Can Acid Volatile Sulfides (AVS) Influence Metal Concentrations in the Macrophyte <i>Myriophyllum aquaticum</i>?

The difference between the molar concentrations of simultaneously extracted metals (SEM) and acid volatile sulfides (AVS) is widely used to predict metal availability toward invertebrates in hypoxic sediments. However, this model is poorly investigated for macrophytes. The present study evaluates metal accumulation in roots and stems of the macrophyte <i>Myriophyllum aquaticum</i> during a 54 day lab experiment. The macrophytes, rooting in metal contaminated, hypoxic, and sulfide rich field sediments were exposed to surface water with 40% or 90% oxygen. High oxygen concentrations in the 90% treatment resulted in dissolution of the metal-sulfide complexes and a gradual increase in labile metal concentrations during the experiment. However, the general trend of increasing availability in the sediment with time was not translated in rising <i>M. aquaticum</i> metal concentrations. Processes at the root-sediment interface, e.g., radial oxygen loss (ROL) or the release of organic compounds by plant roots and their effect on metal availability in the rhizosphere may be of larger importance for metal accumulation than the bulk metal mobility predicted by the SEM-AVS model

Sediment and metal deposition.

<p>Box plots (median, 25^th, 75^th percentile and standard deviation) of seasonal difference in deposited sediments (A) and deposited Cd (B) in a tidal marsh and restored marsh (CRT).</p

Average metal concentrations (µg g⁻¹), calculated metal deposition per surface unit (µg cm⁻² y⁻¹) and estimated total accumulated metals in the different zones of the Schelde estuary (10³ kg y⁻¹).

<p>The average estimated sedimentation rate (kg m⁻² y⁻¹) and total surface for the marshes (in 2012) and expected future areas displayed.</p

Correlation coefficients (R-values) between the different metals and sediment characteristics.

<p>All correlations were significant (p<0.001).</p

Modeled Cd deposition in a developping marsh.

<p>Modeled evolution of marsh elevation and Cd deposition. Elevation of the marsh and mean high water level (MHWL), both in m TAW (Belgian reference height) on the left Y-axis. Cd deposition (µg cm⁻² a⁻¹) on the right Y-axis.</p

Estimated input and output of trace metals in the Schelde estuary (10³ kg y⁻¹), based on literature and own calculations (^aBaeyens et al. (1997) [6]; ^bDe Smedt et al. (1997) [8]; ^cBaeyens et al. (2005) [38]; ^dThis study).

<p>Total metal deposition (tons per year) and metal removal in marshes of the entire estuary compared the estimated riverine input (%), for the period 2005–2010 and for a future scenario with an additional surface area of restored marshes implemented.</p

Map of the area.

<p>Location of the Schelde estuary (A) and the study area (CRT) within the estuary (B).</p

Detailed map of the study area.

<p>Sampling locations for the subtidal samples, tidal flat and tidal marsh samples along a transect and the location of the CRT.</p

Average metal concentrations (µg g⁻¹) and sediment characteristics (% dw) in the different areas for winter and summer.

<p>Significant differences (p<0.05) between seasons within an area are underlined and differences between areas within a season are indicated with letters (a, b, c for winter; x, y, z for summer).</p