A system (water–sediment) under prolonged anaerobiosis: harmful levels of chemical species

ABSTRACT Models for assessing sediment quality describe the occurrence of a continuous matter and energy exchange process at the sediment–water interface, and the displacement of nutrients and metals from the sediments to the water column affecting its quality. Although these models are highly used for studying reservoirs and lakes, there is a gap between them regarding the assessment of rivers in heavily urbanized areas without access to basic sanitation, where high loads of untreated effluents from domestic and industrial sources arrive. This work evaluated this condition on the Barigüi River, an urban water system in southern Brazil. During hypoxic incubations (45 days), the concentrations of dissolved oxygen (DO), pH, redox potential (Eh), orthophosphate (POrto), total phosphorus (PT), ammonia (NH3), total alkalinity (TA), and metals Cr, Fe, Cd, Zn, and Cu were monitored in incubated systems (water/sediment). In this study, we present the evidence of the possible resuspension of ammonia from the sediments to the water column by mass balance. We have determined the accumulation rate in relation to time for concentrations of total phosphorus, total Fe, ammonia, and total alkalinity of d(φ)/dt = 4.2 mg.L−1 per day, deteriorating its quality.