Declining atmospheric deposition impacts forest soil solution chemistry in Flanders, Belgium Arne Verstraeten 15 th Meeting of the ICP Forests Expert Panel on Soil and Soil Solution, 11 April 2013, Ljubljana, Slovenia

I will present : National deposition and soil solution trends for Flanders forests ( ) (Verstraeten et al., 2012) Some results for soil solution DOC ( ) - trends - seasonality - role of DOC deposition ongoing analysis for national data

1. Deposition and soil solution trends Objectives: Trend analysis for stand deposition of N, S and base cations (Ca, K, Mg) Trend analysis for soil solution fluxes of N, S, base cations (Ca, K, Mg) and Al tot Make an ion budget for N and S Discuss the results in relation to critical loads and levels

Study area Data from 5 ICP Forests Level II plots were selected: - 2 coniferous - 3 deciduous PlotCoordinatesElevationTemperaturePrecipitationTree speciesAgeFormer land useBasal areaThroughfallStemflow NEm°Cmm years m²/ha% Coniferous forests RAV51°24'07''05°03'15'' Pinus nigra subsp. laricio80heath BRA51°18'28''04°31'11'' Pinus sylvestris81heath Deciduous forests WIJ51°04'11''03°02'14'' Fagus sylvatica75arable GON50°58'31''03°48'15'' Quercus robur, Fagus sylvatica92old growth HOE50°44'45''04°24'47'' Fagus sylvatica101old growth

Sample collection 2 times per month 10 throughfall collectors 5 stemflow collectors (beech) lysimeters for soil solution: - organic layer (zero-tension) -topsoil -subsoil -deeper mineral soil 3 locations, 2-3 collectors per depth Throughfall collectors 10 m

Chemical analysis on 500 ml composite subsamples of each fraction pH en conductivity concentrations of cations (Ca 2+, K +, Mg 2+, Na +, NH 4 + ) and anions (Cl -, SO 4 2-, NO 3 - ) with ion chromatography Al tot concentration with emission spectrometry

Data handling stand deposition = throughfall + stemflow soil water fluxes were calculated using Na + as a “tracer ion” for each soil depth trend analysis: Seasonal Mann-Kendall trend test (Hirsch & Slack, 1984) cross-site statistics: ANOVA/Tukey’s range test

Results Deposition trends ( ) Plot Stand precipitation NH 4 + NO 3 - NH 4 + /NO 3 - ratio mean slope mean slopechange mean slopechange mean slopechange Coniferous forests RAV636ans 1901d-69*** bns 2.96c-0.09***-37 BRA784bns 1576c-49*** bns 2.24b-0.05***-32 Deciduous forests WIJ712abns 1370bc-72*** a-7* bc-0.09***-39 GON657ans 1155b-49*** a-9* b-0.06***-31 HOE743bns 806a-42*** a-12*** a-0.05***-38 Stable 40-59% decline of NH % decline of NO 3 - only in deciduous stands Decline of NH 4 + /NO 3 - ratio from 2.44 to 1.90

56-68% decline of SO % decline of base cations 45-74% decline of potentially acidifying deposition PlotSO 4 2- BC (Ca 2+ + K + + Mg 2+ ) Potentially acidifying mean slopechange mean slopechange mean slopechange Coniferous forests RAV1229bc-63*** a-11* d-127***-50 BRA1380c-70*** b-25*** c-93***-45 Deciduous forests WIJ1021ab-59*** bc-19* b-120***-71 GON1212bc-62*** d-23** a-84***-72 HOE869a-53*** c-47*** a-56***-74 Deposition trends ( )

Annual deposition

Results Soil solution trends ( ) Decline through nearly the entire soil profile SO 4 2-

NH 4 + -restricted to the organic layer (nitrification) -only decline in BRA NH 4 + and NO 3 - NO 3 - -decline through nearly the entire soil profile Soil solution trends ( )

Decline in the mineral soil BC (Ca + K + Mg) Soil solution trends ( )

Decline in the mineral soil Al tot Soil solution trends ( )

Ion budget for SO 4 2-, NO 3 - en NH 4 + For each depth soil solution fluxes of N and S (output) were compared to stand depositions (input) Ratio: output/input*100 Differences between input and output were tested with a paired t-test Results

Organic layer of coniferous forest accumulates N, while net losses were observed in deciduous forests, reflecting differences in litter decomposition rate. Highest NO 3 - leaching was observed in a deciduous plot (GON, 76% of input) SO 4 2- leaching >> inputs, indicating SO 4 2- desorption delays recovery Ion budget for SO 4 2-, NO 3 - en NH 4 +

Critical load for lichens in temperate forests: 3.1 kg N ha -1 y -1 (Fenn et al., 2008) In 2010 depositions in the 5 plots were still 4-8 times higher Lichens Ground vegetation Critical load for ground vegetation in temperate forests: kg N ha -1 y -1 (UNECE, 2007). In 2010 only respected in the organic layer of 1 plot, and exceeded with 22-69% elsewhere Critical loads

increase, but still <0, except in the organic layer of 1 plot 1) Acid Neutralizing Capacity (ANC) (ANC = Ca 2+ + K + + Mg 2+ + Na + – Cl - – SO 4 2- – NO 3 - ) Critical limits

Acidification continues…

Decline of BC/Al ratio at most plots 2) BC/Al ratio (BC/Al = Ca 2+ + K + + Mg 2+ / Al tot ) Critical limits

Critical limit for root damage / growth reduction Pinus: BC/Al<1.2 exceeded at both locations. Quercus/Fagus: BC/Al<0.6 exceeded in the mineral soil of 1 plot.

Potentially acidifying depositions declined substantially in the 5 plots between 1994 and 2010 Forest soils continue to acidify Recovery is delayed by simultaneous decline of base cation depositions and long-term buffer processes in the soil (e.g. SO 4 2- desorption) Conclusions

2. Dissolved Organic Carbon (DOC) Ongoing analysis for national data 5 Level II plots trends / seasonal patterns soil solution DOC ( ) role of DOC delivered by deposition

DOC concentrations (mg l -1 ) increased nearly through the whole soil profile increased in precipitation (open field) remained stable in stand precipitation

DOC fluxes (kg ha -1 y -1 ) soil solution fluxes showed few significant changes precipitation fluxes increased stand deposition fluxes remained stable

Coniferous forest plots showed higher carbon losses (51–56 kg ha-1 y-1) than deciduous forest plots (19–30 kg ha-1 y-1) Trends Coniferous forest plots showed higher carbon losses (51–56 kg ha -1 y -1 ) than deciduous forest plots (19–30 kg ha -1 y -1 )

Seasonal patterns – depositions vs. soil solution concentrations characteristic peak for soil solution near end of growing season preceded by a peak of deposition fluxes during summer

Correlation between DOC fluxes (Spearman) mean annual soil solution fluxes and deposition fluxes of DOC were correlated, except in the mineral topsoil

Soil solution vs. deposition fluxes of DOC ± linear relationship between deposition of DOC and soil solution flux of DOC may reflect difference in forest type or acid deposition load ?

Fluxes of DOC in relation to organic layer DOC flux (100%) stand deposition delivered 50-52% and 27-40% of organic layer DOC flux in coniferous and deciduous forest stands respectively may reflect difference in forest type or acid deposition load ?

Conclusions soil solution DOC concentrations increased ( ) soil solution DOC fluxes showed less marked trends (due to variation in annual precipitation surplus?) coniferous forest plots showed higher carbon losses (51–56 kg ha -1 y -1 ) than deciduous forest plots (19–30 kg ha -1 y -1 ) concentrations and fluxes of DOC decreased from the organic layer towards the deeper mineral soil, but in plots on poor sandy soils DOC concentrations were highest in the topsoil soil solution DOC concentrations and fluxes seem to be strongly influenced by stand depositions of DOC: 1.mean annual soil solution fluxes and deposition fluxes of DOC were correlated, except in the mineral topsoil 2.stand deposition delivered 50-52% and 27-40% of organic layer DOC flux in coniferous and deciduous forest stands respectively 3.seasonal patterns of deposition and soil solution DOC were related, with the peak of soil solution concentrations near the end of the growing season (August–November) being preceded by a peak of DOC depositions (May–August)

Thanks for your attention !