Abstract
Abstract The Bacanga River Estuary is socioeconomically important due to artisanal fishing and aquaculture. It is blocked by a dam and is under human pressure along its drainage basin, intensifying the eutrophication process. This study reports on the occurrence of phytoplankton blooms and trophic state (TSI and TRIX) at six sampling sites during the annual cycle. The estuary was divided into downstream and upstream regions. Higher salinity, turbidity, depth, and lower dissolved oxygen levels were found downstream; whereas, high levels of chlorophyll a and nutrient concentrations were observed in both regions. There were blooms of Leptocylindrus danicus (1.45 × 106 cells L-1) and Skeletonema costatum (1.89 × 106 cells L-1) downstream; whereas phytoflagellate proliferation, such as those of Chlamydomonas sp. (13.17 × 106 cells L-1), Euglena gracilis (7.84 × 106 cells L-1), and Euglena proxima (1.03 × 106 cells L-1) were recorded upstream, with Chlamydomonas sp. as the discriminant species of this zone. Both trophic indices (TSI; TRIX) indicated elevated trophic conditions for the estuary, classifying it as hypereutrophic. Nevertheless, TSI only showed a significant relationship with some specific phytoplankton blooms. Thus, TSI seems to be the trophic index with a better response in the assessment of estuarine ecological functioning.
Highlights
Eutrophication in estuaries has been a major ecological problem that is caused by the inputs of natural and anthropogenic nutrients through the discharge of sediments, the atmosphere, the ocean, or even through the exchange of nutrients with the coastal region (Ferreira et al, 2011; Statham, 2012; Cloern et al, 2014; Hayn et al, 2014; Monteiro et al, 2016)
This study aimed to relate the occurrence of phytoplankton blooms and trophic state using the trophic state index (TSI) and trophic index (TRIX) indices to assess the ecological functioning of the Bacanga River Estuary (BRE) and the effects of nutrient enrichment on the phytoplankton community
The Bacanga River estuary is a coastal system with variations in salinity, depth, and algal blooms in the two estuarine regions
Summary
Eutrophication in estuaries has been a major ecological problem that is caused by the inputs of natural and anthropogenic nutrients through the discharge of sediments, the atmosphere, the ocean, or even through the exchange of nutrients with the coastal region (Ferreira et al, 2011; Statham, 2012; Cloern et al, 2014; Hayn et al, 2014; Monteiro et al, 2016). Lopes anthropogenic pressures that compromise their water quality and biodiversity, causing a loss of habitat and a reduction in the quality of life of riverside communities. Because of these impacts, it is necessary to characterize and assess the current conditions of these environments based on an ecosystemic and trophic approach (Cloern, 2001; Herrera-Silveira et al, 2009; Smith and Schindler, 2009; Ferreira et al, 2011; Cotovicz-Júnior et al, 2012a).
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