Water quality and trophic index in tropical riverine ecosystem under environmental impact

ABSTRACT

The objective of this investigation was to quantify the spatial-temporal variability of 20 physical, chemical and microbiological water quality parameters (including the trophic state index - TSI) in the Lower Jari River, Amapá, Brazil, typical of floodplain ecosystems. Water samples were collected quarterly in a stretch of 80 km of the river, from September 2013 to June 2014. After analysis, these parameters were compared with values established by the CONAMA Resolution 357/2005 (Class 2). Multivariate analysis (correlation, Kruskal-Wallis and cluster hierarchical) showed that the only parameter that varied spatially was the dissolved oxygen (DO) (p<0.05), due to the strong influence of the stretch reaeration. On the other hand, the other parameters - color, turbidity, electrical conductivity, biochemical oxygen demand (BOD), NH₃, P, pH, SO₄, Mg, Cl^-, thermotolerant coliforms (TC), Escherichia coli and chlorophyll-a - showed only significant temporal variation (p<0.05). We conclude that variation of the TSI ranged from oligotrophic, mesotrophic until ultraoligotrophic. Color, TC and E. coli parameters presented non-compliance with legislation, suggesting relative, but significant, influence, both of hydrological and environmental impacts (urban, industries and hydroelectric plant of Santo Antonio do Jari). Both factors explain not only the seasonal variation of TC, E. coli and color during the rainy season (p<0.05), but also the correlation among color, turbidity, temperature, DO, Cl^-, NH₃, Mg, DBO, SO₄, pH, E. coli, TC and chlorophyll-a, along the hydrological cycle and its seasonal dynamics (p<0.05), indirectly influencing the behavior of the TSI (p<0.05).

Keywords:
parameters; space-seasonal variation; hydrologic influence; multivariate analysis