Benthic macroinvertebrates and the quality of the hydric resources in Maratá Creek basin (Rio Grande do Sul, Brazil)

PEREIRA¹, D. & DE LUCA¹, S.J.

¹ Instituto de Pesquisas Hidráulicas (IPH), Universidade Federal do Rio Grande do Sul (UFRGS).

e-mail: daniel_pereira_dp@hotmail.com

ABSTRACT: The current study was performed as a monitoring study of the surface hydric resources of the Maratá stream, Caí river basin, Rio Grande do Sul State, Brazil to evaluate the relationship between indexes and indicators of water quality and the density, richness and diversity of benthic macroinvertebrates. Water and benthic macroinvertebrate samples were collected at four different sampling stations, using a Surber sampler. The average velocity and the streamflow were also measured. Through multivariate analysis, similarity matrices between sample units were obtained based upon the values of: 1) the traditional indicators of water quality; 3) the Aquatic Life Protection Index; 3) the Trophic State Index; 4) the Essential Parameters of Aquatic Life Preservation Index; 5) the density of macroinvertebrates; 6) the Margalef Richness Index; 7) the Simpson Diversity Index; 8) the Shannon-Wiener Diversity Index; 9) the Streamflow and 10) the Average river velocity. The matrices were then submitted to a randomization test, in order to identify the spatial and temporal variation of the indexes and indicators. Correlations between the indexes and indicators matrices were tested using the Mantel and randomization test. The water quality indicators and the CETESB indexes showed no spatial but temporal variations, being mostly affected by the hydrological cycle. The flow and the indicators of water quality presented positive correlations, because the water quality decreased towards the river mouth. The density, richness and diversity of the macroinvertebrate families showed no correlation with the indicators of water quality and with the CETESB indexes. Other factors, such as the physical features of the fluvial environment, affected the structure of the macroinvertebrate community.

Key-words: Environmental indexes, water quality, benthic macroinvertebrates.