Relationship between potentially toxic elements and macrophyte communities in the Sava river

Abstract

Freshwater ecosystems are at significant risk of contamination by potentially toxic elements (PTEs) due to their high inherent toxicity, their persistence in the environment and their tendency to bioaccumulate in sediments and living organisms. We investigated aquatic macrophyte communities and the concentrations of As, Cu, Cd, Cr, Pb, Zn, Ni and Fe in water and sediment samples to identify a pollution pattern along the Sava River and to investigate the potential impact of these PTEs on the diversity and structure of macrophyte communities. The study, which covered 945 km of the Sava River, showed a downstream increase in sediment concentrations of the analyzed elements. Both species richness and alpha diversity of macrophyte communities also generally increase downstream. Ordinary and partial Mantel tests indicate that macrophyte communities are significantly correlated with sediment chemistry, but only weakly correlated with water chemistry. In the lowland regions (downstream), beta diversity decreases successively, which can be attributed to an increasing similarity of environmental conditions at downstream sites. Species richness is relatively low at sites with low concentrations of Cr, Cd, Fe, and Cu in the sediment. However, species richness increases to a certain extent with increasing element concentrations; as element concentrations increase further, species richness decreases, probably as a result of increased toxicity. Some species that are generally more tolerant to high concentrations of PTEs are: Ceratophyllum demersum, Iris pseudacorus, Najas marina, Butomus umbellatus, Vallisneria spiralis, Potamogeton gramineus and Bolboschoenus maritimus maritimus. Potamogeton perfoliatus and the moss species Cinclidotus fontinaloides and Fontinalis antipyretica have narrow ecological amplitudes in relation to the concentrations of PTEs in the sediment.

Keywords: Aquatic vegetation; Biodiversity; Heavy metals; Macrophyte communities; Potentially toxic elements; Sava river.

Fig. 1

Map of the Sava River basin with sampling sites (labelled 1–15, see Table 1).

Fig. 2

Distribution of elements in water samples (Sampling sites labelled 1–15, see Table 1).

Fig. 3

Distribution of PTEs in sediments (Sampling sites labelled 1–15, see Table 1).

Fig. 4

Diversity components of macrophyte communities along the Sava River: a) species richness; b) equitability; c) Alpha diversity; d) Beta diversity (Sampling sites labelled 1–15, see Table 1).

Fig. 5

Relationship between water chemistry and macrophyte communities along the Sava River (Sampling sites labelled 1–15, see Table 1).

Fig. 6

Relationship between sediment chemistry and macrophyte communities along the Sava River (Sampling sites labelled 1–15, see Table 1).

Fig. 7

Distribution of macrophyte species with respect to concentrations of elements in sediment samples (y axes = concentration of elements in mg kg⁻¹. Each label on x axis specifies particular species).

Fig. 8

Relationship between the species richness of macrophyte communities and concentrations of elements in sediment along the Sava River (x-axis = concentration of elements in mg kgL⁻¹; y-axis = species richness).