Abstract
This study aims to evaluate the biofiltration ability of higher aquatic vegetation of the Selenga delta as a barrier for heavy metals and metalloids (HMM) flows into the Lake Baikal. Main aquatic vegetation species have been collected from deltaic channels and inner lakes: Nuphar pumila, Potamogeton perfoliatus, P. pectinatus, P. natans, P. friesii, Butomus umbellatus, Myriophyllum spicatum, Ceratophyllum demersum, Phragmites australis. Analysis of the obtained data showed that regardless of the place of growth hydatophytes spiked water-milfoil (M. spicatum) and the fennel-leaved pondweed (P. pectinatus) most actively accumulate metals. Opposite tendencies were found for helophytes reed (Ph. australis) and flowering rush (B. umbellatus), which concentrate the least amount of elements. This supports previous findings that the ability to concentrate HMM increases in the series of surface – floating – submerged plants. Regarding river water, the studied macrophyte species are enriched with Mn and Co, regarding suspended matter – Mo, Mn and B, regarding bottom sediments – Mn, Mo and As. We identified two associations of chemical elements: S-association with the predominant suspended form of migration (Be, V, Co, Ni, W, Pb, Bi, Mn, Fe and Al) and D-association with the predominant dissolved form of migration (B, U, Mo, Cr, Cu, Zn, As, Cd, Sn and Sb). Due to these associations three groups of macrophytes were distinguished – flowering rush and reed with a low HMM content; small yellow pond-lily and common floating pondweed with a moderate accumulation of S-association and weak accumulation of D-association elements; and clasping-leaved pondweed, fennel-leaved pondweed, and pondweed Friesii accumulating elements of both S and D groups. The results suggest that macrophytes retain more than 60% of the total Mn flux that came into the delta, more than 10% – W, As, and from 3 to 10% B, Fe, Co, Mo, Cd, V, Ni, Bi, Be, Cu, Zn, Cr, U, Al. The largest contribution is made by the group of hydatophytes (spiked water-milfoil and pondweed), which account for 74 to 96% of the total mass of substances accumulated by aquatic plants.
Highlights
In recent years, the growing attention has been paid to ecology and geochemistry of river deltas and their wetland systems (Cui et al 2009; Iqbal 2010; Thorslud et al 2017; Wang et al 2014)
Large water discharges of the Selenginsky sector cause a rare presence of aquatic plants in the channels and a large number of macrophytes in the intra-delta lakes Zavernyaekha and Tolstonozhikha, and at the waterstream mouths in the Sor Cherkalov bay
The Lobanovsky sector with moderate water discharges is characterized with small amount of aquatic plants
Summary
The growing attention has been paid to ecology and geochemistry of river deltas and their wetland systems (Cui et al 2009; Iqbal 2010; Thorslud et al 2017; Wang et al 2014). Due to increasing anthropogenic pressure on the catchments, the role of deltas as natural filters on the path of substance flows of natural and anthropogenic origin is becoming increasingly important (Thorslund et al 2017). The aquatic plants provide important environmental services, such as storage of pollutants. They are often utilized in constructed wetlands to reduce contaminant loads in rivers (Rai. 2009; Patel and Kanungo 2010; Leto et al.2013; Sun et al 2013; Guittonny-Philippe et al 2014). Macrophytes, play an important role in the processes of deposition of substances in river deltas
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