the impacts of transboundary air pollution on acid sensitive lakes

julian aherne, heidi scott, andrew burton, colin whitfield, kevin adkinson, thomas cummins, and others…

Ireland’s Environment 2012: EPA-STRIVE Research ConferenceTrinity College Dublin [28 June 2012]

overview | atmospheric pollution can adversely affect the natural environment leading to significant impacts on ecosystem services.

sulphur and nitrate dioxide cause acidification.

excess nitrogen causes decreased ecosystem biodiversity.

heavy metals and persistent organic pollutants may accumulate in soil and water and cause damage to the environment and human health.

as a consequence, during the last two decades international policies have focused on reducing emissions of transboundary air pollutants.

source: www.apis.ac.uk

objective | the principal objective was to assess the impacts of major transboundary air pollutants on acid-sensitive lakes and soils, their response to reductions in emissions of sulphur and nitrogen oxides, and to address knowledge gaps in relation to the levels of heavy metals and persistent organic pollutants in semi-natural ecosystems.

• assess response of rainfall chemistry to emissions reductions • evaluate response of surface waters (predominantly small upland

headwater lakes) to changes in atmospheric deposition• evaluate the levels and controls on trace metals in acid-sensitive lakes• evaluate the influence on sea-salt on acidification of lakes• evaluate the drivers of long-term patterns in surface waters• evaluate the controls on green house gases…• characterise the physico-chemical characteristics of acid sensitive soils• evaluate total and methylmercury in the soil and water • evaluate the presence of POPs in the soil and water of selected

headwater lake catchments

emission reductions | western | marine | semi-natural ecosystems | climate

location of monitoring stations contributing precipitation chemistry to the co-operative programme for monitoring and evaluation of the long range transmission of air pollutants in Europe (EMEP [Chemical Co-ordinating Centre]).

(a) assess response of rainfall chemistry to emissions reductions

one-day back-trajectory wind-rose plots showing the proportion (%) of air by direction and source during the period 1989–2009 for sites in west (Mayo) and east (Wicklow)

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Non-marine sulphate (mg L–1)

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Valentia ObservatoryTurlough HillThe BurrenRidge of CapardOak ParkGlenveaghJohnstown CastleLough NavarMedian concentration

Nitrate (mg L–1)

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long-term annual trend (1991–2009) in non-marine sulphate, nitrate and ammonium concentration in precipitation (mg L–1) at EMEP stations

sensitivity of surface waters to acidification based on soil and geology

(b) evaluate response of headwater lakes to changes in atmospheric deposition

survey lakes sampled during spring 1997 and 2007 (n = 77)

significant decreases in SO42–, nmSO4

2– and non-marine base cations, and significant increases in alkalinity between the 1997 and 2007 lake surveys, suggesting that lakes have responded to reductions in long-range transboundary air pollution. However, there were no significant changes in surface water pH and AlT. It is likely that inter-annual variations in sea salt inputs and DOC concentrations (organic acidity) may have contributed to the delay in recovery of pH.

sensitivity of surface waters to acidification based on soil and geology

(c) evaluate the levels and controls on trace metals in acid-sensitive lakes

trace metal survey lakes sampled during spring 2008 (n = 122)

order of total trace metal concentrations (µg L–1) was (highest to lowest) : Fe > Al > Mn > Sr > B > Zn > Ba > Ti > Mo > Se > V = As > Bi > Cr > Ni = Cu > Cd > Pb > Tl > Co > U > Hg. The study lakes were strongly dominated by Fe, Al and Mn, measurements BDL were common for certain elements such as Be (100% BDL), Cd (79%), Se (40%), Co (39%) and Pb (29%).

fractions: trace metals (i.e., Al, Mn, Fe, Ni, Cu, Zn, Sr, Ba, V and B) were predominantly in dissolved form; although elevated particulate fractions were observed for Mn (20%), Al (25%) and Fe (33%). The dissolved labile phase was the dominant form for Sr (98%), Ba (90%), Mn (78%) and Zn (75%). In contrast, the dissolved non-labile phase was dominant for Cu (78%), Ni (67%), Fe (58%), V (58%) and Al (48%).

toxicity: trace metal concentrations were low, within the range of pristine global surface water concentrations; however, dissolved zinc, cadmium, inorganic labile aluminum and manganese may potentially reach levels harmful to aquatic organisms in some lakes (~20%).

sources: redundancy analysis indicated that metals were predominantly derived from geochemical weathering. However, a number of trace metals (e.g., lead, zinc) were correlated with anthropogenic atmospheric deposition (non-marine sulphate), suggesting atmospheric sources or elevated leaching owing to acidic deposition. Dissolved organic carbon (DOC) was a major driver associated with higher concentrations of dissolved metal fractions.

(d) evaluate the levels and controls on green house gases

ghg: the majority of lakes were supersaturated with CO2, N2O and CH4.

principal components analysis indicated that higher levels of CH4 and N2O supersaturation were exhibited under different land-cover conditions. Methane supersaturation was highest in lower elevation catchments with an evaporative hydrologic character and high organic carbon concentration. In contrast, lakes characteristic of N2O supersaturation were low in carbon and located in more rapidly flushed higher elevation catchments.

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Valentia Observatory

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Daily chloride (mg L–1)

Julian day (2008)

March 10: Valentia Observatory 1967.0 (mg L –1)

“Lowest March pressure on record for Ireland on 10th” Met Eireann, Monthly Weather Bulletin, March 2008.

“Deep depressions passing close to or over Ireland brought very unsettled conditions, with strong winds and spells or rain or showers each day. All areas received heavy rain between the 9th and 11th… The same periodproduced very strong winds…”

(e) evaluate the influence on sea-salt on acidification of lakes

sodium:chloride ratio in lake water during 2007 (left) and 2008 (right) surveys

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Box-plot comparison of paired lake chemistry (n ~ 50) observations from the

2007 and 2008 surveys, before and after the 10 March 2008 sea-salt event.

(f) & (g) POPs and Hg in headwater catchments: intensive study catchments

Concentrations of POPs in Water at Study Lakes (n=5)

POPs

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Total HCH

Total endosulfan

Total cyclodienes-a

Total cyclodienes-b

Total DDT

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Total PCBs

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(e) evaluate the presence of POPs in the soil and water of lake catchments

water: mean ± S.D. (n=3) lake concentrations of POPs estimated from SPMDs deployed during the period from July, 2009 to January, 2010 at the five study sites. Other OCPs include OCS, HCB, Methoxyxhlor, and Pentachloranisole.

Concentrations of POPs in Soil at Study Sites (n=5)

POPs

Total PAHs

Total PBDEs

Total DDT

Total other OCPs

Total PCBs

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Concentration of POPs per m2 of Soil at Study Sites (n=5)

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soil: concentrations (left) and pool (right) of POPs measured in soils at the five study sites ( ng/g and µg/m2), sampled during October 2010. Other OCPs include HCHs, Cyclodienes-a and b, Endosulfan, OCS, HCB, Methoxyxhlor, and Pentachloranisole.

• physical, meteorological, and chemical parameters exhibited correlations with POPs in SPMDs and soil samples, e.g., lake:catchment ratio, rainfall, DOC, and source air (e.g., Endosulfan and % overland air).

• the role of media partitioning for many of the compounds is apparent. Even in highly organic soils, HCHs, HCB, Endosulfan, and less-chlorinated PCBs have a tendency to revolatilize or washout more readily and are more likely to be captured in SPMDs. Whereas, ‘heavier’ compounds, e.g., PAHs, PBDEs, and the more-chlorinated PCBs bind to soil and sediments.

• observed concentrations were well within, or below, the range of ‘background’ values from continental Europe and internationally.

POPs summary

(e) evaluate total and methylmercury in the soil and water

water: averages concentrations of THg (n= 6) and MeHg (n= 4) in study lakes between 2010 and 2011.

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THg = –2.458 + (0.327 * TOC) + (0.261 * Na+) – (1.178 * SiO2) – (0.606 * d18O) Adj R2 = 0.56

MeHg (ng/L)

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MeHg = –0.0602 + (0.0023 * Conductivity) + (0.0215 * Gran Alkalinity) + (0.0501 * SiO2) + (0.0031 * Turbidity) Adj R2 = 0.48

relationships between THg (and MeHg) in water and lake chemistry

soil: averages concentrations (left) and pools (right) of THg in soil at the five study catchments, October 2010.

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Age Chronology of SGI Peat Core

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Age Chronology of MUL Peat Core

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Fluxes of THg in MUL Peat Core

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Fluxes of THg in SGI Peat Core

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• various physical and chemical parameters exhibited correlations with Hg in water and soil samples; notably THg is strongly influenced by the level of organic matter in soil and water

• lake concentrations of Hg in this study were similar to levels measured in water and soils elsewhere.

• peat core records indicate there have been significant decreases since the highest peaks (1950–1980s), indicative of regulation and enforcement of Hg emissions.

• northwestern sites appear to have highest levels of THg and MeHg in lake water and soils.

Hg summary

overall conclusions

1. precipitation chemistry shows a significant response to emission reductions of sulphur dioxide (and tentative for nitrogen oxides)

2. in concert, lake chemistry has responded to reduced anthropogenic sulphur deposition, but pH has not changed owing to increases in dissolved organic carbon

3. trace metal concentrations were low, dominated by iron, aluminium and manganese; however, dissolved zinc, cadmium, inorganic labile aluminum and manganese may potentially reach levels harmful to aquatic organisms

4. lakes were supersaturated with GHGs; however, effluxes contributed little to national emissions. Methane and nitrous oxide are strongly related to landscape characteristics

5. Sea-salt events can have significant and widespread impacts on lake chemistry (albeit temporary)

6. levels of POPs and Hg were low, consistent with background regions and strongly associated with organic carbon

climate: potential future changes to biogeochemical cycling of carbon (soil organic matter / dissolved organic carbon) and climate variability (storminess) will influence acid status, trace metals and mercury, and POPs in semi-natural ecosystems…