Spatial and temporal variation in heavy metal contamination ofNereis andCerastodema

Abstract

In the Wadden Sea, heavy metals representa long-term risk for organisms. Therefore, we investigated spatial and temporal variation ofPb, Hg and Cd contents in benthic organistas. Considering the high va¡ ability of individual condition and size of the bivalve Cerastoderma edule and the polychaete Nereis diversicolor, it was only partly possible to estimate different bioavailabilities. Organisms, as well as some sediment samples, were collected at six sampling sites in the backbarrier area of the East Frisian island of Spiekeroog, Germany. According to both species, the results indicated similar microgeographic pattems. Additionally, data pointed to a higher bioavailability ofPb and Hg at the coastal, fine grained sampling sites than at the other stations. Therefore, the spatial variability seemed to coincide more with the sediment composition than with the spatially, rather homogeneous, contamination of the pelitic fraction (<20 gm grain size). Respecting the temporal variation between November 1992 and November 1994, samples of animals resulted in relatively high levels ofheavy metals in spring and low ones in summer, which coincided with intrinsic, temporal rest¡ factors such reproduction, food intake and others. The results gaste hints for optimizing monitoring concepts.

Linear stability criteria in a reaction-diffusion equation with spatially inhomogeneous delay

“…This may be natural, such as the variation of potassium and phosphorus across Australia (Bolland & Allen, 1998) but there is increasing work concer ning the amount of arti® cially introduced (pollution) metal in natural systems, for example, copper and lead through urban run-oþ (Vesk & Allaway, 1997). These variations result in a diþ erence of uptake by¯ora and fauna, although the rate of uptake can also be aþ ected by variations in, for example, sediment composition in a relatively homogeneously contam inated area (Bietz et al, 1997). Small spatial variations in contam inant levels have been found, for example, in yellow perch in the St Lawrence river (Ion et al, 1997) and low variation relative to the spatial scale in benthic organisms in the Wadden Sea (Bietz et al, 1997).…”

“…These variations result in a diþ erence of uptake by¯ora and fauna, although the rate of uptake can also be aþ ected by variations in, for example, sediment composition in a relatively homogeneously contam inated area (Bietz et al, 1997). Small spatial variations in contam inant levels have been found, for example, in yellow perch in the St Lawrence river (Ion et al, 1997) and low variation relative to the spatial scale in benthic organisms in the Wadden Sea (Bietz et al, 1997). Such variations, especially in heavy metals, are known to strongly aþ ect the behaviour and performance of living organisms such as the response of purple urchins to zinc (Phillips et al, 1998).…”