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| Titel |
Surface water acidification and critical loads: exploring the F-factor |
| VerfasserIn |
L. Rapp, K. Bishop |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 13, no. 11 ; Nr. 13, no. 11 (2009-11-17), S.2191-2201 |
| Datensatznummer |
250012057
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| Publikation (Nr.) |
 copernicus.org/hess-13-2191-2009.pdf |
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| Zusammenfassung |
As acid deposition decreases, uncertainties in methods
for calculating critical loads become more important when judgements have to
be made about whether or not further emission reductions are needed. An
important aspect of one type of model that has been used to calculate
surface water critical loads is the empirical F-factor which estimates the
degree to which acid deposition is neutralised before it reaches a lake at
any particular point in time relative to the pre-industrial, steady-state
water chemistry conditions.
In this paper we will examine how well the empirical F-functions are able to
estimate pre-industrial lake chemistry as lake chemistry changes during
different phases of acidification and recovery. To accomplish this, we use
the dynamic, process-oriented biogeochemical model SAFE to generate a
plausible time series of annual runoff chemistry for ca. 140 Swedish
catchments between 1800 and 2100. These annual hydrochemistry data are then
used to generate empirical F-factors that are compared to the "actual"
F-factor seen in the SAFE data for each lake and year in the time series.
The dynamics of the F-factor as catchments acidify, and then recover are not
widely recognised.
Our results suggest that the F-factor approach worked best during the
acidification phase when soil processes buffer incoming acidity. However,
the empirical functions for estimating F from contemporary lake chemistry
are not well suited to the recovery phase when the F-factor turns negative
due to recovery processes in the soil. This happens when acid deposition has
depleted the soil store of BC, and then acid deposition declines, reducing
the leaching of base cations to levels below those in the pre-industrial
era. An estimate of critical load from water chemistry during recovery and
empirical F functions would therefore result in critical loads that are too
low. Therefore, the empirical estimates of the F-factor are a significant
source of uncertainty in the estimate of surface water critical loads and
related calculations for quantifying lake acidification status, especially
now that acid deposition has declined across large areas of Europe and North
America. |
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