The influence of drained peat soils on diffuse nitrogen
pollution of surface water
Anatoli Vassiljev and Irina Blinova
ABSTRACT
Eutrophication caused by excess nutrient loads is the main problem for Estonian surface waters.
Even after the drastic decrease in the application of mineral fertilizers at the beginning of the 1990s,
the concentrations of nitrogen and phosphorus in many rivers remained at undesirable and
unexpectedly high levels. The investigation showed that drained peat soils are an important source of
nitrogen export to the surface waters. Runoff of nitrogen from drained peat soils is, on average,
1.5-fold higher than from agricultural lands in Estonia.
Anatoli Vassiljev (corresponding author)
Tallinn University of Technology,
Ehitajate tee 5, Tallinn 19086,
Estonia
E-mail: avasil@staff.ttu.ee
Irina Blinova
National Institute of Chemical Physics and
Biophysics,
Akadeemia tee 23, Tallinn 12618,
Estonia
Key words | diffuse pollution, nutrients, peat soils, river water quality
INTRODUCTION
According to the Water Framework Directive (), good
status of surface water must be achieved by the year 2015.
However, the eutrophication, caused by enlarged loads of
nutrients (nitrogen and phosphorus) from watersheds, still
remains one of the most important problems for surface
waters in Estonia (Iital et al. ). In many rivers, the con-
centrations of nutrients exceed the upper hydrochemical
limit values of good status established in Estonia (3 mg/L
for total nitrogen and 0.08 mg/L for total phosphorus
(Classes )). Nitrogen concentrations in some rivers
exceed the limit five-fold. It is sometimes impossible to
explain such high nitrogen concentrations by known pol-
lution sources. This fact impedes elaboration of the
effective water protection measures.
According to current opinion, the drastic increase of sur-
face water pollution by nutrients during the late 1970s was
caused, above all, by effluent discharge (point sources) and
by intensive use of commercial fertilizer in agriculture (dif-
fuse pollution). As a result, primary attention has been
focused on the measures for reducing the nutrient loads
from the above-mentioned sources. Reconstruction of old
sewage treatment plants and opening new ones has signifi-
cantly decreased nutrient pollution load from point
sources during the last decades. However, it has been esti-
mated that in Estonia diffuse sources play a noticeable
role in the formation of the total nutrient load. For example,
60% of the total annual nitrogen load and 40% of the total
phosphorus load from the Lake Peipsi watershed (nearly
one-third of the territory of Estonia) come from diffuse
sources (Vassiljev & Stålnacke ). The changes in the
agricultural sector of Estonian economy at the beginning
of the 1990s led to a drastic decrease in the application of
mineral fertilizers (Figure 1) and also in livestock popu-
lation. Nevertheless, very little evidence that these changes
in agricultural practices noticeably affected the concen-
trations of nutrients in rivers was found (Blinova &
Vassiljev ; Stålnacke et al. ; Lepistö et al. ).
The nutrients runoff from some watersheds remained at
undesirable and unexpectedly high levels. This fact confirms
the opinion that the impact of agriculture (particularly use
of mineral fertilizers) on the pollution of surface water by
nutrients was overestimated (Thomas et al. ).
Hoffmann et al.() hypothesized that intensive pol-
lution of surface water by nutrients in Sweden and Finland
in the 1960s was caused not only by agricultural activity
but also by wide-scale melioration, which was conducted
at the same time. The significant increase of nutrient
runoff from drained areas was also observed after the drai-
nage of forests and peatlands (Lundin & Bergquist ;
Prévost et al. ). Peat soils can act as a source as well
352 © IWA Publishing 2012 Hydrology Research | 43.4 | 2012
doi: 10.2166/nh.2012.117
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