Aluminium. The Link between Increase in Water Colour and DOC and Reduction in Acid Rain. Al-DNOM flocks in a raw water treatment work

Transcription

1 Aluminium The Link between Increase in Water Colour and DC and Reduction in Acid Rain Al-DNM flocks in a raw water treatment work Rolf D. Vogt University of slo 13th Int.ISS

2 Increasing Dissolved Natural rganic Matter (DNM) in surface waters in Northern Europe and North-Eastern America ICP Waters, Skjelkvåle, 2003 Large increases in dissolved carbon concentration across the UK may be a combined response to climate change and decreasing acid deposition Regional trend results for ICP Waters sites for the period Evans et al., 2005

3 Increased color in surface waters in SE Norway Eikebrokk et al., 2004 Color increase in slo s raw waters: Maximum color levels from monthly samples A doubling or almost tripling of color in some sources from

4 Increased DC in surface waters in UK UK Acid Waters Monitoring Network, Evans et al., 2006 DC concentration increases in streams and lakes : Lakes -2 Jul-88 Jul-89 Jul-90 Jul-91 Jul-92 Jul-93 Jul-94 Jul-95 Jul-96 Jul-97 Jul-98 Jul-99 Jul-00 Jul-01 Jul-02 Jul-88 Jul-89 Jul-90 Jul-91 Jul-92 Jul-93 Jul-94 Jul-95 Jul-96 Jul-97 Jul-98 Jul-99 Jul-00 Jul-01 Jul-02 standardised concentration Streams standardised concentration -2 Concentration standardized plots Since 1988, there has been, on average, a 91% increase in DC concentrations of UK lakes and streams

5 Color is changing more than DC ongve et al., 2004 The change that took place by the end of 2000 was > 40% for color and only 11 13% for DC This implies changes in the composition of DNM gher M w, more hydrophobic and more humic

6 Possible causes for changes in DNM amount and quality NRDTEST Workshop, Vogt 2003 Three main causes: 1. Climate variation 2. Land use changes 3. Changes in Anthropogenic deposition Considered shift Key variable factors Climate variation Precipitation amount Precipitation intensity Snow relative to rain Spring flood ydrologic connectivity Soil moisture Water retention time Fall and winter temperature Radiation Land use changes Forestation Species iomass Drainage Site preparation Changes in Atmospheric deposition Reduced acid rain Accumulated N Sea-salts DNM Conc. /- /- /- /- /- /-? /- /-?

7 1. Climate variation The Intergovernmental Panel on Climate Change, IPCC 2001 Increased temperature and precipitation Northern hemisphere over the 20th century 1990s being the warmest decade of the millennium. Precipitation increased by 5-10% 5 Likely also an increase in heavy precipitation events

8 Relation between precipitation intensity UV absorbency and DNM and DNM Variation in color and DC is well correlated to runoff DNM in the forest floor is larger and more colored than in the mineral soil 0,700 0,600 0,500 0,400 0,300 0,200 Fall Spring Summer irkenes catchment 0, Discharge L sek -1 Waterworks, slo, data from ongve et al., 2004 Climate can not alone explain the unprecedented high DC concentration and color in 2001 Evans et al. (2006) argue that climatic factors may not be the dominant drivers of DC change.

9 2. Land-use change There has been an increase in the terrestrial organic mass over the past two decades This is evident as a significant carbon sink Nature; Schimel et al., 2001 gh DNM flux from watersheds with: Large soil pools of humus relative to mineral soil NIJS Forestation increase DNM leaching

10 y 2000, relative to mid-1980s, sulfur deposition had decreased regionally 3. Decrease in Acid Rain Wright, R.F., et al. 2005; SFT, 2005; a.o. by >50% in Europe by ~40% in North America Sulfate concentrations in surface waters dropped by between 30 70%.

11 Empirical relation between acid rain and DNM The same regions experiencing a decrease in 2 S 4 are experiencing an increased DNM In the 70 and 80ties reduction in the color in lakes were reported in the regions suffering acid rain (Dixit et al., 2001) Exceedence of acid in meq/m2/yr Skjelkvåle et al., 2001 Evans et al., 2006

12 DNM solubility is linked to its charge Charge of DNM is increased by: Increased p Decreased concentration of cations Esp. Al 3 and Ca Ca 2 A-/TC 0,08 0,07 0,06 0,05 0,04 0,03 0,02 0,01 0 / / / / / h / a a / / / / / a / / / / / / / / / / / / / / / / / a a aa a / / / / / / / / / / / / / a a a / / / g / / g a / / g a a h E s ah a E h a a a a a a hs E a a ae a / g g g a a E g E a hs a a h a a h h a h gh s E h g g / / / s hs s E E g E g hs h h shs a s g a g h E h E hs h hs hs E E a a E s h / hs h hs s s hs s E h g hs g s s s h a h hs as hs h h hs s hs s s s g g s s hshs hs h s hs hs s g s s hs s hs h h s hhs hs s ss hs 0 0,005 0,01 0,015 0,02 0,025 Alo/TC UMEX data hs hs hs p has not changed much in acid sensitive dystrophic watersheds as a result of less acid rain ICP Waters, Skjelkvåle, 2003

13 gh Al concentration in regions with acid rain Acid rain = Strong mineral acidity along with increased fluxes of sulfate, serving as a mobile anion Allow for elevated concentrations of Al in acid sensitive mineral soil waters Dystrophic and ligothrophic watersheds Skjervatjern irkenes Ciekon renna Czerniawka Janow Ratanica ueq/l Ali N4 NaK CaMg S4 N3

14 Al effect on DM The excellent properties of Al i as a flocculent and coagulant may be clearly envisioned at water treatment works were Alum (i.e. Al 2 (S 4 ) 3 ) is used for removal of DM View down into processing raw water added 15 mg Al/L at p 5.9 at ærum vann AS

15 % change in DC vs. change in mobile anions DC Workshop, slo; Monteith et al, 2006 % change in DC concentration % change in DC concentration Sulphate sulphate theil slope (microeqs l -1 yr -1 ) Sulphate Chloride % change in DC concentration % change in DC concentration Chloride chloride theil slope (microeqs l -1 yr -1 ) Sulphate Chloride ([Ca2] [Mg2]) < 150 µeq l y = x R 2 = [S 4 2- ] [Cl - ] theil slope (microeqs l -1 yr -1 ) -6 [S 4 2- ] [Cl - ] theil slope (microeqs l -1 yr -1 ) -6 Rising temperature, declining S 2-4 deposition and changing seasalt (Cl - ) loading accounted for 65 % of the 91 % increase in DC in UK (Evans et al., 2006)

16 Main spatial variation in DNM quality explained by S deposition NMiNiC study; Vogt et al., 2004 Principal component analysis on 21 selected parameters from 5 sites and 2 seasons PCA indicate that sites with less S-deposition have DNM with higher: suva M W Tot. S deposition g m -2 yr -1 1,2 1 0,8 0,6 0,4 0,2 R 2 = 0, PC1 (41.4%) PC2 (20.7%) 0.5 Cond. Mat. PS IX 0.25 suva Phenol Arom/Aliph Mw C:N -; C- DM SAR 0 Tot-C K[a]P Radii SFE C=C; C- P-A m/z Spin density Phenol/Arom PD PC1 (41.4%)

17 Conclusions 10 out of 11 ICP Waters regions in Europe and North America seeing decreased acid rain showed increasing DC trend The increased DNM is more colored, higher Mw and more hydrophobic DNM in sites receiving less loads of acid rain are more colored, higher Mw and more hydrophobic Changes in the concentration of dissolved inorganic aluminum is a likely underlying governing factor for increased DNM in dystrophic and oligothrophic watersheds draining mineral forest soils.

18 Acknowledgement NRDTEST for funding Profs. Egil Gessing,, ans Martin Seip, Don Monteith and several reviewers for valuable comments Monteith and the ICP program for data