Biomonitoring ecological status of two reservoirs of the Brazilian semi-arid using phytoplankton assemblages (Q index)

Biomonitoramento do estado ecológico de dois reservatórios do semiárido brasileiro utilizando assembleias fitoplanctônicas (índice Q)

Aim

Assess whether the assembly index is a suitable tool for biomonitoring of aquatic ecosystems of semi-arid environment.

Methods

Monthly, samples were collected between October 2011 and May 2012 in Santa Cruz do Apodi (5°43'59"S; 46" 00 119 "W) and Pau dos Ferros (6°08'30.12" S; 038°10'59 880"W) reservoirs.

Results

The Pau dos Ferros reservoir, shallow, turbid and eutrophic showed dominance of the functional group S_N throughout the sample period. Total phytoplankton biovolume ranged between 20 and 70 mm³.L^–1, the lowest values coincided with the increase of the mixing zone and transparency, which occasioned a change in composition of the phytoplankton community. Pau dos Ferros reservoir was categorized as poor for most of the sample period. The Santa Cruz do Apodi reservoir was characterized as meso-eutrophic, exhibiting low total phytoplankton biovolume (0.04 to 0,4 mm³.L^–1) and greater diversity in the phytoplankton composition. It showed moderate condition during most of the period.

Conclusion

In summary, the index Q reflected well the changes in phytoplankton composition, being a good indicator for biomonitoring of these systems.

phytoplankton; water quality; assemblage index; functional groups