Coastal sediments of Guam were analyzed for excess accumulations of N from terrestrial sources. Sedimentary aluminum and iron were used as tracers of terrestrial soils in nearshore sediments. Total organic nitrogen (TON) accounted for >98% of coastal sedimentary N in almost all cases, and ranged from 8 to 100μmol N g^-1 dry sediment (average of ca. 30), while KCl-exchangeable NH₄⁺ and NO_x (nitrite plus nitrate) were almost always less than 0.6 and 0.04 μmol g^-1, respectively. In most cases, Al and Fe levels reflected erosion of nearby Al- and Fe-rich sources but were not related to the amount of any N fraction in any easily described manner. Regardless of the presence of nearby sources of terrestrial material, coastal environments that are naturally depositional generally contained fine-grained sediments with greater amounts of particulate Al, Fe, TON, and NH₄⁺ and very low or undetectable NO_x. Organic matter in coastal sediments does not contain any terrestrial signal until the TON contents increase to >100 μmol N g^-1. In many cases, aluminum is a better tracer of terrigenous material than iron because of preferential sequestering of iron in biochemical reactions.

Natural or accelerated runoff from land does not produce a persistent N signal in sediments as strong as that of Fe and provides relatively little N that persists in sediments compared with N from in situ fixation and oceanic import. Seepage and infiltration of nitrate-rich aquifer water from the northern carbonate platform appears to be the single largest source of terrestrial nutrients to the coastal zone.

If nutrients are in fact "enriched" in Guam's coastal zone, they do not appear in the sediment and may be already incorporate into biomass, which was not measured in this study. Alternately, eroded particulate nutrients may be rapidly mineralized and exported from coastal areas in dissolved form.