Nicolas Bogaert

Heavy metal contents (Cd, Cu, Zn) in spiders (Pirata piraticus) living in intertidal sediments of the river Scheldt estuary (Belgium) as affected by substrate characteristics

Metals are transferred into the food web by ground-dwelling organisms, among others. This study aimed to identify the most important factors that determine the bioavailability of heavy metals to the spider Pirata piraticus living in the intertidal sediments of the Scheldt estuary (Flanders, Belgium). At five locations, which represent a varying degree of metal contamination and salinity, the superficial layer of sediments was characterised for physico-chemical properties and heavy metal (Cd, Cu, Zn) content and extractability. Spiders were sampled at the same locations and analysed for Cd, Cu and Zn. Higher Cd, Cu and Zn contents were found in spiders on sites with lower total metal contents in the sediment. These sites were closest to the river mouth and were characterised by a higher salinity. Significant, positive correlations were found between the chloride content of the sediments and the Cd, Cu and Zn content of P. piraticus. Similarly, a strong relationship was observed between the ratio of exchangeable Cd and Zn to the total cation exchange capacity and the contents of these elements in P. piraticus. These field data indicated that salinity, cation exchange capacity and exchangeable metal contents were of most importance in determining bioavailability of heavy metals in these intertidal sediments.

Within-field variability of mineral nitrogen in grassland

Abstract The within-field variability of soil mineral nitrogen (Nmin) in a grazed grassland of 8000 m2 was examined. NO3–-N concentrations were characterized by a high spatial variability. This can be explained by the uneven deposition of animal excreta. All NH4+-N as well as NO3–-N values were lognormally distributed, before and after the grazing season. At the end of the grazing season the largest part of the variability of NO3–-N was found for NO3–-N concentrations measured within a distance of a few metres. A high variability for NO3–-N over very short distances was also indicated by a large nugget variance. During the grazing season, observed mean Nmin values increased from 22 to 132 kg N ha–1. Regions with clearly higher NO3–-N concentrations could be identified. These zones matched with the drinking place and the entrance of the pasture, places which were more frequently visited than others. High residual N levels in autumn led to relatively high losses of N, mostly by leaching, during the subsequent drainage period. Knowing the variability of Nmin, the number of samples needed to estimate the average Nmin in a field could be calculated for different probabilities and various degrees of precision. From the spatial distribution of the Nmin concentrations and the restrictions imposed by the new European decree, adapted fertilizer strategies can be proposed at least for places where systematically higher Nmin concentrations can be expected.

Determination of Cd, Cu, Pb and Zn in woodlouse (Oniscus asellus)

Abstract The aim of this study was to assess the performance of selected destruction methods for the determination of heavy metals (Cd, Cu, Pb and Zn) in woodlouse (Oniscus asellus). A vigorous total analysis involving microwave destruction with HF, HCl and HNO3 (method 1) was used as a reference method. Consistently low values for the dry ashing method may indicate incomplete dissolution of the elements and/or losses through volatilisation. Method 3 (concentrated HNO3) that frequently is used in literature, produced erroneous values for Cd, Cu and Pb. Results were consistent with the microwave digestion, provided H2O2 was used during digestion (method 4, HNO3/H2O2). Method 5 (HNO3/HCIO4, one destruction step) yielded low recoveries when only one destruction step was applied. Applying two destruction steps (method 6) resulted in values consistent with the microwave method, but was at the expense of reproducibility and rendered the method more lengthy and laborious. Because of the very good performance combined with speed and simplicity, destruction with HNO3/H2O2 (method 4) emerged as the most convenient method.

Heavy metal concentrations in the spiders Pirata piraticus (Clerck, 1757) and Clubiona phragmitis (C.L. Koch, 1843) along the Scheldt Estuary (Belgium).

Wetland ecosystems may be affected by deposition and accumulation of heavy metals. Metal concentrations in the spiders Pirata piraticus and Clubiona phragmitis living in marshes along the river Scheldt (Flanders, Belgium) were analyzed. The organisms were sampled on seven sites along a gradient from freshwater to brackish marshes. Except for lead, P. piraticus contained higher metal concentrations than C. phragmitis. This is related to physiological and ecological differences between species. No correlation was found between metal concentration in the organisms and soil total concentration.