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You are here: Home / The European environment – state and outlook 2010 / Country assessments / Portugal / Freshwater - State and impacts (Portugal)

Freshwater - State and impacts (Portugal)

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SOER Common environmental theme from Portugal
Published: 26 Nov 2010 Modified: 08 Apr 2011

 

In 2007 the volume of water abstracted amounted to 977 563 000 m3, an increase of 7.3 % over 2006, showing that volumes abstracted continue to rise. The Algarve river basin district, in the south of the country, had a significant level of abstraction, 320 l/person/day, because it is the most prominent tourist region and consequently has a high floating population. This is something of a paradox, since it is one of the regions with the lowest average rainfall yet with the most golf courses, which consume a great deal of water. It also has the highest average temperatures and the least available water, particularly in summer.

 

Surface waters

 

In terms of water quality, the number of surface water monitoring stations recording quality as good has increased year on year, reaching 35.5 % in 2008. However the number of stations recording poor or very poor, 36.5 %, has also increased, although only slightly.

 

Figure 1 Surface water quality in 2008

Fig. 1 - Surface water quality in 2008Fig. 1a - Surface water quality in 2008
 

Source: INAG, 2009

 

For additional information on water resources

http://snirh.pt/

 

Extreme situations also occur: in the Lima, Cávado/Ribeiras Costeiras and Arade river basins, 100 % of water analysed was categorised as “good”, while the Lis/Ribeiras Costeiras, Mira, Ribeiras do Oeste and Sado river basins recorded the worst results in 2008, with 100 % of water samples from the Lis/Ribeiras Costeiras river basin being categorised as “very poor”.

 

Figure 2 Surface water quality by river basin in 2008

Fig. 2 - Surface water quality by river basin in 2008 Source: INAG, 2009

 

Nitrates

As regards nitrates in rivers, 100 % of stations recorded concentrations below 25 mg/l for the maximum, annual and winter average values. Annual and winter average concentrations in over 50 % of stations were stable. Maximum concentrations tended to decrease in over 60 % of stations. In reservoirs, more than 90 % of stations recorded maximum annual and winter average concentrations below 25 mg/l. Annual and winter average concentrations in more than 70 % of stations were highly stable. In summary, there were not considered to be any urgent situations in terms of groundwater nitrate concentration.

In the context of Directive 91/676/EEC concerning the protection of waters against pollution caused by nitrates from agricultural sources, from 2004 to 2007 more than 90 % of stations with a groundwater level above 5 m recorded a nitrate concentration of less than 40 mg/l. In addition, more than 80 % of stations with a groundwater level of less than 5 m also recorded concentrations below the threshold of 40 mg/l. The results show that for most monitoring stations, the average nitrate ion concentration in the water appeared to be stable.

Table 2 Average nitrate concentration – Continental Portugal

TYPE

QUALITY CLASSES – Continent

Average (mg NO3/l) (2004-2007}

% Stations

 

 

< 25

25 – 39.99

40 – 50

> 50

Groundwater (0 – 5 m)

72.1

8.8

5.9

13.2

Groundwater (5 – 15 m)

89.7

10.3

0.0

0.0

Groundwater (15 – 30 m)

85.7

10.4

1.3

2.6

Groundwater (> 30 m)

92.3

5.1

0.0

2.6

Captive

100

0.0

0.0

0.0

Karst

79.3

12.4

2.1

6.2

Source: INAG / DGADR, 2008

 

To summarise the global assessment of results, in the period from 2004 to 2007 there were no urgent situations in terms of this parameter.

Eutrophication 

Eutrophication is reflected in greater primary productivity and consequently in reduced dissolved oxygen and pH levels in the water. In extreme situations this can lead to loss of fauna and flora and a reduction in the quality of water for human consumption. In order to assess the trophic status of the principal reservoirs in continental Portugal for the period from 2004 to 2007, the total phosphorus and chlorophyll-a concentration was measured in 29 stations. Some 72 %, corresponding to 21 reservoirs, are eutrophic, while 28 %, corresponding to eight reservoirs, are mesotrophic.

 

Figure 3 Development of the trophic status of reservoirs

Fig. 3 - Development of the trophic status of reservoirs

 

 

Source: INAG, 2008

 

An analysis by river basin district shows that in the 2006/2007 hydrological year the highest percentage of stations in which the status of reservoir water was categorised as eutrophic occurred in the Tejo (64 %), Sado and Mira (57 %) river basin districts.

 

Figure 4 Trophic status of reservoirs by river basin district in continental Portugal in 2006/2007

Fig. 4 - Trophic status of reservoirs by river basin district in continental Portugal in 2006/2007

 

 

Source: INAG, 2008

 

Portugal has recorded a positive, consistent and sustained improvement in both the quality of water distributed and the number of mandatory analyses for controlling such water. Data for the past decade bear witness to a clear improvement in water quality control, with a fall in percentages of missing analyses and analyses in breach of the parametric values. In 2008, sampling frequency compliance rates, percentage of analyses carried out, stood at 99.29 %, maintaining the rising trend recorded in previous years. Parametric value compliance rates also increased, rising from 97.43 % in 2007 to 97.62 % in 2008.

In terms of protecting public health, it is essential to prevent bathing water pollution. In 2008, coastal and transitional bathing waters achieved the best performance in the last five years, with 89.4 % being categorised as “good” and only 1.1 % as “poor”, with the Regional Health Authority prohibiting bathing in 0.2 % of waters. Inland bathing water recorded a decrease in compliance in relation to the mandatory values, the rate falling from 93.5 % in 2007 to 92.8 % in 2008. The same occurred with compliance in relation to the guide values, which fell by 1.2 %, from 43.5 % in 2007 to 42.3 % in 2008, a year in which bathing was prohibited in 5.2 % of such waters.

 

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