Use of δ13c, δ15n, and carbon to nitrogen ratios to evaluate the impact of sewage-derived particulate organic matter on the benthic communities of the Southern California Bight

We measured stable isotope ratios (delta C-13 and delta N-15) of particulate organic matter (POM) sources and benthic organic matter compartments as well as sediment C to N ratios from the coastal area of the southern end of the Southern California Bight (SCB). We used the isotopic values to evaluate the relative importance of the major POM sources to the sediment and two benthic macroinvertebrates. Application of a simple model to sediment delta C-13 values suggested that sewage-derived POM (SDPOM) supplies an average of 48% of the organic C to study area sediments. Application of a similar model to Spiophanes duplex delta C-13 values suggested that SDPOM from wastewater treatment plants discharging into the SCB could supply up to 57% of the C assimilated by this important benthic macro invertebrate in areas as far away as 26 km from SDPOM inputs. The stable isotope data for Amphiodia urtica were more difficult to interpret because of the complex feeding habits of this organism.