Response of the biomass and the C:N:P composition of the first trophic level of a Pampean stream to the highest drought in the last 20 years: a case report

LEGGIERI LEONARDO RAMÓN; FERREIRO NICOLÁS ANDRÉS

ECOLOGÍA AUSTRAL

ASOCIACIÓN ARGENTINA DE ECOLOGÍA

Lugar: Buenos Aires; Año: 2015 vol. 25 p. 172 - 181

0327-5477

Benthos, epiphyton, seston, free-floating filamentous algae and aquatic plants provide food and shelter to the rest of trophic levels of the stream. Here we studied the effect of drought on their biomass and elemental composition in the La Choza Pampean stream by comparing 2007, with ~1200 mm annually, with 2008, with annual ~600mm (40% less that historical). Given that the abundance of these communities depend principally on the mass transfer in the boundary layer at low speeds and the drift downstream, we postulate (H1) that a dry year creates unfavorable conditions for aquatic plants and seston, and favorable for free-floating, epiphytic and benthic filamentous algae on a Pampean stream. As Pampean streams are rich in nutrients, we also postulate (H2) there will be no significant inter-annual changes in their elemental compositions. Low flow rates of 2008 resulted in a higher conductivity, pH and available light, without appreciable changes in the typical high nutrient concentrations. The drought resulted in lower discharges (