Interação água-sedimento na degradação da qualidade da água de reservatórios tropicais semiáridos

Abstract

: Aim: The aim of this study was to verify the phosphorus vertical distribution in the water column, and relate it to the phosphorus release from sediment, during a period of extreme drought. Methods: Were analyzed two reservoirs of the Rio Grande do Norte semi-arid region, during the period of May 2015 to June 2016. Were analyzed: suspended solids (SS), chlorophyll-a (Chl-a), dissolved oxygen (OD) 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 stratified period. Cruzeta presented a OD minimum of 1mg L-1, however only two months. The values of phosphorus distributed in the water column were enough high for both reservoirs, Gargalheiras presented the higher TP and PP, while Cruzeta presented the higher SRP. The Chl-a and SS also were consistente with phosphorus: Chl-a was higher in Gargalheiras, while SS, mainly inorganic, were higher in Cruzeta. Some months have anoxic conditions at the bottom also presented the higher TP and SRP, which may indicate release. In addition, the excessively high values during the shallower months may have been the influence of wind, there ressuspension of sediment, providing release. Conclusions: The distribution of phosphorus forms and amounts in the water column is important for restoration plans of eutrophic lakes, however, it isn’t enough. It is necessary to know the P flux released and existing P forms for to understand variables that influence in release mechanisms.