Trophic Transfer of Cd, Cu, Pb, Zn, P and Se in Dutch Storage Water Reservoirs

Abstract

Heavy metals are naturally omnipresent in aquatic systems. Excess amounts of heavy metals can accumulate in organisms of pollution impacted systems and transfer across a food web. Analysing the food web structure and metal contents of the organisms can help unravel the pathways of biomagnification or biodilution and gain insight in trophic linkages. We measured heavy metals and other elements in mussel bank detritus and organisms of the Biesbosch reservoirs (the Netherlands) and linked those to stable isotopic signatures. The heavy metal contents (cadmium, copper, lead, and zinc) were often lowest in benthivorous, omnivorous and piscivorous species (mainly fish); whereas, phosphorus contents were lower in the autotrophs. Mussel bank detritus contained the highest amounts of heavy metals. The heavy metals were negatively correlated with δ¹⁵N values. For selenium no clear trend was observed. Furthermore, there was a negative correlation between fish length and some heavy metals. Based on all 20 analysed elemental contents, similarities between species became apparent, related to niche or habitat. This study confirms that elemental contents of species can differ between feeding guilds and/or species, which can be attributed to metabolic and physiological processes. The organisms in higher trophic levels have adaptations preventing metal accumulation, resulting in lower contents. Within the fish species biodilution occurs, as most metal contents were lowest in bigger fish. Overall, the metals did not seem to biomagnify, but biodilute in the food web. Metal analyses combined with isotopic signatures could thus provide insights in metal transfer and possible trophic linkages within a system.

Fig. 1

Locations of the three reservoirs in the Brabantse Biesbosch: (1) Petrusplaat, (2) Honderd en Dertig and (3) De Gijster (Verstijnen et al. , © under CC BY 4.0). Water flows in South-North direction from River Meuse to (1) Petrusplaat

Fig. 2

Heatmaps of the correlations between elements, separately for quagga mussels, fish and primary producers. Red = negative correlation, green = positive correlation. The brighter or more intense the colour, the stronger the correlation. Bright red: r = − 1. Bright green: r = 1

Fig. 3

Boxplots showing i.a. the 25th (left box), 50th (median) and 75th (right box) percentile of the selected relevant elements, depicted from the different clusters (Fig. 2), sorted on ascending median values (µg/g dry weight), grouped per organism/taxon and coloured by feeding guild. a phosphorus, b cadmium (based on the adjusted values), c copper, d lead, e zinc and f selenium. N.A. no applicable feeding guild (mussel bank detritus and seston)

Fig. 4

Average elemental contents (µg/g dry weight ± standard deviation; on a log-scale) of the selected relevant elements (depicted from the different clusters in Fig. 2) versus δ¹⁵N (stable isotope ratios from Verstijnen et al. 2019), grouped per organism/taxon and coloured by feeding guild. a phosphorus, b cadmium (based on the adjusted values), c copper, d lead, e zinc and f selenium. N.A. no applicable feeding guild (mussel bank detritus and seston)

Fig. 5

Average elemental contents (µg/g dry weight ± standard deviation; on a log-scale) of the selected relevant elements (depicted from the different clusters in Fig. 2) versus δ¹³C (stable isotope ratios from Verstijnen et al. 2019), grouped per organism/taxon and coloured by feeding guild. a phosphorus, b cadmium (based on the adjusted values), c copper, d lead, e zinc and f selenium. N.A. no applicable feeding guild (mussel bank detritus and seston)

Fig. 6

Dendrogram based upon elemental contents. The red boxes indicate clusters divided over ten groups. The height of the branches indicates the degree of similarity between each other

Fig. 7

Zinc contents (µg/g dry weight) related to fish length (mm) of the studied species