KAZALCI OKOLJA

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Values ​​of parameters used for monitoring the organic loading of rivers have greatly reduced since 1996, however ammonia levels remain much higher than natural background. The observed reduction in organic loading corresponds to an increase in the share of population whose wastewater is treated at wastewater treatment plants. The nutrient loading varies considerably among rivers of the Adriatic and the Danube river basins. Average annual concentrations of nitrate in Drava, Sava and Soča river catchments and in the Adriatic rivers are within the natural background, but nitrate values are higher in Mura river catchment. The values ​​of orthophosphate are above the natural background values in all rivers of the Danube basin. Trends indicate that further reduction of nutrients in rivers cannot be expected.


The indicator shows the level of nutrient and organic matter loading of rivers due to human activities. Nitrate and orthophosphate are representative parameters for nutrient loading, and biochemical oxygen demand and ammonia are representative parameters for organic loading. The parameters were measured in water samples taken in the course of regular monitoring of surface water quality.

Nitrate and ortophosphate are the main nutrients required for the growth of algae, mosses and aquatic plants in rivers. In non-polluted waters they are present at very low concentrations that mostly depend on geological properties and soil types in the catchment area. These so called natural or background values range for nitrate in Slovenian rivers between 0.2 and 0.9 mg NO3-N/l depending on their ecological type. Background value for orthophosphate according to EEA is 0.01 mg PO4-P/L (EEA). Nitrate and orthophosphate concentrations in water that exceed background values are a result of human activities, mainly agriculture and urban/industrial wastewater discharge. The surplus of nutrients in rivers leads to a deterioration in the normal functioning of the ecosystem, reduced biodiversity and eutrophication, which is problematic mainly in standing or slowly running waters. High nitrate content may also compromise the quality of drinking water, which is no longer suitable for drinking when nitrate concentration exceeds 10 mg NO3-N/l (50 mg NO3/l).

Biochemical oxygen demand (BOD) and ammonia are the main indicators of organic water pollution. The values of both parameters are usually elevated as a result of urban and industrial wastewater discharge and leaching of nutrients from agricultural land. The BOD is the amount of dissolved oxygen (in mg O2/l) needed (i.e. demanded) by aerobic organisms to break down organic matter present in a given water sample at a certain temperature over a specific time period. It is usually expressed as BOD5, which tells us how much oxygen is consumed per litre of sample over 5 days of incubation at 20°C. Background values for BOD5 range between <1 and 1.4 mg O2/l in Slovenian rivers. In an aquatic environment, ammonia also represents an increased demand for oxygen. In the nitrification process, ammonia is converted (through oxidation) to nitrite and then to nitrate, thus contributing to the eutrophication process. In small quantities, nitrite is toxic to water organisms as is ammonium, which is derived from ammonia under certain conditions (a combination of water temperature, salinity and pH-value). Ammonia represents a risk for drinking water sources as well. Background value for ammonia according to EEA is 0,015 mg NH4-N/L.


Charts

Figure VD10-1: Average annual concentrations of nitrate (mg NO3-N/L) in rivers
Sources: 

Standardised Database for Water Quality Monitoring, Slovenian Environment Agency (2020)

Show data

Mura[mg N/L]

Drava[mg N/L]

Sava[mg N/L]

Danube river basin[mg N/L]

Soča[mg N/L]

Adriatic rivers[mg N/L]

Adriatic river basin[mg N/L]

Slovenia[mg N/L]

background concentration (max)[mg N/L]

1996

1.65

1.53

1.22

1.31

0.88

0.73

0.84

1.20

0.90

1997

1.61

1.43

1.25

1.31

0.95

0.59

0.83

1.21

0.90

1998

1.58

1.52

1.11

1.21

0.92

0.77

0.88

1.14

0.90

1999

1.83

1.39

1.15

1.24

1.03

0.81

0.95

1.18

0.90

2000

1.42

1.42

1.12

1.19

0.87

0.79

0.84

1.11

0.90

2001

1.34

1.21

1.10

1.14

0.78

0.74

0.77

1.06

0.90

2002

1.65

1.14

1.09

1.13

1.01

0.97

1

1.11

0.90

2003

1.61

1.42

1.28

1.34

0.79

1.07

0.88

1.27

0.90

2004

1.44

1.73

1.18

1.30

0.94

1.16

1

1.24

0.90

2005

2.44

1.54

1.27

1.46

0.99

0.87

0.96

1.36

0.90

2006

3.34

1.85

1.32

1.76

1

0.73

0.91

1.55

0.90

2007

2.40

1.32

1.32

1.55

0.93

0.79

0.87

1.47

0.90

2008

1.89

1.23

1.09

1.25

0.97

0.64

0.88

1.19

0.90

2009

2.44

1.33

1.26

1.50

1.04

0.70

0.96

1.45

0.90

2010

2.17

1.41

1.18

1.44

0.93

0.58

0.73

1.35

0.90

2011

2.04

1.22

1.27

1.43

0.84

0.62

0.76

1.34

0.90

2012

2.02

1.17

1.17

1.33

1.16

0.62

1.04

1.30

0.90

2013

2.08

1.10

1.15

1.37

1.31

0.91

1.04

1.34

0.90

2014

2.30

1.15

1.16

1.38

1.38

0.61

1.07

1.36

0.90

2015

2.10

1.04

1.11

1.28

1.28

0.63

1.08

1.26

0.90

2016

2.09

1.21

1.08

1.26

1.03

0.48

0.85

1.22

0.90

2017

2.17

1.27

1.04

1.35

0.93

0.61

0.84

1.24

0.90

2018

2.37

1.24

1.07

1.40

0.96

0.59

0.78

1.30

0.90

2019

2.44

1.03

1.06

1.31

0.96

0.61

0.78

1.28

0.90

Figure VD10-2: Average annual concentrations of orthophosphate (mg PO4-P/L) in rivers
Sources: 

Average annual concentrations of orthophosphate (mg PO4-P/L) in rivers

Show data

Mura[mg P/L]

Drava[mg P/L]

Sava[mg P/L]

Danube river basin[mg P/L]

Soča[mg P/L]

Adriatic rivers[mg P/L]

Adriatic river basin[mg P/L]

Slovenia[mg P/L]

background concentration[mg P/L]

1996

0.07

0.02

0.04

0.04

0.01

0.02

0.01

0.03

0.01

1997

0.04

0.02

0.03

0.03

0.01

0.01

0.01

0.03

0.01

1998

0.08

0.03

0.07

0.07

0.01

0.01

0.01

0.06

0.01

1999

0.07

0.03

0.05

0.05

0.01

0.02

0.01

0.05

0.01

2000

0.10

0.04

0.07

0.07

0.02

0.02

0.02

0.06

0.01

2001

0.14

0.03

0.07

0.07

0.01

0.02

0.02

0.06

0.01

2002

0.12

0.03

0.06

0.06

0.01

0.01

0.01

0.05

0.01

2003

0.16

0.02

0.09

0.09

0.01

0.01

0.01

0.08

0.01

2004

0.06

0.03

0.07

0.07

0.01

0.01

0.01

0.05

0.01

2005

0.12

0.03

0.05

0.06

0.01

0.01

0.01

0.05

0.01

2006

0.05

0.04

0.08

0.07

0.01

0.01

0.01

0.06

0.01

2007

0.12

0.04

0.10

0.09

0.01

0.01

0.01

0.08

0.01

2008

0.07

0.04

0.03

0.04

0.01

0.01

0.01

0.03

0.01

2009

0.04

0.06

0.04

0.04

0.01

0.02

0.01

0.04

0.01

2010

0.05

0.08

0.03

0.04

0.01

0.01

0.01

0.04

0.01

2011

0.05

0.05

0.05

0.05

0.01

0.01

0.01

0.04

0.01

2012

0.06

0.09

0.07

0.07

0.01

0.01

0.01

0.06

0.01

2013

0.04

0.07

0.04

0.05

0.02

0.01

0.01

0.05

0.01

2014

0.04

0.04

0.05

0.04

0.01

0.01

0.01

0.04

0.01

2015

0.06

0.03

0.08

0.07

0.01

0.02

0.01

0.06

0.01

2016

0.06

0.04

0.03

0.04

0.01

0.01

0.01

0.04

0.01

2017

0.07

0.05

0.04

0.05

0.01

0.01

0.01

0.04

0.01

2018

0.06

0.03

0.03

0.03

0.01

0.01

0.01

0.03

0.01

2019

0.07

0.04

0.03

0.04

0.01

0.01

0.01

0.04

0.01

Figure VD10-3: Average annual values of biochemical oxygen demand - BOD5 (mg O2/L) in rivers
Sources: 

Average annual values of biochemical oxygen demand - BOD5 (mg O2/L) in rivers

Show data

Mura[mg O2/L]

Drava[mg O2/L]

Sava[mg O2/L]

Danube river basin[mg O2/L]

Soča[mg O2/L]

Adriatic rivers[mg O2/L]

Adriatic river basin[mg O2/L]

Slovenia[mg O2/L]

background concentration (max)[mg O2/L]

1996

4.70

3.20

3.30

3.40

2.10

1.90

2

3

1.40

1997

5.60

3.10

3.40

3.50

1.70

3.10

2.20

3.20

1.40

1998

4.80

2.60

2.70

2.80

1.80

2.20

2

2.70

1.40

1999

5

3

2.90

3

1.30

2.50

1.70

2.80

1.40

2000

6.20

2.30

2.90

3.10

2

2.10

2

2.80

1.40

2001

4.50

2.30

2.90

2.90

1.50

2.90

2

2.70

1.40

2002

5.30

3

2.70

3

2.10

3.10

2.50

2.90

1.40

2003

7.90

2.80

3.30

3.70

2.20

2.10

2.20

3.50

1.40

2004

6.10

2.20

3

3.40

1.60

1.50

1.60

3

1.40

2005

5.30

1.90

2.40

2.70

1.50

1.70

1.60

2.50

1.40

2006

1.90

1.90

1.70

1.80

0.90

1.60

1.20

1.60

1.40

2007

1.80

1.30

1.60

1.60

1.20

1.30

1.20

1.50

1.40

2008

1.50

1.50

1

1.10

0.90

1.10

0.90

1.10

1.40

2009

1.70

1.50

0.90

1.20

1

0.90

0.90

1.20

1.40

2010

1.50

1.70

1.10

1.30

0.90

1

0.90

1.30

1.40

2011

1.40

1.60

1.60

1.60

1

1.10

1

1.50

1.40

2012

1.50

2

1.50

1.60

0.70

1.20

0.90

1.50

1.40

2013

1.20

1.30

1.20

1.20

0.70

0.70

0.70

1.20

1.40

2014

1.30

1.10

1.20

1.20

1.10

1

1

1.20

1.40

2015

1.40

1.30

1

1.10

0.80

1.30

0.90

1.10

1.40

2016

1.30

1.40

0.80

1

1

1.20

1.10

1

1.40

2017

1.50

1.40

1

1.20

0.80

1.30

0.90

1.10

1.40

2018

1.60

1.20

1

1.20

0.70

1

0.80

1.10

1.40

2019

1.70

1.10

0.90

1.10

0.70

0.70

0.70

1.10

1.40

Figure VD10-4: Average annual concentrations of ammonia (mg NH4-N/L) in rivers
Sources: 

Average annual concentrations of ammonia (mg NH4-N/L) in rivers

Show data

Mura[mg N/L]

Drava[mg N/L]

Sava[mg N/L]

Danube river basin[mg N/L]

Soča[mg N/L]

Adriatic rivers[mg N/L]

Adriatic river basin[mg N/L]

Slovenia[mg N/L]

background concentration[mg N/L]

1996

0.62

0.22

0.44

0.42

0.18

0.19

0.18

0.36

0.02

1997

0.54

0.22

0.63

0.56

0.13

0.16

0.14

0.47

0.02

1998

0.50

0.16

0.43

0.40

0.05

0.06

0.05

0.33

0.02

1999

0.30

0.16

0.24

0.23

0.02

0.15

0.07

0.20

0.02

2000

0.42

0.12

0.37

0.34

0.04

0.07

0.05

0.28

0.02

2001

0.30

0.11

0.29

0.26

0.03

0.18

0.08

0.22

0.02

2002

0.48

0.16

0.31

0.30

0.02

0.05

0.03

0.25

0.02

2003

0.57

0.13

0.36

0.35

0.05

0.06

0.05

0.30

0.02

2004

0.31

0.14

0.34

0.31

0.01

0.04

0.02

0.25

0.02

2005

0.21

0.14

0.26

0.24

0.02

0.04

0.03

0.19

0.02

2006

0.16

0.09

0.34

0.28

0.02

0.10

0.04

0.22

0.02

2007

0.14

0.08

0.23

0.18

0.02

0.07

0.04

0.16

0.02

2008

0.07

0.11

0.12

0.11

0.01

0.02

0.01

0.10

0.02

2009

0.13

0.14

0.24

0.20

0.03

0.01

0.02

0.18

0.02

2010

0.12

0.14

0.14

0.14

0.01

0.03

0.02

0.12

0.02

2011

0.10

0.15

0.36

0.28

0.02

0.03

0.03

0.24

0.02

2012

0.10

0.15

0.38

0.29

0.02

0.02

0.02

0.25

0.02

2013

0.07

0.08

0.20

0.15

0.02

0.01

0.01

0.13

0.02

2014

0.09

0.07

0.10

0.09

0.02

0.02

0.02

0.08

0.02

2015

0.07

0.03

0.05

0.05

0.02

0.02

0.02

0.05

0.02

2016

0.08

0.08

0.05

0.06

0.03

0.03

0.03

0.06

0.02

2017

0.12

0.09

0.08

0.09

0.01

0.03

0.02

0.07

0.02

2018

0.10

0.07

0.05

0.07

0.03

0.02

0.02

0.06

0.02

2019

0.12

0.11

0.08

0.09

0.01

0.01

0.01

0.09

0.02

Figure VD10-5: Proportion of sampling sites with upward/downward trends for different parameters
Sources: 
Enotna zbirka podatkov monitoringa kakovosti voda, Agencija Republike Slovenije za okolje (2020)
Show data

in the natural background range[number of sampling sites in %]

decreasing[number of sampling sites in %]

probably decreasing[number of sampling sites in %]

no trend[number of sampling sites in %]

probably increasing[number of sampling sites in %]

increasing[number of sampling sites in %]

NH4

17.60

32.40

5.90

43.10

0

1

BPK5

76

11

3

8

1

1

oPO4

32.60

9.80

4.30

51.10

0

2.20

NO3

29.30

8.70

5.40

51.10

2.20

3.30


Goals

- the goals of the Water Framework Directive (Directive 2000/60/ES) on preservation and improvement of the water environment;

- the goals of the Nitrates Directive (91/676/EEC) on reduction and prevention of water pollution by nitrates from agriculture;

- the goals of the Directive on urban wastewater treatment (91/271/EEC) for protection of the environment against harmful impacts of wastewater discharge;

- the goals of the Directive on the quality of water intended for human consumption (98/83/EC);

- Goal 6 from Agenda 2030, to ensure availability and sustainable management of water and sanitation for all;

- the goals stated in other regulations on water protection and water use.


Nitrate concentrations in the observed period were only slightly above the background values, which range between 0.2 and 0.9 mg N/l in Slovenian rivers depending on their ecological type. Increase in nitrate values ​​in the Mura river catchment since 2005 is observed as an increase in annual average concentrations at most of the sampling sites on Mura and its tributaries: Ledava with tributaries, Kučnica and Ščavnica. Orthophosphate values in rivers also differ among river catchments. In Soča river and Adriatic rivers orthophosphate is in the range of the background 0.01 mg P/L, but in the rivers of the Danube basin it is well above the background, from which Mura river catchment stands out with the highest values in recent years​​.

 

Trends analysed for individual sampling sites with longer historical data sets show that nitrate and orthophosphate concentrations are already in the range of natural background at one third of the sampling sites and are decreasing at around 15 % of the sampling sites in the analysis. However, at the remaining 50 % of sample sites improvement cannot be expected, as the trend analysis does not show any changes or it even shows that a slight increase in values can be expected. Nitrogen and phosphorus loading of rivers can be due to draining from agricultural areas or municipal and industrial sewage however, we cannot separate the sources based on monitoring data.

 

Organic loading of rivers decreased considerably from 1996 to 2006, and since then the BOD5 values remain close to the range of the natural background, which ranges between <1 and 1.4 mg O2/l in most Slovenian rivers. The decrease is larger in eastern part of Slovenia than in the western part, where the organic loading of rivers has also been lesser in the past. Trends analysed for individual sampling sites with longer historical data sets show that BOD5 values at around 90 % of the sampling sites are in the natural background range or decreasing. Trends of ammonia concentrations show that only about 20 % of the sampling sites are in the natural background range (0,015 mg NH4-N/L) and only at about 40 % of the sampling sites decreasing trends are observed.

 

Urban wastewater is usually the main source of pollution with organic substances. As wastewater discharge and treatment has been improving in Slovenia for several years, observed changes in the parameters of organic load are expected. The indicator VD02: Wastewater treatment shows that the share of the population whose wastewater is treated by wastewater treatment plants is considerably higher since 2004. The percentage of secondary and tertiary wastewater treatment, which removes the majority of organic substances and some nutrients, is also increasing.



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