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.; PEDROZO, F.; MAGES, M.
Lugar:
Caviahue, Argentina
Reunión:
Workshop; 6th Meeting of the IAVCEI Committee on volcanic lakes (CVL); 2004
Resumen:
The pH often is
understood as the main variable that affects the biota of acidic waterbodies.
However, the pH is a key factor controlling many other physical and chemical
factors. In general, the decrease of the pH alters the species composition of
attached algae because only are present acid-resistant species. In some acidic
habitats, the high metal concentrations in the water seems to limit algal
development due to toxicity. The ecological effects of the deposition of metal
hydroxides has been less studied than the toxicity by metals or by the acidity.
The deposition of Iron or Aluminium hydroxides affect the periphyton and
invertebrates more than the pH or the dissolved metals (McKnight & Feder,
1984). It was also noted that metal hydroxide deposition could change the
physical conditions of the substrate, leading to a reduction of periphyton
growth on rocks. The periphyton structure
was surveyed along an acid-neutral gradient in a natural acidic river (Agrio
River, Neuquén, Argentina). In each sampling site temperature, pH and
conductivity were measured and water samples were collected for chemical
analysis. Periphyton samples were taken 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
(Trolope and mainly Ñorquín 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.
The dominant algae species present in the periphyton were Ulothrix spp
and Klebsormidium sp, while 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. Despite that the
dominant algae species present in the periphyton still were Ulothrix spp
and Klebsormidium sp, chlorophyll and density decreased markedly at this
point as well as diversity. Some selected elements (S, Cl, Ca, Fe, Al and P)
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 (6.2 mg L-1), because Trolope River
entrance. 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.