Lead, mercury and cadmium content in bottom sediments, reed (Phragmites australis) beds and great pond snails (Lymnaea stagnalis) in fishponds and the role of littoral zones in their accumulation.

摘要

We studied the contents of cadmium (Cd), lead (Pb) and mercury (Hg) in common reed (Phragmites australis), great pond snails (Lymnaea stagnalis), and in littoral bottom sediments in 18 fishponds in two regions of the Czech Republic. We also assessed the impact of environmental factors on heavy metal accumulation in these three components of littoral ecosystem. Cadmium and lead values were significantly higher in bottom sediments (median values 0.70 and 13.4 mg.kg-1) than in reed (0.014 and 0.51 mg.kg-1) and snails (0.074 and 0.81 mg.kg-1). Cadmium values in reed stems positively correlated with Cd values in great pond snails (Spearman's rank correlation, r_s=0.62; p<0.05). Cadmium and lead contents in reed stems positively correlated with each other (r_s=0.56; p<0.05). The mercury values in snails (0.043 mg.kg-1) were higher than in sediments (0.040 mg.kg-1) and these were higher than in reed stems (0.010 mg.kg-1). We also found higher mercury contents in reed stems and higher cadmium contents in great pond snails in eastern compared to western parts of investigated ponds. Based on the principal component analysis (PCA) performed on heavy metal values, relative reed beds rate in the pond perimeter was negatively correlated with the sample scores on the first PCA axis and the orientation of sampling site and fish stock density negatively correlated with the second PCA axis. Our results proved the important role of littoral sediments in Cd, Pb and Hg accumulation, and the suitability of great pond snails for mercury stress biomonitoring in fishponds. In conclusion, littoral reed beds play a very important role in toxic element uptake in fishponds. The results contribute to the understanding of heavy metal cycles and their accumulation in fishponds under semi-natural conditions and in less affected landscape, and can be used as reference values for comparison with more damaged sites.