Water-sediment interaction on the water quality degradation of semi-arid tropical reservoirs

Herika Cavalcante, Fabiana Araújo, Vanessa Becker


Aim: The aim of this study was to verify vertical distribution of phosphorus in the water column and relate it to the phosphorus release from sediment during a period of extreme drought. Methods: Two reservoirs in the semi-arid region of Rio Grande do Norte were analysed during a period from May 2015 to June 2016. Analyses were performed for: suspended solids (SS), chlorophyll-a (Chl-a), dissolved oxygen (DO) and temperature. Vertical profiles were set for total phosphorus (TP), total dissolved phosphorus (TDP), particulate phosphorus (PP), dissolved organic phosphorus (DOP) and soluble reactive phosphorus (SRP). Results: Gargalheiras presented anoxic conditions near the sediment for several months during the stratified period and in two of the months Cruzeta had a minimum DO value of 1mg L-1. Both reservoirs presented noticeably high values of phosphorus distributed in the water column. Gargalheiras presented the highest TP and PP, while Cruzeta presented the highest SRP. Chl-a and SS Showed proportional growth as phosphorus, Chl-a was higher in Gargalheiras, while SS (mainly inorganic), were higher in Cruzeta. Some of the months which had anoxic conditions at the bottom also presented the highest values of TP and SRP, which may indicate release. In addition, the excessively high values during the shallowest months may have been due to the influence of wind favouring release through resuspension of sediment. Conclusions: The distribution of phosphorus forms and their quantities in the water column are important for restoration plans of eutrophic lakes, however, it is not enough. It is necessary to know the flux of P release and existing P forms to understand variables that influence release mechanisms.


phosphorus release; extreme drought; internal loading.

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