Fatty acids as sensitive tracers of sewage sludge carbon in a deep-sea ecosystem

Dumping into the open ocean is considered a viable political option to cope with the rapidly increasing global production of municipal sewage sludge. However, before such an option can be justified, the impact of mega- scale dumping upon the marine environment must be fully addressed scientifically. Here we present a methodology whereby the impact of sewage dumping upon deep-sea invertebrates can be tracked. We examined the relative abundances and carbon isotopic compositions of membrane fatty acids of the sea urchin Echinus affinus from one deep-sea site heavily affected by municipal sewage sludge dumping (Sludge Max; Dumpsite DWD 106) and one marginally affected (station 13; 18 km SSE of DWD 106). Such analyses reveal marked differences linked to the relative importance of sewage sludge in diet. 18:2(n-6) is much more abundant in Sludge Max urchins with similar, highly 13C-depleted isotopic compositions in all samples (δ13C = -25.8 to -27.8‰). Conversely, 20:5(n-3), is most abundant in station 13 individuals and has less negative δ13C values at both sites (δ13C = 20.7 to -22.6‰). We propose that the relative abundance and stable isotopic composition of 18:2(n-6) and 20:5(n-3) can be used to indicate the importance of sewage sludge in the diet of E. affinus.

Duke Scholars

Author Cindy Van Dover Marine Science and Conservation