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Brazilian sediment quality criteria were established based on pseudo-total metal contents, which is not suitable to determine their bioavailability and the ecological risk for aquatic biota. Therefore, the geochemical speciation of five metals (Cu, Fe, Ni, Pb and Zn) was determined to assess the distribution and ecological risk of sediments in a tropical shallow reservoir from Brazil. The paper aims to discuss these issues.

A survey of metals in ten representative stations of surface sediments (0-20 cm) from Carlos Botelho (Lobo-Broa) Reservoir was conducted during the dry season in April 2014. Sediment parameters were measured in situ. The geochemical speciation of metals was carried out using the modified three-stage BCR-701 procedure (Davutluoglu et al., 2011) and compared with pseudo-total metal contents.

Contamination at S-1 and S-8 was more severe than other sampling sites, especially for Cu, Ni, Pb and Zn. Metals such as Cu, Ni and Zn occasionally may be associated with adverse biological effects based on the comparison with sediment quality guidelines. The risk assessment code suggests no risk for Fe and low risk for Cu and Ni.

Geochemical speciation of metals could be useful in developing effective management strategies to control metal pollution in the Lobo-Broa Reservoir. Substantial amounts of Pb (classified as medium risk) were bound to humic substances and/or insoluble metal sulfides, and could pose serious risk to the benthic community through the food chain. Zinc at S-1, S-3 and S-8 showed high risk, indicating that an appreciable portion of Zn could be available to aquatic biota.

Animal liquid manure contains large amounts of phosphorus (P), which is susceptible to runoff losses when manure is surface-applied on farms as a soil amendment. Even very small quantities of P can have a large impact on waterways and lead to eutrophication. Previous studies have shown that flue gas desulfurization (FGD) gypsum, a coal combustion by-product, can reduce P losses from runoff in soils. Therefore, the authors hypothesize that FGD gypsum could reduce nutrients in liquid manure prior to field applications. The purpose of this paper is to evaluate the effect of FGD gypsum to reduce P and suspended solids (SS) concentrations in liquid manure, also determining its proper rate(s) and minimum time of reaction.

The experimental design was completely randomized with three replicates. Each plot was constituted by a polyvinyl chloride (PVC) column (1 m height and 0.15 m diameter). Dairy liquid manure and FGD gypsum rates (0, 0.62, 1.25 and 2.5 mgl⁻¹) were added to the PVC columns and manually shaken for two minutes. Sampling was performed at 0.35, 0.65 and 0.95 m depths after 0 (immediately after shaking), 4, 8, 16 and 24 hours. Amount of phosphorus was determined by a colorimetric method and solids concentration by mass difference.

FGD gypsum reduced P concentrations in the liquid manure after four hours of reaction. The most effective rate was 0.62 mgl⁻¹at a 0.35 m depth. FGD gypsum increased SS concentrations in depth in all treatments.

There are growing concerns regarding the fate of nutrients, especially phosphorus, from land application of animal waste. The results indicated that treating liquid manure in the settling tanks with FGD gypsum before field application can be particularly useful on farms where surface-manure is applied, reducing potential losses of P following manure applications, and consequently the eutrophication risk to waterways.