Water Quality Biomonitoring on the Doce River in Brazil, Near a Pulp Mill Effluent Discharge

摘要

Water quality chemical and biological monitoring was used to assess environmental impacts caused by a pulp mill effluent discharge including structural changes in aquatic communities and temporal and geographic trends. Three sampling stations were selected at upstream, downstream and the effluent discharge mixing point. Each station was divided into three sampling locations (left and right banks and central channel). Planktonic organisms were sampled with nylon nets held against the flow. For zooplankton quantitative studies, water was filtered in nylon nets and the final volume was preserved in flasks. For phytoplankton quantitative studies, sample were placed in flasks and preserved with Lugol's solution. Benthic macroinvertebrates were collected with a Petersen grab sampler. All aquatic organisms were counted and identified under a microscope, and separated into community groups, where population structures were defined by measurement.Physical and chemical data show little difference along the river near the mill, with higher values of phosphate, fecal and total coliforms, associated with untreated urban sewage discharge, upstream from the effluent discharge. During the winter, precipitation and water levels decreased, the runoff was diminished and water clarity increased. Solar radiation intensity and nutrient concentrations were also highest. Because of these factors, phytoplanktonic organisms increased, causing high densities of algae. However, phytoplankton density did not indicate that the Doce River is undergoing eutrophication. Like phytoplankton, zooplankton were most abundant at low water levels, and seasonal variations in primary production affected the distribution of aquatic organisms. This was the greatest factor influencing population distributions in the river. Algal densities often increased below the effluent outfall because of nutrients in the effluent. Despite increases in algal density in affected areas, the richness and diversity indices were reduced at some sampling points. The benthic macroinvertebrate population from each sampling station shows structural and density variations associated with upstream polluted waters, causing differences in organism trophic level distribution.