Effect of Acid rain and Climate on TOC and the functional characteristics of NOM

Transcription

1 Effect of Acid rain and Climate on TOC and the functional characteristics of NOM Rolf D.Vogt, Egil Gjessing and Lars Evje 1

2 Possible causes for increases in DNOM The parameters exhibit corresponding fluctuations in the various water sources This implies that the changes are controlled by external factors Fluctuations in temperature and humidity NAO winter index ± 0 C Reductions in acid rain Increase are change in primary production 2

3 Climatic DNOM fluctuations There are strong correlations between runoff intensity and TOC l Changes in precipitation pattern may explain increases in TOC conc. No significant correlation between NAO winter index and TOC concentration Correlations between temperature and TOC is less clear l Perhaps an decrease in number of days below freezing and thinner snowpack may be important TOC mg C L Fall Spring 12 Summerr Discharge L sek -1 3

4 Effect of reduction in Acid rain In the 70 and 80ties reduction in the colour in lakes were reported in the regions suffering by acid With a decrease in S-deposition one should expect an increase in the NOM This was explained by that weak humic acids were protonised making them more hydrophobic This may only contribute to the observed increases as NOM also increases in areas not influenced by acid rain. 4

5 Increase or change in primary production More efficient forestry 29-57% increase in growth in Østlandet, Sørlandet and Trøndelag NIJOS, 2000 More decideous than coniferous NIJOS, 2000 Increase in amount and diversity of moss NIJOS, 2001 Plausible causes: Enhanced growing season, with long and mild falls NIJOS 2001 Accumulation of Nitrogen Increased CO 2 partial pressure 5

6 Parameter Min Max Tot S dep (g S/m 2 /y) Peat (%) Precipitation (mm) Latitude 58,23 63,10 Growing season (days) Size (ha) Retention time (yr) Volume (10 6 m 3 ) Site characteristics Span a large range in anthropogenic deposition, relative biotope coverage and climate All sites are similar in that they are dominated by: Unmanaged coniferous forests with heather on Podzolic soils & Histosols on Gneiss or granite bedrock 6

7 Hietajärvi 7

8 Valkea-Kotinen 8

9 Svartberget 9

10 Birkenes 10

11 Skjervatjern 11

12 Water chemistry Large span in water chemistry Parameter min max H + (µm) Ca 2+ (µeq/l) TOC (mg C/L) Total Al (µm) Si (µm) Conductivity (ms/m) All low ionic strength and oligothrophic 12

13 DNOM material: Methods Reverse Osmosis (RO) isolates Isolated L spring and fall surface water sample Ion exchanged Me 2+ for Na + Up concentrated to 25L Rota-Evaporated Freeze dried Recovery of 85-90% Represent a non-labile DNOM material enabling multidimensional characterisation and thereby parameter comparison 13

14 Methods DNOM characterisation methods Elemental analysis C and N Fractionation XAD8 + CEx & AEx SEC CE CZE + CGE FI-ESI/MS Structure λ254, 400 & 600nm FTIR FES TLS ESR 13 C CPMAS NMR Functionality Carboxylic and hydroxyl acidity Potentiometric ph titration Biodegradability Incubation Partitioning coefficients for PAH B[a]P, pyrene, TCB, TBDE Macrophyte response Photosynthetic oxygen production, Guajacol peroxidase 14

15 Results DNOM characteristics Great spans in bio-physicochemical characteristics of the DNOM Parameter C:N (Wt%) HPO-A (%) Mw (kd) Radii (nm) suva Min , Max Despite: a common biological origin (i.e. conifer forest with ferns) and Cond.mat. HIX Spin density (g -1 ) Arom/Aliph m/z overall base-flow conditions during sampling Tot-COOH (meq g -1 ) BDOM (%) Kd B[a]P Macrophyte resp

16 Correlations Disclaimer Correlation Does Not Imply Causation Correlations may be fortuitous due to the limited number (N=10) of samples be due to a co-variation with a third parameter This is especially the case regarding the site characteristics, as many of these parameters are inherently correlated This presentation therefore only suggests possible conceptual links between empirically correlated parameters 16

17 Average absolute correlation The water and site characteristics that on average explained most of the variation in the DNOM characteristics were H + activity in solution Total S-deposition Average deposition from 1989 to 1999 Parameter H + Total S deposition NO 3 - OD 600nm Al OD 400nm Temperature % rock Wet S deposition Cl- % thin humus layer OD 254nm Si TOC % histosol avg. r

18 Empiric relationship between S-deposition vs. TOC & OD600nm The amount of TOC increases with decreasing S deposition The colour increases more than the amount of TOC The DNOM changes also character svisa R 2 = R 2 = S-deposition / yr mg C/L 18

19 Strong correlations with S deposition Less S deposition gives DNOM that is: more acid larger and more coloured less aromatic lower in N-content better carriers of PAH DNOM characteristics Total COOH Pot Low Mw SAR Aromatic SFE C:N EA Mw SEC r Kd Pyrene

20 Average absolute correlation The site and water characteristics that on average explained most of the variation in the DNOM characteristics were H + activity in solution Total S-deposition Average deposition from 1989 to 1999 OD at 600nm OD at 600, 400 and 254nm are all related to the TOC Much of the quality of DNOM is given by the TOC Parameter H + Total S deposition NO 3 - OD 600nm Al OD 400nm Temperature % rock Wet S deposition Cl- % thin humus layer OD 254nm Si TOC % histosol avg. r

21 Strong correlations with colour The more TOC the more Hydrophobic Dense DNOM DNOM chracteristics HPO-B HPO-N r Mw/radii

22 PCA on combined dataset 8+10 RO isolates from Gjessing et al. and Vogt et al. NOM-typing NOMiNiC Main PC describe the differences in the two datasets Possibly due to differences in elevation and the % lakeof total catchment area Second PC describe the content of DNOM Sites are clustered Small seasonal effects 22

23 Climate vs. Results DNOM characteristics The proportion of Phenolics decrease further north The proportion of Humics increase with increasing length of summer and retention time Increasing temperature may give rise to less carboxylic acidity Site NOM characteristics characteristics r Latitude Phenols RFI-A TLS Growing season Humic RFI-C TLS Temperature Tot COOH Pot Retention time Humic RFI-C TLS Precipitation PODAlgae response

24 Principal component analysis Low robustness 10 samples, 20 parameters PC1 gradient Increasing size Increasing colour Increasing ability to sorb PAH Phenolic carboxylic acidity PC2 gradient Increasing humification More condensed Lower spin densities PC2 (18%) 0,6 0,4 0,2 0-0,2-0,4 Phenol Arom/Aliph SAR BDOM SFE Radii Cond.mat. HIX Algea resp. suva C:N C=C; COOm/z HPO-A Phenol/Arom Spin density -0,6-0,4-0,2 0 0,2 0,4 0,6 PC1 (43%) Mw O-H; C-O Tot-COOH KB[a]P 24

25 Explanatory variables to the main PC Total S deposition {H+} Growing season (days) PC1 PC2 PC Site characteristic r p 1 Total S-deposition from 1989 to ,944 0,000 2 H + conc. in original water sample Length of growing season 0,931 0,802 0,000 0,005 25

26 Conclusions These correlations indicate that: As the S-deposition decreases we may find More coloured and high Mw DNOM that is Better to adsorb micro-pollutants More rich in carboxylic acidity More humic and condensed DNOM is found in More acid waters Sites with longer growing season 26