residuals of lm(cumulative water flux ~ time) in function of time Clear correlation for deposition and soil solution. Overestimation when storms bring high amount of Na + landward