Diatomáceas perifíticas como bioindicadoras de qualidade de água na microbacia do Urumari Santarém (Pará, Brasil).
Resumo
Diatoms (Ochrophyta, Bacillariophyceae) are microalgae that occur in all aquatic environments, accounting for most of the primary production in the oceans and freshwaters, constituting an expressive portion of the periphyton in these environments. Periphytic diatoms have been used as indicators and monitors of water quality in several countries. In Brazil, few studies with this approach were carried out, restricted to the south of the country, and nonexistent in Amazonian rivers. The Urumari is an urban stream located in the municipality of Santarém that it has suffered the consequences of the population growth in its surroundings. In order to identify diatom species with potential use as indicators of water quality, samples were taken from September 2018 to March 2019, in five sampling stations, comprising upper, middle and lower portions of Urumari. Artificial acrylic samplers were used for colonization of the periphyton, which were submerged for 30 days. In all, 220 taxa were registered, belonging to 17 families and 35 genera. Of these, 26 occurred with abundance above 5% in the samples. The most representative genera were Eunotia (24%), Pinnularia (19%), Nitzschia (7%) and Navicula (6%). The most downstream station (E5) had the highest dominance values. The Shannon-Wiener index ranged from 2.5 to 3.5. Eunotia parasiolli, Frustulia saxonica and Nitzschia palea occurred in 100% of the samples. The principal components analysis indicated a spatial gradient of organic contamination, from upstream to downstream, characterized by decreased dissolved oxygen concentration and increased BOD, pH and nitrogen and phosphorus concentrations. The results of the canonical correspondence analysis, TWINSPAN and IndVal indicated that there is a significant spatial variation in the composition and structure of the diatom assemblies, with substitution of some species for others with greater tolerance to organic pollution, along the course of the igarapé do Urumari. Thus, it was possible to select species with a potential indicator value and to relate them to four scenarios or groups of water quality: group I: Eunotia femoriformis, E. parasiolli, E. conectival 13; group II: Brachysira procera, Eolimna minima, Placoneis merinensis, Pinnularia brauniana; group III: Achnanthidium exiguum, Frustulia cf. crassinervia, Pinnularia microstauron, Sellaphora pupula; group IV: Encyonopsis frequentiformis, Frustulia quadrisinuata, Navicula cryptotenella, N. cryptocephala, Nitzschia palea, Stenopterobia planctonica. The results indicated that diatom species are highly sensitive to physical and chemical changes in water even when the range of these variations is not very large and confirm that these organisms can be a valuable tool for the diagnosis and monitoring of watercourses that suffer impacts of human activities. Although, the Urumari igarapé has not already yet its original characteristics, it still presents moderate impacts in its way when compared to other urban rivers of Brazil, and possibly can be recovered in relatively small time, if the necessary actions are carried out.
Os arquivos de licença a seguir estão associados a este item: