Variable Uptake of Selenium: Exposing Bryophytes in Situ to a Se-Gradient Watershed

We investigated the uptake of selenium (Se) at 14 sites in a Se-rich watershed, using an aquatic bryophyte (Hygrohypnum ochraceum). We expressed uptake using the symbol Kd to underscore the relationships between Se in water and Se in plants as "partitioning coefficients"related to the bases of aquatic food chains. A 2-way analysis of variance (ANOVA) was performed with Kd as the dependent variable and season and stream segment (location) as main effects. Selenium concentrations, measured as dissolved Se, total Se, and pore water Se, were also examined. There were significant differences in Kd values with respect to stream segment (P < 0.001); however, the differences were mainly not associated with season, although pore water Se showed a slight association with season (P = 0.052). The interaction effects between season and stream segment were significant for dissolved Se (P = 0.016) and total Se (P = 0.041). Further analysis showed strong negative correlations to the 3 Se water concentrations in spring (dissolved Se: r = -0.973, P < 0.001; total Se: r = -0.972, P < 0.001; pore water Se: r = -0.867, P < 0.001). Fall associations of Kd values to the 3 Se water concentrations were considerably weaker. Dissolved Se and total Se both still showed statistically significant positive correlations to Kd in the fall, but total Se did not. Based on the results of recent studies, it appears that the bryophytes might have preferentially bioconcentrated selenite over selenate in the upper watershed basin rather than in the lower basin. To conclude, the bryophytes appeared to be suitable natural receptors of Se at the bases of numerous food chains in a complex watershed by exhibiting differences in Se uptake based on site location, season, and diverse Se water concentrations.