Algal recolonization following an extraordinary drought in permanent lowland streams

NICOLOSI GELIS, MARÍA MERCEDES; COCHERO, JOAQUÍN; BAUER, DELIA E.; GÓMEZ, NORA

ECOLOGÍA AUSTRAL

ASOCIACIÓN ARGENTINA DE ECOLOGÍA

Lugar: Buenos Aires; Año: 2023 vol. 33 p. 60 - 73

0327-5477

Droughts reduce habitat and fragment the continuity of running water systems producing lasting effects on sediment biota affecting the density and biomass of algae. When droughts occur, the survival of algae and cyanobacteria of the biofilm depends on different alternatives to overcome the stress. In Pampean streams, periods of low flow that cause desiccation stress in the biofilm may be linked to El Niño/Southern Oscillation phenomenon, and to water management practices, including irrigation and extraction, that can reduce stream base flows for prolonged periods, reducing wetted area and dewatering the stream bed. The primary aim of this study was to determine the response of epipelic algal communities, analyzed by greater algal groups (Cyanobacteria, Euglenophyta, Dinoflagellates, Green Algae, Diatoms) to desiccation as a disturbance, in streams that are not subjected to frequent periods of drought. First, we studied the in situ vertical distribution of epipelic algae in stream sediment during the drought period as a refuge strategy, along with the vertical distribution of sediment humidity in 10 cm sediment corers divided in six segments at depths 0-1 cm (uppermost layer), 1-2 cm, 2-3 cm, 3-4 cm, 4-5 cm and 5 -10 cm. Secondly, we analyzed the recolonization patterns of the epipelic algal assemblage after the drought by studying the succession of autotrophic organisms, in order to better understand the role of sediments as a source of algae populations. For this, 2 cm deep corers were placed with water in microcosms and monitored for a total of 2 weeks. Given the local anthropogenic pressures, including irrigation and water extraction it is important to understand the responses of aquatic communities to flow alteration events. Our results indicate that when the streams are affected by a severe drought algae and cyanobacteria survive, and could be related with the moisture content of the sediment. Besides, after hydratation of the sediment the community reacts quickly increasing their density. Cyanobacteria were the most resistant group to desiccation and the one who had the faster reaction to hydratation