Heavy delta N-15 in intertidal benthic algae and invertebrates in the Scheldt Estuary (The Netherlands): Effect of river nitrogen inputs

The study investigated delta N-15 in the intertidal benthic food webs from the middle Westerschelde Estuary and the middle Oosterschelde. Much heavier delta N-15 values were observed for the main benthic primary producers and invertebrates in the Westerschelde Estuary. In the Oosterschelde, mean delta N-15 values ranged from 1.4 to 7.3 parts per thousand for SOM and suspended POM, respectively, to 6.3 to 9.1 parts per thousand for Fucus vesiculosus and benthic diatoms, respectively. Mean delta N-15 values in benthic invertebrates ranged from 9.7 parts per thousand for Gammarus locusta to 15.4 parts per thousand for Tubificoides sp. In the Westerschelde Estuary, mean delta N-15 increased from 8.1 to 8.6 parts per thousand for suspended POM and SOM, respectively, to heavier delta N-15 from 15.9 to 28.5 parts per thousand for F. vesiculosus and benrhic diatoms, respectively. Mean delta N-15 for intertidal invertebrates ranged from 18.1 parts per thousand for Lumbricillus sp. to 20.7 parts per thousand for Eulimnogammarus obtusatus. Higher enrichment in N-15 in benrhic primary producers and invertebrates from the Westerschelde Estuary are most likely due to the incorporation of N-15-enriched DIN carried by the Scheldt River by benthic algae and, then by benthic consumers. These results point to the fact that delta N-15 in benthic estuarine food webs may respond directly to anthropogenic nitrogen inputs delivered into estuaries by rivers which drain highly urbanized areas. (C) 2000 Academic Press.