Assessing Nutrient Sources
This IAN newsletter explores the assessment of nutrient sources using stable isotope signatures of various marine organisms. This technique was developed in Moreton Bay, Australia for mapping sewage plumes, and was also used to determine the extent of aquaculture effluent (shrimp ponds) and to distinguish agricultural runoff (sugar cane) from other sources. The stable isotope ratio of nitrogen in organisms can be used to determine the influence of different nitrogen sources. A high δ15N signature (the ratio of 15N to 14N) typically indicates influence by sewage, septic or animal waste, whereas a low or negative δ15N identifies fertilizer inputs. The technique, unlike traditional water quality measurements, detects only bioavailable nutrients and integrates nutrient history over time. This technique will be used in the Choptank and Patuxent Rivers during the Spring and Summer of 2003, with results made available on the IAN website.