| Major fluxes of sulphur
and dissolved inorganic nitrogen were estimated in Central European mountain
ecosystems of the Bohemian Forest (forest lakes) and Tatra
Mountains (alpine lakes) over the industrial period. Sulphur outputs from these
ecosystems were comparable to inputs during a period of
relatively stable atmospheric deposition (10-35 mmol m-2 yr-1)
around the 1930s. Atmospheric inputs of sulphur increased
by three- to four-fold between the 1950s and 1980s to ~140 and
~60 mmol mm-2 yr-1 in the Bohemian Forest
and Tatra Mountains, respectively.
Sulphur outputs were lower than inputs due to accumulation in soils, which was
higher in forest soils than in the sparser alpine soils
and represented 0.8-1.6 and 0.2-0.3 mol m-2, respectively, for the
whole 1930-2000 period. In the 1990s, atmospheric inputs of sulphur decreased
80% and 50% in the Bohemian Forest and Tatra Mountains, respectively, and
sulphur outputs exceeded inputs. Catchment soils became
pronounced sources of sulphur with output fluxes averaging between 15 and 31
mmol m-2 yr-1. Higher sulphur accumulation in the forest
soils has delayed (by several decades) recovery of forest lakes from
acidification compared to alpine lakes. Estimated deposition of dissolved
inorganic nitrogen was 53-75 mmol m-2 yr-1 in the Bohemian
Forest and 35-45 mmol m-2 yr-1 in the Tatra Mountains in
the 1880- 1950 period, i.e. below the empirically derived
threshold of ~70 mmol m-2 yr-1, above which nitrogen
leaching often occurs. Dissolved inorganic nitrogen was
efficiently retained in the ecosystems and nitrate export was negligible (0-7
mmol m-2 yr-1). By the 1980s, nitrogen deposition
increased to ~160 and ~80 mmol m-2 yr-1 in the Bohemian
Forest and Tatra Mountains, respectively, and nitrogen output increased to
120 and 60 mmol m-2 yr-1. Moreover, assimilation of
nitrogen in soils declined from ~40 to 10-20 mmol m-2 yr-1
in the alpine soils and even more in the Bohemian Forest,
where one of the catchments has even become a net source of nitrogen. In the
1990s, nitrogen deposition decreased by ~30% and DIN
output decreased to < 70 and 35 mmol m-2 yr-1 in the
Bohemian Forest and Tatra Mountains, respectively. New steady-state
conditions, with negligible nitrogen export, could be reached in future but at
lower nitrogen depositions than in the 1930s.
Keywords: emission, deposition, acidification, nitrogen-saturation, recovery,
sulphate, nitrate, ammonium, mountain lakes |