Influence of Current Velocity on Cadmium Accumulation by an Aquatic Moss and the Consequences for Its Use as a Biomonitor

Abstract

Aquatic mosses are widely used as biomonitors of contaminant concentrations in running waters. The results of several previous studies suggest that metal concentrations in mosses are influenced by current velocity and that this variable should be taken into account when mosses are used as metal biomonitors. However, in these studies, the purported influence of water velocity was confounded by other uncontrolled variables. We conducted our study to test the influence of current velocity on Cd accumulation by the riverine moss Fontinalis dalecarlica. We found no difference in Cd accumulation over 2 weeks by moss exposed in the laboratory to a constant Cd concentration over a wide range of current velocities (0.01-0.70 m s-1) that occur in the field. Similarly, the results of a field experiment, in which we exposed F. dalecarlica in a Cd-contaminated creek to four current velocities (0.05-0.50 m s-1), confirmed that in nature Cd accumulation by this moss is not influenced by current velocity. We show that a bioaccumulation model that ignores current velocity describes Cd accumulation by F. dalecarlica very well. Our results suggest that current velocity does not have to be considered when using aquatic mosses as metal biomonitors.

Quantifying ‘humics’ in freshwaters: purpose and methods

“…Some authors have applied empirical relationships linking 'humics' concentrations and UV-vis absorption values (e.g. 'humics' concentration = 64.52A 326 in Croisetière et al [62]). These empirical relationships are usually derived from correlations established on a certain number of similar water systems.…”

Effect of Current Velocity on Cd Accumulation in the Aquatic Moss Fontinalis antipyretica

“…Although in recent years an important effort has been made towards standardizing biomonitoring techniques with aquatic mosses (see e.g., [6,8]), other environmental factors that affect the relationship between the pollutant levels in the biomonitors and the water cannot be standardized. These factors include physicochemical parameters of the water, such as pH, temperature, dissolved organic matter, conductivity and velocity [9,10]. These factors affect the uptake of pollutants by aquatic mosses, in both passive (collecting organisms living in the water body objective to the study) and active biomonitoring (collecting pieces of moss material, i.e., moss "transplants", from unpolluted sites and exposing them in the study site, in the "moss bag technique").…”

“…The DBL is the layer of water in a current next to a surface where, because of the friction with the solid, the flow slows to the point where the main way for elements to go through it is by diffusion [11]. Thus, Croisetière et al [10] hypothesized that at higher velocities this layer will become thinner, making it easier for pollutants to reach the surface of the moss. However, Gonçalves et al [12] hypothesized that the increased number of particles carried by rapid flowing waters implies that a greater amount of particles will be retained on the surface of the moss tissues, thus enhancing accumulation of elements.…”

“…To date, the effect of water velocity on pollutant concentrations in aquatic mosses has scarcely been considered. As far as we are aware, only the aforementioned study by Croisetière et al [10] has analyzed the effect of the current velocity on element accumulation considering every other factor involved. These researchers determined Cd concentration in the moss Fontinalis dalecarlica exposed to different current velocities and did not find any significant correlation between the flow velocity and Cd concentrations in the moss.…”

More than inorganic copper is bioavailable to aquatic mosses at environmentally relevant concentrations

“…Given that they take up metals very rapidly and efficiently, we based our analysis on the kinetic response of the aquatic mosses. Because Croisetière et al [21] showed that the bioaccumulation kinetics of Cd by aquatic mosses did not depend on the current velocity, we extrapolated the results obtained in batch experiments to the aquatic environment and then analyzed how different types of DOM modified copper bioavailability at environmentally relevant contamination levels.…”