Regional increases in DNOM. Decrease in Acid Rain through lower Aluminium levels. Rolf D. Vogt University of Oslo

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1 Regional increases in DNM Decrease in Acid Rain through lower Aluminium levels Rolf D. Vogt University of slo

2 utline There has been an increase in DC and especially color The increase has occurred in acid rain impacted regions Clear relationship between S 4 and DC Aluminum (Al) is a powerful remover of DNM, especially of the more colored fraction Reduced Acid rain lower [Al] increased [DNM] and color Decreased mobilization of inorganic aluminum species from poor acid mineral soils, due to the decline in acid deposition, is likely to be the main underlying factor for the increased conc. of DNM

3 Increasing Dissolved Natural rganic Matter (DNM) in surface waters in Northern Europe and North-Eastern America Regional trend results for ICP Waters sites for the period ICP Waters, Skjelkvåle, 2003

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

7 Climate variation The Intergovernmental Panel on Climate Change, IPCC 2007 Northern misphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years. Eleven of the last twelve years ( ) rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850)

8 Likewise, the 10 year running average temperature in southern Norway has increased steadily up to 1,8ºC since An important exception is the period , having temperatures more close to the 30 year norm. The temperature increase was greatest in the winter.

9 Relation between precipitation intensity 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 UV absorbency 0,700 0,600 0,500 0,400 0,300 0,200 Fall Spring Summer irkenes catchment 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. 0, Discharge L sek -1 Waterworks, slo, data from ongve et al., 2004

10 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 which is the result of: Re-growth on abandoned agricultural land Fire prevention Responses to environmental changes, such as longer growing seasons, and fertilization by carbon dioxide and accumulation of nitrogen. Recovery from acid rain Nature; Schimel et al., 2001

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

12 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) Skjelkvåle et al., 2001

13 Empirical relation between acid rain and DNM

14 Sulfur as a driving force Color (mg Pt l -1 ) in Lake Elvåga, air temperature and precipitation in the area throughout the experimental period ( ). Color (mg Pt/l) in Lake Elvåga vs. precip(mm)*(1/ds4) Riise et al., 2006

15 % change in DC vs. change in mobile anions DC Workshop, slo; Monteith et al, 2006 % change in DC concentration Sulphate sulphate theil slope (microeqs l -1 yr -1 ) Sulphate + Chloride 14 % change in DC concentration Chloride Sulphate + Chloride ([Ca2+] + [Mg2+]) < 150 μeq l chloride theil slope (microeqs l -1 yr -1 ) % change in DC concentration [S 4 2- ] + [Cl - ] theil slope (microeqs l -1 yr -1 ) Rising temperature, declining S 4 2- deposition and changing seasalt (Cl - ) loading accounted for 65 % of the 91 % increase in DC in UK (Evans et al., 2006) % change in DC concentration y = x R 2 = [S 4 2- ] + [Cl - ] theil slope (microeqs l -1 yr -1 )

16 DNM solubility is linked to its charge Charge of DNM is increased by: Increased p Decreased concentration of cations Esp. Al 3+ p has not changed much in acid sensitive dystrophic watersheds as a result of less acid rain 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 ae 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 h h s hhs hs s ss hs hs s s hs s 0 0,005 0,01 0,015 0,02 0,025 Alo/TC hs hs hs UMEX data ICP Waters, Skjelkvåle, 2003

17 Mobile anions and Al Acid rain = Strong mineral acidity along with increased fluxes of sulfate, serving as a mobile anion Allow for elevated concentrations of Al i in acid sensitive mineral soil waters Dystrophic and ligothrophic watersheds ueq/l Ratanica Janow Czerniawka renna Ciekon irkenes Skjervatjern + Ali N4+ Na+K Ca+Mg S4 N3

18 Empirical relation between Aluminum and DNM quality

19 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

20 Main 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 1,2 Tot. S deposition g m -2 yr ,8 0,6 0,4 0,2 R 2 = 0, PC1 (41.4%)

21 The increased DNM is easy to remove Along with increased DNM there is an increase in molecular size and hydrophobicity Increased suva In general, hydrophobic macro-molecules are easy to remove and pose less health risk 3 2,5 2 Peak height (mau) 1,5 1 0,5 0 Raw water Sedimentation Flotation AC-A AC- Treated water peak I peak II peak III peak IV peak V Tuhkanen, 2003

22 Conclusions 10 out of 11 ICP Waters regions in Europe and North America seeing decreased acid rain showed increasing DC trend In the UK the geographical distribution of DC trend is similar to that for S 4 2- and Cl - trends o Sites with low base cation concentration show greatest sensitivity to change in [Cl - ]+[S 4 2- ] 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 governing factor for these trends in dystrophic and oligothrophic watersheds draining mineral forest soils.