Effects of development time, biomass and ferromanganese oxides on nickel sorption by stream periphyton

Procedurally defined periphyton frequently includes substantial quantities of hydrous iron (Fe) and manganese (Mn) oxides. As these oxides are strong sorbers of heavy metals, their presence may complicate estimation of metal bioaccumulation by periphyton. We examined the relationship between nickel (Ni) sorption and the development time, biomass, and Fe and Mn oxide conten t of stream periphyton. Development time, the time during which periphyton accrued on submerged tile substrata, was used to provide variation in bioma ss, Fe and Mn levels. Stream periphyton from four development times was exp osed to Ni for 2 h in the laboratory, and then ashed. Development time was significantly associated with ash-free dry mass (AFDM), Fe and Mn levels (A NOVA, P less than or equal to0.003). Ni extracted by a mild reductant (hydr oxylamine hydrochloride) was significantly associated with development time , and with AFDM, Fe and Mn levels (linear models, P less than or equal to0. 0002). A subsequent acid digestion yielded similar associations with the sa me variables (linear models, P less than or equal to0.0001). For both extra ctions, AFDM was significantly and positively correlated with Fe (r = 0.68 and 0.89) and with Mn (r = 0.77 and 0.93) (Spearman rank, P less than or eq ual to0.005). These data demonstrate the importance of periphyton developme nt time in influencing both metal sorption and levels of biomass and ferrom anganese oxides. The data also suggest that metal contaminant levels in per iphyton should not be attributed automatically to biotic sorption. Periphyt on metal-accumulation studies conducted where ferromanganese oxide concentr ations are elevated should address the potential metal-sorbing roles of Fe and Mn oxides within the periphyton matrix. (C) 2001 Elsevier Science Ltd. All rights reserved.