Portugal
f
285
Fig. 11.2. Map of the Ria de
Aveiro lagoon
receiving urban sewage (Hall 1980). As a result, water quality became
inadequate for aquaculture and table salt production, two of the main
economical activities in the Ria.
A study undertaken in 1989 (Alcantara et al. 1990), reports comparatively low nutrient levels in the marine-influenced area of the lagoon
(N0 3 - -N 1.4-2.3 JlM, NHt -N 0.9-1.8 JlM and PO~- -P 0.2-0.3 JlM)
contrasting with the high levels found in some of the interior sections of
the channels (Vouga river: N0 3 - -N 20 JlM, NHt -N 8 JlM and PO!--P
0.7 JlM and in Largo da Coroa: N0 3 - -N 40 JlM, NH4+ -N 20 JlM and PO~-P 4 JlM). Chlorophyll a concentrations ranged from 12 to 49 mg m -3 in
the Vouga river and inner parts of the lagoon, while in most of the more
marine areas the values always remained below 7 mg m -3.
Besides fertilizers used in agriculture, other nutrient sources may add
to eutrophication. Some industries discharge their effiuents to nearby
streams, mainly a paper mill (Caima Pulp Company) and a chemical
complex located at Estarreja which is not provided with a complete
sewage system. The effiuents of this industrial unit contain large amounts
of ammonia, nitrates, sulphates and metals. The effect of the nutrients
discharged is apparent in the extensive infestation of some areas with
attached macrophytes (Hall 1980).
f
285
Fig. 11.2. Map of the Ria de
Aveiro lagoon
receiving urban sewage (Hall 1980). As a result, water quality became
inadequate for aquaculture and table salt production, two of the main
economical activities in the Ria.
A study undertaken in 1989 (Alcantara et al. 1990), reports comparatively low nutrient levels in the marine-influenced area of the lagoon
(N0 3 - -N 1.4-2.3 JlM, NHt -N 0.9-1.8 JlM and PO~- -P 0.2-0.3 JlM)
contrasting with the high levels found in some of the interior sections of
the channels (Vouga river: N0 3 - -N 20 JlM, NHt -N 8 JlM and PO!--P
0.7 JlM and in Largo da Coroa: N0 3 - -N 40 JlM, NH4+ -N 20 JlM and PO~-P 4 JlM). Chlorophyll a concentrations ranged from 12 to 49 mg m -3 in
the Vouga river and inner parts of the lagoon, while in most of the more
marine areas the values always remained below 7 mg m -3.
Besides fertilizers used in agriculture, other nutrient sources may add
to eutrophication. Some industries discharge their effiuents to nearby
streams, mainly a paper mill (Caima Pulp Company) and a chemical
complex located at Estarreja which is not provided with a complete
sewage system. The effiuents of this industrial unit contain large amounts
of ammonia, nitrates, sulphates and metals. The effect of the nutrients
discharged is apparent in the extensive infestation of some areas with
attached macrophytes (Hall 1980).