Geoscience Reference
In-Depth Information
150
300
Al
i
NO
3
-
200
100
SO
4
2-
100
50
0
60
0
90
Ca
2+
K
+
60
40
30
20
Mg
2+
0
0
Date (month-year)
Figure 7.8
The 1998-2008 trend in chemistry of major inlet of Plešné Lake (Bohemian
Forest). Elevated terrestrial export of NO
3
−
results from hot and dry summer 2003 and
forest dieback (2005-8) (J. Kopá
ˇ
ek unpublished data).
the dominant strong acid anion, and its leaching governs Al toxicity of soil
solutions and surface waters, depletes soil base saturation and delays soil and
water recovery from acidification. The important question is to what extent the
elevated Al concentration in soil solution is toxic to fine roots and mycorrhiza.
A reduction of mycorrhizal fungi would leave more NH
4
+
for nitrification and
result in raised NO
3
(and consequently Al) leaching, thus causing a positive
feedback in terrestrial NO
3
export.
In areas receiving increasing inputs of atmospheric N, the long-term fate of N
retained in catchments remains a major source of uncertainty in projecting
acidification and recovery in freshwater ecosystems. Typically, catchments retain
70%-100% of the incoming N (Dise & Wright 1995; Wright
et al
. 2001). Long-
term (30+ years) monitoring records do not point to dramatic changes in this %
retention over time (Wright
et al
. 2001). Climate change affects the retention and
loss of N in catchments. Yet, clearly, N cannot go on accumulating forever in these
ecosystems. The question is, thus, when and under what circumstances will the N be
leached from the terrestrial ecosystems to give acidification problems in freshwater
ecosystems, and will climate change ameliorate or exacerbate the problem?
Acid episodes
Superimposed upon chronic acidification of surface waters are acid episodes that
cause sudden temporary decreases of pH and ANC. Acid episodes are frequently
triggered by drought, floods, rapid snowmelt and inputs of wind-borne sea salts.
Search WWH ::
Custom Search