Results
Acidification and chemical
recovery
Deposition of S and N at Langtjern peaked during the late 1960s at 9.8
kg S ha-1 yr-1 (61 meq
m-2 yr-1) and 8.8 kg N
ha-1 yr-1 (63 meq
m-2 yr-1) (averaged over 1965-1969)
(Figure 2 ). After the 1960s, S deposition gradually declined
towards the current level of 1.1 kg S ha-1yr-1 (6.6 meq m-2yr-1) (2018-2022 average) and is expected to remain
more or less constant towards 2100 under the emission scenario of
current legislation (CLE). Deposition of N was more variable, showing
two other peaks after the 1960s, and is currently (2018-2022) at 3.7 kg
N ha-1 yr-1 (26.5 meq
m-2 yr-1).
Streamwater chemistry follows patterns that are typical for acidified,
but recovering, streams (Figure 3): strong declines in
SO4 and SAA, following the temporal change in S
deposition; declines in base cations (and SBC), in particular in Ca and
Mg, and increases in pH and TOC. Labile Al shows the strongest decline.
The other strong acid anions Cl and NO3 also decline,
where Cl is currently at a fairly constant level of circa 10 µeq
l-1, similar to SO4. Nitrate is
present in very low concentrations relative to SO4because of high retention in the catchment. pH, ANC and ANCoaa are
currently at 5.16, 61.5 µeq/L and 24.0 µeq/L, respectively (averaged
over 2018-2022), which is below MAGIC-simulated preindustrial levels
(5.38 (pH), 73.6 µeq/L (ANC) and 34.7 µeq/L (ANCoaa), respectively)
(Table 1 ).
Organic acidity, calculated from the charge balance between strong acid
anions and major cations, increased markedly over time, balancing 33%
of the base cations during the end of the 1980s and 73% for 2018 to
2022 (Figure 4). On an equivalent basis, organic acids have dominated
SAA at Langtjern since 2000-2004. Charge density of TOC increased from
4.3 to 5.7 µeq/mg C since the end of the 1980s (Figure 5 ).
MAGIC hindcasts of historical acidification and
recovery
Model performance for individual and compound variables were evaluated
for a set of performance statistics (Table 2). MAGIC described levels
and variations for major cations, major anions, pH and ANC well (Figure
3). The variation was described best
(r2>0.7) for the SAA and its
constituents, dominating base cations Ca and Mg, ANC, ANCoaa, organic
acids and pH. These variables also had low normalized RMSE’s
(<0.7), except for variables associated with, or affected by,
organic acidity such as ANCoaa, labile Al, and organic matter charge
density – these variables also had relatively low values for NSE,
illustrating systematic overestimation (organic acids, ANCoaa, charge
density). The overestimation of organic acidity was primarily related to
an overestimation of the TOC charge density with on average ca 1 µeq
mg-1 TOC (Table 1; Figure 5). The variables that were
described with least bias (|bias| <1) were
those that showed least temporal variation (Figure 3), while those
described with a large bias (|bias|>
|5|) were ANC, ANCoaa and organic acids.
Since organic acidity is such an important part of the total charge
balance, model simulation of other ions is very sensitive to its level.
Decreasing of organic acidity in MAGIC leads to lowering of the base
cation concentrations, so optimizing organic acidity in MAGIC can come
at the cost of good optimization of SBC and therefore pH and ANC.
However, the upward trend in organic acidity was described well, which
is a novel aspect of MAGIC modelling.
The hindcast of all the elements, from 1850 to 1973, was driven by the
change in deposition (Figure 2 ). Preindustrial pH, ANC, ANCoaa,
and TOC were higher than current-day values and much higher than their
values during the period when acidification peaked (Table 1 ).
Base saturation decreased from 23.2% (preindustrial) to 19.4%
(present-day).
MAGIC projections of future acidification and
recovery
Deposition of S and N in 2050 under the CLE deposition was 56% and 67%
of 2015 deposition, respectively, where 2015 was used as the reference
year. The catchment became warmer and wetter during 1974-2022, as
indicated by trends (Sen slopes, MK test (Sen 1968)) in annual
temperature, precipitation and discharge, which are +0.38oC decade-1 (p<0.0001),
+39 mm decade-1 (p<0.1) and + 40 mm
decade-1 (p<0.01), respectively. The climate
scenario RCP8.5 predicted less climate change than these empirical
climate data, but the locally adapted climate scenario RCP8.5* gave a
higher mean discharge (+80mm) compared with average discharge for 1974
to 2022 (Figure 6 ).
The Constant Climate scenario did not result in more chemical recovery
in 2050 and 2100 than observed for 2018-2022 (Figure 3 ), while
locally adapted RCP8.5* and RCP8.5 resulted in a slight reacidification
(Table 1 ). RCP8.5* had a slightly stronger effect on
acidification than RCP8.5, as a consequence of higher discharge and thus
higher base cation export. Chemical acidification status in 2100 was
markedly below the preindustrial water quality indicators pH, ANC and
ANCoaa. The reacidification is driven by the depletion of base cation
stores from the catchment soils due to increased element export related
to the increased discharge. The three future scenarios give rather
similar results, with organic acidity dominating over mineral acidity
(Figure 4 ) and where the strongest climate change scenario
results in a slight reacidification (reduction of ANC with 5.2 µeq/l
(Table 1)).
Sensitivity analysis
We tested the necessary increase in weathering rates to obtain
preindustrial base saturation and ANC in 2100 in a sensitivity analysis
(Table 3) where the weathering rates were increased with a fixed
percentage from year 2000 for three climate scenarios. The uncertainty
intervals for both RCPs are related to uncertainty intervals for future
precipitation, illustrating the importance of precipitation for
estimation of weathering rates. For the ‘constant climate’ scenario, the
annual increase was 0.54%, and the two RCPs had median increases in
weathering rates of 0.59% and 0.96%, resulting in weathering rates in
2100 that were a factor 1.7 to 2.5 higher than in 2000. Interestingly,
it took relatively less weathering to reach preindustrial ANC than for
preindustrial BS% as a consequence of lower expected acid deposition in
the future compared to pre-industrial. The cumulative excess
contribution of base cations from enhanced weathering were 33%
(ConstantClim), 36% (RCP8.5) and 68% (RCP8.5*), to reach preindustrial
base saturation. To reach preindustrial ANC, these numbers were 35%
(RCP8.5) and 59% (RCP8.5*).
Discussion
The monitoring data demonstrate strong chemical recovery from
acidification at Langtjern, similar to other strongly acidified surface
waters in Norway (De Wit et al. 2023), elsewhere in Europe and North
America (Bukaveckas 2021; Garmo et al. 2014; Houle et al. 2022; Kopacek
et al. 2021; Lawrence et al. 2021; Sterling et al. 2022) and in Japan
(Sase et al. 2021). Simultaneously, DOC at Langtjern has increased and
now contributes more to the total anion charge in the streamwater than
the strong acid anions. The site is thus moving towards a state
dominated by natural-, rather than anthropogenic acidification. Browning
is a common feature for surface waters in boreal regions, primarily
related to reduced acid deposition (de Wit et al. 2021; Monteith et al.
2007). To what extent and at what time scale organic acidity will
dominate anthropogenic acidification is not well-known, however.
Assumptions about natural levels of organic acidity have considerable
implications for assessments of the anthropogenic contribution to
surface water acidity (Erlandsson et al. 2011) and the necessity of
liming to accelerate recovery (Laudon et al. 2021). Humic charge density
for DOM increased, as found earlier (De Wit et al. 2007), suggesting
that both increased solubility and decreased deprotonation of humic and
fulvic acids control the return to naturally acidified systems and
pre-industrial water quality.
The last MAGIC application for Langtjern was done based on the period
1974 to 2003 (Larssen 2005). We used the same soil and historical
deposition data. In our study, we optimized for 1974 to 2022 and
captured the trend in chemical recovery with hardly any bias, which is
considerably better than Larssen (2005), where MAGIC underestimated the
positive trend in ANC, overestimating peak acidification ANC and
underestimating ANC in the early 2000s. Larssen (2005) reported
relatively poor model performance for K, Na, Mg and Cl compared with
MAGIC applications for two other acidified catchments in southernmost
Norway, which could indicate that the relatively poor simulation of ANC
levels at Langtjern were related to other major cations and anions than
SO4 and Ca. Also, an internal source of S in the
Langtjern catchment (6 meq m-2 yr-1)
was assumed by Larssen, contrary to our study, which could lead to
overemphasizing the importance of background SO4 at the
cost of anthropogenic SO4 and anthropogenic
acidification. This is illustrated by the substantially higher hindcast
for preindustrial ANC in our study (e.g. ANC of 80 µeq
l-1 (Figure 3 ) than in Larssen (2005) (e.g. ANC
of 40 µeq l-1). Furthermore, the longer time series in
our study presents a stronger dataset for model calibration. The
inclusion of changing organic acidity in our study, where Larssen
assumed constant organic acidity, cannot explain the poorer description
of recovery by Larssen since organic acidity counteracts changes in
mineral acidity, leading to a lower response in ANC to changes in SAA.
The increases in DOC and organic acidity were described tolerably well
by MAGIC albeit more poorly than mineral acidity. The levels of organic
acidity at Langtjern were somewhat overestimated possibly indicating
that organic acid properties at Langtjern are outside the range for
values for organic acid deprotonation reported by Hruska et al. (2003).
The organic charge density estimated in our study was between 4.4 and
5.7 µeq g-1 C, which agrees with the values previously
calculated for Langtjern (De Wit et al. 2007).
The MAGIC-forecasted pH, ANC and ANCoaa under reduced S deposition and
current climate were not yet back at preindustrial levels in 2100, which
to a great degree was related to depleted base cation stores. Climate
change acted through increasing discharge and thereby further depleting
base cation stores and thereby leading to a slight reacidification. Such
tendencies have already been observed in humus-rich acidified lakes in
Eastern Norway (de Wit et al. 2023), which was attributed to organic
acidity rather than climate change. However, TOC and organic acidity are
also climate-sensitive, in particular to precipitation (de Wit et al.
2016), a feature that is currently not included in MAGIC. Increased
catchment base cation export related to discharge is textbook knowledge,
but changes in soil base cation stores for periods shorter than 3 to 5
decades are typically difficult to measure (Ahrends et al. 2022).
We showed in a sensitivity analysis, using new features of MAGIC-Forest,
that a doubling in weathering rates would be required to achieve
preindustrial base saturation and associated water quality in 2100. An
even higher weathering would be necessary to compensate for enhanced
soil base cation loss under higher runoff from climate change. While it
is clear that mineral weathering rates are higher under forested versus
non-forested sites (Berner 1997), generally higher in moist versus dry
climates (West et al. 2005), and are promoted by higher
pCO2 and organic acids (Bargrizan et al. 2020), it is
difficult to constrain weathering rates based on empirical measurements
(Koseva et al. 2010; Kronnas et al. 2019). However, unexpected
widespread increases in dissolved silicates and calcium have been
observed in Norwegian lakes (de Wit et al. 2023), possibly providing
indirect evidence of recent, enhanced weathering rates. We conclude that
chemical recovery at Langtjern may be impacted – positively and
negatively – by climate change. Continued monitoring is needed to
evaluate which drivers will prove to be strongest.
Our study illustrates that a combination of long-term monitoring and
process-oriented modelling is key for predictions of water quality under
changing environmental conditions. Our assessment points towards an
ongoing transition from anthropogenic to natural acidification in
surface waters, due to reduced acid deposition and stronger impact of
climate, humic compounds, and possibly land use change as drivers
determining the surface water acidity status.
Acknowledgements
This work was conducted as part of the CatchCaN project (The fate and
future of carbon in forests), funded by the Technology Agency of the
Czech Republic (TA CR) project number TO 01000220. We acknowledge
EMEP/MSC-W (http://emep.int/mscw) for the provision of historical
deposition data and projections of future deposition. Arne Stuanes, Dick
Wright and Kari Austnes are gratefully acknowledged for helpful comments
on the manuscript.
Conflict of interest
The authors declare no conflicts of interest
List of Figures
Figure 1 Map of the Langtjern
catchment
Figure 2 Total atmospheric
deposition of SO4 and N (sum of NOx and
NHy) at the Langtjern catchment in meq
m-2 yr-1. Historical (1850-1973) and
future deposition, following current legislation policy (CLE), provided
by EMEP. Deposition of SO4 is corrected for seasalt
contribution.
Figure
3 Empirical flow-weighted mean annual element concentrations from 1974
to 2022 (open circles) and MAGIC-simulations for 1850 to 2100, for
SO4, Cl, NO3, pH (and H+), Na, K, TOC
(expressed on an equivalent basis), ANC, ANCoaa, labile Aluminum (lAl)
SBC and SAA. The future scenarios include EMEP deposition according to
current legislation (CLe) in combination with constant climate (dotted
line), RCP8.5 (blue line) and locally adapted RCP8.5* (red line).
Figure
4 Five-year averages of the equivalent sum of strong acid anions (SAA),
organic acids and sum of base cations (SBC) in µeq/l. Hatched and plain
bars show simulated data by MAGIC in a preindustrial decade, at peak
acidification and for future (2090-2100) scenarios (ConstantClim: CLe
deposition, no climate change; CLe+RCP8.5, CLe+RCP8.5*).
Figure
5 Simulated and empirical TOC charge density (µeq/mg TOC, top panel) and
organic acidity (in µeq/l) (bottom panel). Open circles show empirical
estimates, open squares and lines show MAGIC simulation.
Figure 6 Annual runoff (mm) at
Langtjern for 1850-2100. Open circles: empirical data; 1850-1973:
modelled runoff using averaged climate for 1971–2000. Future runoff
2023-2100: dotted line, constant climate (discharge equal to pre-1974);
blue line, RCP 8.5 (change relative to predefined period 1971-2000); red
line, RCP8.5* (change relative to empirical runoff for 2000 to 2022).
List of Tables
Table 1 Key MAGIC model results
for preindustrial time (mean 1850-1860), peak acidification (1965-1974
), current situation (2018-2022), and future (2090-2100), and for the
different climate scenarios. All with CLe deposition (constant climate;
RCP8.5, RCP8.5*), all with constant weathering. Last column shows
results sensitivity analysis (for RCP8.5* only, increased weathering).
Table 2 MAGIC calibration
performance statistics over 1974-2022 including Nash-Sutcliffe
efficiency (NSE), root mean squared error (RMSE), coefficient of
determination (r2), standardized root mean squared
error (RMSE/std) and bias (the mean signed difference between modeled
and observed values).
Table 3 Estimation of required
increase in weathering rates (in %) and resulting cumulative additional
base cation input from weathering over 2000–2100 (expressed as % of
base cation inputs from weathering for 2000-2100 under constant
weathering), to return soil base saturation, ANC or pH back to their
pre-industrial levels, for three climate scenarios. The intervals show
interquartile range based on the interquartile range of predicted
precipitation under the RCPs.
References
Ahrends B, Fortmann H, Meesenburg H (2022) The Influence of Tree Species
on the Recovery of Forest Soils from Acidification in Lower Saxony,
Germany. Soil Syst. 6(2): 25
Augustin F, Houle D, Gagnon C, Couture S, Courchesne F (2015)
Partitioning the impact of environmental factors on lake concentrations
and catchment budgets for base cations in forested ecosystems. Applied
Geochemistry 53: 1-12
Bargrizan S, Smernik RJ, Mosley LM (2020) Constraining the carbonate
system in soils via testing the internal consistency of pH, pCO(2) and
alkalinity measurements. Geochem. Trans. 21(1): 10
Berner RA (1997) Paleoclimate - The rise of plants and their effect on
weathering and atmospheric CO2. Science 276(5312): 544-546
Bukaveckas PA (2021) Changes in acidity, DOC, and water clarity of
Adirondack lakes over a 30-year span. Aquatic Sciences 83(3): 11
Clark JM, Chapman PJ, Heathwaite AL, Adamson JK (2006) Suppression of
dissolved organic carbon by sulfate induced acidification during
simulated droughts. Environmental Science & Technology 40(6): 1776-1783
Cosby BJ, Ferrier RC, Jenkins A, Wright RF (2001) Modelling the effects
of acid deposition: refinements, adjustments and inclusion of nitrogen
dynamics in the MAGIC model. Hydrology and Earth System Sciences 5(3):
499-517
Cosby BJ, Hornberger GM, Galloway JN, Wright RF (1985) Modeling The
Effects Of Acid Deposition - Assessment Of A Lumped Parameter Model Of
Soil-Water And Streamwater Chemistry. Water Resources Research 21(1):
51-63
de Wit HA, Couture RM, Jackson-Blake L, Futter MN, Valinia S, Austnes K,
Guerrero JL, Lin Y (2018) Pipes or chimneys? For carbon cycling in small
boreal lakes, precipitation matters most. Limnology and Oceanography
Letters 3(3): 275-284
de Wit HA, Garmo Ø, Jackson-Blake L, Clayer F, Vogt RD, Austnes K, Kaste
Ø, Gundersen CB, Guerrerro JL, Hindar A (2023) Changing water chemistry
in one thousand Norwegian lakes during three decades of cleaner air and
climate change. Global Biogeochemical Cycles:
De Wit HA, Mulder J, Hindar A, Hole L (2007) Long-term increase in
dissolved organic carbon in streamwaters in Norway is response to
reduced acid deposition. Environmental Science & Technology 41(22):
7706-7713
de Wit HA, Stoddard JL, Monteith DT, Sample JE, Austnes K, Couture S,
Folster J, Higgins SN, Houle D, Hruska J, Kram P, Kopacek J, Paterson
AM, Valinia S, Van Dam H, Vuorenmaa J, Evans CD (2021) Cleaner air
reveals growing influence of climate on dissolved organic carbon trends
in northern headwaters. Environmental Research Letters 16(10): 13
de Wit HA, Valinia S, Weyhenmeyer GA, Futter MN, Kortelainen P, Austnes
K, Hessen DO, Raike A, Laudon H, Vuorenmaa J (2016) Current Browning of
Surface Waters Will Be Further Promoted by Wetter Climate. Environmental
Science & Technology Letters 3(12): 430-435
Erlandsson M, Cory N, Folster J, Kohler S, Laudon H, Weyhenmeyer GA,
Bishop K (2011) Increasing Dissolved Organic Carbon Redefines the Extent
of Surface Water Acidification and Helps Resolve a Classic Controversy.
Bioscience 61(8): 614-618
Evans CD, Monteith DT, Reynolds B, Clark JM (2008a) Buffering of
recovery from acidification by organic acids. Science of the Total
Environment 404(2-3): 316-325
Evans CD, Reynolds B, Hinton C, Hughes S, Norris D, Grant S, Williams B
(2008b) Effects of decreasing acid deposition and climate change on acid
extremes in an upland stream. Hydrology and Earth System Sciences 12(2):
337-351
Garmo ØA, Skjelkvale BL, de Wit HA, Colombo L, Curtis C, Folster J,
Hoffmann A, Hruska J, Hogasen T, Jeffries DS, Keller WB, Kram P, Majer
V, Monteith DT, Paterson AM, Rogora M, Rzychon D, Steingruber S,
Stoddard JL, Vuorenmaa J, Worsztynowicz A (2014) Trends in Surface Water
Chemistry in Acidified Areas in Europe and North America from 1990 to
2008. Water Air and Soil Pollution 225(3):
Grennfelt P, Engleryd A, Forsius M, Hov O, Rodhe H, Cowling E (2020)
Acid rain and air pollution: 50 years of progress in environmental
science and policy. Ambio 49(4): 849-864
Hanssen-Bauer I, Førland EJ, Haddeland I, Hisdal H, Mayer S, Nesje A,
Nilsen JEØ, Sandven S, Sandø AB, Sorteberg A, Ådlandsvik B (2015) Klima
i Norge.Kunnskapsgrunnlag for Klimatilpasning, oppdatert i 2015.NCCS
report 2/2015. In: NCCS report 2/2015, NCCS, Oslo, Norway. Norwegian
Centre for Climate Services, Oslo, Norway. p 203
Helliwell RC, Simpson GL (2010) The present is the key to the past, but
what does the future hold for the recovery of surface waters from
acidification? Water Research 44(10): 3166-3180
Hindar A, Torseth K, Henriksen A, Orsolini Y (2004) The significance of
the North Atlantic Oscillation (NAO) for sea-salt episodes and
acidification-related effects in Norwegian rivers. Environmental Science
& Technology 38(1): 26-33
Houle D, Augustin F, Couture S (2022) Rapid improvement of lake
acid-base status in Atlantic Canada following steep decline in
precipitation acidity. Canadian Journal of Fisheries and Aquatic
Sciences 79(12): 2126-2137
Hruska J, Kohler S, Laudon H, Bishop K (2003) Is a universal model of
organic acidity possible: Comparison of the acid/base properties of
dissolved organic carbon in the boreal and temperate zones.
Environmental Science & Technology 37(9): 1726-1730
Kopacek J, Hejzlar J, Kana J, Porcal P, Turek J (2016) The sensitivity
of water chemistry to climate in a forested, nitrogen-saturated
catchment recovering from acidification. Ecological Indicators 63:
196-208
Kopacek J, Kana J, Porcal P, Stuchlik E (2021) Diverse effects of
accelerating climate change on chemical recovery of alpine lakes from
acidic deposition in soil-rich versus scree-rich catchments*.
Environmental Pollution 284: 10
Koseva IS, Watmough SA, Aherne J (2010) Estimating base cation
weathering rates in Canadian forest soils using a simple texture-based
model. Biogeochemistry 101(1-3): 183-196
Kronnas V, Akselsson C, Belyazid S (2019) Dynamic modelling of
weathering rates - the benefit over steady-state modelling. Soil 5(1):
33-47
Larssen T (2005) Model prognoses for future acidification recovery of
surface waters in Norway using long-term monitoring data. Environmental
Science & Technology 39(20): 7970-7979
Laudon H, Sponseller RA, Bishop K (2021) From legacy effects of acid
deposition in boreal streams to future environmental threats.
Environmental Research Letters 16(1): 10
Lawrence GB, Baldigo BP, Roy KM, George SD (2021) Trends and current
status of aluminum chemistry in Adirondack headwater streams 30 Years
after the Clean Air Act Amendments of 1990. Atmospheric Environment 249:
13
Lund E, Garmo OA, de Wit HA, Kristensen T, Hawley KL, Wright RF (2018)
Reduced Acid Deposition Leads to a New Start for Brown Trout (Salmo
trutta) in an Acidified Lake in Southern Norway. Water Air and Soil
Pollution 229(11): 12
Lydersen E, Larssen T, Fjeld E (2004) The influence of total organic
carbon (TOC) on the relationship between acid neutralizing capacity
(ANC) and fish status in Norwegian lakes. Science of the Total
Environment 326(1-3): 63-69
Monteith DT, Stoddard JL, Evans CD, de Wit HA, Forsius M, Hogasen T,
Wilander A, Skjelkvale BL, Jeffries DS, Vuorenmaa J, Keller B, Kopacek
J, Vesely J (2007) Dissolved organic carbon trends resulting from
changes in atmospheric deposition chemistry. Nature 450(7169): 537-540
Norling MD, Jackson-Blake LA, Calidonio JLG, Sample JE (2021) Rapid
development of fast and flexible environmental models: the Mobius
framework v1.0. Geosci. Model Dev. 14(4): 1885-1897
Norling MN, Kaste Ø, Wright RF (this issue) A biogeochemical model of
acidification: MAGIC is alive and well.
Oulehle F, Fischer M, Hruska J, Chuman T, Kram P, Navratil T, Tesar M,
Trnka M (2021) The GEOMON network of Czech catchments provides long-term
insights into altered forest biogeochemistry: From acid atmospheric
deposition to climate change. Hydrological Processes 35(5): 18
Posch M, Aherne J, Moldan F, Evans CD, Forsius M, Larssen T, Helliwell
R, Cosby BJ (2019) Dynamic Modeling and Target Loads of Sulfur and
Nitrogen for Surface Waters in Finland, Norway, Sweden, and the United
Kingdom. Environmental Science & Technology 53(9): 5062-5070
Reuss JO (1990) Critical loads for soils in Norway. Analyses of soils in
eight Norwegian catchments. In: NIVA report. NIVA, Oslo. p 78
Sase H, Saito T, Takahashi M, Morohashi M, Yamashita N, Inomata Y,
Ohizumi T, Nakata M (2021) Transboundary air pollution reduction rapidly
reflected in stream water chemistry in forested catchment on the sea of
Japan coast in central Japan. Atmospheric Environment 248: 10
Schopp W, Posch M, Mylona S, Johansson M (2003) Long-term development of
acid deposition (1880-2030) in sensitive freshwater regions in Europe.
Hydrology and Earth System Sciences 7(4): 436-446
Sen PK (1968) Estimates Of Regression Coefficient Based On Kendalls Tau.
Journal Of The American Statistical Association 63(324): 1379-&
SFT (2001) Overvåking av langtransportert forurenset luft og nedbør.
Årsrapport - Effekter 2000. SFT-rapport 834/01, TA-1830/2001. p83-87.
Skjelkvale BL, Stoddard JL, Jeffries DS, Torseth K, Hogasen T, Bowman J,
Mannio J, Monteith DT, Mosello R, Rogora M, Rzychon D, Vesely J, Wieting
J, Wilander A, Worsztynowicz A (2005) Regional scale evidence for
improvements in surface water chemistry 1990-2001. Environmental
Pollution 137(1): 165-176
Sterling S, Clair TA, Rotteveel L, O’Driscoll N, Houle D, Halfyard E,
Keys K (2022) Kejimkujik calibrated catchments: A benchmark dataset for
long-term impacts of terrestrial and freshwater acidification.
Hydrological Processes 36(2): 8
Stuanes AO, Abrahamsen G, Rosberg I (1995) Acidification of soils in
five catchments in Norway. Water Air and Soil Pollution 85(2): 635-640
Valinia S, Kaste O, Wright RF (2021) Intensified forestry as a climate
mitigation measure alters surface water quality in low intensity managed
forests. Scandinavian Journal of Forest Research 36(1): 15-31
Vogt RD, Skancke LB (2022) Overvåking av langtransportert forurenset
luft og nedbør. Årsrapport–Vannkjemiske effekter 2021. NIVA report
7778-2022; Miljødirektoratet report 2347-2022:
Vuorenmaa J, Augustaitis A, Beudert B, Clarke N, de Wit HA, Dirnbock T,
Frey J, Forsius M, Indriksone I, Kleemola S, Kobler J, Kram P, Lindroos
AJ, Lundin L, Ruoho-Airola T, Ukonmaanaho L, Vana M (2017) Long-term
sulphate and inorganic nitrogen mass balance budgets in European ICP
Integrated Monitoring catchments (1990-2012). Ecological Indicators 76:
15-29
Watmough SA, Aherne J, Alewell C, Arp P, Bailey S, Clair T, Dillon P,
Duchesne L, Eimers C, Fernandez I, Foster N, Larssen T, Miller E,
Mitchell M, Page S (2005) Sulphate, nitrogen and base cation budgets at
21 forested catchments in Canada, the United States and Europe.
Environmental Monitoring And Assessment 109(1-3): 1-36
West AJ, Galy A, Bickle M (2005) Tectonic and climatic controls on
silicate weathering. Earth and Planetary Science Letters 235(1-2):
211-228