Biomonitoring of aquatic and semiaquatic plants under chemical pollution

The increasing anthropogenic impact on ecosystems highlights the growing importance of studying vegetation responses to inorganic and organic pollutants in deltaic and coastal bay environments. This study evaluates morphometric indicators of ecological stress in vegetation from different ecological groups, specifically helophytes and mesophytes, within the super- and subaqueous landscapes of the lower Don River in Russia, including its delta and the coasts of the Taganrog Bay. Analysis of plant species revealed a high level of metals and polycyclic aromatic hydrocarbons (PAHs) accumulation in the following cosmopolitan plants: common reed (Phragmites australis (Cav.) Trin. ex Steud), couch grass (Elytrigia repens (L.) Nevski), and eastern cocklebur (Xanthium orientale L.). Using analysis of variance, factor analysis, and correlation analysis, it was shown that the accumulation of metals and PAHs in plant organs depends on the sampling area, the content of pollutants in soils, their properties, as well as the species-specific characteristics of the plants. The accumulation of pollutants in roots is higher than in stems. The concentration of metals in plants followed the order: Mn > Cr > Ni > Zn > Pb > Cu > Cd. The degree of pollutant accumulation in the roots and stems of cosmopolitan plants decreased in the sequence: X. orientale > E. repens > P. australis. Plants growing in the northern part of the Don River delta and along the northern shore of the Taganrog Bay were exposed to the highest total toxic load. Metal accumulation in plants depends mainly on anthropogenic load and species traits, while PAH accumulation is driven by their physicochemical properties, especially water solubility. Using dispersion analysis, it was shown that in habitats with increased anthropogenic pressure, the studied plant species exhibited changes in growth characteristics. Significant reductions in stem length were observed in X. orientale, while stem length increased in E. repens, indicating an active response triggered by changes in environmental conditions along a gradient of rising metals and PAHs levels in the soil.