INVESTIGADORES
BAFFICO Gustavo Daniel
congresos y reuniones científicas
Título:
Periphyton algal community along a gradient of pH: Agrio River from pH 2 to 7
Autor/es:
BAFFICO, G.; MAGES, M.; PEDROZO, F.
Lugar:
Caviahue, Argentina
Reunión:
Workshop; International Workshop Geogenically Acidic Water Systems: Volcanic Waters, Mining Lakes and Rivers; 2004
Institución organizadora:
CRUB - UNComahue
Resumen:
The periphyton structure
was surveyed along an acid-neutral gradient in a natural acidic river (Agrio
River, Neuquén, Argentina) and its tributaries. In each sampling site
temperature, pH and conductivity were measured and water samples were collected
for chemical analysis. Periphyton samples were taken by mean of a sampler of
known surface (10 cm2) in order to determine algal biomass
(chlorophyll a concentration), algal density (Utermöhl counts) and
species diversity. Results showed that pH increased and conductivity decreased
as the Agrio River receives tributaries of different chemical characteristics.
In the Upper Agrio River changes were slight as a consequence of Jara River
entrance, but in the Lower Agrio River changes were more marked because of
Trolope and mainly Ñorquín entrance. Jara River is a small tributary with low
pH and conductivity that produce a slight change in Agrio River. Trolope River
is a freshwater, neutral river of flow comparable to Agrio River at this point.
The effects on Agrio River of this freshwater incoming were a slight increase
in pH and decrease in conductivity, as well as precipitation of a red material
on the stones of the channel. Periphyton chlorophyll and density increase
markedly at this point. Ñorquín River is an alkaline river of minor flow compared
with Agrio River. But the effects of this incoming on Agrio River were a marked
increase in pH and decrease in conductivity, as well as precipitation of a
grey-white material on the stones of the channel. Periphyton chlorophyll and
density decreased markedly at this point. Some selected elements (SO4,
Cl, Ca, Fe, Al and TP) change along the Agrio River. In general, there are a
dilution along the river, but in some cases a precipitation of a certain
element occur as a consequence of the pH increase. For example, Fe decrease
markedly between RA Outflow (16.8 mg L-1) and RA Salto (Trolope
River entrance) (6.2 mg L-1). The Iron concentration continues
decreasing until RA Ruta 21 (0.2 mg L-1). Red precipitates are
present along this portion of the river. A similar behaviour is observed in the
Al concentration. In the Lower Agrio River, is evident a sequence in the
dominance of the buffer system from the outflow to the place where the waters
are neutralized.