Decadal oscillations of the aquatic chemistry of river waters in Latvia

INTERNATIONAL CONFERENCE WATER RESOURCES ASSESSMENT AND SEASONAL PREDICTION
KOBLENZ, 13-16 October 2015
Decadal oscillations of the aquatic
chemistry of river waters in Latvia
D. Porshnov and prof., Dr.hab.chem. M. Klavins
Faculty of Geography and Earth Sciences,
University of Latvia,
Riga, Latvia
Study area
Daugava River (Western Dvina)
Largest river of Latvia and also one of the biggest rivers in
the Baltic region. It is 1005 km long and its basin size is
87900 km2, including territories of Latvia, Belorussia and
Russia. Mean annual water runoff: 20,4 km3.
More than half of the river discharge takes place during
spring floods, and the water discharge pattern is
characterised by steep fluctuations of water discharge
intensity.
Depth of groundwater active exchange zone is 200-350 m,
aeration zone, mostly consisted of sand and is 1-15 m
deep.
In the previous studies, a 26-year periodicity of the flow
of the Daugava River was considered as the main period,
which includes smaller cycles of 2, 6 and 13 years
Lielupe River
Lielupe is the second biggest river of Latvia. Length of
Lielupe is 119 km, basin area 17600 km2, mean annual
runoff 3.6 km3.
Lielupe receives the major part of its discharge from
direct surface run-off, spring floods dominate.
The geological structure of catchment is characterised by
several meters thin layer of quaternary deposits (mainly
limnoglacial clay). Underlying Devonian deposits,
mainly dolomite, limestone, sandstone and clay embed
very close to surface and often expose in river valleys.
Observed oscillations of discharge intensity are quite
similar to Daugava River
800
700
600
500
400
300
200
100
Discharge Lielupe, Kalnciems, (m3/sec)
900
0
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
Discharge Daugava, Jekabpils (m3/sec)
Discharge
180
160
140
120
100
80
60
40
20
0
Anthropogenic loads of nutrients
Changes in socio-economic conditions after the collapse of
USSR led to unprecedented reduction of environmental loads
Use of mineral fertilisers reduced 10 times in 3 years, after
regaining the independence
Reformation of wastewater treatment also led to significant
reduction of loads from point sources
Ammonia nitrogen
Character of self purification of both catchments strongly
differs
Loamy catchment of Lielupe demonstrates rapid release of
ammonia from surface of fields, that not strongly connected
with runoff intensity. It looks very possible that now self
purification of soils in this catchment is finished.
In the case of Daugava situation is different. Release of
ammonia demonstrates strong relation with runoff. It is very
possible that self purification of soils is not finished till now
and the next maximums of discharge intensity will led to the
increase of export values.
Nitrate nitrogen
Situation with nitrate nitrogen is different. In the
case of Daugava, weak downward trend can be
observed, while Lielupe do not demonstrate any
trends.
This fact can be explained with development of
agriculture in basin of Lielupe and also with
nitrification of ammonia sorbed on clay minerals
Release of nitrates is not finished in both
catchments and upward trends can be prognosed for
next years and also detected now.
Phosphate phosphorous
Color
3500
3000
2500
2000
1500
1000
Total Organic Carbon Export in Lielupe,
Kalnciems (t/day)
4000
500
100
0
0
1977
1978
1980
1981
1983
1984
1986
1987
1989
1990
1992
1993
1995
1996
1998
1999
2001
2002
2004
2005
2007
2008
2010
1977
1978
1980
1981
1982
1984
1985
1987
1988
1989
1991
1992
1994
1995
1997
1998
1999
2001
2002
2004
2005
2006
2008
2009
Total Organic Carbon Export in Daugava,
Jekabpils (t/day)
Total Organic Carbon
800
700
600
500
400
300
200
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
0
1984
10
1983
15
1982
20
1981
25
Total iron flux in Lielupe, Kalnciems (t/day)
30
1980
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
Total iron flux in Daugava (Jekabpils) (t/day)
Total iron
2
1
5
0
Interaction of riverine iron export and Solar
irradiance
Furthermore our results shows significant
correlation between export values of total iron
and total solar irradiation data measured by
satelite, during Virgo project.
It can be explained by fluctuations of
groundwater levels with similar periodicity
reported by Latvian hydro geologists*
Today it is only hypotesis, but work will
continue
*:Levina N., Levins I., Prols J., Straume J. Use and monitoring of drinking groundwater
resources in Latvia (in Latvian). Geological Service of Latvia, Riga, 1995.
r=0.16
r=0.15
Conclusions
• Oscillational patterns are characteristic for aquatic chemistry of the largest rivers
of Latvia
• Didecadal oscillations are natural for export of nutrients by waters of Daugava,
similar pattern can be observed in the flux of nitrate nitrogen from catchment of
Lielupe.
• Decadal oscillations are natural for water color and export of total iron in both
rivers.
• Process of brownification in rivers of Latvia is strongly connected with solar
drivers.
Thank You for attention
Historical centre of Riga and Daugava River